Laboratory and field performance investigation of pre-swollen crumb rubber modified asphalt mixtures
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International Journal of Pavement Research and Technology Journal homepage: www.springer.com/42947
Laboratory and field performance investigation of pre-swollen crumb rubber modified asphalt mixtures Angela Farinaa*, M. Emin Kutaya, Michele Lanotteb a
Department of Civil and Environmental Engineering, Michigan State University, 428 S. Shaw Lane, Room Number 3546,East Lansing, MI 48824, USA b Department of Civil Infrastructure and Environmental Engineering, Khalifa University of Science and Technology, Abu Dhabi, UAE Received 22 June 2020; received in revised form 29 September 2020; accepted 5 October 2020
Abstract
The pre-swollen crumb rubber (PSCR) is a pelletized rubber produced by the reaction of scrap tire rubber particles with bitumen -compatible oil at elevated temperatures. It does not require a prior blending with bitumen, and it can be added directly at an asphalt plant. A laboratory investigation was carried out to evaluate the performance of plant-produced PSCR modified mixtures for surface and intermediate courses and analyze their suitability for low-traffic volume road in cold environment applications. Linear viscoelastic properties, rutting and thermal cracking performance were investigated in the laboratory. The presence of pre-swollen rubber particles and, in particular, the bitumen-compatible oil softened the mixtures as indicated by the dynamic modulus master curves. The different mechanical responses led to an enhancement of thermal cracking resistance but increased the rutting susceptibility of the PSCR mixtures. Despite the laboratory findings, no rutting was observed after five years of service life based on visual inspection of the field test sections constructed in Michigan with PSCR-modified Hot-Mix Asphalt (HMA). A few transverse cracks were generated in the lanes where the control mix with neat bitumen was used. Those cracks did not propagate into the PSCR modified material, in agreement with the laboratory findings. Keywords: Pre-swollen crumb rubber, dry technology, rubberized asphalt, performance testing, field conditions
1. Introduction Crumb rubber (CR) from scrap tires has been used as an additive in asphalt pavements since the 1960s in the United States [1]. Two techniques are recognized worldwide to include CR in asphalt mixtures: ‘wet process’ and ‘dry process’ [2]. The interaction between rubber particles and other components of the mixture varies considerably between these two techniques. In the former case, CR particles are used as a polymeric modifying agent of the base bitumen in which they can be partially or entirely digested. In the dry technology, CR particles are used as partial replacement of the aggregate structure, and their interaction with the asphalt binder is minimal [3]. Products of the wet process have been reported to enhance the resistance to rutting and cracking of asphalt mixtures significantly since the early applications [4-8]. During the production process of CR-modified bitumen (CRMB), the combined action of high
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