Effect of Superplasticizers on Concrete-Steel Bond Strength

Abstract

The effects of superp 1 asti ci zers on concrete-steel bond strength are studied. Key variables are degree of consolidation, concrete slump, both with and without a superplasticizer, concrete temperature, and bar position. #8 deformed reinforcing bars were used with a 2 in. cover and a 10 in. bonded length. Concrete slumps ranged from 1-3/4 in. to 9 in. Three specimen depths were used. All specimens were modified cantilever beam specimens. Based on the experimental results, high slump superplasticized concrete pro vi des a 1 ower bond strength than 1 ow slump concrete of the same strength. Superpl asti ci zed concrete pro vi des a higher bond strength than high slump regular concrete with the same slump and water-cement ratio. Vibration of high slump concrete increases the bond strength compared to high slump concrete without vibration. Bond strength decreases as the amount of concrete below a bar increases, but the greatest effect appears to occur with top-cast (i.e. upper surface) bars.