ON THE TOUGHNESS OF HIGH STRENGTH CONCRETE WITH STEEL FIBRES OF DIFFERENT LENGTHS

摘要

The test series reported is part of a research program aimed at defining tools for static design of structural elements made of High Strength Steel Fibre Reinforced Concrete (HSFRC). One of the parameters that had to be decided upon for the design of static structural tests was the fibre type. On the one hand, longer, 60-mm fibres can bridge wider cracks and provide increased toughness, and on the other hand, mixes with shorter, 30-mm fibres can be consolidated more readily. In order to clarify this issue and to evaluate whether structural test results with one type of fibre (short) are indicative of static behaviour of HSFRC elements with another type of fibres (long), we performed toughness tests of specimens with both fibre types. The four-point bending tests were carried out on 115-N/mm2 150xl50x600-mm beam specimens with "short" (30-mm) and "long" (60-mm) hooked-end steel fibres that had similar aspect ratios of 60～65. The test results showed a pronounced difference between the responses of the two specimen types at relatively large displacements. However, a closer examination of the results showed that within a certain deflection range the responses of the two mixes were similar. It was evaluated that the (calculated) crack opening that corresponds to this deflection is beyond the criterion usually specified in design codes for serviceability limit state and within the range of RC members ultimate limit state.