Effect of Water/Cement Ratio on the Properties of Brick Aggregate Concrete

Abstract

Brick aggregate is widely used in concrete mixes for building construction in Bangladesh. This research aims to examine the effect of the water/cement ratio on the properties of brick aggregate concrete. The study focuses on two types of mixing ratios with different water/cement ratios. Mixing ratios (in volume) are considered 1:2:4 and 1:1.5:3, and water/cement ratios (in weight) are 0.40, 0.50, 0.60, and 0.70. The basic properties of hardened concrete, including compressive strength, modulus of elasticity, and splitting tensile strength, are investigated. The properties of the concrete are examined according to the ASTM standard. Tests have shown that the compressive strength of the concrete, the tensile strength, and the modulus of elasticity decrease with the increase in the water/cement ratio. The brick aggregate concrete's strength and stiffness improve with cement content up to a water/cement ratio of 0.40 to 0.55; after this point, the rate of improvement declines as water content increases beyond the hydration demand of cement up to a water/cement ratio of 0.60. The results of this study have a significant impact on the construction sector, which will help to put the work into practice to ensure quality control.

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6th International Conference on Advances in Civil Engineering (ICACE-2022)
21-23 December 2022
CUET, Chattogram, Bangladesh
www.cuet.ac.bd/icace
EFFECT OF WATER/CEMENT RATIO ON THE PROPERTIES OF BRICK
AGGREGATE CONCRETE
H. A. Rashid1*, B. A. Nur2, M. A. Rashid3
1Postgraduate student, Department of Civil Engineering, BUET, Bangladesh, email: engr.mmharg@gmail.com
2Postgraduate student, Department of Civil Engineering, BUET, Bangladesh, email: bmasohag@gmail.com
3Professor, Department of Civil Engineering, DUET, Bangladesh, email: marashid@duet.ac.bd
*Corresponding Author
Abstract
Brick aggregate is widely used in concrete mixes for building construction in Bangladesh. This research aims to
examine the effect of the water/cement ratio on the properties of brick aggregate concrete. The study focuses on
two types of mixing ratios with different water/cement ratios. Mixing ratios (in volume) are considered 1:2:4
and 1:1.5:3, and water/cement ratios (in weight) are 0.40, 0.50, 0.60, and 0.70. The basic properties of hardened
concrete, including compressive strength, modulus of elasticity, and splitting tensile strength, are investigated.
The properties of the concrete are examined according to the ASTM standard. Tests have shown that the
compressive strength of the concrete, the tensile strength, and the modulus of elasticity decrease with the
increase in the water/cement ratio. The brick aggregate concrete's strength and stiffness improve with cement
content up to a water/cement ratio of 0.40 to 0.55; after this point, the rate of improvement declines as water
content increases beyond the hydration demand of cement up to a water/cement ratio of 0.60. The results of this
study have a significant impact on the construction sector, which will help to put the work into practice to
ensure quality control.
Keywords
Concrete, brick aggregate, water/cement ratio, compressive strength, building construction materials.
1. Introduction
The effect of the water/cement ratio on concrete properties is the main concern from the start of its use. Brick
aggregate is a commonly used concrete manufacturing material in Bangladesh. It has higher water absorption
capability, which requires in-depth analysis, and previous studies on the impact of the water/cement ratio in
concrete confirms this [1-4]. Rashid et al. studied higher-strength concrete made with crushed brick aggregate.
The study used hand-crashed, well-burned, and hand-made bricks, and the sample was prepared using four
mixing ratios with four water/cement ratios. It used 19 mm (0.75 inches) downgrade brick aggregate and
admixture, but the study did not specify for which mixing ratio the equation was valid. Also, the admixture was
utilized for lower water/cement ratios but not for grater water/cement ratios, which may be related to a
deference in compaction and workability [3].
Singh studied the brick aggregate high-strength concrete. The study reported that the compressive strength
decreases as the water/cement ratio increases and grows faster with a higher water/cement ratio [4]. Abram's and
Rashid's experimental methodologies were almost identical; Abram utilized stone aggregate, while Rashid used
brick aggregate. Abram created an equation and indicated that the compressive strength of stone aggregate
concrete based on the water content made the mix workable. In addition, the volume of water required for
hydration affects the splitting tensile strength of concrete. However, the study did not specify the upper limit of
the validity of equations, and the study did not link the compressive strength of the air content in concrete [5].
