Performance Grade (PG) Bitumen
PERFORMANCE GRADE (PG) BITUMEN
Performance Grade (PG) Bitumen, introduced through the Strategic Highway Research Program (SHRP) in the US between 1987 and 1993, addresses the inadequacies of penetration and viscosity grading systems. Under the Superpave system, PG Bitumen is graded based on its performance in extreme temperatures, offering a comprehensive solution for modified and unmodified bitumens. This grading system ensures that asphalt binders possess suitable properties for the environmental conditions they will encounter in the field.
The PG system classifies binders according to their performance in both hot and cold temperatures, allowing for selection based on expected climatic conditions, traffic speed, and volume adjustments. Utilizing a common set of tests, the PG system measures physical properties directly linked to pavement performance at service temperatures. Notably, acceptance limits remain consistent but must be met at specific pavement temperatures and traffic conditions.
The Long-Term Pavement Performance (LTPP) provides an algorithm to calculate pavement temperature based on the air temperature. By determining the highest and lowest temperatures of the pavement, the system selects bitumen that performs well within that temperature range. This approach surpasses the limitations of penetration and viscosity grading systems, addressing parameters like rutting, fatigue cracking, and thermal cracking in HMA pavements.
Superpave PG Bitumen is grounded in the concept that asphalt binder properties should align with the conditions under which they are used, considering climatic conditions and aging factors. While utilizing a common battery of tests like older grading systems, the Superpave PG system specifies that asphalt binders must pass these tests at temperatures dependent on the specific climatic conditions of the area of use. This approach enhances the precision and completeness of the relationships between asphalt binder properties and conditions of use compared to older systems.
ADVANTAGES OF PERFORMANCE GRADE (PG) BITUMEN
- PG addresses current traffic and climatic conditions, unlike traditional penetration and viscosity grading systems based on past experiences.
- PG considers actual traffic volume and vehicle speed, providing a more accurate representation of load duration.
- Superpave grading indicates the working temperature range of the binder, offering insights into low and high-temperature performance.
- PG accounts for the visco-elastic nature of bitumen, considering the influence of temperature and rate of load application on its behavior.
- Different petroleum sources may result in binders with distinct rheological behaviors, a factor not addressed by conventional grading methods.
- Superpave is designed for both modified and unmodified bitumens, unlike conventional methods that are limited to unmodified bitumens.
- Superpave covers both short-term and long-term aging behavior of binders, utilizing tests like the rolling thin film oven test (RTFOT) and pressure aging vessel (PAV).
- PG recognizes three main distress mechanisms affecting pavement performance: rutting, fatigue cracking, and thermal cracking. It considers bitumen properties at different temperatures to address each distress mechanism effectively.
CONTRAST THE PERFORMANCE GRADE WITH THE PENETRATION AND VISCOSITY GRADE
| 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 measured are directly related to field performance by engineering principles. |
| The range of pavement temperatures at any one site is not adequately covered. For example, there is no test method | 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. |
| 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. | The entire range of pavement temperatures experienced at a particular site is covered. |
| Asphalt binders can have significantly different characteristics within the same grading category. | Three critical binder ages are simulated and tested: 1. Original asphalt binder prior to mixing with aggregate. 2. Aged asphalt binder after HMA production and construction. 3. Long-term aged binder. |
| 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 |
OXIDIZED BITUMEN IS NOT WORK AS PG
Oxidized bitumen is not suitable for PG applications. Despite constituting 85% of bitumen production (approximately 90 million tons per year), oxidized and residual bitumen lack essential properties for meeting modern pavement requirements. Enhancing the performance of oil bitumen, especially oxidized bitumen, commonly involves the use of polymer modifiers. Polymer-modified bitumen offers notable advantages over conventional bitumen, including increased elasticity, flexibility, durability, temperature resistance, and aging resistance, along with improved adhesive and cohesive properties.
APPLICATION OF PERFORMANCE GRADE (PG) BITUMEN
- PG52-28: Ideal for paving in new construction and pavement rehabilitation, suitable for both dense-graded and open-graded Hot Mix Asphalt (HMA). It can also be used for sealing edges, crack sealing, and spray applications on bridge decks and pavement protective membranes.
- PG58-22: Well-suited for paving in new construction and pavement rehabilitation, applicable to both dense-graded and open-graded HMA. It is also suitable for sealing edges, crack sealing, and spray applications on bridge decks and pavement protective membranes.
