Experimental study of high-temperature resistance of alkali-activated slag crushed aggregate mortar

Rational utilization of blast furnace slag improves resource utilization rate and is a measure to ameliorate environmental degradation and climate crisis. Alkali-activated slag cementitious material (AASCM) has high temperature resistance and can provide material choice for high temperature environment construction and building fire resistance. In order to solve the thermal incompatibility problem between aggregate and paste of AASCM mortar with natural aggregate, a special type of mortar with alkali-activated slag as cementitious material was examined, which aggregates consisted of crushed and sieved particles of alkali-activated slag paste. The compressive strengths of 126 cubic and 126 prismatic specimens during and after high-temperature treatment were investigated. The test results showed that both the compressive and flexural strengths of the mortar during and after high-temperature treatment decreased with increasing temperature. Moreover, the compressive strength of the mortar after high-temperature treatment was higher than that during the treatment in which strength grade and temperature were constant. The formulated equations for calculating the compressive and flexural strengths during and after high-temperature treatment provided a basis for evaluating the fire resistance of this new type of masonry material. The microstructure and composition of the mortar were analyzed using scanning electron microscopy with energy-dispersive spectrometry and X-ray diffraction. At 600 °C, the mortar gradually produced new products akermanite, merwinite and gehlenite.