Improvement of boundary effect model in multi-scale hybrid fibers reinforced cementitious composite and prediction of its structural failure behavior

Abstract The inclusion of multi-scale hybrid fibers in cement-based materials exhibits excellent crack resistance performance at multi-level than that of single type or size of fiber. Multi-scale hybrid fiber reinforced cementitious composites (MHFRCCs) can be served as a building material with stringent crack resistance requirements for civil structure such as pipeline, river levee, nuclear reactor, water tower, and sewage treatment sedimentation tank. The tensile strength (ft) and fracture toughness (KIC) are two important size independent material parameters for guiding structural safety design and stability assessment. In this study, the real ft and KIC of MHFRCCs were determined by three-point bending test based on the boundary effect model. The average aggregate particle size with a large proportion was chosen as the “representative aggregate (d1 = 0.45 mm) by using grading curve. The fiber long axis dimensions that appear most frequently on the cross section were selected as the “representative fiber (d2 = 0.28 mm for steel fiber and d3 = 0.0794 mm for polyvinyl alcohol fiber) according to the statistical analysis of backscattered electron imaging. The fracture failure behaviors of MHFRCC structure were predicted based on the determined ft and KIC values, and the structural fracture failure bands with ±15% variations were established. In addition, the microstructure analysis of MHFRCC revealed multi-scale enhancement mechanism in the cement matrix. Finally, the complete fracture process images and P-CMOD curve were divided into three stages: pre-cracking stage, crack stable propagation stage, and unstable failure stage. This analysis would be helpful to understand the fracture crack resistance effect of multi-scale hybrid fibers at multi-level within cement matrix.