Strain-rate-dependent performance of alkali-activated binder-based ultra-high strength concrete

Ultra-high performance concrete(UHPC) is a superior protective material in impact and blast resistance, but negatively influences the environment due to the large amount of cement consumption and CO₂ emissions during the preparation process. Alkali-activated binders were invented as a promising alternative to Portland cement for preparing UHPC in a method that saves energy and emits less CO₂. However, the strain-rate-dependent performance of alkali-activated binder-based ultra-high strength concrete (AAB-UHSC) is still unknown. Therefore, this work focused on the strain-rate-dependent performance, e.g., dynamic mechanical properties, energy absorption and failure patterns, of AAB-UHSC materials incorporated with different steel fiber contents, as well as the microdamage at different strain rates. The quasi-static compression test, split Hopkinson pressure bar test, the sieving test and the scanning electron microscope test were carried out. The results indicated that the AAB-UHSC material is a strain rate-dependent material, the different stress-strain curves corresponding to different failure patterns vary with the strain rate, and an obvious strain rate transition zone existed for different failure patterns, as did the energy for different failure patterns. Additionally, the addition of steel fibers could effectively enhance the dynamic macromechanical performance and reduce the microdamage. An impact toughness index suitable for AAB-UHSC was defined. Eventually, a modified ZWT dynamic constitutive model with a new damage evolution equation for the AAB-UHSC material was proposed, and results show that this model can well describe the stress-strain relationship of the AAB-UHSC under impact load.