The two-lane bridge that carries Connecticut Route 32 over the Willimantic River in the town of Windham was built in 1868 – so old it’s eligible for federal funding under the National Historic Preservation Act.
Not surprisingly, the bridge has evolved since its construction. A steel superstructure was added to the stone arch substructure. Instead of stone, the deck is reinforced concrete that’s regularly overlaid with asphalt as the wearing surface. Average daily traffic (ADT) was 14,300 in 2016 but is projected to reach 21,300 in 2036.
The deck expands and contracts with New England’s seasonal temperature fluctuations. The Connecticut Department of Transportation (CTDOT) salts the driving surface to keep it from freezing over in winter. Both activities threaten the integrity of the reinforcing steel in the concrete by opening the door to corrosion. So, before the state mills up and replaces the asphalt overlay, damage to the concrete deck is patched.
To minimize inconvenience to the driving public and avoid the expense of rerouting traffic, CTDOT requires repair material to reach 2000 psi compressive strength in 2 hours. For decades, the state has patched concrete roads and bridge decks with a product that surpasses that requirement: concrete made with Rapid Set® DOT Cement.
A blend of ASTM C1600 calcium sulfoaluminate (CSA) Rapid Set® Cement and plasticizer, DOT Cement reaches 3140 psi (21.6 MPa) at 1.5 hours. It’s air-entrained for long life in freeze-thaw regions like New England. Locally sourced coarse aggregate, sand, and water are added to the cement powder at the jobsite in a portable mechanical mixer or, for greater efficiency in larger jobs like the Windham Route 32 bridge, a computer-controlled volumetric mixer that produces up to 80 yards of material at a time.
That’s exactly what contractor McNamee Construction did for the Windham Route 32 bridge. These photos show a fairly typical partial-depth patching process using DOT Cement.
