Asphalt pavement is characterized as a flexible surface. It is composed of several layers consisting of different construction materials. The layers are structured to distribute the weight of the traffic, initially by spreading it then passing it on to the layer underneath.
The following are the three primary functional layers:
1. Subgrade: Subgrade is the bottom layer created by compacting the soil to bear the load transferred from the layers above.
2. Sub-base: This is the layer above the subgrade to provide structural support. It also acts as a barrier to the contaminants from the subgrade from reaching the layers above.
3. Surface layer: This is the beautiful, top black layer that you see.
Pavement failure is caused by several factors, such as water infiltration, excessive temperature causing expansion/contraction, UV rays, and traffic load.
The Primary Causes for Pavement Failure
Subgrade failure is the most significant cause of asphalt pavement failure. Extensive deterioration in the subgrade soil eventually leads to its failure. The main signs of subgrade failure include:
- An uneven pavement surface
- Formation of ripples across the pavement surface
- Visible depressions on the surface
- Deformation of pavement near the edges
A few of the reasons for the subgrade failure are the use of poor-quality soil, which is unable to withstand the load, inadequate thickness of the pavement, and heavier than the planned traffic load.
The main drivers of sub-base stability are sub-base strength, proper binding between the layers, and compactness of base materials. Below is a description of how each of these factors can fail.
A.) Sub-base strength is compromised due to the following reasons:
- Use of substandard aggregate
- Not implementing proper mix design
- Lack of necessary thickness
B.) Weakening of the binding action: Under heavy traffic load, the material particles in the sub-base and base layers start moving independently, causing the layers to move separately instead of as a whole.
C.) Erosion of baselayer material: When the top layer severely deteriorates, base layer material begins to loosen, creating potholes. To prevent premature top-layer deterioration, it is necessary to estimate the traffic load and calculate top-layer thickness accordingly.
Surface Layer Failure
The surface layer of an asphalt pavement bears the direct load of vehicular traffic. Therefore, it should be the strongest to withstand not only wheel load but the climatic conditions also. Extreme care should be exercised in designing and planning for the installation of the surface layer. The critical factors for the strength and stability of the surface layer are:
- Proper asphalt mix
- Accurate estimation of the wheel load for an appropriate layer thickness
- High-quality binder applied in sufficient quantity
- Superior-quality, high-grade aggregate comprising of gravel, crushed stone, sand, etc.
Quality Asphalt in Green Bay offers a full range of commercial and residential asphalt paving services, including asphalt paving, asphalt seal coating & crack filling, concrete paving, trucking and site work.
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