Design of Low-Heat and Crack-Resistant Mass Concrete: Mix Proportioning and Influence of Critical Parameters

Mass concrete is prone to cracking induced by high early-age temperature rise and significant shrinkage stress, which severely compromises structural durability and safety. Aiming to achieve “low temperature rise and high crack resistance,” this study systematically optimized raw material selection and conducted experimental investigations on mix proportioning and the influence of critical parameters. The proposed design was subsequently validated through a field application. The results indicate that a fly ash content of 35% effectively improves workability, mitigates early-age shrinkage and reduces the heat of hydration. The incorporation of a high-performance expansive agent not only retards the hydration process and delays the temperature peak but also generates compensatory expansion at early ages, significantly reducing shrinkage during the cooling phase. Additionally, a polypropylene fiber dosage of 1.2 kg/m3 was found to optimally balance workability with crack resistance enhancement, resulting in less than 5% reduction in early-age strength. Field applications demonstrate that the concrete with the optimized mix proportion exhibits excellent workability and rapid early strength development. Specifically, the expansive agent delayed the temperature peak to 78 h and generated significant chemical expansion, effectively compensating for shrinkage caused by cooling. The findings provide critical insights into the construction-stage behavior of mass concrete, enabling improved safety control through better prediction and mitigation of early-age thermal and shrinkage effects. This study offers theoretical and technical support for the design of mass concrete characterized by low temperature rise and high crack resistance.