- PG58-28: Mainly used in paving for new construction and pavement rehabilitation in both dense-graded and open-graded HMA. Additionally, it is suitable for spray applications on bridge decks and pavement protective membranes, especially in very cold areas.
- PG58-34: Primarily utilized in the upper half of eastern Washington and on higher elevation roadways. It is a paving asphalt cement designed for Hot Mix Asphalt (HMA) production, suitable for sealing edges, crack sealing, and paving in both new construction and pavement rehabilitation in dense-graded and open-graded HMA.
- PG58-40: Ideal for high elevation roadways, serving as paving asphalt cement for HMA production. It is also applicable for sealing edges and crack sealing in both new construction and pavement rehabilitation.
- PG64-22: Suitable for paving in new construction and pavement rehabilitation, usable in both dense-graded and open-graded HMA. It can be employed for sealing edges, crack sealing, and spray applications on bridge decks and pavement protective membranes. Known for potentially reducing tenderness issues in HMA mixtures.
- PG64-28: Designed for paving in both new construction and pavement rehabilitation, fitting for both dense-graded and open-graded HMA. It is also suitable for spray applications on bridge decks and pavement protective membranes, primarily used in the lower half of Eastern Washington.
- PG70-22: Primarily used in high-traffic areas, serving as the paving asphalt cement for HMA production. It is versatile for sealing pavement edges and crack sealing.
Which PG asphalt is most effective against thermal cracking?
- PG 64 -22
- PG 76 -22
- PG 64 -28
- PG 58 -34
Which PG binder offers superior resistance to rutting?
- PG 82 -22
- PG 76 -28
- PG 70 -28
- PG 76 -22
Consideration of Traffic Speed and Volume in Binder Selection
- Examples
- Base Grade PG 58 -22
- Toll road (high volume): PG 64-22
- Toll booth (high volume, slow traffic): PG 70-22
- Rest area (high volume, standing traffic): PG 76-22
SBS MIXING WITH BITUMEN TO MAKE PG GRADE
SBS is commonly blended with bitumen to achieve PG grades. Thermoplastic elastomers, especially SBS, serve as popular bitumen modifiers, offering a combination of high strength, elasticity, heat resistance, adhesion, and improved low-temperature properties. However, their widespread use is hindered by the high cost. A potential solution is to partially or fully substitute them with more affordable polymers.
TECHNICAL DATA SHEET OF PERFORMANCE GRADE BITUMEN (PG)
| PG 46 | PG52 | PG 58 | PG 64 | PG 70 | PG 76 | PG 82 | |
|---|---|---|---|---|---|---|---|
| Grade range | -34 to -46 | -10 to -46 | -16 to -40 | -10 to -40 | -10 to -40 | -10 to -34 | -10 to –34 |
| Average 7-day maximum pavement design temperature (°C) | < 46 | < 52 | < 58 | < 64 | < 70 | < 76 | < 82 |
| Minimum pavement design temperature (°C) | >-34 to >-46 | >-10 to >-46 | >-16 to >-40 | >-10 to >-40 | >-10 to >-40 | >-10 to >-34 | >-10 to >-34 |
| Original binder | |||||||
| Flash-point temperature, D92; min. (°C) | 230 | ||||||
| Viscosity, D 4402: max. 3 Pa × s, test temperature (°C) | 135 | ||||||
| ynamic shear, D7175: G*/sind, min. 1.00 kPa; 25 mm plate, 1 mm gap; test temperature at 10 rad/s (°C) | 46 | 52 | 58 | 64 | 70 | 76 | 82 |
