Effect of Rice Husk Ash on the Mechanical Properties and Microstructure of Concrete Subjected to High Temperatures
Henrique dos Santos Kramer, Alec Sobroza Daronco, Alexandre Silva de Vargas, Larissa Degliuomini Kirchhof, Eugênio Bastos da Costa, Rogério Cattelan Antocheves de Lima
Abstract
Mineral admixtures in portland cement–based concrete, such as rice husk ash (RHA), improve the mechanical strength and durability under normal conditions and ambient temperature. However, more knowledge is needed on the behavior of concretes with these materials when subjected to fire conditions. Fire conditions are characterized by an expressive increase in temperature in the structure in a short period. Thus, this study aimed to evaluate the effect of partial portland cement replacement with RHA in concretes subjected to different temperatures. Parameters examined were mineral composition with X-ray diffraction (XRD), compressive mechanical strength, static modulus of elasticity, and mass loss after heating. The mineral composition of concretes with and without RHA replacement after heating was similar. Partial replacement of cement with RHA improved the mechanical performance with higher compressive strength up to a temperature of 400°C. The static modulus of elasticity degraded more sharply than mechanical strength due to dehydration of cementitious matrix and fissuring. No explosive spalling was observed for all temperatures tested, and the mass loss was similar for both concretes. This indicated no adverse effects in the partial replacement of portland cement with RHA from a mineral point of view.