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EFFECTS OF EXPOSURE TO ELEVATED
TEMPERATURES ON PROPERTIES OF CONCRETE
CONTAINING RICE HUSK ASH
School of Civil Engineering
Universiti Sains Malaysia
June 2011
Dissertation submitted as partial fulfillment of
the requirements for the degree of
Master of Science (Structural Engineering)
By
MOHAMMED KADHIM HALOOB
AL-Majidi
ii
ACKNOWLEWGEMENTS
I would like to show my personal appreciation to Allah s.w.t for His blessings and
keeping me in pink of health during my commission to accomplish my research.
I would like to give my deepest thanks and appreciation to my supervisor Associate
Prof Dr Megat Azmi Megat Johari , not only for his support and motivation during the
research , but also for his high humanity feelings with his students and other people.
I would like to thanks all my family members for their support during my studies, even
if they are far away from me.
My gratitude and pleasure to my friend Mr. Salam Razaq who support me involved that
have given me a lot of cooperation and assistance to complete my dissertation and my
appreciation to my dearest friends Ahmed Jaber Al-Mansoori and Yassar Mohammed
for supporting me in life in foreign country.
School of Civil Engineering technicians are very much appreciated for giving me some
good advices and encouragement to keep on going and upgrade my performance during
trials to finish up my research.
Finally, I hope that my findings in this research will expand the knowledge in this
Field and contribute to all of us in future.
Mohammed Kadhim Haloob
iii
EFFECTS OF EXPOSURE TO ELEVATED TEMPERATURES ON
PROPERTIES OF CONCRETE CONTAINING RICE HUSK ASH
ABSTRACT
In the present investigation, a feasibility study is made to utilize the Rice Husk Ash as an
admixture in concrete and to investigate the impact of elevated temperatures on the
properties of concrete. The proportions of water, cement, fine aggregate and coarse
aggregate with maximum size 20 mm and grade of concrete is achieved to 30 MPa as
per ACI. 5%, 10%, 20% and 30% of cement is replaced by weight with rice husk ash for
the study to arrive at the optimum replacement. They are tested at room temperature and
exposed to 200,400, 600, 800 °C temperatures for 1 hour. The specimens were exposed
under the same condition for each temperature level. All specimens were moist cured for
28 days after casting. Before being exposed to the elevated temperatures, the specimen
were dried in an electric oven for 24 hours at temperature 105ºC. Tests were carried out
on specimens cooled slowly to room temperature after exposure to elevated temperature.
The specimens were tested for compressive strength, splitting tensile strength, ultrasonic
pulse velocity, modulus of elasticity, flexural strength, porosity and water absorption.
Use of rise husk ash in concrete not only reduces cost but also improves resistance
against elevated temperatures and durability. The obtained results showed that, density
of concrete and compressive strength, flexural strength and modulus of elasticity, after
exposure to elevated temperature was increased by increased rice husk ash, while
porosity and water absorption decreased with increasing rice husk ash. Those results
ensure the importance of using rice husk ash to modification of concrete. The
utilization of Rice Husk Ash (RHA) in concrete is environmental friendly and reduces
the carbon dioxide emission.
iv
ABSTRAK
Dalam penyiasatan ini, ujian keberkesanan dibuat untuk memanfaatkan Abu Sekam
Padi; Rice Husk Ash (RHA) sebagai campuran pada konkrit dan untuk mengetahui kesan
suhu tinggi pada sifat-sifat konkrit. Kandungan air, simen, agregat halus dan agregat
kasar untuk semua gred M 20 konkrit adalah berdasarkan ACI. 5%, 10%, 20% dan 30%
simen digantikan oleh berat dengan abu sekam padi untuk kajian untuk sampai pada
penggantian optimum. Sampel diuji pada bilik dan suhu tinggi iaitu suhu 200, 400 600,
800 ⁰C suhu selama satu jam tanpa tekanan. Spesimen didedahkan dalam keadaan yang
sama untuk setiap peringkat suhu. Perbandingan antara sifat-sifat konkrit selepas
pendedahan diselidiki. Semua spesimen dirawat di dalam air selama 28 hari. Sebelum
didedahkan ke suhu yang tinggi, spesimen dikeringkan dalam oven elektrik selama 24
jam pada suhu 105 º C. Ujian dilakukan pada spesimen yang telah disejukkan perlahan-
lahan sehingga suhu bilik selepas terdedah kepada suhu yang tinggi. Spesimen diuji
untuk kekuatan mamptan, belahan tegangan, halaju dedenyut bunyi, modulus
kekenyalan, kekuatan lentur, kelianagn dan penyerapan air. Penggunaan abu sekam padi
bukan sahaja mengurangkan kos malah meningkatlan daya kekuatan dalam pendedahan
kepada suhu yang tinggi. Keputusan menunjukkan ketumpatan, kekuatan mampatan
tekanan, kelenturan dan modulus kekenyalan konkrit, selepas di dedahkan kepada suhu
yang berbeza meningkat seiring dengan penambahan abu sekam padi. Manakala
keliangan dan tahap penyerapan air berkurang dengan peningkatan jumlah abu sekam
padi di dalam adunan konkrit. Ini membuktikan kepentingan abu sekam padi kepada
modifikasi struktur pada konkrit. Pemanfaatan penggunaan abu sekam padi pada konkrit
adalah mesra alam dan mengurangkan pembebasan karbon dioksida.
v
TABLE OF CONTENT
Page
ACKNOWLEDGEMENTS ii
ABSTRACT iii
ABSTRAK iv
TABLE OF CONTENTS V
LIST OF TABLES X
LIST OF FIGURES Xii
LIST OF APPENDIX xv
CHAPTER ONE: INTRODUCTION
1.1 Background 1
1.2 Problem statement 3
1.3 Objectives 4
1.4 Scope of work 5
CHAPTER TWO: LITERATURE REVIEW
2.1 Introduction 7
2.2 Pozzolan 7
2.3 Introduction to rice husk 9
2.3.1
Composition of rice husk 10
vi
2.3.2 Rice husk ash 12
2.3.3 Rice husk ash Concrete 13
2.4 Workability of fresh concrete containing RHA 14
2.5 Properties of hardened concrete containing RHA 16
2.5.1 Porosity and water absorption capacity 16
2.5.2 Compressive strength of concrete containing RHA 17
2.5.3 Tensile and flexural strength of concrete with RHA 19
2.6 General behavior of fire damaged on normal concrete 21
2.7 Behaviour of concrete at elevated temperature exposure 22
2.7.1 Reactions in concrete exposed to elevated temperature 22
2.7.2 Effect of temperature exposure on cement paste 24
2.7.3 The effect of elevated temperature on aggregates 25
2.7.4 Effect of elevated temperature on concrete containing mineral
admixture
27
2.8 Summary 30
CHAPTER THREE : METHDOLOGY
3.1 Introduction 31
3.2 Concrete materials 31
3.2.1 Cement 33
3.2.2 Aggregate 34
3.2.3 Water 35
3.2.4 Superplasticizer 35
vii
3.2.5 Rice husk ash 35
3.3 Design of concrete mixes 37
3.4 Sample preparation 38
3.4.1 Concrete mixing 38
3.4.2 Filling the moulds 39
3.4.3 Curing 41
3.5 Testing 43
3.5.1 Slump test 43
3.5.2 Compacting factor test 44
3.5.3 Unit weight test 46
3.5.4 Ultrasonic pulse velocity (UPV) test 46
3.5.5 Compressive strength test 48
3.5.6 Splitting tensile strength test 49
3.5.7 Modulus of rupture test 50
3.5.8 Porosity and water absorption tests 52
2.5.9 Modulus of elasticity Test 53
CHAPTER FOUR : RESAULTS AND DISCUSSIONS
4.1
Introduction 54
4.2
Sieve Analysis 55
4.2.1 Sieve analysis of coarse Aggregate 55
4.2.2 Sieve analysis of fine Aggregate 57
viii
4.3
Rice husk ash 58
4.4
Fresh concrete testing 59
4.4.1 Slump test 59
4.4.2 Compacting factor test 61
4.4.3 Unit weight test 62
4.5
Hardened concrete testing 64
4.5.1 Compressive strength 64
4.5.1.1 Compressive strength analysis after exposure to
elevated temperatures
65
4.5.2 Splitting tensile strength 70
4.5.3 Ultrasonic pulse velocity (UPV) 74
4.5.4 Flexural strength 79
4.5.5 Modulus of elasticity 83
4.5.6 Porosity test 86
4.5.7 Water absorption test 90
4.6 Relationship between relative residual compressive strength
and porosity
95
4.7 Relationship between relative residual compressive strength
and splitting tensile strength
96
4.8 Relationship between residual compressive strength and UPV 97
4.9 Relationship between residual porosity and UPV 98
ix
CHAPTER THREE : CONCLUSION AND
RECOMMENDATIONS
5.1 Conclusions 99
5.2 Recommendations for further research 102
x
LIST OF TABLES
Page
Table 2.1 Chemical composition of rice husk 10
Table 2.2 Ultimate analysis of rice husk 10
Table 2.3 Chemical properties of RHA 12
Table 2.4 Physical properties of RHA 13
Table 2.5 Mechanical properties of concrete 20
Table 2.6 Mechanical properties of hardened concrete (w/c=0.40)
20
Table 3.1 Chemical composition of a typical portland cement 33
Table 3.2 Mix proportions of concrete 37
Table 3 .3 Number of concrete specimens used in the Project 40
Table 3.4 Guideline of UPV test pulse 47
Table 4.1 Slump value of fresh concrete samples 60
Table 4.2 Compaction factor test result and Interpretation 61
Table 4.3 Designed unit weight and m
easured unit weight for different
percentage of RHA
63
Table 4.4 Compressive strength values (MPa) for concrete containing
different percentage of RHA at different temperatures exposure
66
Table 4.5 Splitting tensile strength values (MPa) for concrete containing
different percentage of RHA at different temperatures exposure
71
Table 4.6 UPV values (km/sec) for concrete containing different
percentage of RHA at different temperatures exposure
77
Table 4.7 Flexural strength values (MPa) for concrete containing different
percentage of RHA at different temperatures exposure
81
Table 4.8 Modulus of elasticity values (GPa) for concrete containing of
RHA at different temperatures exposure
84
xi
Table 4.9 Porosity values (%) for concrete containing different
percentage of RHA at different temperatures Exposure
88
Table 4.10 Water absorption values (%) for concrete containing of RHA at
different temperatures exposure
93
xii
LIST OF FIGURES
Page
Figure 1.1 Tall building fire burned 3
Figure 1.2 Flowchart of overall scope of work 6
Figure 2.1 Slump variation of gap-graded concretes made with different
fineness at constant superplasticizer content
15
Figure 2.2 Result of residual compressive strength of olive oil ash
Concrete
29
Figure 3.1 Flowchart of research overview 32
Figure 3.2 RHA production 36
Figure 3.3 Grinding machine 36
Figure 3.4 Concrete mixer 38
Figure 3.5 RHA with portland cement 39
Figure 3.6 Compacting of concrete samples using vibrating table 40
Figure 3.7 Moist concrete curing 41
Figure 3.8 Furnace 42
Figure 3.9 Slump test 44
Figure 3.10 Compacting factor test 45
Figure 3.11 Ultrasonic pulse velocity test instrument 47
Figure 3.12 Compressive strength machines 48
Figure 3.13 Splitting tensile strength machines 50
Figure 3.14 Flexural test machine 51
Figure 3.15 Vacuum saturation apparatus 52
Figure 3.16 Modulus of elasticity machine 53
xiii
Figure 4.1 Graph on sieve analysis for 20 mm coarse aggregate
56
Figure 4.2 Graph on sieve analysis for fine aggregate 57
Figure 4.3 Particle size of RHA 58
Figure 4.4 Influence of RHA on slump of concrete 60
Figure 4.5 Results of compacting factor test 62
Figure 4.6 Results of unit weight test 63
Figure 4.7 Compressive strength of concrete with different RHA
replacement levels at 28 days in room temperature
64
Figure 4.8 Residual Compressive Strength versus
RHA replacement level 67
Figure 4.9 Effect of RHA replacement levels on relative compressive
strength at different temperatures
67
Figure 4.10 Relative compressive strength of concretes at different elevated
temperature exposure
68
Figure 4.11 Splitting tensile strength for different RHA replacement levels
at 28 days in room temperature
70
Figure 4.12 Residual splitting tensile strength versus RHA replacement
levels at different temperature
72
Figure 4.13 Effect of RHA replacement levels on relative splitting tensile
strength at different temperatures
72
Figure 4.14 Relative splitting tensile strength of concretes at different
elevated temperature exposure
73
Figure 4.15 Ultrasonic
pulse velocities versus RHA replacement level at 28
days in room temperature
75
Figure 4.16 Residual
UPV versus RHA replacement level at different
temperature
77
Figure 4.17 Effect of RHA replacement levels on relative UPV at different
temperatures
78
Figure 4.18 Relative UPV of concretes at different elevated temperature
exposure
78
xiv
Figure 4.19
Flexural strength versus RHA level of replacement in moist
curing at 28 days
79
Figure 4.20 Residual
flexural strength versus RHA replacement level at
different temperature
81
Figure 4.21 Effect of RHA replacement levels on relative flexural strength
at different temperatures
82
Figure 4.22 Relative flexural strength of concretes at different elevated
temperature exposure
82
Figure 4.23 Modulus of elasticity versus RHA level of replacement at 28
days in room temperature
83
Figure 4.24 Residual
modulus of elasticity versus RHA replacement level at
different temperature
85
Figure 4.25 Effect of RHA replacement levels on relative modulus of
elasticity at different temperatures
85
Figure 4.26 Relative elastic modulus of concretes at different elevated
temperature exposure
86
Figure 4.27 Porosity versus RHA replacement level at 28 days in room
temperature.
87
Figure 4.28
Residual porosity versus RHA replacement level at different
temperature
89
Figure 4.29 Effect of RHA replacement levels on relative porosity at
different temperatures
89
Figure 4.30 Relative porosity of concretes at different elevated temperature
exposure
90
Figure 4.31 water absorption versus RHA level of replacement at 28 days in
room temperature
91
Figure 4.32 Residual
water absorption versus RHA replacement level at
different temperature
93
Figure 4.33 Effect of RHA replacement levels on relative water absorption
at different temperatures
94
Figure 4.34 Relative water absorption of concretes at different elevated
temperature exposure
94
xv
Figure 4.35 Relationship between residual compressive and porosity
95
Figure 4.36 Relationship between residual compressive strength and
splitting tensile strength
96
Figure 4.37 Relationship between residual compressive strength and UPV 97
Figure 4.38 Relationship between residual UPV and porosity 98
LIST OF APPENDIX
A Sieve analysis
B Result of compressive strength tests
C Result of splitting tensile strength tests
D
Result of ultrasonic pulse velocity tests
E Result of Porosity tests
F Result of water absorption tests
G Result of flexural strength tests
H
Result of modulus of elasticity tests
1
CHAPTER 1
INTRODUCTION
1.1 Background
Concrete is a construction material that is widely used in many different
structures, including houses, commercial buildings, roadways, bridges, underground
structures, and waterfront structures. Concrete is a composite material produced from
aggregate, cement, water and sometimes with added additives. Concrete should be
strong enough to carry superimposed loads, impermeable and durable throughout its
anticipated life. So, for making structure or concrete products, a mixture of cement,
water, aggregates as well as admixtures should be carefully proportioned to obtain the
optimum quality and economy for any use (Shoukry et al., 2011).
Concrete can be exposed to elevated temperatures during fire or when it is close to
furnaces and reactors. The mechanical properties of concrete, such as strength, elastic
modulus and volume deformation, decrease remarkably upon heating resulting in a
decrease in the structural quality of concrete. High temperature is one of the most
important physical deterioration processes that influence the durability of concrete
structures and may result in undesirable structural failures. Therefore, preventative
measures such as choosing the right materials should be taken to minimize the harmful
effects of high temperature on concrete (Bahar, 2008).
2
Concrete is the most widely used material in civil construction. Relatively, to its
use, the cost of the using concrete is even greater, mainly because of the manufacturing
cost of the cement Portland, its main component. There are several ways to engineer
concrete with equivalent properties by using less cement. Chemical admixtures allow
reducing cement consumption for a given strength or increasing workability without
increasing cement consumption. Also for environmental issue the use of waste material
such as rice husk ash as a supplementary cementitious material would bring about
positive technical and environmental benefits.
Rice husk is an agricultural residue which accounts for 20% of the 649.7 million
tons of rice produced annually worldwide. The produced partially burnt husk from the
milling plants when used as a fuel also contributes to pollution and efforts are being
made to overcome this environmental issue by utilizing this material as a supplementary
cementitious material. The chemical composition of rice husk is found to vary from one
sample to another due to the differences in the type of paddy, crop year, climate and
geographical conditions. Rice-husk ash (RHA) is a fine pozzolanic material. The
utilization of rice husk ash as a pozzolanic material in cement and concrete provides
several advantages. The pozzolanic activity of RHA depends on, silica content, silica
crystallization phase, size and surface area of ash particles (Ganesan et al., 2008)
Many excellent publications have shown that RHA can be used as a partial cement
replacement material to produce high strength concrete and increased durability of
concrete such as permeability. This research reports an investigation on the effect of
elevated temperatures exposure on properties of concrete containing RHA temperatures.
Figure 1.1 shows a 56- storey building Fire burned out of control for 17 hours.
