A recycling approach of natural stone from crushed concrete based on freeze-thaw modification and usage of spalling mortar as recycled fine aggregate

• Published in: Construction & building materials Vol. 416; p. 135287
• Main Authors: Xia, Peng, Wang, Shiqi, Chen, Keyu, Meng, Tao, Chen, Xudong, Gong, Fuyuan
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 16.02.2024
• Subjects: Freeze-thaw modification; RCA; recycled concrete; Sodium silicate; Spalling mortar; Spalling mortar; RCA; Sodium silicate; Freeze-thaw modification; recycled concrete
• ISSN: 0950-0618; 1879-0526
• DOI: 10.1016/j.conbuildmat.2024.135287

To address the challenge posed by traditional methods of modifying recycled concrete aggregates (RCA), which struggle to achieve properties comparable to natural coarse aggregates (NCA) while ensuring a high utilization rate, this paper proposes a combination of freeze-thaw modification and sodium silicate modification. The process subjects the RCA to freeze-thaw cycles (FTC) to detach the attached mortar, which results in the extraction of recycled aggregates (Near-NCA) with properties similar to NCA, along with the spalling mortar (SM). These materials are used in the recycled concrete and mortar, respectively. Considering the inferior properties of SM, sodium silicate solutions are employed to modify it, serving as a replacement for river sand in the recycled mortar. The outcomes reveal that concrete cast using Near-NCA demonstrates mechanical properties comparable to ordinary concrete. Furthermore, the sodium silicate proves to be effective in modifying SM, reducing its crushed index and water absorption by approximately 30%. Through the SEM and XRD, it is determined that these improvements can be attributed to the formation of C-S-H gel. Finally, a multi-objective model is developed to consider modification effects, carbon emissions, energy consumption, economic and time costs, with the utilization of TOPSIS for determining the optimal modification plan. •This paper proposes a method that combines freeze-thaw modification with mineralization strengthening.•Modifying spalling mortar with sodium silicate solution can improve its various properties.•The modification mechanism of sodium silicate is investigated through microscopic tests.•The TOPSIS method is utilized to obtain the optimal modification scheme considering multiple objectives.