Evaluation of Bridge Deck With Shrinkage-Compensating Concrete.

摘要

Concrete bridge decks are susceptible to premature cracking and to corrosion of reinforcing steel. Low-permeability concrete does not always ensure durability if the concrete has excessive cracks that facilitate the intrusion of aggressive solutions. Cracks in concrete can occur when a restrained mass of concrete changes volume including drying shrinkage because of water loss. These types of shrinkage cracks can be counteracted with the use of shrinkage-compensating concrete (SC concrete). SC concrete is expansive cement concrete that when properly restrained by reinforcement can expand an amount equal to or slightly greater than the anticipated drying shrinkage. The purpose of this study was to investigate the effectiveness of SC concrete using Type K expansive cement in reducing cracks in bridge decks. The bridge deck on the Route 613 Bridge over the South Fork Shenandoah River in Warren County in the Virginia Department of Transportation’s Staunton District was selected for study. Restrained length change bar specimens showed expansion until the 7-day moist curing period (when tested in accordance with ASTM C878). The results showed that a bridge deck with fewer transverse cracks than typically found in decks constructed with Type I/II cement can be constructed with Type K cement concrete. There were several longitudinal cracks (reflective cracks) caused by the differential movement of the beams at the keyway that could not be prevented by the use of SC concrete. No special construction equipment or techniques are required for satisfactory placement of SC concrete, but slump loss under hot weather conditions is a more serious problem in SC concrete than in normal portland cement concrete. Hence, for successful placement of Type K cement concrete, sufficient prior planning and proper mix design development are needed. Another concern is the availability and cost of Type K cement since it is not routinely used. 17