3
Figure 1.1: Tall building fire burned
1.2 Problem statement
Although cement is the important material in the construction field around the
world, the use of cement has created serious pollution problems around the world. The
environmental impact caused by the increase in the extraction of natural resources and
higher CO2 emissions during the cement production has given rise to the search for more
efficient and environmental-friendly materials. The increasing cement consumption
would increase the contribution of cement production industry in CO2 emissions. Hence,
it causes the air pollution to the environment. However; RHA is a waste material so the
4
environmental benefits are related to the disposal of waste materials and to reduce usage
of cement in concrete.
However, most of the building use concrete as main construction material with
Ordinary Portland Cement as a binder. The performance of concrete structures exposed
to aggressive environmental exposures such as fire should be assessed, which influences
the mechanical properties of the concrete. Therefore, to predict and to reduce the
significant effect of fire on the concrete, the research about the behaviors of concrete
with Rice Husk Ash due to fire exposure should be carried out.
1.3 Objectives
The main objectives of this study are:
1- To compare the properties of concrete containing Ordinary Portland Cement and
concrete with a different percentage of RHA.
2- To study and quantify the influence of the elevated temperature on the
engineering properties of concrete containing various percentages of rice husk
ash.
5
1.4 Scope of work
This research investigates the effects of RHA replacement on the properties of
concrete grade of 30 such as compressive strength, splitting tensile, modulus of
elasticity, flexural strength, Ultrasonic Pulse Velocity (UPV), Porosity and Water
Absorption at the elevated temperatures. The proposed method involves the preparation
of five concrete mixes with the different percentage of rice husk ash: 5%, 10%, 20%,
30% and control mix without RHA as a reference. Ordinary Portland cement (OPC) will
be used as the main binder material, coarse and fine aggregate and water. The value of
water/binder ratio and quantity of superplasticizer used is fixed. The samples will be
kept in the laboratory with in a control environment, after 28 days specimens they will
be dried at 105 ºC for 24 hours before they are exposed to elevated temperatures at 200,
400, 600, 800 ºC for 1 hour. Then the properties of the concrete will assessed by
compressive strength, ultrasonic pulse velocity value (UPV), flexural strength, modules
of elasticity, porosity, water absorption and spilt tensile strength tests.
After all the tests and experiments have been carried out, the suitability of RHA as
cement replacement in concrete can be assessed. However, the comparison between
properties of concrete without RHA and concrete containing RHA at moist curing ages and
elevated temperatures exposure can be made. The overall scope of work of the study is
summarized in Figure 1.2.
6
Figure 1.2: Flowchart of overall scope of work
Sample preparation
Different percentage of RHA in concrete
mix 5%, 10%, 20%, 30% and control mix as
references
A
fter
28 days curing sample
D
ry at 105ºC for 24 hours in electric oven.
Exposure to elevated temperature for 1 hour at
200ºC
400 ºC
600 ºC
800 ºC
And control temperature
DATA ANALYSIS
Testing
Compressive strength
UPV
Splitting tensile
Modulus of elasticity
Flexural strength
Porosity and water absorption
7
CHAPTER 2
LITERATURE REVIEW
2.1 Introduction
The prevailing interest in the use of eco-friendly materials towards improving
mechanical and durability properties of OPC concrete may as well require careful
assessment on other vital properties such as fire resistance. The issue of fire resistance is
very important since structural concrete is required to preserve structural actions over a
desired length of time known as fire rating (Neville, 2005)
This chapter briefly explains about the researches that had been done previously
by other researches which are related to this study. For the information, there are many
researches regarding the effect of RHA as cement replacement in concrete. The
parameters include strength performance, porosity, and durability of concrete. Moreover,
researches regarding the effect of concrete exposed to elevated temperature had also
been done.
2.2 Pozzolan
Pozzolans are finely divided materials used in concrete in relatively large
amounts and mainly used as cement replacement in order to enhance early and long term
performance. The use of these materials, to some extent, reduces the cost of concrete
production.
8
The American Society of Testing and Materials (ASTM) defines pozzolan as a
siliceous or alumina-siliceous material which in itself possesses little or no cementations
value but that in a finely divided form and in the presence of moisture will chemically
react with alkali and alkaline earth hydroxides at ordinary temperatures to form or assist
in forming compounds possessing cementitious properties.
Some pozzolans are natural and others are industrial by-products and both
contain silica in amorphous form and that would react with calcium hydroxide (C-H) to
form more cementitious calcium silicate hydrate (C-S-H) and contribute to the concrete
strength. These materials include volcanic ash, diatomaceous earths, condensed silica
fume, pulverized fly ash, natural pozzolan and rice husk ash. It contains some form of
amorphous reactive silica which may combine with lime in presence of water to form C-
S-H (Nehdi et al. 1998).
Naturally occurring pozzolanic materials were used in early concretes, but when
a pozzolanic material is used in conjunction with a Portland cement, the calcium
hydroxide that takes part in the pozzolanic reaction is that produced from the cement
hydration quantities of calcium silicate hydrate are produced:
2S+3CH→C3S2H3
The reaction is clearly secondary to the hydration of the Portland cement, which has to
lead to the name ‘latent hydraulic material’ in the list of alternatives above. The products
of the pozzolanic reaction cannot be distinguished from those of the primary cement
hydration, and therefore, make their own contribution to the strength and other
properties of the hardened cement paste and concrete (Ahmed Eldagal and Elmukhtar,
2008)
9
In addition to increase the strength of concrete, the presence of pozzolan also
improves the resistance of concrete to acid attacks and other aggressive ions attacks. The
expansion due to alkali-silica reaction and sulfate attack would reduce considerably. The
frost resistance has been found to be significantly improved by adding pozzolan to the
concrete mix (Mehta and Folliard, 1995). The lower generated heat of secondary
hydration also reduces the risk of cracking.
2.3 Introduction to rice husk
Rice's plant is one of the plants that absorbs silica from the soil and assimilates it
into its structure during the growth. Rice husk is the outer covering of the grain of rice
plant with a high concentration of silica, generally more than 80-85%. It constitutes
about 20% of the weight of rice. It contains about 50% cellulose, 25–30% lignin, and
15–20% silica. When the rice-husk is burnt rice-husk ash (RHA) is generated. On
burning, cellulose and lignin are removed leaving behind silica ash (Siddique, 2008).
The husk can be converted to a useful form of energy to meet the thermal and
mechanical energy requirements of the rice mills themselves when used as a fuel also
contributes to pollution, and efforts are being made to overcome this environmental
issue by utilizing this material as a supplementary cementing material. The chemical
composition of rice husk is found to vary from one sample to another due to the
differences in the type of paddy, crop year, climate and geographical conditions
(Ghassan, 2010).
The composition of ash and lignin varies slightly depending on the kinds of rice
husk as shown in Table 2.1. The critical composition of rice husks from different kinds
also varies slightly (Table 2.2). The rice husk has a large dry volume due to its low bulk
10
density (90-150 kg/m3) and possesses rough and abrasive surfaces that are highly
resistant to natural degradation. Disposal has become a challenging problem.
Table 2.1: Chemical composition of rice husk (Hwang and Wu, 1989)
Chemical composition (%)
C H O N S CL ASH Reference
38.3 5.7 39.8 0.5 0.0 0.0 15.5 Tillman (1978)
39.4 5.5 36.1 0.5 0.2 0.2 18.2 Anderson (1977)
39.5 5.5 37.7 0.8 0.0 0.0 16.5 Yand (1980)
Table 2.2: Ultimate analysis of rice husk (Hwang and Wu, 1989)
Rice Husk
Extractives Chemical Composition
Alcohol-
benzene
1%
NaOH
Hot
Water
Holo-
cellulose Ash Lignin
Japonica 1.8 32.3 5.4 53.9 13.6 24.8
India 2.1 30.6 5.1 54.3 11.7 25.8
Anhydrous
Rice Husk - - 8-15 40-50 15-50 25-30
2.3.1 Composition of rice husk
Rice husk can be burnt into ash that fulfils the physical characteristics and
chemical composition of mineral admixtures. The controlled temperature and
environment of burning yields better quality of rice-husk ash as its particle size and
specific surface area are dependent on burning condition. For every 1000 kg of paddy
milled, about 200 kg (20%) of husk is produced, and when this husk is burnt in the
boilers, about 50 kg (25%) of RHA is generated. Completely burnt rice-husk is grey to
white in color, while partially burnt rice-husk ash is blackish (Abu Bakar et al., 2010).
Rice husk combustion technology has developed from open air burning in the
field (around 1970s) to combustion using liquidized layers method (around 1990s).
11
Temperature and combustion period can be controlled in liquidized layers combustion
method. However, researchers who study RHA usually build their own
incinerator/furnace or collect ash from rice mill. Despite the studies on pozzolanic
activity of RHA, its use as a supplementary cementitious material, and its environmental
and economical benefits are available in many literatures, very few of them deal with
rice husk combustion and grinding methods. Only moderate temperature and short
period are required in this method (Zain et al., 2011).
Research on producing rice husk ash (RHA) that can be used in concrete is not
new. The form of silica obtained after combustion of rice husk depends on the
temperature and duration of combustion of rice husk. Mehta (1979) suggested that
essentially amorphous silica can be produced by maintaining the combustion
temperature below 500ºC under oxidizing conditions for prolonged periods or up to
680ºC with a hold time less than 1 min. However, Yeoh et al., 1979 reported that RHA
can remain in the amorphous form at combustion temperatures of up to 900ºC if the
combustion time is less than 1 hour, while crystalline silica is produced at 1000ºC with
combustion time greater than 5min.
Using X-ray diffraction, it was observed that at burning temperatures up to
700ºC, the silica was in an amorphous form. At 400ºC, polysaccharides begin to
depolymerize. Above 400ºC, dehydration of sugar units occurs. At 700ºC, the sugar units
decompose. At temperatures above 700ºC, unsaturated products react together and form
a highly reactive carbonic residue. The X-ray data and chemical analyses of RHA
produced under different burning conditions showed that the higher the burning
temperature, the greater the percentage of silica in the ash. Potassium (K), Silica (S),
12
Calcium (Ca), Magnesium (Mg) as well as several other components was found to be
volatile (Nehdi et al., 2003)
2.3.2 Rice husk ash
RHA is a highly pozzolanic material. The non-crystalline silica and high specific
surface area of the RHA are responsible for its high pozzolanic reactivity. RHA has been
used in lime pozzolana mixes and could be a suitable partial replacement for Portland
cement (Sata et al. 2007).
RHA is a very fine material. The average particle size of rice-husk ash ranges
from 5 to 10μm. The typical chemical composition and physical properties of RHA are
given in Tables 2.3 and 2.4 (Mehta 1992; Bui et al., 2005; Zhang et al., 1996). For RHA
to be used as pozzolan in cement and concrete, it should satisfy requirements for
chemical composition of pozzolans as per ASTM C618. The combined proportion of
silicon dioxide (SiO2), aluminum oxide (A12O3) and iron oxide (Fe2O3) in the ash should
be not be less than 70%, and Loss on ignition should not exceed 12% as stipulated in
ASTM requirement (Abu Bakar et al. 2010).
Table 2.3: Chemical properties of RHA
Chemical properties
constituent
SiO2 Al2O3 Fe2O3
CaO MgO
SO3 Na2O
K2O Loss on
ignition
Mehta
(1992) 87.2 0.15 0.16 0.55 0.35 0.24 1.12 3.68 8.55
Zhang et
al. (1996) 87.3 0.15 0.16 0.55 0.35 0.24 1.12 3.68 8.55
Bui et al.
(2005) 86.98
0.84 0.73 1.4 0.57 0.11 2.46 ----- 5.14
13
Table 2.4: Physical properties of RHA
Physical properties Specific
gravity(g/cm3)
Mean particle
size(µm)
Fineness: passing
45µm (%)
Mehta (1992) 2.06 -------- 99
Zhang et al. (1996) 2.06 -------- 99
Bui et al. (2005) 2.10 7.4 ----
2.3.3 Rice husk ash concrete
Rice-husk ash is a mineral admixture for cement and concrete. The behavior of
cementitious products varies with the source of RHA. Most mineral admixtures have a
favorable influence on the strength and durability of concrete. In the case of RHA, its
chemical effect is related to the fact that when produced by controlled combustion it is a
highly pozzolanic material which combines quickly with calcium hydroxide forming a
secondary C–S–H; the physical effect is linked to particle size (less than 45 µm on
average), which produces a refinement on the pore structure, acts as the nucleation point
for hydration process (Rodríguez de Sensale, 2010).
Zhang et al. (1996) studied the effect of RHA on the hydration, microstructure
and interfacial zone between the aggregate and paste. Based on the investigation, they
concluded that calcium hydroxide [Ca(OH)2] and calcium silicate hydrates [C-S-H] were
the major hydration and reaction products in the RHA paste because of the pozzolanic
reaction the paste incorporating RHA had lower Ca(OH)2 content than the control
Portland cement paste.
Yu et al. (1999) reported that improvement of concrete properties is achieved on
addition of RHA and this may be attributed to the formation of more C-S-H gel and less
14
portlandite in concrete due to the reaction between RHA and the Ca+, OH− ions or Ca
(OH)2.
RHA concrete is like fly ash/slag concrete with regard to its strength
development but with a higher pozzolanic activity it helps the pozzolanic reactions occur
at early ages rather than later as is the case with other partial cement replacement
materials (Malhotra, 1995). The employment of rice husk ash as a pozzolanic material in
cement and concrete provides several advantages, such as improved strength and
durability properties, reduced material costs due to cement savings, and environmental
benefits related to the disposal of waste materials and to reduced carbon dioxide
emissions.
2.4 Workability of fresh concrete containing RHA
Usually typical concrete mixtures contain too much mixing water because of two
reasons: Firstly, the water demand and workability are significantly influenced by
particle size distribution, particle packing effect, and voids present in the solid system.
Typical concrete mixtures do not have an optimum particle size distribution, and this
accounts for the undesirably high water requirement to achieve certain workability.
Secondly, to plasticize a cement paste for achieving an acceptable consistency, much
larger amounts of water than necessary for the hydration of cement have to be used
because Portland cement particles, due to the presence of electric charge on the surface,
tend to form flocks that trap volumes of the mixing water (Givi et al., 2010).
Bui et al. (2005) investigated the influence of rice husk ash on the slump of
concrete mixtures. Two types (PC30 and PC40) of ordinary Portland cement were used.
15
Cement PC 30 and PC 40 had Blaine specific surface area of 2700 and 3759 Cm2/g,
respectively. Three water/binder ratios were used. Rice husk ash was used to replace in
three different percentage of 10%, 15% and 20% by mass of PC. The superplasticizer
was added to all mixtures for obtaining high workability. In all mixtures with water to a
binder ratio and the amount of superplasticizer were kept constant to investigate the
influence of RHA on workability. Figure 2.1 shows the influence of RHA content on the
slump of gap-graded mixtures. It is clear that slump decreased with the increase in RHA
content for the same dosage of superplasticizer.
Figure 2.1: Slump variation of gap-graded concretes made with different fineness
at constant superplasticizer content (Bui et al., 2005)
At a given water to cement ratio, small addition (less than 2% to 3% by weight of
cement) of RHA may be helpful for improving the stability and workability of concrete
by reducing the tendency towards bleeding and segregation. This is mainly due to the
large surface area of rice husk ash, which is in the range of 50 to 60 m²/g. Large
16
additions would produce dry or unworkable mixtures, unless water-reducing admixtures
or superplastizers are used. Due to the adsorptive character of cellular rice husk ash
particles, concrete containing RHA requires more water for a given consistency.
2.5 Properties of hardened concrete containing RHA
The properties of hardened concrete containing RHA are explained which
include porosity, water absorption, tensile and flexural strength as well as compressive
strength.
2.5.1 Porosity and water absorption capacity
One of the main sources of contamination of concrete in structures is water
absorption, which influences durability of the concrete and also has the risk of alkali
aggregate reactions. The more impermeable the concrete, the greater will be its
resistance to deterioration. The incorporation of pozzolan such as fly ash reduces the
average pore size and results in a less permeable paste (Chindaprasirt et al., 2005).
Previous studies have identified that commonly permeability of blended cement
concrete is commonly less than that of plain cement paste. It was observed that the
integration of RHA in the composites could cause an extensive pore refinement in the
matrix and in the interface layer, thereby decreasing water permeability (Rodríguez de
Sensale, 2006). The radial expansion of Portland cement hydration products in
pozzolanic particles would have a pore modification effect. Therefore, presence RHA in
concrete reduces the interconnectedness among pores. This occurrence can be coupled
with perfection on the interfacial transition zones among the cement matrix and
aggregate. The permeability will decrease rapidly with the progress of the hydration.
The presence of pozzolan leads to greater precipitation of cement gel products than
17
occurs in Portland cement alone, which more effectively block the pores helping to
reduce permeability (Givi et al., 2010).
Incorporation of the RHA in concrete reduced the porosity and the Ca(OH)2
amount in the interfacial zone; the width of the interfacial zone between the aggregate
and the cement paste compared with the control Portland cement composite was also
reduced. However, the porosity of the rice-husk ash composite in the interfacial zone
was higher than that of the silica fume composite (Zhang et al., 1996).
Saraswathy and Song, (2007) studied the effect of partial replacement of cement
with RHA at different replacement levels on the porosity and water absorption of
concrete and reported that the coefficient of water absorption for rice husk ash replaced
concrete.
2.5.2 Compressive strength of concrete containing RHA
Inclusion of RHA as a partial replacement of cement enhances the compressive
strength of concrete, but the optimum replacement level of OPC by RHA to give
maximum long term strength enhancement has been reported between 10% up to 30%.
All these replacement levels of RHA are in percentage by weight of the total binder
material (Givi et al., 2010).
