Cement Lives and Contributes to Building Collapse

Abstract

In any cement-based constructions - buildings, roads and other infrastructure, the major living unit is the cement member. It is therefore of utmost importance to understand the cement and cement-based materials “living ecosystem” to be able to select the right cement type and guarantee the service life span. Cement minerals harden producing various forms of solid minerals hydrates and the deterioration processes start almost immediately. Cement-based structures can auto catalyze its own deterioration and collapse. Hydrated cement-based materials contain calcium silicate hydrates of various CaO:SiO2 ratio, calcium aluminates and ferrite hydrates, calcium sulpho-aluminates hydrates, Ca(OH)2 , CaCO3. The aggressive media are known to corrode cement-based materials. They include acidic gases like SO2, CO2, H2S, solutions containing H+, Cl-, SO_4^(2-), etc. and heat. This paper investigates the thermodynamic feasibility of reactions taking place between the hydrated cement minerals and the three mentioned aggressive media. Cement is not a universal binding material. Cement types are designed for application-specific purposes. The durability of cement-based structure and the service environment is highly dependent of the compatibility of their chemistry.
Terrorist activities have come to us. There is no reason why people building bungalows should pay the same as those building high rising for cement. Cement minerals hydrates are very liable to the destructive effects of targeted heat. Consequently, buildings above two-storey should be built using steel framework. The national building code should be revised in line with the current reality.

Full text

Cement Lives and Contributes to Building Collapse
Engr. Prof. Joseph O. Odigure
Federal University of Technology, Chemical Engineering Department, Minna, Nigeria
Tel: 08033787849. E-mail: josephodigure@futminna.edu.ng
@
The Nigerian Institution of Structural Engineers
2014 Annual Conference, Sheraton Hotel and Towers, Ikeja, Lagos, Nigeria
Thursday 23rd October 2014
Introduction
In any cement-based constructions - buildings, roads and other infrastructure, the major living unit is the
cement member. It is therefore of utmost importance to understand the cement and cement-based
materials “living ecosystem” to be able to select the right cement type and guarantee the service life
span. Cement minerals harden producing various forms of solid minerals hydrates and the deterioration
processes start almost immediately. Cement-based structures can auto catalyze its own deterioration and
collapse. Cl2
Hydrated cement-based materials contain calcium silicate hydrates of various CaO:SiO2 ratio, calcium
aluminates and ferrite hydrates, calcium sulpho-aluminates hydrates, Ca(OH)2 , CaCO3. The aggressive
media are known to corrode cement-based materials. They include acidic gases like SO2, CO2, H2S,
solutions containing H+, Cl-, 
, etc. and heat. This paper investigates the thermodynamic feasibility
of reactions taking place between the hydrated cement minerals and the three mentioned aggressive
media. It shall briefly discuss their use in developing new cement types as a means to mitigate building
collapse.
The Portland Cement
Portland cement is a pulverized substance made-up of discrete ingredients that develop strong binding
properties when mixed with water. Table 1 and 2 show the oxide and mineralogical compositions
formed during clinker production (Odigure J. O., 2014).
Table 1: Oxide Composition of Ordinary Portland Cement
Oxide form Range (wt %)
CaO 60.2-66.3
SiO 18.6-23.4
Al2O3 2.4-6.3
Fe2O3 1.3-6.1
SO3 1.7-4.6
MgO 0.6-4.8
Na2O+K2O 0.05-1.2

Table 2: Cement Minerals and Products
Compound Name Oxide Formula Mineral Name
Tricalcium Silicate (C3S), 3CaO.SiO2 Alite
Dicalcium Silicate (C2S), 2CaO.SiO2 Belite
Tricalcium Aluminate (C3A) 3CaO.Al2O3 Aluminate
Tetracalcium Alumino ferrite (C4AF), 4CaO.Al2O3.Fe2O3 Ferrite
Calcium hydroxide (CH) CaO.H2O Portlandite
Calcium sulphate dehydrate(C
S
H2) CaO.SO3.2H2O Gypsum
Calcium oxide (C) CaO Lime
Thermodynamic Investigation of Cement Mineral Hydrates Corrosion
Atmospheric Acidic Gases
Thermodynamic investigation of corrosion reactions of the various minerals hydrates in cement-based
structures show that the amount of Gibbs free energy required is determined by the partial pressure of
the corroding gases (Babushkin V. I., Matveev G. M. and Mchedlov-Petrocyan O. P. (1986)). For
example 1
5(5.6.5.5)++ 0.5+ 0.9=.2+6
5….
∆
=−79.79kcal.(.) = 1.364
The reaction constant =
(
..)
The partial pressure required for this reaction to be initiated, can easily be calculated from equation
below given the pressure of the second.

