Iowa Department of Transportation
Iowa Highway Research Board
Kejin Wangkejinw@iastate.edu email >
PCC Engineer, CP Tech Center
Brent Pharesbphares@iastate.edu email >
Bridge Research Engineer, BEC
About the research
Bridge deck overlays have been adopted as an effective deck service life extension tool by the Iowa Department of Transportation (DOT) since the 1970s. High performance Concrete (HPC-O) and Type O PCC (PCC-O) are the most commonly used materials for rigid overlays. A three-day (72-hour) wet curing procedure is specified in Iowa standard specifications. Due to the high cost of traffic control for heavily traveled urban highways, it is highly desired to reduce the traffic interruption as much as possible by getting the work done at night or on weekends. To meet this need, thin epoxy overlays were tested recently with good success and it has been adopted as a bridge preservation tool for decks that are still in good or fair conditions. However, when an overlay of considerable thickness is needed and when significant patching is required, another overlay system, a high-early-strength latex-modified concrete (LMC-VE) overlay, has been proven as a better choice. LMC-VE has been used successfully when a bridge lane can be closed for 1 to 2 days, such as over a weekend, and in many situations, a lane can be closed only for 8 hours or less, necessitating only a night closure. Researchers have indicated that compared with other early strength overlays, LMC-VE overlay is more durable and less prone to shrinkage-induced problems while having higher resistance to chloride ion penetration. When LMC-VE is placed on hydro-demolition prepared bridge deck surfaces, a service life of the deck can be expected to be over 75 years, and the high initial cost of a LMC-VE can be offset by its extended service life. Thus, use of LMC-VE overlays is an ideal choice for expedited construction. Several states (e.g., Virginia, Ohio, Missouri, Kentucky) have already explored the applications of LMC-VE overlays in their bridge construction projects.
Currently, the Iowa DOT is planning to try a LMC-VE overlay at a district 2 bridge (BRFN-015-4(18) -39-32, Emmet 119, IA 15 over Black Cat Creek, letting on 11/20/18). This will be the first trial placement of LMC-VE overlay in Iowa. Documenting the construction procedure, evaluating the short term and long-term performance, and summarizing the experience and lessons learned from the project is essential for future bridge deck overlay decision making and provides design and construction guidance for future practice.