The use of recycled tire rubber in asphalt pavements to improve the overall performance, economy, and sustainability of pavements has gained considerable attention over the last few decades. Several studies have indicated that recycled tire rubber can reduce the permanent deformation of flexible pavements and enhance its resistance to rutting, reduce pavement construction and maintenance costs, and improve the resistance to fatigue damage. This paper provides a systematic and critical overview of the research on and practice of using recycled tire rubber in asphalt pavements in terms of engineering properties, performance, and durability assessment. This critical analysis of the state-of-the-art should enhance the understanding of using recycled tire rubber in asphalt pavements, define pertinent recommendations, identify knowledge gaps, and highlight the need for concerted future research.

This study explores highly eco-efficient preplaced aggregate concrete mixtures having superior tensile characteristics and impact resistance developed for pavement and infrastructure applications. A fully recycled granular skeleton consisting of recycled concrete aggregate and recycled tire rubber granules, and steel wire fibers from scrap tires are first placed in the formwork, then injected with a flowable grout. Considering its very high recycled content and limited mixing and placement energy (only the grout is mixed, and no mechanical vibration is needed), this material has exceptional sustainability features and offers superior time and cost savings. Moreover, typical problems of rapid loss of workability due to the high-water absorption of recycled aggregates and the floating of lightweight tire rubber granules are prevented since the aggregates are preplaced in the formwork. The much higher granular content and its denser skeleton reduce the cementitious dosage substantially and provide high volume stability against shrinkage and thermal strains. The behavior under impact loading of this sustainable preplaced recycled aggregate concrete, incorporating randomly dispersed steel wire fibers retrieved from scrap tires, was investigated using a drop weight impact test. The results show that recycled tire steel wire fibers significantly enhanced the tensile and impact properties. A two-parameter Weibull distribution provided an accurate prediction of the impact failure strength of the preplaced recycled aggregate concrete mixtures, allowing to avert additional costly laboratory experiments.

This experimental study explores the development of highly eco-efficient concrete. This concrete incorporates 50% higher coarse aggregate content compared with normal concrete, thus reducing cement demand, and its granular skeleton is entirely recycled. Moreover, it adopts a unique energy-efficient placement technique whereby the granular skeleton is first preplaced in the form and then injected with a flowing grout, which considerably reduces the energy of mixing and placement. Various mixtures incorporating recycled concrete aggregate along with recycled rubber granules and steel wire fibres retrieved from scrap tyres were made. The mechanical strength and post-cracking behaviour of the eco-efficient concrete were evaluated. While tyre rubber decreased mechanical strength as expected, scrap tyre steel wire fibres enhanced the tensile and flexural behaviour, exhibiting superior energy absorption and ductility compared to the brittle failure of the control mixture. The results provide an insight into the level of recycled tyre rubber and steel wire that could be combined with recycled concrete aggregate to achieve durable and cost-effective eco-efficient preplaced recycled aggregate and rubberised concrete for sustainable non-structural applications.