Low Cracking Concretes for the Closure Pours and Overlays of the Dunlap Creek Bridge

About the report:

Joints, wide cracks, and poor-quality concretes facilitate the intrusion of chlorides, causing corrosion in bridge decks and substructures. In this study, joints were replaced with closure pours (link slabs) consisting of low permeability fiber-reinforced concretes resistant to wide cracking; overlays consisted of concretes with a low cracking potential and low permeability. Closure pours and overlay concretes had portland cement and a supplementary cementitious material for low permeability. Three different fibers, polyvinyl alcohol, polypropylene, and steel were used in the closure pours; a compressive strength of 3,000 psi at 24 hours was sought. Latex-modified concrete with Rapid Set cement but without fibers was also included since it is commonly used in closure pours.

In the overlays, five different materials were used: (1) latex-modified concrete with Rapid Set cement, (2) silica fume concrete (SFC) alone, (3) SFC with shrinkage reducing admixture, (4) SFC with lightweight coarse aggregate, and (5) SFC with lightweight fine aggregate. A compressive strength of 3,000 psi at 3 days was sought. Two parallel bridges located on Route 64 over Dunlap Creek in Alleghany County, Virginia, each with five simple spans, were selected for study. The performance of the closure pours and overlay concretes was observed after two to three winters.

Fiber-reinforced concretes with the desired strength and low permeability were achieved in the closure pours. The surveys after two to three winters indicated mostly tight cracks (<0.1 mm [0.004 in] in width) that would resist penetration of solutions. The overlays also achieved the specified strength and low permeability. There were minimal tight cracks except in one section with the latex-modified concrete with Rapid Set cement in the left lane of the westbound bridge. There were extensive cracks in that section that were attributed to plastic shrinkage from adverse weather conditions at placement and the fact that a truck had caught fire in that lane.

The study recommends that fiber-reinforced concretes be used when early strengths are needed. Further experimental installations with different fibers would indicate the optimum type and amounts for crack control. SFC overlays with shrinkage reducing admixture, with lightweight coarse aggregate, or with lightweight fine aggregate are ready for implementation in the field.

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