Size effects on tensile properties and compressive strength of engineered cementitious composites

In this study, the size effects on tensile properties and compressive strength of engineered cementitious composites (ECC) were investigated via experimental studies. Plane (2-D) and block (3-D) dogbone-shaped specimens were tested under uniaxial tension to study the size effect on tensile properties. Cubes and cylinders of different sizes were tested under uniaxial compression to study the size effect on compressive strength. The effect of water/binder (w/b) ratio on the compressive strength of ECC was also studied. Five w/b ratios (i.e., 0.20-0.42) were considered to cover a wide strength range. Three polyethylene (PE) fiber volume contents 0%, 1% and 2% were added to cubes for three different sizes (i.e., L = 40 mm, 50 mm and 100 mm) under five w/b ratios. Both of the plane and block dogbone-shaped specimens exhibited strain-hardening behavior accompanied with multiple micro-cracks under uniaxial tension. The size effects on the tensile properties of ECC were discussed, and the experimental scaling factors of tensile properties of block specimen to plane specimen were established and compared with the theoretical value. Additionally, the influences of specimen shape and specimen size on the compressive strength of ECC were stressed. The compressive strength of ECC decreased as the increasing specimen size regardless of the w/b ratio. It is also concluded that the compressive strength discrepancy caused by different specimen shape was negligible at 2% fiber volume content when the cube edge length was equal to the cylinder diameter. Furthermore, a size effect law for cubes with a high reliability was proposed based on fracture mechanics, and a correlation between the compressive strength of cube at any size and that of standard cylinder was deduced, providing a helpful strength conversion reference for ECC.