What is penetration grade bitumen?
BAKHTAR BITUMEN, penetration grade bitumen is a refinery bitumen manufactured at different viscosities. The penetration test is carried out to characterize the bitumen, based on the hardness. Thus, it has the name of penetration bitumen. The penetration bitumen grades ranges from 15 to 450 for road bitumen. But the most commonly used range is 25 to 200. The partial control of fluxing the residual bitumen with the oils can help in bringing the required hardness.
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.
Penetration Grade Bitumen is a standard usually applied as a Paving Grade Bitumen essential for road construction and for the production of asphalt pavements with superior properties. BAKHTAR BITUMEN, bitumen is produced from the vacuum residue (short residue) feedstock. The difference is by penetration range only. The penetration grade bitumen has a thermoplastic property which causes the material to soften at high temperatures and to harden at lower temperatures. This unique temperature/viscosity relationship is important when determining the performance parameters such as the adhesion, rheology, durability and application temperatures of bitumen.
BAKHTAR BITUMEN, Penetration Grade Bitumen is specified by the penetration and softening point test. The designation is by penetration range only.
The main Penetration Grade Bitumen is Bitumen 60/70 which is normally used for all the markets. Penetration grading’s basic assumption is that the less viscous the asphalt, the deeper the needle will penetrate. This penetration depth is empirically (albeit only roughly) correlated with asphalt binder performance. Therefore, asphalt binders with high penetration numbers (called “soft”) are used for cold climates while asphalt binders with low penetration numbers (called “hard”) are used for warm climates.
Penetration grading has the following asphalt concrete characteristics:
- Penetration depth of a 100 g needle 25° C (77° F).
- Flashpoint temperature. Ductility at 25°C (77°F).
- Solubility in trichloroethylene.
- Thin film oven test (accounts for the effects of short-term aging that occurs during mixing with hot aggregate).
- Retained penetration.
- Ductility at 25° C (77° F)
BAKHTAR BITUMEN, Penetration is determined using an empirical test method. A sample of the bitumen in a small container is stabilized in a water bath at a standard temperature (normally 25 C). A prescribed needle, weighing 100g, is allowed to bear on the surface of the bitumen for 5 sec. The bitumen is defined as the distance, in units of 0.1mm, that the needle penetrates into the bitumen.
As different samples of bitumen grade bitumen have different chemical compositions and their manufacturing is controlled in different ways, they may vary in consistency from semi-solid at room temperature to semi-liquid at the same conditions.
The penetration numbers obtained by means of the penetration test indicate the hardness of the bitumen. 15 “pen” bitumen is the hardest and 450 pen bitumen the softest. In the construction industry, the term “penetration grade bitumen” is often abbreviated to “pen bitumen” or simply “pen bit”.
BAKHTAR BITUMEN, Penetration grade bitumen forms the basis of other road binders such as cutbacks, emulsions, and polymer-modified binders, which are all discussed below.
Bitumen grades are specified primarily in terms of their needle penetration (referred to as ‘pen’). Soft bitumen has high pen numbers and hard bitumen have low pen numbers. Within specifications, however, there are certain other criteria which must be met including softening point, solubility, and resistance to hardening. Descriptions of these test methods, which form the basis for most bitumen specifications, now follow.
Penetration test
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This Test involves exposing bitumen sample 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.
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 types of unmodified bitumen have approximately equal penetration (800 dmm) and viscosity (1200 Pas). The softening point is, therefore, an approximation of the equi-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.
Advantages of penetration grade bitumen
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- The test is done at 25° C (77° F), 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).
The test is quick and inexpensive. Therefore, it can easily be used in the field