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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techniques for integrating CNTs into aqueous suspensions, as demonstrated by Carriço et al. (2018) (+21.1% using sonication for 45 min in 3 cycles of 15 min), Hawreen et al. (2019) (+22.5% employing magnetic stirring in water with surfactant and sonication for 30-45 min), and Irshidat (2021) (+23.0% through dispersion in water and manual agitation followed by sonication for 20 min). It is worth noting that the high increase in f c due to a small CNT content may seem counter-intuitive and, based on the tests carried out in this work, the authors rely on the findings of the literature to explain it: the improvement in the paste/aggregate interface, the reduction in porosity, large pores and interconnectivity between them and the promotion of cement hydration can create synergies that improve the performance of concrete; further studies need to be conducted to look for other explanations. In terms of f ct , the improvements seen in this study surpassed those referenced above (+34.7% against +22.0%, maximum) yet did not reach the levels achieved by Song et al. (2020), who used a simpler approach of mixing with water and sonication (+34.7% against +49.3%). When considering P and UPV, the advantage of pre-dispersing CNTs in cement was observed only at a 0.05% CNT content. However, employing CNTs in aqueous suspensions in other studies showed similar or superior outcomes, even with higher CNT concentrations. It is worth noting that the variations obtained in the properties studied in this study are of the same order of magnitude as those found in a previous study by the authors (Reis et al., 2024). From this standpoint, dispersing CNTs in an aqueous solution is easier and potentially more efficient than using them in a powdered state. Even though there are effective methods for dispersing powder, such as mixing CNTs with cement particles in isopropanol, as utilized in this investigation, these methods show promise at the lab scale. Nevertheless, their effectiveness might be constrained in a commercial setting, as Son et al. (2023) have indicated. Moreover, employing CNTs in industrial-grade aqueous suspensions led to notable enhancements in the strength and ductility of concrete, especially within the initial seven days, which is a pivotal phase for developing cracks due to drying shrinkage and the heat of hydration (Song et al., 2017). This fact implies that dispersing CNTs in water could be more efficient for mitigating early-age cracking in concrete and might reduce the need for extensive testing compared to using powdered nanotubes. Hence, opting for CNTs dispersed in water at an industrial scale emerges as a more feasible and reliable method for incorporating CNTs into concrete, i.e., industrial dispersion significantly outperforms those methods used in laboratory settings, in agreement with previous research (Marcondes and Medeiros, 2016). 4. Conclusions This paper provides compelling evidence that adding CNTs to concrete significantly enhances its mechanical and physical attributes. Incorporating CNTs, even in minimal amounts such as 0.05% and 0.10% by weight of cement, resulted in substantial improvements in f c (up to 23% increase), f ct (up to 35% increase), P (up to 12% reduction), and UPV (up to 4% increase). Exploring the form (whether in powder or aqueous suspension) and the concentration of CNTs, which significantly influence the concrete's resultant properties, was crucial to the investigation. The method chosen for CNT dispersion is critical in determining its effectiveness in enhancing the quality of concrete. The study found the technique of pre-dispersing CNTs in cement particles using an isopropanol medium effective in this context. However, compared to other research, the dispersion of CNTs in aqueous suspension offers a simpler and potentially more efficient solution, particularly when considering applications on an industrial scale. This comparison highlights the need for methods that are effective in a laboratory setting and scalable and practical for real-world construction scenarios. Furthermore, the study draws attention to the potential difficulties in scaling up the pre-dispersion technique for industrial applications, as used in this research. In contrast, using CNTs dispersed in aqueous suspension, especially in industrial-grade dispersion methods, offers a more pragmatic and efficient approach for large-scale construction. This finding points towards a future direction for the construction industry, where the choice of materials and methods is as much about efficacy as it is about scalability and practicality in diverse application contexts.