28 SPRING/SUMMER 2023 BACK TO BASICS Longitudinal Joint Construction & Compaction Tim Kowalski, Application Support Manager, Wirtgen Group When I travel around the country, driving on all kinds of highways, I can always tell the side of the road that was paved last by the side of the joint that fails first. Because this has become such a problem around the country, many states have introduced a longitudinal density specification to try and produce better joints that last as long as the actual pavement. This means we will have to pay attention to this challenging area of our industry. So, how do we build a better joint? Based on what I have seen over my 33 years of travels across North America, these are the procedures that I can share. Do not pinch the joint immediately after the mix has been placed (unless you are paving in the echelon). Instead, start on the low side or outer area of the mat being placed. Because most roads have at least a 2% slope, it is better to compact against gravity and push the mix toward the joint and not away from it. I like this practice for a few reasons. It allows compaction of the outside edge so that, when compacting the joint, there is resistance to the upper portion of the mat. This allows the operator to push the material to the joint and not away from it. It also gives the cold joint time to warm up with the mix being placed. When compacting the joint, there will be a better bond and a tighter joint, reducing moisture penetration and deterioration. Here are steps to follow for longitudinal joint compaction using this method. After compacting the outside portion and moving to the upper portion of the mat, make your pass towards the paver using vibration on both drums or with vibration and oscillation, but stay four to six inches off of the cold joint (See Figure 1). This leaves a small area of mix that is not compacted but will be forced into the area between the cold joint and the compacted hot mat. When returning on your next pass, cover the four to six inch area with both drums but running static only (See Figure 2). All the force and energy from the vibration is concentrated onto the cold side of the joint, which will begin to crush the rock and cause it to fail first. Now, some will say that there is too much material at the joint when compacted in this manner. This is something that can be adjusted at the paver with the joint matcher—something that needs to be worked through with the screed operator. Another way to ensure better compaction at the joint is using oscillation. Compact the same way as you would with double vibration, staying four to six inches off the joint going towards the paver. When returning over that area, shut the vibration drum off and run in static but keep the oscillation drum on. Oscillation will compact the joint better than static and will not destroy the cold joint like you would if you were running vibration. This will give you a much tighter sealing joint to reduce moisture penetration. One option unfamiliar to most operators is the offset of the drums. Some manufacturers offer this feature for several advantages, including joint compaction. Most offsets are approximately six to seven inches. So, when compacting the joint, put the front vibratory drum 100% on the hot mat while staying four to six inches off the joint and run vibration. The rear drum covers the uncomplicated area between the cold joint and what the front drum just compacted. Run the rear drum in static or—my personal preference—oscillation mode, so the joint is compacted in one pass. You can do the same thing when returning over the joint. This is how to build better joints on all pavements and all materials. For those using pneumatic rollers as an intermediate in your roller train, do not be afraid to run over the joint with the rubber Figure 1. 1st Pass Off the Joint HOT ROLLER DRUM 4–6” Creates a Confined Edge and Raised Area COLD
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