Analysis of the Effect of MgO Expansive Agent on the Expansion Performance of Cement Mortar Under Constant and Variable Humidity Curing Conditions
LIU Kuisheng1, CUI Yong2,3, YU Xiao1, LUAN Haitao1, SONG Qida1, CHEN Jiajun1, MA Zixiang1, FANG Kuizhen3,*
1 Beijing Urban Construction Group Co.,Ltd., Beijing 100088, China 2 CCTEG Coal Mining Research Institute, Beijing 100013, China 3 School of Civil Engineering, Tsinghua University, Beijing 100084, China
Abstract: Crack control and performance optimization in cement-based materials are pivotal goals in the field of civil engineering. While traditional shrinkage compensation methods are somewhat effective, they are limited by high costs and application constraints. Magnesium oxide (MgO) expansive agents have recently garnered widespread attention due to their cost-effectiveness and efficiency. However, research on the performance and compensation mechanisms of MgO under varying humidity conditions remains insufficient. This study focuses on the performance of cement-based materials incorporated with MgO under constant and variable moisture curing regimes. By examining the restrained expansion rate, mineral composition of hydration products, morphology, and distribution, as well as the hydration degree of MgO, this work delves into the humidity sensitivity of MgO in cement-based materials. Findings indicate that the restrained expansion rate of cement mortar containing 8% M-type MgO increases with the curing humidity, with a critical threshold humidity of 80% for expansion and shrinkage. The stability of the cement mortar with 8% M-type MgO is maintained under both high humidity-slow cycle and low humidity-fast cycle curing regimes. The reaction degree of the MgO expansive agent in cement paste increases with humidity, ranging from 20%—45%. The product Mg(OH)2 primarily forms around the MgO particles in a gel state, transforming into rod-shaped crystals as the humidity reaches 100%.
刘奎生, 崔勇, 于晓, 栾海涛, 宋奇达, 陈佳俊, 马子翔, 房奎圳. 恒湿与变湿养护条件下MgO膨胀剂对水泥砂浆膨胀性能的影响分析[J]. 材料导报, 2025, 39(7): 24020085-7.
LIU Kuisheng, CUI Yong, YU Xiao, LUAN Haitao, SONG Qida, CHEN Jiajun, MA Zixiang, FANG Kuizhen. Analysis of the Effect of MgO Expansive Agent on the Expansion Performance of Cement Mortar Under Constant and Variable Humidity Curing Conditions. Materials Reports, 2025, 39(7): 24020085-7.
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2025, Vol. 39 
