International Concrete Abstracts Portal

Geopolymer, an inorganic polymer material, has recently gained attention as an eco-friendly alternative to Portland cement. Numerous studies have explored the potential of geopolymer as a primary structural material. This study aimed to examine the efficacy of geopolymer composites as repairing and strengthening materials rather than as structural materials. We collected and analyzed data from 782 bond strength tests and 164 structural tests including those on beams, beam-column connections, and walls. The analysis focused on critical factors affecting the bond strength of geopolymer composites with conventional cementitious concrete, and the structural behaviors of reinforced concrete members repaired or strengthened with these composites. Our findings highlight the potential of geopolymer composites for enhancing the resilience and toughness of existing damaged or undamaged concrete structures. Additionally, they offer valuable insights into the key considerations for using geopolymer composites as repair or strengthening materials, providing a useful reference for future research in this field.

ACI 318 permits the use of mechanical couplers for Grade 60 (420 MPa) bars in hinge regions, but not for higher-grade bars. This restriction was introduced due to limited testing of mechanical couplers under inelastic strain demands and is hindering the use of higher-grade bars in seismic regions. Eleven mechanical couplers splicing Grade 80 (550 MPa) bars through varying connection details were tested in a uniaxial testing machine to evaluate their performance compared to bare bars under reversed cyclic inelastic strain demands, akin to those experienced in hinge regions of special seismic systems. The low-cycle fatigue life of coupled subassemblies is compared to those of the bare bars tested under the same loading protocol. Results indicate that some coupled bars can have equivalent fatigue life to the bare bars, while others can have substantially reduced fatigue life. A qualification test is proposed to qualify mechanical splices for use in seismic hinge regions of special concrete systems.

This research aims to investigate cyclic responses of axially restrained diagonally reinforced coupling beams, where the applied axial force was proportional to the beam axial elongation. Six diagonally reinforced concrete coupling beams with an aspect ratio of 2.0 were tested under reverse cyclic displacements. The key test parameters included the magnitude of axial restraint and shear stress demand. The test results showed that the specimen deformations were primarily attributed to the beam end rotation. Specimen peak strength, which increased as the axial restraint was applied, can be reasonably estimated using probable flexural strength at the beam ends where the axial restraint force was considered. All specimens exhibited a minimum of 6.0% chord rotation prior to failure, and the failure mechanism was associated with the damage at beam ends and reinforcement anchorage. The ultimate chord rotation capacity, shear rigidity, and flexural rigidity of the specimens were found to be insensitive to both shear stress demand and the magnitude of axial restraint. Axially restrained specimens showed significantly reduced axial elongation compared to those without axial restraint. The axial elongation of specimens without axial restraint can be adequately estimated using existing models. Analysis indicated an average flexural and shear rigidity of 0.13E_cI_g and 0.41G_cA_g, respectively, for all tested specimens.

Interface shear transfer is vital to maintain the structural integrity of concrete composite elements. Therefore, shear connectors are provided at the concrete joint interface to maintain such integrity. Due to its high tensile strength and non-corrodible nature, glass fiber-reinforced polymer (GFRP) reinforcement can be used as shear connectors in composite elements, particularly those in harsh environments. Fifteen pushoff specimens were constructed and tested to failure. The specimen consisted of two L-shaped concrete blocks cast at two stages to provide the cold joint interface. The test parameters were the type, shape, and ratio of shear-friction reinforcement and concrete strength. It was demonstrated that GFRP-reinforced concrete (RC) specimens with reinforcement ratios of 0.36% or more could resist the shear-friction stresses similarly to their steel-RC counterparts. Also, increasing the concrete strength increased the shear-friction capacity significantly. Moreover, the design model in the Canadian Highway Bridge Design Code resulted in very conservative predictions.

For the past several decades, there has been an ongoing academic challenge to understand the shear-transfer mechanism in reinforced concrete (RC) members, particularly in those with small shear span-depth ratios, also known as deep beams. Analytical uncertainty regarding shear strength inevitably increases when those deep members are strengthened in shear using externally bonded fiber-reinforced polymer (FRP) composites. This study aims to investigate the complex, interrelated effects of short shear span-depth ratios and FRP composites on RC deep beam members. To this end, the fundamental formulations of the dual potential capacity model (DPCM) are extended to RC deep members reinforced with externally bonded FRP composites. The proposed model can consider the various types of FRP composites, fiber bonding configurations, and fiber layouts, and various failure modes of concrete and FRP reinforcements are also reflected. A total of 131 shear test results of RC deep and short members with externally bonded FRP composites are carefully collected, and those are added to the existing database of RC slender members strengthened with FRP composites. On this basis, the proposed approach is verified by comparing test results with analysis results, and a reasonable level of analytical accuracy is achieved. The statistical data distribution of strength ratios between the test and analytical results is consistent across a range of shear span-depth ratios from approximately 0.7 to 4.0. Overall, the proposed DPCM approach provides a useful tool for analyzing the shear strength of RC deep beam members strengthened with externally bonded FRP composites.