Asphalt Plug Joint Installation Best Practices

Asphalt plug joints are the simplest and most economical type of bridge expansion joint, suitable for movements up to 25 mm. Correct installation is critical for achieving the expected service life of 10-15 years. Surface preparation is the most important step in asphalt plug joint installation. The existing concrete or asphalt must be removed to the full depth of the joint, typically 50-75 mm. The substrate must be clean, dry, and free of loose material. Any cracks or voids in the substrate must be repaired before the joint is installed. Backer rod installation provides a backing for the asphalt plug and controls the depth of the joint material. The backer rod is a closed-cell polyethylene foam rod that is compressed into the joint gap. The diameter of the backer rod should be 25% larger than the joint gap width to ensure a tight fit. Primer application to the joint substrate improves the adhesion of the asphalt plug material. The primer is applied to the clean, dry substrate and allowed to cure for the specified time before the asphalt plug material is placed. Insufficient primer or insufficient curing time reduces the adhesion and can cause premature failure. Asphalt plug material placement requires the material to be heated to the correct temperature before placement. The material is poured into the joint and compacted to the level of the adjacent road surface. Overfilling must be avoided because the excess material will be displaced by traffic, creating a bump at the joint. Curing time must be allowed before the joint is opened to traffic. The material must cool to below 60 degrees C before traffic is allowed on the joint. Opening the joint to traffic before the material has cooled sufficiently can cause permanent deformation of the joint surface.