Geotechnical construction activities, such as shield tunneling and pile foundation construction, generate large amounts of high-water-content waste slurry, making its disposal and resource utilization challenging. This paper introduces a CO ₂ -foamed carbonation solidification technique using a composite binder system made of reactive magnesium oxide (MgO), slag, and calcium carbide slag. The mechanical behavior of the lightweight carbonated slurry was investigated through Unconsolidated Undrained (UU) triaxial compression tests under various confining pressures. Quantitative results indicate that the reactive MgO dosage significantly governs strength evolution; an optimum MgO dosage of 10% yielded the highest peak stress of 190.8 kPa (at 50 kPa confining pressure), while the softening coefficient peaked at 0.46 with a 13% dosage. Regarding the CO ₂ foam impact, varying the foam content from 36% to 52% resulted in softening coefficients ranging between 0.20 and 0.50. The 36% foam dosage provided the optimal structural stability with a peak stress of 179 kPa, whereas excessive foam leads to greater pore connectivity, worsening strain-softening. Confining pressure significantly affects the material’s hardening and residual strength. Based on these findings, an improved constitutive model was developed using damage evolution and a modified Duncan–Chang framework, providing accurate descriptions of the material’s elastic, hardening, post-peak softening, and residual characteristics. This study advances our understanding of CO ₂ -foamed carbonated MgO-based slurry, offering new insights for both solidification/stabilization and carbon sequestration of high-water-content waste slurry.

To provide a unified description of the monotonic and cyclic compressive responses of concrete after freeze–thaw exposure, a one-dimensional phenomenological damage–plasticity constitutive framework is proposed. Freeze–thaw-induced pre-damage is quantified by the degradation of the initial static stiffness. A Mander-type equation is employed to describe the monotonic envelope, while residual strain is introduced to characterize plastic deformation. A signed stiffness variable is defined to distinguish pre-peak compaction from post-peak mechanical damage, and the unloading and reloading paths are represented by piecewise power-law functions for the pre-peak and post-peak regimes. The model is evaluated using 36 monotonic compression curves of recycled coarse aggregate self-compacting concrete subjected to sulfate freeze–thaw cycles and cyclic compression data for ordinary concrete subjected to seawater freeze–thaw cycles. After independent identification of the envelope-shape parameters, the monotonic responses yield an average R² of 0.978 and an average NRMSE of 0.041, whereas the complete cyclic responses yield an average R² of 0.941 and an average NRMSE of 0.066. Because the model parameters are identified separately using data from each freeze–thaw exposure level, these accuracy measures characterize parameter calibration and response reconstruction rather than independent prediction of untested exposure states. Freeze–thaw exposure causes substantially greater degradation of the initial static elastic modulus than reduction in peak stress, indicating that stiffness, strength, peak strain, and envelope shape should be treated as state variables at different hierarchical levels. The cyclic unloading stiffness exhibits both pre-peak enhancement and post-peak degradation, confirming the necessity of separately representing compaction and mechanical damage. The proposed model provides a unified representation of the monotonic envelope, residual deformation, and principal cyclic hysteretic characteristics of freeze–thaw-damaged concrete.

Concrete exposed to sub-zero and elevated temperatures exhibits strongly non-monotonic mechanical behavior governed by different physical mechanisms. Existing thermo-mechanical constitutive models commonly account for temperature-dependent degradation, but many are formulated for a specific temperature regime, and explicit treatment of reversible freezing-induced strengthening and irreversible high-temperature damage within a single constitutive structure remains limited. This study develops a unified thermo-elastoplastic damage model for concrete over the temperature range from −40 to 800 °C within the framework of irreversible thermodynamics. Plasticity is formulated in the effective-stress space, while compressive damage is driven by the damage energy release rate. Temperature effects are incorporated through evolution laws for compressive strength, elastic modulus, peak strain, and the shape parameters of the ascending and descending branches. Ice-induced strengthening is represented through reversible modifications of stiffness and strength thresholds, whereas high-temperature dehydration and microcracking are represented through irreversible thermal damage. The model was calibrated using published low-temperature compression data for C30–C50 concrete and complete high-temperature stress–strain curves for normal-strength concrete. The normalized curve-shape laws were subsequently assessed using high-strength concrete curves after normalization by their measured peak stress and peak strain, while selected components of the three-dimensional extension were assessed using residual HSC60 true-triaxial data. The calibrated model represented the freezing-point strength valley, sub-zero strengthening and embrittlement, non-monotonic strength evolution at intermediate temperatures, and progressive high-temperature ductilization. Complete high-temperature normal-strength concrete curves were reproduced with R² values of 0.94–0.99, while the normalized multiaxial strength assessment yielded an average relative error of approximately 8%. These results support the internal consistency of the formulation and the limited cross-strength-grade applicability of the normalized curve-shape laws, rather than unrestricted predictive capability. Further independent experiments are required before application beyond the material, moisture, thermal-history, and loading conditions represented by the available datasets.