Mix Proportion Optimization Design and Microstructure Study of UHPC Containing Polyvinyl Alcohol Fibers Based on Response Surface Method

To explore the influence of polyvinyl alcohol fibers (PVA fibers) on the mechanical properties of ultra-high performance concrete (UHPC), this work adopted the Box-Behnken test design method in the response surface method to construct a quadratic polynomial regression model and studied the effects of different binder-sand ratio, dosage of silica fume, dosage of fly ash, and dosage of metakaolin on the compressive strength of UHPC matrix. The optimum ratio of UHPC containing PVA fibers was obtained by optimizing the design, and the microstructure of UHPC containing PVA fibers was described by scanning electron microscope (SEM). The results showed that the binder-sand ratio had the greatest influence on the compressive strength of UHPC matrix, followed by the dosage of fly ash, and the dosage of silica fume and metakaolin had a smaller influence; the compressive strength of the UHPC matrix reached its maximum value when the cement-sand ratio was 1.10, the silica fume dosing was 4.70%, the fly ash dosing was 18.30%, and the metakaolin dosing was 6.55%, at which time the 28 d compressive strength and tensile strength of the UHPC containing PVA fibers were 122 MPa and 11.5 MPa, respectively; PVA fibers showed good bonding performance with the matrix, had a denser microstructure, and exhibited excellent mechanical properties, especially in tensile properties.