Jun Chen

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.

Bored pile waste slurry generated during bridge substructure construction exhibits high water content and stable colloidal properties, resulting in difficult solid–liquid separation and severe environmental risks. To improve solid–liquid separation and facilitate efficient disposal, this study systematically investigated the flocculation and dewatering performance of the slurry using three typical flocculants (Anionic polyacrylamide (APAM), cationic polyacrylamide (CPAM), and polymeric aluminum chloride(PAC)) through sedimentation tests, supernatant purification monitoring, particle size analysis, zeta potential measurements, and specific filtration resistance tests. The results show that flocculant type and dosage significantly affect treatment efficiency. Organic flocculants outperform inorganic PAC in both particle aggregation and dewatering improvement. Among them, APAM exhibits a prominent low-dose advantage; at an optimal dosage of 0.2–0.3% (corresponding to a pure reagent dosage of 10–15 mg/L based on wet slurry), it effectively reduces the slurry water content and lowers supernatant suspended solids below the 50 mg/L discharge standard within 80 min. Mechanistically, PAC provides primarily electrostatic neutralization, whereas APAM and CPAM achieve composite flocculation through charge neutralization, adsorption bridging, and sweep capture. Benefiting from efficient low-dose neutralization and long-chain bridging effects, APAM significantly reduces filtration resistance and forms stable flocs. Overall, an APAM dosage of 10–15 mg/L is the optimal scheme for in situ treatment of bored pile waste slurry, providing technical support for the efficient management and controlled disposal of engineering slurry under similar geological conditions.