Frost resistance improvement of recycled powder concrete by chemical admixtures

The sustainable recycling of construction waste is a critical challenge in civil engineering. Recycled powder (RP) shows great potential as a supplementary cementitious material, but the deterioration in frost resistance it causes limits the application of recycled powder concrete (RPC) in cold regions. This study screened the polycarboxylate superplasticizer (PC) with optimal compatibility with RP through adsorption tests and systematically compared the improvement effects of antifreeze water-reducer (AR), air-entraining agent (AE), and antifreeze agent (AF) on frost resistance. Macroscopic properties were evaluated via freeze-thaw cycle tests, and microscopic mechanisms were analyzed using scanning electron microscopy (SEM), super depth of field (SDF) imaging, and mercury intrusion porosimetry (MIP). Results indicated that after 200 freeze-thaw cycles, the frost resistance improvement ranked as 1% AF > AR > 5% AE. Quantitative analysis revealed that AF optimized the pore structure, reducing the proportion of harmful pores > 200 nm by 8.73%, significantly increasing hydration products, and effectively inhibiting frost heave damage. The study confirms that AF effectively enhances the durability of RPC, providing technical support for the resource utilization of construction waste in concrete engineering in cold regions.