Influence of Asphalt Mixing Plant Recycled Powder as Cement Replacement on Concrete Performance

Asphalt mixing plant recycled powder (RP) is a solid waste generated during asphalt mixture production, and its efficient resource utilization is urgently needed. This study investigates the feasibility of utilizing RP as a cement replacement material in C30 concrete. The effects of RP on the workability, mechanical properties, drying shrinkage, hydration kinetics, and microstructure of concrete were systematically evaluated at replacement ratios ranging from 0% to 28%. The results indicate that RP incorporation reduces the fluidity of fresh concrete, with a maximum slump reduction of 21.1%. Both compressive and splitting tensile strengths decrease continuously with increasing replacement ratio. The higher relative early-age strength gain of RP mixtures in compressive strength mainly stems from their much lower absolute strength rather than accelerated hydration; isothermal calorimetry further revealed that RP retards hydration and reduces both the peak and cumulative heat release, while the dilution effect suppresses the formation of hydration products (C-S-H gel), thereby inhibiting strength development. Consequently, the 28-day compressive strength fails to meet the C30 design standard at a 28% replacement ratio. In addition, RP exacerbates drying shrinkage owing to its high water absorption. Pore structure analysis showed that moderate RP increased the proportion of gel pores while concurrently increasing mesopores and macropores; the pore-structure evolution at replacement ratios beyond 14% requires further investigation. Considering workability, mechanical performance, and volume stability, 14% is recommended as the maximum replacement ratio that satisfies the engineering acceptance requirements. Within this limit, RP demonstrates viability as a cement replacement material, offering a promising pathway for the high-value utilization of asphalt-related industrial solid waste and contributing to the low-carbon development of the concrete industry.