From October 1987 to March 1993, Strategic Highway Research Program (SHRP) was conducted in the United States. The program was focused on the development of new methods for assessing the performance of bitumen binders. The research resulted in the development of a new method known as Superior Performing Asphalt Pavements (Superpave).
The main specifications of this method included:
Using the efficiency criterion for bitumen binders and asphalt concrete
Considering climatic conditions in application of bitumen
The problems studied in this method are as follows:
Winter low-temperature bitumen cracking not related to loading
Bitumen fatigue cracking due to loading
Summer high-temperature bitumen deformation due to loading
The primary objective behind determining the new specifications was to facilitate the purchase of bitumen products of better quality because these specifications will clearly describe the product for potential buyers. The new specifications also guarantee the proper performance of bitumen in coating. Climatic conditions are important factors in the efficiency of coating, but limited research has been conducted on this issue due to limited time and quite similar weather conditions. Moreover, they would not be precise if the loading factor is not taken into consideration. The producers all around the world, has been started to produce this type of bitumen which POC is a prominent in this regard. Having installed SHRP systems, Pasargad Oil Company is capable of selling bitumen to its customers based on PG method. It worth to remind that in the past, penetration was used as a factor for bitumen grading. In performance grade, the focus is on the mechanical specification of bitumen while in penetration grade, experimental parameters are involved. In Iran, pen-grade is more common, but in some cases, PG has better be used for a better performance. Today, a PG is defined for polymer modified bitumen and pure bitumen based on environmental conditions and temperature. A wider PG range means higher resistance and more favorable specifications. Pasargad Oil Company has the capacity to produce all these grades. This company first conducted climate zoning in Iran to specify the appropriate bitumen for different geographical zones.