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 three-dimensional (3-D) nonlinear finite element analysis (FEA) 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 FEA. For length-to-height ratio (L/h) above 4, horizontal reinforcement has negligible effect on the restraint, and for L/h above 8, 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 and CIRIA C766 predict shrinkage-induced crack widths conservatively and reasonably accurately.

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 million gross tons (MGT), and sleeper spacing of 610 mm (24 in.). Comparative analysis using the CSA S806 design standard and ACI 440.4R design guide revealed that predictions based on CSA S806 were less conservative than those from ACI 440.4R 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 design code refinement for BFRP applications.

Industrial facilities (such as offshore platforms, power plants, and treatment plants) are typically labyrinthine structures because they possess intricate layouts (resembling mazes or labyrinths), and most of their structural walls are interconnected. These reinforced concrete (RC) structural walls need to be designed for eight simultaneous demands. The existing U.S. codes provide limited procedural guidance for the design of these walls. A novel panel-based ACI (PACI) design approach for RC walls, rooted in the design concepts and formulations of ACI 349 and ACI 318.2, is proposed. The PACI approach is validated using two validation and verification (V&V) approaches. For the first V&V approach, existing experimental data is used to estimate PACI approach-based reinforcement areas, which are then compared against the reinforcements provided in the experiments (and against the reinforcement areas suggested by the Eurocode 2 [EC2] sandwich model approach). Benchmarked numerical models are developed to compare the capacities of specimens using PACI-based reinforcements with experimentally observed capacities, and with EC2-based reinforcement. For the second V&V approach, analytical data of publicly available design demands for real-world structures are used to estimate PACI-based reinforcements for a critical region of a nuclear power plant. Numerical models are developed to compare the capacities of the panels with PACI-based reinforcements against the design demands. The results from V&V1 approach showed that the PACI approach: 1) suggests similar reinforcement areas than those used in the experiments, with an average ratio of PACI suggested reinforcement areas over experimental provided areas of 0.97 for all 21 tests; and 2) suggests similar reinforcement areas that those suggested by the EC2 approach, with an average ratio of EC2-based reinforcement areas over PACI-based reinforcement of 1.01 for all 21 tests as well. For the V&V2 approach, the numerical capacities of the models with PACI suggested reinforcements are greater than or equal to the design demands. The V&V studies illustrate that, despite its methodological simplicity, the PACI approach results in reinforcement recommendations that closely approximate the outcomes derived from the more rigorous procedures inherent to the EC2 approach. The design implementation of the PACI approach is also illustrated using sample calculation.

Inverse analysis methods proposed by current standards for extracting the tensile properties of tension-hardening cementitious materials from indirect tension tests (for example, flexural prism tests) are considered either cumbersome and can only be performed by skilled professionals or apply to certain configuration and specimen geometries. Significant discrepancies are reported between the results of direct tension (DT) tests and inverse analysis methods. This has eroded confidence on flexural tests as a method of characterization of tension-hardening ultra-high-performance concrete (UHPC) and has motivated its abandonment in favor of DT testing. Additional concerns are size sensitivity, variability, and lack of robustness in the results of some methods. However, DT tests are even more difficult to conduct and results are marked by notable scatter. This is why some codes allow for bending tests at least for quality control of UHPC. To address the limitations of the bending tests in providing an easy and quick method for reliable estimation of the tensile characteristic properties of UHPC, a new practical method is developed in this paper based on a forward analysis (FA) of third-point bending tests. A unique aspect of the approach is that it considers the nonlinear unloading that occurs in the shear spans of the prism after strain localization in the critical region. The method was used to derive charts for direct estimation of the tensile properties from quality control bending tests, for the commonly used flexural specimen forms and material types. The goal of the study is to provide a practical alternative in characterization of tension-hardening UHPC materials. Results obtained using the proposed FA method are in good agreement with the tensile response from DT tests. However, it is noted that due to the presence of a strain gradient in bending tests and the larger strain gauge lengths employed in some DT tests, the strain values at localization from DT tests tend to be more conservative.

A slag-based zero-cement concrete (ZC) was newly developed as an alternative, eco-friendly material to Portland cement concrete. To investigate the bond performance between ZC and steel reinforcing bars, lap splice tests were conducted for ZC beams. Fourteen beams (two cementitious normal concrete (NC) beams and twelve ZC beams) were tested at the ages of 6 days (45 MPa (6.53 ksi)) and 28 days (60 MPa (8.7 ksi)). For steel reinforcement, Grade 600 MPa (87.0 ksi) reinforcing bars were used. The test parameters included the concrete type, concrete strength (i.e., concrete age), reinforcing bar diameter, concrete cover thickness, ratio of actual lap splice length to required lap splice length, and use of stirrups. The test results showed that the performance of ZC beams was comparable to that of the counterpart NC beams in terms of moment–deflection relationship, damage mode, and reinforcing bar stress at the peak load. This result indicates that the bond performance of ZC was equivalent to that of NC with identical compressive strength. The bar development length specified in current design codes safely predicted the reinforcing bar stress of the ZC beams at failure: current design codes are applicable to the reinforcing bar development length design of ZC members.