A new way to measure and model limestone strength under corrosion
Hao Li defended his PhD thesis at the Department of Mechanical Engineering on October 15th.
Limestone may look solid and eternal, but deep underground, invisible chemical reactions are quietly eating away at its strength. The PhD research of Hao Li uncovered how this microscopic corrosion—tiny pores enlarging, minerals dissolving—can dramatically weaken rock structures and alter how they fail under stress. By combining experiments, imaging, and new modeling approaches, he found that chemical damage reduces the rock’s strength, limits the benefit of confining pressure, and can now be better predicted through an improved strength criterion and a new chemo-mechanical damage model. These insights help engineers design safer underground spaces, stabilize tunnels and slopes, and secure CO₂ storage for climate mitigation.
Limestone, one of the world’s most common building and geological materials, is highly vulnerable to chemical attack. When exposed to water of varying acidity, it begins to dissolve at the microscopic level—a process that gradually alters its pores and weakens the mineral bonds holding it together. Through detailed experiments and imaging with scanning electron microscopy (SEM), nuclear magnetic resonance (NMR), and X-ray diffraction (XRD), the research of traced how these chemical reactions reshape the rock’s inner structure. As pores grow and merge, cracks initiate earlier, making the material more prone to failure under stress.
Measuring the moment of breakdown
To better understand when limestone begins to fail, the researcher developed a Volumetric Strain Response Method (VSRM) that detects the precise point when microcracks start to form. Two new indicators—the dilatancy resistance state index and its maximum variation—make it possible to identify this threshold more accurately than before. The results show that the stress needed to initiate cracks decreases as chemical corrosion increases, but rises under higher confining pressures. In other words, pressure can temporarily help hold a weakened rock together, but not forever—once the inner structure is too damaged, collapse becomes inevitable.
Predicting strength in a changing chemical world
To translate these observations into practical tools, he enhanced the well-known Hoek–Brown strength criterion by including a porosity-dependent kinetic parameter that evolves with chemical exposure. This refined model accurately predicts how rock strength changes with pH, time, and confining pressure, achieving excellent agreement with experiments (R² > 0.96). This advancement allows engineers to predict how rocks will behave in chemically aggressive environments, a critical step for underground storage of CO₂, radioactive waste disposal, and tunneling projects.
Linking chemical corrosion to mechanical weakening
Finally, Li developed a new constitutive model that connects chemical damage and mechanical stress in one framework. It introduces two key ideas:
- Effective Chemical Damage (ECD) – distinguishing between visible and hidden corrosion effects, and
- Random Energy Release Rate (RERR) – representing how energy is unevenly distributed in a rock’s microstructure.
Together, these describe how chemical and mechanical damage evolve in tandem, following an S-shaped progression that reflects real-world rock behavior under pressure and corrosion.
From the lab to the underground
This research bridges the gap between microscopic chemistry and large-scale engineering performance. It not only deepens our scientific understanding of how rocks fail but also provides new tools for predicting and preventing geological hazards. As the world looks to store CO₂ underground and build safer infrastructure, knowing how rocks respond to both pressure and chemistry will be vital. Limestone, it turns out, has much to teach us about resilience—and fragility—beneath the surface.
This research is part of the broader line on multi-scale modeling of chemo-mechanical processes in porous geomaterials, with applications in underground construction, rock mechanics, and COâ‚‚ storage engineering.
Title of PhD thesis: . Supervisors: Prof. David Smeulders, Prof. Z. Sun, and Dr. Leo Pel.