Exploration of crumb rubber modified asphalt as a durable low noise surface in Hong Kong

Researches have demonstrated that crumb rubber modified asphalt (CRMA), not only enhances the mechanical performance of bituminous mixtures, but also re-uses the scrap tires and reduces rolling noise due to the improved viscosity of the binder and thus elasticity of the bituminous mix at service temperature, giving a "cushion" effect on the noise generation from vibration source. CRMA has lower rutting potential because of its higher resilient modulus and tensile strength at high temperatures. CRMA pavements, which are mainly built with open-graded or gap-graded mixtures, reduce noise levels by up to 3-5 dB compared to traditional dense-graded asphalt pavements. However, due to the addition of high-viscosity crumb rubber powders, higher mixing and compacting temperatures are required for asphalt pavement construction. As a result, compared to asphalt pavements built with regular asphalt binder, more odour, volatile organic compounds (VOCs) and particulate matters (PMs) are expected during construction, causing higher health concerns to construction workers. In Hong Kong, CRMA pavements are being explored to capture the benefits of improved durability and reduced noise. At the same time, concerns of potential higher emissions during production and construction are addressed by adding warm mix additives to reduce mixing and paving temperatures. This paper reports the initial findings of the CRMA study.