Influence of granulated rubber from waste tires on ASR expansion, microstructure, and mechanical properties of mortars

The paper presents the results of research on the effect of partially replacing the sand fraction in cement mortar mixes with granulated rubber (GR) from waste tires on the potential for alkali–silica reaction (ASR) occurrence. ASR is a significant durability issue in cement-based composites, which can lead to substantial expansion and cracking in these materials. The study also analyzed the influence of rubber aggregate on the mechanical properties of mortars, particularly compressive and flexural strength, as well as on the microstructure of the mortars. Additionally, the impact of NaOH on the properties of granulated rubber aggregate was evaluated. Reference mortars were prepared using moderately reactive sand (R1) and highly reactive sand (R3), while in the experimental mixes, rubber aggregate was used as a volumetric replacement for a specific sand fraction at levels of 15% and 30%. ASR-related expansion tests were conducted in accordance with the RILEM AAR-2 guidelines. The results showed that partially replacing sand with rubber aggregate effectively reduced ASR-induced expansion, likely due to the rubber’s ability to absorb stress and restrict moisture migration, thereby mitigating the reaction. However, the use of rubber aggregate also led to a decrease in both compressive and flexural strength, which is a typical effect when introducing elastic materials, such as rubber, into cementitious mixes. The findings highlight the potential of granulated rubber from waste tires recycled as a sustainable additive in cement-based materials to control ASR, especially in structures exposed to aggressive environmental conditions. Additionally, the use of this type of aggregate aligns with the principles of the circular economy by utilizing rubber waste and simultaneously delivering both environmental and performance benefits.