The microstructural and hardening behaviour of tricalcium silicate pastes in the presence of calcium chloride

A sequential examination of strength development in terms of microhardness was studied during paste hydration of C 3 S in the presence of 2 and 5% CaCl 2 and at w/s ratios of 0.3 or 0.5. An attempt has been made to relate strength with microstructural features studied by means of Scanning Electron Microscopy. Generally, at earlier periods it was found that the 2% addition of CaCl 2 gave the strongest material; the effect was most pronounced in the 6‐month sample of the series with 0.3 w/s. The high strength for the sample prepared at a w/s ratio of 0.3 may be related to a high CaO/SiO 2 C‐S‐H‐phase, low porosity, and possibly a hydrated calcium hydroxy chloride complex. The pore size distribution was also measured. In general, the higher the porosity the lower the strengths but the relationship was not perfectly linear even on the semi‐logarithmic plot.