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摘要
In this paper, a highly active MgO expansive agent (MEA) with an active reaction time of 41 s was incorporated into ultra-high performance concrete (UHPC) and its effects on the workability, mechanical properties and volumetric stability of UHPC were investigated. Characterization of porosity and pore structure by mercury intrusion method, and the microscopic morphology of the hardened mortars were analyzed by SEM and EDS. The results showed that UHPC will reduce its fluidity and mechanical properties by incorporating MEA, but can significantly compensate for the early autogenous shrinkage of UHPC. The maximum doping of MEA should not exceed 12% of the total amount of cementitious materials. MEA decreases the porosity of UHPC, and refines it, especially for < 50 nm pore size, which is an important reason for the ability of MEA to compensate for the autogenous shrinkage of UHPC. The microscopic test results showed that the main reason for the swelling is that the MEA hydrates in situ to form dense Mg(OH)2, the inhibited crystallization will generate crystallization pressure, which leads to volume expansion. From the EDS results, it can be seen that the boundary between MEA without cementing ability and its hydration products and cement slurry gradually blurs with curing age, and UHPC will tend to be denser. ? 2023 Journal of Functional Materials.
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