Corrosion of conventional steel reinforcement is responsible for numerous structurally deficient bridges, which is a multi-billion-dollar challenge that creates a vicious cycle of maintenance, repair, and replacement of infrastructure. Repair of existing structures with fiber-reinforced polymer (FRP) has become widespread due to multiple advantages. Carbon FRP’s superior tensile strength and stiffness make it particularly effective in shear and flexural strengthening of reinforced concrete (RC) beams. This experimental study incorporates carbon fiber polymer composite bars and wraps to study and report on the flexural behavior of RC beams. By employing a combination of CFRP bar and wrap for strengthening RC beams, this study observed an approximate 95% improvement in flexural load capacity relative to control RC beams without strengthening. This substantial enhancement highlights the effectiveness of integrating CFRP in structural applications. Nevertheless, the key observation is the failure mode due to this combination providing significant insights into the changes facilitated by this combination approach.

Polymer concrete (PC) is recognized for its lightweight nature, wear resistance, and rapid curing, making it well-suited for the repair of deteriorated infrastructure. This research critically addresses the challenge of enhancing overlay adhesion to compromised substrates by uniquely evaluating the role of pristine versus functionalized multi-walled carbon nanotubes (MWCNTs) in improving polymer concrete (PC) bond strength, particularly on concrete deteriorated by sulfate attack. PC mixtures containing varying concentrations of MWCNTs (0%, 0.25%, and 0.5% by weight) were prepared and tested for their mechanical properties, including compressive strength, modulus of rupture, and pull-off strength. Pull-off tests were conducted to assess the bond between PC overlays and Portland cement concrete (PCC) substrates. To examine the effects of substrate deterioration, PCC specimens were cured under two conditions: standard and sulfate-exposed environments. The results showed that neat polymer concrete (PC-Neat) achieved a high average pull-off strength of 2.82 MPa under normal conditions. Incorporating 0.25% pristine MWCNTs (PC-P25) significantly reduced the bond strength to 0.039 MPa. In contrast, improved performance was observed with functionalized MWCNTs. The addition of 0.5% COOH-functionalized MWCNTs (PC-FC50) yielded a pull-off strength of 2.22 MPa under normal conditions and 1.65 MPa in sulfate environments. Notably, under sulfate exposure, functionalized MWCNTs enhanced the bond strength by up to 15% compared to PC-Neat, highlighting their potential in aggressive environments. This distinct improvement in bond strength presents a significant finding, demonstrating a novel pathway for developing more resilient repair materials for infrastructure exposed to aggressive chemical environments.

Deterioration of infrastructure is recurring phenomena and requires rapid resurrection, it is always better to be early than late. To keep up and improve, American infrastructure requires rapid reforms. Building materials that are resilient and innovative must govern the existing counterparts. Fiber Reinforced Polymers (FRP) have proven itself to be adaptive, lightweight, having high tensile strength and corrosion proof, perfectly suitable for the current weathering defects that rose in civil infrastructures. Under FRP the 3D printed thermoplastic woven like a loom where the interlocking of two directional fiber layers is perpendicular to each other, could be potentially used as reinforcement, which this paper primarily focuses on. Typically, Carbon FRP (CFRP) tapes are considered CFRP to have greater tensile strength and have higher repulsive property towards the chemicals. The tapes are classified as lattice, which is mainly the tape arrangement. Also, this paper incorporates the interaction between the 3D printed CFRP and the concrete (plain cement Concrete, ultra high-performance concrete (UHPC) and polymer concrete and observe its flexural properties) beams. The former study related to 3D printed thermoplastic material using as a reinforcing material is limited. Hence, it is believed that the results from the paper aim to establish new design criteria and standards, providing valuable insights for future engineering applications and infrastructure projects. Results show the ductility behavior of the UHPC beam with the CFRP tapes were significant compared to the other beams. The ductility recorded was >20 mm. The failure pattern showed the tension failure i.e. the CFRP tapes failure before the concrete rupture for each type of concrete.

