Sulfate attack resistance of recycled aggregate concrete with NaOH-solution-treated crumb rubber

This study investigates the sulfate attack resistance of recycled aggregate concrete with NaOH-solution-treated crumb rubber (CR). For this purpose, several recycled aggregate concrete mixes were developed using different concentrations (10%, 20% and 30%) of NaOH-solution-treated CR and different CR particle sizes (0.16-0.3 mm, 0.85-2 mm and 10-20 mm). The performance, including mass loss, residual compressive strength, relative dynamic modulus of elasticity (RDME) and microstructure, was evaluated in the sulfate environment. Results reveal that the macroscopic performance of recycled aggregate concrete with CR presents three stages: the early enhancement or slow declining stage, middle declining stage and subsequent accelerated declining stage. The addition of CR particles could improve the sulfate attack resistance of recycled aggregate concrete, and the effect was more significant for the NaOH-solution-treated CR particles than for the untreated CR. Moreover, 0.16-0.3 mm CR particles and 20% NaOH solution pretreatment were the optimum conditions in this assessment range to enhance the sulfate attack resistance. Although the surface scaling tended to worsen in recycled aggregate concrete mixtures with 10-20 mm CR due to its weaker mortars, the mixtures were still durable in sulfate attack conditions owing to their higher residual RDME and compressive strength than those of recycled aggregate concrete. The results of the analysis of corrosion products through X-ray diffraction and the microstructure through scanning electron microscopy are consistent with the macroscopic performance. (C) 2021 Elsevier Ltd. All rights reserved.