| 摘要 |
It has been determined that a specific type of emulsion SBR can be used to modify asphalt cement to greatly enhance the resistance to shoving, rutting and low temperature cracking of asphalt concretes made therewith. It has further been determined that this emulsion SBR is compatible with virtually all types of asphalt and that modified asphalt cements made therewith have extremely high levels of force ductility, tenacity and toughness. The SBR used to modify asphalt cement in the practice of this invention is a blend of (i) a high molecular weight styrene-butadiene rubber having a weight average molecular weight of at least about 300,000 and (ii) a low molecular weight styrene-butadiene rubber having a weight average molecular weight of less than about 280,000; wherein the ratio of the high molecular weight styrene-butadiene rubber to the low molecular weight styrene-butadiene rubber is within the range of about 80:20 to about 25:75; and wherein the bound styrene content of the high molecular weight styrene-butadiene rubber differs from the bound styrene content of the low molecular weight styrene-butadiene rubber by at least 5 percentage points. These SBR compositions are comprised of repeat units which are derived from styrene and 1,3-butadiene, wherein the styrene-butadiene rubber composition has a number average molecular weight as determined by field flow fractionation which is within the range of about 50,000 to 150,000 and wherein the styrene-butadiene rubber has a light scattering to refractive index ratio which is within the range of 1.8 to 3.9.
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