Deterioration of Cement-Fly Ash Composite Binder Materials Exposed to Elevated Temperature

The deterioration behavior of cement-fly ash composite binder materials exposed to elevated temperature was studied in the present investigation. With the temperature continuous rising, the surface microstructure evolution of cement-fly ash composite materials was observed in a real-time mode. And the pore structure of the hardened paste undergoing high temperatures was investigated by mercury intrusion porosimetry (MEP) test. The results showed that thermal cracking of hardened paste developed continuously from the surface to the interior and hydration products decomposed gradually with the increase of temperature. Both the processes make the pores of the hardened pastes become coarser as well as the significant increase of the porosity, hence leading to worse deterioration of the microstructure and decline of the strength. The experimental results showed that the morphological effect and micro-aggregate effect of fly ash could improve the microstructure of cement-fly ash composite materials effectively, and the active effect of fly ash reduced the content of calcium hydroxide in the paste significantly. Both of them make contributions to the high temperature resistance of cement-fly ash composite materials.