58.51−0.5
Calcium hydrates of silicates, aluminates and ferrites constitute more that 75% of Cement minerals. At
atmospheric  = 0.21atm, the required equilibrium 
= 10.atm. for reaction to be initiated with
calcium silicates hydrates. For other cement minerals; sulpho aluminates - 
= 10.atm.,
aluminates - 
= 10.atm., Ca(OH)2 - 
= 10.atm.
The equilibrium partial pressure for CaCO3 in cement-based materials is the least 
= 10.atm at
= 10.atm. It will in presence of O2 and moisture form CaSO4.2H2O + CO2. Cement containing
CaCO3 is more resistive to the deteriorating effect of SO2 gases.
In presence of CO2 the various cement minerals hydrates earlier mentioned react to form CaCO3 at
partial pressure of above 10-7atm. For calcium silicate hydrate the required equilibrium partial pressure

is = 10.atm., sulpo aluminates has the best resistance with = 10.atm and Ca(OH)2 the
least = 10.atm. The atmospheric partial pressure of CO2 is 10-3.5atm.
H2S is the most dangerous of the gases, with 1065 times more reactive than SO2 and 10135 times more
than CO2. Table 3 shows the ascending order of resistance of the cement minerals hydrates to acidic
gases.
Table 3 Order of Resistance to Atmospheric Acidic Gases Attack
Partial
pressure, P Order of Resistance to Atmospheric Acidic Gases Attack
CH CAH CSH CASH CaCO
3



- 10
-
60.94
10
-
58.44
10
-
57.69
10
-
53.57



10
-
13.1
- 10
-
8.28
10
-
7.52
-
Aggressive Solutions
Apart from coming in contact with atmospheric gases, cement-based materials serve in soil and water
bodies; that have their concentration of H+ or pH varying from 0 to 14.
5.6.5.5+ 10= 10.5+ 5 +6∆
=−123.2.(.)
 = 5lg[ ] - 10lg[]
 =123.2
1.364 =+90.3 = 5 lg[]+ 10
lg[]= 18.08 −2
For cement containing carbonaceous additive as commonly used in Nigeria, the CaCO3 might react with
the hydrated calcium aluminates minerals. In acidic solution the reaction could be
...11+ 10= + 16++ 2 
∆
= 2566.87. (.)
 = lg[]+ 2lg[]−10lg[]
The high ∆
 value shows that combined CaCO3 in hydrated Portland cement-based structure are very
resistive to acidic environment.
In excess, CaCO3 will react to release CO2, water and soluble Ca2+ salts.
+ 2= ++∆
=−13.27. (.)
lg[]= 13.23 −2
The behavior of excess CaCO3 in relation to other minerals needs to be investigated, however its gradual
leaching will greatly compromise the mechanical strength.

