Chloride ingress in microsilica concrete

The paper presents experimental results on chloride ingress and water absorption of microsilica concrete. To investigate the interaction of cement, water and microsilica content on diffusion characteristics and porosity (water absorption), 36 concrete mixes with water/cement ratios ranging from 0·4 to 0·9 and cement contents between 250 and 450 kg/m³ were studied. The microsilica content varied between 5 and 15%. Curing was under two conditions, 20°C, 100% RH and 35°C, 25% RH.

The results show that a relationship exists between chloride concentration and W/C ratio, the relationship being different for the various microsilica contents. The effect of high W/C ratios is much more pronounced in low microsilica content mixes (0 and 5% addition). The chloride ingress is also sensitive to cement content in low microsilica contents mixes (0 and 5%), but not in high microsilica content mixes (10 and 15%).

The diffusion coefficient, D_c, is not significantly affected by microsilica content, for mixes made at a constant W/C ratio.