In this blog post, we’ll examine the causes of potholes on roads, the structural characteristics of asphalt pavement, and methods for preventing potholes as well as repair techniques.
How do potholes form on roads?
Sinkholes, which have become a major issue recently, are even threatening our daily lives. A sinkhole refers to a phenomenon where the ground surface subsides due to the formation of empty spaces within the subsoil. While potholes on roads may appear similar at first glance, their underlying causes are different. Potholes are round depressions that form on the surface of paved roads. They occur when water penetrates the asphalt pavement and, combined with the effects of freezing and thawing as well as repeated vehicle loads, causes damage to the pavement structure. While understanding the soil characteristics and underground structures of a specific area is crucial for sinkholes, potholes can be prevented and repaired by thoroughly understanding the structure of asphalt pavement and the construction process.
Why do voids in asphalt pavement cause potholes?
To prevent potholes, it is necessary to understand asphalt pavement. The key component of asphalt pavement is aggregate. Aggregate refers to stones of various sizes; the smaller ones include fine aggregate, such as sand, while the larger ones are coarse aggregate, such as gravel. Aggregate, as the term implies, serves as the structural framework. Paving involves mixing heated asphalt with aggregate; if the aggregate is considered the “bones,” then the asphalt is like the “flesh.” However, unlike bones and flesh, a certain amount of empty space remains between the asphalt mixture and the aggregate after construction.
These voids affect the durability and watertightness of asphalt pavements and can be a major factor in the formation of potholes. In particular, if cracks develop in the pavement or the voids become excessively large, rainwater or melted snow can easily penetrate the pavement. In cold weather, the infiltrated water freezes and expands in volume, and the repeated cycle of freezing and thawing can damage the interior of the pavement. When combined with the repeated loads from vehicles, the pavement material weakens and breaks away, ultimately leading to potholes. Therefore, when constructing asphalt pavement, it is essential not only to ensure the proper mix of aggregate and asphalt but also to maintain an appropriate void ratio and compaction level to prevent water from easily penetrating the pavement. Properly managing voids and reducing water infiltration into the pavement is a key method for preventing potholes.
How can potholes be repaired?
There are two main approaches to repairing potholes. The easiest and quickest method is to temporarily fill the pothole directly with asphalt mixture. However, since it is difficult to secure aggregates large enough to match the size and depth of the pothole and to mix them precisely, asphalt-based repair materials are sometimes used to fill the damaged area. However, compared to asphalt concrete containing aggregate, this method has the drawback of being more likely to deform or become damaged again under traffic loads. Nevertheless, because it is simple and quick to implement, it can be used as an emergency or temporary pothole repair method.
The second method involves cutting or excavating a rectangular section of the pavement surface that is larger than the pothole itself, removing the damaged portion, and partially repaving the road. This approach has the advantage of allowing for an inspection of the asphalt pavement condition around the pothole, enabling the repair of any areas that may be prone to further damage. Furthermore, unlike the previous method, this approach uses asphalt concrete containing appropriate aggregate, allowing for a more reliable restoration of the damaged pavement structure. However, applying this method presents the challenge of having to temporarily restrict or suspend road use in the construction zone. Furthermore, since it requires various construction processes and equipment—such as cutting, excavation, waste disposal, and compaction—it imposes a greater financial burden and takes more time to complete than the method of directly filling the pothole with asphalt-based repair material.
Why is it difficult to completely eliminate potholes?
Methods for preventing potholes, which pose a threat to paved roads, are actually widely known. Nevertheless, the reason potholes are still commonly seen on roads is that it is practically difficult to maintain an appropriate void ratio and compaction level while completely preventing water infiltration. Furthermore, as a road ages, repeated exposure to vehicle loads, temperature fluctuations, and moisture causes cracks to form on the road surface; these cracks, along with the voids within the pavement described earlier, can serve as pathways for water infiltration. Once cracks form, water can easily penetrate the pavement, and repeated cycles of freezing and thawing during cold weather increase the likelihood of potholes forming. While potholes formed in this way can be repaired using various methods, it is difficult to completely prevent new cracks and damage from occurring due to road aging, repeated traffic loads, temperature changes, and moisture penetration. Therefore, if technologies that reduce cracking and water penetration—while properly managing the void content and compaction of asphalt concrete—are further developed, it will be possible to significantly reduce the occurrence of potholes and improve road safety and service life.
