Effect of Calcium-Magnesia Compound Expansive Agent on the Macroscopic Performance and Microstructure of Concrete

This study aims to discuss the effects of calcium-magnesia compound expansive agent on the mechanical strength, shrinkage, and creep of concrete. On this basis, the expansive mechanism is investigated by using XRD, TG measurement, and MIP with percolation and backbone fractal dimension analysis. It is shown that replacing fly ash with calcium-magnesia compound expansive agent has little effect on the axial compression strength, but significantly reduces the elastic modulus. Moreover, increasing the amount of expansive agent from 0% to 12% leads to a reduction in autogenous shrinkage values by 9.1% to 14.8% at 180 days while causing an increase in creep by 24.5% to 37.8%. Concurrently, the porosity of the concrete increases with the addition of the calcium-magnesia compound expansive agent, and the proportion of gel and medium capillary pores in the total porosity also increases. However, fractal dimension analysis shows that it also decreases the complexity of overall connectivity of interconnected pores. Furthermore, the results obtained from TG also indicate that the calcium-magnesia compound expansive agent is beneficial for the formation of gel hydration products.