Experimental Study on Mechanical Properties of Graded EPS–Steel Fiber-Reinforced Concrete

This study designs the aggregate gradation and calculates the benchmark mix proportion of concrete based on two sets of regression coefficients. Copper-plated micro-steel fibers and graded EPS (expanded polystyrene) particles, with varying volume ratios of cementing materials, were incorporated into concrete specimens of C30, C40, and C50 grades made from fine aggregates and gravel. The specimens underwent compressive strength, flexural strength, and slump tests to investigate and analyze the effects of steel fibers and graded EPS on the mechanical properties of concrete. A modified equation for the similar bending-to-compression ratio coefficient was established, and a method for calculating the extreme value of the similar bending-to-compression ratio under the combined action of graded EPS and steel fibers was proposed, in order to predict the optimal dosage of steel fibers and graded EPS. The results show that for concrete of all grades (fine aggregate and gravel groups), the compressive and bending failure modes exhibited high consistency. After incorporating EPS, the specimens displayed some ductility during compressive failure, and compressive strength was negatively correlated with the volume fraction of EPS. As the volume fraction of EPS increased, the workability of the concrete decreased. At 7 days of curing, the uniaxial compressive strength of the concrete specimens was 60–75% of the 28-day strength. The tensile failure of graded EPS–steel fiber concrete was divided into four stages. For every 0.25% increase in steel fiber volume fraction, the increase in flexural strength was most likely between 14.35% and 17.61%, with the maximum growth rate being approximately 27%, and the distribution of growth rates was relatively dispersed. When applying the current bending-to-compression ratio model to calculate the flexural strength of concrete under the combined action of graded EPS and steel fibers, a significant deviation from the experimental values was observed. By introducing the modified similar bending-to-compression ratio coefficient equation, a conversion relationship between compressive strength and flexural strength was established. The adjusted R-value was 0.989, and a comparison of the predicted values with the experimental results showed high accuracy, offering considerable reference value.