RESEARCH ON CRACK CONTROL ABILITY OF HIGH TOUGHNESS CONCRETE UNDER TENSILE LOAD

The model of multiple cracking of high toughness concrete is established by analyzing the interface stress of fiber in the cement matrix. Based on this model, the effects of friction bond strength, chemical bond strength, matrix cracking strength and elastic modulus of fiber on the strain and crack width at the end of multiple-cracking zone are analyzed. The analysis results show that the strain and the crack width decrease with the increase of the friction bond strength; the strain increases and the crack width decreases with the increase of the chemical bond strength; the strain and the crack width increase with the increase of the matrix cracking strength; the strain and the crack width decrease with the increase of the elastic modulus of fiber. The crack control ability of high toughness concrete with initial crack defects is researched through direct tensile test. The notched specimens are used in the research. The test results show that, when the initial crack-depth ratio is 0.2, the ultimate stress is 5.3MPa at the notch and is 4.3MPa at the non-cutting position, and the phenomenon of multiple cracking appears in the whole specimen, and the crack width is controlled in less than 0.1mm. When the initial crack-depth ratio is 0.4, the ultimate stress is 5.8MPa at the notch and is 3.5MPa at the non-cutting position, and the development of cracks is not controlled effectively by the fibers at the fracture plane. Therefore, only some similar arc cracks appear near the notch of the specimen.