Power ultrasound enhancement of diatomite-containing cement-based composites: multi-scale composite engineering of the interfacial transition zone and micromechanical homogenization

This study investigates the multi-scale composite engineering of diatomite powder (DP)-modified micro-concrete subjected to power ultrasound (PUS) treatment. The main findings demonstrate that the combined DP+PUS treatment significantly improves macroscopic performance, increasing 28-day compressive strength by 60% in diabase (DI, 43.6 MPa) and 55% in limestone (LS, 44.1 MPa) systems, despite a 20% cement replacement. Microstructurally, DP selectively eliminates large macropore defects (>1000 nm) predominantly localized at the aggregate-paste boundary, as independently confirmed by fluorescence microscopy and SEM, reducing their volume fraction from 5.22% to 0.26% (DI) and from 3.43% to 0.56% (LS). In limestone systems, PUS further decreases the interfacial transition zone (ITZ) width by ∼62% (from ∼150 μm to 57.4 μm) and increases cement matrix hardness by 27.4%. Lu-Torquato spatial modelling confirms that this ITZ narrowing reduces the 3D weak-phase volume fraction from 3.0% to 1.1%, effectively disrupting the percolated interfacial network. Mori–Tanaka micromechanical homogenization further predicted a corresponding 7.5% increase in composite elastic modulus (32.2 → 34.6 GPa), confirming the mathematical coherence between microstructural refinement and macroscopic stiffness gains. These results provide direct experimental evidence that macroscopic strength is primarily governed by the selective elimination of large macropores and ITZ refinement rather than a mere reduction in total bulk porosity.