Abstract
Recently, crumb rubber modifier or CRM has become prevalent in the construction of flexible pavements. This work addresses the phase separation that is commonly encountered with asphalt-rubber binders subjected to prolonged storage between production and use. Air blowing, accompanied by high shear mixing at elevated temperatures, was used to produce many asphalt-rubber blends in an attempt to discover a binder which resists phase separation. These air-blown, rubber-modified binders were subjected to various physical and chemical tests to elucidate the performance, rubber particle size, and oxidation as a function of curing time and curing conditions. This investigation revealed that air blowing improved the performance (as determined by the SuperpaveTM performance grading procedure) of the asphalt-rubber blends. Air-blown asphalt-rubber blends experienced as many as three high temperature performance grade increases compared to the high temperature performance grade of the neat, original binder. The addition of 10% by weight rubber to the binder also improved the low temperature performance grade. Thus, curing a binder with the addition of air and rubber was found to cause a substantial increase in the performance grade span. In addition, several blends, which were subjected to an elevated temperature for a prolonged period of time, were found to resist phase separation. The type of asphalt binder utilized for the blend seemed to have a significant effect on the extent of settling of the rubber particles that occurred. For example, blends with a resin as the asphalt type exhibited more compatibility (less separation) with the rubber modifier than blends with an AC-10 asphalt. Air blowing also seemed to lead to an improvement in the stability of the rubber particles in the asphalt binder, which was likely enhanced by the reduction in the rubber particle size due to air blowing.
Bauer, Shauna Erin (1997). The effect of air blowing on the properties of rubber-modified asphalt binder. Master's thesis, Texas A&M University. Available electronically from
https : / /hdl .handle .net /1969 .1 /ETD -TAMU -1997 -THESIS -B3852.