Optimized mix design method of ultra-high performance concrete (UHPC) and effect of high steel fiber content: Mechanical performance and shrinkage properties

In this study, UHPC was successfully prepared based on the Modified Andreason and Andersen (MAA) model (distribution modulus m = 0.23 was confirmed) and Excel solver tool. Subsequently, the effect of steel fiber content (0%-6% by volume) on the mechanical properties and shrinkage properties was investigated. It was found that the compressive and flexural strengths increased significantly with the increase of steel fiber content from 0 % to 5 %, but decreased when it exceeded 5 %. The split tensile strength was always increased. In addition, the plastic shrinkage, autogenous shrinkage, and drying shrinkage of UHPC were reduced by 18.3%-67.4 %. It indicated that incorporating higher content of steel fiber into UHPC could enhance mechanical strength, but the mixing approach should be optimized when content of steel fiber exceeds 5%. In addition, the prevalence of steel fiber agglomeration was shown under X-CT, but the agglomeration of steel fiber still led to an increase in UHPC properties within a certain range. The air content of UHPC with 6 % fiber content is 3.5 %, which shows the reasonableness and good performance of the mix proportion calculated by the Excel solver demonstrated in the article. The article can lay a light on the industrial design and preparation of UHPC.