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Longitudinal joints are joints formed during hot mix asphalt (HMA) pavement construction. These joints are formed when a new lane of hot mix asphalt pavement is placed adjacent to a previously placed lane.
An improperly constructed longitudinal joint forms the weakest link threatening the whole pavement system.
This article discusses the various techniques used to construct longitudinal joints for asphalt pavements.
Construction of Longitudinal Joints in Asphalt Pavement
1. No Treatment Method
In this method, the hot mix is placed in a lift with vertical edges on both sides. When the lift is rolled, the unconfined edge of the initial lane is sloughed off to form a natural angle of repose. Here, no raking or luting is performed to keep the slope.
The raking is performed once the fresh lane is placed, followed by rolling and compaction.
2. Bumping Unconfined Edges
This method is similar to no treatment method, except luting or raking is performed to get an unconfined edge before the movement of the paver. Then, the mat is rolled after paving the second lane, as shown in Figure-3.
3. Tapered or Notched Edge Method
In this method, a paver attachment is used to build a stable edge slope on the unconfined edge of the mat. Slopes of 1:6 and 1:3 vertical to horizontal, are commonly used. This is later followed by the final compaction.
4. Cutting Back the Joint
In this method, the longitudinal edge of the previously placed lane is cut back using a saw to remove the difference in densities between the lanes. The previously placed mix is cut back for a distance of 1 to 2 inches.
The newly exposed vertical face of the old lane is provided with a tack coat, and then the second lane is paved.
5. Overlapping the Joint Method
Overlapping method is generally used when the “cutting back the joint” method cannot be employed. In this method, the new mat is laid to overlap the previously placed mat. For this, the end gate of the paver must have an extension above the adjacent mix of not more than 1 to 1 ½ inches.
Sufficient overlapping material is necessary to conduct proper compaction. The height of the new mix over the compacted mix should be ¼ inches for each 1 inch of the compacted mix.
6. Joint Re-heaters Method
In this method, the cold side of the joint is pre-heated using a propane-fired or infrared heater. This method improves the adhesion at the joint and allows more contact with the new material, thus improving the tensile strength at the joint.
The efficiency of longitudinal joints is dependent on how efficiently and straightly the first lane is constructed. If the first lane is right, the joint is efficiently matched with the adjacent lane.
The proper compaction of the unconfined edge of the first lane also determines the durability of longitudinal joints.
Longitudinal joints are joints formed during the construction of hot mix asphalt (HMA) pavement. These joints are formed when a new lane of hot mix asphalt pavement is placed adjacent to a previously placed lane.
The overlapping method is generally used when the “cutting back the joint” method cannot be employed. In this method, the new mat is laid to overlap the previously placed mat. For this, the end gate of the paver must have an extension above the adjacent mix of not more than 1 to 1 ½ inches.