The synergistic effects of magnesium oxide expansive agent and nano-silica on the performance of ultra-high-performance concrete
The mechanical properties and early autogenous shrinkage of ultra-high-performance concrete(UH-PC)were experimentally investigated with the incorporation of magnesium oxide expansive agent(MEA)and nano-silica(NS).XRD and SEM were conducted to analyze the early hydration reactions and hydration prod-ucts.The results indicate that the addition of MEA and NS both reduces the flowability of UHPC,and their combined incorporation further decreases flowability.The introduction of MEA decreases the compressive strength of UHPC at different ages,while the addition of appropriate amounts of NS and MEA significantly im-proves both compressive strength and early autogenous shrinkage of UHPC.Microscopic tests using XRD and SEM reveal that NS effectively reduces the content of calcium hydroxide in the UHPC system.The UHPC with 0.5％NS and 6.0％MEA has a denser structure and no obvious macropores and flake calcium hydroxide,which makes the UHPC have good volume stability and mechanical properties.
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