Another researcher attempted to use crushed brick aggregate as a partial substitute for natural coarse aggregate
in the properties of concrete to produce higher-strength concrete. The study discovered that recycled brick
aggregate could be used as coarse aggregate in concrete [6]. Shamsai et al. reported that the water/cement ratio
of 0.33 to 0.50 improved compressive strength by 34.4 to 35.2 percent [7]. With a mixture ratio of 1:2:4 and a
water/cement ratio of 0.50, a study attained a maximum compressive strength of 23.71 N/mm2 after 28 days of
hydration [8].
2. Materials and Methods
2.1. Grain Size Analysis
The laboratory investigation of fine aggregate and coarse aggregate grain size were analyzed. Fig. 1, shows the
fine aggregate 50% fine sand mixed with 50% coarse sand, and Fig. 2, shows brick chips aggregates grain size
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6th International Conference on Advances in Civil Engineering (ICACE-2022)
21-23 December 2022
CUET, Chattogram, Bangladesh
www.cuet.ac.bd/icace
curve. The water absorption capacity of bricks was 11.33%, and bulk specific gravity in SSD condition was
2.77.
Fig. 1: Fine aggregate grain size curve.
Fig. 2: Coarse aggregate grain size curve.
2.2. Casting of Specimens
The properties of hardened concrete are affected not only by the properties of the ingredient materials but also
by the casting procedure and curing. We attempted to repeat this sequence of mixing, compaction, and curing.
The following is the casting procedure.
2.3. Batching and Mixing
In this study, a cylinder was used to determine the volumetric properties of all of the concrete ingredients except
water. A tilting type concrete mixture machine is used to mix concrete in this study. The coarse aggregate and
some of the mixing water were added prior to starting the rotation of the mixing machine. The shape and design
of the vanes fixed inside the drum determines the efficiency of the mixing operation. The mixing process should
be continued after loading the mixer machine until a thoroughly and properly mixed concrete is obtained. At the
end of the mixing process, the concrete should be of uniform color and consistency.
2.4. Placing and Compacting
Concrete compaction is the process of removing entrapped air from concrete. Air is likely to become trapped in
the concrete during the placement and mixing process. The specimen and cylinder were placed on a flat,
vibration-free surface. The concrete was poured into the specimens using a blunted trowel. To ensure proper
consolidation, a 5/8-inch diameter rod was used to tamp the concrete in the specimen, with three layers and 25
blows in each layer.
2.5. Concrete Curing
Curing is the process of keeping concrete moist enough to allow cement hydration to continue. The cylinders
were kept at room temperature for 24 hours after casting before being released from the specimen. The final
strength is heavily influenced by the initial moisture and temperature conditions. Immersion of specimens in
water is the best method of concrete curing because it meets all curing requirements, including hydration
promotion, shrinkage elimination, and heat absorption during hydration. The specimen in this study was
immersed in water for 28 days.
3. Testing of Specimens
3.1. Compressive Strength
Cylindrical concrete specimens of 6-inch x 4-inch cylinder size were used to determines the compressive
strength. It applies only to concrete where the unit weight exceeds 50 lb./cft. The test method involves an axial
compression load to the specimen cylinders at a rate within a specified range until a failure occurs. The
compressive strength of the test specimens computes by dividing the maximum stress achieved during the test
0
20
40
60
80
100
4.75 2.36 1.18 0.6 0.3 0.15 0.075
Fine Sand 50% and Coarse Sand 50%,
Grain Size
0
20
40
60
80
100
75 37.5 19 9.5 4.75 2.36 1.18
Brick Chips, Grain Size
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6th International Conference on Advances in Civil Engineering (ICACE-2022)
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CUET, Chattogram, Bangladesh
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by its cross-section. Loading is applied continuously. When the machine is idling, the moveable head moves at a
speed of 0.05 inches/min. This test method meets the ASTM standard specification C39/C39 M-99 requirements
[9]. Table 1 shows the compressive strength test results.
Table 1. The water/cement ratio affects the compressive strength of different blends.
