Production of MgO-type expansive agent in dam concrete by use of industrial by-products

A novel MgO-type expansive agent in a designed formula has been prepared with industrial by-products—magnesite, serpentine and dolomite calcined at 1150 °C for 1 h. The compositions of expansive agent were studied by X-ray diffractometry (XRD), DSC and scanning electron microscopy (SEM), and the results showed that the main phases were MgO, CaO and C2S. The hydration of CaO to Ca(OH)2 is quick and can be completed in 3 days in water at 20 °C, and MgO to Mg(OH)2 is slow and about 57% MgO hydrates into Mg(OH)2 in 180 days under the same condition, which is quicker than in water. The hydrations of CaO and MgO generate expansions in early and later age, respectively. The shrinkage of roller compacted concrete will be compensated by adding the expansive agent. The utilization of these industrial by-products in the construction of hydraulic dams not only compensates the shrinkage of dam, but also reduces the environmental pollution.