Mechanical properties, microstructure, and non-destructive strength prediction of alkali-activated fly ash-slag recycled coarse aggregate concrete after exposure to elevated temperatures

作者：Hang Jing, Li‐Da Chen, Xu Liu, Mengying Li · 发表于：Case Studies in Construction Materials · 年份：2025 · DOI：10.1016/j.cscm.2025.e05630 · 被引用次数：1 · 研究领域：Recycled Aggregate Concrete Performance、Concrete and Cement Materials Research、Innovative concrete reinforcement materials

Alkali-activated recycled concrete (AARC), formed by combining recycled coarse aggregate (RCA) with an alkali-activated binder, exhibits superior mechanical performance and offers a promising sustainable, low-carbon alternative to conventional concrete. However, under fire exposure, elevated temperatures readily cause strength degradation in concrete structures, which poses serious risks to practical applications. To investigate the macro and micro degradation of AARC after high-temperature exposure and to enable rapid strength prediction and damage assessment, this study tested AARC samples with RCA replacement rates of 0 %, 25 %, 50 %, 75 %, and 100 % under conditions of 20, 200, 400, 600, and 800 °C. Macro behavior was assessed through visual inspection, mass loss, compressive tests, flexural tests, splitting-tensile tests, and failure-mode analysis. Microstructure was examined by BSEM and TG. Finally, ultrasonic testing supported a non-destructive strength-prediction model, and WPT-derived WPES provided an index for thermal-damage evaluation. Experimental results showed that compared to the reference state at 20 °C, AARC with 0 % and 25 % RCA exhibited compressive strength increase of 4.4 % and 1.4 % at 200 °C, respectively. At 600 °C, AARC with 100 % RCA shows a 41.4 % reduction in compressive strength, whereas ordinary concrete decreases by 55 %. Accordingly, the 100 % RCA AARC exhibits better thermal stability. At 400 °C, the flexural and splitting tensile strength of ...