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Performance Grade (PG) Bitumen
It is a specialized type of bitumen graded based on its performance under different temperatures, specifically high and low temperature pavement services. This grading system addresses issues such as rutting at high temperatures and thermal cracking at low temperatures. The PG grades are determined by the climatic temperatures within a week, considering the highest temperature for high climatic conditions and the possibility of thermal cracking at low temperatures.
For high-temperature performance, rutting is a major concern. The temperature is measured within a week, and the highest recorded temperature is considered as the high climatic temperature. PG grades are divided into 6 ºC (43 ºF) increments, with the average seven-day maximum pavement temperature ranging from 46 ºC (114 ºF) to 82 ºC (180 ºF). For example, bitumen PG 64–10 meets performance criteria at an average seven-day maximum pavement temperature of 64 ºC (147 ºF) and a minimum pavement temperature of –10 ºC.
Performance Grading Should:
• Include measures describing stress
– Strain Relationships under field loading.
• Consider the pavement conditions
– Temperature, traffic speed, traffic volume, and pavement structure.
• Include acceptance limits derived from experience and actual field performance.
Variables that affect Binder Selection:
• Geographic Area:
– Air Temperature, Solar radiation
– Pavement Temperature: Max & Min
• Traffic volume: High, Medium, Low
• Traffic speed: Fast, Slow
• Pavement Structure: Strong, Weak
– Stress and strain
Methods of Selection:
• Select base grade based upon:
– Geographic Area
– Air Temperature
– Pavement Temperature
• Adjust base grade based upon:
– Traffic Speed
– Traffic Volume
Variables affecting binder selection include geographic area, air temperature, solar radiation, pavement temperature (maximum and minimum), traffic volume, traffic speed, and pavement structure (stress and strain). The selection method involves choosing a base grade based on geographic area, air temperature, and pavement temperature, followed by adjustments based on traffic speed and volume.
It’s essential to note that the maximum pavement temperature is usually higher than the air temperature by about 20 ºC (68 ºF) due to the dark color of the pavement, which absorbs and retains heat. PG grades are broadly categorized into modified and unmodified bitumen types. To differentiate them, the low and high-temperature grades are added together. If the sum is greater than 90, the substance is likely a polymer-modified binder. For instance, a PG 76–22 is considered a polymer-modified binder with a sum of 98, while a PG 64–10 is an unmodified binder.
Application of Performance Grade (PG) Bitumen:
- PG52–28: Used in paving for new construction and pavement rehabilitation, in dense-graded and open-graded Hot Mix Asphalt (HMA). Also applicable for sealing edges of new to old paving and crack sealing. Other uses include spray applications for bridge deck and pavement protective membrane with fabrics.
- PG58–22: Primarily used in paving for new construction and pavement rehabilitation in both dense-graded and open-graded HMA. It can also be used for sealing edges of new to old paving and crack sealing. Additionally, suitable for spray applications on bridge decks and pavement protective membranes with fabrics.
- PG58–28: Used in paving for both new construction and pavement rehabilitation, in both dense-graded and open-graded HMA. Suitable for spray applications on bridge decks and pavement protective membranes with fabrics.
- PG58–28 (for very cold areas): Generally used in very cold regions.
- PG58–34: Primarily used in the upper half of Eastern Washington and on higher elevation roadways. It is paving asphalt cement primarily used for the production of Hot Mix Asphalt (HMA). Applications include paving for new construction and pavement rehabilitation in both dense-graded and open-graded HMA. Also used for sealing edges of new to old paving and crack sealing.
- PG58–40: Primarily used on high elevation roadways. It is paving asphalt cement for the production of Hot Mix Asphalt (HMA) and can be used for sealing edges of new to old paving and crack sealing.
In summary, Performance Grade bitumen is crucial for ensuring the longevity and durability of pavements in varying climatic conditions. The careful selection of PG grades based on geographic, traffic, and pavement factors is essential to address specific performance requirements. The application of PG bitumen in different scenarios, such as new construction, rehabilitation, and various asphalt mix types, further highlights its versatility in the field of pavement engineering.
Standard Specification Of Performance Grade:
Standard Specification Of Performance Grade