Bond Studies of Reinforcing Bars in Silica Fume Concrete

This paper reports on research in progress conducted at the American University in Beirut to evaluate the effect of silica fume on bond and anchorage of reinforcement in high performance concrete (HPC) structures. The program includes testing the effect of a wide range of variables on the bonded strength of beam bar splices and bars anchored in pullout specimens. Results of the first phase of the research program have been analyzed. Ten 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 of cement by silica fume and the casting position. Test results indicated that replacement of 5 to 20 percent of the cement by an equal weight of silica fume resulted in an average 8 percent reduction in bond strength regardless of casting position.