Published in 2017
Connections, closure pours, and joints in bridges are often sources of distress because of cracks and openings. Wide separation facilitates the penetration of harmful solutions that can lead to costly repairs. Cracks are caused by volumetric changes attributable to moisture and temperature and the application of service loads after the concrete has hardened. Poor bonding between the existing concrete and new concrete can lead to separation or opening. Wide cracks or openings within the material or at the interface and leaking joints allow the ingress of water and chemicals, causing damage to the bridge deck sections and the bridge substructure through corrosion of reinforcing steel, alkali-silica reactions, sulfate attack, and freeze-thaw damage.
This study was designed to evaluate properties of fiber-reinforced concrete and cementitious composites in controlling cracking for bridge deck closure pours (i.e., link slabs). Plastic and hardened mixture properties of high-performance fiber-reinforced concrete (HPFRC) were evaluated, with emphasis on deflection hardening, flexural toughness, and bond strength. A secondary objective was to evaluate various bond strength tests for use in prequalification or quality assurance of mixtures. The addition of a small number of discontinuous fibers to a conventional concrete matrix minimizes cracking, but the size of these cracks still permits the intrusion of harmful solutions. High volumes of suitable fibers used in HPFRC produce multiple very tight cracks (<0.1 mm wide), which do not allow for the ingress of water and other harmful solutions. Thus, HPFRC offers a potential solution by controlling cracks and providing satisfactory bond strengths.
The study recommends that VDOT’s Structure and Bridge Division conduct field pilots of HPFRC mixtures that undergo deflection hardening to be used for closure pours (i.e., link slabs), and shear keys. The study also recommends that VDOT’s Materials Division evaluate the California bond test (CA 551) for closure applications as part of field pilot projects. Pilots have already been initiated in VDOT’s Staunton and Richmond districts.
Michael C. Brown, Ph.D., P.E., Levon C. Hoomes
Last updated: November 11, 2023