PSI - Issue 28

Angeliki-Eirini Dimou et al. / Procedia Structural Integrity 28 (2020) 1679–1685 Author name / Structural Integrity Procedia 00 (2019) 000–000

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1. Introduction The incorporation of carbon-based nanomaterials (CBNs) in construction materials and the changes in mechanical properties and electrical properties has been gaining scientific interest since the past decade. Several studies have shown that the incorporation of such materials in the initial matrix improves the mechanical properties significantly. For instance, Hawreen et al. (2018) found that the addition of multi-walled carbon nanotubes at a concentration of 0.05 to 0.1 wt% of the binder leads to a 33 % increase of the flexural strength. Liew et al. (2017) concluded that the compressive and flexural strengths cement composites were improved by 17.3 % and 16.3 %, respectively when carbon nanotubes were added at 0.1 wt%. One very important category of CBNs is comprised of graphene and its derivatives, graphene oxide (GO) and reduced graphene oxide (rGO). GO is an oxidised graphene sheet that contains organic functional groups, such as epoxide and hydroxyl groups. If GO is subjected to reduction, a big part of functional groups is removed and the graphene structure partially returns, thus resulting in rGO as described in Konios et al. (2014). When these materials are incorporated in cement-based matrices, the mechanical properties are enhanced. For example, Baomin and Shuang (2019) found that cement composites with 0.06 wt% dispersive graphene nanoplatelets display an increase in compressive and flexural strength at a percentage of 11 % and 28 %, respectively. Wang et al. (2015) showed that the compressive and flexural strength of the cement paste increased by 90 % and 40 %, respectively when GO is incorporated at 0.05 wt% of the binder. A significant number of studies refer to the incorporation of rGO into cement matrix. Madbouly et al. (2020) found that the compressive strength of the final composite increases by 27 % and 38 %, when rGO is added at concentrations 0.04 and 0.05 wt% of the binder, respectively. Prabavathy et al. (2020) examined different concentrations of rGO in cement mortars (up to 0.2 wt% of the binder) and found that compressive strength increases when rGO is added up to 0.1 wt% and then it drops, while it is still increased in comparison to the plain cement matrix. Wang et al. (2017) found that specimens with 0.2 wt% concentration of rGO display 27 % increase of flexural strength and 20 % increase of compressive strength. Table 1 presents the effect of the incorporation of rGO in cement composites, as well as its concentration in the matrix and the dispersion methods applied.

Table 1. Information on rGO/cement nanocomposites (mechanical performance and dispersion method)

Concentrations of rGO in the matrix (wt%)

Optimal concentration of rGO (wt%)

Effect of the optimal concentration of rGO 44 % increase of compressive strength (28 days) 38 % increase of compressive strength (28 days) 27 % increase of flexural strength 20 % increase of compressive strength 35 % increase of flexural strength 20 % increase of compressive strength

Article

Dispersion method

Prabavathy et al. (2020) Madbouly et al. (2020)

Sonication with probe type sonicator for 30 min Ultrasonication process (at 250 Watt and frequency of 20 kHz) for 20 min No aqueous dispersion – mechanical mixing of solids for 5 h at 400 r/min in a planetary ball then passed through 300 mesh screen naphthalene water reducer mixed with rGO powder in the 1500 W ultrasonic cell crusher for 60 min (probe type sonicator) 0.1wt % was used for different sonication times of 1, 2, 4, 6, and 8 h 0.05% and 0.2% were studied at the 1 h and 4 h sonication time

0.05 – 0.10 – 0.15 – 0.20

0.10

0.01 – 0.02 – 0.03 – 0.04 – 0.05

0.05

Wang et al. (2017)

0.2 – 0.4 – 0.6 – 0.8 – 1

0.2

Zhang et al. (2020)

0.05 – 0.5 – 1 – 2 – 4

2

Valizadeh Kiamahalleh et al. (2020)

0.1 at 4 h sonication time

91 % increase of compressive strength

0.05 – 0.1 – 0.2

To incorporate CBNs in the cement matrix, successful dispersion in the mixing water is necessary. This task has been a very difficult challenge to overcome so far, not only in the case of cement-based composites but also in all CBN