A chip seal or seal coat is a type of surface treatment known as a bituminous surface treatment (BST). This treatment involves the application of a liquid asphalt material onto the pavement surface, followed by a thin layer of aggregate that is placed at a thickness of no more than 0.5 inches. Typically, BSTs are used on pavements that have lower traffic volumes. This type of treatment is designed to help protect the pavement from the damaging effects of water, sun, and other environmental factors. Additionally, BSTs can help to improve the skid resistance of the pavement surface, which can enhance safety for drivers.
Types of Bituminous Surface Treatments
1. Single Surface Treatment
A bituminous surface is created by applying bitumen onto a surface that has been prepared beforehand. This process is done only once, and the surface is then immediately rolled. It is recommended to use a pneumatic-tired roller for this process.
2. Multiple Surface Treatment
This method of treatment involves multiple applications of bitumen, typically 2 or 3 layers. Each layer is accompanied by a decrease in aggregate size compared to the previous layer. It is important to immediately roll each layer with a pneumatic-tired roller. This process ensures that the layers are properly compacted and bonded together.
Material Requirement of Bituminous Surface Treatments
1. Aggregate
A. Size
The recommended size for aggregate used in single surface treatments should be uniform, ideally ranging from 1⁄2 to 1⁄4 inches (13 to 6 mm). On the other hand, for multiple surface treatments, the aggregate size should range from 1 to 1⁄2 inches (25 to 13 mm) for the bottom layer, while each succeeding layer should utilize aggregate of approximately 1⁄2 inch in size.
In multiple treatments, larger aggregates can be used. However, it is important to note that aggregates exceeding 1⁄2 inch (13 mm) can result in undesirable tire noise. Therefore, it is recommended to avoid using larger sized aggregates in order to prevent objectionable tire noise.
B. Shape
The preferred shape for aggregate is cubic. Any flat or elongated shapes are not desirable. Flat aggregates have a tendency to align themselves on their flat sides, which can result in them being completely covered with bituminous material. This is not ideal. Similarly, rounded aggregates have a tendency to roll and are not good at staying in place, which makes them poor at retaining the bituminous material. Therefore, they are also considered undesirable. The best shape for aggregate is cubic as it ensures good coverage and retention of bituminous material.
C. Cleanliness
Maintaining cleanliness of the aggregate is crucial for ensuring optimal performance. Coarse aggregates that are coated with fine material or contain dust will hinder proper adhesion of bitumen to the aggregate. This can lead to poor performance and loss of cover aggregate. To prevent this, it is advisable to limit the amount of aggregate passing through the No. 200 mesh screen to no more than 1% of the total weight. By adhering to this recommendation, the quality of the asphalt mix can be improved, leading to better performance and durability.
2. Bitumen
The bitumen used in the surface treatment is classified into three types.
A. Asphalt Cement
The requirement for asphalt cement is that it must be homogeneous and free from water. Additionally, when heated to 347°F (175°C), it should not foam. In order to meet the necessary standards, the asphalt cement must conform to the requirements outlined in the table below.
B. Cutback Asphalt
The requirement for cutback asphalt is that it must not foam when it is heated to the temperature required for application. Additionally, it should meet the standards outlined in the table.
C. Emulsified
The given context can be rewritten into paragraphs as follows:
Paragraph 1: Homogeneity and Separation in Emulsified Asphalt The emulsified asphalt is expected to be homogeneous after being mixed thoroughly. However, if freezing has caused any separation, the emulsified asphalt shall not be tested. The reason for this is that emulsified asphalt separated by freezing may not meet the required standards. Therefore, it is essential to ensure that the emulsified asphalt remains homogeneous during transportation, storage, and handling.
Paragraph 2: Conformance of Emulsified Asphalt In order to meet the necessary requirements, emulsified asphalt shall conform to the specifications listed in the table below. It is crucial to adhere to these standards to ensure the proper performance of the asphalt. Any deviation from the prescribed requirements can result in inferior quality of the final product, which can have adverse effects on the roadways or other surfaces where it is applied. Therefore, it is crucial to test the emulsified asphalt for its conformity before using it for any construction or repair work.
Application Process of Bituminous Surface Treatments
The road surface maintenance requires repairing potholes and filling in cracks. Additionally, before applying surface treatment, the road surface should be cleaned using an approved method, such as a rotary broom.