From the solution pH, the concentration of  can be calculated. At the equilibrium reaction the
calcium silicates hydrates CSH concentration is [1.8x10-3] with a pH = 10.4. At below this value CSH
will continue to dissociate and dissolve into the solution. All cement hydrates are unstable when their
alkalinities fall below their threshold values. The threshold value for Ca(OH)2 - pH = 12.5, aluminates –
pH = 11.43 and sulpho aluminates – pH = 10.17. The depletion of Ca(OH)2 is the primary cause of the
leaching of other cement hydrates from cement-based structures. The correct use of limestone in cement
helps to mitigate the effect of aggressive solution but when in excess could produce non-binding
Ca(OH)2 and CO2. Table 4 shows the threshold pH limit values in ascending order below which the
hydrates dissolution are initiated
Table 4 Threshold pH limit values for hydrates dissolution
Parameter Threshold pH limit values for cement hydrates
CH CAH CSH CASH
pH 12.5 11.43 10.4 10.17
Analyses of Tables 3 and 4 show that the nature of the environment plays a considerable role in
determining the durability of the cement-based structure. The different types of cement are designed to
specific needs of their application areas. This is done by either during the clinker production of at the
grinding stage; production of cement.
Heat
In service life, cement-based materials receive heat. The heat received is dissipated in localized heating
and changing the entropy of the minerals hydrates. These high energetic heat molecules on adsorption
by the cement minerals hydrates experience polymorphism, dehydration and consequently lose of the
bonding/strength. The heat received dQ per unit time dt by the first law of thermodynamic is converted
to kinetic movement of the minerals hydrates dE and potential energy change for work done because of
volume change by released gases pdv.
The behavior of mineral hydrates when exposed to heat can be estimated from their Gibbs free energy of
formation at 298K.
5.6.5.5=5.6.3+ 2.5∆
=−1.95.(.)
∆
=−1.95 = −1.364
= 10. =
.= 1.154
The dehydration of calcium silicates hydrates is thermodynamically feasible with very minimum supply
of heat (8.16KJ). A single molecule of tobemorite on instant dehydration can release a pressure of about
1.154 time higher that the atmospheric pressure.
4..19= 4..13+ 6∆
= 3.36.(.)
Sulpho aluminates

3..332= 3..12+ 32+ 20
∆
=−660.23.(.)
= 10.= 1.36.
For cement, containing carbonates additives
..11=.++ 11
∆
=−410.32.(.)
= 10.= 1.68.
1.68atm. is equivalent to 168kPa (kN/m2). 11H2O gives a mass equivalent of 2.29x10-25kg
(http://www.unitconversion.org/). By the law of motion F = ma, the expected initial ao =
168000/2.29x10-25 = 7.33x1021m/s2. Therefore the initial velocity of steam libration = 2.7x1011m/s. This
is about 90 times the speed of light (3.0x108m/s).
Sustained and sudden dehydration of billions cement minerals hydrates in closed or well-compacted
enclosure will be accompanied by considerable expansion and crack formation. In cement-based
structure, this will lead to chain propagation of cracks. The reaction will only stop when the heat source
is removed or the pressure equilibrated with the atmospheric and the material is able to reclaim its initial
morphology. Otherwise, it will explode.
An experiment conducted by Hager (2013) for cement paste and concrete showed that as cement paste is
heated to temperature of 500–550oC, the portlandite decomposes: Ca(OH)2 = CaO + H2O. The
dehydration process of the C-S-H gel starts at much lower temperature, almost immediately on heating
and rapidly increases thereafter with reduction in volume and increased porosity of the cement matrix.
Nigeria Cement Types
The presented thermodynamic studies of the various cement minerals hydrates show their expected
kinetic behavior and mechanism when subjected to acidic gases, aggressive solutions and thermal shock
(Odigure J. O., 2002, 2005, 2009). These kinetic behavior and mechanism of the individual mineral
hydrate can be used to formulate specific cement type for specific application. The current NIS 444-1 is
not user or application specific.
Chemical Composition
The chemical composition of the Nigerian cement is available in various publications. Our observations
from 2002 to 2010 showed that
 There is a growing change in the chemistry of cement produced locally and imported into the
country in the past twelve years. It is also important to note that all the imported cement are
CEM II.