SL Water/Cement
Ratio Compressive Strength, 𝑓
𝑐
′ (MPa) Mix
Ratio, 1:1.5:3 Compressive Strength, 𝑓
𝑐
′ (MPa) Mix
Ratio, 1:2:4
1 0.40 19.56 16.40
2 0.50 18.21 15.56
3 0.60 13.01 14.51
4 0.70 12.40 14.11
Fig. 3: Picture of a cylinder during a compressive strength test.
3.2. Splitting Tensile Strength
The test applies compressive line load along the opposite generators of a concrete cylinder placed with its axis
horizontal between platens. The magnitude of split cylinder strength computes the equation, 𝑓
𝑠𝑝 =2𝑃
𝜋𝑑𝑙 . In this
test 24-pieces of cylinder specimens with various water/cement mixing ratios are tested. The ASTM
specifications C 496-96 implies to determine the splitting tensile strength of cylindrical concrete [10]. Table 2
shows the test results.
Table 2. The water/cement ratio affects the splitting tensile strength of different blends.
SL Water/Cement
Ratio Splitting Tensile Strength, 𝑓
𝑠𝑝 (MPa) Mix
Ratio 1:1.5:3 Splitting Tensile Strength, 𝑓
𝑠𝑝 (MPa)
Mix Ratio 1:2:4
1 0.40 1.81 1.29
2 0.50 1.48 1.06
3 0.60 0.83 0.92
4 0.70 0.61 0.72
Fig. 4: Picture of a cylinder during a splitting tensile strength test.
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6th International Conference on Advances in Civil Engineering (ICACE-2022)
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CUET, Chattogram, Bangladesh
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3.3. Concrete Modulus of Elasticity
The modulus of elasticity of a cylinder specimen computes as uniaxial compression stress. The deformation is
measured by observing fixed dial gauges in fixed gauge lengths. The strain is calculated by dividing the dial
gauge reading by the gauge length, and the stress is by dividing the applied load by the surface of the cross-
section. The stress-strain relationship establishes itself after a series of readings. The modulus of elasticity is
calculated using the tangent drawn to the curve at the origin. This test complies with the ASTM standard
specification C 469-94 [11]. The modulus of elasticity of concrete is equal to 40% of the ultimate strength of
concrete (corresponding strain). Table 3 displays the modulus of elasticity of several specimens obtained from
the experimental investigation.
Table 3. The water/cement ratio affects the modulus of elasticity of different blends.
SL Water/Cement
Ratio Modulus of Elasticity, EC (MPa) Mix
Ratio, 1:1.5:3 Modulus of Elasticity, EC (MPa) Mix
Ratio, 1:2:4
1 0.40 4562 4255
2 0.50 4146 3903
3 0.60 3413 3485
4 0.70 2991 3334
Fig. 5: Picture of a cylinder during a modulus of elasticity test.
4. Results and Discussions
4.1. Comparison of Compressive Strength
Table 1 shows that the compressive strength of concrete decreases as the water/cement ratio increases. The
strength of concrete depends mainly on the strength of the cement paste, and the strength of the cement paste
rises with the cement content and falls with the air content. Fig. 6 depicts the variation in compressive strength
of brick aggregate concrete with variation in water/cement ratio and relative strength reduction.
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6th International Conference on Advances in Civil Engineering (ICACE-2022)
21-23 December 2022
CUET, Chattogram, Bangladesh
www.cuet.ac.bd/icace
Fig. 6: The water/cement ratio affects the compressive strength.
4.2. Comparison of Splitting Tensile Strength
Table 2 shows the splitting tensile strength of brick aggregate concrete decreases with increasing water/cement
ratio for all mixes. The tensile strength of concrete depends on emptied pores left by water mixed during
specimen preparation. Although water increases with higher cement-content concrete, the splitting tensile
strength is higher than that of lower cement-content concrete up to a water/cement ratio of about 0.60.
The bonding strength between aggregate surfaces and cement paste depends on the cement quantity. The higher
the cement content, the greater the tensile strength up to about 0.60 water/cement ratio. Beyond this point,
concrete with higher cement has lower tensile strength than concrete with lower cement because excessive
segregation with rich mix leaves more pores and non-uniform coating around aggregate particles, resulting in
lower tensile strength. Fig. 7 shows the strength of concrete reduces with rich mixtures up to a water/cement
ratio of 0.60 after the trend reverses.
Fig. 7: The water/cement ratio affects the splitting tensile strength.
