Application of magnesium oxide expansive agent in hydraulic concrete in China

This paper reviews and summarises the use of magnesium oxide (MgO) in hydraulic concrete in the following projects in China: Baishan hydropower station unexpectedly discovered the beneficial effects of MgO; Dongfeng hydropower station actively used MgO as an expansive agent for the first time in the main project; Changshaba hydropower station used MgO expansive agent for the first time in a full arch dam; Huangjiazhai hydropower station broke through 6% of MgO content for the first time in normal state concrete; and Dahe reservoir broke through 6% of MgO content for the first time in roller-compacted concrete. Findings indicate that the production process, transportation equipment, pouring process, burying of observation instrument, and so on, for concrete mixed with MgO are exactly the same as concrete without MgO. The long-term autogenous volume deformation of MgO concrete presents a good delayed micro-expansion discipline, which matches the long temperature drop process of dam concrete. The use of MgO expansive agent in dam concrete improves concrete's anti-cracking ability, simplifies temperature control measures of dam concrete, speeds up construction progress and saves project investment. At the same time, this paper points out the appropriate quality standards for the MgO expansive agent used in dam concrete and its soundness content that shall not be exceeded.