Effect of a novel negative temperature early-strength agent in improving concrete performance under varying curing temperatures

This study investigates the effect of a novel negative temperature early-strength agent (NEA) in enhancing concrete performance under varying curing temperatures, with a discussion on the underlying mechanism through analysis of hydration products and microstructure.The results indicate NEA markedly accelerates early cement hydration, reduces setting time, and enhances compressive strength. Moreover, the efficacy of NEA is more pronounced at lower temperatures. With an optimal dosage of 3 %, the incorporation of NEA leads to a remarkable 285.9 % increase in compressive strength at 28 days under -5 degrees C curing temperature. Despite accelerating cement hydration can induce increased chemical shrinkage, NEA effectively mitigates early freezing expansion under negative temperature and significantly diminishes chloride ion permeability. Higher temperatures facilitate early cement hydration but also compromise long-term hydration continuity. Consequently, the highest hydration degree and loweast porosity are observed at 28 days under 5 degrees C curing temperature. NEA's air-entraining component introduces numerous superfine pores into the paste, augmenting early pore volume while optimizing pore structure. As the early-strength component fosters hydration, these pores undergo further filling and refinement, ultimately reducing the total pore volume at 28 days. This study provides insights into optimizing concrete performance in cold environments.