Failure mechanisms of cementitious composites modified by hybrid toughening phases: insights from acoustic emission multifractal behavior

This paper combined uniaxial compression with synchronous acoustic emission (AE) monitoring to decipher how a hybrid toughening phase (HTP) – specifically, glass/polyacrylonitrile dual fibres – alters the damage evolution of cement-tailings composites. Multifractal detrended fluctuation analysis (MF-DFA) confirmed the multifractal character of the AE records. The key structural consequence of fibre incorporation is a redistribution, rather than a uniform suppression, of energy dissipation. Quantitatively, the multifractal spectral width Δα widened from 1.472 to 2.212 (1:6 mix), pointing to enhanced spatial heterogeneity during the main rupture stage. Because Δα alone cannot distinguish fibre-specific dissipation from general matrix damage, we developed a spectral asymmetry index. Near the critical failure boundary (peak > 0.3), the index captures a sharp left-to-right skewness inversion that isolates discrete, high-energy events – events we link directly to fibre snap. A tight negative linear correlation (slope: −0.050) between Δα and the Hurst exponent H(2) enabled us to formulate a multifractal-derived warning criterion. Precursory thresholds for the fibre-modified composites (0.452–0.549) sit consistently above those of the base matrices (0.331–0.359). Taken together, this framework translates the continuous alert signals characteristic of brittle failure into discrete, pulsed precursors, offering a fine-grained picture of the progressive crack-arrest mechanism supplied by the fibre network.