What is Asphalt Overlay?

Asphalt overlay is a mixture of aggregates, sand, asphalt, and additives that serves as the final layer applied to the surface of roads and streets using asphalt paving machines. This overlay has a sticky nature and is used to enhance asphalt, strengthening and protecting road surfaces against factors such as wear, cracking, and separation, as well as to prevent water accumulation and infiltration into the underlying layers of asphalt. Overall, asphalt overlays improve the driving conditions on roads and streets. With this common method, asphalt surfaces that have cracks and potholes can be effectively repaired with high quality.

Why is Waterproofing Asphalt Important?

Waterproofing or rehabilitating asphalt is one of the crucial goals in civil engineering, significantly aiding in maintaining performance and extending the lifespan of asphalt overlays on roads and streets. Its importance becomes clear when it prevents the destructive and negative effects of water on the surface of the asphalt overlay and its infiltration into the structure.

The main objectives of asphalt waterproofing include preventing water infiltration, reducing material resistance, structural failures, and cracks; protecting and preventing damage to the asphalt overlay from wear, rainfall, and vehicle traffic; increasing the lifespan of asphalt structures; enhancing driver safety; improving road security and preventing traffic accidents. Interestingly, Germany and the UK were the first countries to produce geosynthetics, while France was the first country to use geosynthetic products to strengthen asphalt overlays in the late 1960s.

Benefits of Using Geogrid in Asphalt Rehabilitation

One of the geosynthetic products extensively used for asphalt rehabilitation and strengthening its surface is geogrid. This product is made from polyester and polyethylene; sometimes, a combination of these materials with similar substances like polyvinyl chloride and polypropylene is used to produce geogrids.

Key features of this product include tensile strength, resistance to ultraviolet rays, chemical resistance, etc. Based on the production process, geogrids are categorized into three groups: extruded, knitted, and bonded, and from a tensile construction perspective, they are divided into uniaxial, biaxial, and triaxial geogrids. Triaxial geogrids are used to enhance the load-bearing capacity of asphalt pavements. The most significant benefits of using geogrids in asphalt rehabilitation include:

Increased stability of the road structure

Reduced risk of cracking and road fractures

Lower maintenance and repair costs

Enhanced road resistance to erosion and damage

Improved lifespan of the road and strengthened structure

Road stability under adverse conditions and increased driving safety

Reduced environmental impacts and increased recycling of materials used in the road structure

Decreased energy consumption

Reduced environmental pollution

Lower need for road repairs and reconstruction

Quick and easy implementation

No need for specialized labor for installation

Prevention of moisture and water infiltration beneath the asphalt pavement

How to Implement Asphalt Geogrid

The implementation of asphalt rehabilitation using geogrids involves several steps:

Surface Preparation: The asphalt pavement surface is prepared, and if necessary, the road surface geometry is corrected.

Crack Sealing: Cracks wider than 4 mm on the asphalt are sealed using suitable bituminous materials.

Cleaning the Surface: After sealing, the asphalt surface is cleared of any soil materials. To enhance the strength of the rehabilitation, a suitable layer of asphalt is applied, selected based on the underlying layer or the condition of the asphalt surface and the local climate.

Geogrid Deployment: The asphalt geogrid is extracted from its plastic cover, which protects it from external factors during transport. Geogrid installation can be done manually or mechanically. For large areas, the geogrid is installed using a roller attached to road construction machinery.

Final Layer Application: Finally, the top layer is applied.

Advantages of Asphalt Geocomposite in Strengthening Asphalt Overlay

Asphalt geocomposite is another type of geosynthetic product used in the rehabilitation of asphalt roads and streets. This product consists of a nonwoven geotextile layer made from polypropylene combined with geonets and geomembranes, reinforced with fiberglass. It is composed of various layers.

Important features of asphalt geocomposite include very high tensile strength, resistance to ultraviolet rays, a high melting point and thermal resistance, lightweight, chemical resistance, environmental compatibility, wear resistance, durability, effective drainage, and high cost. The advantages of asphalt geocomposite in strengthening and rehabilitating asphalt overlays include:

Delaying the growth of reflective cracks in the new asphalt overlay

Creating adhesion between the old and new asphalt layers

No need for specialized labor for installation

Quick and easy installation of asphalt geocomposite

Significant reduction in long-term maintenance costs for asphalt overlays

Usable over excavation strips

Increased strength and resistance of the asphalt overlay against heavy loads and vehicle traffic

Prevention of water and moisture infiltration into the underlying asphalt layers

Prevention of undesirable deformation and increased cracking of asphalt

Increased lifespan of asphalt road structures

Reduction in construction costs due to lower needs for heavy materials

High flexibility and adaptability to structural changes

How to Implement Asphalt Geocomposite

The implementation of asphalt geocomposite to strengthen asphalt overlays involves four stages:

Initial Preparation: The asphalt surface is thoroughly cleaned, and damaged layers are removed and cleaned.

Strengthening: A primer geotextile is applied to enhance strength and durability and to strengthen the bond on the asphalt overlay.

Geocomposite Installation: The asphalt geocomposite is installed on the overlay and the primer geotextile.

Compaction and Stabilization: Using road construction machinery and rollers, the asphalt geocomposite is compacted to the overlay surface and stabilized in place.

Benefits of Using Geotextile in Asphalt Rehabilitation

Geotextile is another type of geosynthetic product widely used in asphalt rehabilitation. This product is produced as a flat fabric using polymer materials like polyester and polypropylene. Placing a geotextile layer between the old asphalt overlay and the new one can prevent issues such as potholes and cracks. The main benefits of using geotextile in strengthening asphalt overlays include:

Waterproofing the subgrade and asphalt surface by creating a hydraulic barrier

Increasing the time for reflective cracks to develop in the old asphalt overlay

Enhancing tensile capacity and preventing surface settlement of the asphalt

Reducing the thickness of the asphalt layer by placing a geotextile layer between the new and old pavements

Impact absorption and stress modulation between the asphalt overlay layers

Increasing durability and reducing maintenance costs

Eliminating the milling phase and replacing asphalt

Factors Affecting Asphalt Rehabilitation Costs

Various factors influence the costs of asphalt rehabilitation. The most significant factors include:

Calculation of the area of the road or street based on square meters or linear meters

Type of asphalt and geosynthetic product as the polymer base

Thickness of the asphalt overlay layer

Number of laborers

Number of equipment required for rehabilitation and strengthening

Condition of the asphalt infrastructure

Accessibility of the road or street location

Proximity for transporting or moving materials needed for asphalt overlay rehabilitation

Public or private employer and contract conditions

Weather conditions and their impact on the work pace

Conclusion

In this article, we discussed asphalt overlays, the importance of waterproofing asphalt, and the benefits of using geosynthetic products such as geogrid, geocomposite, and geotextile in asphalt rehabilitation. We explained how these products can prevent cracks and potholes in asphalt surfaces on roads and streets, significantly extending the lifespan of asphalt. Finally, we introduced the factors affecting the costs of asphalt overlay rehabilitation. We hope you find the information provided in this article useful.

Asphalt Rehabilitation: The Benefits of Using Geosynthetics and Strengthening Asphalt Surfaces

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