International Concrete Abstracts Portal

Reinforced concrete (RC) members undergoing shrinkage are susceptible to cracking when restrained; however, studies on this behavior are limited. Thus, the main objective of this paper is to present crack-widths, crack-patterns, and shrinkage strains from an experimental study on three RC walls with aspect ratios of 3.26 and 1.08, and horizontal reinforcement ratios of 0.2% and 0.35%, as well as a rectangular tank with 0.24% reinforcement. A 3-D nonlinear finite element (FE) analysis is conducted, and the results reveal that although the model predicts strains and maximum crack-widths reasonably well, the crack-pattern differs from the experiments. The possible reasons for this difference are discussed, and a parametric study is done to propose design equations to estimate restraint factors along the wall centerline for different aspect ratios. These equations can be used to estimate the cracking potential in the design stage without the need for a nonlinear FE analysis. For L/h above four, horizontal reinforcement has a negligible effect on the restraint, and for L/h above eight, full-height cracks can be expected due to almost uniform restraint. Finally, the design codes are compared, and it is found that ACI 207.2R-07 and CIRIA C766 predict shrinkage-induced crack-widths conservatively and reasonably accurately.

The aim of the current research is to investigate the distinctive geometry of deep box girders under horizontal curvature. Six specimens were cast and tested to investigate the effect of both web and flange thickness and section height under horizontal curvature conditions. It was found that when using strut and tie modelling (STM) as is, i.e., with the struts passing through both box girder webs, the results differed from the experimental data by 45 to 53%. However, when the STM was modified to include the influence of both flanges and the counteracting torsional shear resulting from the horizontal curvature on both webs, the results of the STM aligned more closely with the experimental results, reducing the difference to 7 to 32%. The shear generated by torsion had a minimal effect compared to the conventional shear, particularly due to the box girder’s geometry, especially when its span-to-effective depth ratio is low.

The challenges of deterioration and increasing maintenance costs in steel-reinforced concrete railway sleepers emphasize the urgent need for innovative, durable, and sustainable alternatives. This study evaluated the shear strength of precast concrete sleepers prestressed with basalt fiber-reinforced polymer (BFRP) rods, using normal self-consolidating concrete (NSCC) and fiber-reinforced self-consolidating concrete (FSCC). Seven full-scale specimens, each 2590 mm (8 ft, 6 in.) in length and prestressed to 30% of the tensile strength of BFRP rods in accordance with the Canadian Highway Bridge Design Code (CHBDC), were tested to assess cracking loads, ultimate strength, bond behavior, and failure mechanisms. All tests were conducted in accordance with the American Railway Engineering and Maintenance-of-Way Association (AREMA) guidelines. The results indicate that all specimens met AREMA design load requirements without visible cracks or slippage based on a train speed of 64 km/h (40 mph), annual traffic of 40 MGT (million gross tons), and sleeper spacing of 610 mm (24 in.). Comparative analysis using CSA S806-12 (R2021) design standard and ACI 440.4R-04 (R2011) design guide revealed that predictions based on CSA S806-12 (R2021) were less conservative than those from ACI 440.4R-04 (R2011) for the shear strength of BFRP prestressed sleepers. The BFRP rods exhibited excellent tensile performance, with minimal prestress losses, and their sand-coated surface ensured efficient load transfer by preventing slippage and enhancing the bond strength. FSCC specimens demonstrated delayed cracking, enhanced crack control, and ductility compared to NSCC specimens. These findings highlight the potential of BFRP prestressed concrete sleepers, particularly when combined with FSCC, as a sustainable solution for railway infrastructure, emphasizing the need for a design code refinement for BFRP applications.

The production of Ordinary Portland Cement (OPC) is a major contributor to carbon emissions. One immediate and viable solution is the use of optimized concrete mixtures that employ a decreased quantity of cement and increased dosage of high-range water-reducing (HRWR) admixtures. This study investigates five different concrete mixtures with varying w/c (0.37 to 0.42) and reduced cement contents. The mixtures with “low cement + high dosage HRWR admixture” content had over 30% increase in mechanical strength and presented 40% lower water absorption, and 68 to 97% higher formation factor, indicating enhanced durability. The optimized concrete mixtures with reduced cement and lower w/c have a service life increase of up to 117% and a life-cycle cost reduction of 29%. The application of “low cement + high dosage HRWR admixture” mixtures can improve the sustainability of concrete mixtures by reducing cement and water contents and increasing the service life of concrete in severe environments.

Corrosion in reinforcing steel bars is a critical factor influencing the durability and structural performance of reinforced concrete structures. This paper investigates the effects of corrosion on the mechanical properties of thermo-mechanically treated steel bars. The study parameters included bar diameter, corrosion technique, and varying corrosion levels (CLs). The impressed current technique was used to accelerate corrosion. Load-displacement data from uniaxial tensile tests were analyzed to determine stress-strain relationships of corroded bars. The results showed that the mechanical properties of the bars were unaffected by diameter or corrosion technique. However, a consistent reduction in both nominal yield strength and ultimate strength was observed with increasing CLs, while the elastic modulus remained unchanged. The strength factors for yield strength and ultimate strengths of the corroded bars varied in the range of 0.0013 to 0.015 and 0.0032 to 0.012, respectively, which were higher than reported in the literature. The fracture strain of the bars decreased at higher CLs. Predictive models were developed to estimate the residual mechanical properties, which are crucial for defining the constitutive relations needed to determine analytical stress-strain behavior. Analytical methods for determining these constitutive relations were also proposed, showing a good correlation with the experimental stress-strain curves.