International Concrete Abstracts Portal

Infilled cementitious composite (ICC) is produced by infilling cementitious paste into a designed aggregate skeleton. This approach enables the incorporation of both coarse aggregate and fibers while maintaining adequate fresh and hardened performance at minimal paste volume. In this study, ultra-high-performance concrete (UHPC) pastes incorporating supplementary cementitious materials were infilled into fiber-aggregate skeletons (FAS) with macro steel fiber volumes ranging from 0 to 2.0%, yielding a total of 16 ICC mixtures. The FAS packing density, UHPC infilling ability, and the fresh, mechanical, and microstructural properties of both UHPC paste and the resulting ICC were evaluated. The 28-day compressive strength of ICC ranged from 96.0 (13.9 ksi) to 121.6 MPa (17.6 ksi), while the first-cracking flexural strength increased by up to 61.8% at a fiber volume of 2.0%. The cement content of ICC ranged from 229 to 1116 kg/m3 (14.3 to 69.7 lb/ft3). Relative to the corresponding conventional UHPFRC without coarse aggregate, ICC reduced material cost by up to 50% and embodied CO2 by up to 55%. These findings demonstrate that ICC can provide a low-carbon, material-efficient pathway for sustainable structural concrete.

This paper presents post-fatigue residual punching shear strength experiments of two identical sections reinforced by glass fiber-reinforced polymer (GFRP) rebar in a large bridge deck (15.24 m x 3.89 m x 0.21 m) supported by steel girders spaced at 3.05 m. The experiment was designed to isolate the influence of fatigue loading type on residual punching shear strength. The sections have experienced 3 million cycles of service loads, one using pulsating loads (PL) and the other using rolling loads (RL). Although the RL section suffered more stiffness degradation (71%) than the PL section (54%), both had comparable punching shear strengths (Vu), within 4%. Available equations, including ACI and CSA code regulations, underestimated Vu by 24-54% because they do not account for end restraints, which generate compressive membrane effects that significantly increase the punching shear capacity of concrete slabs. Nonlinear finite element analysis was conducted and used to examine interactions between multiple loading axles as well as offset of the loads from the center. Vu under 2 half axles spaced at 1.2 m (i.e., the 2 axles likely to interact in design truck CL-625 of the Canadian Highway Bridge Design Code) increases by only 34% compared to a single load.

Hollow concrete columns (HCCs) are an effective structural system in construction, offering high strength and stiffness while maintaining low self-weight. Limited research to date has focused on hollow square concrete columns reinforced with fiber-reinforced polymer (FRP) bars. This paper investigates the structural behavior of hollow square concrete columns (HSCCs) reinforced with glass FRP (GFRP) bars and ties under eccentric loading. Twelve hollow square reinforced concrete (RC) columns were cast with a square cross section of 400 x 400 mm and an inner circular hollow of 150 mm in diameter and 2000 mm in height. The tested specimens were divided into three groups based on the longitudinal reinforcement ratio (1.2%, 1.6%, and 2.9%). Each group consisted of four identical columns tested under four levels of eccentricity (e/h = 10%, 20%, 40%, and 80%) to investigate their influence on the structural behavior of the columns. The test results reveal that the eccentricity level had a more significant effect on the structural performance of these columns than the reinforcement ratio. The failure mode of the specimens tested under low eccentricity levels was compression-controlled, starting with concrete crushing. Contrarily, the failure mode of the specimens tested under high eccentricity levels was tension-dominated failure. Furthermore, increasing the eccentricity level from 10% to 20%, 40%, and 80% decreased the axial load capacity of the column by approximately 13%, 52%, and 80%, respectively. Lastly, increasing the reinforcement ratio enhanced the post-peak behavior of the columns. These findings offer critical insights into the structural behavior of hollow square concrete columns (HSCCs) reinforced with GFRP bars and are expected to guide design engineers and contribute significantly to North American standards and design guidelines for HSCCs reinforced with GFRP reinforcement.

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.