 the chemical composition of most cements manufactured or imported in the country did not
comply with both the NIS and ISO requirements for a standard cement but did for a special type
cement.
 Presently the most common additive used is limestone.
The report of 2010 experiments on the cement brands in the Nigeria market conduct by the National
Roads and Buildings Research Institute is presented Table 5.
Table 5 Chemical Composition of 14 Cement Brands in the Nigeria Market
Para
mente
rs
Chemical Composition of 14 Cement Brands in the Nigeria Market
A
B
C
D
E
F
G
H
J
K
L
M
N
P
SiO
2
19.4
19.78
19.5
19.12
20.04
19.38
18.04
18.69
18.25
16.7
16.79
22.67
19.86
17.76
Al
2
O
3
4.49
4.4
4.78
4.76
4.52
5.25
4.95
4.64
4.57
4.34
5.26
5.54
5.89
4.47
Fe
2
O
3
3.15
3.36
3.13
3.32
3.45
3.57
3.08
2.95
3.2
2.8
2.37
4.07
4.6
3.16
CaO
61.3
62.45
61.26
62.22
60.88
62.58
61.73
64.83
64.47
64.9
63.14
58.58
61.38
63.47
MgO
3.11
2.11
3.85
4.15
2.49
2.37
0.81
1.44
1.28
1.83
1.34
1.54
1.59
2.37
SO
3
2.72
3.12
2.77
2.43
3.12
1.92
3.28
1.21
2.75
2.19
2.56
2.25
3.14
3
P
2
O
3
0.1
0.03
0.1
0.08
0.04
0.15
0.11
0.22
0.27
0.07
0.16
0.09
0.17
0.13
Mn2O3
0.12
0.07
0.03
0.05
0.04
0.11
0.18
0.07
0.08
0.01
0.09
0.06
0.12
0.15
TiO
2
0.21
0.26
0.28
0.63
0.28
0.29
0.25
0.29
0.3
0.2
0.3
0.43
0.39
0.27
Cr
2
O
3
0.89
0.61
1.08
1.01
0.57
0.58
0.39
0.88
0.92
0.36
0.42
0.52
0.9
4.04
IR
0.65
0.38
1.27
0.33
2.72
2.56
2.89
1.54
1.92
1.54
0.64
1.32
1.54
0.74
LOI
2.63
2.38
2.45
3.9
4.37
8.23
8.45
7.09
6.92
8.77
6.6
3.45
4.56
2.56
Others
0.94
1.03
0.94
0.39
1.23
Total
99.4
99.65
100.1
102.4
103.8
105.2
102.4
102.7
103.5
103
100.5
100.1
103
102.2
The latest analysis performed in South African University laboratory presented below showed an
additive content of about 25%.

Analysis of Table 5 is presented in Table 6
Table 6 Analysis of Table 5
Parameters
Calculated %
value of Additive using Loss on Ignition for Some Cement Samples in Nigerian Market
A
B
C
D
E
F
G
H
J
K
L
M
N
P
Insoluble
Residue, %
0.65
0.38
1.27
0.33
2.72
2.56
2.89
1.54
1.92
1.54
0.64
1.32
1.54
0.74
Loss on
Ignition, %
2.63
2.38
2.45
3.9
4.37
8.23
8.45
7.09
6.92
8.77
6.6
3.45
4.56
2.56
Estimated
Ca- based
additive, %
5.98
5.41
5.47
8.86
9.93
18.7
19.2
16.1
15.7
19.9
15
7.8
10.
4
5.82
The results for the 14 cement brands in the Nigerian market showed that six (6) brands have Loss of
Ignition values well above 5% required by NIS and 10 brands above the ISO value of 3%.
Nine (9) brands fell below the ISO value of 0.75 for Insoluble Residue, but all brands were within the
NIS recommended.
All the cement brands manufacturers have used either one form of additive based on the LOI value or
the cement were poorly stored in the warehouses. I want to believe they all used additives because a
moisture content of this value will lead to caking of the cement. The estimated CaCO3 content used as
additive ranged from 5 to 20%. By global practices, cement can be produced with up to 8% additive
without change in nomenclature. Ten (10) of the fourteen (14) brands did not conform to the ISO
requirement.
The compressive strength of the cement produced showed that all except for H were above the minimum
32.5MPa required. This was achieved because of the high degree of fineness for ordinary Portland
cement of 28.8-30.0m2/kg (Table 7).
4/9/2013 15:56
PANalytical
Results quantitative - Majors Acid32
Major ele ment analysis by XRF, Rh Tube, 3kWatt
BD = Below Detection
Note: LOI = weight loss or gain at 1000ºC.
LOI (loss on ignition) includes the total of volatiles content of the rock (including the water combined to the lattice of silicate minerals) and the gain on ignition related to the oxidation of the rock (mostly due to Fe).
Sample name Meas. date/time Al2O3 CaO Cr2O3 Fe2O3 K2O MgO MnO Na2O P2O5 SiO2 TiO2 L.O.I. Sum Of Conc.
(%) (%) (%) (%) (%) (%) (%) (%) (%) (%) (%) (%) (%)
YUSUF cement Majors Basic32 7/13/2014 22:05 3.87 61.09 bdl 2.47 0.37 1.15 0.02 0.12 0.07 15.71 0.18 11.22 96.25

