The structural performance of reinforced concrete (RC) members affected by alkali–silica reaction (ASR) is difficult to predict because of the multi-scale phenomena. Recent structural tests reveal that the performance of RC members also depends on ASR-induced crack patterns, including localized cracks and dispersed microcracks. Additionally, microscopic factors, such as crack-filling by gel and presence of microcracks, are relevant. To explore this in detail, a computational system for finite element analysis of ASR-damaged RC members was developed. This study numerically investigated the structural behavior of ASR-affected RC members based on localized/dispersed crack patterns and microscopic factors. The applicability of the developed computational system was verified by comparing the analysis results with experimental data. The analysis results showed that ASR-damaged RC members with dispersed microcracks exhibited highly ductile behavior, while those with localized cracks failed in shear. This is because the dispersed crack pattern prevents the shear crack propagation and enhances the mechanical contribution of gel filling cracks, while the localized ASR cracks facilitate critical crack propagation, leading to failure, and minimize the gel-filling effect. Through the analytical investigations, it was found that the localized ASR cracks can result in significant loss of structural performance; thus, this study recommends the assessment of structural capacity of RC members in the case where the localized cracks were observed.

Tunnels that cross fault crush zones are subject to local deformation along these zones during earthquakes. Because the tunnel axis and the fault plane generally intersect in a three-dimensional manner, evaluating structural performance by using three-dimensional FEM is reasonable, and to this end selection of an appropriate damage indicator is required. To establish a damage evaluation method for the safety of tunnels subjected to local deformation, three-dimensional FEM analysis was carried out on previous loading experiments, the failure modes were analyzed, and the applicability of several damage evaluation indicators was verified. As a result, the damage to the tunnel in the model experiments was broadly classified into in-plane shear in the longitudinal section and out-of-plane shear in the longitudinal or transverse section. Performance evaluation using compressive damage indicators including minimum principal strain when the limit state of a tunnel is defined as the point at which the resistance to slippage in the crush zone is maximum was found to be feasible. Moreover, the results of the sensitivity analysis showed that evaluation based on the minimum principal strain is broadly applicable. Additionally, a limit value considering element size was proposed.

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.

This paper evaluates the efficiency of polypropylene fibers in improving the tensile and flexural characteristics of fiber-reinforced alkali-activated slag composites with strain-hardening behavior. Several different composites were produced and the mechanical properties of the composites were investigated during compressive and flexural tests. Furthermore, the mid-span curvature of the beams was measured by applying the digital image correlation technique to the flexural tests, and the curvature-deflection diagrams of the composites were analyzed and demarcated by structural mechanics. Finally, an analytical model considering strain-hardening behavior was proposed by fitting the calculated moment-curvature diagrams to the experimental results to recognize the tensile behavior of composites more precisely than the existing indirect methods. The results showed that an ultra-high tensile strain capacity was obtained for composites cured under laboratory conditions. Also, it was found that the fiber interfacial bond with the matrix was improved by using slag with lower Al₂O₃ content. Moreover, weakening the interfacial transition zone between the fine aggregate and the paste, the heat-treatment curing reduced the fracture energy of the composites which is favored to make strain-hardening cementitious composites.

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.

Carbonated wollastonite-based clinker is proposed as a potential novel supplementary cementitious material. The clinker can be synthesized from limestone and a silica source, and exhibits a CO₂-footprint after carbonation, which is approximately 60-70% less than the one of Portland cement. When carbonated, a silica-rich amorphous phase forms besides various polymorphs of calcium carbonate. When the carbonated clinker is blended with Portland cement, hydration is accelerated, and a significant pozzolanic reaction of the silica-rich amorphous phase takes place. This leads to a positive contribution to compressive strength. In a blend with 30% replacement of Portland cement by the carbonated wollastonite-based clinker almost the same mortar compressive strength is reached after 28 days compared to the plain Portland cement. Further investigations, especially regarding the production of the carbonated clinker, the durability of concrete incorporating this novel material, and life cycle analyses as well as economical assessments are needed.

