Mechanical properties and durability of mortar with rice husk ash calcined at low temperature

Abstract

In past studies, rice husk ash (RHA) calcined at 1000 °C or higher was found active. They can be alkali-activated or induce pozzolanic reactions in cement hydrates. However, calcination at high temperature consumes much energy. In addition, most RHA is produced at an open-aired site. The burning temperature cannot be so high even in a power plant. In view of these issues, this study explores the mechanical properties and durability of mortar in the presence of RHA produced at low temperature. During the experiments, the rice husk was calcined under different temperature (400-1000 °C). Results showed that the properties of the RHA met the requirements in ASTM C618. Then, the mortar was prepared at w/c of 0.6, the cement in mortar was replaced by RHA by 5%-20% by volume, and the compressive strengths of the mortar were conducted. The 10% was found the optimum. Specimens with RHA calcined under 800 had higher strengths higher than those with RHA calcined at 1000 °C. However, the specimens with RHA calcined at 400 °C had the highest compressive strength at all ages possibly due to high remaining carbon content which absorbed water and reduced the w/c. Further results also showed that the shrinkage did not change significantly with the calcining temperature and dosage of the RHA, but the expansion due to alkali-silica reaction was effectively inhibited at 10%. RHA calcined by 400 °C had the best inhibition on expansion due to alkali-silica reaction (ASR) than that calcined by 800 °C or 1000 °C.