Optimization design of ultrahigh-performance concrete based on interaction analysis of multiple factors

Ultrahigh-performance concrete (UHPC) has been applied in practical engineering owing to its good workability and high crack resistance. Rational design for UHPC is necessary for optimizing its performance. Thus, in the present study, a multi-factor interaction analysis was conducted to identify the optimal mix proportion of UHPC according to an orthogonal design, and then the properties of the optimized UHPC were evaluated. Multi-performance and multi-levels were introduced in the orthogonal design, and the optimization level range of each factor was determined by combining a range and variance analysis with a multi-factor interaction analysis. The mix proportion for the test was determined within the optimized variation range of each factor following the requirements of performance. Subsequently, the workability, mechanical properties, durability, and microstructure of the optimized UHPC were investigated. The results indicated that the fluidity, compressive strength, and flexural strength of the UHPC based on the optimized mix proportion were significantly improved. The optimized UHPC had higher resistances to chloride ion penetration and long-term drying shrinkage than ordinary concrete. Moreover, hot water curing significantly accelerated the hydration process of UHPC. As the curing age increases, hydration products fill the internal pores, and the UHPC paste becomes denser. The pores distributed in the interfacial transition zone between the steel fibers and paste are gradually filled by the hydration products. Thus, the bond performance between the steel fibers and paste is improved.