Bond of Top-Cast Bars in Bridge Decks

Abstract

The effects of consolidation method and two-course construction on the bond strength of top-cast reinforcement in concrete bridge decks were studied as functions of slump, bleed. and slab depth. Consolidation was varied using vibrator spacing and insertion time. Four top covers were studied: !4 and 3 in. (19 and 76 mm) monolithic and 3 in. (76 mm) two-course with either !4 or 1 in. (19 or 25 mm) first course cover. Bond test specimens were of two types: shallow, with 8 in. (203 mm) of concrete below the reinforcement, and deep. with 24 in. (610 mm) of concrete below the reinforcement. Concrete densities were obtained from drilled cores. Based on the experimental work, high-density internal vibration provides improved bond over low-density internal vibration. A 3 in. (76 mm) monolithic cover provides higher bond strength than 3 in. (76 mm) two-course cover. Increased concrete slump has a negative effect on bond strength for top-cast reinforcement. Deep slabs made with stiff, well-consolidated concrete can provide the same bond strengths as shallow slabs.