Zhang et al. (1996) investigated the influence of 10% RHA inclusion as a partial
replacement of cement on the compressive strength of concrete and compared it with the
compressive strength of concrete containing 10 % silica fume (SF) at a Water/Cement
ratio of 0.40. Compressive strength results up to the age of 730 days show that RHA
concrete, in general, achieved higher strength than control concrete mixture but lower
than that of silica fume concrete.
18
Wada et al. (1999) demonstrated that RHA mortar and concrete exhibited higher
compressive strength than the control mortar and concrete. They have further reported
excellent strength development at the early stages even without steam curing for RHA
mortar and concrete. Mahmud et al. (1996) reported 15% cement replacement by RHA
as an optimal level for achieving maximum strength.
Ganesan et al. (2008) concluded that concrete containing 15% of RHA showed
an utmost compressive strength and loss at elevated content of more than 15%. El-
Dakroury and Gasser (2008) reported that using 30% RHA as a replacement of part of
cement could be considered optimum for all content of W/C ratios in the investigated
mortars because of its high value of compressive strength.
De Souza Rodrigues et al. (2006) reported the RHA concrete had a higher
compressive strength at 91 days in comparison to that of the concrete without RHA. The
increase in compressive strength of concretes with residual RHA may also be justified
by the filler (physical) effect. It is concluded that RHA can provide a positive effect on
the compressive strength of concrete at early ages. Besides, in the long term, the
compressive strength of RHA blended concrete produced by controlled incineration
shows better performance.
Bui et al. (2005) concluded that RHA can be used as a highly reactive pozzolanic
material to improve the microstructure of the interfacial transition zone between the
cement paste and the aggregate in high performance concrete, which would increase the
compressive strength of concrete with the replacement level of up to 20%.
19
2.5.3 Tensile and flexural strength of concrete with RHA
Habeeb et al. (2009) investigated the effects of concrete incorporating 20% RHA
as a partial replacement of cement at three different particle sizes. In their study the
tensile strength of concrete increased systematically with increasing RHA replacement.
The results of tensile and flexural strength are shown in Table 2.5. According to
Rodríguez de Sensale (2006) and Sakr (2006), the use of RHA with average particle size
of 11.5µm resulted in significant improvement in flexural strength.
Also Habeeb et al. (2009) reported that the coarser RHA particle mixture showed
the least improvement in tensile and flexural strength. Zhang et al. (1996) concluded that
the addition of RHA to concrete exhibited an increase in the flexural strength and the
higher strength was for the finer RHA mixture due to the increased pozzolanic reaction
and the packing ability of the RHA fine particles.
The flexural strength of RHA modified, ASTM C 78, is higher than that of
normal concrete. Table 2.6 shows the flexural strength at 28 days of prisms made with
concrete containing 10% RHA as a substitute for cement compared to prisms made with
normal concrete (Zhang and Malhotra, 1996).
20
Table 2.5: Mechanical properties of concrete (Habeeb et al, 2009)
Flexural strength (MPa) Tensile splitting(MPa)
Age (days) Age (days)
mix 28 90 180 28 90 180
CM
a
4.5 4.9 5.1 2.6 2.8 2.9
20 F1
b
4.9 5.4 5.5 2.9 3.0 3.2
20 F2
c
5.0 5.4 5.7 3.2 3.3 3.5
20 f3
d
5.2 5.7 6.1 3.2 3.5 3.9
a Control mix
b RHA with a average particle size of 31 .3 µm
c RHA with average particle size of 18.3 µm
d RHA with average particle size of 11.5 µm
Saraswathy and Song (2007) reported the compressive, splitting tensile strength
and bond strength of concrete in which cement was partially replaced with RHA. At 28-
day the results show that compressive strength increases with the increase in RHA
content. At 28 days, all the rice husk ash replaced concretes exhibited higher
compressive strength than the control concrete; inclusion of RHA (up to 25%) as partial
replacement of cement did not affect the splitting tensile strength of concrete. After 25%
replacement level, a slight decrease in splitting tensile strength was observed; and the
entire rice husk replaced concretes showed higher bond strength values than the
conventional concrete.
Table2.6: Mechanical properties of hardened concrete (w/c=0.40) (Zhang and Malhotra,
1996)
Rice Husk Ash
(%)
Age (Days) Splitting tensile
(MPa)
Flexural(MPa) e.Modulus
(GPa)
0 28 2.7 6.3 29.6
10 28 3.5 6.8 29.6
21
2.6 General behavior of fire damaged on normal concrete
Concrete can be exposed to elevated temperatures during fire or when it is close
to furnaces and reactors. The mechanical properties of concrete, such as strength, elastic
modulus and volume deformation, decrease remarkably upon heating resulting in a
decrease in the structural quality of concrete. High temperature is one of the most
important physical deterioration processes that influence the durability of concrete
structures and may result in undesirable structural failures. Therefore, preventative
measures such as choosing the right materials should be taken to minimize the harmful
effects of high temperature on concrete (AydIn, 2008).
The high temperature behavior of concrete is greatly affected by material
properties, such as the properties of the aggregate, the cement paste and the aggregate-
cement paste bond, as well as the thermal compatibility between the aggregate and
cement paste (Arioz, 2007).
Damage of the concrete attributable to fire has been summarized in three
principle types of alteration which are cracking and micro cracking in the surface zone,
alteration of the phases in aggregate and cement paste, and the dehydration of the
cement hydrate (Newman and Choo, 2003)
Cracking and micro cracking in the surface zone is usually sub-parallel to the
external surface and leads to flake and breaking away of surface layers. Cracks also
commonly develop along aggregate surfaces, presumably reflecting the differences in a
coefficient of linear thermal expansion between cement paste and aggregate. Larger
cracks can occur, particularly where reinforcement is affected by the increase in
temperature.
22
Alteration of the phases in aggregate and cement paste is normally relate to
oxidation and dehydration. Loss of moisture can be rapid and probably influences crack
development. The paste generally changes colour and various colour zones can develop.
Changes from buff or cream to pink tend to occur at about 300ºC and from pink to
whitish grey at about 600ºC. Certain type of aggregate also shows colour changes, which
can sometimes be seen within individual aggregate particles.
The dehydration of the cement hydrates also occur, which can take places within
the concrete at a temperature a little above 100ºC. It is often possible to detect a broad
zone of slightly porous light buff paste, which represents the dehydrated zone between
100 and 300ºC.
2.7 Behaviour of concrete at elevated temperature exposure
Concrete is well known for its capacity to endure high temperatures and fires,
owing to its low thermal conductivity and high specific heat. However, it does not mean
that fire as well as higher temperatures does not affect the concrete. Characteristics such
as color, compressive strength, elasticity, concrete density and surface appearance are
affected by high temperature. Therefore, improving concrete’s fire resistance is a field of
interest for many researchers lately.
2.7.1 Reactions in concrete exposed to elevated temperature
During the last few years, analytical and computation methods have been greatly
developed in the field of concrete building exposed to high temperature or accidental
fire. The mechanical properties such as strength, modulus of elasticity and volume
stability of concrete are significantly reduced during these exposures. This may result in
23
undesirable structural failures. Therefore, the properties of concrete retained after a fire
are still of importance for determining the load carrying capacity and for reinstating fire-
damaged constructions (Poon et al, 2004).
There are a number of physical and chemical changes, which occur in concrete
subjected to heat. Some of these are reversible upon cooling, but others are non-
reversible and may significantly weaken the concrete structure after a fire. Most porous
concrete contain a certain amount of liquid water. This begins to vaporise if the
temperature exceeds 100 °C, usually causing a build-up of pressure within the concrete.
In practice, the boiling temperature range tends to extend from 100 °C to about 140 °C
due to the pressure effects. Beyond the moisture plateau, when the temperature reaches
about 400 °C, the calcium hydroxide in the cement will begin to dehydrate, generating
more water vapour and also bringing about a significant reduction in the physical
strength of the material. Other changes may occur in the aggregate at higher
temperatures. For example, quartz-based aggregates increase in volume, due to a mineral
transformation, at about 575°C, whilst limestone aggregates will begin to decompose at
about 800°C. In isolation, the thermal response of the aggregate itself may be straight
forward but the overall response of the concrete due to changes in the aggregate can be
much different. For example, differential expansion between the aggregate and the
cement matrix may cause cracking and spalling. (Fletcher et al, 2007).
Concrete is a composite material produced from aggregate, cement, and water.
Therefore, the type and properties of aggregate also play an important role on the
properties of concrete exposed to elevated temperatures. The strength degradations of
concretes with different aggregates are not the same under high temperatures (Savva et
al., 2005). This is attributed to the mineral structure of the aggregates. Quartz in
24
siliceous aggregates polymorphically changes at 570°C with a volume expansion and
consequent damage. In limestone aggregate concrete, CaCO3 turns into CaO at 800–900
°C, and expands with temperature. Shrinkage may also start due to the decomposition of
CaCO3 into CO2 and CaO with volume changes causing destructions (Yüzer et al.,
2004). Consequently, elevated temperatures and fire may cause aesthetic and functional
deteriorations to the buildings. Aesthetic damage is generally easy to repair while
functional impairments are more profound and may require partial or total repair or
replacement, depending on their severity (Arioz, 2007).
2.7.2 Effect of temperature exposure on cement paste
Although concrete is generally believed to be an excellent fire proofing material,
many recent studies have shown extensive damage or even catastrophic failure at high
temperatures, particularly in high strength concrete. Pozzolanic materials are
customarily employed as an active addition or substitution to ordinary Portland cement
in concrete mixtures due to their capacity for reacting with lime, and the resulting
enhancement in strength and durability of concrete (Seleem et al., 2011).
The related studies show that hardened cement paste plays a key role in this
deterioration process. Loss in structural quality of concrete, especially the strength and
fracture generally exhibit a complex dependency on the developed phase composition
and pore structure of hardened cement paste. High temperatures induce a loss in strength
and elastic modulus and increase both the elastic deformability and creep by altering the
physico-chemical composition of the cement paste. Factors affecting the shape of stress–
strain curve are the type of binder and aggregate, the type of admixtures and aggregate,
the aggregate–cement ratio and storage conditions. It was found that the loss in
25
structural quality of concrete due to a rise of temperature is influenced by its degradation
through changes induced in basic processes of cement hydration and hardening of the
binding system in the cement paste of concrete (Janotka and Nürnbergerová, 2005).
Under elevated-temperature exposure, the Portland cement paste experience
physical and chemical changes that contribute to development of shrinkage, transient
creep, and changes in strength. Key material features of hydrated Portland cement paste
affecting the properties of concrete at the elevated temperatures are its moisture state
(i.e., sealed or unsealed), chemical structure (i.e., loss of chemically bound water from
the C-S-H in the unsealed condition, CaO/SiO2 ratio of the hydrate in the sealed
condition, and amount of Ca(OH)2 crystals in sealed or unsealed conditions), and
physical structure (i.e., total pore volume, including cracks, average pore size, and
amorphous/crystalline structure of solid) (Naus,2005).
2.7.3 The effect of elevated temperature on aggregates
Many common coarse aggregates are unsuitable for high-temperature service
because they contain quartz, which exhibits a large volume change at ~575°C.
Accordingly, crushed stone and gravel-based aggregates suitable for use are limited to
diabase trap rock, olivine, pyrophylite, emery, and the expanded alumino silicates
(shales, clays, and slates). The latter can be used up to temperatures in the range of
1000ºC to 1150°C. In principle, all refractory grains may be used as aggregates, but in
practice, most aggregates for refractory concretes contain mainly alumina and silica in
various forms. The most widely used aggregates are probably calcined flint or kaolin
containing 42 to 45% Al203. Refractory aggregates such as crushed firebrick (30 to 45%
Al203) are stable to temperatures of 1300°C. For temperatures up to 1600°C, aggregates
26
such as fused alumina or carborundum can be used; for temperatures up to 1800°C,
special white calcium-aluminate cement and a fused-alumina aggregate are required.
Sand, gravel, and trap rock aggregates are generally used in calcium-aluminate cement
mixes for temperatures below 260°C. Table 3 presents examples of typical aggregates
for dense refractory (Naus, 2005).
Limestone aggregate had generally been shown to give good fire resisting
performance but not all design codes have found the evidence consistent enough to give
design guidance differentiating that performance. There are several reasons why
limestone aggregate can be expected to give improved resistance to degradation. First,
the aggregates have a lower coefficient of thermal expansion than a siliceous aggregate,
and they are closer to that of cement paste, giving lower internal stresses on heating. It is
because of: there are so sold-state phase changes in limestone aggregates within fire
exposure conditions. On heating to temperature in excess of 660ºC, calcium carbonates
begin to break down, similarly above 740ºC for magnesium carbonates. During a
breaking down, the mineral release carbon dioxide, which in itself an endothermic
reaction, but the release of carbon dioxide is claimed to give blanketing protection
against heat transfer. The residual aggregate particles also have lower thermal
conductivity, further reducing heat transfer into the concrete (Newman. 2003).
Turker, (2001) investigated the micro-structure and strength of the concretes
exposed to fire. In this study, mortars containing ordinary Portland cement and three
aggregate types were subjected to 100, 250, 500, 700 and 850ºC for 4 hours. Unlike the
mortars with quartz and limestone, at high temperatures cracking was observed in the
aggregate itself for the mortars with pumice instead of crack propagation at the interface.
Therefore, it was concluded that the interface was strong when pumice was used.
27
2.7.4 Effect of elevated temperature on concrete containing mineral admixture
Savva et al. (2005) have studied the influence of high temperatures on concrete
mechanical properties and properties that affect the measurement by non – destructive
methods (rebound hammer and pulse velocity) of concrete containing various levels
(10% and 30%) of pozzolanic materials. Three types of Pozzolans, one natural pozzolan
and two lignite fly ashes (one of low and the other of high lime content) were used for
cement replacement. Two series of mixtures were prepared to use limestone and
siliceous aggregates. The Water/binder and the cementitious material content was
maintained constant for all the mixtures. Concrete specimens were tested at 100, 300,
600 and 750 ºC for 2 hours without any imposed load, and under the same heating
regime. At the age of 3 years, tests of compressive strength, modulus of elasticity,
rebound hammer and pulse velocity come out. Results indicate that the residual
properties of concrete as well as rebound and pulse velocity versus heating temperatures
are established (Ahmad, 2010).
A number of research studies indicated that the addition of silica fume highly
densifiess the pore structure of concrete, which results in explosive spalling due to the
build-up of pore pressure by steam. Since the evaporation of physically absorbed water
starts at 80ºC, which induces thermal cracks, such concretes showed inferior
performance as compared to pure OPC concretes at elevated temperatures. On the other
hand, the addition of fly ash (FA), or ground granulated blast furnace slag (GGBS),
enhances the fire resistance of concrete. Yigang et al. (2000) indicated that the
compressive strength of FA concrete at 250ºC was more than the original unfired
strength. Moreover, the FA concrete retained higher strengths than the pure OPC
28
concrete at higher temperatures up to 650ºC and found that the addition of FA
completely eliminated all visible surfaces cracking for specimens heated up to 600ºC
(Poon et al. 2003)
Hammer (1995), compared the data obtained from the high-strength light-weight
and normal-weight concretes containing 0–5% silica fume (SF) which was exposed to
20, 100, 200, 300 and 450ºC with the data of the concretes, which were not exposed to
high temperatures. It was found that at 450ºC, normal weight concrete containing 0% SF
showed the best performance but the behavior of the others was similar to each other. At
600 ºC light weight concrete with 5% SF and normal weight concrete without SF were
similar to each other, and they showed the best performance by a strength loss of 48%
relative to the control concrete exposed to 20 ºC. When the concrete temperatures were
200–300ºC, reductions in compressive strength were between 25–35 % (Sancak et al.
2008).
Diederichs et al. (1989) prepared three high strength concrete mixes
incorporating SF, FA, and GGBS independently. The concrete specimens were subjected
to a maximum temperature of 900ºC. The GGBS concrete showed the best performance
followed by FA and SF concretes.
Metakaolin (MK) has been added to the list of commercial pozzolans, and
thought of as being an excellent material for producing high performance concrete. It is
gaining popularity due to its consistent composition and production, light color, and
rapid pozzolanic reaction, the compressive strength development, porosity and pore size
distribution of MK concrete, was found to be very close or superior than the SF
29
concrete. However, these superior properties of MK concrete, can result in poor fire
resistance. The MK concrete showed a distinct pattern of strength gain and loss at
elevated temperatures. After gaining an increase in compressive strength at 200ºC, it
maintained higher strengths as compared to the corresponding SF, FA, and pure OPC
concretes till 400ºC. A sharp reduction in compressive strength was observed after
400ºC followed by severe cracking and explosive spalling. Within the range 400º–
800ºC, MK concretes suffered more loss and possessed lower residual strengths than the
other concretes (Poon et al. 2003).
Al-Akhras et al. (2009) have done a research regarding the concrete containing
olive oil ash (OWA) at elevated temperatures exposure. The result is shown in Figure
2.2. From the result obtained, they found that the performance of OWA concrete
exposed to elevated temperatures was observed to be better compared to control
concrete. Moreover, the performance of OWA concrete exposed to elevated
temperatures increased while the OWA content was increased from 7% to 22%.
Figure2.2: Result of residual compressive strength of olive oil ash concrete
(After Al-Akhras et al., 2009)
30
2.8 Summary
Generally, from this chapter it can be summarized that there are many factors,
which could influence the behavior of concrete due to the temperature exposure. Many
researches had been done with various types of mixtures, material, testing and, etc. From
these researches; it was found that concrete also will act differently to the different
condition treatment.
