INSIDE THE DOT
South Dakota Department of Transportation
Evaluation of In-Service Bridge Decks, Second-Time Deck Overlay Failures and Deck Condition Survey Procedures
Christina Bennett, Office of Research
1/1/1900 - 1/1/1900
Recently, several second-time overlays on Interstate 90 in the Pierre Area developed extensive delamination and longitudinal cracking within two years of placement. In addition, a structure on SD 49 slated for bridge deck overlay replacement was found to have substrate concrete of extremely poor quality. These incidents highlighted a need to re-evaluate current procedures with regard to our bridge deck overlay program. SDDOT has been overlaying bridge decks with latex-modified and low slump overlays for more than two decades with excellent results. Many of the earlier overlays have reached the end of their service lives and are being replaced with new low slump overlays. Since there are a significant number of bridges in the program for second-time overlays, the possibility of shortened overlay life needs to be minimized.Petrographic analysis of the overlay and substrate concrete from these bridges indicated that the delamination plane occurred in the original substrate concrete just below the grout bond layer. Factors identified which may have contributed to the premature failures were Alkali-Silica Reaction (ASR) in both the overlay and substrate, freeze-thaw damage in the substrate concrete and differential thermal stresses between the overlay and substrate. Bond was not identified as a problem. In addition, second-time overlays require nominal removal of the original overlay and the deck is subjected to a far more aggressive removal process than the minimal scarification used on a first-time overlay, which may contribute to substrate concrete damage. Other factors may include poor surface preparation and high-speed traffic during the initial curing of the overlay. An attempt to eliminate all first-time overlay concrete on some subsequent overlays nearby resulted in a significant increase in cost due to steel above the substrate/overlay interface and the need for multiple shallow passes by the scarification machine. Because of the increase in cost, a determination needs to be made whether all of the old overlay concrete needs to be removed and if a chain drag alone is effective in detecting poor concrete. In addition, existing overlays may be in-service too long which results in extensive damage to substrate concrete and increases the likelihood of premature failure of second-time overlays. Research is needed to determine the failure mechanisms involved in poorly performing second-time overlays, the distribution of these failures statewide, testing procedures which can detect areas of potential failure and bond strength or substrate concrete condition requirements necessary to insure good performance. In addition, bridge deck survey procedures capable of detecting problem areas with second-time overlays and unsound concrete for any overlay are needed. The results from this research should provide a means for identifying deteriorated concrete, removing it in a cost effective manner and optimizing the evaluation process for deciding when and whether to overlay a given bridge or to replace the entire bridge deck.
1 To determine the failure mechanisms involved in poorly performing second-time overlays and to develop procedures which will help determine whether and when to overlay bridges, either for the first or second time, before major damage has occurred to substrate concrete.
2 To evaluate suitable methods for detecting poor quality concrete and/or interfacial substrate damage on existing overlays or original bridge decks and for ensuring its removal prior to overlay.
3 To develop surface preparation strategies which will facilitate removal of existing concrete in an effective, economical fashion and can be applied to all deck overlays.
1 Perform a literature search on surface preparation techniques, equipment, factors affecting overlay performance, specifications, technologies for assessing quality of substrate concrete prior to overlayment, curing requirements and methods of acceptance.
2 Meet with the technical panel to discuss the project and scope of work and review a draft survey as outlined in Task 3.
3 Conduct a survey of states to determine current practices and performance issues and obtain suitable information for use in conducting the research.
4 Collect appropriate information from the Office of Bridge Design on bridge deck overlay history and performance.
5 Perform visual examination of cores from overlays statewide, which will be made available as a result of an extensive coring program that is already underway. Apply petrographic, Scanning Electron Microscopy (SEM) and other appropriate examination techniques to determine damage mechanisms on a minimum of 24 cores representing a cross-section of overlay types and locations.
6 Conduct visual surveys of 22 bridges sampled as part of the coring program including crack width and distribution and perform bond testing on the in-place overlays.
7 Observe standard practices, including concrete removal, surface preparation, construction, and curing, on several overlay projects to gauge their potential impact on performance.
8 Examine various methods for detecting poor quality concrete prior to overlayment including Ground Penetrating Radar, Infrared or other appropriate techniques and apply any suitable techniques to an actual second-time bridge overlay project during construction.
9 9. Develop and submit plan notes for inclusion into the above construction project. The plan notes should outline an experimental plan for testing various surface preparation strategies to determine the effect of surface preparation methods on bond strength. The application of these strategies should be monitored during construction to evaluate their suitability for removing unsound concrete with respect to efficiency and cost-effectiveness including appropriate testing.
10 Monitor the performance and effectiveness of the various surface preparation techniques for one year following completion of the overlay.
11 Develop guidelines for bridge deck condition survey procedures and interpretation of survey results which will allow optimization of timing for bridge deck overlays, avoid bond problems and poor overlay performance and preclude placement of overlays on inappropriate candidate bridges.
12 Develop guidelines for appropriate economically feasible surface preparation techniques to insure removal of all poor quality concrete while minimizing damage to existing concrete prior to overlay placement.
13 Submit an interim report no later than September 30, 2001 providing preliminary recommendations, if any are available, which can be incorporated into the construction program for 2002.
14 Recommend necessary changes to specifications, construction practices and evaluation procedures.
15 Prepare a final report and executive summary of the literature review, research methodology, findings, conclusions, guidelines and recommendations.
16 Make an executive presentation to the SDDOT Research Review Board at the conclusion of the project.
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