What is penetration grade bitumen?
The penetration grade bitumen is refinery bitumen that is manufactured at different viscosities. The penetration test is carried out to characterize the bitumen, based on the hardness. Thus, it has the name penetration bitumen. The penetration bitumen grades range from 15 to 450 for road bitumen. But the most commonly used range is 25 to 200. This is acquired by controlling the test carried out i.e. the distillation process. The partial control of fluxing the residual bitumen with the oils can help in bringing the required hardness.
The BS EN 1426 and BS EN 1427 provides the penetration and softening point values for the respective grades, as from Table-1. This will help in identifying the equiviscosity and the hardness of the bitumen grade.
The grades are represented by the penetration values i.e. For example, 40/60 as a penetration value of 50 ± 10.
The BS EN 13303 also gives the measure of loss on heating with respective limits for all penetration bitumen grades. This measure is to ensure that there are no volatile components present.
Penetration Grade Bitumen is specified by the penetration and softening point test. The designation is by penetration range only.
Penetration test
The Tests involves subjecting a sample of bitumen to needle bitumen under specified conditions of time, temperature and load. In most cases, the test is carried out at 25°C with a load of 100g for a duration of 5 s. Low-temperature bitumen is also measured occasionally with the usual conditions being 5°C with a load of 200 g for the 60s. The depth of bitumen of the needle into the surface of the bitumen is measured in tenths of a millimeter (dmm); hence 200 pen bitumen has a needle penetration of 200 dmm at 25°C when measured with a load of 100g for 5 s. It is common practice to describe the penetration of a particular bitumen without the unit, i.e. 100 pen means a penetration of 100 dmm.
Softening Point Test the Softening Point Test° involves preparing discs of bitumen and determining the temperature at which these discs are unable to support a standard metal ball (Fig. 2.8). At the softening point, all unmodified bitumen have approximately equal penetration (800 dmm) and viscosity (1200 Pas). The softening point is, therefore, an approximation of the equip-viscous temperature (EVT) for bitumen. It is possible to obtain an estimate for the temperature susceptibility of the bitumen from a knowledge of the penetration and softening point. Equations developed by Pfeiffer and Van Doormal2() demonstrate that a Penetration-Index (PI), which estimates the effect of temperature on the properties of the bitumen, can be determined. The higher the PI, the more temperature susceptible will be the bitumen. The PI has traditionally been used as part of the specification for bitumen, particularly in mainland Europe.
Advantages of penetration grade bitumen
- The test is done at 25° C which is reasonably close to a typical pavement average temperature.
- May also provide a better correlation with low-temperature asphalt binder properties than the viscosity test, which is performed at 60° C (140° F).
- Temperature susceptibility (the change in asphalt binder rheology with temperature) can be determined by conducting the test at temperatures other than 25° C (77° F).
- test is empirical and does not measure any fundamental engineering parameter such as viscosity.
- Shear rate is variable and high during the test. Since asphalt binders typically behave as a non-Newtonian fluid at 25° C (77° F), this will affect test results.
- Temperature susceptibility cannot be determined by a single test at 25° C (77° F).
Specification :
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