Furthermore, although OPC is not ‘environmental friendly’ in their production
due to the releasing of carbon dioxide to the atmosphere; but until today the use of OPC
as a main binder material in concrete still higher than other materials. Therefore, the
continuous researches need to be done in order to improve the performance of those
concrete structures. Since, building always exposed to the natural hazards such as fire,
the performance with regards to fire resistance should be investigated. This is because
after the event of fire, the assessments must be carried with the minimum damage and
should be economic.
31
CHAPTER 3
METHODOLOGY
3.1 Introduction
This chapter briefly explains the materials, preparation of sample, mix-
proportions and test procedures used in the research. Most of the methods of testing are
based on British Standard (BS) and American Standard (ASTM). The overview of the
research work is shown in Figure 3.1.
For the first phase, the information concerning the present study is obtained from
various sources such as journal papers, reference book, internet, research papers and
previous dissertations which are related with the title. Everywhere the research, all the
information and knowledge obtained that is beneficial to the present study is analyzed
and discussed with supervisor to improve any findings. To exhibit all the work progress
in achieving the objectives, flow chart is the suitable tool. The entire work plan is shown
in the flow chart whereas the work scheduled will be shown in chart to help in work
planning.
3.2 Concrete materials
As we know, materials are the important constituents in the production of
concrete. In order to produce concrete for research purposes, the qualities and quantities
of concrete materials such as cement, fine aggregate, coarse aggregate, water, rice husk
ash and superplasticizer have to be ensured in good condition. The properties of those
concrete materials are discussed as follows.
32
Figure 3.1: Flowchart of research overview
Sieve
analysis
Sieving passing through
600μm sieve size
Sample preparation
Water
(pipe
water)
Rice Husk
Ash (RHA)
Cement (ordinary
Portland cement)
(OPC)
Fine
Aggregate
(River sand)
Superplasticizer
(GLENIUM
C380)
start
Mix design
Fcu=30MPa
Coarse
aggregate
(Granite)
Tests
UPV
test
Compressive
Strength test
Splitting
tensile
strength
Modulus
of
Rupture
Porosity
test
Modulus of
elasticity test
Water
Absorption
Data analysis
Report Processing
End
Concrete Casting: 200 cubes
Slump test
Unit weight test
Compacting factors test
Exposure to Elev
ated Temperature after 28 days
(200⁰C, 400⁰C, 600⁰C, 800⁰C)
Moist curing (28 days)
33
3.2.1 Cement
There are many types of cement with different compositions and different
function. The cement used in this experiment is pure Ordinary Portland Cement (OPC).
The oxide and compound compositions and fineness of a typical Portland cement are
shown in Table 3.1. The chemical compositions and fineness of cement affect the
strength of concrete. The early strength comes from C3S and the later strength from C2S.
Cement that hydrates more slowly will have a lower initial strength but higher ultimate
strength. The degree of fineness also affects the strength; the rate of hydration increases
with the increase of fineness.
Table 3.1: Chemical compositions of a typical Portland cement
Typical oxide composition (%)
Calculated compound compositions
(using Bogie’s equation) (%)
CaO
63 C
3
A
10.8
SiO
2
20 C
3
S
54.1
Al
2
O
3
6 C
2
S
16.6
Fe
2
O
3
3 C
4
AF
9.1
MgO
1.5 Minor compound
_
K
2
O , Na
2
O
2
SO3
1
Others
1
Loss on ignition
2
Insoluble residue
0.5
Resource: (Neville, 2005)
34
3.2.2 Aggregate
The most important properties of aggregate are shape, texture and maximum
aggregate size. Since aggregate is generally much stronger than cement paste the
strength of the aggregate is less important. Texture of aggregate affects the interlocking
between hardened cement paste and aggregates. Camp (2006) explained that the texture
of aggregate affects the tensile strength but will not affect the compressive strength.
Compressive strength depends on the strength of the aggregate itself. Maximum
aggregate size affect strength in several ways: larger particles reduce the specific surface
area of the aggregate which leads to a reduction in bond strength. Furthermore, larger
aggregate particles tend to restrain volume changes in the cement paste and therefore,
induce some internal stress, which will weaken the concrete. However, these effects can
be off setting by reducing the water content and therefore, the net effect of aggregate
size is small.
Fine aggregate was used as filler and reduce the void in concrete. The fine
aggregate used in the project is natural river sand. Sieve analysis was done according to
BS 812: 1991 to determine the percentage of sample passing each sieve.
Granite aggregate is used as the coarse aggregate in this project. The maximum
size of coarse aggregate used in this research is determined by sieve analysis, which
should comply with British Standard, BS 882: 1992. The relative density of these
aggregates was assumed. The general value of relative density in SSD condition is about
2.65.
The use of coarse aggregate would reduce the demand on the water content and
cement content for strength and workability of concrete mixes. Selection of good quality
35
of coarse aggregate would avoid the problem of bonding between aggregate and cement
mortar from occurring.
3.2.3 Water
According to JKR specification, the water use for concrete mixing must be
cleaned and free from the impurities or reactive agent. In this project, the water used was
obtained from the domestic water supply pipe in the concrete laboratory.
3.2.4 Superplasticizer
In the mix design, in order to produce medium strength concrete, a
superplasticizer needs to be added. The use of superplasticizer is to improve the
workability of the mix since the water per cement ratio is low in concrete. The
superplasticizer used is Glenium C380.
3.2.5 Rice husk ash
The rice husk used in this study was taken from a rice mill in Parit Buntar, Perak.
While, Rice Husk Ash (RHA) was produced from burning of rice husk in the open air.
This was then heated at 600ºC for 4 hours in an electrical furnace according to Singh
(2002), at heating rate of 20ºC per minute, and then allowed to cool down to room
temperature. The ash was then ground in a ball mill machine for 5 hours to get a fineness
that is almost equivalent to OPC fineness requirement which retained on 45μm sieve.
Figures 3.2 and 3.3 shows the production and grinding machine of Rice Husk Ash.
36
Figure 3.2: RHA production
Figure 3.3: Grinding machine
(a)
(b)
(c)
a:RHA partial burning b:RHA burning at 600ºC c:RHA after grinding
for 4 hours
a
b
c
37
3.3 Design of concrete mixes
Concrete mix design is essentially composed of a series of estimations,
calculations, trials/tests and control operations aimed at obtaining a sufficiently
satisfactory of concrete properties such as the percentage of superplasticizer and
water/binder ratio so that an acceptable workability of concrete could be achieved.
Figure 3.4 shows a small mixer machine used for trial mixture of concrete. The target
strength of the concrete mix is 30MPa at 28 days. The water to the binder ratio was fixed
at 0.55. The additive of RHA in different percentage as cement replacement 5%, 10%,
20%, 30%. The mix proportions are listed in Table 3.2.
Table 3.2: Mix proportions of concrete
MIX
Batched quantities (kg/m
3
)
OPC RHA Coarse
aggregate
Fine
aggregate
Water w/c superplasticizer
0% RHA 363 0 979 813 200 0.55 0.3%
5%RHA 344.85 18.15 979 813 200 0.55 0.3%
10%RHA
326.7 36.3 979 813 200 0.55 0.3%
20%RHA
290.4 72.6 979 813 200 0.55 0.3%
30%RHA
254.1 108.9 979 813 200 0.55 0.3%
38
Figure 3.4: Concrete mixer
3.4 Sample preparation
Concrete sample prepared according to BS 1881: Part 131: 1998.
3.4.1 Concrete mixing
The coarse aggregates and sand shall be mixed in the mixer for few minutes.
RHA should be the intimately mixed with cement before mixing. Then, spread the
blended cement-RHA in an even layer over the aggregate. A well mixing is done when
all the aggregates are fully covered by the blended cement-RHA. The water whiskered
with superplasticizer and add slowly within 30 second. The mixing process continued
after all materials have been added for a further 3 minute. Figure 3.5 shows the RHA
mixing with ordinary Portland cement.
39
Figure 3.5: RHA with portland cement
3.4.2 Filling the moulds
For each mixture, 10 cubes (100*100 *100 mm), 20 cylinders (100*200 mm)
and 10 rectangular (280*75*75) are placed on the vibrating machine table. The filling
process is then carried out with 3 layers of compaction to achieve a fully compacted
concrete. Vibration is stopped as soon as the surface of the concrete becomes relatively
smooth and has a glazed appearance to prevent the segregation of concrete and to
achieve maximum compaction of concrete samples. The concrete sample is placed at the
moist environment for 24 hours before removal of mould. Table 3.3 shows the number
of specimens prepared in this research and Figure 3.5 show the mould of the specimens.
40
Table 3.3: Number of concrete specimens used in the project
Elevated
Temperature
Control
Concrete
(0%RHA)
RHA
concrete
(5%
RHA)
Concrete
(10%RHA)
Concrete
(20%RHA)
Concrete
(30%RHA)
27
º
C
8
8
8
8
8
200
º
C
8
8
8
8
8
400
º
C
8
8
8
8
8
600
º
C
8
8
8
8
8
800
º
C
8
8
8
8
8
Total 40 40 40 40 40
Figure 3.6: Compacting of concrete samples using vibrating table
41
3.4.3 Curing
Curing can be described as keeping the concrete moist and warm enough so that
the hydration of cement can continue. More elaborately, it can be described as the
process of maintaining satisfactory moisture content and a favorable temperature in
concrete during the period immediately following placement, so that hydration of
cement may continue until the desired properties are developed to a sufficient degree to
meet the requirement of service. Figure 3.7 shows the curing concrete basin. After 24
hours, the concrete samples shall be removed from their relevant moulds and placed into
the curing tank. All concrete samples were clearly and indelibly marked with an
identification number and code to ensure no mistake. The details of curing method are
explained in BS 1881-111: 1983.
Figure 3.7: Moist concrete curing
42
Next, the specimens were dried at 105 ⁰C condition before being exposed to the
next elevated temperatures. The elevated temperatures in which the specimens were
being exposed were 200⁰C, 400⁰C, 600⁰C, 800⁰C by using an electric furnace in the
laboratory. Figure 3.8 shows the furnace. After reaching to the exposure temperature,
they were kept for one hour before cooling down. All tests were done after those
specimens were cooled to room temperature. The tests performed were ultrasonic pulse
velocity (UPV) test, compressive strength test, splitting tensile test, modulus of elasticity
test, flexural strength test. The main aim of the testing program is to assess the effect of
exposure to elevated temperatures on concrete with and without RHA.
Figure 3.8: Furnace
43
3.5 Testing
The properties of concrete are classified into two categories: fresh and hardened.
The durability of concrete depends upon the mix design and durability of aggregates.
Tests on the fresh concrete were performed to observe the workability and unit weight
and 7 tests on the hardened concrete to obtain the values of compressive strength,
splitting tensile, modulus of elasticity, UPV, flexural strength, porosity, and water
absorption of concrete. The properties which affect the strength and durability of a
concrete structure change over the life of structure, increasing with time.
3.5.1 Slump test
The procedure of slump test should refer to ASTM C143. The slump is a
measure of the consistency of concrete. A slump test indicates how much water has been
used in the mix. Figure 3.9 show the slump test. The less water, the stiffer and stronger
the mix will be. Hence, it is important to control the quality of produced concrete. This
test method covers a determination of the slump of hydraulic-cement concrete, both in
the laboratory and in the field. The procedure of this test is a sample of freshly mixed
concrete is placed and compacted in three layers by rodding in a mould shaped as the
frustum of a cone. The mould is raised, and the concrete allowed subsiding. The vertical
distance between the original and displaced position of the center of the top surface of
the concrete is measured and reported as the slump of the concrete.
44
Figure 3.9: Slump test
3.5.2 Compacting factor test
The compacting factor test (Bartos 1992; Bartos et al., 2002) measures the
degree of compaction resulting from the application of a standard amount of work. The
test was developed in Britain in the late 1940s and has been standardized as British
Standard 1881-103.
The apparatus, which is commercially available, consist of a rigid frame that
supports two conical hoppers vertically aligned above each other and mounted above a
cylinder, as shown in Figure 3.10. The top hopper is slightly larger than the bottom
hopper, while the cylinder is smaller in volume than both hoppers. To perform the test,
the top hopper is filled with concrete but not compacted. The door on the bottom of the
45
top hopper is opened, and the concrete is allowed to drop into the lower hopper. Once all
of the concrete has fallen from the top hopper, the door on the lower hopper is opened to
allow the concrete to fall to the bottom cylinder. A tamping rod can be used to force
especially cohesive concretes through the hoppers. The excess concrete is carefully
struck off from the top of the cylinder and the mass of the concrete in the cylinder is
recorded. This mass is compared to the mass of fully compacted concrete in the same
cylinder achieved with hand rodding or vibration. The compacting factor is defined as
the ratio of the mass of the concrete compacted in the compacting factor apparatus to the
mass of the fully compacted concrete. The standard test apparatus, described above, is
appropriate for maximum aggregate sizes of up to 20 mm. A larger apparatus is
available for concretes with maximum aggregate sizes of up to 40 mm.
Figure 3.10: Compacting factor test
46
3.5.3 Unit weight test
The procedure of unit weight test should refer to ASTM C138. This test method
covers the determination of the weight per cubic foot or cubic meter of freshly mixed
concrete and gives formulas for calculating the yield, cement content, and the air content
of the concrete. Yield is defined as the volume of concrete produced from a mixture of
known quantities of the component materials.
To determine the unit weight of freshly mixed concrete, a cylindrical metal
measure (container) of either 1/10-, 1/5-, or 1/2-cubic-foot capacity is required.
The measure should be filled with fresh concrete and consolidated in three layers. After
each layer is rodded 15 times by rod, i.e. after filling and consolidating, the top surface
is striked off, taking care to leave the measure level full. All excess concrete from the
exterior of the measure should be cleaned. Then weigh the net weight of the concrete
inside the measure is determined by subtracting the tare weight of the measure from the
gross weight of the measure and concrete.
3.5.4 Ultrasonic pulse velocity (UPV) test
This test method covers the determination of the velocity of propagation of
compressional waves in concrete. The Ultrasonic Pulse Velocity test was used to
determine the changes in the concrete which may occur with the replacement of RHA
and exposure at the elevated temperatures. It can thus be assessed using the guidelines
given in Table 3.4, which have been evolved for characterizing the quality of concrete in
structures in terms of the ultrasonic pulse velocity. This test method does not apply to
the propagation of other types of waves within the concrete. Pulses of compressional
47
waves are generated by an electro-acoustical transducer that is held in contact with one
surface of the concrete under test. After traversing through the concrete, the pulses are
received and converted into electrical energy by a second transducer located a distance L
from the transmitting transducer. The transit time T is measured electronically. Figure
3.11 shows the Ultrasonic Pulse Velocity Test instrument. The pulse velocity V is
calculated by dividing L by T. The position of the two transducers can be varied such
that direct, semi-direct, and indirect tests can be performed, which aids in mapping out
the volume of the defect. The method of testing is based on BS1881:1886 using
PUNDIT.
Table 3.4: Guideline of UPV test pulse
Pulse Velocity (km/second)
Quality of concrete
Above 4.5 Excellent
3.5-4.5
Good
3.0-3.5
Medium
Below 3.0
Doubtful
(Civil Engineering Portal, http://www.engineeringcivil.com)
Figure 3.11: Ultrasonic pulse velocity test instrument
48
3.5.5 Compressive strength test
Compressive strength is the most common performance measure used by the
engineer in designing a building and concrete structure. Hence, compressive strength is
the major aspect that was dealt with in this project. Figure 3.12 shows the compressive
machine apparatus. From the compressive strength value obtained, the durability of the
concrete as well can be predicted. The instrument of this test is ELE compression test
machine with capacity of 3000kN.
In this test, about 40 samples of 100mm cubes were used. The test was carried
out based on BS 1881: Part 116: 1983. There were two phases that need to be assessed.
For the first phase, concretes were tested after 28 days of moist curing. For the second
phase, the concretes were tested after heating to the elevated temperatures. In this phase,
the test was done after the specimen was cooled to the room temperature. This phase is
to monitor the residual strength of concretes after exposure to elevated temperatures.
Figure 3.12: Compressive strength machine
49
3.5.6 Splitting tensile strength test
This test method covers the determination of the splitting tensile strength of
cylindrical concrete specimens, such as molded cylinders and drilled cores. This test
method consists of applying a diametral compressive force along the length of a
cylindrical concrete specimen at a rate that is within a prescribed range until failure
occurs. This loading induces tensile stresses on the plane containing the applied load and
relatively high compressive stresses in the area immediately around the applied load.
Tensile failure occurs rather than compressive failure because the areas of load
application are in a state of triaxial compression, thereby allowing them to withstand
much higher compressive stresses than would be indicated by a uniaxial compressive
strength test result.
The splitting tensile strength of the concrete specimens was tested at 28 days.
The (102 mm) and (160 mm) cylindrical specimens were prepared at the same time as
the compressive strength specimens. The specimens were tested following ASTM C
496. The instrument of tensile strength machine is ELE with capacity 3000 kn, Figure
3.13 show the splitting tensile strength machine.
