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BITUMEN PERFORMANCE GRADE
Performance Grade (PG) bitumen is bitumen that is graded based on its performance at different temperatures. The Long-Term Pavement Performance(LTPP) has given a certain algorithm to calculate the temperature of the pavement based on the temperature of the air above. From this, the highest and the lowest temperatures of the pavement are calculated and the bitumen that performs well in that temperature range is selected.
Penetration grading and viscosity grading are somewhat limited in their ability to fully characterize asphalt binder for use in Hot Mix Asphalt(HMA) pavement. Therefore, as part of the Superpave research effort, new binder tests and specifications were developed to more accurately and fully characterize asphalt binders for use in HMA pavements. These tests and specifications are specifically designed to address HMA pavement performance parameters such as rutting, fatigue cracking, and thermal cracking.
LIMITATIONS OF PENETRATION, AC AND AR GRADING SYSTEM
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Penetration and ductility tests are empirical and not directly related to HMA pavement performance.
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Tests are conducted at one standard temperature without regard to the climate in which the asphalt binder will be used.
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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.
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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.
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Asphalt binders can have significantly different characteristics within the same grading category.
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Modified asphalt binders are not suited for these grading systems
SUPER-PAVE BINDER TESTING AND SPECIFICATION FEATURES
THAT ADDRESS PRIOR LIMITATIONS
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The physical properties measured are directly related to field performance by engineering principles. 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.
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The entire range of pavement temperatures experienced at a particular site is covered.
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Three critical binder ages are simulated and tested: Original asphalt binder prior to mixing with the aggregate.
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Aged asphalt binder after HMA production and construction. Long-term aged binder.
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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.
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Grading is more precise and there is less overlap between grades
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Tests and specifications are intended for asphalt “binders” to include both modified and unmodified asphalt cement.
