Performance on the six PG tests vary from one supplier to the next, depending on their crude oil source. Most asphalt cement producers have indicated that the three AC's mentioned above are readily available at little or no increase in cost under the new classification system. The first year under the new system will incorporate all the required testing parameters with a tolerance between labs. This tolerance will be reduced after the first year as laboratories and producers become more proficient with testing and accuracy improves. One of the benefits of performance graded asphalts is the ability to add modifiers which will extend the performance of the material.
Polymers are the most common modifier in use today.
Specifying a PG 64 - 40 offers protection for both high and low temperature extreme problems. The cost of modified asphalt cement is greater, and will increase, as the temperature spread widens. This cost should fall as more modified asphalt is requested and made available. The decision for appropriate PG selection is dictated by environmental conditions, traffic level, and economic considerations at the given paving location. The environmental conditions consist of expected temperatures at the paving location.