Comparative study of the effects of water/binder ratio and silica fume on the volume instability of hydrating cement pastes at early-age

The early-age volume instability of hydrating cement paste mixtures was investigated by chemical and external shrinkage measurements. Test variables included type of binders (CSA Type 10 and CSA Type 10 + 8 % silica fume) and water/binder ratio (0.27, 0.35 and 0.45). All volume change measurements were performed in a temperature-controlled bath kept at 20°C. Complementary determinations of the degree of hydration were carried out on companion samples after 8, 24, 48 and 144 hours of hydration. Test results confirm the significant influence of water/binder ratio on the volume instability of neat cement pastes at early-age. Data also show that the addition of silica fume contributes to increase external shrinkage after setting. Correlations between chemical and external shrinkage test results and degree of hydration are discussed.