50
Figure 3.13: Splitting tensile strength machines
3.5.7 Modulus of rupture test
The modulus of rupture was tested at 28 days for each mixture. At the time of
casting two specimens were moulded following ASTM C 192. Beam specimens had a
cross sectional area of (75mm x 75mm x 285 mm). Specimens were stored in a water
tank following ASTM C 511. The beam specimens were tested following ASTM C 78
using third-point loading, Figure 3.14 shows the flexural strength test and the modulus
of rupture calculated using the equation:
51
R=PL/BD2 …(3.1)
Where
R = the modulus of rupture. (MPa)
P = the maximum applied load indicated by the testing machine (N)
L = the span length (mm)
b = the average width of the specimen at the fracture (mm)
d = the average depth of the specimen at the fracture (mm)
Figure 3.14: Flexural test machine
52
3.5.8 Porosity and water absorption
The objective of the test is to determine the percentage of porosity (P) and water
absorption (A) of the concrete. The testing was carried by using the water immersion
under vacuums. Figure 3.15 shows the vacuum saturation apparatus. The porosity and
water absorption were determined using the following equation:
(%)= (2 − 4)/(2 − 3) …(3.2)
(%)=(2 − 4)/4∗ 100 …(3.3)
Where:
W4 -weight of dried specimen before testing
W2 -weight of specimen in air after testing
W3 -weight of specimen in water after testing
Figure 3.15: Vacuum saturation apparatus
53
3.5.1 Modulus of elasticity
Rate of change the strain as a function of stress. The slope of the straight line
portion of a stress-strain diagram for hardened concrete at whatever age and curing
conditions may be designated. Tangent modulus of elasticity is the slope of the stress-
strain diagram at any point. Secant modulus of elasticity is stress divided by strain at any
given value of stress or strain. It also is called stress-strain ratio.
This test method covers the determination of chord modulus of elasticity
(Young's modulus). The modulus of elasticity of the concrete specimens was tested at 28
days. Figure 3.16 show modulus of elasticity machine. The cylindrical specimens
(102*160 mm) were moulded at the same time as the compressive strength specimens.
The specimens were tested following ASTM C 469.
Figure 3.16: Modulus of elasticity machine
54
CHAPTER 4
RESAULTS AND DISCUSSION
4.1 Introduction
This chapter discusses the result of the experiment work together with the
discussion. In this part, ten types of testing were discussed i.e., slump test, compaction
factor test, unit weight test, compressive strength test, splitting tensile strength test,
modulus of elasticity, modulus of rapture, UPV test, Porosity test and Water Absorption
test, Besides, Rice husk used in this study was obtained from a rice mill in Parit Buntar,
Perak. The rice husk ash (RHA) is produced from the burning of rice husk in a electrical
furnace at heating rate of 20ºC per minute up to 650ºC, maintained at this temperature
for 6 hours, and then allowed to cool down to room temperature. The ash was then
ground in a ball mill machine for 5 hours to get a fineness that is almost equivalent to
OPC fineness requirement which retained on 45μm sieve. In addition comparison
between the different percentage of RHA concrete mixes and the concrete without RHA
and the relationship between concrete properties will also be discussed in this chapter.
The effect of exposure to elevated temperature to concrete made with pure ordinary
Portland cement with the different percentage of RHA is also highlighted and discussed.
Firstly, the sieve analysis is performed to coarse aggregate and fine aggregate. During
the concrete mixing process, slump test, compacting factor test and unit weight are
performed to assess the changes in workability between the five different batches of
concrete. After 28 days of moist curing, all concrete was heated to temperature
105ºC±5ºC for 24 hours, except the concrete samples which has to be tested at 28 days,
55
they were conditioned in room temperature at about 27ºC. After being heated, some of
the samples were exposed to the next elevated temperature. The elevated temperature
exposures are at 200ºC, 400ºC, 600ºC and 800ºC. All tests were done after those
specimens were cooled to room temperature.
4.2 Sieve analysis
The purpose of the sieve analysis is to determine the particle size distribution of
aggregate and whether the aggregates used are in acceptable range as stated in BS 812,
Part1, 1991. It is very important as aggregates contribute to the major bulk volume of
concrete.
4.2.1 Sieve analysis of coarse aggregate
From the sieve analysis shown in Figure 4.1, the weight of the aggregate after the
sieving experiment is 1998.5g which is 0.075% different from first weight. Therefore,
the error of sieving is acceptable since the difference is less than 0.1%. According to
Nawy (1996), coarse aggregates are classified as such if the smallest particle is greater
than 6 mm. The maximum aggregate size is 20mm, which contains about 7.24% of
aggregate. The aggregate size between 10 to 20mm contributes as the main quantity in
the aggregate sample which are altogether contributing around 73% from the total
weight. There is about 0.025% of fine content in the aggregate sample but due to the low
percentage, the effect on concrete properties is insignificant. Actually, if the fine content
in the coarse aggregate is high, water demand will be increased to achieve a desired
level of workability. Hence, with the low content of fine particles, there is no potential
deteriorative effect on the concrete.
56
The actual grading requirements for coarse aggregate depend to some extend on
the shape and surface characteristics of the particles. For instance, angular, sharp,
particles with rough surfaces should have a slightly finer grading in order to reduce the
possibility of interlocking and to compensate for the high friction between the particles
(Neville, 1981).
Figure 4.1: Graph of sieve analysis for 20 mm coarse aggregate (BS 882:1992)
57
4.2.2 Sieve analysis of fine aggregate
Summary of the result for sieve analysis is shown in Figure 4.2. The minimum
weight required for fine aggregate is 500 g. The final weight of the aggregate after the
sieving process is 497.88g which is 0.9% different from initial weight value. Therefore,
the error is acceptable since the difference is less than 1%.
From the results, the range of the particle size sieve is small. The highest amount
of aggregate retained is at sieve size 1.18mm which has 29.13% of the total weight.
Generally, the sample can be considered as the well-graded fine aggregate found from
the fact that all the aggregate grading is well within the limitation in accordance to BS
882: 1992. A well-graded fine aggregate will reduce the voids content. Bond between
aggregate and cement paste is the important factor in the strength of concrete, especially
the flexural strength. There is no doubt then that the grading of aggregate is a major
factor in the workability and strength of a concrete mix.
Figure 4.2: Graph on sieve analysis for fine aggregate (BS 882:1992)
58
4.3 Rice husk ash
The RHA used in this study was taken from a rice mill factory near Parit Buntar.
The rice husk used was partially burnt at the factory, and it was burnt again at 600ºC for
4 hours in the laboratory furnace according to Singh et al, (2002) and then grinded in a
ground machine for 5 hours. The moisture content of RHA is 0.9%. Specific gravity is
2.11 and density of 553.35 kg/m3. The performance of RHA used needs to be assessed.
Therefore, the particle size of RHA determined in mastersizer machine as shown in
Figure 4.3, the maximum Particle size of RHA is 10 µm. In order to produce a
homogeneous and uniform size of particles, the size of RHA used is as fine as of the
cement; this allows us to focus more on the combination effect of RHA and cement on
the porosity and properties of concrete. In this study cement is replaced by weight with
RHA at 0%, 5%, 10%, 20% and 30%.
Figure 4.3: Particle size for RHA
59
4.4 Fresh concrete Test
4.4.1 Slump test
The purpose of the slump test is to assess the concrete mix’s workability. The
test is useful for the site inspection on the fresh concrete to check whether the moisture
content is increasing unexpectedly or the changes in the aggregate grading such as a
reduction of the fine particle in the mixture design (Neville, 1995). The test is finished
within 150 seconds to avoid the loss of workability with time.
For my casting work that had been divided into five batches, which were one
batch for the control mix and another four batches for the RHA 5%, 10%, 20%, 30%
concrete mix. From the results shown in Table 4.1 and Figure 4.4, 5%RHA concrete has
slightly lower slump value with 130 mm than a control mix with 140 mm. This may be
caused by the small amount of replacement of RHA in which has the only little effect on
the workability. Lower slump values for a fresh concrete mix indicate that the concrete
mix is the less workable or lower flow of fresh concrete. Generally, the cement
replacement with RHA causes the reduction in slump or loss in workability. Such
reduction may be due to the physical properties of RHA which has finer mean particle
size with higher total surface area and absorbs more water than OPC. The higher of the
surface area for RHA, the greater the demand for water. Therefore, more water is needed
to grease the mix when the RHA is added. As a result, the amount of water required to
maintain the workability of a mixture also increases. Therefore, the slump value of RHA
mix is lower than a control mix when the amount of water is fixed. Bui et al. (2005)
investigated the influence of rice husk ash on the slump of concrete mixtures made with
water to a binder ratio of 0.34. It is clear that slump decreased with the increase in RHA
content for same level of superplasticizer.
60
Table 4.1: Slump value of fresh concrete samples
Figure 4.4: Influence of RHA on slump of concrete
0
20
40
60
80
100
120
140
160
0% 5% 10% 20% 30%
Slump (mm)
RHA replacement (%)
Mixture Slump value
(mm) Water/Cement Superplasticizer
Control Mix 140 0.55 0.3%
RHA 5 130 0.55 0.3%
RHA 10 110 0.55 0.3%
RHA 20 85 0.55 0.3%
RHA 30 70 0.55 0.3%
61
4.4.2 Compacting factor test
The compacting factor test gives more information about compactability than the
slump test. The test is a dynamic test and thus is more appropriate than static tests for
highly thixotropic concrete mixtures but the amount of work applied to the concrete
being tested is a function of the friction between the concrete and the hoppers, which
may not reflect field conditions. From Table 4.2 and Figure 4.5, the workability of the
concrete mix with 5% of rice husk ash decreases slightly than the control mix. The
workability continuous to decrease from high to medium with increase rice husk ash
replacement in concrete.
Ikpong and Okpala (1992) studied the variation in workability of concrete with
the incorporation of RHA and attained the same level of workability, the mixes
containing rice husk ash required higher water content than those containing only
Ordinary Portland Cement as the binder and if the water content is fixed so the
workability will be decreased.
Table 4.2: Compacting factor test results and interpretation as described in British Road
Note 4 (Wilby, 1991)
Mix Compacting
factor
Slump
(mm)
Degree of
workability
0%RHA 0.95 100-180 High
5%RHA 0.949 100-180 High
10%RHA 0.934 50-100 Medium
20%RHA 0.92 50-100 Medium
30%RHA 0.9 50-100 Medium
62
Figure 4.5: Results of compacting factor test
4.4.3 Unit weight test
Unit weight or density of the fresh concrete can be determined by weighing a
known volume of concrete. The sample is generally weighed immediately before the air
content is determined. The results of unit weight for different percentage replacement of
RHA concrete are presented in Table 4.3 and Figure 4.6. The unit weight of the
concretes varies in the range of 2195 to 2364 kg/m3 depending on RHA content and air
content. The unit weight of most concretes decreased slightly with higher RHA content.
This is because RHA is lighter than cement. Also, the fine and coarse aggregate contents
reduced as the paste volume increased in the presence of RHA. However, the decrease in
the unit weight of concrete caused by RHA was marginal (1.3 to 4.4%). This is perhaps
attributed to the improved physical packing of the fresh concretes due to the finer
particle size of RHA as compared to cement. The replacement of RHAs for cement
results in reductions of density of concretes. This is due to specific density of the RHAs
is much lower than that of cement.
0.89
0.9
0.91
0.92
0.93
0.94
0.95
0.96
0% 5% 10% 15% 20% 25% 30% 35%
Compacting factor
RHA replacement (%)
63
Table 4.3: Measured unit weight for different percentage of RHA
Figure 4.6: Results of unit weight test
4.5 Hardened concrete testing
There are several reasons for testing of hardened concrete. This is because of
test can investigate the fundamental physical behavior of concrete such as elastic
properties and strength characteristics and these tests determined physical material
constants like the modulus of elasticity and quality control.
2200
2220
2240
2260
2280
2300
2320
2340
2360
2380
0 5% 10% 20% 30%
Unit weight (kg/m3)
RHA replacement (%)
Replacement by
RHA
Estimate unit
weight (kg/m3)
0% 2284
5% 2264
10% 2254
20% 2224
30% 2195
64
4.5.1 Compressive strength test
For the compressive test, five batches of casting were prepared for this test. The
first batch is the control mix without rice husk ash as a reference mix. And the other four
concrete mixes with a different percentage of rice husk ash at 5%, 10%, 20% and 30%.
All these replacement levels of RHA are in percentage by weight of the total cement
material. Figure 4.7 shows the comparisons of compressive strength test between the
control mix and concrete with different percentage of RHA in room temperature at 28
days. From the results obtained, it is clear that the compressive strength of RHA
concrete increases as the percentage of RHA replacement increases. The compressive
strength of 5% RHA replacement is 39.12 MPa higher than control mix by 3.53 MPa
and the highest compressive strength at 30% RHA replacement (46.5MPa) in
comparison with other mixtures.
Figure 4.7: Compressive strength of concrete with different RHA replacement levels at
28 days in room temperature
0
5
10
15
20
25
30
35
40
45
50
0% 5% 10% 15% 20% 25% 30% 35%
compressive strength (MPa)
RHA replacement (%)
65
The increase in compressive strength is due to the fact that the pozzolanic
reaction of RHA allowed it to increase the reaction with Ca(OH)2 to produce more
calcium silicate hydrates (C-S-H) resulting in higher compressive strength. In addition,
the fine RHA particles contributed to the strength development by acting as microfiller
and enhancing the cement paste pore structure.
Zhang et al. (1996) reported that achieving higher compressive strength and
decrease of permeability in RHA blended concrete is perhaps caused by the reduced
porosity, reduced calcium hydroxide content and reduced width of the interfacial zone
between the paste and the aggregate.
Yu et al. (1999) stated that the development of more CS-H gel in concrete with
RHA may progress towards the concrete properties due to the reaction among RHA and
calcium hydroxide in hydrating cement.
Dakroury et al. (2008) reported that using 30% RHA as a replacement of part of
cement could be considered optimum for all content of W/C ratios in the investigated
mortars because of its high value of compressive strength.
4.5.1.1 Compressive strength analysis after exposure to elevated temperatures
The compressive strength results after exposure to elevated temperatures are
shown in Table 4.4 and Figure 4.8. The relative compressive strength in comparison to
control mixture and control temperature is given in Figure 4.9 and Figure 4.10
respectively. It is found that the compressive strength at the heating setup can be divided
into two regions of 0–400 ºC and 400–800 ºC. A discrete pattern of strength earns and
then loss was observed in each region. The compressive strength increased during the
66
initial heating at temperature of 200⁰C. On heating to this temperature for one hour, the
compressive strength of all mixture increases from the control temperature values. The
compressive strength of 5% RHA mixture increases from 39.12MPa to 39.415 MPa and
the same behavior happened to all RHA concrete mixtures in which the compressive
strength for 10%RHA concrete increase from 39.48 MPa to 43.84 MPa, 20%RHA
concrete increase from 41.13 MPa to 51.52 MPa and 30% RHA concrete mix increase
from 46.5 MPa to 51.52 MPa as shown in the Table 4.10. A similar increase in strength
was observed in the control mixture increase from 35.95MPa to 37.47 MPa. This
increase may probably be due to the hydration of unhydrated cement, which was
activated as a result of a temperature rise (Poon et al., 2003). Therefore, the hydration
process is further promoted. In addition, the hydration process produces the Ca(OH)2,
hence, the pozzolanic reaction continues to take place at these temperatures. Therefore,
the RHA concrete mixtures have a higher compressive strength than the control mixture.
Table 4.4: Compressive strength values (MPa) for concrete containing different
percentage of RHA at different temperatures exposure
Mix
Temperature 0%RHA 5%RHA 10%RHA 20%RHA 30%RHA
27ºC 35.955 39.12 39.485 41.137 46.5
200ºC 37.47 39.415 43.84 46.06 51.52
400ºC 38.21 41.06 45.005 48.92 49.545
600ºC 24.645 34.265 35.745 37.685 40.28
800ºC 11.6345 12.125 16.19 16.4 17.715
67
Figure 4.8: Residual compressive strength versus RHA replacement level
Figure 4.9:
Effect of RHA replacement levels on relative compressive strength at
different temperatures
0
10
20
30
40
50
60
0
%
5
%
10
%
20
%
30
%
Compressive strength (MPa)
RHA replacement (%)
27°C
200
°
C
400
°
C
600°C
800
°
C
0
20
40
60
80
100
120
140
160
180
0 200 400 600 800
Relative compressive strength (%)
Temperature(ºC)
0
%RHA
5%RHA
10%RHA
20
%RHA
30%RHA
68
Figure 4.10: Relative compressive strength of concretes at different elevated temperature
exposure
At temperature 400ºC, the compressive strength increases slightly for the control
mix from 37.47 MPa to 38.21 MPa. The compressive strength for 5% RHA concrete mix
increases from 39.415 MPa to 41 06MPa, 10% RHA concrete compressive strength
increases from 43.84 MPa to 45 MPa and 20%RHA concrete values increases from
46.06 MPa to 48.92 MPa. The maximum increase in compressive strength value in
comparison to the control concrete mixture was recorded by the 30%RHA concrete mix
which is about 29.6% and the maximum increased in compressive strength value in
comparison to the control temperature value was recorded by 20%RHA concrete which
is about 18.9%. This is because after heating above 200ºC, the unhydrated particles
could become fully dehydrated. Therefore, the compressive strength of the 30% RHA
concrete mixtures start to decrease from 51.52 MPa to 49.54 MPa was recorded because
of the cement content in these mixtures less than control mixture, 5%RHA and
0
20
40
60
80
100
120
140
0% 5% 10% 15% 20% 25% 30% 35%
Relative compressive strength (%)
RHA replacement (%)
27°C
200°C
400
°
C
600°C
800
°
C
69
10%RHA concrete mixtures. Therefore, after all unhydrated particles were fully
hydrated , the hydration products will begin to decompose.
At higher temperatures, the concrete shows decrease in compressive strength. At
a temperature of 600⁰C, the compressive strength of the control mixture decreased from
38.21MPa to 24.64 MPa and also compressive strength values for RHA concrete
mixtures achieved reduction in strength. The relative compressive strength for RHA
concrete mixtures at 600°C are 87.5%, 90.5%, 81.8%, 86.6% for 5%RHA, 10%RHA,
20%RHA, 30%RHA respectively from the room temperature strength values for each
mix. The loss of compressive strength is due to the chemical decomposition and the
change of the cement matrix. The relative compressive strength values for RHA concrete
mixtures are more than control mixture value by about 139%, 145%, 152.9%, 163.4%
for 5%RHA, 10%RHA, 20%RHA, 30%RHA, respectively. Yuzer et al. (2004) observed
serious changes in the mechanical properties of Portland cement mortars exposed to
elevated temperatures. They found that decreases in compressive strength of Portland
cement mortars started at 600ºC in the air cooled samples. Sakr (2005) stated that
reductions in compressive strength of concrete when exposed to elevated temperatures
can be attributed to the dehydration of concrete by driving out of free water and fraction
water of hydration of concrete due to high temperatures.
