Speaker
Description
Building on a decade of expertise in neutron imaging developed by our group, this paper presents a novel experiment focusing on the coupled thermo-hydro-mechanical processes driving concrete spalling at high temperatures.
Conventional methods, limited to post-mortem analysis or intrusive gauges, fall short in capturing the transient (coupling of heat, moisture and stress) that leads concrete behavior at high temperatures.
Operando neutron and x-rays imaging experiments overcome this major limitation by providing direct, quantitative visualization of moisture transport and crack evolution with unparalleled spatial and temporal resolution.
This approach allows us to identify and characterize the interaction between cracking and moisture through flash vaporization. We directly observe how pressurized water within the concrete's pore network, can undergo rapid phase change during the cracking process thus providing enough energy to the system to explain spalling.
By tracking drying fronts, moisture clogs, and their dynamic interaction with growing fissures, this work provides the first experimental evidence defining the role of flash vaporization during spalling.
Consequently, this research establishes neutron imaging not merely as a complementary tool, but as a transformative methodology for validating and advancing predictive models of concrete behavior under extreme conditions.
Building on this experimental framework, the present study also draws upon a preliminary investigation published in 2024 by Felicetti et al. [1], which provided a first controlled demonstration of the thermo-hydro-mechanical mechanisms associated with rapid moisture vaporization in heated concrete. In that study, a concrete cylinder was heated on one face under well-controlled boundary conditions while pore pressure and temperature were continuously monitored. A partially sealed configuration enabled the accumulation of significant vapor pressure (on the order of 1 MPa) despite relatively low saturation and the absence of lateral confinement.
The sudden release of pressure, induced by opening a solenoid valve, triggered instantaneous moisture vaporization at the heated surface, accompanied by a sharp temperature drop of approximately 90 °C, providing clear evidence of the strong coupling between phase change and thermal energy consumption. While this setup successfully isolated and controlled the pressure release mechanism, the depressurization was externally imposed and not associated with the formation of a real fracture within the material.
The experiments presented here extend and generalize those findings by adopting more realistic conditions, in which pressure release occurs naturally as a consequence of cracking and spalling. Through operando neutron and X-ray imaging, we directly observe the onset of fracture, the associated redistribution of moisture, and the subsequent flash vaporization of pore water. The strong agreement between the controlled reference experiment and the present fracture-driven observations confirms the central role of rapid phase change in spalling phenomena, while providing, for the first time, direct experimental evidence under mechanically realistic conditions.
[1] Roberto Felicetti, Ramin Yarmohammadian, Stefano Dal Pont, Alessandro Tengattini. Fast vapour migration next to a depressurizing interface: A possible driving mechanism of explosive spalling revealed by neutron imaging. Cement and Concrete Research. Volume 180, 2024, 107508, ISSN 0008-8846. https://doi.org/10.1016/j.cemconres.2024.107508.
| Country | France |
|---|---|
| Student Awards | I would like to submit this presentation into the InterPore Journal Student Paper Award. |
| Acceptance of the Terms & Conditions | Click here to agree |
