Mechanical properties and avalanche characteristics of reactive powder concrete under different loading conditions by acoustic emission techniques

Reactive Powder Concrete (RPC) is a porous-medium composite material that generates acoustic emission (AE) signals during failure that strongly correlate with avalanche characteristics, distinguishing it from ordinary concrete. This study investigated RPC’s internal damage mechanisms using AE monitoring under cubic compression, axial compression, splitting tension, and four-point bending. The results showed that RPC specimens exhibited the highest ductility under four-point bending and the highest damage resistance under cubic compression. Based on AE energy evolution, the failure process is categorized into four stages: compaction, crack initiation and stable propagation, crack coalescence and unstable propagation, and post-peak failure. The AE peak frequencies were concentrated in the 100–150 kHz range under cubic/axial compression and in the 150–200 kHz range under splitting tension/four-point bending. AE energy signals adhere to a scale-free power law distribution, with exponents of 1.59, 1.45, 1.15, and 1.28 under the four respective loading conditions, all localized within the plateau region of the power law curve. Avalanche characteristics reflect distinct damage mechanisms. Cubic compression involves small-scale signals from matrix-fiber frictional sliding; axial compression features more large-scale signals derived mainly from fracture; and splitting tension and four-point bending produce larger signals associated with fiber pull-out. The avalanche exponents under cubic compression were close to the force-integrated mean-field model, whereas the amplitude and duration exponents under other loading modes approximated the mean-field model. These findings provide a scientific basis for assessing RPC structural damage and facilitating early warnings.