Expansion Performance and Microstructure of High-performance Concrete using Differently Scaled MgO Agents and Mineral Powder

To investigate the assumptions proposed in this paper, the evolution law governing the strength and expansion performance of MgO and nano-MgO micro-expansive concrete in the environment of mineral powder was firstly observed in this study. Secondly, SEM, XRD, and TG-DSC microscopic tests were conducted to reveal the effects of the active mineral-powder admixture on the hydration degree and expansion performance of MgO and nano-MgO in HPC. Our experimental results successfully verified our hypothesis, which indicated that the expansion performance of macro-MgO and nano-MgO was indeed depressed by the addition of active mineral power admixtures, even though the mechanical property of concrete composites was effectively improved. Furthermore, the hydration test also demonstrated the negative interference on the mineral powders, which was induced by the expansion agents. It is found the amounts of hydrates tend to decrease because the mineral powder ratio reaches and exceeds 40%. Moreover, it is also concluded the effect of expansion agents is governed by the alkalinity cement paste, especially for the nano-MgO. In other words, the expansion performance of nano-MgO will vary more obviously with the hydration process, than MgO. The results of this study provide that effective experimental and theoretical data support the hydration-inhibition mechanism of magnesium expansive agents.