William R. Cox, Texas Department of Transportation
Bridge deck cracking provides access for oxygen, moisture, and chlorides to reach and corrode steel reinforcement. The resulting corrosion can cause deck deterioration, increased maintenance, and shorter service life. Repairing cracks in new and existing bridge decks is a means to achieve the planned service life of a bridge deck that has suffered significant cracking.
In Texas, the decision to repair bridge deck cracking is based on the severity of the environment, crack width, and extent of cracking. Moisture in the form of rainfall increases from the western portion of the state, where El Paso experiences an average annual rainfall of about 8 in. (200 mm), to southeastern Texas, where Beaumont receives about 57 in. (1.45 m). Winter applications of deicing chemicals are common in the northern regions of the state while structures along the Gulf Coast experience a marine environment. In these regions, the Texas Department of Transportation (TxDOT) responds to inquiries about the acceptability of deck cracks by recommending that cracks greater than 0.005 in. (0.13 mm) in width be sealed. In other areas of the state, TxDOT recommends crack sealing when crack widths exceed 0.01 in. (0.25 mm). However, in areas of the state that receive little rainfall and chloride exposure is of little concern, TxDOT recommends crack sealing only when crack widths exceed 0.02 in. (0.50 mm).
TxDOT has used the following methods and materials to seal new and existing deck cracks:
• Small, localized areas of cracking are easily repaired by cleaning the cracks with pressurized air free of oil and moisture, followed by hand dispensing of super-low-viscosity epoxy into visible cracks. Plastic condiment bottles, similar to the red ketchup containers found at fast-food restaurants, can be used to dispense and control the amount of epoxy applied.
• For larger areas of cracking, a flood coat of super-low-viscosity epoxy or high-molecular-weight methacrylate monomer effectively seals cracks too numerous to spot treat. Before flood coating, the bridge deck is prepared by abrasive blasting followed by a pressurized air blast to remove laitance and other contaminants. After the epoxy or monomer is applied, the excess is removed by brooming, and fine aggregate is broadcast onto the treated area for skid resistance.
• When an entire deck has extensive cracking, application of a multi-layer thin polymer overlay is considered. The first step prepares the deck surface by shot or abrasive blasting followed by a pressurized air blast to remove laitance and other contaminants that could compromise the bond of the overlay. Two separate polymer/aggregate layers are then placed for a minimum total thickness of 0.25 in. (6.4 mm).
Using these methods and materials limits the direct access of oxygen, moisture, and chlorides to the steel reinforcement and increases the probability that the bridge deck will achieve its expected service life.
Editor’s Note
This article describes Texas’s approach to repair of cracks in bridge decks. Other owners have different criteria. The Editor of HPC Bridge Views would like to hear about other practices.