This paper was presented at the `Advanced Materials' session. An assessment of Ontario scrap tire crumb rubber modified (CRM) hot-mix demonstration projects indicated the wet process (rubber modified asphalt cement - AR) can surpass conventional mixes in performance with favourable life-cycle costs. These findings, and development of improved AR mix design procedures and terminal blended AR with a minimum storage stability of 24 hours, resulted in three AR projects in 1994. A modified dry process project was also successfully completed using finer CRM (30 mesh). The specific project studied involved resurfacing a pavement in Brantford with two lifts of hot mix incorporating AR (about 15 percent 40 to 60 mesh CRM by mass of asphalt cement). This hot mix (about 6 percent AR by mass of mix) was designed, produced, placed and compacted without any problems. During the Marshall mix design, it is important to allow mix conditioning prior to briquette compaction and place a surcharge on the compacted briquette to prevent rebound during cooling. During field compaction, it is necessary to use a soap solution with all rollers (sticky mix) and continue finish rolling until the AR mix has cooled. There were no perceived environmental problems. Overall project monitoring involved mix compliance, compaction, smoothness, friction and resilient properties. (A)
Abstract