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https://nap.nationalacademies.org/catalog/27432/critical-issues-in-transportation-for-2024-and-beyond

Environmental Impacts and Energy Efficiency of Rubberized Warm Mix Asphalt (R-WMA) for Sustainable Road Construction

Rubberized Hot Mix Asphalt (R-HMA), produced by adding between 15-20 percent crumb rubber from scrap tires to the asphalt binder is an environmentally friendly alternative to conventional hot mix asphalt (HMA). Use of R-HMA equates to recycling more than 1,250 scrap tires per one lane-kilometer overlaid with a thin (45 mm) overlay. Apart from recycling benefits, R-HMA has also been shown, through extensive research, to have superior performance in terms of fatigue and reflective cracking, two primary failure modes for asphalt pavements. Half the thickness of R-HMA will provide the same cracking life as full thickness HMA for overlays of cracked pavement according to research conducted by the University of California Pavement Research Center (UCPRC). However, more widespread use of R-HMA is limited by the need to produce and construct these mixes at much higher temperatures. Because of the higher viscosity of rubberized asphalt binder, production of R-HMA requires higher temperatures than are required for mixing of conventional HMA (190°C to 220°C [375°F to 425°F] for R-HMA compared to 140°C to 160°C [280°F to 320°F] for HMA). While R-HMA uses waste tire material and extends the life of pavements, it comes at the cost of increased energy consumption, emissions, odors, and fumes during production and construction due to higher temperature requirements. New technology is now available to reduce the production temperatures by between 15°C and 55°C (30°F to 100°F). These technologies collectively are referred to as Warm Mix Asphalt (WMA). The use of warm-mix asphalt technologies can potentially reduce these temperatures by up to 55°C (100°F) without any negative effects on performance. No research is being carried out to quantify the environmental benefits and energy savings. This information is needed by road and environmental authorities to support decisions to use Rubberized Warm Mix Asphalt (R-WMA) in rehabilitation projects nationwide.