Uniaxial Compression Test and Performance Analysis of Multiscale Modified Concrete

Mixing material such as fibers into concrete is an effective method to change the brittle behavior of concrete. To reduce the internal defects of concrete and improve the mechanical performance and crack resistance of concrete, this study proposed the design concept of multiscale modified concrete. To further investigate the feasibility of the design concept, the two-stage test method is adopted to study the performance of multiscale modified concrete. First, carbon nanotubes (CNT) and ${\mathrm{CaCO}}_3$ whiskers were mixed into concrete, and the optimum contents of CNT and ${\mathrm{CaCO}}_3$ whiskers were determined by uniaxial compression test. Subsequently, based on the optimum contents of CNT and ${\mathrm{CaCO}}_3$ whiskers, polyvinyl alcohol fibers (PVAF), steel fibers (SF), and rubber particles (RP) were further mixed into concrete, and the uniaxial compression test and scanning electron microscopy (SEM) test were completed. From the test results, the influence of materials contents on the mechanical performance of concrete was analyzed, an accurate and reasonable compressive stress–strain model was established, and the comprehensive toughness evaluation index of concrete considering the multiple factors influence was presented. The comprehensive toughness evaluation results show that the multiscale modified concrete has outstanding compressive strength and toughness when the contents of CNT, ${\mathrm{CaCO}}_3$ whiskers, PVAF, SF, and RP are 0.6%, 6.0%, 0.075%, 1.0%, and 0%, respectively. The SEM results revealed that adding materials of various sizes into concrete can hinder the growth of cracks and improve the cracking pattern of concrete.