Effect of graphene oxide on the rheological properties of cement pastes

Highlights

• The addition of GO into the cement caused a noticeable reduction in fluidity and increased rheological parameters.

• GO encapsulated silica fume (GOSF) was prepared. Compared with SF pastes, GOSF pastes had better rheological properties, indicating the addition of GO improved rheological properties.

• A possible mechanism was proposed to explain the different effects of GO on the rheological properties of cement pastes.

• The research provides a pathway to utilizing GO in cement based materials.

Abstract

The effects of graphene oxide (GO), silica fume (SF) and graphene oxide encapsulated silica fume (GOSF) on the rheological properties of cement pastes were investigated. It was found that the addition of GO into the cement caused a noticeable reduction in fluidity and increased rheological parameters. However, GOSF pastes had better fluidity and lower rheological parameters at a same dosage of SF, indicating that the addition of GO lowers the rheological parameters. A possible mechanism was proposed to explain the different effects of GO on cement pastes. The research provides a pathway to utilizing GO in cement based materials.

Introduction

Cement is the key component of concrete and mortar, which is one of the most important and widely used building materials. The incorporation of admixtures [1], [2], [3] and fibers [4], [5], [6] is now an important technique in improving the properties of cement composites, such as rheological properties, strength, durability, etc. Recently, the development of nanomaterials, such as carbon nanotubes (CNTs) and graphene, has provide opportunities to improving the performance of cement pastes [7], [8]. Many studies have been carried on the effect of CNTs on the cement hydration and mechanical properties of cement composites [7], [9], [10], [11], [12]. With the addition of small amounts of CNTs, the compressive and flexural strengths of cement composites were improved [13], [14], [15].

As a graphene derivative, two-dimensional graphene oxide (GO) has several oxygen-containing functional groups such as hydroxyl, carbonyl, epoxy groups and carboxylic groups, rendering GO sheets hydrophilic. GO has a large surface area and good mechanical properties [16], [17]. Consequently, GO shows a better gain in compressive strength at a lower concentration when compared to CNT reinforced cement [12]. The introduction of GO in cement not only can regulate hydration but also improve the tensile, flexural and compressive strengths of the cement paste [8], [18], [19], [20], [21], [22]. Lv et al. [19] discovered that when the content of GO was 0.03%, the cement composites exhibited remarkable increase in tensile strength (78.6%), flexural strength (60.7%) and compressive strength (38.9%).

However, similar to the other nanomaterials such as nanosilica and CNTs, the addition of GO into the cement affects the fluidity and increased rheological parameters [8], [21], [22], [23]. Pan et al. [22] noted the reduction in workability was about 42% via a mini-slump test with the incorporation of 0.05 wt.% GO. Gong et al. [23] examined the rheological behaviors of GO reinforced cement composite with the aid of the conventional mini-slump test accompanied by the rheological studies. It was found that small proportions of GO increased both the viscosity and yield stress of fresh cement paste. Moreover, the viscosity increased with the size of GO, confirming the influence of geometry on the workability. These studies infer an inverse correlation between the concentration of GO and workability. It is widely accepted that the large surface area of nanomaterials demands more water to wet their surface, thereby reducing the free water content required for lubrication. Moreover, large scale agglomerates of nanomaterials in cement matrix lead to lower fluidity. However, the work on the influence of GO on the rheological properties of cements is still scarce.

In this paper, the effects of GO on the rheological properties of cement pastes was investigated. It was found that the addition of GO into the cement caused a noticeable reduction in fluidity and increased rheological parameters. Then GO was modified onto the surface of silica fume (SF) to prepare graphene oxide encapsulated silica fume (GOSF). It is expected that GOSF will achieve a good dispersion of GO and SF in the cement matrix by the synergetic effect of the surface activity of GO and the shape effect of SF. Compared with cement pastes with SF, GOSF pastes had higher fluidity and lower rheological parameters, indicating the addition of GO improved rheological properties. Combined with the results of reduced graphene oxide, the possible mechanism was discussed to explain the different effects of GO on cement pastes in the paper. The research provides a pathway to utilizing GO in cement based materials.