Optimized Mix Design Method of Ultra-high Performance Concrete (UHPC) and Effect of High Steel Fiber Content: Mechanical performance and Shrinkage Properties

Abstract

In this study, UHPC was successfully prepared based on the Modified Andreason and Andersen (MAA) model (distribution modulus 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.