Bond of Top-Cast Bars in Bridge Decks

The effects of consolidation method and two-course construction on the bond strength of top-cast reinforcements 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: 3/4 and 3 in. (19 and 76 mm) monolithic and 3 in. (76 mm) two-course with either 3/4 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. 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.