At exposure temperature of 800ºC the values of compressive strength decrease to
67.7% from the room temperature value for a control mix and the decrease of
compressive strength for RHA concrete mixtures is about 69%, 59%, 66.5%, 62% for
RHA concrete mixtures 5%RHA, 10%RHA, 20%RHA, 30%RHA respectively from
room temperature. This is due to the concrete start to decompose severely and the
70
bonding between the aggregate and then paste is weakened, because the paste contracts
following loss of water while the aggregate expands. Careful examination of failure
surfaces confirms such debonding phenomena. Xiao and Konig, (2004) stated that the
compressive strength of ordinary concrete started to decrease drastically when the
temperature reached above 400ºC, and at 800 ºC, the strength loss was about 80%.
4.5.2 Splitting tensile strength
The results of splitting tensile strength are shown in Figure 4.11. All the RHA
concrete mixes and control mix in room temperature at 28 days achieve similar results in
splitting tensile strength. According to the results, the splitting tensile strength increases
with the increase of RHA content in the concrete mixtures. The splitting tensile
increased from 2.345MPa to 2.789MPa by adding 5%RHA to the concrete, and 3.307
MPa 3.22, MPa and 3.287 MPa for 10%, 20%, 30% RHA concrete mixtures,
respectively. This result seems to agree with the finding of De Sensale, (2006) and Sakr.,
2006) that the tensile properties have been enhanced by adding RHA to the mixture, the
use of RHA resulted in significant improvement in the tensile strength.
Figure 4.11: Splitting tensile strength for different RHA replacement levels at 28 days
in room temperature
0
0.5
1
1.5
2
2.5
3
3.5
0% 5% 10% 15% 20% 25% 30% 35%
Splitting tensile strength (MPa)
RHA replacement (%)
71
When the concrete specimens are exposed to elevated temperatures, the splitting
tensile strength values show decrease for all concrete mixes. Table 4.5 and Figure 4.12
show the splitting tensile strength values in concrete mixes at age of (28) days and from
the relative residual splitting tensile strength comparison in control mix values and room
temperature values in Figures 4.13 and 4.14, respectively. It can be observed that the
splitting tensile strength decrease during initial temperature (200ºC) for all concrete
mixtures. The splitting tensile strength for a control mix decreased from 2.34MPa to
2.16 MPa and all RHA concrete mixtures decrease (5%-13%) from room temperature
value for each mix. The reduction in splitting tensile strength is due to decomposition of
calcium silicate hydrate. The splitting tensile strength for RHA concrete mixture at 200
ºC is more than splitting tensile strength for control mixture, the relative tensile strength
is about 123%, 141%, 131%, 132.5% for 5%RHA, 10%RHA, 20%RHA, 30%RHA
concrete mixture respectively from the control mix. This is due to the fact that the
pozzolanic reaction of RHA and the fine RHA enhancing the cement paste pore
structure.
Table 4.5: Splitting tensile strength values (MPa) for concrete containing different
percentage of RHA at different temperatures exposure
Mix
Temp 0%RHA 5%RHA 10%RHA 20%RHA 30%RHA
27ºC 2.3455 2.789 3.307 3.22 3.287
200ºC 2.1635 2.66 3.05 2.834 2.866
400ºC 1.919 2.3505 2.56 2.42 2.43
600ºC 1.28 1.3695 1.46 1.4 1.35
800ºC 0.625 0.635 0.735 0.649 0.5775
72
Figure 4.12: Residual splitting tensile strength versus RHA replacement levels at
different temperature
Figure 4.13:
Effect of RHA replacement levels on relative splitting tensile strength at
different temperatures
0
0.5
1
1.5
2
2.5
3
3.5
0%RHA 5%RHA 10%RHA 20%RHA 30%RHA
Splitting tensile strength (MPa)
RHA replacement (%)
27°C
200
°
C
400°C
600°C
800
°
C
0
20
40
60
80
100
120
140
160
0 200 400 600 800 1000
Relative residuall tensile strength (%)
temperature (ºC)
0%RHA
5%RHA
10
%RHA
20%RHA
30%RHA
73
Figure 4.14: Relative splitting tensile strength of concretes at different elevated
temperature exposure
At temperature of (400ºC), the splitting tensile strength decreased for all concrete
containing RHA and control mix. The decreased in splitting tensile strength for the
control mix from 2.16MPa to 1.919 MPa, the relative splitting tensile strength is about
84%, 77.5%, 75%, 74% for RHA concrete mixes 5%RHA, 10%RHA, 20%RHA,
30%RHA respectively from room temperature and the relative splitting tensile about
122%, 133.5%, 126%, 126.5% for RHA concrete mixtures 5%RHA, 10%RHA,
20%RHA, 30%RHA respectively from the control mixture.
At temperature of (600ºC), the splitting tensile strength decreased for the control
mix by about 45% from room temperature value and the decrease for concrete mixes
containing RHA ranged between 51%-59%. The highest relative residual rate of splitting
tensile strength is for concrete containing 5%RHA compared with the room temperature
value that is about (49%) and the least relative splitting tensile is for 30%RHA concrete
mix about (41%). The highest relative residual rate of splitting tensile strength for RHA
0
20
40
60
80
100
120
0% 5% 10% 15% 20% 25% 30% 35%
Relative splitting tensile strength (%)
RHA replacement (%)
27°C
200°C
400
°
C
600°C
800°C
74
concrete mixtures is for 10%RHA concrete mix compared with control mixture value
that is about (114%) and the least value relative splitting tensile strength is for 30%RHA
concrete mixture which is about (105%).
At the highest exposure temperature of 800ºC, the concrete shows a sharp
decrease of splitting tensile value. The decrease of strength to 73% for a control mix
from the room temperature value and the decrease of splitting tensile is about 77%, 78%,
80% and 93% for RHA concrete mixtures 5%, 10%, 20% and 30% respectively from
room temperature splitting tensile values for each mix. This severe strength loss is
attributed not only to the decomposition of the hydration products but also to the thermal
incompatibility between aggregates and cement paste. The effect of crack coalescence is
more considerable in the splitting tensile strength than the compressive strength. This
largely explains why the rate of the splitting tensile strength loss compared to
compressive strength loss increases with the increase in temperatures.
4.5.3 Ultrasonic pulse velocity (UPV)
The Ultrasonic Pulse Velocity (UPV) systems are designed to identify and map
voids, honeycomb, cracks, delaminations, and other damage in concrete, wood,
masonry, stone, ceramics, and metal materials. UPV tests are also performed to predict
strength of concrete. For example, the higher the velocity, the better of the quality of
concrete.
From Figure 4.15, the result shows an increasing trend for RHA concrete mixes
respectively from a control mix at room temperature. The pulse velocity for 5%RHA is
3.79 (km/sec) slightly higher than a control mix 3.64 (km/sec) and means that the quality
of concrete is getting better as RHA increases at age 28 day. It is due to the hydration
75
process of cement and as well as a pozzolanic reaction for the concrete mixes, which
contain RHA.
Figure 4.15: Ultrasonic pulse velocities versus RHA replacement level at 28 days in
room temperature
According to Safiuddin et al. (2010) suggests that the use of RHA improved the
quality of concrete through reduced porosity and densification of its pore structure. The
physical and chemical modification of the pore structure of concrete occurs in the
presence of RHA due to its microfilling and pozzolanic effects. This results in pore
refinement and porosity reduction leading to a dense pore structure in both bulk paste
matrix and transition zone of concrete that contributes to the increase in ultrasonic pulse
velocity.
When the concrete specimens are exposed to elevated temperature, the result
shows a dramatic reduction in ultrasonic pulse velocity with increasing temperature as
shown in Table 4.6 and Figure 4.16. The velocity decreases, meaning the quality of
3.6
3.65
3.7
3.75
3.8
3.85
3.9
3.95
4
4.05
0% 5% 10% 15% 20% 25% 30% 35%
pulse velosity(km/sec)
RHA replacment (%)
76
concrete is getting lower in comparison to the concrete at the room temperature
condition. Figures 4.17 and 4.18 show the relative residual UPV in comparison to
control mix and room temperature respectively, the loss in pulse velocity is due to the
combination of the effects of drying, internal cracking as well as to the changes in the
microstructure of the paste on heating, leading to chemical decomposition. The bonding
between aggregate and binder has been weakened because of the heat. As a result, the
quality of the concrete is affected.
Comparing the control concrete mixture and RHA concrete mixtures, it can be
observed that the quality of RHA concrete mixtures is better than that of the normal
concrete in almost all the scenario and condition, including moist curing at the age of 28
day and at elevated temperatures exposures. The maximum different of UPV between
RHA concrete mixtures and control mix occure at 600ºC, the relative pulse velocity are
154%, 157%, 161%, 162% for 5%RHA, 10%RHA, 20%RHA, 30%RHA respectively
from the control mix. According to the general classification of the quality of concrete
on the basis of the pulse velocity which is given in Table 3.7 in Chapter 3, the quality of
concrete mixes can be regarded in two phases at the elevated temperatures. At phase 27-
200ºC, the pulse velocity range between 3.3– 4 km/sec, so the quality of concrete mixes
can be regarded as good quality concrete and the second phase 400-800ºC, the pulse
velocity range of 0.2-2.27 km/s, therefore, the quality of concrete mixes can be regarded
as poor and very poor quality concrete, this is because as the temperature increases, the
chemical decomposition causes the bonding to weaken and the quality of the concrete is
affected.
77
Table 4.6: UPV values (km/sec) for concrete containing different percentage of RHA
at different temperatures exposure
Figure 4.16: Residual UPV versus RHA replacement level at different temperature
0.00
0.50
1.00
1.50
2.00
2.50
3.00
3.50
4.00
4.50
0%RHA 5%RHA 10%RHA 20%RHA 30%RHA
Ultrasonic pulse velosity (km/sec)
RHA replacement (%)
27°C
200
°
C
400
°
C
600°C
800
°
C
Mix
Temp 0%RHA 5%RHA 10%RHA 20%RHA 30%RHA
27ºC 3.64 3.79 3.77 3.82 4.00
200ºC 3.30 3.46 3.55 3.47 3.72
400ºC 2.22 2.62 2.63 2.64 2.66
600ºC 1.13 1.75 1.78 1.83 1.85
800ºC 0.64 0.71 0.75 0.68 0.65
78
Figure 4.17: Effect of RHA replacement level on relative UPV at different temperatures
Figure 4.18: Relative UPV of concretes at different elevated temperature exposure
0
20
40
60
80
100
120
140
160
180
0 200 400 600 800 1000
Relative residual UPV (%)
temperature(ºC)
0%RHA
5%RHA
10
%RHA
20%RHA
30
%RHA
0
20
40
60
80
100
120
0% 5% 10% 15% 20% 25% 30% 35%
Relative residual UPV (%)
RHA replacement (%)
27°C
200°C
400
°
C
600°C
800°C
79
4.5.4 Flexural strength
The flexural strength of concrete with RHA was tested according to ASTM C 78.
The flexural beams were prepared, cured in the standard manner and tested using the
three point loading method. The flexural strength is the ability of a beam or slab to resist
failure in bending. The results of the flexural strength test are shown in Figure 4.19. The
values were in the range of 3-3.92 MPa in room temperature at 28 days of moisture
curing. The results show that the addition of RHA to concrete resulted in an increase in
the flexural strength and the higher flexural strength was for the 20%RHA mixture
which is about 3.92 MPa. This is due to the increased pozzolanic reaction and the
packing ability of the RHA fine particles (Zhang and Malhotra, 1995).
Figure 4.19: Flexural strength versus RHA level of replacement in moist
curing at 28 days
0
0.5
1
1.5
2
2.5
3
3.5
4
4.5
0% 5% 10% 15% 20% 25% 30% 35%
flexural strength (MPa)
RHA replacement (%)
80
When the concrete was exposed to high temperature the flexural strength for all
concrete mixtures with or without RHA reduce from the control temperature as shown in
Table 4.7 and Figure 4.20 and the relative residual flexural strength in comparison to
control mix value and room temperature value, respectively is shown in Figures 4.21 and
4.22. At 200ºC temperature, the flexural strength reduce for control mix from 3.02 MPa
to 2.95 and the RHA concrete mixtures values became 3.05MPa, 3.19MPa, 3.97 and
3.19 for 5%RHA, 10%RHA, 20%RHA, 30% RHA respectively. Similar to splitting
tensile strengths of concrete, the flexural strength decreased with temperature rise. Once
again the binder material type had influenced the extent of strength loss.
At 400ºC temperature, the flexural strength for control mix reduce to 60% from
room temperature, the relative flexural strength for 5%RHA, 10%RHA, 20%RHA and
30%RHA concrete mixtures is about 52%, 54%, 51% and 52% respectively from room
temperature and 134%, 153%, 167.7%, 168% from control mixture.
The decrease in flexural of control concrete mixture is much more compared to
that of RHA concrete mixtures. And this shows that RHA concrete is more resistant to
the effect of high temperature. However, above 600 ºC, decrease in the strength of both
concretes rapidly increases. The reason for this is that there is no significant change in
concretes up to a temperature of 300 ºC in aggregate and mortar phases, and that there
are significant changes in aggregate and cement phases after this temperature. These
results are in aggrement with the results of various research studies (Janotka, 1999; Saad,
1996). The highest value of flexural strength was recorded by 20%RHA at all
temperature exposures.
81
Table 4.7: Flexural strength values (MPa) for concrete containing different percentage
of RHA at different temperatures exposure
Figure 4.20: Residual flexural strength versus RHA replacement level at different
temperature
0.00
0.50
1.00
1.50
2.00
2.50
3.00
3.50
4.00
4.50
0%RHA 5%RHA 10%RHA 20%RHA 30%RHA
flexural strength (MPa)
RHA replacement (%)
27
°
C
200
°
C
400°C
600
°
C
800
°
C
Mix
Temp 0%RHA 5%RHA 10%RHA 20%RHA 30%RHA
27 3.02 3.12 3.38 3.92 3.40
200 2.95 3.05 3.19 3.79 3.19
400 1.20 1.62 1.84 2.01 1.95
600 0.51 0.64 0.67 0.89 0.75
800 0.09 0.11 0.13 0.16 0.13
82
Figure 4.21: Relative flexural strength at different temperatures
Figure 4.22: Relative flexural strength of concretes at different elevated temperature
exposure
0.00
20.00
40.00
60.00
80.00
100.00
120.00
140.00
160.00
180.00
200.00
0 200 400 600 800 1000
Relative flexural strength
Temperature (°C)
0
%RHA
5%RHA
10%RHA
20
%RHA
30%RHA
0.00
20.00
40.00
60.00
80.00
100.00
120.00
0% 5% 10% 15% 20% 25% 30% 35%
Relative residual flexural strength (%)
RHA replacement (%)
27°C
200°C
400
°
C
600°C
800°C
83
4.5.5 Modulus of elasticity
The elastic modulus, defined as the ratio of the elastic modulus, taken as the
tangent to the stress-strain curve at the origin. The results of the modulus of elasticity are
shown in Figure 4.23. The values of the static modulus of elasticity were in the range of
(16.4 - 24.9) GPa. It can be noted that the addition of RHA to concrete exhibited the
increase on the elastic properties; the highest value was recorded by 20%RHA concrete
mixture. This is due to the increased reactivity of the RHA. Concretes incorporating
pozzolanic materials usually show comparable values for the elastic modulus in
comparison to the OPC concrete (Giaccio et al., 2007; Sata et al., 2007).
Figure 4.23: Modulus of elasticity versus RHA level of replacement at 28 days in room
temperature
After exposed to elevated temperature, the elastic modulus decreased with a
temperature rise as shown in Table 4.8 and Figure 4.23. The relative modulus of
elasticity in comparison to the control mixture and room temperature in Figures 4.24 and
4.25 respectively shows that at 200ºC temperature, the elastic modulus value increased
0
5
10
15
20
25
30
0% 5% 10% 15% 20% 25% 30% 35%
Modulus of elasticity (GPa)
RHA replacement(%)
84
for all concrete mixtures with or without RHA, the relative elastic modulus for control
mixture is about 107% from room temperature and about 135%, 116%, 120.5%, 116.5%
for 5%RHA, 10%RHA, 20%RHA, 30%RHA, respectively. Moisture had an effect on
the modulus of elasticity of concrete also, though not as great as temperature. A
completely saturated specimen will have a lower modulus of elasticity than an oven dry
specimen.
At 400ºC temperature, the elastic modulus decreases for control mix 41% from
room temperature value and about 11.5%, 43%, 23%, 12% for 5%RHA, 10%RHA,
20%RHA, 30%RHA concrete mixtures, respectively. This is due to the dehydration
progressed and the bond between materials was gradually lost. With further increase in
temperature, Up to about 600ºC the elastic modulus of all concrete mixtures decreased
in a similar fashion, reaching to about (45%- 74%) of its initial values.
