Review of Mechanical Properties and Hydration for Eco-Friendly UHPC—Role of Reactive Powders and Supplementary Cementitious Materials

Ultra-high-performance concrete (UHPC) is an emerging cementitious material owing to its excellent mechanical properties and durability, and it has received extensive attention and research around the world. In recent years, it has become a major research topic in the search for greener reactive powders, supplementary cementitious materials (SCMs) and suitable curing regimes that can effectively reduce the carbon emissions and preparation costs of UHPC. This study provides a review of the latest research results obtained in recent years on the compressive and flexural strength and hydration of UHPC containing low-carbon SCMs under different curing conditions. It has been shown that many low-cost admixtures, such as industrial waste, agricultural waste, nanomaterials and natural mineral powders, can be used as reactive powders or SCMs in the preparation of UHPC. Moreover, the mechanical strength and microstructure of UHPC incorporated with appropriate dosages of SCMs are not significantly weakened. This is due to the fact that these admixtures usually have good activity, and their physical and chemical filling effects can effectively mitigate the property losses caused by the reduction in the cement dosage. Meanwhile, high-temperature curing conditions, including steam, hot water and autoclave curing, can greatly promote the mechanical properties and microstructure of low-carbon UHPC at an early age. This is conducive to further reducing the comprehensive cost of UHPC, thus enhancing the prospects of UHPC’s application in engineering sites. Moreover, some insights into future research directions regarding low-carbon UHPC, such as intelligent materials and the combination of several reactive powders, are presented at the end.