A comprehensive review on treatment methods for end-of-life tire rubber used for rubberized cementitious materials

The use of end-of-life tire (ELT) rubber in rubberized cementitious materials (RCM) as a partial alternative aggregate has attracted the attention from researchers and industries in the recent decades. While the ELT rubber can be advantageous, such as by increasing fracture toughness, ductility, permeability, and thermal insulation of the concrete, it can negatively impact the other engineering properties, such as elastic modulus, mechanical strength, stiffness, and shrinkage. This reduction in performance may be attributed to the poor interfacial contact and bonding between the rubber particles and cement paste. This manuscript presents a comprehensive literature review on how ELT rubber has been physically and/or chemically treated to improve the properties of the rubberized cementitious composite. Specifically, this work (i) summarizes various treatment methods that have been employed to treat the ELT rubber surface before use in RCM; (ii) presents the hypothesized mechanism(s) behind each treatment method as well as the changes in the ELT rubber's microstructure (if applicable); and (iii) provides discussions and comparisons between the developed pretreatment methods for ELT rubber. Two metrics – strength recovery index (SRI) and strength gain (SG) – are introduced to assist with comparisons. Also, recommendations are provided to assess the most effective pretreatment methods for ELT rubber in RCM in terms of engineering properties.