MGO-TYPE DELAYED EXPANSIVE CEMENT

The idea that MgO can be used as an expansive component in concrete came from practice. The addition of MgO is to compensate the thermal shrinkage during the period of the temperature-decreasing process in mass concrete. In this paper, the delayed expansive properties of MgO and its effects on porosity, pore structure, permeability, sulfate resistance and strength of the hardened cement paste (hcp) are discussed in detail. The experimental results show that the expansion of cement pastes takes place between age 1 day and 180 days, and ceases at near age 180 days. The free expansion of hcp increases the total porosity and the size and volume of macropores in hcp, hence increasing the permeability and reducing the sulfate resistance and the compressive strength of hcp. The restrained expansion of hcp can produce a "self-compaction" in hcp, causing the reduction of the porosity and the size and volume of macropores, which is beneficial to improving the physical and mechanical properties of hcp.