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.

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 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.

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 theory of ionic diffusion in water-saturated porous solids with surface electric charges has been constructed by using the general theory of diffusion, Gauss’s law, and the condition of electrical neutrality. The theory derives the diffusion rate of ions not from the gradient of the ionic concentration but from the gradient of the chemical potential of ions. The chemical potential is obtained by rigorously solving the Poisson-Boltzmann equation that is derived by connecting the general theory of diffusion and the condition of electrical neutrality with Gauss’s law. Application of the theory to the ionic diffusion from an outer solution into a pore solution surrounded by two parallel charged plates indicates that the maximum concentration of ions penetrable into the pore solution is lower than that of the outer solution, though the penetration rate is not much affected by the surface charge. A simple approximation method of calculating the diffusion rate without solving the Poisson-Boltzmann equation is presented.