Enhancing Cementitious Composites with Functionalized Graphene Oxide-Based Materials: Surface Chemistry and Mechanisms

Abstract

Graphene oxide-based materials (GOBMs) have been widely explored as nano-reinforcements in cementitious composites due to their unique properties. Oxygen-containing functional groups in GOBMs are crucial for enhancing the microstructure of cementitious composites. A better comprehension of their surface chemistry and mechanisms is required to advance the potential applications in cementitious composites of functionalized GOBMs. However, the mechanism by which the oxygen-containing functional groups enhance the response of cementitious composites is still unclear, and controlling the surface chemistry of GOBMs is currently constrained. This review aims to investigate the reactions and mechanisms for functionalized GOBMs as additives incorporated in cement composites. A variety of GOBMs, including graphene oxide (GO), hydroxylated graphene (HO-G), edge-carboxylated graphene (ECG), edge-oxidized graphene oxide (EOGO), reduced graphene oxide (rGO), and GO/silane composite, are discussed with regard to their oxygen functional groups and interactions with the cement microstructure. This review provides insight into the potential benefits of using GOBMs as nano-reinforcements in cementitious composites. A better understanding of the surface chemistry and mechanisms of GOBMs will enable the development of more effective functionalization strategies and open up new possibilities for the design of high-performance cementitious composites.

Keywords: cementitious composites; graphene oxide-based materials; nano-reinforced materials; oxygen functional groups; surface chemistry.

Figure 6

(a) (left) After 28 days of curing, the microstructure of cement paste was analyzed; (middle) The control sample showed many pores and microcracks, while the addition of GO resulted in few isolated crystals due to more hydration products; (right) Addition of rGO led to a denser microstructure with fewer pores [8]; Adapted from Ref. [8]. Copyright 2020 Elsevier. (b) Moderately reduced rGO was found to have the highest cement hydration, while highly reduced rGO led to a decline in cement hydration, indicating the need to balance the reduction degree of GO with the defects in the graphene structure [9]; Adapted from Ref. [9]. Copyright 2017 American Chemical Society. (c) A mild thermal annealing process enhances GO properties by promoting the phase transition of graphitic domains. Oxygen diffusion on the GO surface leads to hybridization of significant oxide and graphite regions, resulting in a mixture of sp² and sp³ domains. A diagram featuring carbon (yellow), oxygen (red), and hydrogen (blue) atoms is provided [101]; Adapted from Ref. [101]. Copyright 2017 American Chemical Society. (d) GO contains epoxy and hydroxyl groups attached to the edge, which can be removed in high- and low-oxygen environments. Epoxy-rich GO domains lose more carbon and oxygen atoms as the oxygen cluster increases [98]. Adapted from Ref. [98]. Copyright 2016 Elsevier.

Figure 1

Scope of this review. This review mainly focuses on the various oxygen functional groups present in GOBMs and their integration into cementitious composites for performance improvement. Created with BioRender.com.

Figure 2

(a) Various chemical methods have been employed to synthesize GO from graphite and subsequently exfoliate it, determining the C-to-O ratio in GO [11]. Adapted from Ref. [11]. Copyright 2020, Elsevier. The high surface area, porosity, and water absorption of GO contribute to a more compact composite material structure, thereby improving its mechanical properties. SEM micrographs were taken to observe the microstructure of the cement specimens, where (b) represented the specimens without GO and a w/c ratio of 0.35, and (c) represented the specimens with GO and a w/c ratio of 0.35 [29]. Adapted from Ref. [29]. Copyright 2019 Elsevier. GO serves as a catalyst for cement hydration products, thereby enhancing interfacial interactions among different substrates. SEM was used to observe the ITZ in (d) RFA mortar samples and (e) RFA mortar with GO samples at different magnifications after 7 days [30]. Adapted from Ref. [30]. Copyright 2018 Elsevier.

Figure 3

SEM analysis investigated the use of (a) HO-G and (b) GO/HO-G as nanofillers in cement composites. The images show that the composites containing HO-G and GO/HO-G have a dense texture without porosity or cracks, while GO/HO-G composites exhibit a flower-like pattern of hydrated crystals, indicating a unique interaction with cement hydration products [74]. Adapted from Ref. [74]. Copyright 2022 Royal Society of Chemistry.

Figure 4

(a) The carboxyl group of GO reacts with Ca²⁺ of cement hydration products, forming a strong covalent bond that leads to the formation of a three-dimensional network structure. This structure enhances the interfacial bond between the cement matrix and the reinforcing material [35]; (b) SEM images show that the hydrated products are inserted into the 3D network structure of GO nanosheets [35]. Adapted from Ref. [35]. Copyright 2016 Elsevier.

Figure 5

(a) Under optimal shear and minimal collision force conditions, graphite powder is oxidized and exfoliated at the edge, resulting in the production of EOGO [77]; Adapted with permission from Ref. [77]. Copyright (2018). MDPI Open access article under the Creative Commons Attribution License. (b) The microstructure of cement composites containing EOGO was analyzed by SEM, showing amorphous hydration products in boxes 1, 3, and 5, and needle-like crystals of ettringite at points 2 and 4. A schematic diagram depicted the interaction between EOGO and cement particles, represented by gray and black dots, respectively [59]; (c) This figure displays the crystallization process of cement hydration products within the cement pores on day 3 (left) and day 28 (right) in the absence of EOGO [59]; (d) When incorporated into cement composites, EOGO can act as an activation point for crystallization, resulting in a more densely packed composite material [59]. Adapted from Ref. [59]. Copyright 2019 Elsevier.

Figure 7

(a) SEM images were used to compare the microstructures of (left) the control sample, (middle) GO-containing cement complex, and (right) FGO-containing cement complex. Needle-like crystals (ettringite) were observed in all three samples, but the FGO-containing complex had fewer and smaller crystals. Additionally, the pore size decreased in the order: control sample > GO-containing complex > FGO-containing complex [68]. The scale of the top, middle and bottom columns are 1mm, 10 μm, and 2 μm respectively. Adapted from Ref. [68]. Copyright 2020 John Wiley and Sons. The concrete surface becomes hydrophobic after silane treatment, achieved by the GS composite emulsion mechanism; (b) IBTS hydrolysis forms Si-OH and Si-O-Si bonds; (c) Si-O-Si bonds undergo dehydration and condensation forming a hydration product with OH bonds, leading to hydrogen bond formation and hydrophobic films, and (d) Si-OH bonds interact with -OH groups of GO, resulting in a thicker, denser hydrophobic layer [103]. Adapted from Ref. [103]. Copyright 2022 Elsevier. Dopamine (DA) enhances interfacial bonding on concrete by inducing ion mineralization on its surface. DFT analysis reveals three stable structures of DA molecules on Ca²⁺ with varying adsorption and charge densities. These structures involve Ca²⁺ adsorbed on (e) nitrogen, (f) oxygen atoms of hydroxyl groups, and (g) carbon rings with different bond lengths. The second structure, which closely resembles the Ca-O bond length in CaO crystals, is the most stable due to its low adsorption energy. Electron accumulation is depicted in yellow, while electron depletion is shown in blue [3]. Adapted from Ref. [3]. Copyright 2020 Elsevier.