5.1 Introduction
The main objective of this research was to observe the effect of superplasticizer on mechanical and durability properties of recycled aggregate concrete. To achieve that objective, concrete cylinder and cube specimens were prepared by natural stone aggregate, recycled stone aggregate and recycled brick aggregate with and without superplasticizer. Various tests both on fresh and hardened concretes were then conducted to evaluate and compare the effect of superplasticizer on mechanical and durability properties of recycled aggregate concrete. Fresh property such as slump and hardened properties such as compressive strength, splitting tensile strength, density, absorption and voids in hardened concrete, rapid chloride permeability and static modulus of elasticity. In addition, non-destructive test such as ultrasonic pulse velocity (UPV) was conducted to evaluate and compare strength test results.
5.2 Conclusions
Based on the experimental investigations done on prepared concrete specimens, the following conclusions can be drawn:
1. Significant improvement of compressive strength was achieved due to the addition of superplasticizer in recycled aggregate concrete. Compressive strength has been increased by 28-35% and 25-30% for stone and brick recycled aggregate concrete respectively for different ranges of natural stone aggregate replacements and age of specimens.
2. Splitting tensile strength of recycled aggregate concrete also showed optimistic results for addition of superplasticizer. Splitting tensile strength has been increased by 5-14% and 6-11% for stone and brick recycled aggregate concrete respectively for different replacement ratios. However, experimental splitting tensile strength is found to be less than that of the value as per ACI 318-14.
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3. Static modulus of elasticity has been enhanced by 21-22% and 22-36% for stone and brick recycled aggregate concrete respectively for different aggregate replacement ratios due to the addition of superplasticizer. In general, this elasticity for recycled stone aggregate concrete is found to be more than that of the value by ACI 318-14. But concrete with the recycled brick aggregate does not follow the same trend.
4. UPV test results have demonstrated positive effect of superplasticizer on the quality of concrete. However, these values are not significant.
5. Density of recycled aggregate concrete has been improved due to addition of superplasticizer, in general. Bulk density increases by 31-36% and 36- 41% for stone and brick recycled aggregate concrete respectively for the range of aggregate replacements considered.
6. Water absorption of recycled aggregate concrete has been decreased by the use of superplasticizer. Water absorption after immersion decreases by 29- 30% and 28-32% for stone and brick recycled aggregate concrete respectively. The same trend is shown for the water absorption after immersion and boiling of concrete specimens.
7. Chloride ion permeability of recycled aggregate concrete was reduced due to the use of superplasticizer. RCPT test results show that total charge passing through the concrete specimens decrease by 5-30% and 11-17%
for stone and brick recycled aggregate concrete respectively for the range of natural aggregate replacements considered in the present study.
5.3 Recommendations for Future Study
Experimental investigation conducted in this research indicates that superplasticizer can be used to enhance the mechanical and durability properties of recycled aggregate concrete. As the test results depend on many parameters and vary abruptly, it needs to be substantiated by further experimental evidences. Some recommendations for future research work are described below:
i. Mechanical and durability properties of recycled aggregate concrete largely depend on the properties of parent concrete. So, recycled aggregate
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concrete should be further tested to observe the effect of superplasticizer by varying properties and age of parent concrete.
ii. Various types of superplasticizer are available in the market. Effect of different types of superplasticizer on mechanical and durability properties of recycled aggregate concrete should be studied to observe variation of test results.
iii. A fixed dosage of superplasticizer is used in this research. Variation in effects should be observed for different dosages of superplasticizer.
iv. The water-cement ratio was kept constant in this study. Different water- cement ratios might be used with superplasticizer to observe the variation in mechanical and durability properties.
v. A longer age of specimens for testing durability property might be considered to correlate it with the effect of superplasticizer.
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119 APPENDIX A
Fig A1: Compressive strength of RSAC with superplasticizer at different ages of cylinder specimens
Fig A2: Compressive strength of RBAC without superplasticizer at different ages of cylinder specimens
0 5 10 15 20 25 30 35
7 days 28 days 90 days
Compressive Strength (MPa)
Curing Age
NACA RSACA 25 RSACA 50 RSACA 100
0 5 10 15 20 25
7 days 28 days 90 days
Compressive Strength (MPa)
Curing Age
NAC RBAC 25 RBAC 50 RBAC 100
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Fig A3: Compressive strength of RBAC with superplasticizer at different ages of cylinder specimens
Fig A4: Effect of superplasticizer on compressive strength of RSAC for 7 days cylinder specimens
0 5 10 15 20 25 30 35
7 days 28 days 90 days
Compressive Strength (MPa)
Curing Age
NACA RBACA 25 RBACA 50 RBACA 100
0 5 10 15 20 25
0% 25% 50% 100%
Compressive Strength (MPa)
% of Recycled Stone Aggregate
Without Superplasticizer With Superplasticizer
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Fig A5: Effect of superplasticizer on compressive strength of RSAC for 90 days cylinder specimens
Fig A6: Effect of superplasticizer on compressive strength of RBAC for 7 days cylinder specimens
0 5 10 15 20 25 30 35
0% 25% 50% 100%
Compressive Strength (MPa)
% of Recycled Stone Aggregate
Without Superplasticizer With Superplasticizer
0 5 10 15 20 25
0% 25% 50% 100%
Compressive Strength (MPa)
% of Recycled Brick Aggregate
Without Superplasticizer With Superplasticizer