Impact of the Properties and Reactivity of Rice Husk Ash on Lime Mortar Properties

Abstract

This paper studies the effect of rice husk ash (RHA) in the properties of hydrated lime (calcium lime-CL90s) mortars with a view to improve their properties and make them more sustainable. The variation in mortar properties was related to the activity of the RHA, which was assessed by measuring its specific surface area, fineness, reactivity, composition, and amorphousness. According to the results, the RHA investigated is a low-temperature, highly reactive ash of high specific surface area that contains crystalline silica and unburnt cellulosic material and was probably produced between 400 and 500°C. Pozzolanic hydrates were clearly present after 24 h, progressively increasing in size and amount (at 3 and 7 days) and linking to each other to form continuous networks after 14 days. The paper concludes that lime replacement by RHA improves mortar workability, lowering water/binder ratio and the amount of water required to reach a specific consistency. RHA also enhances bulk density and lowers the difference between real and bulk densities thus resulting in lower porosity. Lime replacement by RHA enhances strength, and accelerates setting and early strength gain. Finally, with increasing RHA content, lime mortars become progressively stiffer and more elastic, yet remain plastic and thus undergo significant strain before failure.