PSI - Issue 67

Shohana Iffat et al. / Procedia Structural Integrity 67 (2025) 1–7 Iffat et al./ Structural Integrity Procedia 00 (2024) 000–000

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Keywords: cement; graphene oxide; multiwalled carbon nanotubes; compressive strength.

1. Introduction Graphene oxide nanoribbons (GONRs) are produced by longitudinal unzipping of the outer walls of multiwalled carbon nanotubes (MWCNTs) (Kosynkin et al. 2009). Therefore, GONRs have a similar morphology compared to graphene nanoplates (GNPs). Through this unzipping process, some of the outer layers of a given MWCNT are fully unzipped, and the resulting GONR exhibits a larger surface area and greater functionality than the precursor MWCNT. In fact, GONRs are characterized by a high graphene edge content (Kosynkin et al. 2009) that provides larger –COOH edge sites compared to GNPs. As a result, it is expected that dispersibility in aqueous solutions as well as cement matrices will be facilitated. In addition, the resulting GONRs are characterized by a higher aspect ratio compared to GNPs, which is expected to benefit the mechanical amendment of cement composites (Abu Al-Rub et al. 2012). It has been reported that the addition of 0.01% in weight of cement (wt%) (Wang et al. 2022) to 2 wt% (Collins et al. 2012) of MWCNTs and 0.03 wt% (Lv et al. 2016) to 0.5 wt% (Zohhadi 2014) of GNP in cement paste and mortar results in enhanced mechanical properties. Potential mechanisms may include preferential cement hydration through the functional groups on the surface of oxidized MWCNTs and GNPs (Li et al. 2005, Kaur and Kothiyal 2019), a reduction in total pore volume (Li et al. 2005, Nochaiya and Chaipanich 2011), pore-size refinement (Li et al. 2005, Hu et al. 2014), generation of high-stiffness C-S-H (Konsta-Gdoutos et al. 2010), and compaction (densification) of the cement matrix (Liu et al. 2019). This paper presents the first results of mechanical tests on prototype cement concrete amended with GONRs. GONR concentrations of 0.0005 and 0.05 wt% are considered, where the former is one to two orders of magnitude smaller than the lower-bound concentrations used for MWCNTs and GNPs (e.g., Konsta-Gdoutos et al. 2010, Liu et al. 2019). In addition, the effect of the extent of oxidation on GONR dispersion and concrete compressive strength was assessed by varying the oxygen weight content (O%). 2. Methodology 2.1. GONR aqueous suspensions The GONRs were prepared at Savannah River National Laboratory (Aiken, SC) through an oxidative unzipping process adapted from Kosynkin et al. (2009). Defects were created on the edges of the pristine MWCNTs by soaking in concentrated sulfuric acid and o-phosphoric acid, and potassium permanganate was utilized as oxidant. By controlling the amount of oxidant, heating time, and soaking time, the GONRs were produced, and then suspended in deionized (DI) water as shown in Fig. 1. The oxygen contents used were 32.3 O% and 41.3 O%. Aqueous solutions of GONRs in DI water with 0.0125 g/L (Fig. 1a) and 1.25 g/L (Fig. 1b) were utilized to manufacture cement concrete specimens with GONR concentrations of 0.0005 and 0.05 wt%, respectively. The suspensions were ultrasonicated for 15 minutes at a frequency of 40 kHz using an ultrasonic bath sonicator (model CPX 2008, Branson Ultrasonics Corp.). 2.2. Concrete specimens Cylindrical specimens with nominal diameter of 50 mm and height of 100 mm were cast using Type I ordinary Portland cement, GONR aqueous suspensions, silica sand with specific gravity of 2.60, and crushed stone with nominal maximum size of 9.5 mm. A water-to-cement ratio of 0.40 was used for all specimens. Four specimens were cast for each configuration (GONR concentration of 0.0005 and 0.05 wt%, oxygen content of 32.3 and 41.3 O%, and curing time of 7 and 28 days). In addition, four plain concrete specimens were cast using the same DI water as the