Table 4.8: Modulus of elasticity values (GPa) for concrete containing of RHA at
different temperatures exposure
Mix
Temp 0%RHA 5%RHA 10%RHA 20%RHA 30%RHA
27ºC 16.41 16.44 23.17 24.63 19.92
200ºC 17.57 22.29 26.88 29.70 23.21
400ºC 9.62 14.54 15.54 17.89 17.53
600ºC 4.39 6.89 10.95 13.54 9.88
800ºC 2.69 2.55 3.27 5.14 2.75
85
Figure 4.24: Residual modulus of elasticity versus RHA replacement level at different
temperature
Figure 4.25: Effect of RHA replacement levels on relative modulus of elasticity at
different temperatures
0
5
10
15
20
25
30
35
0
%RHA
5
%RHA
10
%RHA
20
%RHA
30
%RHA
Modulus of elasticity (GPa)
RHA replacement (%)
27°C
200
°
C
400
°
C
600°C
800
°
C
0
50
100
150
200
250
300
350
0 200 400 600 800
Relative elastic modulus (%)
Temperature ( °C)
0
%RHA
5
%RHA
10%RHA
20
%RHA
30
%RHA
86
Figure 4.26: Relative elastic modulus of concretes at different elevated temperature
exposure
4.5.6 Porosity test
The results of porosity in Figure 4.27 is show that the porosity for the different
percentage of RHA is reduced compared to control mix in room temperature at 28 days.
The porosity of 5% RHA slightly decreases than control temperature from 12.88 to
12.18, at 10% RHA the porosity is 11.64 followed by a decrease in porosity for
20%RHA to 10.26 and then to 9.39 for 30%RHA. Thus, it was understood that the
physical and chemical effects of RHA modified the open channels at the cement paste
matrix and transition zone of concrete leading to a discontinuous pore structure with
reduced total porosity. Indeed, the presence of RHA contributes to produce a dense pore
structure in concrete by decreasing the amount and average size of the pores (Zhang et
al. 1996).
0
20
40
60
80
100
120
140
160
0% 5% 10% 15% 20% 25% 30% 35%
Relative residual modulus of elasticity
RHA replacement (%)
27°C
200°C
400
°
C
600°C
800°C
87
Figure 4.27: Porosity versus RHA replacement level at 28 days in room
temperature
There is a consensus among several researchers that with partial replacement of
cement by pozzolans, porosity decreases in concrete. Blended (or pozzolanic) cements
are being used worldwide to produce more homogenous hydration products by filling
and segmenting of the capillary voids and produce ultimately more denser and
impermeable concrete (Güneyisi et al., 2007).
When the concrete specimens are exposed to elevated temperatures, the porosity
for all concrete mixtures with or without RHA content increases as shown in Table 4.9
and Figure 4.28. The relative residual porosity in comparison to control mixture and
control temperature is shown in Figures 4.29 and 4.30, respectively. The increase in
porosity is due to heating process which removes the water in the concrete structure
rapidly than at normal condition. According to Chan et al (1999), at elevated
temperatures, concrete will experience the change of pore structure, known as the
‘microstructure coarsening effect’. Therefore, the increasing exposure temperature will
0
2
4
6
8
10
12
14
0% 5% 10% 15% 20% 25% 30% 35%
Porosity (%)
RHA replacement (%)
88
increase the coarsening effect to the concrete pore structure. This will induce higher
degree of interconnectivity in the pore system and increase porosity.
Furthermore, at all exposure temperatures, 30%RHA concrete show the least
value of porosity. At 800 ºC temperature, the porosity of 30%RHA concrete is about
17.99, the relative porosity about 191.5% from room temperature and 81.6% from
control mixture, followed by the porosity of 20%RHA concrete about 21.13% and the
relative porosity about 193.6% according to room temperature and 92% from control
mixture. The highest value of porosity of the control mixture is about 22.03%; the
relative porosity for a control mix at 800 ºC is about 171% from room temperature.
Table 4.9: Porosity values (%) for concrete containing different percentage of RHA at
different temperatures exposure
Mix
Temp 0%RHA 5%RHA 10%RHA 20%RHA 30%RHA
27ºC 12.88 12.18 11.64 10.26 9.39
200ºC 14.35 13.05 12.78 11.68 10.59
400ºC 16.41 15.66 15.07 14 12.23
600ºC 18.365 17.98 17.95 17.36 16.69
800ºC 22.038 21.39 21.13 20.27 17.99
89
Figure 4.28: Residual porosity versus RHA replacement level at different temperature
Figure 4.29: Effect of RHA replacement levels on relative porosity at different
temperatures
0
5
10
15
20
25
0
%RHA
5
%RHA
10
%RHA
20
%RHA
30
%RHA
Porosity (%)
RHA replacement (%)
27
°
C
200°C
400°C
600
°
C
800°C
0
20
40
60
80
100
120
140
0 200 400 600 800 1000
Relative porosity (%)
Temperature (ºC)
0%RHA
5%RHA
10
%RHA
20%RHA
30
%RHA
90
Figure 4.30: Relative porosity of concretes at different elevated temperature exposure
4.5.7 Water absorption test
Percentage of water absorption is a measure of the pore volume in hardened
concrete, which is occupied by water in saturated condition. Water absorption values of
RHA blended concrete specimens were measured as per ASTM C 642 after 28 days of
moist curing. From Figure 4.31, the water absorption for all mixes exhibits the same
behavior as for the case of porosity. RHA concrete mixtures show lower water
absorption value than that of the control mixture; its occurred due to the RHA is finer
than cement. The water absorption decreased by 11%, 18%, 24% and 30% for 5%RHA,
10%RHA, 20%RHA, and 30% RHA respectively from a control mix at room
temperature. The reduction of water absorption for RHA concrete may be due to the
0
50
100
150
200
250
0% 5% 10% 15% 20% 25% 30% 35%
Relative residual porosity (%)
RHA replacement (%)
27
°
C
200°C
400°C
600
°
C
800°C
91
pozzolanic reaction and filler effect which give additional development in concrete
density.
Figure 4.31: Water absorption versus RHA level of replacement at 28 days in room
temperature
Rodrigues et al. (2006) observed that the incorporation of RHA in the composites
could cause an extensive pore refinement in the matrix and in the interface layer, thereby
decreasing water permeability. According to Saraswathy et al.(2007) studied the effect
of partial replacement of cement with RHA at different replacement levels on the
porosity and water absorption of concrete and reported that the coefficient of water
absorption for rice husk ash replaced concrete at all levels was less than control
concrete.
After exposed to elevated temperature, water absorption for all concrete mixtures
increased from the control temperature values as shown in Table 4.10 and Figure 4.32.
The relative water absorption in comparison to control mix and room temperature is
0
1
2
3
4
5
6
7
0% 5% 10% 15% 20% 25% 30% 35%
water absorption (%)
RHA replacement (%)
92
shown in Figures 4.33 and 4.34. At temperature 200ºC, the relative water absorption is
112% for the control mix from room temperature, the maximum increase of water
absorption for RHA concrete mixes at 10%RHA concrete is about 18.2% from the
control temperature value and the least increase for 20%RHA concrete which is about
8.5%.
At temperature 400ºC, the relative water absorption is 130% for the control mix
and increased to 142.5%, 147.7%, 132% and 139% for RHA concrete mixes 5%RHA,
10%RHA, 20%RHA and 30%RHA respectively from the control temperature values and
the relative water absorption is about 91%, 87%, 77% and 74% for 5%RHA, 10%RHA,
20%RHA, 30%RHA concrete mixtures from the control mixture. Water absorption
shows the same behavior with porosity, which increased with elevated temperature.
Therefore, water absorption is quiet related with porosity value because of generally
water fill the pore system. The more pore volume and high interconnected pore system,
the concrete becomes easily to absorb water (Nurulhuda, 2006).
In addition, from the analysis at temperature 800ºC the water absorption shows
the highest increase for all concrete mixes. The water absorption for the control mix
increased to 81.3% from room temperature value and the highest relative water
absorption for RHA concrete mixtures at 30%RHA about 209% from room temperature
value. This is due to the increasing of microcrack and re-hydration reaction. The
occurrence of microcrack may become a path of obtrusion of water. Over, re-hydration
reaction will absorb more water to produce calcium hydroxide.
93
Table 4.10: Water absorption values (%) for concrete containing of RHA at different
temperatures exposure
Figure 4.32: Residual water absorption versus RHA replacement level at different
temperature
0
2
4
6
8
10
12
0%RHA 5%RHA 10%RHA 20%RHA 30%RHA
water absorption (%)
RHA replacement (%)
27°C
200°C
400
°
C
600°C
800°C
Mix
Temp 0%RHA 5%RHA 10%RHA 20%RHA 30%RHA
27ºC 5.8 5.21 4.78 4.43 4.06
200ºC 6.49 5.92 5.65 4.81 4.74
400ºC 7.53 7.42 7.06 5.84 5.64
600ºC 8.59 8.44 8.4 7.45 7.03
800ºC 10.52 10.23 9.77 8.75 8.5
94
Figure 4.33: Effect of RHA replacement levels on relative water absorption
at different temperatures
Figure 4.34: Relative water absorption of concretes at different elevated temperature
exposure
0
20
40
60
80
100
120
0 200 400 600 800 1000
Relative water absorption (%)
Temperature (ºC)
0
%RHA
5%RHA
10%RHA
20
%RHA
30%RHA
0
50
100
150
200
250
0% 5% 10% 15% 20% 25% 30% 35%
Relative residual water absorption (%)
RHA replacement (%)
27°C
200°C
400
°
C
600°C
800°C
95
4.6 Relationship between relative residual compressive strength and porosity
Figure 4.35 shows the relationship between residual compressive strength and
the porosity of concrete at elevated temperature. From the data analysis, at exposure
temperature from 27ºC-400ºC, the increasing of porosity happen with increase the
compressive strength value. This is maybe due to the coarsening effect which opens the
pore capillary. The opening of the pore capillary will induce the hydration of unhydrated
cement particles.
At temperature phase 400-800ºC, the compressive strength decrease significantly
and the porosity also significant increasing. This is due to the significant change in the
concrete structure start to occur. Therefore, since the compressive strength is quiet
related to the microstructure, the decreasing in the compressive strength values had
influenced with increasing of porosity.
Figure 4.35: Relationship between residual compressive and porosit
0
5
10
15
20
25
0
10
20
30
40
50
60
27
200
400
600
800
Porosity (%)
Compressive strength (MPa)
Temperature (ºC)
0%RHA.COMP 5%RHA 10%RHA.COMP 20%RHA
30RHA.COMP 0%RHA.POR 5%RHA.POR 10%RHA.POR
20%RHA.POR 30%RHA.POR
96
4.7 Relationship between relative residual compressive strength and splitting
tensile strength
Figure 4.36 shows the relationship between residual compressive strength and
the splitting tensile strength of concrete at the elevated temperatures. There is a variation
in the ratio of splitting strength/compressive strength. Room temperature has a more
positive effect on the splitting strength than on a compressive strength, but at 200°C
while splitting strength decreases, the compressive strength continues to increase which
shows that splitting strength is more sensitive to the high temperature effect than
compressive strength. The effect of crack coalescence is more significant in the splitting
tensile strength than the compressive strength. This largely explains why the rate of the
splitting tensile strength loss compared to compressive strength loss increases with the
increase in temperatures. The difference in the behaviors of the properties is getting
diminished approximately after around 400°C and disappears after 800°C.
Figure 4.36: Relationship between residual compressive strength and splitting tensile
strength
0.00
1.00
2.00
3.00
4.00
5
.
00
0
10
20
30
40
50
60
27
200
400
600
800
Splitting tensile strength (MPa)
Compressive strength(MPa)
Temperature (°C)
0%RHA.COMP 5%RHA.COMP 10%RHA.COMP 20%RHA.COMP
30RHA.COMP 0%RHA.SPL 5%RHA.SPL 10%RHA.SPL
20%RHA.SPL 30%RHA.SPL
97
4.8 Relationship between residual compressive strength and UPV
Figure 4.37 shows the relation between the residual compressive strength and the
ultrasonic pulse velocity. As temperature increased, the compressive strength increases
until 400ºC but the pulse velocity decrease from room temperature but still the quality of
the concrete would be classified good as indicated in Table 3.4 the guideline of UPV test
Pulse. After exposure to higher temperature of up to 400ºC, the compressive strength
decrease as pulse velocity. This is due to chemical decomposition of the concrete matrix
and the bonding between aggregate and binder has been weakening because of the heat.
Figure 4.37: Relationship between residual compressive strength and UPV
0.00
0.50
1.00
1.50
2.00
2.50
3.00
3.50
4.00
4.50
0
10
20
30
40
50
60
27 200 400 600 800
UPV)km/sec)
Compressive strength (MPa)
Temperature(ºC)
0
%RHA.COMP
5
%RHA.COMP
10
%RHA.COMP
20
%RHA.COMP
30
RHA.COMP
0
%RHA.UPV
5
%RHA.UPV
10
%RHA.UPV
20
%RHA.UPV
30%RHA.UPV
98
4.9 Relationship between residual porosity and UPV
Figure 4.38 shows that the increase in temperature exposure cause the porosity to
increase but the pulse velocity value decreased. Since, pulse velocity is regarding to the
microstructure condition which is performance of pulse velocity is much better when the
microstructure became denser. Therefore, the increasing in exposure temperature will
induce the increasing in pore structure by the ‘coarsening effect’ (Chan et al, 1991), and
will reduce the pulse velocity value. The pulse velocity and porosity are also influenced
by the moisture condition which is the increasing of the temperature will remove the
water from the concrete.
Figure 4.38: Relationship between residual UPV and porosity
0
5
10
15
20
25
0.00
0.50
1.00
1.50
2.00
2.50
3.00
3.50
4.00
4.50
27
200
400
600
800
porosity (%)
UPV (km/sec)
Temperature (°C)
0
%RHA.UPV
5
%RHA.UPV
10
%RHA.UPV
20
%RHA.UPV
30%RHA.UPV 0%RHA.POR 5%RHA.POR 10%RHA.POR
20%RHA.POR 30%RHA.POR
99
CHAPTER 5
CONCLUSIONS AND RECOMMENDATIONS
5.1 Conclusions
In this chapter, all the findings obtained from the research will be concluded.
Basically, the research investigated the suitability of Rice Husk Ash (RHA) as partial
cement replacement in concrete in moist curing condition and at elevated temperature
exposure. Based on the results of various tests on the properties of RHA concrete and
comparing these with the control mixture, the following conclusions can be drawn:
The replacement of RHA in concrete would reduce the slump value and
compacting factor compared to normal OPC concrete.
The replacement of RHA in concrete tends to reduce the unit weight of
concrete.
Increasing RHA fineness would enhance the strength of blended concrete;
this due to the increased pozzolanic activity and that RHA will act as
microfiller in the concrete matrix.
RHA is an effective pozzolan and resulted in enhancement in the compressive
strength of concrete. Its presence in concrete mixes has led to the increase in
compressive strength at 28 days water curing. 30 %RHA replacement was the
most optimum replacement and the relative compressive strength of 30%RHA
concrete about 130% from the control mix at 28days in room temperature.
100
The mechanical properties in terms of flexural and tensile strength have been
significantly improved with the inclusion of RHA, with the 20% RHA and
30%RHA showing the highest improvement. On the other hand, the value of
modulus was comparable with a slight increase in the RHA concrete mixtures
and the highest value at 20%RHA concrete mixture.
The inclusion of RHA enhanced the durability related properties of the
concrete by reducing the porosity and water absorption. Hence, it is expected
that the concrete contain RHA will have better durability performance under
aggressive exposure conditions.
Generally, the compressive strength further increases when they are
subjected to high temperature up to 200⁰C-400ºC. The 30%RHA concrete
has slightly higher compressive strength than normal OPC concrete in
moisture curing age and exposure temperature up to 400⁰C. However, when
subjected to higher temperature 400ºC-800ºC, the strength decrease and the
compressive strength RHA concrete would be higher than normal OPC
concrete, although both concrete strength would be in decreasing trend.
Generally, the tensile strength value for all concrete mixtures at the elevated
temperature start to decrease from the initial temperature at 200ºC. The
splitting tensile strength of concrete was more sensitive to high temperatures
than the compressive strength. RHA concrete mixtures higher tensile strength
than the control mix at all elevated temperatures and the highest value at
30%RHA concrete.
101
The elastic modulus of the all concrete mixtures increased at lower range of
elevated temperature, the relative modulus are (107%−135%) from room
temperature when exposing in the temperature 200℃. Then decrease at
higher temperature exposure. At 800 ℃, the relative elastic modulus was
only 14%−21% of the value at room temperature. 20%RHA concrete mixture
had the highest elastic modulus at all temperature exposure.
The flexural strength shows the same behavior with splitting tensile strength.
At a higher temperatures, the flexural strength values decrease. The relative
flexural strength values decrease at 200ºC temperature about (93%-98%) and
at 600ºC temperature the relative strength is about (27%-23%) from room
temperature. 20%RHA concrete mixture had a better flexural strength than
other mixes at all temperature exposure.
According to the results of the ultrasonic pulse velocity, it was decreased as
temperature increased. The relative UPV decrease to 90%-93% from room
temperature then continuous to decrease until 800ºC temperature where the
relative UPV is about 16%-20% from room temperature. The RHA concrete
mixtures shows better pulse velocity values than the control mix at all
temperature exposure and the best replacement at 20%RHA concrete.
Generally, the porosity and water absorption for all mixtures increased at
high temperature exposure due to concrete will experience the change of pore
structure, known as the ‘microstructure coarsening effect’. The RHA
concrete mixtures show dense pore structure than a control mix.
102
5.2 Recommendations for further research
Along the project, a few ideas have risen up and further research should be
looked into them.
The use of RHA in civil construction, besides reducing the environmental
pollution factors, the concrete characteristics have several improvements. In
general, the use of RHA as partial cement replacement material could improve
the long term properties of concrete.
