Hydration and hardening properties of reactive magnesia and Portland cement composite

Hydration and hardening properties of reactive magnesia and Portland cement composite were evaluated with macro and micro property tests, in order to better understand systematically hydration and hardening mecha-nisms of reactive magnesia and Portland cement composite. Reactive magnesia content (10 wt%, 35 wt%, 50 wt %, 65 wt% and 90 wt%) obviously affects the hydration and hardening properties of reactive magnesia and Portland cement composite. As the main hydration product of reactive magnesia, Mg(OH)2 crystal shape affected by inner alkaline environment and Mg(OH)2 crystal amount influence the macro volume expansion performance. The Mg(OH)2 crystal size in hardened reactive magnesia and Portland cement composite pastes can be bigger than 2 mu m and is big enough to cause micro crack in hardened RMPC pastes, and at the same time to heal micro crack in moist curing condition (20 & PLUSMN; 2 & DEG;C and relative humidity > 95%). The loose cluster structure of Mg(OH)2 crystals leads to low binding property of RMPC pastes and causes the increases of the amount of pores in range of 0.1-1 mu m in hardened RMPC pastes. The findings will be beneficial for mixture proportion design, manufacture control and properties optimization of reactive magnesia and Portland cement composite concrete.

Automated summary

The hydration and hardening properties of reactive magnesia and Portland cement composite were evaluated through macro and micro property tests. The content of reactive magnesia significantly affects the hydration and hardening properties of the composite. The size of Mg(OH)2 crystals in the hardened composite can cause micro cracks and also heal them under moist curing conditions. The loose cluster structure of Mg(OH)2 crystals leads to poor binding properties and an increase in pore quantity in the hardened composite.