SURFACE MODIFICATION OF FLY ASHES WITH CARBIDE SLAG AND ITS EFFECT ON STRENGTH AND AUTOGENOUS SHRINKAGE OF CEMENT PASTES

摘要

Particle surfaces of grade III fly ashes were modified through mixing with carbide slag and calcining at 850°C for 1h. Mineralogical compositions and surface morphology of fly ashes before and after modification were analyzed by X-ray diffraction analyzer (XRD) and scanning electron microscope (SEM) equipped with energy dispersive spectrometer (EDS). Effect of surface-modified fly ashes on compressive strength and autogenous shrinkage of cement pastes were examined. Microstructures of cement pastes were examined by mercury intrusion porosimeter(MIP) and SEM. Results show that β-C2S was formed on surface of fly ashes after modification. Hydration of β-C2S on surface-modified fly ashes densifies interface zone and enhances bond strength between particles of fly ashes and hydrated clinkers. In addition, surface modification of fly ashes tends to decrease total porosity and 10-50nm pores of cement pastes. As a result, surface modification of fly ashes increases compressive strength and reduces autogenous shrinkage of cement pastes.