Impact of early-age exposure to power ultrasound on the micromechanical properties of hardened cement paste
Phys. Rev. Materials 10, 105604 – Published 22 October, 2026
DOI: https://doi.org/10.1103/cbnp-56ch
Abstract
Cement paste serves as the universal binder in concrete, formed by mixing water with Ordinary Portland Cement (OPC). In its fresh state, cement paste behaves as a reactive suspension in which cement grains continuously dissolve, while colloidal calcium silica-hydrate (C-S-H) particles precipitate and progressively build a percolated load-bearing structure that densifies and hardens through hydration. Like many colloidal gels and concentrated suspensions, cement paste is sensitive to external stimuli such as mechanical vibrations and temperature variations. Here, we investigate the impact of power ultrasound (PUS) applied to OPC paste during the very early stages of hydration on the micromechanical properties of the hardened material. Fresh cement pastes are exposed to PUS at different amplitudes and durations before curing for 28 days. Microindentation testing reveals a progressive degradation of hardness, indentation modulus, and creep modulus with increasing PUS exposure. Remarkably, all mechanical properties collapse onto master curves controlled by the cumulative ultrasonic exposure. Microscratch testing further reveals enhanced acoustic-emission activity in sonicated samples, consistent with the development of additional mesoscale defects within the hardened material. In contrast, nanoindentation measurements show that the intrinsic mechanical properties of the individual phases composing the hardened paste—low-density and high-density C-S-H—remain largely unaffected. Together, these results indicate that PUS primarily alters the microstructure of hardened cement paste at scales larger than those of the hydration products themselves. These findings offer valuable experimental insights into novel pathways for modifying the mechanical properties of reactive colloidal gels.
