CONCRETE REINFORCED WITH DEFORMED STEEL FIBERS .2. TOUGHNESS CHARACTERIZATION

Four deformed commercial fibers with widely different geometries were investigated in steel fiber reinforced concrete. The fibers investigat ed include crimped fibers with circular and flat sections and end-defo rmed fibers with hooked and conical ends. Three matrixes with compress ive strengths of 42, 52, and 85 MPa were reinforced with fibers at a d osage rate of 40 kg/m3, and properties such as compressive strength, e lastic modulus, etc., were determined. The focus of the study, however , was toughness assessment and characterization, for which beam specim ens were tested in four-point bending with accurate deflection measure ments. Toughness improvements were characterized using ASTM C 1018 and the Japanese Society of Civil Engineers Standard SF-4 techniques. An attempt was also made to qualitatively relate the fiber-matrix bond-sl ip information generated from pullout tests in Part 1 of this paper to flexural load-deflection behavior. A strong influence of both fiber g eometry and matrix strength on toughness characteristics of fiber rein forced concrete was observed. The fibers deformed only at the extremit ies were, in general, more effective than those deformed along their e ntire lengths. The bond-slip data appear to correlate well, at least i n the qualitative sense, with the flexural load-deflection plots. The paper points out limitations of the current methods of toughness chara cterization and proposes an alternative technique addressing commonly raised concerns.