Rice husk ash as an additive in mortar - Contribution to microstructural, strength and durability performance

Facing the urgent need for more sustainable construction materials all over the world, mortars containing the agricultural by-product Rice Husk Ash (RHA) as supplementary cementitious material (SCM) were investigated. Pozzolanic activity, microstructural investigations through Scanning electron microscopy (SEM) and X-ray diffraction (XRD) analysis, compressive strength and durability properties were examined and compared to properties of mortars either without SCM or with equivalent amounts of fly ash and limestone powder. It was found that mortar samples with a cement substitution of 25 wt.-% by RHA showed a higher strength than the comparison samples at hydration ages of 7 to 90 days. Durability investigations, namely carbonation resistance and capillary suction, showed an increased performance of RHA mortars due to their dense microstructure. Microstructural analysis found that especially in the early hydration during the first hours after water addition, an accelerated reaction rate of the RHA mortars led to an increased heat flow and thus build-up of hydration products. A strong pozzolanic reaction, calculated through the measurement of decreasing crystalline phase amounts with XRD, was shown with increasing hydration time. Altogether, the investigations provide important insights into the usability of RHA in concrete. The enhanced strength development as well as the low water absorption and thus small capillary porosity indicate that the RHA is a suitable pozzolanic additive for both sustainable and durable concrete.

Automated summary

This study investigated the properties of mortars containing Rice Husk Ash (RHA) as supplementary cementitious material (SCM) for sustainable construction. The results showed that mortars with 25% substitution of cement by RHA exhibited higher strength, durability, and a denser microstructure compared to the control samples. RHA demonstrated a strong pozzolanic reaction, leading to enhanced strength development and improved durability of concrete. These findings provide important insights into the usability of RHA in concrete and its potential for sustainable construction.