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 ( f t ) and fracture toughness ( K IC ) are two important size independent material parameters for guiding structural safety design and stability assessment. In this study, the real f t and K IC 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 ( d 1 = 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 ( d 2 = 0.28 mm for steel fiber and d 3 = 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 f t and K IC 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. • Backscattered electron imaging was used to determine hybrid fiber morphologies based on statistical analysis. • The relationship between fictitious crack growth and the fibers-aggregates system was established. • Size independent fracture parameters of MHFRCC were determined using boundary effect model. • Structural failure curves/bands were constructed to predict the fracture behavior of MHFRCC. • Microscopic analysis and complete fracture process images confirmed the multi-scale crack resistance mechanism for MHFRCC.