International Concrete Abstracts Portal

This paper investigates the significance of thermal diffusion on chloride diffusion in concrete under high ambient temperature in arid climates. Of particular interest is to study the effects of silica fume (SF) and ground granulated blast furnace slag (GGBS) on chloride penetration into concrete subjected to temperature gradient conditions. This was achieved by making three sets of concrete samples—the control samples, the samples containing 5% SF, and the samples containing 5% SF and 50% GGBS. These samples were exposed to a NaCl environment under isothermal and thermal gradient conditions. The total and free chloride contents of the exposed samples were determined via potentiometric titration. The total chloride concentration of the samples exposed to thermal gradient conditions could be 1.3–6 times higher than those exposed to isothermal conditions at the same temperature. The addition of SF and GGBS yielded significantly lower total and free chloride contents than the control samples under isothermal and thermal gradient conditions. While thermal gradient significantly reduces the chloride binding capacity, adding SF and GGBS increases this ability. SEM analysis revealed microstructural changes in concrete due to high temperature and thermal gradients, with larger and deeper pores in samples exposed to thermal gradient. Numerical estimation of chloride concentration and the corrosion initiation time of a reactor containment building was also performed using the modified chloride diffusion equation, including the effects of mass- and thermo-diffusion.

Fabric-reinforced cementitious matrix (FRCM) technology has emerged as a promising solution for the reinforcement of existing buildings, particularly in seismically active regions. This paper presents a comprehensive review of experimental research methods focusing on the seismic performance of masonry-infilled reinforced concrete (RC) frames retrofitted with FRCM. Drawing on a wealth of literature from various regions, this review synthesizes advancements in FRCM technology, experimental techniques, and theoretical frameworks. Key aspects explored include material properties testing, bond behaviour between fabric and matrix, and the seismic behaviour of masonry-infilled RC frames. Additionally, the significance of in-plane and out-of-plane behaviours is discussed, highlighting the importance of comprehensive testing methodologies. This paper also examines advancements in experimental equipment, such as shake tables, underscoring their pivotal role in simulating realistic seismic conditions. Overall, this review provides a systematic foundation for further research on the efficacy and potential of FRCM technology in structural reinforcement, contributing to the ongoing discourse in seismic engineering and retrofitting strategies.

The changes of the microscopic pore structure for concrete under cyclic axial compression accelerate chloride-ion penetration, reducing the durability of concrete structures. To address this, a chloride-ion migration experiment for concrete was conducted under cyclic axial compression, and the pore structure and pore group content of concrete were quantitatively characterized through equilibrium moisture content testing. In addition, a multiscale theoretical model for the chloride-ion diffusion coefficient in concrete was established based on the multiphase sphere model. The results show that cyclic loading forms an open hysteresis loop in the concrete's stress–strain curve, which evolves in the direction of increasing strain. Under loading, the microscopic pore structure of concrete coarsens, with an increase in the proportion of large capillary pores and gel pores, and a decrease in the proportion of small capillary pores. The model demonstrates good applicability when the chloride-ion diffusion coefficient is less than 22 × 10–12 m2/s. The model analysis indicates that the influence of cyclic axial compression loading on chloride-ion diffusion coefficient is more pronounced when the initial porosity ranges from 0.1 to 0.3. In addition, the more complex the microstructure of the concrete, the less its chloride-ion diffusion coefficient is affected by load-induced damage. At the same DI/Dm ratio, Dc/Dm gradually decreases with increase the volume fraction of coarse aggregates, but when DI/Dm reaches 15, the variation of Dc/Dm becomes negligible, approximately equal to 0.86. This indicates that when the ITZ exhibits a higher porosity content, the increased availability of chloride-ion transport pathways counteracts the blocking effect of coarse aggregates on chloride ions.

This study investigates the impact of innovative diatom and cyanobacteria strains at varying concentrations on microbe concrete. The study examines the behavior of two separate species of microalgae, specifically diatom (Fragilaria sp. CCAP1029) and Synechocystis PCC 6803 cyanobacteria, on concrete. The study confirmed that bio-concrete has greater strength than conventional concrete across all concentrations. The specimens containing Synechocystis PCC 6803 demonstrated a significant enhancement in compressive strength and splitting tensile strength, with a rise of 21.66% and 10.34%, respectively. Furthermore, utilizing all the introduced microalgae significantly reduced the corrosion rate of non-accelerated samples. Additionally, the analysis (SEM and EDX) revealed the existence of microbiological calcite precipitation within the concrete’s pores. The study’s findings emphasize the effectiveness of the introduced microorganisms in enhancing and improving the mechanical properties and encourage crack healing in microbial concrete.

This research investigates the flexural performance of strengthened rubberized concrete beams via bottom, side, and hybrid near-surface mounted (NSM) approaches using GFRP/steel rebars. Eleven strengthened specimens, alongside one control, were subjected to four-point loading setup till failure. The investigation focused on three key parameters: strengthening technique (bottom, side, or hybrid), NSM bar area, and bar type (GFRP or steel). The results revealed significant improvements across various performance metrics. It was demonstrated that NSM strengthening enhanced the beam’s cracking loads by up to 90%. Correspondingly, the strengthened beam’s yield and ultimate loads witnessed enhancements up to 48% and 79%, respectively. Notably, the load-carrying ability of GFRP bars consistently outperformed steel bars. Additionally, increasing the quantity of NSM strengthening proved beneficial, with bottom placement offering a slight advantage due to a larger internal lever arm. The proposed hybrid NSM technique, employing three 8-mm-diameter GFRP bars, emerged as the most effective strengthening scheme. However, utilizing four bars resulted in decreased effectiveness due to overlapping tensile stresses and accelerated debonding failure. Finally, the experimental results were compared to analytical predictions, with close agreement observed. The experimental-to-predicted analytical result ratio varies from 0.84 to 1.01%, indicating the validity of the analytical approach.