Mapping of cracking sequence of polyvinyl alcohol-steel hybrid fiber reinforced high-strength engineered cementitious composite under uniaxial tension

In the present paper, cracking sequence of high-strength engineered cementitious composite with the characteristic of low drying shrinkage (LSECC) under tension was experimentally studied by continually photographing during loading. The specific objective is to investigate the development of crack opening of each individual crack occurred during loading. Four Engineered cementations composite mixtures with water to binder ratio of 0.20, 0.25, 0.30, and 0.35 (LSECC-0.20, LSECC-0.25, LSECC-0.30, and LSECC-0.35) were used in the tests. Using the photographers taken during the test, crack width of each crack occurred during loading are determined according to the difference between solid material and crack on gray level. The test results show that cracks in ECC under tensile load are formed according to a temporal sequence. The opening width of each crack grows in a controllable and gradual manner with the increase of tensile strain. At a given strain level, crack width of different crack is not equal and the distribution of crack width is affected by matrix strength of the composite. Maximum crack width and the tensile strain capacity at the moment may be utilized to characterize the tensile performance of the composite that can guarantee both of tensile ductility and long-term durability. As maximum crack width equals 60 μm, at which the permeability of ECC may not be influenced by the cracks, higher strength ECC with water to binder ratio of 0.20 and 0.25 (LSECC-0.20 and LSECC-0.25) shows obvious higher tensile strain capacity and more cracks of narrow opening. By contrast, lower strength ECC with water to binder ratio of 0.30 and 0.35 (LSECC-0.30 and LSECC-0.35) shows relatively lower tensile strain and fewer cracks of narrow crack opening as crack width is limited below 60 μm. With the increase of tensile strain and the maximum crack width, much wider cracks (larger than 60 μm) are formed in lower strength ECC comparing to that of higher strength ECC.