Compression performance analysis of multi-scale modified concrete based on response surface method

The natural multi-scale defects in concrete are important factors affecting the performance. To comprehensively improve the performance of concrete, a method of adding variety materials into concrete to improve the defects from nano-micron-millimeter scales is proposed, and carbon nanotubes (CNTs), calcium carbonate whiskers (CCW), PVA fiber, steel fiber and rubber particles are selected for tests. The whole tests are completed by the phased test method. Firstly, CNTs and CCW are added into concrete, and the optimal content scheme of CNTs and CCW is determined. On this basis, this study designed and completed the multi-scale modified concrete test that further added PVA fiber, steel fiber and rubber particles according to response surface method (RSM). Finally, combined with RSM, hybrid effect coefficient and scanning electron microscope (SEM), the multi-scale modified concrete test results are analyzed. The analysis results indicated that the regression equation established by RSM has high accuracy and can effectively predict concrete mechanical properties under different materials content. Steel fiber and PVA fiber can improve concrete performance, while rubber particles can improve the deformation capacity and reduce the peak stress and toughness. When the contents of CNTs, CCW, PVA fibers, steel fibers and rubber particles are 0.6 %, 6 %, 0.075 %, 1 % and 0 % respectively, the multi-scale modified concrete has the best mechanical properties.