Preparation of red mud-calcium carbide slag-based low-carbon lightweight aggregate concrete: mechanical performance and interfacial transition zone microstructural analysis

Abstract

To broaden the resource utilization range of red mud (RM) and calcium carbide slag (CCS), this study prepared low-carbon lightweight aggregate concrete (LLC) based on RM-CCS-based artificial lightweight aggregate ceramsite synthesized through cold-bonded pelletization technology. It investigated the development rules of mechanical performance of novel cold-bonded LLC under different conditions. Moreover, for the prepared specimens, the quantitative relation between ultrasonic pulse velocity (UPV) and compressive strength was established, and the microstructure of the interfacial transition zone (ITZ) was analyzed. Results show that the LLC specimen showed more excellent axial compressive strength and higher tension-compression than ordinary concrete. To be specific, the 28-day axial compressive strength (f_ck), the tensile strength (f_tk) and the flexual strength (f_fk) were 87.8–91.8 %, 10.3–11.0 %, and 10.2–11.2 % of cube compressive strength (f_cu,k). The 28-day UPV values of the prepared LLC specimen ranged from 4.254 to 4.786 km/s, suggesting a high compactness degree. The quantitative relations of f_cu,k, f_ck, f_tk, and f_fk were established through statistical regression, with favorable correlation. According to micro-structural analysis results, the thickness of the ITZ in LLC was approximately 80 μm, suggesting that the prepared RM-CCS-based lightweight aggregate showed favorable water absorbing and returning capability. Due to the internal curing of lightweight aggregate on cement mortar near the interface region, the structure became more compact, reaching a higher hydration degree. The analysis of the calcium-to-silicon (Ca-to-Si) ratio and microhardness test results validated the high intensity of ITZ in both chemical and physical dimensions, thereby enhancing the overall LLC mechanical performance.