Evaluating fracture resistance of basalt fiber reinforced mortar to mode I/III load using edge notched disc bend (ENDB) specimen: Insights from acoustic emission and morphological analysis

Failures of the topcoat in pavement structures often occur due to mixed mode I/III traction; however, incorporating basalt fibers (BFs) into cement mixtures can effectively enhance mortar toughness and improve service conditions. To gain a deeper insight into the fracture behavior of BF-reinforced cement mixture, the Edge Notch Disc Bend (ENDB) testing with acoustic emission (AE) technique was first conducted on BF reinforced mortar specimens considering three different dosages of BFs (0%, 0.3% and 0.8% by weight). Four fracture parameters, including effective fracture toughness (K-e), effective work of fracture (W-p), effective critical fracture toughness (K-eff) and effective critical work of fracture (Wp-eff), were employed to assess the fracture performance of BF-reinforced mortars. The results show that the K-e for mode III is significantly lower than that for mode I, while W-p is critical for mode III. Interestingly, the increase in K-e, K-eff, W-p and Wp-eff is closely associated with the micro behavior involved in reducing the effective critical distance. Then, the digital reconstruction of fracture surfaces was performed, revealing that the fractal and roughness characteristics of the fracture surface subjected to mode & Iukcy;& Iukcy;& Iukcy;& Iukcy;& Iukcy;& Iukcy; loading are more pronounced than those under mode I loading. These results can be further enhanced by the fiber crack-bridging effect. Moreover, it is validated that the out-of-plane shear failure induced by tensile stress occurs specifically under pure mode & Iukcy;& Iukcy;& Iukcy;& Iukcy;& Iukcy;& Iukcy; loading state (K-& Iukcy;c>K(& Iukcy;& Iukcy;& Iukcy;c )and 90% shear-type waveforms), which illustrates the feasibility of applying pure mode III load under ENDB testing. By analyzing variations in dominant frequency and b value, we demonstrate that mortars with higher BFs content exhibit a greater prevalence of shear-type microfractures characterized by smaller rupture scales and weaker heterogeneity under mode & Iukcy;& Iukcy;& Iukcy;& Iukcy;& Iukcy;& Iukcy; loading conditions. These findings can offer a novel perspective on elucidating the crack-bridging effect of fibers during the rupture of fiber-reinforced mixtures.