Bitumen graded by performance grade (PG) is one that behaves differently under different temperatures. Based on the air temperature above the pavement, the Long-Term Pavement Performance (LTPP) has provided an algorithm for calculating pavement temperature. The bitumen that performs best at those temperatures is chosen based on the highest and lowest temperature of the pavement.
The penetration grading of asphalt binder and the viscosity grading used in Hot Mix Asphalt (HMA) pavements cannot fully characterize their characteristics. Hence, as a part of Superpave Research, new binding tests and specifications have been developed to more accurately and comprehensively characterize asphalt binders utilized in HMA pavements. A number of characteristics of modern asphalt pavements such as rutting, fatigue cracking, and thermal cracking are addressed in these tests and specifications.
Based on the principle that the properties of an HMA asphalt binder should be related to how it is used, Superpave performance grading (PG) has been developed. For asphalt binders, this involves expected climatic conditions as well as aging considerations. Therefore, the PG system uses a common battery of tests (as the older penetration and viscosity grading systems do) but specifies that a particular asphalt binder must pass these tests at specific temperatures that are dependent upon the specific climatic conditions in the area of use.
This concept is not new – selection of penetration or viscosity graded asphalt binders follows the same logic – but the relationships between asphalt binder properties and conditions of use are more complete and more precise with the Superpave PG system. Information on how to select a PG asphalt binder for a specific condition is contained in the Superpave mix design method. The table below shows how the Superpave PG system addresses specific penetration, AC, and AR grading system general limitations.
Features of Superpave Performance Grading of Bitumen
The Superpave performance grading system makes use of a new set of bitumen tests. The method incorporates the following salient features:
- The system includes tests and specifications for bitumen binders. This bitumen binder may have either modified or unmodified bitumen.
- The field performance by the engineering principles will influence the physical properties determined from the Superpave bitumen tests. That is, it is not achieved by experience alone.
- The bitumen simulation for a period of 5 to 10 years, to understand its performance with age was developed. This is a long-term bitumen aging test.
- The tests and specifications of the Superpave system intend to avoid three main damages in bitumen i.e. raveling, fatigue cracking, and thermal cracking. These failures happen at high, intermediate, and low temperatures respectively.
- During Winter a bending beam rheometer and direct tension tester are used to measure the bitumen rheological properties at the project site.
Prior Limitations vs. Superpave Testing and Specification Features
| Limitations of Penetration, AC and AR Grading Systems | Superpave Binder Testing and Specification Features that Address Prior Limitations |
|---|---|
| Penetration and ductility tests are empirical and not directly related to HMA pavement performance. | The physical properties of bitumen measured are directly related to field performance by engineering principles. |
| Tests are conducted at one standard temperature without regard to the climate in which the asphalt binder will be used. | Test criteria remain constant, however, the temperature at which the criteria must be met changes in consideration of the binder grade selected for the prevalent climatic conditions. |
| The range of pavement temperatures at any one site is not adequately covered. For example, there is no test method for asphalt binder stiffness at low temperatures to control thermal cracking. | The entire range of pavement temperatures experienced at a particular site is covered. |
| Test methods only consider short-term asphalt binder aging (thin film oven test) although long-term aging is a significant factor in fatigue cracking and low temperature cracking. |
Three critical binder ages are simulated and tested:
|
| Asphalt binders can have significantly different characteristics within the same grading category. | Grading is more precise and there is less overlap between grades. |
| Modified asphalt binders are not suited for these grading systems. | Tests and specifications are intended for asphalt “binders” to include both modified and unmodified asphalt cement. |
Specifications of Performance Grade(PG) Bitumen
| Max. Design Temp. | PG 46 | PG 52 | PG 58 | PG 64 | PG 70 | PG 76 | PG 82 | ||||||||||||||||||||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Max. Design Temp. | -34 | -40 | -46 | -10 | -16 | -22 | -28 | -34 | -40 | -46 | -16 | -22 | -28 | -34 | -40 | -10 | -16 | -22 | -28 | -34 | -40 | -10 | -16 | -22 | -28 | -34 | -40 | -10 | -16 | -22 | -28 | -34 | -10 | -16 | -22 | -28 | -34 |
| Original | |||||||||||||||||||||||||||||||||||||
| ≥ 230°C | Flash Point | ||||||||||||||||||||||||||||||||||||
| ≤ 3 Pa-s @ 135°C | Rotational Viscosity | ||||||||||||||||||||||||||||||||||||
| ≥ 1.00 kPa | DSR G*/sin 𝛿 (Dynamic Shear Rheometer) | ||||||||||||||||||||||||||||||||||||
| 46 | 52 | 58 | 64 | 70 | 76 | 82 | |||||||||||||||||||||||||||||||
| (Rolling Thin Film Oven) RTFO, Mass Change ≤ 1.00% | |||||||||||||||||||||||||||||||||||||
| ≥ 2.20 kPa | DSR G*/sin 𝛿 (Dynamic Shear Rheometer) | ||||||||||||||||||||||||||||||||||||
| 46 | 52 | 58 | 64 | 70 | 76 | 82 | |||||||||||||||||||||||||||||||
| (Pressure Aging Vessel) PAV | |||||||||||||||||||||||||||||||||||||
| 20 hours, 2.10 MPa | 90 | 90 | 100 | 100 | 100(110) | 100(110) | 100(110) | ||||||||||||||||||||||||||||||
| ≤ 5000 kPa | DSR G*/sin 𝛿 (Dynamic Shear Rheometer) Intermediate Temp. = [(Max. + Min.)/2] + 4 | ||||||||||||||||||||||||||||||||||||
| 10 | 7 | 4 | 25 | 22 | 19 | 16 | 13 | 10 | 7 | 25 | 22 | 19 | 16 | 13 | 31 | 28 | 25 | 22 | 19 | 16 | 34 | 31 | 28 | 25 | 22 | 19 | 37 | 34 | 31 | 28 | 25 | 40 | 37 | 34 | 31 | 28 | |
| S ≤ 300 MPa m ≥ 0.300 | BBR S (creep stiffness) & m-value (Bending Beam Rheometer) | ||||||||||||||||||||||||||||||||||||
| -24 | -30 | -36 | 0 | -6 | -12 | -18 | -24 | -30 | -36 | -6 | -12 | -18 | -24 | -30 | 0 | -6 | -12 | -18 | -24 | -30 | 0 | -6 | -12 | -18 | -24 | -30 | 0 | -6 | -12 | -18 | -24 | 0 | -6 | -12 | -18 | -24 | |
| If BBR m-value ≥ 0.300 and creep stiffness is between 300 and 600, the Direct Tension failure strain requirement can be used in lieu of the creep stiffness requirement | |||||||||||||||||||||||||||||||||||||
| Ꜫ f ≥ 1.00% | DTT (Direct Tension Tester) | ||||||||||||||||||||||||||||||||||||
| -24 | -30 | -36 | 0 | -6 | -12 | -18 | -24 | -30 | -36 | -6 | -12 | -18 | -24 | -30 | 0 | -6 | -12 | -18 | -24 | -30 | 0 | -6 | -12 | -18 | -24 | -30 | 0 | -6 | -12 | -18 | -24 | 0 | -6 | -12 | -18 | -24 | |
How to read a PG Grade?
