PSI - Issue 67

E.D. Reis et al. / Procedia Structural Integrity 67 (2025) 39–46 Reis et al. / Structural Integrity Procedia 00 (2024) 000 – 000

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1. Introduction The urgency to reduce carbon emissions in the construction industry has highlighted the need to rethink the use of conventional materials, especially in cement production, one of the biggest villains in this scenario. The search for more sustainable and durable alternatives brings nanotechnology to the center of discussions (Shah et al., 2016). The cement industry is known for its significant CO 2 emissions, contributing substantially to global warming (Petroche and Ramirez, 2022). The necessity to reduce carbon emissions becomes evident when the growing demand for infrastructure is considered, thereby stimulating research efforts towards innovative solutions. According to Rissman et al. (2020), decarbonizing the global industry by 2050 – 2070 is essential to achieving climate stabilization and limiting global warming to 2 °C. In this context, carbon nanotubes (CNTs) emerge as a promising alternative. By exploiting this particular form of carbon, nanotechnology offers the possibility of developing more resistant and sustainable materials. For example, Murcia et al. (2023) used CNTs to produce bio-polymer concrete, which showed excellent durability resistance against aggressive environments and had a carbon footprint 50% lower than ordinary Portland cement concrete. However, the challenge lies in the efficient dispersion of these nanotubes in cementitious materials, a technical barrier that needs to be overcome more effectively (Parveen et al., 2013). Several approaches are used in the literature to disperse CNTs in cement matrices, including magnetic stirring, mechanical stirring, sonication, and surfactant addition, which are chosen based on the type of CNT supplied, whether in aqueous suspension or powder form (Carriço et al., 2018; Hassan et al., 2019; Hawreen et al., 2019; Irshidat, 2021; Mohsen et al., 2019; Parvaneh and Khiabani, 2019; Shao et al., 2022; Song et al., 2020). Considering these references, each one employs different combinations of these techniques and concentrations (up to 2%), reflecting the diversity of approaches and the lack of a standard method in the area. This fact indicates a field of research still under development, where optimizing the dispersion of CNTs in Portland cement-based materials, especially concrete, remains a topic open to innovation and improvements in existing methodologies. Hence, exploring and improving the methodologies proposed in the literature is essential, aiming at effectiveness and applicability on an industrial scale (Adhikary et al., 2020). CNT production costs are high due to high temperature-dependent synthesis procedures and high capital costs to set up (Makgabutlane et al., 2020). Therefore, overcoming these challenges is vital to achieving decarbonization and lowering the price of CNTs, allowing these innovations to become economically feasible. From this standpoint, the present study aims to examine the impact of various techniques for dispersing CNTs on the quality of concrete. In doing so, it compares the effects of incorporating CNTs on the compressive strength, tensile strength, porosity, and ultrasonic pulse velocity of concrete, as observed in this experimental investigation, with those documented in the existing literature. It is worth noting that this research is part of a more extensive investigation into the bonding behavior between steel bars and concrete enhanced with CNTs. As such, it presents findings and perspectives that hold significant value for ongoing research endeavors. 2. Materials and Methods The concrete production utilized the Brazilian Type CPV-ARI RS Portland cement (ABNT, 2018a), comparable to CEM I of the EN 197-1 standard (EN, 2011). The fine aggregate was natural sand possessing a fineness modulus of 2.75, a maximum diameter of 2.4 mm (ABNT, 2003), and a specific gravity of 2.632 g/cm 3 (ABNT, 1987). The coarse aggregate consisted of gneiss gravel exhibiting a fineness modulus of 4.92, a maximum diameter of 9.5 mm (ABNT, 2003), and a specific gravity of 2.646 g/cm 3 (ABNT, 1987). The nanomaterials employed were multi walled carbon nanotubes (MWCNTs, not implemented in control samples), selected from the CTNano, Brazil, synthesized through chemical vapor deposition, with estimated lengths ranging from 5 μm to 30 μm, with external diameter varying from 10 to 30 nm, and purity surpassing 93% (NanoView, 2022). The isopropanol utilized for dispersing the CNTs was the absolute grade of the EMFAL brand (EMFAL, 2019). The additives included the polycarboxylate-type superplasticizer and hydration stabilizer in water suspension. It should be mentioned that the following methodology was used in previous research by the authors (Reis et al., 2024). Still, different specimens were considered in each investigation to assess whether the variations would be of the same order of magnitude.