Bond Strength of Reinforcement in High Performance Concrete: Role of Silica Fume, Casting Position, and Superplasticizer Dosage

Abstract

Little research is reported in the literature on the effect of pozzolans such as silica fume on structural behavior of reinforced concrete, namely on bond and anchorage characteristics of reinforcing bars in concrete. The objectives of the study were to investigate the effect of silica fume on bond and anchorage characteristics of reinforcing bars in high performance concrete, to study the validity of the upper limit of 70 MPa (10,000 psi) imposed by the American Concrete Institute (ACI) Building Code 318-95 on the concrete compressive strength for determination of development length, and to evaluate the reliability of the empirical equation of Orangun, Jirsa, and Breen in estimating the bond strength of deformed bars embedded in high strength concrete. Sixteen beam specimens were tested. Each beam was designed to include two bars in tension, spliced at the center of the span. The splice length was selected so that bars would fail in bond, splitting the concrete cover in the splice region, before reaching the yield point. The beams were loaded in positive bending with the splice in a constant moment region. The variables used were the percentage replacement by weight of cement by silica fume, casting position, and the superplasticizer dosage. Test results indicated that replacement of 5-20% of the cement by an equal weight of silica fume resulted in an average 10% reduction in bond strength regardless of casting position or the superplasticizer dosage used.