| Rolling thin film oven residue (T 240) | |||||||
| Mass loss, max. % | 1.00 | ||||||
| Dynamic shear, D7175: G*/sind, min. 2.20 kPa; 25 mm plate, 1 mm gap; test temperature at 10 rad/s (°C) | 46 | 52 | 58 | 64 | 70 | 76 | 82 |
| Pressure ageing vessel residue (PP 1) | |||||||
| PAV ageing temperature (°C) | 90 | 90 | 100 | 100 | 100 (110) | 100 (110) | 100 (110) |
| Dynamic shear, D7175: G* × sind, max. 5000 kPa; 8mm plate, 2 mm gap; test temperature at 10 rad/s (°C) | 10 to 4 | 25 to 7 | 25 to 13 | 31 to 16 | 34 to 19 | 37 to 25 | 40 to 28 |
| Creep stiffness, D 6648: S, max 300 MPa; m-value, min. 0.300; test temperature at 60 s (°C) | –24 to –36 | 0 to –36 | –6 to –30 | 0 to –30 | 0 to –30 | 0 to –24 | 0 to –24 |
| Direct tension, D6723: failure strain, min. 1.0%; test temperature at 1.0 mm/min. (°C) | –24 to –36 | 0 to –36 | –6 to –30 | 0 to –30 | 0 to –30 | 0 to –24 | 0 to –24 |
| TEST METHOD | LIMIT | ASTM | ASSHOT | PG 58-22 | PG 70-16 | PG 76-10 | PG 64-22 |
|---|---|---|---|---|---|---|---|
| Flash Point C | 230 C Min | D92 | T48 | 303 | 300 | 320 | 312 |
| Rotational Viscosity @ 135 C | 3 Pa.s Max | D4402 | T316 | 0282 | 0.425 | 0.425 | 0.325 |
| DRS (C) | 58 | 70 | 76 | 64 | |||
| G/sin (C) 10 rad/s | 1.0 KPa Min | D7175 | T315 | 1.51 | 1.1 | 1.2 | 1.14 |
| RTFOT G*/sin (C) 10 rad/s | 2.20 KPa Min | D7175 | T315 | 2.71 | 2.3 | 2.25 | 2.9 |
| Change of Mass after RTFOT | 1% Max | D2872 | T240 | 0.08 | 0.12 | 0.12 | 0.06 |
| PAV | D5621 | R28 | 100(110) (C) T (C) | 100(110) (C) T (C) | 100(110) (C) T (C) | 100(110) (C) T (C) | |
| DRS G/sin (C) 10 rad/s | KPa 5000 Max | D7175 | T315 | 3330 | 2440 | 2720 | 2950 |
| BBR (C) | -12 | -6 | 0 | -12 | |||
| Stiffness Mpa | 300 Mpa Max | D6648 | T313 | 266 | 206 | 176 | 234 |
| m-value | 0.03 Min | D6648 | T313 | 0.309 | 0.32 | 0.35 | 0.3 |
| PROPERTY | UNIT | PG 46-34 | PG 46-28 | PG 52-28 | PG 58-28 | PG 58-22 | PG 64-22 | METHOD AASHTO |
|---|---|---|---|---|---|---|---|---|
| Original Binder | ||||||||
| Absolute Viscosity @ 60 C | Poise | 295 | 295 | 560 | 915 | 1120 | 2030 | T 202 |
| Penetration at 25 C | dmm | 300 | 300 | 180 | 130 | 110 | 70 | T 49 |
| Specific Gravity at 15.6 C | ≥ 1.00 | ≥ 1.00 | ≥ 1.00 | ≥ 1.00 | ≥ 1.00 | ≥ 1.00 | T 228 | |
| Flash Point, COC | C | 230 | 230 | 230 | 230 | 230 | 230 | T48 |
| Rotational Viscosity @ 135 C | Pa.s | 3.00 | 3.00 | 3.00 | 3.00 | 3.00 | 3.00 | T 316 |
| Dynamic Shear @ Grade Temperature | C | 46 | 46 | 52 | 58 | 58 | 64 | |
| G*/sin @ 10 rad/sec | kPa | ≥ 1.00 | ≥ 1.00 | ≥ 1.00 | ≥ 1.00 | ≥ 1.00 | ≥ 1.00 | T315 |
| RTFOT Residue | ||||||||
| Mass Loss | % | ≤ 1.00 | ≤ 1.00 | ≤ 1.00 | ≤ 1.00 | ≤ 1.00 | ≤ 1.00 | T 240 |
| Dynamic Shear @ Grade Temperature | C | 46 | 46 | 52 | 58 | 58 | 64 | T 315 |
| G*/sin @ 10 rad/sec | kPa | 2.20 | 2.20 | 2.20 | 2.20 | 2.20 | 2.20 | |
| PAV Residue (Aging Temperature, C) | 90 | R 28 | ||||||
| Dynamic Shear @ Grade Temperature | C | 10 | 13 | 16 | 19 | 22 | 25 | |
| G*/sin @ 10 rad/sec | kPa | 5000 | 5000 | 5000 | 5000 | 5000 | 5000 | T 315 |
| Creep Stiffness @Grade Temperature | C | -24 | -18 | -18 | -18 | -12 | -12 | |
| S | Mpa | ≤ 300 | ≤ 300 | ≤ 300 | ≤ 300 | ≤ 300 | ≤ 300 | T 313 |
| m-value | ≥ 0.30 | ≥ 0.30 | ≥ 0.30 | ≥ 0.30 | ≥ 0.30 | ≥ 0.30 | T 313 |