4.3. Comparison of Modulus of Elasticity
Table 3 shows the modulus of elasticity determines the strength and porosity of the concrete. According to Fig.
8, the modulus of elasticity of concrete made with a mix ratio of 1:1.5:3 up to a water/cement ratio of around
10
12
14
16
18
20
0.4 0 0.5 0 0.6 0 0. 7 0
Strength, Mpa
W/C Ratio
Compressive Strength Test Results
Compressive strength, (MPa) Mix ratio 1:1.5:3
Compressive strength, (MPa) Mix ratio 1:2:4
0.50
0.70
0.90
1.10
1.30
1.50
1.70
1.90
0.4 0 0.5 0 0.6 0 0.7 0
Strength, Mpa
W/C Ratio
Splitting Tensile Strength Test Results
Compressive strength, (MPa) Mix ratio 1:1.5:3
Compressive strength, (MPa) Mix ratio 1:2:4
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6th International Conference on Advances in Civil Engineering (ICACE-2022)
21-23 December 2022
CUET, Chattogram, Bangladesh
www.cuet.ac.bd/icace
0.60 is higher than that of concrete made with a mix ratio of 1:2:4. Because excess water content leaves more
pores, resulting in more deflection. However, the compaction level and the strength of the cement paste ensure
that the concrete has a higher modulus of elasticity with the 1:1.5:3 mixing ratio. Beyond this water/cement
ratio, concrete segregation leaves more pores in hardened concrete as water content increases, as it does in a rich
mix, and thus the modulus of elasticity of concrete made with the mix ratio of 1:1.5:3 is greater than that of
concrete made with the mix ratio of 1:2:4. Because of the good compaction level, the reduction of modulus of
elasticity of concrete made with ratios of 1:1.5:3 is lower than that of concrete made with ratios of 1:2:4. As the
amount of water/cement increases, so does the rate of reduction. The stress-strain diagram for water/cement
ratio 0.60 with the mix ratios of 1:1.5:3 and 1:2:4 are presented in Figs. 9 and 10, respectively.
Fig. 8: The water/cement ratio affects the modulus of elasticity.
Fig. 9: The stress-strain diagram of brick aggregate concrete made with 1:1.5:3 mix ratios and a water/cement
ratio of 0.60.
2500
3000
3500
4000
4500
5000
0.4 0 0.5 0 0.6 0 0.7 0
Strength, Mpa
W/C Ratio
Modulus of Elasticity Test Results
Compressive strength, (MPa) Mix ratio 1:1.5:3
Compressive strength, (MPa) Mix ratio 1:2:4
0.00
2.00
4.00
6.00
8.00
10.00
12.00
14.00
16.00
18.00
0.000 0.005 0.010 0.015 0.020 0.025
Stress
Strain
Stress-Strain Curve, Mix Ratio 1:1.5:3
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6th International Conference on Advances in Civil Engineering (ICACE-2022)
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Fig. 10: The stress-strain diagram of brick aggregate concrete made with 1:2:4 mix ratios and a water/cement
ratio of 0.60.
5. Conclusions
The study found that the compressive strength, tensile strength, and modulus of elasticity of brick concrete are
higher for water/cement ratios ranging from 0.40 to 0.55. Following that, as the water/cement ratio increases
from 0.60 to higher, these strengths decrease. The water/cement ratio greater than 0.60 is insignificant with
higher cement content. Numerous studies can be made on the physical and chemical properties of brick
aggregate concrete made with different water/cement ratios and the impact of the water/cement ratio on air void
in concrete. Other properties of brick aggregate concrete, such as durability and fatigue strength, might be worth
investigating. Additionally, more water/cement ratios can be used at short intervals, like 0.40, 0.45, 0.50, 0.55,
0.60, 0.65, and 0.70, to investigate the effect of the water/cement ratio on the properties of concrete.
6. Acknowledgements
We like to express our gratitude to the Department of Civil Engineering, Dhaka University of Engineering &
Technology (DUET), Gazipur, and laboratory technicians for assisting us in obtaining the resources we required
to conduct the laboratory investigation.
References
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2.00
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0.000 0.005 0.010 0.015 0.020 0.025
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6th International Conference on Advances in Civil Engineering (ICACE-2022)
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CUET, Chattogram, Bangladesh
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2011.
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[10]
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[11]
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