Dowel bar retrofit

A dowel bar retrofit (DBR) is a method of reinforcing cracks in highway pavement by inserting steel dowel bars in slots cut across the cracks. It is a technique which several U.S. states' departments of transportation have successfully used in repairs to address faulting in older jointed plain concrete pavements. The typical approach is to saw cut and jackhammer out the slots for the dowels. Following dowel placement the slots are then typically backfilled with a non-shrink concrete mixture (grout) and the pavement is diamond-ground to restore smoothness.

As a vehicle travels on jointed concrete roads the weight of the vehicle passes from one concrete panel to the next. As the vehicle traverses the joints its weight is placed on the edge of the panel, where the panel is least able to withstand the deflection force. This can cause cracks as pavement shears off the edge of the panel. On older highways built in the early-to-mid 20th century, dowel bars (steel rods) were placed across the joints to help transfer the load from one panel to the next.

This was discontinued because the dowel bars tended to corrode and required frequent replacement. Stainless steel dowel bars are more resistant to corrosion, but stainless steel is relatively expensive compared to other materials. Instead, for several decades, the cohesion between the panels and the strength of the roadbed was relied upon to collectively distribute the load from one panel to the next, a concept known as aggregate interlock. Over time the joints and roadbed tended to break down under stress, resulting in cracks and displacement of the panels. Most highways in the United States built as part of the Interstate Highway System from the 1950s to the 1980s relied solely upon aggregate interlock and began to show problems in the 1970s and 1980s.

In contemporary highway construction since the mid-1990s, dowel bars are once again placed across joints and at intervals along the pavement. Today, dowel bars are coated with epoxy to prevent the corrosion problems seen in earlier installations.

Many states are retrofitting older highways with epoxy-coated dowel bars. The retrofit begins with cutting of six slots (three in each wheel path) across all transverse joints or cracks. The slots are cut with ganged diamond saws that make six cuts in each wheel path. The concrete between the saw cuts is then removed with lightweight jackhammers (heavy-weight jackhammers tend to damage the concrete around the cuts). The epoxy-coated dowel bars are placed in the slots, then the slots are filled with grout and the joints or cracks are filled with waterproof caulk. The final step is to diamond-grind the joint to remove both excess grout and any displacement of the panels.

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Wikipedia