PG's grading system is based on climate, so the grade notation includes high and low pavement service temperatures. In order to describe the climate associated with high temperatures, we use an average pavement temperature for 7 consecutive days, which accounts for rutting, which takes time to develop.
The minimum pavement temperature is used for describing the low temperature climate; thus, it is the minimum pavement temperature which describes the low temperature climate. Both low and high temperature PG grades are graded in 6°C increments. Maximum pavement temperatures averaged 46 degrees Celsius over 7 days, and minimum pavement temperatures averaged 46 degrees Celsius over 7 days.
In order to meet performance requirements, a binder identified as PG 64-10 must comply with minimum and maximum pavement temperatures of 10°C and 64°C over a period of 7 days. Since a dark color pavement absorbs and retains heat, maximum pavement temperatures are typically about 20°C higher than air temperatures. Temperatures above one inch below the surface of the pavement are typically measured. As a result, the pavement temperature is equal to the air temperature on the surface.
A common durability of 98% is used, so when the PG 64-10 binder is selected, it should perform satisfactorily under normal service conditions at locations with extreme pavement temperatures between -10°C and 64°C throughout its lifetime, with a minimum level of 98% confidence. In areas with unusual traffic conditions such as interstate highways or bus stops or intersections with slow traffic, can be used one or two grades stiffer asphalt binder to prevent the problem.
Anywhere there is a need for more performance and durability, polymer modified binders are used. A number of paved areas and maintenance applications use polymer modified binders in place of asphalt due to their increased resistance to rutting, thermal cracking, fatigue damage, and temperature sensitivity.
Generally, the polymer modification is required when good rutting resistance at high temperatures and good thermal cracking resistance at low temperatures are simultaneously required in one application. Contact the best bitumen suppliers in UAE for queries.
Application of PG Bitumen
PG 52-28 is dominantly used in paving for both new construction and road care and also in both dense-graded and open-graded Hot Mix Asphalt (HMA). This product could also be used for sealing cracks in paving and also the edges. Other applications include spraying in places like bridge deck and pavement protective membrane with fabrics.
PG 58-22 is initially used in paving for both dense-graded and open-graded Hot Mix Asphalt (HMA) and also in road construction usages as well as spraying and crack sealing applications.
PG 58-28 is initially used in paving for both dense-graded and open-graded Hot Mix Asphalt (HMA) and also in road construction usages as well as spraying and crack sealing applications. This grade is widely used in very cold areas.
PG 58-34 is generally used in the higher elevation roadways. This grade is a paving asphalt cement dominantly used for the production of Hot Mix Asphalt (HMA). It could also be used for sealing the edges of new to old paving and cracks sealing.
PG 58-40 is primarily used on the high elevation locations. This grade is paving asphalt for the production of Hot Mix Asphalt (HMA). It can be easily used for sealing purposes and crack treating as well.
PG 64-22 is mostly used in paving for both new construction and pavement treatment projects and in both dense-graded and open-graded Hot Mix Asphalt (HMA) as well as others. It can be easily used for sealing purposes and crack treating too. Other uses include spray applications for bridge decks and pavement protective layer with fabrics and some modifications.
It has been reported that with proper aggregate selections and asphalt content, HMA with PG64-22 as the binder may show less tenderness compared to a similar mixture with a lower viscosity/softer asphalt. This will lead to a significant reduction of typical tenderness problems of mixture shoving and checking during pavement surface scuffing and rolling and markings caused by traffic immediately after paving.
PG 64-28 is primarily used in road construction and paving for new and pave care projects and in both dense-graded and open-graded HMA. Other uses include spray applications for bridge deck and pavement protective layer with fabrics. PG64-28 is generally used for the locations with low elevation.
PG 70-22 is primarily used in areas with high traffic volume and is also the paving asphalt cement used for the production of Hot Mix Asphalt (HMA). This grade is also a good choice for sealing the edges of pavement and for crack sealing.
PG Grades with the best resistance in thermal cracking- PG 64 -22
- PG 76 -22
- PG 64 -28
- PG 58 -34
- PG 82 -22
- PG 76 -28
- PG 70 -28
- PG 76 -22
- PG 64-22
- PG 70-22
- PG 76-22