Elucidating the rate-dependent shear failure mechanism in cement fractures based on multi-parameter acoustic emission analysis

Gaining insight into the rate-dependent shear failure behavior of cement fractures is crucial for the design and safety evaluation of cement-based structures. Direct shear tests were conducted under constant normal load (CNL) conditions with multi-parameter acoustic emission (AE) monitoring. As the shear rate increased from 2.5 mm/min to 20 mm/min, the peak shear stresses for groups SA, SB, and SC decreased from 2.95 MPa, 2.61 MPa, and 2.21 MPa–2.23 MPa, 1.87 MPa, and 1.69 MPa, corresponding to reduction rates of 24.4 %, 28.4 %, and 23.5 %, respectively. Similarly, the residual shear stresses declined from 2.86 MPa, 2.21 MPa, and 1.67 MPa–2.02 MPa, 1.81 MPa, and 1.57 MPa, with reduction rates of 29.4 %, 18.1 %, and 5.9 %, respectively. The results demonstrated a negative correlation between shear stress and shear rate, attributed to a transition from gnawing failure (GF) to sliding failure (SF). AE signals showed distinct activity near peak shear stress, emphasizing their effectiveness in capturing failure evolution. Crack classification using the RA–AF method combined with a Gaussian Mixture Model (GMM) verified the GF-to-SF transition and the corresponding proportions of crack types, consistent with multifractal analysis. Dominant tensile cracks were associated with the degradation of second-order asperities. Additionally, a higher post-peak stress drop rate (PPSDR) at low shear rates indicates a transition in frictional behavior, whereas a lower PPSDR at higher rates reflects the persistence of stable sliding friction. This study contributes significantly to a better understanding of the rate-dependent shear failure mechanism in cement fractures.