International Concrete Abstracts Portal

The present study demonstrates the feasibility of using longitudinal hybrid reinforcement in concrete columns in seismic zones. In this research, four concrete columns were constructed and subjected to quasi-static cyclic loading, featuring a combination of steel and glass fiber-reinforced polymer (GFRP) longitudinal reinforcement. Two reference columns were fabricated and reinforced in the longitudinal direction with steel bars. These columns had a 400 × 400 mm (15.8 × 15.8 in.) cross-section and 1850 mm (72.8 in.) overall height. All the columns were reinforced with GFRP crossties and spirals in the horizontal direction. The variable parameters were the transverse reinforcement spacing, axial load ratio, and column configuration. The outcomes of this research clearly showed that reinforced concrete (RC) columns that are properly designed and detailed longitudinally with hybrid reinforcement (GFRP/steel) could achieve the drift limitation in building codes with no strength degradation. Further, these hybrid-RC columns displayed enhanced energy dissipation capacity, superior ductility, and improved post-earthquake recoverability compared to columns reinforced longitudinally with steel. The promising results of this study represent a step towards the use of longitudinal hybrid reinforcement in lateral-resisting systems.

This study investigated the serviceability behavior and strength of polypropylene-fiber (PF) reinforced self-consolidating concrete (PFSCC) beams reinforced with glass fiber-reinforced polymer (GFRP) bars. Five full-scale concrete beams measuring 3100 mm long × 200 mm wide × 300 mm deep (122.1 × 7.9 × 11.8 in.) were fabricated and tested up to failure under four-point bending cyclic loading. Test parameters included the longitudinal reinforcement ratio (0.78, 1.18, and 1.66%) and polypropylene fiber (PF) volume (0, 0.5, and 0.75% by concrete volume). The effect of these parameters on serviceability behavior and strength of the test specimens is analyzed and discussed herein. All the beams were evaluated for cracking behavior, deflection, crack width, strength, failure mode, stiffness degradation, and deformability factor. The test results revealed that increasing the reinforcement ratio and PF fiber volume enhanced the serviceability and flexural performance of the beams by effectively restraining crack widths, reducing deflections at the service and ultimate limit states, and decreasing residual deformation. The stiffness exhibited a fast-to-slow degradation trend until failure for all beams, at which point the beams with a higher reinforcement ratio and fiber volume evidenced higher residual stiffness. The cracking moment, flexural capacities, and crack width of the tested beams were predicted according to the North American codes and design guidelines and compared with the experimental ones. Lastly, the deformability for all beams was quantified with the J-factor approach according to CSA S6-19. Moreover, the tested beams demonstrated adequate deformability as per the calculated deformability factors.

Noncorrosive fiber-reinforced polymer (FRP) reinforcement presents an attractive alternative to conventional steel reinforcement, which is prone to corrosion, especially in harsh environments exposed to deicing salt or seawater. However, FRP rebars’ lower axial stiffness leads to greater crack widths when FRP reinforcing bars elongate, resulting in significantly lower flexural stiffness for FRP-reinforcing bar-reinforced concrete members. The deeper cracks and larger crack widths also reduce the depth of the compression zone. Consequently, both the aggregate interlock and the compression zone for shear resistance are significantly reduced. Additionally, due to their limited tensile ductility, FRP reinforcing bars can rupture before the concrete crushes, potentially resulting in sudden and catastrophic member failure. Therefore, ACI Committee 440 states that through a compression-controlled design, FRP-reinforcing bar-reinforced concrete members can be intentionally designed to fail by allowing the concrete to crush before the FRP reinforcing bars rupture. However, this design approach does not yield an equivalent ductile behavior when compared to steel-reinforcing bar-reinforced concrete members, resulting in a lower strength reduction, ϕ, value of 0.65. In this regard, using FRP-reinforcing bar-reinforced ultra-high-performance concrete (UHPC) members offers a novel solution, providing high strength, stiffness, ductility, and corrosion-resistant characteristics. UHPC has a very low water-to-cementitious materials ratio (0.18 to 0.25), which results in dense particle packing. This very dense microstructure and low water ratio not only improves compressive strength but also delays liquid ingress. UHPC can be tailored to achieve exceptional compressive ductility, with a maximum usable compressive strain greater than 0.015. Unlike conventional designs where ductility is provided by steel reinforcing bars, UHPC can be used to achieve the required ductility for a flexural member, allowing FRP reinforcing bars to be designed to stay elastic. The high member ductility also justifies the use of a higher strength reduction factor, ϕ, of 0.9. This research, validated through large-scale experiments, explores this design concept by leveraging UHPC’s high compressive ductility, cracking resistance, and shear strength, along with a high quantity of noncorrosive FRP reinforcing bars. The increased amount of longitudinal reinforcement helps maintain the flexural stiffness (controlling deflection under service loads), bond strength, and shear strength of the members. Furthermore, the damage-resistant capability of UHPC and the elasticity of FRP reinforcing bars provide a structural member with a restoring force, leading to reduced residual deflection and enhanced resilience.

Portland cement has played a significant role in the construction of major infrastructure and building structures. However, in light of the substantial CO₂ emissions associated with its production, there is a growing concern about environmental issues. Accordingly, the development of eco-friendly alternatives is actively underway. Geopolymer represents a class of inorganic polymers formed via a chemical interaction between solid aluminosilicate powder with alkali hydroxide and/or alkali silicate compounds. Concrete made with geopolymers, as an alternative to Portland cement, generally demonstrates comparable physical and durability characteristics to ordinary Portland cement concrete (OPC). Research on the material properties of geopolymer concrete (GPC) has made extensive progress. However, the number of large-scale tests that were conducted to assess its structural performance is still insufficient. Additionally, there is a shortage of comprehensive studies that compile and analyze all the structural experiments conducted thus far to evaluate the GPC’s potential. Therefore, this study aimed at compiling and analyzing a number of bond, flexural, shear, and axial strength tests of GPC to assess its potential as a substitute for OPC and to identify its distinctive characteristics compared to OPC. As a result, it is considered that GPC can be used as a substitute for OPC without any structural safety issues. However, caution is needed in terms of deflection and ductility, and additional experiments are deemed necessary in the aspect of compressive strength of large-scale members.

The behavior of carbon fiber-reinforced polymer (CFRP) flexural strengthened reinforced concrete beams under reversed cyclic loading has not been sufficiently studied. In this paper, normal strength concrete is used, with a typical steel ratio (0.5%), to build full-scale rectangular beams strengthened on top and bottom with flexural unanchored and anchored CFRP sheets. Five identical beams were examined under fully reversed cycles up to failure following the AC 125 displacement loading protocol. The first beam was tested as an un-strengthened control specimen. The second and third beams were tested as strengthened specimens using thin sheets with and without fiber anchors. On the other hand, the fourth and fifth beams were tested when strengthened using thick sheets with and without fiber anchors. Specimens with thin sheets underwent higher ductility and lower hysteresis pinching relative to the thick ones. The results are comparatively discussed and compared to a phenomenological cyclic analysis model showing promising correspondence.