Cast-in-place Concrete Slab

Cast-in-place Concrete Slab type bridges have no beams under the decks, but instead utilize reinforcing steel embedded in the bottom of relatively thick concrete slabs to carry the loads. These types of bridges have been common in Ohio since the 1920s. Many of the early bridges were single spans, but since the 1950s many have been multiple spans, continuous over the piers. 

Slab type bridge

Concrete Slab Bridge, showing edge deterioration due to water flow from the top surface of the deck.

Use of "drip strip" along upper edge of deck, to minimize water flow to the underside.

Extensive water-related deterioration on underside of concrete slab bridge.

Concrete slab bridges have been relatively maintenance-free over the years, but it is important to keep chlorides and moisture from reaching the primary reinforcing steel. On simple span bridges, the primary reinforcing steel is located in the bottom of the slab, but in continuous slabs, it is important to realize that primary reinforcing is also located in the top of the slab in the area over the piers. Preventive maintenance is the same for concrete slabs as previously noted for concrete bridge decks on steel/concrete beams.  For concrete slabs with over-the-side drainage, it is also important to protect the sides and undersides, as previously discussed.

Preventive Maintenance Recommendations:

• Sweep and water flush the deck surface and gutters once per year, after last roadway application of winter deicing salts.
 
• Seal deck surface with silane/siloxane every 5 years.
 
• Seal cracks in deck surface with high molecular weight methacrylate (HMWM).
 
• On slabs with over-the-side drainage, seal the deck sides and adjacent 18-inches of undersides with epoxy/urethane.