International Concrete Abstracts Portal

The heterogeneous pore structure and weak interfacial transition zones associated with reclaimed asphalt pavement (RAP) aggregates adversely affect the durability of cement concrete. This paper quantitatively evaluates the influence of aggregate packing on pore network characteristics and transport properties of RAP concrete. Concrete mixtures were proportioned using a conventional particle size gradation (PSG) method and a particle packing–based method (PPM). X-ray computed tomography was used to quantify pore structure and connectivity, while sorptivity, open porosity, ultrasonic pulse velocity, and electrical resistivity were measured to assess transport behavior. Compared to PSG mixtures, RAP concrete mixtures designed with the PPM approach showed a more refined pore network, shorter pore throats, and higher tortuosity due to better aggregate packing and reduced meso-scale pore connectivity. These microstructural changes resulted in significant reductions in sorptivity and open porosity, along with improved ultrasonic pulse velocity and electrical resistivity. The results demonstrate that packing-optimized mixture proportioning effectively mitigates transport-related durability concerns in RAP concrete.

While the layer-by-layer approach can accurately predict the moment-curvature (M-Phi) response of ultra-high-performance concrete (UHPC) beams, it is computationally intensive and cumbersome for designers. This study proposes a simplified equivalent rectangular stress-block method, aligning with conventional concrete design practices. The proposed method is validated using a database of 224 UHPC beams, including rectangular, T, and I-shaped sections, both prestressed and non-prestressed. The ratio of experimental to predicted moment capacities ranges from 0.95 to 1.13, with an overall average of 1.10 and a coefficient of variation of 16%, demonstrating good accuracy. Parametric analysis indicates that the maximum reinforcement ratio for singly reinforced UHPC beams ranges from 6 to 8%. To ensure ductile behavior and prevent compression-dominant failure in over-reinforced sections, it is recommended to provide compression-side reinforcement up to 50% of the area of primary tension reinforcement. The proposed approach offers a practical tool for UHPC flexural design suitable for researchers and practicing engineers.

This study investigates the shear behavior of 141 lightweight concrete (LWC) beams without stirrups that were tested and reported in the literature. The specimens had different types of reinforcement (such as basalt fiber-reinforced polymer, carbon fiber-reinforced polymer, glass fiber-reinforced polymer, steel reinforcement) and types of fiber inclusion (basalt fiber, glass fiber, polypropylene fibers, steel fiber). The test results demonstrated that the main governing parameter is the shear-span-to-effective depth ratio, a/d, whereby the beams with a/d ≤ 2.5 exhibited higher shear strength. Beams with a/d ≥ 3.0 exhibited flexure-dominated behavior and brittle shear failure. Increasing the longitudinal reinforcement ratio in the range of 0.5 to 2.5% enhanced the experimental shear strength owing to a reduction in crack widths and an increase in stiffness. Steel-reinforced beams outperformed fiber-reinforced polymer-reinforced beams due to the higher stiffness of steel. Fibers had a beneficial effect on shear performance; steel fibers enhanced the shear strength by up to 125%, whereas glass fiber and basalt fiber resulted in moderate improvements in the concrete shear capacity, and polypropylene fibers primarily increased the ductility. Consequently, the shear behavior in lightweight concrete beams is controlled by geometry, reinforcement ratio, stiffness, and fiber bridging.

In the seismic design of reinforced concrete (RC) bridge structures, torsion frequently occurs in piers and may degrade their effective stiffness. However, this effect is not explicitly considered in contemporary seismic design codes and the existing literature. To address this gap, this study utilizes a calibrated finite-element model to conduct a comprehensive parametric analysis, quantifying the impact of torsion on the effective stiffness of square RC piers under combined loading. The findings reveal a non-linear response: while effective stiffness remains stable or marginally increases at low torsion levels, it degrades significantly once the torsion ratio (T/Tu) exceeds 0.4–0.5. The rate of this degradation is primarily governed by the axial load ratio and the longitudinal reinforcement ratio. Furthermore, the sensitivity of effective stiffness to these design parameters, along with longitudinal reinforcement spacing, is highly dependent on the applied torsion level. Drawing on these results, this study proposes an empirical equation to predict a torsion-influence coefficient. This formulation facilitates the accurate estimation of effective stiffness for RC piers subjected to coupled bending and torsion, thereby enhancing the reliability of performance-based seismic design.

The national concrete building code ACI CODE-318-19 permits the use of mechanical splices for Grade 60 (420 MPa) bars in hinge regions, but not for higher grade bars due to concerns over ductility and fatigue performance under reversed cyclic loading in the inelastic range of behavior. This study evaluates the seismic performance of mechanical splices with Grade 80 (550 MPa) ASTM A706 longitudinal bars through full-scale testing of four concrete walls detailed to satisfy ACI CODE-318-19 requirements for special structural walls. Walls were tested under constant compressive axial load and reversed cyclic displacements until loss of lateral strength and instability. Mechanical couplers were placed at the base of the cantilever walls. Coupler types and the manufacturing process of the coupled Grade 80 (550 MPa) longitudinal reinforcing bars were varied. The low-cycle fatigue performance of mechanical splices in the walls was compared with that of nominally identical mechanical splices tested under reversed inelastic cycles in air. Mechanical splices exhibited similar fatigue performance trends in both in-air and in-concrete tests. Findings support the development of a new seismic category for mechanical splices, incorporating strain-based pre-qualification using a reversed inelastic cyclic protocol representative of seismic demands in hinge regions.