International Concrete Abstracts Portal

The interference between steel fiber and coarse aggregate reduces the homogeneity of fiber distribution and orientation, which may compromise the expected reinforcing effectiveness of steel fibers in concrete. Traditional destructive testing techniques constrain the quality control of steel fiber distribution in prefabricated concrete segments; developing an inductance-based technique contributes to non-destructive characterization of steel fiber distribution. This work uses a Helmholtz coil to solve the magnetic field non-uniform distribution, thereby designing an inductor device to improve the accuracy of steel fiber distribution monitoring within concrete. On this basis, a multi-parameter experiment was designed to study the coupling effect of coarse aggregate and steel fiber, with key variables including water-to-binder ratio, coarse aggregate gradation, steel fiber mixing sequence, vibration duration, and casting flow distance. The C50 concrete mixture incorporates fly ash (75 kg/m³) as a supplementary cementitious material to improve workability and particle packing density. The primary findings are as follows: the induction-based method enables non-destructive evaluation of steel fiber content and orientation in steel fiber‑reinforced concrete containing coarse aggregate (SFRC‑CA), demonstrating high detection efficiency. The larger the aggregate size and water-binder ratio, the worse the steel fiber distribution uniformity. Improper vibration will lead to steel fiber thickness-related settlement, while the longer the flow distances, the more uneven the orientation of the fiber. These results offer important reference for material design and quality control of precast SFRC-CA components.

For the assessment of existing reinforced concrete slab bridges, the shear capacity under concentrated loads and transition to flexural failure are under discussion. Previous research showed an increased shear capacity for slabs under concentrated loads close to the support, so that for assessment, positions farther from the support became governing. This experimental research studies the flexural and shear capacity of reinforced concrete slabs under concentrated loads. For this purpose, six slabs representing 1:2-scale continuous slab bridges were tested at various positions from the support and along the width. The results show two main failure modes: flexural failure (onset of yielding of the reinforcement), and shear failure. Secondary punching was observed as well. The comparison between the test results and calculation methods shows that all considered methods perform reasonably well when both shear and flexure are considered, and the effective width in shear is included, with average tested-to-predicted capacities between 0.92 (Regan’s method) and 1.39 (Extended Strip Model [ESM]) and coefficients of variation between 15% (Regan’s method) and 25% (ACI 318-19 and Eurocode 2). These insights can be used for the assessment of existing reinforced concrete slab bridges.

Research presented in this paper is part of a program investigating the durability of fiber-reinforced polymer reinforcement after exposure to a marine environment or elevated temperatures. This paper presents the results of an experimental study on the tensile behavior of basalt fiber-reinforced polymer (BFRP) bars after exposure to elevated temperatures under different heating protocols. Under the steady-state heating protocol, specimens were exposed to elevated temperatures up to 250°C (482°F) first and then subjected to monotonically increasing load until failure. In other testing protocols, specimens were exposed to a specific sustained stress level first, keeping deformation or load constant, and then heated until failure. Under these conditions, specimen stress levels varied from 39 to 91%. Results showed that different testing protocols yielded different results, and the criticality shifted between protocols depending on the stress level. Lastly, a direct comparison was made between BFRP and glass fiber-reinforced polymer (GFRP) bars tested under identical conditions. The direct comparison showed that thermal degradation of BFRP at higher stress levels was comparable with that of GFRP bars, whereas GFRP bars exhibited superior performance at lower stress levels.

The aging reserve of bridges in the United States needs load-rating assessments to ensure sufficient load-carrying capacity and safety. Bridges without sufficient capacity to carry the legal loads are load-posted. These load limits reroute traffic, which may result in traffic congestion and longer routes, and, thus impose inconvenience on travelers and significant costs to society. This paper investigates the potential for improvement in the load-rating process for simple-span concrete slab bridges. Such bridges are load-rated by the Texas Department of Transportation using simplified load-rating procedures, which are intended to be conservative and can have varying degrees of accuracy compared to the actual behavior of bridges. Finite element modeling was conducted to simulate the expected behavior of a representative concrete slab bridge, and the model was calibrated using experimental test data. The equivalent width results were compared with estimates from established design specifications and empirical guidelines. The methods developed for concrete slab bridges with integral curbs provided accurate estimates of moment demand for curb sections. In addition, an established analytical approach in the literature accurately predicted the moment demand for interior slab sections under one-lane loading, while the equations in current design specifications performed well for two-lane loading cases.

Prestressed hollow-core slabs (PHCSs) were extensively employed in residential construction in earlier decades, yet the extent of prestress loss in these aged structures that have experienced long-term service remains unquantified, despite its governing influence on structural performance. With the current emphasis on renovating aging residential areas, various retrofitting approaches were proposed to enhance loading capacities and extend service life; however, the long-term performance of such strengthened structures requires thorough investigation. This study examines five full-scale PHCSs through comparative experimental testing: two unstrengthened specimens, two carbon fiber-reinforced polymer (CFRP)-strengthened specimens, and one composite slab-strengthened specimen. A two-phase loading protocol, combining low-level cyclic loading and monotonic loading, is implemented to evaluate prestress loss and ultimate capacity. The experiment reveals an average prestress loss of 17.64%, and CFRP strengthening and superimposed strengthening yield immediate improvement of cracking load by 25% and 58%, respectively. The experimental results are validated by numerical simulations and compared with theoretical calculations specified in design codes. Furthermore, upon experimental and simulation results, a probability density evolution method (PDEM)-based approach is developed to assess time-dependent structural reliability, incorporating material degradation models and inherent uncertainties. The proposed methodology enables accurate estimation of prestress loss in aged PHCSs and systematically evaluates the long-term performance of different strengthening methods.