Table 7 Effect of ground fineness on Compressive Strength for Some Cement Samples in Nigerian
Market
Parameters Effect of ground fineness on Compressive Strength for Some Cement Samples in Nigerian Market
A B C D E F G H J K L M N P
Fineness, m
2
/kg x10
(28.8-30) 42 35.8 35.6 34.6 41 43.3 39 34.7 32.6 33.6 34.3 36.5 37.1 32.3
Compressive strength of
Mortar, MPa 51.5 57.4 60.0 55.0 56.2 53.4 42.5 30.4 39.74 46.7 36.7 52.2 44.9 44.7
Compressive strength,
concrete MPa 37.9 48.7 40.3 48.6 44 44.4 31 24.5 34.4 37.1 25.3 39.4 35.3 35
Observations
Nigeria market is dominated by limestone Portland cement of 32.5 and 42.5MPa mechanical strength.
Our cement, by thermodynamic calculation is relatively unstable in acidic solution as excess CaCO3 are
present. Thermodynamically, cement-containing CaCO3 will produce more gases on heating.
Building Collapse
Thermodynamic calculations show that limestone Portland cement is easily attacked by acidic gases,
aggressive solutions and heat. The reliability of any cement-based material to attack is dependent on the
mineral mix of the cement and use/type of additives. Cement matrix are alkaline with pH > 12.
Therefore, any activity that will reduce this threshold value will accelerate the deterioration of the
structure. High portlandite content promotes easy acidic gases penetration and thus corrosion.
The decomposition/dehydration energy for sulpho aluminates ∆
=−660.23.(.) and
carboaluminates ∆
=−410.32.(.). Their released pressurized water vapour is at 1.36
and 1.68atm/mol. respectively. The reaction is thermodynamically very feasible at standard condition.
On initial by a target heat source, the vaporized steam in ideal situation can develop a velocity 90 times
higher than that of light. This is a considerable force knowing that there are millions of these hydrates
molecules in the matrix. When the source of heat is sustained for a given period, the structures will
become spongy, experience intensive cracking and collapse. Sudden dehydration produces non-binding
oxides and the shock waves (cracks) are induced by the supersonic velocity (v = 2.7x1011m/s) of the
steam produced in the process.
Cement-based structure strength is considerably weakened by heat and can easily collapse on
application of force. The understanding of cement chemistry is very important in preventing building
collapse or demolition.

Conclusion/New Design
Cement is not a universal binding material. Cement types are designed for application-specific purposes.
The durability of cement-based structure and the service environment is highly dependent of the
compatibility of their chemistry.
Terrorist activities have come to us. There is no reason why people building bungalows should pay the
same as those building high rising for cement. Cement minerals hydrates are very liable to the
destructive effects of targeted heat. Consequently, buildings above two-storey should be built using steel
framework. The national building code should be revised in line with the current reality.
I wish also to use this opportunity to call for collaboration in establishing the proposed National Centre
for Cement Development and Application Risk at FUT Minna. The society is changing; our comfort
zone equilibrium has changed. No knowledge can stand on itself.
Acknowledgements
I wish to acknowledge the Tertiary Education Trust Fund TETFund for providing the grant
TETFUND/FUTMINNA/2014/18 and TETFUND/FUTMINNA/2014/21 for this research. The Board of
Research, Federal University of Technology, Minna for the support in establishing the Cement Centre.
Finally, I also wish to acknowledge the Covenant University, Ota for providing the enabling
environment during my sabbatical leave for productive work.
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