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This study aims to investigate the effect of the infilled frames through various important parameters (i.e., the openings’ percentage in infill walls - several columns on the first floor are removed - partial infilled) in the RC structures, subject to progressive collapse scenarios. To this end, 3D finite element models were constructed by using the software ABAQUS. Numerical and experimental results were compared to substantiate the finite element models’ capability of simulating the experimental models’ behavior of Al-Chaar et al. (2002) in an accurate manner. The results showed that there was good agreement between experimental and numerical results. Moreover, the results indicated that there was a significant effect, which cannot be neglected, on the progressive collapse resistance; the reduction ratios in vertical displacement at the regions removed columns can reach up to 80%.

Currently, the researchers’ endeavors focus on the incorporation of recycled waste tires from worn-out tires, such as tires-rubber particles in the concrete mix, which contributes to solving the accumulated waste tires problem. However, the crumb rubber inclusion can result in a significant reduction in mechanical properties. Moreover, in fiber-reinforced concrete (FRC), hybrid fibers are more effective in arresting cracks macro/micro than a single fiber type. Therefore, using hybrid fiber is essential to address the problems of strength decline and sustainability, simultaneously. To this end, this study aims to examine the impact of polypropylene (PP) fiber and steel fiber hybridization on the fracture characteristics of plain and rubberized concrete prisms to identify the fibers’ optimized mixture proportion. Prism specimens, measuring 100 × 100 × 500 mm (width × depth × length) were, therefore, prepared for this purpose. The variables involve different ratios of PP fiber (0%, 0.1%, 0.175, 0.25%, 1.0%) and steel fiber (0%, 0.75, 0.825, 0.9%, 1.0%) with/without crumb rubber (1–2 mm in size) with a partial replacement ratio of 20% by volume of fine aggregate (natural sand). In experimental studies, FRC prisms with crumb rubber achieved more significant improvements in the fracture characteristics than those with/without crumb rubber. By contrast, the concrete compressive and tensile strengths decreased due to the crumb rubber replacement. The specimen, reinforced with hybrid 0.1% PP-0.9% steel fiber-reinforced rubberized concrete, produced higher levels of fracture energy of approximately 3716.6 N/m, i.e., 13 times higher than that of plain concrete. More importantly, the most significant improvement in compressive and tensile strengths has been observed for the mixture with hybrid 0.1% PP-0.9% steel fiber.

Steel fibers are nowadays increasingly employed for improving the fracture behavior of concrete. However, the fiber alignment in fiber reinforced concrete (FRC) plays a significant role in its fracture behavior. This paper presents a method for aligning fibers in the desired direction, which is done by pouring concrete in the molds through a steel hopper, developed for this application. Both regular (without a notch) as well as notched beam specimens were cast using two steel fiber volume fractions of 0.8% and 1.2%. The beam specimens were tested in flexure under a central point load. The fracture parameters of FRC containing aligned steel fibers were compared with the FRC having randomly distributed fibers. The test results demonstrate the success of the method employed for aligning fibers. The FRC having 0.8% aligned steel fibers was almost as good as the FRC containing 50% more (i.e., 1.2%) random fibers. Mathematical analysis was carried out for the alignment of steel fibers achieved using the developed hopper and to predict the fiber orientation factor. The test results are in good agreement with the predicted values.

This research investigates the bond performance of metakaolin based geopolymer concrete (GPC). Pullout tests were conducted for steel and GFRP bars embedded in plain and fiber-reinforced GPC. Three types of mixes were adopted to produce plain and steel fiber-reinforced GPC by controlling both alkaline solids to metakaolin ratio and sodium silicate to sodium hydroxide ratio. Comparative reference tests were also performed on cement concrete. Concrete splitting was observed for plain geopolymer mixes with both GFRP and steel bars. The steel fiber-reinforced GPC having GFRP bars experienced bar pullout while specimens with steel bars failed by concrete splitting, bar pullout, or bar rupture. For cement concrete mixes, the bond strength of steel bars was better than that of GFRP bars. The average normalized bond strength of plain GPC mixes was generally lower than that of cement concrete by 11%–27% and 21%–40% for steel and GFRP bars, respectively. The inclusion of steel fibers in GPC improved the bond performance for specimens with steel and GFRP bars by 7%–45% and 33%–114%, respectively. A model is proposed for the prediction of bond strength of GFRP and steel rebars embedded in plain and fiber-reinforced GPC.

Ordinary Portland cement (OPC) is commonly adopted as an effective binder in the production of concrete and cementitious mortars. The metakaolin (MK) based geopolymer (GP) binder offers a sustainable alternative to the OPC due to its essential environmental and technical benefits in reducing the carbon footprint. In the present study, two conventional and six GP repair mortars were used. Three GP mortars were plain (without fibers), and the remaining three were produced by mixing Polyvinyl-alcohol (PVA) fibers. The GP mixes were produced by varying sand content, alkaline solids to MK, and sodium silicate to NaOH ratios, resulting in different molar ratios. The test specimens were prepared by overlaying a 5 mm thick layer of repair mortar on a concrete substrate for conducting pull-off strength tests. This research was undertaken to investigate the effect of exposure to elevated temperatures on the performance of bond strength of GP mortar used as a repair material. The test specimens were subjected to ambient temperature and elevated temperatures of 200 and 400 °C for a duration of 3 h before conducting pull-off tests. The test results revealed that the selected GP mixes could be a promising alternative repair material for structures due to their good bond strength performance. The addition of fibers in stable mixes of GP mortars enhanced the bond strength at ambient as well as when exposed to 200 °C, through crack control mechanism.

Fiber-reinforced polymer (FRP) has proven its efficiency as a strengthening material of ordinary concrete. However, the research on the effect of these materials on geopolymer concrete is still less understood. Due to the excellent mechanical and environmental properties of geopolymer concrete, the compression behavior of confined high strength geopolymer concrete (HSGC) is experimentally and analytically investigated and compared with high strength cement concrete (HSC). The confined cylindrical test specimens of HSGC and HSC were tested in compression. The cylinders were confined using three schemes of FRP, namely one and two layers of Glass FRP (GFRP) and one layer of carbon FRP (CFRP). The stress–strain behavior of the HSGC is compared with HSC for different levels and types of confinement. For low confining pressure, there was a definite peak followed by descending portion of the stress–strain curve, whereas for high confining pressure, initially, the stress increases nonlinearly with strain, and after reaching a certain level of stress, it becomes asymptotic to a positive slope straight line. A single equation is proposed for predicting all curves of HSGC and HSC for low as well as high confining pressures. The validation of the model is also successfully shown with the data taken from the literature for a wide range of confinement levels.