There is a growing demand for fine amorphous silica in the production of
special cement and concrete mixes. Silica fume and the other pozzolans is
currently filling the market. Due to the limited supply of silica fumes and the
demand being high, this has necessitated the search for other mineral admixture
a great interest. RHA is a general term describing all types of ash produced from
burning rice husk, which is a waste product of rice industry.
RHA was reported to have very high silica content that’s depending on the time
of incineration and certain temperature. At 500ºC - 800ºC amorphous silica is
formed and at greater temperatures, crystalline silica is formed. The type of
RHA suitable for pozzolanic activity is amorphous rather than crystalline.
Alternatively, the RHA used can also be produced or milled to a much finer
size than cement, having a very small particle size of 10 microns or so much
finer will help fills the interstices in between the cement and aggregate. That is
where the strength and density come from.
103
For future used, the percentage of replacement of cement with RHA could be
increased in the range between 35%-50%, so that effect of higher replacement of
RHA can be analyzed.
Equally, the financial competitiveness of the material should be pointed out,
since concrete with rice husk ash replacement by weight of cement will
definitely have a lower cost compared to those using other types of additions.
This research is to find out the performance of concrete with a different
percentage of RHA replacement by weight of cement when exposed to elevated
temperature. The performance of the concrete construction due to fire should be
assessed. In order to improve this research, the time and the condition of
exposure should be more variable. The comparison to the actual fired building
also should be done purposely to get actual behaviors of concrete properties due
to fire.
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Appendices
APPENDIX A
SIEVE ANALYSIS
Table A1: Sieve analysis for fine aggregates
Sieve Opening
(mm)
Passing % Upper Lower
5 97.4 100 89
2.36 82.32 100 60
1.18 53.312 100 30
0.0006
33.08 100 15
0.0003
14.738 70 5
0.00015 6.272 15 0
0 0.424 0 0
Sieve
size(mm)
Sieve (g) Sample +
sieve (g)
Retained
(g)
% Retained
% Passing
10mm
------
-----
------
------
------
5mm
490
503
13
2.611071
97.4
2.36mm
380.4
455.8
75.4
15.14421
82.32
1.18mm
395.26
540.3
145.04
29.13152
53.312
600µm
408.74
509.9
101.16
20.31815
33.08
300µm
369.09
460.8
91.71
18.4201
14.738
150µm
270.07
312.4
42.33
8.502049
6.272
75µm
344.2
357.4
13.2
2.651241
3.632
pan
420.86
436.9
16.04
3.22166
0.424
total
497.88
100
Fine aggregates sample weight = 500 g
Table A2: Sieve analysis for course aggregates
Sieve Opening
(mm)
Passing % Upper Lower
37.5 100 100 100
20 92.75 100 85
14 52.77 70 0
10
19.71 25 0
5
0.1 5 0
2.36 0 0 0
0 0 0
Sieve
size(mm)
Sieve (g) Sample +
sieve (g)
Retained
(g)
% Retained
% Passing
37.5
1251.4
1251.4
0
0
100
20
905.5
1050.2
144.7
7.24043
92.75
14
1050.3
1850.2
799.9
40.02502
52.77
10
1158.3
1819.4
661.1
33.07981
19
.7
15
5
909.8
1302.1
392.3
19.62972
0.1
2.36
805.2
805.2
0
0
0
pan
950.4
950.9
0.5
0.025019
0.00075
1998.5
100
Coarse aggregates sample weight = 2000 g
APPENDIX B
COMPRESSIVE STRENGTH
Table B: Result of experimental of Compressive Strength Test
NO Temperature
0%RHA Average 5%RHA Average 10%RHA Average 20%RHA Average 30%RHA Average
1
27ºC
36.34
35.955
38.81
39.12
37.46
39.485
40.03
41.14
47.4
46.5
2 35.57 39.43 41.51 42.25 45.6
3
200ºC
38.8
37.47
33.76
39.415
44.14
43.84
45.16
46.055
46.87
51.52
4 36.14 45.07 43.54 46.95 56.17
5
400ºC
38.52
38.21
42
41.065
44.31
45.005
48.33
48.92
52.41
49.545
6 37.9 40.13 45.7 49.51 46.68
7
600ºC
25.29
24.645
32.93
34.265
36.11
35.745
37.13
37.685
39.21
40.28
8 24 35.6 35.38 38.24 41.35
9
800ºC
9.909
11.6345
10.62
12.125
17.38
16.19
18.4
16.4
17.53
8.95
10 13.36 13.63 15 14.4 17.9
Figure B: Compressive Strength Test
0
10
20
30
40
50
60
0 200 400 600 800
Compressive strength (MPa)
Temperature (ºC)
0
%
5
%
10%
20
%
30
%
APPENDIX C
SPLITTING TENSILE STRENGTH
Table C: Result of experimental Splitting Tensile Strength
NO Temp 0%RHA Average 5%RHA Average 10%RHA Average 20%RHA Average 30%RHA Average
1
27ºC
2.38
2.35
2.76
2.79
3.61
3.31
3.39
3.23
3.19
3.28
2 2.31 2.82 3.01 3.06 3.38
3
200ºC
2.13
2.16
2.63
2.66
3.05
3.06
2.54
2.83
2.89
2.87
4 2.20 2.69 3.06 3.11 2.84
5
400ºC
2.12
1.92
3.08
2.35
2.20
2.46
2.53
2.42
2.02
2.08
6 1.72 1.63 2.72 2.31 2.14
7
600ºC
1.30
1.28
1.30
1.37
1.03
1.21
1.29
1.07
1.39
1.35
8 1.26 1.44 1.39 0.85 1.31
9
800ºC
0.70
0.63
0.66
0.59
0.51
0.50
0.50
0.55
0.67
0.58
10 0.55 0.51 0.50 0.60 0.49
Figure C : Splitting Tensile Strength
0
0.5
1
1.5
2
2.5
3
3.5
0 200 400 600 800
Splitting Tensile Strength (MPa)
Temperature (ºC)
0
%RHA
5%RHA
10
%RHA
20%RHA
30%RHA
APPENDIX D
ULTRASONIC PULSE VELOCITY
Table D: Result of ultrasonic pulse velocity tests
NO
TEMPERATURE
0%RHA
AVG
5%RHA
AVG
10%RHA
AVG
20%RHA
AVG
30%RHA
AVG
1
27
3.68
3.643331
3.783102
3.7938
3.571429
3.76853
3.73599
3.823666
3.955175
4.001879
2
3.61
3.804692
3.965631
3.911343
4.048583
3
200
3.29
3.30125
3.506721
3.460568
3.410253
3.545618
3.510825
3.47461
3.809524
3.722944
4
3.31
3.420753
3.680982
3.438395
3.636364
5
400
2.21
2.22143
2.826189
2.620824
2.723559
2.636206
2.688172
2.641103
2.642008
2.667503
6
2.23
2.415459
2.548853
2.594034
2.692998
7
600
1.05
1.13499
1.745708
1.74698
1.789976
1.78
1.898134
1.83
1.88798
1.850061
8
1.22
1.748252
1.763668
1.753873
1.812141
9
800
0.62
0.636715
0.75
0.71
0.773196
0.74545
0.7
0.68
0.665188
0.651404
10
0.65
0.67
0.717703
0.66
0.63762
Figure D: Ultrasonic Pulse Velocity
0.00
0.50
1.00
1.50
2.00
2.50
3.00
3.50
4.00
4.50
0 200 400 600 800
UPV (km/sec)
Temperature (°C)
0%RHA
5
%RHA
10%RHA
20%RHA
30
%RHA
APPENDIX E
POROSITY
Table E: Result of experiment Porosity test
NO Temperature
0%RHA Average
5% RHA Average
10%RHA Average
20%RHA Average
30%RHA
Average
1
27°C
14.14
12.88
12.66
12.18
11.94
11.64
11.56
10.27
11.08
9.40
2 11.63 11.70 11.34 8.98 11.05
3
200°C
14.24
14.36
12.96
13.05
12.75
12.78
11.46
11.68
10.59
10.59
4 14.48 13.14 12.81 11.91 9.40
5
400°C
15.81
16.41
15.33
15.66
15.94
15.08
13.89
14.00
12.23
12.23
6 17.01 15.99 14.22 14.12 13.29
7
600°C
17.59
18.37
17.45
17.98
17.93
18.50
16.92
17.37
17.51
16.70
8 19.14 18.51 19.08 17.82 15.88
9
800°C
22.04
22.03
20.90
21.39
19.69
21.13
21.22
20.28
17.52
17.99
10 22.02 21.88 22.57 19.34 18.46
Figure E: Porosity test
0
5
10
15
20
25
0 200 400 600 800
Porosity (%)
Temperature (ºC)
0%RHA
5%RHA
10
%RHA
20%RHA
30%RHA
APPENDIX F
WATER ABSORPTION
Table F: Result of experimental Water Absorption Test
NO TEMPERATURE
0%RHA Average 5% RHA Average 10%RHA
Average 20%RHA Average 30%RHA Average
1
27°C
6.43
5.80
5.48
5.21
4.25
4.78
4.03
4.43
4.19
4.07
2 5.17 4.94 5.31 4.83 3.94
3
200°C
6.43
6.49
5.87
5.92
5.60
5.65
4.71
4.81
4.63
4.74
4 6.56 5.97 5.70 4.91 4.86
5
400°C
7.19
7.53
7.51
7.42
7.16
7.06
5.78
5.84
5.25
5.64
6 7.88 7.33 6.96 5.90 6.03
7
600°C
8.17
8.59
8.77
8.44
8.13
8.41
7.24
7.45
7.55
7.03
8 9.01 8.11 8.68 7.66 6.52
9
800°C
10.64
10.52
10.04
10.23
9.01
9.77
9.21
8.76
8.20
8.50
10 10.40 10.42 10.53 8.30 8.80
Figure F: Water Absorption Test
0
2
4
6
8
10
12
0 200 400 600 800
Water Absorption (%)
Temperature (ºC)
0%RHA
5
%RHA
10
%RHA
20%RHA
30
%RHA
APPENDIX G
Flexural Strength Test
Table G: Result of experimental Flexural Strength Test
NO Temperature
0%RHA Average 5%RHA Average 10%RHA Average 20%RHA Average 30%RHA Average
1
27ºC
2.79053
3.015689
3.000302
3.115289
3.25296
3.38472
4.065487
3.923007
3.53939
3.399739
2
3.240847 3.230276 3.51648 3.780527 3.260089
3
200 ºC
2.980379
2.953476
2.867105
3.04869
3.17917
3.18787
3.827354
3.78869
3.125612
3.19139
4
2.926572 3.111757 3.196569
3.750027 3.257167
5
400 ºC
1.171034
1.200219
1.61
1.621
1.654074
1.836167
1.986791
1.95333
1.999514
2.012779
6
1.229404 1.632 2.018259
1.91987 2.026044
7
600 ºC
0.533
0.5105
0.724136
0.638279
0.69917
0.665855
0.95245
0.892314
0.611668
0.746779
8
0.488 0.552421 0.632539
0.832178 0.88189
9
800 ºC
0.097156
0.097055
0.114157
0.117067
0.105084
0.13
0.268545
0.159215
0.088616
0.13288
10
0.096954 0.119976 0.154916
0.049884 0.177144
Figure G1: Flexural Strength Test
0.00
0.50
1.00
1.50
2.00
2.50
3.00
3.50
4.00
4.50
0 200 400 600 800
flexural strength (MPa)
Temperature (ºC)
0
%RHA
5%RHA
10%RHA
20
%RHA
30%RHA
Flexural Strength test samples
Force-stroke curve for 0%RHA:
FIGURE G: Force- stroke curves at 27ºC for specimen 0%RHA
Figure G2: Force- stroke curve at 27ºC for specimen 0%RHA
FIGURE G3: Force- stroke curves at 200ºC for specimen 0%RHA
FIGURE G3: Force- stroke curves at 400ºC for specimen 0%RHA
Figure G3: Force- stroke curves at 200ºC for specimen 0%RHA
Figure G4: Force- stroke curves at 400ºC for specimen 0%RHA
Figure G5: Force- stroke curves at 600ºC for specimen 0%RHA
Figure G6: Force- stroke curves at 800ºC for specimen 0%RHA
Force-stroke curve for 5%RHA:
Figure G7: Force- stroke curves at 27ºC for specimen 5%RHA
Figure G8: Force- stroke curves at 200ºC for specimen 5%RHA
Figure G8: Force- stroke curves at 400ºC for specimen 5%RHA
Figure G9: Force- stroke curves at 600ºC for specimen 5%RHA
Figure G10: Force- stroke curves at 800ºC for specimen 5%RHA
Force-stroke curve for 10%RHA:
Figure G11: Force- stroke curves at 27ºC for specimen 10%%RHA
Figure G12: Force- stroke curves at 200ºC for specimen 10%RHA concrete
Figure G12: Force- stroke curves at 400ºC for specimen 10%RHA concrete
Figure G13: Force- stroke curves at 600ºC for specimen 10%RHA concrete
Figure G14: Force- stroke curves at 800ºC for specimen 10%RHA concrete
Force-stroke curve for 20%RHA:
Figure G15: Force- stroke curves at 27ºC for specimen 20%RHA concrete
Figure G16: Force- stroke curves at 200ºC for specimen 20%RHA concrete
Figure G17: Force- stroke curves at 400ºC for specimen 20%RHA concrete
Figure G17: Force- stroke curves at 600ºC for specimen 20%RHA concrete
\
Figure G18: Force- stroke curves at 800ºC for specimen 20%RHA concrete
Force-stroke curve for 30%RHA:
Figure G18: Force- stroke curves at 27ºC for specimen 30%RHA concrete
Figure G19: Force- stroke curves at 200ºC for specimen 30%RHA concrete
Figure G20: Force- stroke curves at 400ºC for specimen 30%RHA concrete
Figure G21: Force- stroke curves at 600ºC for specimen 30%RHA concrete
Figure G22: Force- stroke curves at 800ºC for specimen 30%RHA concrete
Appendix H
Modulus of Elasticity
Table H: Result of experimental of Elastic Modulus
NO Temperature 0%RHA Average 5%RHA Average 10%RHA
Average 20%RHA Average 30%RHA
Average
1
27ºC
16.11111
16.41087
15.97
16.45
24.12
23.17
23.34
24.63875
18.70
19.92
2 16.71064 16.92 22.21 25.9375 21.14
3
200ºC
18.0748
17.5724
22.84
22.30
25.49
26.89
27.95
29.70714
23.77
23.22
4 17.07 21.75 28.28 31.46429
22.67
5
400ºC
8.76
9.623243
13.43
14.54
14.33
15.55
16.82
17.895
17.96
17.53
6 10.48649 15.66 16.76 18.97 17.10
7
600ºC
4.688889
4.392063
7.76
6.90
9.03
10.96
13.20833
13.54861
11.62
9.88
8 4.095238 6.04 12.89 13.88889
8.14
9
800ºC
3.18975
2.699875
1.636364
2.558182
2.74
3.28
4.76
5.14
3.46
2.75
10 2.21 3.48 3.82 5.53 2.05
Figure H1: Modulus of Elasticity Test
0
5
10
15
20
25
30
35
0 200 400 600 800
Modulus of Elasticity (GPa)
Temperature (ºC)
0
%RHA
5%RHA
10%RHA
20
%RHA
30%RHA
Modulus of elasticity samples
Graphs of Stress- Strain for 0%RHA concrete samples
Figure H2: Stress- Strain curve at 27ºC for 0%RHA concrete
Figure H3: Stress- Strain curve at 200ºC for 0%RHA concrete
Figure H4: Stress- Strain curve at 400ºC for 0%RHA concrete
Figure H5: Stress- Strain curve at 600ºC for 0%RHA concrete
Figure H6: Stress- Strain curve at 800ºC for 0%RHA concrete
Graphs of Stress- Strain for 5%RHA concrete samples
Figure H7: Stress- Strain curve at 27ºC for 5%RHA concrete
Figure H8: Stress- Strain curve at 200ºC for 5%RHA concrete
Figure H9: Stress- Strain curve at 400ºC for 5%RHA concrete
Figure H8: Stress- Strain curve at 600ºC for 5%RHA concrete
Figure H9: Stress- Strain curve at 800ºC for 5%RHA concrete
Graphs of Stress- Strain for 10%RHA concrete samples
Figure H10: Stress- Strain curve at 27ºC for 10%RHA concrete
Figure H11: Stress- Strain curve at 200ºC for 10%RHA concrete
Figure H12: Stress- Strain curve at 400ºC for 10%RHA concrete
Figure H13: Stress- Strain curve at 600ºC for 10%RHA concrete
Figure H14: Stress- Strain curve at 800ºC for 10%RHA concrete
Graphs of Stress- Strain for 20%RHA concrete samples
Figure H14: Stress- Strain curve at 27ºC for 20%RHA concrete
Figure H15: Stress- Strain curve at 200ºC for 20%RHA concrete
Figure H16: Stress- Strain curve at 400ºC for 20%RHA concrete
Figure H17: Stress- Strain curve at 600ºC for 20%RHA concrete
Figure H18: Stress- Strain curve at 800ºC for 20%RHA concrete
Graphs of Stress- Strain for 30%RHA concrete samples
Figure H19: Stress- Strain curve at 27ºC for 30%RHA concrete
Figure H20: Stress- Strain curve at 200ºC for 30%RHA concrete
Figure H21: Stress- Strain curve at 400ºC for 30%RHA concrete
Figure H22: Stress- Strain curve at 600ºC for 30%RHA concrete
Figure H23: Stress- Strain curve at 800ºC for 30%RHA concrete
