The Iowa Method for bridge deck overlays has been very successful in Iowa since its adoption in the 1970s. This method involves removal of deteriorated portions of a bridge deck followed by placement of a layer of dense (Type O) Portland Cement Concrete (PCC). The challenge encountered with this type of bridge deck overlay is that the PCC must be mixed on-site, brought to the placement area and placed with specialized equipment. This adds considerably to the cost and limits contractor selection. A previous study (TR-427) showed that a dense PCC with high-range water reducers could successfully be used for bridge deck overlays using conventional equipment and methods. This current study evaluated the use of high performance PCC in place of a dense PCC for work on county bridges. High performance PCC uses fly ash and slag to replace some of the cement in the mix. This results in a workable PCC mix that cures to form a very low permeability overlay.

TRB's National Cooperative Highway Research Program (NCHRP) Synthesis 423: Long-Term Performance of Polymer Concrete for Bridge Decks addresses a number of topics related to thin polymer overlays (TPOs). Those topics include previous research, specifications, and procedures on TPOs; performance of TPOs based on field applications; the primary factors that influence TPO performance; current construction guidelines for TPOs related to surface preparation, mixing and placement, consolidation, finishing, and curing; repair procedures; factors that influence the performance of overlays, including life-cycle cost, benefits and costs, bridge deck condition, service life extension, and performance; and successes and failures of TPOs, including reasons for both.

The Iowa Method for bridge deck overlays has been very successful in Iowa since its adoption in the 1970's. This method involves removal of deteriorated portions of a bridge deck followed by placement of a layer of dense (Type O) Portland Cement Concrete (PCC). The challenge encountered with this type of bridge deck overlay is that the PCC must be mixed on-site, brought to the placement area and placed with specialized equipment. This adds considerably to the cost and limits contractor selection, because not all contractors have the capacity or equipment required. If it is possible for a ready-mix supplier to manufacture and deliver a dense PCC to the grade, then any competent bridge deck contractor would be able to complete the job. However, Type O concrete mixes are very stiff and generally cannot be transported and placed with ready-mix type trucks. This is where a "super-plasticizer" comes in to use. Addition of this admixture provides a substantial increase in the workability of the concrete - to the extent that it can be delivered to the site and placed on the deck directly out of a ready-mix truck. The objective of this research was to determine the feasibility of placing a deck overlay of this type on county bridges within the limits of county budgets and workforce/contractor availability.

At head of title: National Cooperative Highway Research Program.

Chloride-ions penetrating into bridge decks and corroding the steel have been a major problem. As the steel corrodes it exerts stresses on the surrounding concrete. When the stresses exceed the strength of the concrete, cracks or delaminations occur. This, of course, causes deterioration and spalling of bridge deck surfaces. Both the Latex and Iowa Method were used to repair bridge decks for this project. The concrete was removed down to the steel and replaced with approximately 1 1/2 inches of low slump or latex modified concrete. The removal of unsound concrete below the top layer of steel was sometimes necessary. The objective of this project was to determine if the bridge overlays would provide a cost effective method of rehabilitation. To do this, unsound and delaminated concrete was removed and replaced by an overlay of low slump or latex modified concrete.

"The main objective of this research is to develop a cost-effective ultra-high performance concrete (UHPC) for bonded bridge deck overlays. The high durability and mechanical properties of such repair material can offer shorter traffic closures and prolong the service life of the pavement. The UHPC was optimized using supplementary cementitious materials (SCMs), proper combinations of sands, and adequate selection of fiber types and contents. Packing density studies included paste, sand, and fiber combinations. The robustness of optimized UHPC mixtures to variations of mixing and curing temperatures was examined. The efficiency of various shrinkage mitigation approaches in reducing autogenous and drying shrinkage of optimized UHPC mixtures was evaluated. This included the use of CaO-based and MgO-based expansive agents, shrinkage-reducing admixture, and pre-saturated lightweight sand. Optimized UHPC mixtures were cast as thin bonded overlays of 25, 38, and 50 mm in thickness over pavement sections measuring 1 × 2.5 m2. Early-age and long-term deformation caused by concrete, humidity and temperature gradients, as well as cracking and delamination were monitored over time. Test results indicate that the designed UHPC mixtures exhibited relatively low autogenous shrinkage and drying shrinkage. The G50 mixture had the lowest autogenous and drying shrinkage of 255 [mu]m/m at 28 days and 55 [mu]m/m at 98 days, respectively. All tested UHPC mixtures exhibited a high mechanical properties and excellent frost durability. The use of 60% lightweight sand led to significantly reduction in autogenous shrinkage from 530 to 35 [mu]m/m. Test results indicate that there was no surface cracking or delamination in UHPC overlays after 100 days of casting"--Abstract, page iii.

Bridges in Kansas are exposed to winter conditions, including deicing chemicals used to keep the roads and bridges clear of ice and snow. These chemicals and water are harmful to the concrete and the steel reinforcing bars used in bridge structures. The objective of this study was to develop a durable thin bonded overlay with chloride resistance to protect the reinforcing steel of the bridge deck. Overlays were developed and monitored after their initial placement on four bridges. The overlay materials selected by the Kansas Department of Transportation (KDOT) had promising results from laboratory testing. Four different overlay materials were selected based upon KDOT's laboratory results and were tested on four separate bridge decks. Three of the bridges are located in Greenwood County and one in Sedgwick County. All four bridges were new construction; the three in Greenwood County are pre-stressed concrete girder design and the Sedgwick County Bridge is a steel girder design. The data from the testing and monitoring were used to determine if there are benefits to using thin bonded overlays for bridge deck wearing surfaces and which types of thin bonded overlays have the largest benefits. The materials chosen for the overlays were: Type IP cement concrete, Type IP cement with 3% silica fume concrete, Type I / II cement with 5% silica fume and polypropylene fibers concrete, and Type II cement with 5% silica fume and steel fibers concrete. Construction samples and bridge deck cores were tested for compressive strength, permeability, chloride concentration, overlay adhesion, and cracking resistance. The permeability tests showed the overlays containing the Type IP cement were the least permeable while the steel and polypropylene fiber overlays were the most permeable. The Type IP cement overlays meet the design specification of passing less than 1,000 coulombs (1.5 inch thickness); however, the overlays with the fibers do not. The ability of each overlay to resist chloride ion migration will only truly be known as 'in service' time accrues. Based upon the chloride ion contamination after five years, all overlays would appear to be functioning equally unless there is cracking in the overlay.

Fifty randomly selected concrete bridge decks in New York State, overlaid with low-slump concrete, were studied in 1985 after an average of 5 years of service. The investigation included recording surface defects, measuring delamination and half-cell potentials, and sampling and testing for deck chloride profile. Conclusions are drawn with regard to the nature and significance of the observed damage, and estimates are made of service life expectancy. Policy implications for the New York State Department of Transportation are discussed.