Electro-deposition repairing concrete crack technique is of vital importance to prolong the service life of the concrete structure in the marine environment. In this paper, the repairing effect using seawater as an electrolyte was compared with ZnSO₄ solutions, and the mechanism of electro-deposition repairing concrete cracks under seawater environments was investigated. Besides, various parameters such as electrode materials, electrode distances and current density were studied in seawater. The experimental results indicated that electro-deposition repair using seawater is highly effective compared to using ZnSO₄ solutions. The Cl^- removal efficiency can reach to 16.25% with titanium mesh as the anode and seawater as the electrolyte. The main crystal mineral composition using seawater is brucite, calcite and aragonite, and the percentages of Mg(OH)₂, Ca(OH)₂ and CaCO₃ are approximately 68%, 7% and 23%, respectively. Rather than Na⁺, Mg²⁺ and Ca²⁺ in seawater were the primary ions promoting the repair of concrete cracks. When the seawater and titanium mode was used, the reaction products were the densest and the repairing effect was the best. Furthermore, when the titanium electrode distance was 0 mm and the current density was 0.25 to 0.5 A/m², the electro-deposition repairing effect was the best. This paper presents a new method for the research of electro-deposition repairing concrete cracks in the submerged zone of marine environment.

The tension stiffening behavior of reinforced concrete (RC) prisms, affected by the aggregate volume expansion induced by neutron irradiation, were numerically investigated using a rigid body spring network model. First, the model was validated by comparison with the uniaxial tension test results of wet- and dry-cured (with volume contraction of concrete) RC prisms. Subsequently, different degrees of expansion strain were applied to the aggregate elements in the RC prism model and the uniaxial tension loading was simulated again. Tension stiffening decreased under larger radiation-induced volume expansion of the aggregate owing to the corresponding decrease in the concrete tensile strength with increasing damage, this behavior changed considerably according to the restraint condition. Indeed, the Young’s modulus of the restrained concrete after aggregate expansion was larger than that of the unrestrained concrete after aggregate expansion. However, the compressive stress in the concrete after aggregate expansion was effectively transmitted to the rebar during uniaxial tension loading; this behavior indicated that RC could maintain its integrity under uniaxial tension even after 0.5% aggregate linear expansion.

This study investigates the wet carbonation of concrete fines with CO₂ and natural air gas bubbling in a carbonation system at low temperatures. After the air- and CO₂-wet carbonations, the properties of a solution and hydrated cement paste powder are determined. In the air and CO₂-wet carbonations, more Ca is extracted into the solution at a low temperature of 5°C. This high Ca concentration in the solution through air-wet carbonation primarily originates from the portlandite and unhydrated phases of the cement paste. Even in solutions with high pH values, the rehydration process and C–S–H decomposition occur simultaneously in air-wet carbonation. Moreover, CO₂-wet carbonation indicates that the decalcification of C–S–H occurs rapidly, even in the presence of portlandite. Air-wet carbonation presents a potential method for the direct air capture of CO₂ using concrete waste fines in a short period.

The coefficient of thermal expansion (CTE) of cement paste is an essential parameter for estimating cracks of cement-based structures, including under normal operating conditions. The CTE of low-heat Portland cement pastes dried for a long term at various relative humidities were measured by applying trapezoidal temperature history. The measured CTE was a convex function when displayed versus relative humidity and was highest at the relative humidity of 58%. At the relative humidity of 11%, the CTE was similar to the one of the fully dried sample. Based on a drying shrinkage model in the literature that classifies pore water as free liquid water and adsorbed water, we computed pore pressure change and corresponding strain, from which the CTEs were estimated. The microstructural rearrangements of cement paste due to long-term drying were taken into account by obtaining pore size distributions from water vapor sorption isotherm. The CTEs predicted with the model agree well with the measured ones.