Orthogonal Experiment on the Mechanical Properties of Tuff Mechanism Sand Concrete

Against the backdrop of global natural sand scarcity and stringent ecological protection policies, tuff mechanism sand has emerged as a promising alternative fine aggregate for concrete, especially in coastal infrastructure hubs like Ningbo, where abundant tuff resources coexist with acute natural sand shortages. However, existing research on TMS concrete lacks systematic multi-factor optimization, while the performance regulation mechanism of TMS remains unclear, hindering its application in large-scale engineering. To address this gap, this study employed a L16(4⁵) orthogonal experimental design to systematically investigate the effects of five key factors, including fineness modulus, sand ratio, fly ash-to-ground granulated blast-furnace slag ratio, stone powder content, and water–binder ratio, on the 3 d, 7 d, and 28 d compressive, splitting tensile, and flexural strengths of TMS concrete from Ningbo. The results indicate that all three strengths exhibit rapid growth from 3 d to 7 d and stable growth from 7 d to 28 d, with the 3 d compressive strength accounting for 72.5% of the 28 d value, while flexural strength shows the lowest 3 d proportion (63.1%) and highest late-stage growth rate. Range analysis reveals that water–binder ratio is the dominant factor controlling compressive strength and splitting tensile strength, whereas fineness modulus dominates flexural strength. The optimal fineness modulus values for compressive, splitting tensile, and flexural strengths are 2.60, 2.90, and 2.30, respectively; a stone powder content of 0% optimizes compressive and flexural strengths, while 6% is optimal for splitting tensile strength. Notably, the interaction between fineness modulus and water–binder ratio exerts a statistically significant effect on compressive strength (p = 0.008), while the other interactions are negligible. This study fills the gap in research on multi-factor synergistic optimization of TMS concrete and provides targeted mix proportion designs for different engineering requirements. The findings not only enrich the theoretical system of manufactured-sand concrete but also offer practical technical support for the resource utilization of TMS in medium-to-high-strength concrete engineering, aligning with the sustainable development goals of the construction industry.