The feasibility of using natural rice husk ash in structural concrete (part II): durability

Abstract Waste incorporated in construction materials should be used, whenever possible, without processing in order to avoid environmental impact and additional costs. Rice husk ash (RHA) is a pozzolan that must be ground before use in order to increase its fineness and reactivity with Portland cement when it is used as a cementitious material. This study investigates natural rice husk ash (NRHA), without processing, replacing 15% of Portland cement, in mass. The NRHA was ground together with the aggregates in the mixer drum. Part I of this study presented the test results regarding microstructure, mechanical strength and shrinkage, including 25% content; Part II presents durability test results (carbonation, chloride penetration, electrical resistivity, water absorption, oxygen permeability and alkali-silica reaction - ASR), compared with a reference concrete with 100% cement and with ground RHA (GRHA). The results showed that it is feasible to use 15% NRHA in concrete, as it presents higher performance when cement with pozzolans is used, and near or even better performance than GRHA mixtures for most of the variables analysed. The study concludes that 15% of NRHA in structural concrete is feasible and produces a more sustainable material.