International Concrete Abstracts Portal

This study presents comprehensive investigations of the potential of uncalcined and calcined vanadium tailings (VT) for use as a supplementary cementitious material (SCM). The VT was calcined at 550, 650, 700, 750, and 850°C (1022, 1202, 1292, 1382, and 1562°F). The composition of uncalcined and calcined VT and dehydration and dehydroxylation processes was investigated. The effects of calcination on the mineralogical properties, molecular structure, and morphological characteristics of the VT were also investigated. The pozzolanic reactivity of uncalcined and calcined VT was evaluated using direct and indirect tests. Peaks associated with kaolinite were observed through thermal, mineralogical, and molecular analyses of the VT. Scanning electron microscope investigations of uncalcined and calcined VT revealed iron-rich aluminosilicate platelets. Calcination enhanced the pozzolanic reactivity of VT. The VT calcined at 700°C (1292°F) exhibited the highest pozzolanic reactivity, evidenced by the highest degree of dehydroxylation, the highest chemically bound water content, and a strength activity index approximately 35% higher than that of uncalcined VT.

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.

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 318-19, CSA A23.3-24, CSA S806-12, and 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 (glass fiber-reinforced polymer [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 (0.008Ef for spirals), outperformed other codes, aligning with approximately 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 (Mmax/Mo) 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 substantial increase in moment capacity (Mmax) compared to the unconfined nominal moment capacity (Mo) due to delayed bar buckling under effective confinement. However, columns with GFRP longitudinal bars observed a softer response, and the determination of the probable moment to calculate the shear demand remains questionable and requires more analytical investigations.

An experimental study was conducted to compare the long-term performance of two partially prestressed concrete (PC) beams reinforced with either bonded carbon fiber-reinforced polymer (CFRP) tendons (CFRP-PC) or steel strands (steel-PC) under 1200-day sustained loading. The deflections increased rapidly during the first 200 days and then at a slower rate. The final-to-initial deflection ratio was 1.58 for the CFRP-PC beam and 1.45 for the steel-PC beam. The final-to-instantaneous maximum crack-width ratio was approximately 2.00 for both beams. Based on the age-adjusted effective modulus method (AEMM), a finite element analysis (FEA) program was developed and calibrated using the experimental results. Parametric simulations were subsequently performed on 14 beams. A modification of the suggested equation in ACI 440.1R-15 was proposed to predict the time-dependent deflection of PC beams, which exhibits an improved correlation with the experimental results as compared to the design standards.

This study investigates the bending performance of fiber-reinforced cementitious composite (FRCC) beams reinforced with fiber-reinforced polymer (FRP) bars through experimental and analytical programs. A one-sided cyclic bending test with controlled displacement for polyvinyl alcohol FRCC (PVA-FRCC) beams reinforced with aramid FRP and aramid FRCC (A-FRCC) reinforced with carbon FRP and section analysis were conducted. Both beams were designed primarily to fail in compression to avoid brittle failure due to FRP rupture. The load capacity of A-FRCC beams is found to be higher than that of PVA-FRCC beams. Both specimens showed ductile behavior after the peak. Compression tests of rectangular columns were also conducted to determine the section reduction factors compared to the cylindrical compression test. Using Popovics’ model on the compression side and tensile stress-crack width relationship on the tension side, the stress-strain relationships for the FRCCs are developed. The adaptability of the models is checked by section analysis, and it showed good agreement with bending test results.