Reinforced concrete (RC) structures are among the most prevalent in the construction industry. However, various in-service conditions such as loading, environmental exposure, and construction practices can lead to the formation of concrete cracks. In extreme cases, these cracks may propagate through the cross-section of structural members, creating section pre-cracks. This study examines the influence of section pre-cracks on the shear failure behavior of RC deep beams (with a shear span-to-depth ratio of 1.57) through three-point bend-loading tests and 3D RBSM analysis. The primary experimental variables include the number of pre-cracks (one or two) and their width (0.5 mm or 1.0 mm). The findings reveal that pre-cracks significantly reduce the initial stiffness and shear strength of deep beams, primarily by disrupting the transmission of axial compressive stress in the concrete, thereby diminishing the contribution of arch action to shear strength. Furthermore, it is observed that the greater the total width and number of pre-cracks, the more significant the reduction in shear strength. In addition, combining both experimental tests and numerical simulations, a total of 48 deep beams were subjected to shear failure tests. Based on the shear strength data, two degradation models for shear strength (one representing the average trend and the other a conservative lower-bound envelope model) were developed in relation to the total crack width.

Cementitious coatings are used to treat concrete structures as they retard the ingress of harmful liquids and gases as well as adhere to the substrate functioning homogeneously to resist external loads. This research presents a valuation study of the influence of polymer cement mortar (PCM) as a treatment for concrete surfaces. The adhesion strength, water permeability, chloride ion penetration, and accelerated carbonation experiments were conducted on cement mortar coatings with 0%, 3%, 6%, and 9% polymer additions by weight of cement. The polymer in this study is a terpolymer of vinyl acetate, vinyl versatate, and acrylic ester (VA-VV-Ac) and the cement is Blast Furnace Slag Blended Cement (BFSC). The results reveal that VA-VV-Ac PCM coatings maintain high adhesion strength after exposure to cyclic thermal loading compared to the non-polymer sample. Moreover, adding the terpolymer led to increased hydrophobicity and resistance to carbonation and chloride ions. The microstructure analysis using SEM and digital microscope images uncovered that PCM has a smaller large void ratio and fewer cracks at the sand-cement paste transition zones.

This study aims to investigate the effect of nitrite/nitrate-based antifreeze agent solution (CN45) on the early hydration of early-strength cement mortar under low-temperature conditions. The performance of CN45 under two different low-temperature environments was discussed. The results show that the optimal antifreeze effect is achieved with 5.72% of CN45 at −5 °C. Additionally, the antifreeze effect is temperature-dependent. At 0 °C, considering cost factors, there is no need to add antifreeze to meet the engineering requirements. CN45 mitigates the hydration delay caused by low temperatures by accelerating the hydration of C₃S and βC₂S, thereby improving early compressive strength. These findings provide theoretical support for the use of CN45 in high-early-strength cement applications in cold environments.

The spatial distribution of aggregate particles was evaluated using conventional stereological procedures and point process statistical analysis for two-dimensional concrete sections. First, the influence of the image resolution on evaluation results was assessed, and the representative volume element and the image resolution necessary for accurate measurements were determined. Next, the interparticle spacing and paste–aggregate proximity were characterized using the mean free distance and spherical contact distribution function of the aggregate particles. These distances were discussed in relation to the likelihood of the presence and connectivity of interfacial transition zones (ITZs) formed in the vicinity of the aggregate particles. The size of the representative volume element used for evaluating the interaggregate distance was approximately comparable to the maximum aggregate size when the image file size was fixed. The common feature of the aggregate distribution was a random mixture of small aggregate particles and slightly smaller cement grains. The random mixture naturally produced clustered and sparse regions simultaneously comprising small aggregates and cement grains. The characteristic spatial structure derived from the actual distribution of aggregates differed considerably from that generally assumed for ITZs and their percolation. The method employed in this study provides the actual interaggregate distance and suggests the presence of porous regions throughout the cement paste matrix, and not just in the ITZs.

Mechanisms of rebar corrosion in reinforced concrete structures are to be clarified, as it significantly affects long-term structural durability. Among various causes of corrosion, moisture plays a primary role of deterioration by promoting electrochemical reactions in embedded rebar. Here, to grasp spatially and temporally moisture distribution within cementitious materials is a key issue for durability assessment and maintenance planning in reinforced concrete structures. Consequently, an application of Electrical Impedance Tomography (EIT) to monitoring moisture in cement-based materials is studied. The distribution of moisture was manipulated by varying the location and size of the water reservoir, as well as the ambient temperature. The EIT system successfully visualizes conductivity changes associated with moisture diffusion, and the reconstructed images show good agreement with discolored areas caused by water penetration. It is also found that potential difference data could estimate moisture content. Some limitations in spatial resolution are observed, particularly for regions farther from the electrodes, due to the diffusive nature of the electrical current in EIT. These results state the potential use of EIT for moisture monitoring in cementitious materials, while further study must be addressed for practical field applications.