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 cement industry´s strategy in many countries is to reduce its CO2 emissions to diminish greenhouse effects. This strategy is to reduce these emissions by decreasing the clinker content in their new formulations, replacing it by using supplementary cement materials 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, defining as 15% the maximum allowable content as limestone cement (LSC). Nevertheless, in Latin America and other countries, this limestone filler content restriction is not that strict, allowing contents as much as 35%. This investigation includes experimental results obtained from Portland cement mortars where inert limestone fillers used were between 20% and 30% by clinker replacement, and only 24-hour curing was considered. Results obtained include mechanical (compressive strength), physical (electrical resistivity, total void content, capillary porosity), and chemical (carbonation after one-year natural exposure) performance of such mortars. The carbonation coefficients (kCO2) obtained after 1-year exposure in a natural urban environment were 17.3, 22.9, and 24.5 mm/y½ for 23%, 27%, and 29% LSCs, respectively. These results were comparable higher than typical kCO2 values of ~ 4 mm/y½ obtained from ordinary Portland cement-based mortars having 90 to 95% clinker content.

Crack densities obtained from on-site surveys of 74 bridge deck placements containing concrete mixtures with paste contents between 22.8% and 29.4% are evaluated. Twenty of the placements were constructed with a crack-reducing technology (shrinkage-reducing admixtures, internal curing, or fiber reinforcement) and 54 without; three of the decks with fiber reinforcement and nine of the decks without crack-reducing technologies involved poor construction practices. The results indicate that using a concrete mixture with a low paste content is the most effective way to reduce bridge deck cracking. Bridge decks with paste contents exceeding 27.3% had a significantly higher crack density than decks with lower paste contents. Crack-reducing technologies can play a role in reducing cracking in bridge decks, but they must be used in conjunction with a low paste content concrete and good construction practices to achieve minimal cracking in a deck. Failure to follow proper procedures to consolidate, finish, or cure concrete will result in bridge decks that exhibit increased cracking, even when low paste contents are used.