INFLUENCE OF AGGREGATE ON THE BOND STRENGTH OF CORRUGATED STEEL FIBER WITH ULTRA-HIGH PERFORMANCE CONCRETE

The article examines the effect of the volume content and particle size of the aggregate on the bond strength of corrugated steel fiber to ultra-high performance concrete of various compositions. The study was conducted by pulling out a single fiber from concretes with a compressive strength in the range of 56–175 MPa with a volume concentration of aggregate from 0 to 0.4 m3 /m3 and a maximum particle size of 0.4–0.8 mm. It was found that the bond strength of corrugated steel fiber depends on the parameter Stot, reflecting the total surface area of the aggregate in the composition, the calculation of which uses both the volume concentration and the particle size of the aggregate. Test results indicate that the bond strength can be increased to 42 % by changing the parameter Stot from 0 to 12.4∙103 m2. The contribution of the aggregate to the bonds strength is only observed if there is no destruction of the cement paste under the fiber bends. Analytical investigations revealed that cement paste with a compressive strength of 143–146 MPa is capable of withstanding the force generated by fiber pullout without deteriorating. The contribution of the aggregate to the bond strength is either minimal or completely absent if the strength of cement paste is lower than the specified value. Empirical equations were obtained for predicting the bond strength of corrugated steel fiber, taking into account various mix design parameters, including cement compressive strength, water-cement ratio, silica fume content, volume concentration and particle size of the aggregate. The average and maximum relative error between the calculated and experimental values were between 4.5 and 11.1 %, respectively.