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In asphalt pavement construction and maintenance projects, adequate bonding between constructions lifts and especially between the existing road surface and an asphalt overlay is critical in order for the completed pavement structure to behave as a single unit and provide adequate strength. If adjacent layers do not bond to one another they essentially behave as multiple independent layers – none of which are designed to accommodate the anticipated traffic-imposed bending stresses. Inadequate bonding between layers can result in delamination (de-bonding) followed by longitudinal wheel path cracking, fatigue cracking, potholes, and other distresses such as rutting that greatly reduce pavement life.

A good layer bond between the individual asphalt layers is necessary for a long service life of the asphalt pavement. For many years, bitumen emulsions have been used to bond the layers together in accordance with the requirements and bitumen sprayers are being used for applying prime coat and tack coat for adequate bonding of asphalt layers to adjacent base or asphalt layer. By effectively distributing bitumen emulsions, bitumen sprayers ensure the optimal bonding of pavement layers, resulting in long-lasting and durable road surfaces.

The bitumen sprayer is designed to distribute the bitumen evenly over the surface, ensuring that the asphalt adheres properly and forms a strong, durable surface. Typically, bitumen is heated to temperatures between 150°C (302°F) and 190°C (374°F) before being sprayed onto the road surface. These high temperatures are necessary to liquefy the bitumen and make it easier to apply and spread evenly. The bitumen sprayer consists of a tank that holds the bitumen, a heating system to keep the bitumen at the right temperature, a pump to circulate the bitumen, a spray bar with nozzles to distribute the bitumen, and controls to regulate the flow and pressure of the bitumen.

The bitumen sprayer is typically mounted on a truck or trailer and operated by a trained operator. The operator drives the sprayer along the road while spraying the bitumen onto the surface. The speed at which a bitumen sprayer operates can vary depending on factors such as the type of equipment, road conditions, and project requirements. However, in general, bitumen sprayers typically operate at a speed range of 5 to 15 kilometres per hour. This range allows for effective and controlled application of bitumen (asphalt) on road surfaces, ensuring proper coverage and adherence to the roadbed. The spray bar can be adjusted to vary the width and thickness of the layer of bitumen, depending on the specific requirements of the project.

Bitumen sprayers have dramatically changed the landscape of road construction. These machines allow for efficient, uniform, and high-quality application of bitumen, ensuring longevity and improved performance of roads.

Bitumen sprayers ensure consistent and uniform application of the bitumen across the road surface. This uniform coating enhances the overall quality and appearance of the road, providing a smooth and well-bonded surface. The controlled and precise application of bitumen emulsion by sprayers improves the adhesion between layers of road construction materials. This strong bond enhances the durability and longevity of the road, reducing the risk of premature pavement failures. Bitumen sprayers offer cost-effective solutions for road construction projects. Their precise application reduces material wastage and minimizes the need for additional repairs or maintenance. Moreover, the uniform distribution of bitumen emulsions ensures optimal utilization, saving both time and resources. By ensuring proper coating uniformity and enhanced adhesion, bitumen sprayers contribute to the durability and performance of road surfaces. The resulting roads exhibit improved resistance to cracking, rutting, and moisture damage, extending their service life. Bitumen sprayers also promotes environmental sustainability in road construction. The controlled spraying process reduces overspray and minimizes the release of harmful emissions.

Several equipment-related adjustments and settings are critical to achieving uniform prime coat / tack coat placement. Essentially the nozzle size and patterns, spray bar height and distribution pressure must work together to produce uniform coat application.

It is important to use the right size nozzles for the job depending on the desired application rate and the type of coat material. These nozzles should be spaced at proper equal distance from each other on spray bar for uniform spraying. In addition, all the nozzles should be working properly and are not blocked partially or fully. Further, for uniform spraying these nozzles are to be set at the correct angle (approx. between 15 to 30 degrees) to the axis of the spray bar.

Generally, the best applications results from a “double lap” or “triple lap” coverage. “Double/triple lap” means that the nozzle spray patterns overlap one another such that every portion of the pavement receives spray from exactly two/three nozzles. Nozzle spray patterns should be identical to one another along a sprayer spray bar. Differing coverages will result in streaks and gaps in the tack coat.

Spray bar height should remain constant while spraying application. Too low spray bars result in streaks, while too high spray bars cause excessive nozzle overlap resulting in an excessive application rate. Pressure within the spray bar must be capable of forcing the coat material out the spray nozzles at a constant rate. Inconsistent pressure will result in non-uniform application rates. It is very important to have the coat material at the proper application temperature in order to obtain a uniform spray on the pavement surface.

The forward travel speed of the bitumen sprayer must be controlled to assure that the application rate is correct.  If the sprayer travels too fast, the amount of coat applied to the pavement surface will be reduced. The opposite effect occurs if the sprayer travels too slowly for a given spray bar nozzle size and pump pressure. For example, in case of tack coat application, too little tack coat can result in inadequate bonding between layers. Too much tack coat can create a lubricated slippage plane between layers, or can cause the tack coat material to be drawn into an overlay, negatively affecting mix properties and even creating a potential for bleeding in thin overlays.