A comprehensive review on application of scrap tire rubber for sustainable thermal insulation material in civil engineering

Due to the increasing concerns on renewable energy exploration and sustainable construction development, the recycling of solid wastes had become a widespread practice globally. Combined utilization of scrap tire rubber with soil or other geomaterials for developing thermal insulation material in civil engineering was being considered as one of the viable answers to the rapid accumulation of these scrap tire stockpiles in an environmentally friendly way. To achieve the successful large-scale application of scrap rubber tires as insulation material in infrastructure construction, this paper summarized the classification systems, the physicochemical properties, and the environmental impacts of varied types of scrap tire rubber reported in the latest literature and reviewed the state of the art of thermal conduction behaviors of rubber-soil composites. The findings indicated that the physicochemical properties of scrap tire rubber differed according to tire type, production technology, and rubber particle morphology, which should be clearly checked before field application. A unified classification system and a standardized pre-treatment process of scrap rubber tires were probably helpful to promote wider regulatory acceptance. Small rubber particles exhibited superior capacity in enhancing insulation, but large ones may be more suitable for field application due to their lower manufacturing cost. Particle contact mechanics was one of the key points to explore the thermal conduction mechanism of rubber-soil composite. Rubber/soil particle morphology description and calculation time optimization were two challenges in numerical computation, which could be expected to be solved with the assistance of artificial intelligence techniques. The coupled effects of stress and temperature on thermal conduction of composite were recommended to be further investigated with anticipation of achieving more theoretical breakthroughs. The multi-material hybrid approach would be one of the feasible ways to further enhance insulation efficiency of such rubber-based composites.