polymer modified asphalt
Polymer modified asphalt is a type of asphalt mixture in which the binder has been altered from it’s common state by polymer addition, to a more durable and elastic product with more temperature stability, resistance to cracking, and resistance to rutting. Modified polymer asphalt binder is more viscous (thicker) which can translate into better adhesion to the aggregate particles, and in turn can improve durability. It is commonly specified in areas with heavy truck traffic and/or slow moving truck traffic. The other driving factor regarding the need for specifying polymer modified asphalt is whether or not the performance grade temperature fluctuation is greater than 90 degrees. In terms of performance graded asphalt (Example PG 70-22), the first number represent the average 7 day max temp, the second represents the minimum pavement design temperature likely to be experienced. For example a PG 76-22 mix will often require the use of polymer in the binder where a PG 64-22 will typically not. About 10-25% of current asphalt binder produced is modified. One of the more commonly used polymer modifiers is Styrene-butadiene-styrene (SBS). Polyvinyl Chloride (PVC) and Atactic Polyprpylene (APP) are also sometimes specified as polymer additives along with several other types of polymers. Polymer in crumb, pellet, or powder form is added to the hot asphalt binder at the asphalt plant through varying processes and technologically advanced mixing methods. Polymers add to the cost of the binder but as the binder is a relatively small portion of the overall asphalt mix cost (e.g. aggregate and production costs) the cost increase is commonly justified in relation to overall life cycle and maintenance costs of a pavement. Placing Polymer modified polymer asphalt can be more difficult due to it’s thicker nature.