Nanomaterial-Modified Epoxy Adhesives for Structural Retrofitting

Structural retrofitting with Fiber-Reinforced Polymer (FRP) systems has emerged as a leading solution for enhancing the performance and durability of aging concrete structures. Central to the effectiveness of these systems is the choice of adhesive, as it facilitates stress transfer between the FRP reinforcement and the concrete substrate. However, traditional Neat Epoxy (NE) adhesives exhibit limitations, such as brittleness and poor resistance to crack propagation, which hinder their performance in structural applications. Nanomaterial-Modified Epoxy Adhesives (NMEAs) offer a promising alternative, significantly improving the mechanical, thermal, and bonding properties of epoxy systems [1,2].

Enhancements in mechanical and thermal properties

The incorporation of carbon-based nanomaterials such as Carbon Nanotubes (CNTs), Carbon Nanofibers (CNFs), and graphene into epoxy matrices enhances fracture toughness, tensile strength, and thermal stability. These improvements stem from strong interfacial interactions between the nanoparticles and the epoxy, as well as effective crack-bridging mechanisms. For instance, adding 0.1wt.% single-walled CNTs increased fracture toughness by 13% and compression-after-impact strength by 3.5% [3]. Silicon-based nanomaterials, such as silica nanoparticles and Montmorillonite (MMT) nano clay, also enhance epoxy properties by reducing void content and increasing stiffness. The uniform dispersion of nanoparticles within the matrix plays a critical role in achieving these benefits [4,5].

Chemical and microstructural properties

Nanoparticles also influence the chemical structure of epoxy adhesives, as evidenced by Fourier-Transform Infrared (FTIR) and Raman spectroscopies. These techniques reveal changes in functional groups and molecular structure, providing insights into the interactions between nanoparticles and the polymer matrix. For example, the formation of ester bonds in CNT-modified epoxies highlights the chemical reactivity between nanoparticles and the epoxy system [6].

Microstructurally, the degree of crystallinity in nanocomposites is pivotal for determining their mechanical performance. X-ray Diffraction (XRD) studies show that nanoparticles can act as nucleating agents, enhancing crystallinity, or as impurities, disrupting ordered structures. The effect is concentration-dependent and varies with the type of nanoparticle used [7].

Applications in FRP structural retrofitting

NMEAs have shown significant promise in both Externally Bonded Reinforcement (EBR) and Near Surface Mounted (NSM) FRP systems. For instance, CNT-modified epoxies improved the flexural capacity and toughness of reinforced concrete beams and columns [2,8]. In NSM- FRP applications, silica- and clay-modified epoxies increased loadcarrying capacity and ductility, highlighting their potential for addressing the limitations of traditional NE adhesives [9,10].

Environmental and sustainable benefits

Beyond mechanical performance, NMEAs contribute to sustainable construction practices by extending the lifespan of retrofitted structures and reducing material waste. Life cycle assessments demonstrate the environmental advantages of using NMEAs over traditional adhesives, aligning with global efforts to minimize construction-related carbon emissions [11].

Nanomaterial-modified epoxy adhesives represent a transformative advancement in structural retrofitting. By addressing the limitations of NE adhesives and enhancing the performance of FRP systems, NMEAs pave the way for more durable and sustainable infrastructure. Future research should focus on optimizing nanoparticle dispersion techniques, exploring hybrid nanomaterial systems, and conducting long-term performance studies under diverse environmental conditions [1,3,8].

1. Al-Zu’bi M, Fan M, Anguilano L (2022) Advances in bonding agents for retrofitting concrete structures with fibre reinforced polymer materials: a review. Construct Build Mater 330: 127115.
2. Al-Zu’bi M, Fan M, Anguilano L (2024) Near-surface mounted-FRP flexural retrofitting of concrete members using nanomaterial-modified epoxy adhesives. J Build Eng 84: 108549.
3. Al-Zu’bi M, Fan M, Bertolesi E, Anguilano L (2024) A review on retrofitting concrete members with near-surface mounted-fiber reinforced polymer composites. Struct Concr 25(3): 2242-2268.
4. Irshidat MR, Al-Saleh MH, Almashagbeh H (2016) Effect of carbon nanotubes on strengthening of RC beams retrofitted with carbon fiber/epoxy composites. Mater Des 89: 225-234.
5. Al-Zu’bi M, Anguilano L, Fan M (2023) Carbon-based and silicon-based nanomaterials for enhanced structural adhesives. Solid State Phenomena 354: 151-159.
6. Al-Zu’bi M, Fan M, Anguilano L (2023) Effect of incorporating carbon- and silicon-based nanomaterials on the physico-chemical properties of a structural epoxy adhesive. Polymer Testing 128: 108221.
7. Morimune S, Nishino T, Goto T (2014) Graphene oxide reinforced poly (vinyl alcohol) nanocomposites. Compos Sci Technol 107: 120-128.
8. Al-Zu’bi M, Shhabat M (2024) A review of repairing heat-damaged RC beams using externally bonded-and near-surface mounted-CFRP composites. Compos Part C: Open Access 15: 100519.
9. Huttunen-Saarivirta E, Vaganov GV, Yudin VE, Vuorinen J (2013) Characterization and corrosion protection properties of epoxy powder coatings containing nanoclays. Prog Org Coat 76(4): 757-767.
10. Al-Zu’bi M, Fan M, Anguilano L (2023) Parametric investigation of flexural performance of concrete prisms retrofitted with near-surface mounted FRP bars. Composites Part C: Open Access 12: 100421.
11. Al-Zu’bi M, Shamass R, Piana F (2025) Mechanical performance and life cycle assessment of BFRP-reinforced AAC slabs strengthened with basalt macro-fibers. Construct Build Mater 330: 108564.