Influence of MgO-type expansive agent hydration behaviors on expansive properties of concrete

The hydration behaviors and expansive properties of MgO-type expansive agent curing at different temperatures and environment were investigated. When the curing temperatures changed from 25 °C to 50 °C, the conductivities of MgO samples increased from 40 to 80 μs/cm, and the hydrations of MgO were quickened up obviously. Through SEM observation, the hydration product of MgO cured at 50 °C for 28 day was about 2–3 μm in length. The expansion of pastes with 5% of the MgO-type expansive agent was from 0.36% to 1.01% when the curing temperature changed from 25°C to 50 °C. When 8% of the MgO-type expansive agent was added, the early shrinkage of concrete was reduced. The expansion ratio increased with the curing temperature, and the expansive cracking of concrete with MgO-type expansive agent might be decreased by blending fly ash.