Application of consistency-based water-to-binder ratio to compensate workability loss in concrete modified with rice husk ash

Abstract

Rice husk ash is a material that has the potential to replace cement partially. Many research works concluded that besides having some environmental advantages, the use of rice husk ash (RHA) also improves the hardened properties of concrete. This experimental study addresses the effect of the RHA on the basic properties of ordinary Portland cement by evaluating the standard consistency, initial setting time, and final setting time of RHA-added cement. This study also presents the fresh and hardened properties of concrete modified with RHA. The replacement of cement was done with five different percentages (0%, 5%, 10%, 15%, and 20%) of RHA. Samples were also segregated based on the two different methods of the selection of water to binder (w/b) ratio. In the first method w/b ratio was kept constant at 0.45 for all cement replacement percentages (RHA%). In the second method, the w/b ratio was selected based on the standard consistency of the modified cement. The findings of the experimental study show that standard consistency is increased with the increment in RHA%. A small increase in the initial setting time can be noticed with lower RHA% (5% and 10%), however, higher RHA% causes a decrease in the initial setting time. No significant change in the final setting time was found due to the addition of RHA. The workability of the concrete decreases significantly with respect to RHA% in the case of constant w/b ratio samples. But in consistency-based w/b ratio samples, RHA% has an insignificant effect on workability. The compressive strength of concrete increases with the increase in RHA% up to a 10% value for the constant w/b ratio samples. However, an insignificant change was noticed due to RHA% when the consistency-based w/b ratio had been applied. The study concludes that the strength of concrete can be improved by cement replacement with RHA with some sacrifice in terms of workability. But if we add extra water to compensate for the workability loss, we can replace cement with RHA without any significant strength loss.