Electric Arc Furnace slag (EAF slag) reuse is currently limited by its inconsistent chemical composition and volume instability. However, the alkaline composition suggests the possibility to use this material for carbon capture and storage. This study investigated the CO₂ uptake of EAF slag using a direct aqueous carbonation technique. The process was implemented at room temperature and ambient pressure, with minimized energy consumption. The CO₂-reactive phases were identified through X-ray diffraction analysis. Different CO₂ quantification techniques were employed: thermogravimetric analysis, acid digestion and thermal decomposition. The replicability of experiments and quantification techniques was assessed through analysis of variance and pairwise comparisons. The average CO₂ uptake and coefficient of variation resulted respectively 7.9% and 9.0%, with a carbonation degree of about 34%, proving that this simple mineralization process can be promising even in mild conditions.

Current practice reveals that no adaptation of self-healing concrete mix designs are made for the introduction of healing agents. However, the inclusion of healing agent may downgrade the concrete properties to some extent. Therefore, an optimization of mix design is necessary in order to eliminate the possible negative effects induced by the healing agents and also to potentially improve the self-healing and self-sealing abilities. In this paper, seven concrete mix designs were studied with crystalline admixture (CA) as a prospective healing agent to stimulate the autogenous healing mechanism. Several design parameters were opted namely (1) dosage of CA from 0 to 2% by cement mass, (2) water-cement (w/c) ratio between 0.46 and 0.52, and (3) cement content in the range of 320 to 360 kg/m³. The self-healing and self-sealing performances were investigated by the indicators of crack closure and the permeability rate, respectively. Results showed that the addition of CA demonstrated an advanced progress on the crack closure with increasing the healing time. The size of the crack considerably influenced healing performance. All in all, the effects of mix design parameters in terms of improvements of healing and sealing efficiencies are discussed and a recommendation for optimizing the mix design is proposed.

Moisture transport is the key phenomenon indicating the deterioration of the durability and structural performance of concrete structures. Although various studies have attempted to evaluate moisture transport in concrete, an anomalous behavior, which does not follow the root-t law compared to other porous material, was not explicitly taken into account. To quantitatively evaluate anomalous moisture transport, this study developed a couple of numerical methods between the truss-network model (TNM) and the rigid-body-spring model (RBSM) for this purpose. The colloidal behavior of calcium-silicate-hydrate (C-S-H), which is the major phase of cement-based material, was introduced to consider the anomalous behavior and mechanical response regarding the microstructural change of cement paste as well as cracks that significantly accelerate the moisture transport in concrete. The numerical results indicated that both microstructural change of cement paste and rapid absorption through cracks cause anomalous behavior. In addition, the numerical results suggest that volumetric change of cement paste should rely on water content related to the colloidal behavior of C-S-H in order to reproduce the realistic expansion and the closure of cracks during a rewetting process that affects structural performance and durability of concrete.

This work focuses on gas (air) flow through a model crack meant to represent a natural crack in concrete as accurately as possible. The purpose of the present study, which builds on previous works of the authors, is twofold: first, to highlight the test accuracy and second, to examine the impact of different crack geometries, relative to the same concrete formulation, on various aspects such as crack pressure distributions, the mass flow versus square pressure gradient relationship, and inlet and outlet pressure drops. The study reveals that while there is some variability in the results for a given crack geometry, this variability is relatively controlled, given the technical nature of the experiment. Additionally, the study shows that different crack geometries mainly affect results on small crack openings (smaller than 50 µm), whereas they remain negligible for those relative to larger openings (larger than 100 µm).

Concrete slurry waste is generated at concrete plants and generally re-used in new batches of concretes. Due to the presence of hydrated cement paste it has the potential to be carbonated prior to re-use in order not only to store CO₂, but also to enhance its reactivity in blends with cement. In this study, a concrete slurry waste obtained at a ready-mix concrete plant was investigated. For accelerated carbonation, a wet process was used at laboratory scale. The carbonated product was dried afterwards, characterized and used as supplementary cementitious material. When carbonated, the hydrate phases of the concrete slurry waste decomposed to calcite, gypsum and a silica-alumina gel. When blended with Portland cement (30% replacement by mass) early hydration kinetics was accelerated by the carbonated concrete slurry waste. The pozzolanic reaction of the silica-alumina gel consumed a significant part of the portlandite and showed a slightly positive contribution to compressive strength compared to inert quartz powder and to the uncarbonated concrete slurry. This offers the use of carbonated concrete slurry waste to store CO₂ in concrete with the additional benefit of reducing the cement content.

Mechanical stress can promote dissolution of calcium hydroxide in concrete; combined with carbonation, this may accelerate creep, damage, and corrosion. The existing microstructural simulators struggle with stress-induced dissolution processes, because of their strong chemo-mechanical coupling. This article presents results from recent Kinetic Monte Carlo simulations of dissolution and precipitation of solid phases, described as mechanically interacting particles. Chemo-mechanical coupling is embedded in the chemical reaction rates, featuring both chemical potentials of ions in solution and mechanical stress in the solid. The simulations are applied to a calcium hydroxide crystal, at chemical equilibrium in a solution of its ions but compressed between two stiff platens. Depending on the applied stress, the crystal partially dissolves and recrystallizes, producing an apparent viscoplastic deformation process. The simulation results inform mathematical creep laws with a size effect, as the strain rate depends on the crystal size. Upper-bound creep moduli for typical calcium hydroxide crystals in concrete are estimated as 237 to 2370 GPa, and carbonation would likely reduce them. This indicates that stress-induced dissolution of calcium hydroxide may underpin the nonlinear acceleration of concrete creep during carbonation. An experimental strategy to assess this mechanism is finally proposed, leveraging the size effect argument.