Influence of MgO-bearing expansive agent in different activities on deformation of cement pastes

The microstructures of MgO-bearing expansive agent(MEA) were characterized by X-ray diffraction(XRD),scanning electron microscope(SEM)and N2 adsorption,and the deformation of cement pastes containing different dosages of MEA with different activities under different curing conditions was studied.Results showed that MEA particles were consisted of MgO crystals.When the grain size of MgO increased,the inner pore diameter increased,and the specific surface decreased.MEA with higher activity would cause a larger early expansion and a smaller final expansion when cement pastes were cured in water at 20 and 30 ℃.MEA with lower activity would cause a smaller early expansion and a larger final expansion when cement pastes were cured in water at 20 and 30 ℃.With the admixture amounts of MEA increasing,the expansion of cement pastes increased.MEA in cement pastes cured at the higher temperature would produce a larger expansion at early age.Drying shrinkage of cement pastes with MEA could be reduced and not be fully compensated.