Pore structure characteristics affecting the permeability of cement paste containing fly ash

Abstract Results are presented from measurements of the permeability of saturated, hardened cement pastes, with and without fly ash. Specimens tested were cured over a temperature range from 20 to 65°C for periods from seven days to one year. The results show that a dramatic reduction in permeability occurs due to the pozzolanic reaction of the fly ash. Porosity estimates from mercury-intrusion porosimetry and helium-comparison pycnometry are used to develop an explanation for the permeability reduction. Traditional explanations, based on a reduction in the volume of large pores, are found to be inadequate.