Influence of silica fume and flyash on chloride diffusion and pH values in cement paste

Abstract The diffusion rate for chloride in cement paste is a parameter of major significance for the resistance of concrete structures to seawater environments. The results of this investigation show that an addition of silica fume or flyash in ordinary Portland cement paste considerably reduces the diffusion rate for chloride. Other factors of major importance for the resistance of the concrete are the composition of the pore solution and the capacity of the cement paste to bind chloride chemically. Measurements of pH values in pore solution pressed out of cement paste show that mineral additions reduce the pH value and this has a negative effect on the capacity of the cement paste to resist reinforcement corrosion. A theoretical estimate, based on partly uncertain material parameters, nevertheless indicates that an addition of silica fume or flyash added in appropriate amounts extends the initiation time for diffusion-controlled chloride-initiated reinforcement corrosion.