Superiority & Constructability of Fibrous Additives for Bridge Deck Concrete Overlays

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Research Report FHWA-ICT-12-003, Illinois Center for Transportation




Concrete overlays are highly susceptible to cracking due to the large surface area that is exposed to drying, the low water to cement ratio, the environmental exposure and loading conditions, the reflected cracks the underlying bridge deck, and the small thickness of the overlay. This research project investigated the potential benefits of synthetic fibrous additives with regard to the performance of bridge deck concrete overlays. Determining practical dosages and types of synthetic fibers that have the ability to enhance overlay performance, while maintaining convenient constructability without complications during mixing and finishing, was a major mission of this research. The project also outlined critical issues essential for successful and durable overlay applications with minimal cracking and delaminations. Various micro- and macro-fiber combinations were added to the fibrous overlay mixtures, resulting in 13 fibrous mix designs (nine LMC, two MSC, and two FAC). An extensive experimental laboratory program was then conducted to evaluate the major performance characteristics of each overlay mix design in terms of workability and finishability, compressive and flexural strengths, shrinkage, toughness, permeability, and bond strength. For further evaluation of the constructability of fibrous overlay—taking into consideration actual field conditions—demonstration bridges were selected and received fibrous overlays through actual IDOT contracts. Life-cycle cost analyses were also conducted to assess potential savings from incorporating fibrous additives within the concrete overlays. This research is pioneering in terms of using fibrous FAC overlay, which could be a potentially sustainable overlay system for preserving bridge decks with lower cost and minimized adverse environmental impact.



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