Physiochemical and mechanical properties of reduced graphene oxide–cement mortar composites: Effect of reduced graphene oxide particle size

Highlights

• The size effect of reduced graphene oxide (rGO) on properties of cement composites is studied.

• Different particle sizes are prepared by different sonication times of 1, 2, 4, 6 and 8 h.

• An increased sonication time from 1 to 4 h results in a decrease in the size of rGO sheets.

• Increase in the sonication time from 4 to 8 h increases the size of rGO.

• Addition of the optimum rGO size of 169.8 ± 5.8 nm to cement composite leads to the highest strength.

Abstract

The use of graphene derivatives to improve the performance of cement mortar composites has received significant attention in recent years. However, because of diversity of graphene derivatives and their properties, which depend on their preparation, it is critical to consider their size, surface chemistry, crystallinity, surface area, and impurity. In particular, there is still lack of understanding on the influence of the graphene particle size on the performance of cement mortar composite. This paper presents the study on the size effect of reduced graphene oxide (rGO) on physiochemical and mechanical properties of cement mortar composites. A series of rGOs with different particle sizes were prepared by different sonication times of 1, 2, 4, 6, and 8 h and then added with optimum dosage of 0.1% to the composites. The mechanical test results revealed that the composite containing rGO with 0.1% dosage and particle size of 169.8 ± 5.8 nm prepared with 4 h sonication time has 53% and 91% higher tensile and compressive strengths at 28 days than the plain cement mortar composite, respectively, which are higher than those obtained by the use of rGO with particle size of 245.0 ± 29.3 nm prepared with 1 h sonication time. This is explained by the higher molecular bonding, hydration degree, and crystallinity of the composite incorporating rGO with a smaller particle size. This study provides a valuable contribution toward better understanding of the influence of rGO particle size on the properties of cementitious composites to optimize their performance.

Introduction

Graphene derivatives, as carbon-based nanomaterials, are starting to be utilized widely to improve mechanical properties of cementitious materials. For industrial applications they have two main forms, namely the graphene oxide (GO) and reduced graphene oxide (rGO), which are produced from pristine graphene [1]. rGO is produced through reduction of oxygen functionalities of GO chemically or thermally [2]. Pristine graphene has high surface area and energy and excellent mechanical properties, but it has low dispersibility properties in water owing to its hydrophobicity, leading to graphene agglomeration in the water that limits its applications [3]. On the other hand, GO has high dispersibility properties in water, but its mechanical properties are weaker compared to that of pristine graphene [4], [5]. rGO can be modified to exhibit favorable properties of both GO (high dispersibility in water) and pristine graphene (excellent mechanical properties) [6]. Therefore, rGO has a great potential to be considered as an ideal graphene material for improving the performance of cementitious materials.

In recent years, several experimental studies have been performed to investigate the mechanical properties of cementitious materials containing graphene nanosheets (e.g. [7], [8], [9], [10], [11], [12], [13], [14], [15], [16], [17]). Most of these studies focused on using GO and reported the beneficial use of this material to improve mechanical properties of cementitious materials. Limited number of studies focused on using rGO in cementitious materials (cement mortar [6], cement paste [18], [19], and geopolymer [20]). These studies revealed the great potential of using rGO to enhance the mechanical properties of cementitious materials. The only study on the use of rGO in cement mortar composite [6] showed that the inclusion of 0.1% rGO produced by 15 min oxygen reduction and 0.2% (wt%) hydrazine with mild level of oxygen functional groups leads to 45% and 84% increase in tensile and compressive strength of cement mortar composites at 28 days, respectively. This study also showed that the tensile and compressive strength enhancements were respectively 20% and 8% higher than those of cement mortar composites containing 0.1% GO obtained from the same graphene source, indicating further improvements of the mechanical properties of cementitious materials through the use of rGO. Recent studies [21], [22] reported that particle size of graphene derivatives exhibits a great impact on their chemical and mechanical properties. To date, the existing studies only focused on the influence of the chemical composition of graphene, level of oxygen functional groups, and dosage, and there is no study on the influence of the graphene derivatives particle size on physiochemical and mechanical behavior of cementitious materials.

To address the above-mentioned research gap, this paper reports a study to assess the effect of the rGO particle size on the physiochemical and mechanical performance of rGO-cement mortar composites. Our recent studies [6], [11] revealed that the GO dosage of 0.1% (by weight of cement) with mild oxygen functional groups, after reducing to rGO, is the optimum to develop the highest strength of cement mortar composites. In the current study, a series of rGO particle sizes of 245.0 ± 29.3, 207.3 ± 18.3, 169.8 ± 5.8, 172.6 ± 1.9 and 183.4 ± 20.8 nm obtained by different sonication times of 1, 2, 4, 6, and 8 h were designed based on the optimum rGO condition developed in our previous two studies, respectively. Scanning electron micrograph (SEM), energy-dispersive x-ray (EDX) spectroscopy, Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), x-ray diffraction (XRD), and axial tension and compression tests were performed on the composites. Findings of this study contribute significantly toward better understanding on how to improve the formulations and properties of rGO in the development of advanced cementitious materials for high performance applications.