Use of Recycled Fine Aggregate in Wet-Mix Shotcrete Mortar Applications: The Role of Styrene–Butadiene Rubber Latex

Abstract

Abstract This study investigates the feasibility of wet-mix shotcrete (WMS) mortars incorporating recycled fine aggregate (RFA), with a particular focus on the role of styrene–butadiene rubber (SBR) latex in mitigating the adverse effects of RFA on shootability and mechanical properties. Two WMS series with water-to-cement ratios of 0.35 or 0.45 were investigated, in which natural sand was replaced with RFA in increments of 25%, up to full replacement (100%). The SBR latex was incorporated at 5% and 7.5% of mixing water. Test results showed that partial substitution of natural sand with low RFA content (i.e., 25% and 50%) enhances shootability, attributed to the rougher surface texture and higher water absorption of RFA that improve internal friction and mechanical bonding with the substrate. However, at higher replacement levels (75% and 100%), shootability deteriorated due to the excessive demand for the superplasticizer. The incorporation of SBR latex proved effective in enhancing shootability across all RFA replacement levels, underscoring the benefits of polymer modification for shotcrete applications. Furthermore, SBR additions helped mitigate strength reductions, particularly in flexural and pull-off bond strengths. Unlike previous studies, which have generally focused on either the rheology of cast mortars or the shootability of traditional WMS, this work offers a comprehensive assessment of rheology, shootability, and bonding to clarify the feasibility of the RFA replacement window and the critical role of SBR latex in wet shotcreting applications. These findings offer tangible guidance to technologists and contractors for designing more sustainable wet-mix shotcrete mortars that are simpler to apply and bond better.

The authors' abstract, as published at the source. Journal of Materials in Civil Engineering, 2026 · DOI ↗