air voids. This will allow the mix to cool quickly and result in lower overall density results. Once the mat is laid, the first pass of the breakdown roller should be eight to 12 inches away from the mat edge, and then the second pass overhangs the edge of the joint by approximately six inches. For both passes, the drum is in static mode. This overall compaction approach creates a bridge over the compacted first pass and the uncompacted edge, alleviating some of the blowout that would happen if you put the drum on hot material on an unsupported edge. Straight paving is critical, and paving against a 90-degree joint (i.e., vertical longitudinal joint) will always help improve performance. Any outside influence on the paver will create a serpentine effect as it moves along the roadway. This is why we recommend against truck-to-hopper paving, as the movements and banging of that truck can affect the path of the paver. Material transfer vehicles (MTVs) can take those stresses from the paver and allow the paver operator to do their job to a much higher standard. It also allows them to move along at a more consistent pace. Since changing speeds is one of the biggest impacts on density, we must be consistent in every approach. MTVs also allow for material remixing to provide temperature uniformity, which leads to a more effortless flow of material to the end gates and a better final product with higher consistency. Compaction speed and proximity to the screed are among people’s most common errors. The freshly laid asphalt mix cannot be allowed to harden for any significant amount of time before compaction if you want to achieve your desired densities. Do not pave too fast. As safety allows, ensure your roller is as close to the screed as possible. This will reduce mat imperfections and increase density. A common mistake is often made because someone said, “You can’t run on hot material.” This is incorrect, especially if the drum is the same temperature as the material. This is important in all regions and particularly critical in northern climates due to freeze cycles and associated heaving. Final Considerations When following these practices, remember this: every mat and every roadway is different. Always work to the specs and demands of the job. Take localized conditions and requirements into consideration when making your paving plan. It’s also important to know your equipment. The responsiveness of each machine will affect the quality of the work. The best practices detailed here will help you improve the lifecycle and performance of your asphalt, lead to a higher-quality product, and result in easier paving for your crews. Most importantly, they help maximize the investment of our transportation departments and federal highway resources and the critical tax dollars that make the work possible. We recommend learning more about this topic with further resources from the Virginia Asphalt Associations, local equipment providers such as Hills Machinery and its paving division, Hills Paving Equipment Division, and local representatives for manufacturers such as Astec. BACK TO BASICS: JOINT CONSTRUCTION AND COMPACTION VAASPHALT.ORG 23
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