Both the pastes and mortars were made in the laboratory for this study. Two kinds of TiO2 with different crystal phase compositions, P25 (75% anatase and 25% rutile, Degussa, Germany) and Anatase (99% anatase, Sigma–Aldrich, USA), were added to an Ordinary Portland cement (OPC, ASTM type I) produced by Green Island Cement Limited of Hong Kong.