Beneficial effect of fly ash on chloride diffusivity of hardened cement paste

Abstract

The rate at which chloride ions penetrate into concrete determines the time period after which the passivity of reinforcing bars begins to break down for corrosion. It is also related to the quality and thickness of the concrete cover and determines the service life of the structure. This study is aimed at investigating the effect of fly ash on chloride diffusivity of hardened cement pastes using the accelerated chloride ion diffusion test method. The results obtained from this test were used to calculate the diffusion coefficient of chloride ions using the Nernst-Plank equation for steady state condition. The results confirmed that the diffusion coefficient of chloride ions values for cement-fly ash pastes lie within the range of 10 −7 and 10 −9 cm 2/s. It was also found that blending cement with fly ash significantly decreases the diffusion coefficient of chloride ions only at the later ages of curing. Furthermore, it was observed that fly ash replacement ratio of 40% gives the best results with respect to chloride diffusivity through cement-fly ash pastes. Water/binder ratio was also found to affect the chloride ion diffusion coefficient through cement-fly ash pastes appreciably at the early ages of curing, but became less important at the later ages of curing.