One way to significantly prolong the useful life of a concrete bridge deck is to install an overlay. This application seals the surface from aggressive chemicals and reduces the impact of aging and weathering. West Fargo, N.D.-based contractor Industrial Builders not only lays claim to one of the first bridge deck overlays in North Dakota, but the contractor has also perfected a unique method to overlay deck surfaces during cold weather months.
In October 2013 the contractor faced the daunting task of applying an epoxy overlay to about 1900 square feet of bridge deck surface in 35° F temperatures. For best overlay performance, however, the epoxy’s components needed to be heated to at least 70° F for 24 hours before use, and the minimum ambient, surface, aggregate, and epoxy temperatures during application needed to be at least 50° F and rising.
Industrial Builders could not afford to wait for warmer temperatures because of the project’s short time frame — the epoxy overlay was a late addition to the overall project, and the scheduled completion date was Nov. 15. But after covering the bridge deck with a tent and then using propane heaters to heat the area, crew members found that their efforts were not enough to raise the deck temperature fast enough.
Thinking outside the tent
The contractor decided to place curing blankets over the hoses of a Thawzall heater, a Model 5A, one of the four that Industrial Builders owns, to heat both the bridge deck and the epoxy in the drums to 70° F. The heater circulates heated fluid through hoses attached to the unit’s heat distribution system, allowing users to uniformly distribute heat and then control temperatures across a covered area.
The tented heating began the day before the epoxy application. When crew members covered the hoses with curing blankets, they were also able to retain the majority of heat generated from the hoses, allowing the deck surface temperature to rise and be maintained to required surface temperatures. When the heater was removed, after having heated for 20 hours, the bridge deck temperature was 56° F.
Making the bridge deck 20 degrees warmer allowed the crew to begin applying the epoxy overlay to the deck surface.
The contractor used Transpo 526, a two-component epoxy polymer that’s ideal for extreme weather conditions such as those encountered in North Dakota. The waterproofing and anti-skid overlay is equipped with deicing capability to reduce or prevent frost and ice formation on bridge and parking decks. And, equally important for the limited time frame of this project, it cures quickly in lower temperatures.
The crew had to apply the epoxy and specified aggregate in two layers. The first layer acts like a penetrating sealer that also bonds the broadcast aggregate to the substrate and fills fissures and voids in the substrate. This creates outgassing, or releasing of air from the concrete, which leaves tiny pinholes. The second layer is necessary to seal any remaining pinholes or voids, and to encapsulate the first layer of aggregate and securely bond the second layer.
After crew members completed the first course, they covered the deck with plywood and curing blankets to keep the aggregate warm. When they began the second course, four hours after starting the first course, the rock temperature reading averaged about 54° F.
Once the application of the epoxy started, it took less than 12 hours to complete.