International Concrete Abstracts Portal

This study evaluates the seismic performance of circular columns reinforced with fiber-reinforced polymer (FRP) bars, focusing on the efficacy of existing code provisions (ACI CODE-318-19, CSA A23.3-24, CSA S806-12, CSA S6-25) in predicting drift and moment capacities. A database of 38 full-scale columns tested under lateral cyclic loading with varying axial load levels, spiral pitches, and reinforcement types (GFRP/steel longitudinal bars) was analyzed to assess code provisions, confinement effectiveness, and strength enhancements. Results demonstrate that CSA S6-25, which incorporates updated FRP compressive strain limits (0.008E_f for spirals), outperformed other codes, aligning with about 85% of experimental data in ideal performance quadrants. Close spiral pitch (≤ 75 mm [2.95 in.]) and low axial loads were critical to achieving drift ratios ≥3% and moment capacity ratios (M_max/M_o) exceeding 2.0. Replacing steel spirals with GFRP spirals did not result in substantial variation in the seismic performance of columns. Columns with GFRP longitudinal bars exhibited comparable ductility and observed a substantial increase in moment capacity (M_max) compared to unconfined nominal moment capacity (M_o) due to delayed bar buckling under effective confinement. However, columns with GFRP longitudinal bars observed a softer response, and the determination of probable moment to calculate the shear demand still remains questionable and requires more analytical investigations.

To address the autogenous shrinkage issue of ultra-high-performance concrete (UHPC), internal curing technology has shown great potential in resolving this challenge by providing additional moisture. To further improve its curing efficiency, this study proposes an innovative internal curing technology that can significantly reduce autogenous shrinkage without increasing the amount of internal curing water or compromising mechanical strength. This approach utilizes perforated cenospheres (PCs) as internal curing agents while substituting internal curing water with urea solutions. In addition to replenishing water, urea solutions, once released into the cement paste, can react with portlandite. This reaction generates CaCO₃; owing to the intrinsic properties of CaCO₃, it has a larger macroscopic volume and a much higher elastic modulus than portlandite. This approach effectively reduces chemical shrinkage while concurrently increasing the stiffness of the cement paste, thereby achieving a significant reduction in autogenous shrinkage. As a result, replacing water with 3% urea solution in PCs enhances the autogenous shrinkage of UHPC, reducing it from less than 50% to over 90%.

The cement industry’s strategy in many countries is to reduce its CO2 emissions to diminish the greenhouse effect. This strategy aims to reduce these emissions by decreasing the clinker content in their new formulations, replacing it with supplementary cementitious materials (SCMs) or inert fillers. One of the most-used additions in Latin America’s cement industry is inert limestone fillers, which is the most inexpensive one. In North America, there are restrictions on using this inert addition in portland cement, with a maximum allowable content of 15% as limestone content (LSC). Nevertheless, in Latin America and other countries, this limestone filler content restriction is not as strict, allowing contents of up to 35%. This investigation includes experimental results obtained from portland cement mortars where inert limestone fillers were used at a replacement level between 20 and 30% by clinker, and only 24-hour curing was considered. Results obtained include mechanical (compressive strength), physical (electrical resistivity, total void content, and capillary porosity), and chemical (carbonation after 1 year of natural exposure) performance of such mortars. The carbonation coefficients (kCO2) obtained after 1 year of exposure in a natural urban environment were 17.3, 22.9, and 24.5 mm/y1/2 for 23%, 27%, and 29% LSCs, respectively. These results were higher than typical kCO2 values of approximately 4 mm/y1/2 obtained from ordinary portland cement (OPC)-based mortars with a 90 to 95% clinker content, and standard 28-day water curing.

During past earthquakes, failures of beam-column joints have commonly been observed on the exteriors of buildings. However, only one side of these joints can be retrofitted because of the presence of beams on the other three sides. Therefore, this study aims to test four exterior beam-column joints with transverse beams, leaving the rear side as the only viable location for placing fiber-reinforced polymer (FRP) laminate. All four test specimens were designed with insufficient joint shear strength, as determined by ACI 318-19 equations, while satisfying the criteria for a strong-column/weak-beam mechanism and sufficient development length for bar anchorage. A total of two un-retrofitted specimens, with and without joint hoops, were constructed as controls. Subsequently, two similar specimens were retrofitted by applying FRP laminate on the rear side. The results show that sufficient FRP laminate can enhance the seismic performance of joints in terms of deformability, energy dissipation, and failure delay.

This study focuses on enhancing the durability of two-component grouting materials by incorporating ground-granulated blast- furnace slag (GGBFS) and replacing cement with industrial waste to reduce environmental pollution. A ternary cementitious system was developed using 30% GGBFS and 10% carbide slag (CS) as partial cement replacements. The research investigates the effects of different water-bentonite ratios, water-binder ratios (w/b), and A/B component volume ratios on the physical and mechanical properties of the grout, including density, fluidity, bleeding rate, setting time, and strength performance. The microstructural evolution and hydration products were analyzed using scanning electron microscopy (SEM), X-ray diffraction (XRD), mercury intrusion porosimetry (MIP), and thermogravimetric analysis (TGA). The findings provide insights for optimizing the mixture design of grouting materials in shield-tunneling applications, with a focus on improving performance and sustainability.