Abstract: To minimize the adverse impact of MgO expansive agent (MEA) on the fluidity of concrete and delay the expansion of MgO concrete, the surface of MEA was modified by adding C-18 unsaturated fatty acid. The activity index, pore structure and hydration heat of modified MEA were measured, and the fluidity and expansion of cement pastes containing modified MEA were investigated to evaluate the modification effect of MEA. Results demonstrated that the activity index of MEA can be improved, the pore structure of MEA can be refined and the hydration heat of MEA can be delayed by modifying MEA. The loss of fluidity of MEA cement pastes can be reduced, and the expansion of MEA cement pastes can be delayed and the later expansion quantity of MEA cement pastes can be increased by modifying MEA.

Key words: cement paste, MgO expansive agent, modification, fluidity, expansion