Before we start asphalting a road, we study the soil structure carefully. This is because the weight of the asphalted road falls on the soil. If the soil is unstable, all the hard work can come to nothing. Therefore, the actual process starts, the soil needs to be prepared by compacting. The addition of lime and cement to the soil accelerates the process. Gravel is placed and made compact over the soil, offering a stable base layer.
The process of asphalting takes place in layers, generally of 6 layers. The bottom most layer has a compression strain of 200 bar, which is quite a feat. The layer above it is made to be moisture resistant and is the actual foundation of the pavement to be made. The 4th layer generally has a depth of 3 inches from top to bottom and is also able to withstand the pressure of 70 bars tensile strength. The 3rd layer is one of the most important ones and is the widest one. It is 4 to 6 inches in depth and has a high resistance value. Its depth or thickness is variable depending on the nature of the entire pavement. The 2nd layer is the thinnest. The surface layer, which is the one we actually see has a depth of 1.5 to 3.5 inches. It is also renewable.