Mix Design and Performance Study of Early-Strength Concrete based on Orthogonal Experiment

Abstract

To investigate the influence mechanism of C-S-H nano-nuclei on the early strength of high-performance concrete in which fly ash partially replaces cement, this study employed an orthogonal experimental method to systematically explore the synergistic effects of three key factors-fly ash content, nano-C-S-H nuclei content, and curing age-on the mechanical properties of early-strength concrete. A four-level, three-factor orthogonal experimental design (L16(4³)) was adopted, with a total of 17 groups of concrete specimens prepared. Their compressive strength, splitting tensile strength, and elastic modulus were tested at different ages ranging from 4 hours to 7 days. Through range analysis and mean comparison, the primary and secondary influence order of each factor on the performance indicators, as well as the variation patterns, were clarified.The results indicate that curing age is the most significant factor affecting the compressive strength, splitting tensile strength, and elastic modulus of early-strength concrete, followed by the content of nano-C-S-H nuclei, while the influence of fly ash content is relatively weaker. As the fly ash content increases (10%–40%), the early compressive strength of concrete shows a slow declining trend. The appropriate incorporation of nano-C-S-H nuclei (2%–4%) can significantly enhance early strength, but excessive addition may lead to a reduction in strength. With the extension of curing time, all mechanical properties improve markedly. Based on comprehensive performance analysis, the optimal mix proportion for early-strength concrete is determined as 20% fly ash content, 2% nano-C-S-H nuclei content, and 7 days of curing. Verification shows that, compared to the reference group without supplementary materials, the optimized group exhibits increases of 19% in compressive strength, 33.3% in splitting tensile strength, and 8% in elastic modulus, demonstrating excellent early-strength performance and engineering applicability.This study quantitatively analyzes the effects of material proportioning and curing regime on the early mechanical behavior of concrete under a dual-admixture system through orthogonal experiments, providing experimental evidence and theoretical references for the mix design and performance regulation of early-strength concrete.