Effects of additives on water permeability and chloride diffusivity of concrete under marine tidal environment

The influences of fly ash (FA), slag (SG), silica fume (SF) and basalt fiber (BF) on time dependent water permeability, chloride diffusivity and microstructure of concrete were studied. Time dependent models for water permeability coefficient (K-w) and instantaneous chloride diffusion coefficient (D-ins) were established. Time dependent porosity, pore size distribution (PSD) and contributive porosity (rho(c)) were determined by MIP. Results show that SF and FA have the best effects on reducing K-w before 240 d. The effects of SF and SG on reducing D-ins are relatively poor, due to their small dosage. K-w and D-ins are increased by adding BF at early exposure period, but decreased after 240 d. Time dependent D(ins )and K-w is basically consistent with time dependent porosity. The stable reduced proportion of pores with size greater than 100 nm and corresponding rho(c) are the leading factors to the decreasing porosity. The correlation between rho(c) with pore size of 100 nm-1000 nm has a higher correlation with K-w than D-ins( .)