Effect of moisture content on mechanical behavior of ultra-high toughness cementitious composites

Abstract

This study presented an investigation into the basic mechanical properties of Ultra-high toughness cementitious composites (UHTCC) under varying moisture levels (0%, 56.5%, and 100%). UHTCC have been recognized for their excellent deformation and crack control abilities, making them ideal for repairing and reinforcing hydraulic structures. In this study, static compressive test and direct tensile test were conducted to determine the influence of free water on compressive strength, tensile stress and strain relationship, elastic modulus and energy absorption ability of UHTCC. Meanwhile, the notched beam fracture test and single fiber pull-out test were also performed to investigate the mechanism behind such phenomenon. The results of the study revealed that as the relative moisture content of UHTCC increased, the compressive and tensile strengths decreased to varying degrees. The softening effect of water on compressive strength of UHTCC was found to be more significant than that on its tensile strength. Furthermore, the direct tensile deformation capacity of UHTCC increased from 2.4% to 4.0% as the relative moisture content increased. Water infiltration into UHTCC was found to have a minimal effect on the number of tensile cracks but significantly increased their width. The results of notched beam fracture and fiber pull-out tests demonstrated that water infiltration led to a 30.4% decrease in matrix fracture toughness, a 37.3% decrease in chemical bonding strength, and a 23.4% decrease in frictional bonding strength between fibers and the matrix. The increased deformation ability of UHTCC in water environments was attributed to the increase in strain hardening energy index (Jb’/Jtip).