When spraying the bituminous material, the specified rate and temperature should be based on the material’s type and grade. The recommended viscosity range for spraying is 20-120 cSt. To achieve the maximum possible chip wetting depth, the cover aggregate should be immediately spread at a specified rate behind the bituminous material spray application. This is important because asphalt cement and road tar have a quick rise in viscosity with cooling, but it is desired in asphalt emulsions and cutback asphalts to optimize the meniscus effect.
The cover aggregate must be applied to the bituminous material within two minutes of the bituminous application using a calibrated self-propelled mechanical spreader or other aggregate spreading device capable of uniformly distributing the aggregate at the specified rate and width. The surface should be rolled immediately after applying the cover aggregate to seat chips in the bituminous membrane, ideally with a pneumatic-tired roller. It is recommended that the speed of the roller does not exceed 5 mph, and depending on environmental conditions, type, and amount of bituminous material, three passes of a 12 to 15-ton pneumatic-tired roller are normally used.
The aggregate should be rolled out within 5 minutes of the bituminous material being applied, and the remaining three coverages should be completed within 30 minutes. To ensure that the bituminous material has set, traffic speed should be controlled until it has hardened. It is recommended that traffic speed not exceed 20 mph for four hours after placement of the surface treatment.
For multiple surface treatments, steps 3 to 6 should be repeated. The application of subsequent coats should only be carried out after the preceding bituminous surface has set and hardened, which normally takes one day.
Precautions during Construction of Bituminous Surface Treatments
It is important to avoid performing surface treatment operations during cold and wet weather conditions. Additionally, the surface on which the treatment will be applied should be clean and dry before beginning the work.
Before initiating the operation, it is necessary to ensure that the air temperature is at least 50°F (10°C) in the shade and increasing. This will provide optimal conditions for the treatment to be applied effectively.
It is essential to avoid performing the operation when the temperature is 60°F or lower and decreasing. If the temperature drops during the application process, it can affect the quality of the treatment and the durability of the surface.
Moreover, it is crucial to refrain from performing the operation in rainy conditions or when there is a likelihood of rain. Rainwater can damage the treatment and prevent it from adhering to the surface properly. Therefore, it is important to choose a day with favorable weather conditions for surface treatment operations to be carried out successfully.
FAQs
What is a bituminous surface treatment?
Bituminous surface treatment (BST), also known as a chip seal or seal coat, is a common method of road surfacing. This treatment involves the application of a liquid asphalt coating to the pavement, followed by a thin layer of aggregate placed on top. The aggregate layer is typically less than half an inch thick, and is intended to provide additional durability and skid resistance to the road surface.
BSTs are most commonly used on roads with lower traffic volumes, as they are not as durable as other road surfacing methods. However, they are a cost-effective solution for maintaining and improving the surface of roads in areas with light traffic. The use of BSTs can also help to prevent the development of more serious road surface problems, such as potholes and cracks.
Overall, BSTs are a useful tool for maintaining and improving the quality of roads in low-traffic areas. While they may not be suitable for high-traffic roads or highways, they are an effective solution for smaller roads and residential streets. By providing additional durability and skid resistance to road surfaces, BSTs can help to ensure the safety and longevity of these important infrastructure assets.
What are the types of bituminous surface treatments?
Single surface treatment involves applying a layer of bitumen onto a prepared surface in a one-time process. The surface is then rolled with a pneumatic-tired roller immediately after the bitumen application. This process creates a bituminous surface that is suitable for various purposes.
On the other hand, multiple surface treatment involves applying bitumen in multiple layers onto a surface that has been prepared beforehand. The aggregate size used in each application is typically smaller than the previous layer. Each layer is immediately rolled using a pneumatic-tired roller after application. This process helps to create a bituminous surface that is more durable and long-lasting. The multiple layers also improve the surface’s resistance to weathering, wear and tear, and other forms of damage.
What are the precautions to be followed during bituminous surface treatment?
Surface treatment operations require specific weather conditions and surface conditions to ensure proper adhesion and durability. These operations should not be carried out during cold and wet weather periods or when both conditions are present. It is crucial to ensure that the surface is clean and dry before performing any work.
Furthermore, it is essential to consider the air temperature before starting the operation. The air temperature should be at least 50°F (10°C) in the shade and rising to ensure optimal conditions for surface treatment. The operation should not be permitted when the temperature is 60°F or less and falling, as this could negatively impact the effectiveness of the treatment.
Additionally, surface treatment operations should not be carried out in the rain or when rain is expected. These conditions could cause the surface to become wet and prevent proper adhesion, ultimately reducing the effectiveness of the treatment. It is essential to consider all weather conditions and surface conditions before starting any surface treatment operations to ensure optimal results.