Effect of Coarse Recycled Aggregate and Rice Husk Ash on Concrete: A Factorial Design Approach

The procedures of the design of experiments have been employed in the current investigation to assess the effects of utilisation of recycled coarse aggregates and rice husk ash in concrete. A general factorial design (two-way ANOVA) is adopted with factors percentage of recycled coarse aggregates with levels of 0% and 100% and percentage of rice husk ash with levels of 5%, 10%, 15%, 20%, 25%, 30%, and 35% for an assessment of the impact of the inclusion of aforementioned materials. Three numbers of replication of the various harden properties (compressive strength after 7, 28, 90 and 365 days, split tensile and flexural strength) and non-destructive parameters (rebound number and ultrasonic pulse velocity) are carried out, which are responses of this research work. The critical analysis of the experimental results of the current study has been performed by adopting a two-way analysis of variance, and the outcomes of the analysis are furnished in terms of analysis of variance table, individual value, contour, main effects and interaction plots. The outcomes of contour and individual plots depict the degradation of strength when the percentage of recycled coarse aggregates has been changed from zero to 100 due to the inferior characteristics of recycled coarse aggregates. Further, around 10-20% reduction in compressive strength has been detected at various curing days with the full substitution of cement with rice husk ash varying curing time and rate of decline are significant in 25-35% of rice husk ash. Similarly, a decrease in tensile strength of concrete is up to 20% can be seen with the usage of 100% recycled coarse aggregates in concrete. However, the inclusion of rice husk ash up to 10-15% has no substantial impact on the strength parameters of concrete, and beyond this range, strength starts declining significantly. The interaction plots conclude about the considerable impact of the interaction of percentage of rice husk ash and recycled coarse aggregates percentage on tensile and non-destructive parameters of concrete. Moreover, change in RN and UPV of concrete after 28 days follows a similar trend to that of strength for incorporating recycled coarse aggregates and rice husk ash. However, the values similar to the control mix could be obtained with the use of 10-15% rice husk ash in concrete with 100% recycled coarse aggregates. Eventually, this study recommends the usage of 100% recycled coarse aggregates with 10-15% rice husk ash for practical applications as no major alteration in workability, strength and non-destructive parameters as compared to the conventional concrete made without recycled coarse aggregates and rice husk ash.