Influence of fly ash content on alkalinity of pore solution and microstructure of cement pastes

Alkalinity of pore solution and microstructure of cement-based materials containing different rate of fly ash were determined and analyzed by means of ex-situ leaching, mercury intrusion porosimetry (MIP) and scanning electron microscopy(SEM). The results show that the alkalinity of pore solution of cement pastes decreases with increase of the adding rate of fly ash, but the pH value of pore solution can be maintained above 12 for a long time. The microstructure of hardened cement pastes containing fly ash is densified gradually with ages. Its porosity reduces, its aperture refines and the ratio of harmless pores in hardened cement pastes increases. The incorporation of fly ash in proper ratios does not debase the stability of the microstructure of cement pastes.