Performance Grade Bitumen
Bitumen Performance Grade is a type of bitumen which is graded according to its performance at different alternating temperatures. There is a tendency to divide PG grade into two divisions of high-temperature and low-temperature pavement services. Here comes the major issue for high-temperature performance which is rutting, that normally takes a while to amass. Thus, the temperature is measured within a week and the highest is considered to be the high climatic temperature. On the other side, there is a possibility for thermal cracking at low temperature. For both high and low temperature, PG grades are graded in 6 c rise. The average seven-day maximum pavement temperature typically changes from 46 c to 82 c and the minimum pavement temperature changes from -46 c to -10 c. For instance, bitumen PG 64-10 meets performance factor at an average seven-day maximum pavement temperature of 64 c also at a minimum pavement temperature of -10c.
Mind the point that maximum pavement temperature is usually higher than the air temperature by about 20c because the dark color of pavement absorbs the heat and keep it. As PG grades are mainly divided into Modified and Unmodified bitumen types, keep in mind the following hint which helps to differentiate the mentioned types. To distinguish the modified from unmodified bitumen, we add both low and high-temperature grades together. If the sum is greater than 90, the substance is likely to be a polymer modified binder. As an example, a PG 76-22 is considered as a polymer-modified binder since the sum is 98. Another example, a PG 64-10 is an unmodified binder.
PG grades generally are mostly applied in paving constructions and reconstructions, sealing of edges, crack sealing, spray applications for bridge deck and in both dense-graded and open-graded Hot Mix Asphalt (HMA). PG grades which are well-structured against thermal cracking are PG 58-34, PG 64-22, PG 64-28 and PG 76-22. PG grades which are resistant to rutting are PG 70-22, PG 70-28, PG 76-28 and PG 82-22.
PG 58-28 is specifically used in very cold regions.