Author : Kafeel Ahmed, Ahmed El Ragi, Uzma Kausar and Sherif El kholy

The addition of steel fibers in high strength concrete bridges the cracks and stops their propagation. The mode of failure becomes less brittle. The confinement provided by these fibers improves the bond strength. The adequate bond is necessary for composite action of steel reinforcing bars and adjoining concrete. There was a need to study the affect of increase in compressive strength of fiber reinforced high strength concrete, on bond performance. Experimental study was done to determine this effect for short embedded lengths in steel fiber reinforced high strength concrete. In this study the complete experimentation was done first for 3.5db embedded length, then for 4.0db embedded length and finally for 4.5db embedded length. The c/db ratio was kept constant. The whole post peak bond behaviour was studied. The results of this experimentation confirmed that by increasing the Compressive strength from 40.0 MPa to 50.0 MPa and 60.0 MPa, the bond strength of deformed steel bar in fiber reinforced high strength concrete increased from 15% to 75%, the corresponding peak load slip increased from 05% to 95%. This increase in bond strength and corresponding peak load slip as a function of increase in compressive strength is for short embedded lengths. This is due to increased mechanical bond strength of concrete keys that resisted the bond stress. This mechanical bond is a function of compressive strength and confinement provided by the steel fibers. Moreover, the crushing of concrete in front of steel bar ribs, takes place at high bond stress. During this the distribution of bond strength over the embedded length remains uniform. The results of this study may have a direct impact on development and splice length provisions of high strength fiber reinforced concrete.

Keywords: Concrete keys, Tangential Stress, Fracture Process Zone, Embedded Length.

Article published in International Journal of Current  Engineering  and Technology, Vol.4,No.1 (Feb- 2014)