Effect of Superplasticizers on Concrete-Steel Bond Strength

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

Bond of Reinforcement to Superplasticized Concrete

The effects of superplasticizers on concrete-steel bond strength were studied. Key variables were degree of consolidation; concrete slump, both with and without a superplasticizer; concrete temperature; and bar position. No. 8 deformed reinforcing bars were used with a 2-in (51mm) cover and a 10 in. (254 mm) bonded length. Concrete slumps ranged from 1 3/4 in to 9in. (44 to 229 mm). Three specimens depths were used. All specimens were modified cantilever beam specimens. The experimental results show that high-slump superplasticized concrete provides a lower bond strength than low-slump concrete of the same strength. Vibration of high-slump concrete increases the bond strength compared to high-slump concrete without vibration. The current ACI top-bar requirements appear to be unconservative for top-cast bars with less than 12 in. (305 mm) of concrete below the bar and are possibly overconservative for nontop-cast bars with more than 12 in. 305 (mm) of concrete below the bar when low-slump concrete is used