Thermal Resilience of Eco-Binary Mortar: an Experimental Study of High-Temperature Exposure

Abstract

Mortar exposed to high temperatures can experience significant degradation in strength and durability. One potential solution is replacing cement with alternative pozzolanic materials, such as Rice Husk Ash (RHA), which has a high silica content when processed under controlled burning conditions. This study investigates the use of RHA as a partial replacement in mortar, with additions ranging from 5 to 20 wt.%. As the amount of RHA increased, the mortar color darkened to a grayish shade. Surprisingly, the inclusion of 5 wt.% RHA resulted in almost double the compressive strength compared to conventional mortar, while 10 and 15 wt.% additions also showed improved performance. However, the addition of 20 wt.% RHA led to a decrease in compressive strength to 12.49 MPa, below that of standard mortar. High-temperature exposure (up to 1,093°C) affected the moisture content of the cement paste, changing its appearance to a whitish-gray color and impacting its mechanical properties. The relative strength values for all samples ranged between 0.35 and 0.16. Thermal analysis showed that free water evaporated between 82 to 140°C, followed by the decomposition of Ca(OH)2 at 445 to 454°C. The results suggest that 5 wt.% RHA provides optimal properties compared to other mixtures. This study highlights that RHA, as a low-cost agricultural waste, can be effectively utilized in the mortar industry, offering an environmentally friendly solution to both waste disposal and sustainability issues.