The fiber/matrix interface is a critical item that affects Fiber Reinforced Polymer (FRP) composites mechanical performance due to its control of the load transfer mechanism. Partially bonded interfaces have been shown to affect the failure mode of FRP composites. This article examines the significance of manipulating the fiber/matrix interfacial bond in 3D printed FRP composites on the mechanical performance of multilayer 3D printed FRP composites. Three designs are investigated with different fiber stacking sequences, fiber orientation, and interfacial bond configurations. The designs have a low coefficient of variation in load fractions between layers to enable a gradual load transfer and progressive failure. Utilizing 3D printer chamber temperature changes, a composite with a controlled bond configuration is achieved using thermal blocks. It was observed that the controlled bond configurations resulted in promoting progressive failure and increased the strain at failure of 3D printed FRP composites. The observations of direct tension tests were supported with interlayer shear strength and interfacial adhesion tests which explained the weakened load transfer in the thermal block configurations. Using the interface manipulation strategy with thermal blocks in 3D printed specimens, a 25% lower interlayer shear strength and a 65% lower interfacial adhesion was achieved compared with un-modified interfaces. These changes attribute to the altered load transfer mechanism in 3D printed glass fiber reinforced composites and high strain to failure of up to 5% using high strength high stiffness fiber orientations. This work does not incorporate any new materials into the thermoplastic-fiber 3D printed structure which has been the strategy of past work to modify mechanical performance. Alternatively, a unique approach by using chamber and print bed temperature characteristics to modify the interfacial bond has been adopted that has shown to promote progressive failures and improve ductility in FRP composites. This study furthers the development of ductile designs in FRP composites with 3D printing technology in aerospace, wind, infrastructure, and automobile applications.

With 3D printing technology, fiber-reinforced polymer composites can be printed with radical shapes and properties, resulting in varied mechanical performances. Their high strength, light weight, and corrosion resistance are already advantages that make them viable for physical civil infrastructure. It is important to understand these composites’ behavior when used in concrete, as their association can impact debonding failures and overall structural performance. In this study, the flexural behavior of two designs for 3D-printed glass fiber composites is investigated in both Portland cement concrete and polymer concrete and compared to conventional fiber-reinforced polymer composites manufactured using a wet layup method. Thermogravimetric analysis, volume fraction calculations, and tensile tests were performed to characterize the properties of the fiber-reinforced polymer composites. Flexural testing was conducted by a three-point bending setup, and post-failure analysis was performed using microscopic images. Compared to concretes with no FRP reinforcement, the incorporation of 3D-printed glass-fiber-reinforced polymer composites in cementitious concrete showed a 16.8% increase in load-carrying capacity, and incorporation in polymer concrete showed a 90% increase in flexural capacity. In addition, this study also provides key insights into the capabilities of polymer concrete to penetrate layers of at least 90 microns in 3D-printed composites, providing fiber bridging capabilities and better engagement resulting in improved bond strength that is reflected in mechanical performance. The polymer material has a much lower viscosity of 8 cps compared to the 40 cps viscosity of the cement slurry. This lower viscosity results in improved penetration, increasing contact surface area, with the reinforcement consequently improving bond strength. Overall, this work demonstrates that 3D-printed fiber-reinforced polymer composites are suitable for construction and may lead to the development of advanced concrete-based reinforced composites that can be 3D-printed with tailored mechanical properties and performance.

Elevated temperature conditions known to improve curing from the onset and during the process of immediate curing are not available in the field, which can hinder the mechanical performance of these strengthening systems. In this study, mechanical testing and material characterization were conducted to identify the effects of subjecting nanomodified epoxy and fiber-reinforced nanomodified epoxy composites to room temperature (RT) (30 °C) and elevated temperature (110 °C) from the onset of curing. Static tensile testing and interfacial adhesion tests were conducted to evaluate the mechanical performance. Differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) were performed to determine curing characteristics to inform on the immediate curing of nanomodified resins cured under the two temperature conditions. Scanning electron microscopy was performed to identify Carbon nanotube (CNT) dispersion characteristics. Overall, due to the incorporation of CNTs in epoxy, RT curing results in upto 62% increase in strain at failure. By supplying additional energy during immediate curing with elevated temperatures, a 51% increase in strength and 42% increase in Youngs Modulus can be observed in the nanomodified epoxy. In CFRP-epoxy composites, due to the incorporation of CNTs in the epoxy, RT curing results in upto 27% increase in strain at failure. By supplying additional energy during immediate curing with elevated temperatures, upto 133% increase in strain at failure is observed and upto 17% increase in strength is observed. CNTs incorporated in CFRP-epoxy composites demonstrated upto 50% increase in interfacial adhesion whereas supplying additional energy for their immediate curing with elevated temperatures, upto 130% increase in interfacial adhesion was observed. TGA and DSC results supported the mechanical observations and show a need for immediate curing when CNTs are used in epoxy matrices.