Fracture toughness testing by means of the SECRBB test specimen

Abstract

The single edge crack round bar in bending (SECRBB) test specimen is a practical test specimen for determining the fracture toughness of concrete. The specimens used in this study were prepared from standard 100 mm and 150 mm diameter cylinders with notch depth ratios within the range 0.2 <aD < 0.5. These specimens were more compact than the SECRBB specimens used by earlier researchers (with other materials) with support span/diameter ratios of only 1.5 and 1.67 for the smaller and larger diameter cylinders respectively. Thus an experimental expression was developed which gave K1P values for both cylinder sizes and hence fracture toughness results were determined.The SECRBB test geometry was used to evaluate the fracture toughness of a number of mixes. The effect of maximum coarse aggregate size was studied with inconclusive results — the fracture toughness was reduced for maximum aggregate sizes of 5 mm and 20 mm compared to the results obtained using 10 mm maximum aggregate size. The effect of adding crimped steel fibres in the mix was also investigated. The fracture toughness increased with increasing fibre content but the increase was only half that obtained from other test geometries. This variation was probably due to the method of manufacture of the specimens and it appears that the fracture toughness of steel fibre reinforced concrete may be sensitive to the method of specimen preparation.