A bridge deck overlay involves the surface application of a thin layer of material in order to prevent deterioration due to water penetration and/or deicing salts. There are numerous commercial products available which may be used to create impermeable layers and add texture to the rolling surface. A typical overlay does not improve the performance capacity of an existing deck, whereas the Ductal® structural overlay provides long-term durability, improved deck protection and increased deck strength. It can also be used to rehabilitate a deck instead of a full deck replacement.
LafargeHolcim's Research Center in France developed the new Ductal® UHPC thixotropic structural overlay solution (a thixotropic material remains fluid when agitated but stays in place when left alone). It has been successfully applied on various projects in Europe, with the largest to date being the famous Chillon Viaducts in Switzerland - a 2.2 km (1.3 mile) long, 4-lane structure.
The new overlay formulation is very different than our Ductal® Joint Fill solution, which is used to connect joints between precast bridge elements. The Joint Fill material must be flowable and self-leveling in order to fill all voids. Most bridges are built with a sloped surface, and a self-leveling product can easily slide out of place. With this in mind, our thixotropic formulation was developed to permit placement on bridge decks with up to 10% slope.
Last month, a 38 mm (1.5 in.) thick Ductal® structural overlay was applied on a 30 m (100 ft) long bridge in Brandon, Buchanan County, Iowa. For this pilot project, we enlisted two Ductal® colleagues from France, who provided valuable on-site expertise and guidance for batching. Collaborators included the Iowa Department of Transportation (Iowa DOT), the Federal Highway Administration (FHWA), Buchanan County, Iowa State University (ISU) and local contractors.
When installing a Ductal® structural overlay, the first step is to grind the existing surface to remove damaged areas and provide a textured, rough surface for bounding. The surface must remain saturated dry.