Oil asphalt is the remaining material that is considered no longer economically viable from the petroleum distillation process in oil refinery plants. We know these materials in three Penetration classes, namely Pen 40/50, Pen 80/70 and Pen 80/100. The lower the penetration number, the harder the asphalt is, the more difficult it is to handle because a higher temperature is needed to make the asphalt soft or liquid. On the other hand, the higher the penetration rate, the easier the asphalt will be to dilute, easy to work with, but it is threatened that it will be difficult to achieve stability of the asphalt mixture, especially in hot climates such as in Indonesia, because asphalt tends to soften at high air temperatures.

Asphalt processing generally requires heating at a temperature of around 1100 – 1700C so that the asphalt becomes runny so that it is easy to pump, move and mix with aggregate or compact. If the asphalt is heated many times and for a long time, a lot of aromatic oil will evaporate so that the asphalt hardens, meaning that the penetration rate decreases. Asphalt with low penetration will be easily oxidized so that it becomes brittle, loses its stickiness, as a result the asphalt layer will be dispersed or loose grains. Therefore, in Indonesia it is determined that the lowest number for penetration of asphalt materials is 50 (Specification of Highways since 2003). Asphalt that is processed into an asphalt mixture will undergo oxidation due to sunlight and reach a penetration of 25, which is the lowest limit of penetration before dissolving.

In areas that are not yet developed, the roads are still empty of traffic, the length of the roads is still small, the axle load of the vehicle is not heavy, we know how to carry out pavement work with Surface Dressing Method (Burtu/Burda) and Macadam Penetration Method. Asphalt with a low penetration rate (pen 40/50) is very suitable for this method and the work is carried out in a labour-intensive manner, where asphalt is supplied with drums that function as a “storage tank”. Heating is enough to use firewood on the side of the road, and when the hot asphalt is poured onto the surface of the semi-compacted rock layer (the layer is still large hollow), the 40/50 asphalt (low penetration, hard asphalt) will dry quickly, cool quickly and thicken. . Asphalt will not "drain off" (flow down). Very suitable, because the asphalt is needed on the surface, to close the cavity so that water does not penetrate.

Instead to make Asphalt concrete As much as possible use asphalt with high penetration (soft asphalt) because the mixing and transportation process takes a long time, which causes the evaporation of natural oils and causes the asphalt to dry and lose its stickiness. Hot Rolled Sheet (HRS) in the 80s used asphalt pen 80/100, using gradation gaps to form larger voids (voids), many small grains to help hold the asphalt in the matrix, therefore the asphalt content in the mixture HRS is usually >7% (other types of asphalt concrete generally range from only 5.3 – 5.8%). Increasing the asphalt content in HRS so that the pavement layer is not easily cracked (because it is more flexible), the surface is more impermeable, not easy to crack, not easy to perforate. The disadvantage is that it is too soft and flexible so it is easy to wavy. When in high speed, the car will vibrate and easily get out of control. With the above experience, oil asphalt was chosen with a penetration rate of 60/70 as the asphalt pavement material. 

In other countries besides the Penetration class it is also known Viskositas Class, in Australia known as AC-2.5, AC-5 and so on. There are also Performance Grade Class, for example which is associated with its resistance to temperature, PG 64-10, PG 70-20 and so on.