Multi-scale Modified Concrete Performance Analysis and Evaluation Based on New Damage Variables

Considering the natural defects in the performance of concrete,the design concept of adopting different sizes materials to improve the performance of concrete on the "nano-micron-millimeter" scale is proposed.Based on this concept,carbon nanotubes,calcium carbonate whiskers,polyvinyl alcohol (PVA) fibers,steel fibers and rubber particles are selected to design and complete the uniaxial compression test of multi-scale modified concrete.Combined with the deficiency of the current research on the damage constitutive model,the damage variable and damage constitutive model based on the energy method are proposed from the perspective of energy consumption.In order to comprehensively evaluate the mechanical properties of concrete,a modified damage variable considering the compressive strength of concrete is proposed.The results show that carbon nanotubes,calcium carbonate whiskers,PVA fibers and steel fibers can effectively improve the mechanical properties of concrete,while rubber particles can reduce the compressive strength of concrete.Compared with the damage variable and damage constitutive model based on Weibull distribution,the damage variable and damage constitutive model based on the energy method can more truly reflect the damage state and performance characteristics of concrete.Evaluation results of concrete comprehensive mechanical properties obtained by modified damage variables are reasonable and credible.