Effect of temperature on the physico-mechanical and microstructure properties of cement pastes containing fly ash and silica fume

Abstract

This study aimed to investigate the effect of heat treatment on the physico-mechanical and microstructure properties of cement pastes containing fly ash (FA) and silica fume (SF). Portland cement (OPC) has been partially replaced by 5% SF and 20, 30, 40 and 50 wt.% FA. After curing, the hardened cement pastes were dried at 100°C for 24 hours, subjected to thermal treatment at the rate of 5°C/min, and heated at temperature of 200, 400, 600, 800, 1000°C for 2 hours, then cooled to room temperature in air. Finally, their bulk density and compressive strength were determined. X-ray diffraction (XRD) and scanning electron microscopy (SEM) methods and were used for identification of the changes in the microstructure of the cement matrices. The results showed that the cement pastes containing 80% OPC + 5% SF + 15% FA is the optimum mix which gives a higher compressive strength and lower bulk density loss. Moreover, this optimum binder has the formation of inner fibers and crystalline needle like Wollastonite, Gehlenite which is responsible for the reduction in compressive strength loss from 800 up to 1000°C.