The Hydration Characteristics and Expansion Machanism of Expansive Cement at Low W/B Ratio

The hydration characteristics and expansion impetus of three kinds of cement paste under free- and confined-curing conditions were investigated, which were respectively mixed with three different kinds of expansive agent at low W/B ratio.The results show that the hydration products of pure cement paste and paste mixed with expansive agent are same,but the amount of hydration products,un-hydrated C 3S and C 2S are obviously different at the same hydration age.At 3d age,the amount of CH in pure cement paste is less than that of paste mixed with expansive agent,but it is reverse when at 28d age.The amount of AFt at 3d and 28d age in pure cement paste is less than those of paste mixed with expansive agent.Regardless of under free- or confined-curing condition,the amount of ettringite produced varies little since 3d age.The joint effect of the tumefaction of gel-ettringite due to water absorption and the expansive pressure on the pore caused by the crystalloid ettringite is the cause of the volume expansion of cement paste,and the former effect is much greater than the latter.