Performance of Bridge Deck Overlays in Virginia: Phase II: Service Life Performance

About the report:

Overlaying bridge decks has remained one of the best rehabilitation methods to extend their service life, and the Virginia Department of Transportation (VDOT) has been a leader in the use of bridge deck overlays.  Although VDOT has extensive experience in overlays, the long-term performance of overlays has not been entirely understood.  One of the biggest challenges for studying the performance of overlays is that only minimal information is available in bridge inventory and inspection records.  This limits any scientific assessment of this system.  Therefore, the purpose of this study was to provide a strong framework for the understanding of the long-term performance of overlays and the factors affecting them. 

This Phase II report reports on an extensive data collection process that led to the development of a robust database of 133 overlaid bridge decks after verification of historical inspection reports, verification of as-built plans and communication with VDOT district bridge engineers.  This helped in developing a model for understanding the amount of time it takes for bridge decks to require the first major rehabilitation and the major factors influencing the durability.  A database of information about overlays that were replaced at the end of their functional service life was compiled.  This helped develop a multiple regression model for understanding the factors that affected the durability of overlays. 

Survival analyses were conducted to estimate the service life of overlays and corresponding risk.  As a preventive method, epoxy concrete (EC) overlays were predicted to serve an average of 20.9 years, with 18 to 22 years at a 95 percent confidence level.  As a rehabilitative method, rigid concrete overlays were predicted to serve an average of 25.9 years, with 21 to 32 years at a 95 percent confidence level.

The recent trend of preferred overlay types has been identified as EC and very-early-strength latex-modified concrete (VELMC) overlays.  EC overlays have proven to be one of the better performing overlays through extensive VDOT experience.  VELMC overlays are an improvement upon latex-modified concrete overlays by vastly reducing the time of construction and thus become more suitable for decreased construction time, reduced traffic disruption, and lessened worker exposure to the field environment. 

An important discovery was the identification of the influence of the degree of deck damage prior to overlaying on the service life of overlays.  Preventive EC overlays should be used in a preventive sense, as the name suggests. If preventive EC overlays are installed on bridge decks with spalls, patches, or delaminations, irrespective of the amount of damage, an increased rate of deterioration in the overlays is likely to follow.

The future performance of rehabilitative overlays such as latex-modified concrete, silica fume, and VELMC overlays will not be influenced by the presence of bridge deck damage prior to overlaying.  This might be because of the removal of deteriorated concrete before these rigid overlays are constructed.  This emphasizes the importance of proper removal of poor quality concrete from bridge decks before overlaying during rehabilitation.

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