Keywords

1 Introduction

Over the past decades, a significant amount of research has been devoted to manipulating the structure of cement hyadration products and the mechanical properties of cement at the nanoscale by using a wide range of nanomaterials such as nanoscale silicon dioxide [1], carbon nanotubes (CNTs) [2], and graphene-based materials [3,4,5,6,7]). Because graphene-based materials are two-dimensional, they possesses good physical and chemical characteristics, making them a suitable option for the next generation of improved cement-based material [8,9,10,11,12]. Many studies [13,14,15,16,17] have demonstrated that graphene and its derivatives, such as graphene oxide (GO), can effectively improve the mechanical characteristics of cementitious materials by increasing the hydration process of the cement and altering the pore distribution in the matrix. Increased durability of GO-reinforced cement mortar can be achieved with only a small amount of additional GO [18]. However, the high cost and poor dispersion of graphene-based compounds prevent their future practical application. The dispersion of graphene materials in the cement matrix [19, 20] is the primary factor that determines how well graphene can reinforce cementitious materials.

It is possible to attribute the aggregation of graphene and its derivative GO to the powerful van der Waals force that exists between nanomaterials as well as the linking effect that Ca2+ and Mg2+ ions have on GO in the cement environment. This is because van der Waals forces are known to exist between nanomaterials [21,22,23]. Graphene and GO in aqueous solution have been prestabilized using a variety of chemical and physical techniques in order to address the issue of their poor dispersion. Graphene-modified cement can be manufactured by combining cement with the prestabilized aqueous solution [14, 23,24,25,26]. However, treatment with ultrasonication for extended periods of time and functionalization with strong acids have adverse impacts on graphene materials, which might cause flaws in the graphene structure.

Here, we describe a novel and uncomplicated technique for the synthesis of graphene–cement (GC) composite. This strategy involves the in-situ development of graphene in the cement matrix (Fig. 1) by carbonization and calcination [27, 28]. In the course of the synthesis procedure, the glucose used as the carbon source is thoroughly combined with the cement [27, 29]. In order to obtain advanced GC material, the mixture is heated further at 800 °C for 2 h, during which the glucose is converted into graphene on the cement particles, which inhibits aggregation and ensures well-dispersed graphene in the cementitious matrix.

Fig. 1
A flow diagram includes the following steps. 1, Raw materials with glucose and cement. 2, Mixing at 1000 rotations per minute for 1 hour. 3, In-situ processing with Nitrogen, 50 milliliters per minute. 4, Cool down. 5, In-situ growth graphene with G C material and cement particle.

Diagram of in-situ graphene grown on cement particles

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2 Methods

2.1 Materials

Glucose (C6H12O6, 98%; Sigma Aldrich) and GO (Suzhou TANFENG graphene Tech) acted as the carbon source and reinforcement material, respectively. Ordinary Portland cement (P.O. 42.5; Jiuqi Building Components) and ethanol (C2H5OH, AR.; Sinopharm Chemical Reagent) were also used in this work.

2.2 Sample Preparation

It is a well known that incorporating a negligible quantity of GO (0.05% by weight) into cement materials can dramatically improve the mechanical characteristics of these materials [5, 13, 30,31,32]. As a result, we carried out a control experiment of adding 0.05 wt% of GO to 100 g of cement. After completely mixing the GO with water, the mixture was sonicated for 30 min by ultrasonic equipment at the highest possible power setting (500 W). Next, the GO solution was included in the cement mix. The production of the new cement paste infused with GO (GOP) followed the same procedure as that of the GC material. In terms of the overall weight of binder, the quantity of GO that was utilized was equal to 0.05 wt%. These techniques provide assurance that the cementitious materials will be capable of meeting the casting standards at the location of the construction project. The GO that is sold commercially has a thickness of roughly 1 nm and a diameter that may reach a maximum of 10 µm. The substance known as GC was created by heating a combination of cement and glucose (carbon source) as shown in Fig. 1. The ratio of cement to glucose powder varied as follows: 100:1, 100:3, and 100:6. The cement and glucose were homogeneously mixed manner at room temperature for 1 h at a rotational speed of 1000 rpm. The mixture was then placed in a furnace to undergo the reaction under a specified high-temperature program while being shielded by N2 as shown in Fig. 1. In this particular investigation, the oven was initially purged with nitrogen at a rate of 50 mL/min before being heated from 25 to 550 °C at a rate of 5 °C/min over 60 min. The temperature inside the furnace then increased by 5 °C every minute until it reached 800 °C, where it remained for 2 h before gradually decreasing to the temperature of the surrounding air. The amount of graphene could be changed by adjusting the bulk amount of glucose, and the yield of pure graphene was determined by using the same techniques. The percentage of graphene that can be yielded was 7%. In order to investigate the effect that in-situ grown graphene development had on the mechanical characteristics of cement paste, we divided the samples into 4 groups: GP-0, GP-1, GP-3 and GP-6 according to the addition amount of glucose before heat treatment as presented in Table 1. Fresh cement paste containing the in-situ growing graphene was pressed into plastic molds with dimensions of 50 × 50 × 50 mm (for the compressive test) and 40 × 40 × 160 mm (for the flexure test). The molds were removed after 24 h and the samples placed in an environment with a relative humidity of 95% for 3, 7, and 28 days, respectively.

Table 1 Mix proportions of different groups
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2.3 Experimental Methods

In the current investigation, a porosimeter capable of detecting pores ranging in size from 5 nm to 100 μm was utilized (equivalent to pressures of 206 MPa and 345 kPa, respectively, which are the highest and minimum that were applied). Raman spectra were obtained with a Renishaw spectrometer that included an excitation laser wavelength of 532 nm. The instrument was also fitted with ×50 lens and was focused to a spot size that was 1 m in diameter. The scanning electron microscopy (SEM) examination was performed in order to investigate the microstructure. The compression test of cubic specimens with dimensions of 50 × 50 × 50 mm and the three-point flexure test of beam members with dimensions of 40 × 40 × 160 mm are both common methods for determining the mechanical properties of cementitious materials. Both of these tests were performed on specimens with dimensions of 50 × 50 × 50 mm. When calculating the amount of compressive stress, the applied force is divided by the area that is being loaded. The loading rate was set at 1.2 mm/min for the compressive strength test, and at 0.05 mm/min for the flexure test.

3 Results and Discussion

3.1 Characterization of GC Material

The conversion of glucose (carbon source) into graphene on cement particles, which took place during the manufacturing process of GC material, was an essential step in our process of dispersing graphene evenly throughout the cement composites. Figure 2 illustrates the morphology of graphene as well as GC. The results of tests using energy dispersive X-ray spectroscopy (EDS) showed a distinct distribution of carbon (Fig. 2b, c). EDS mapping of the GC material showed that the elements carbon, oxygen, calcium, and silicon were all equally distributed throughout the material (Fig. 2e). SEM and atomic force microscopy revealed that the wrinkled nanosheets of graphene generated by glocuse had a thickness of 1.1 nm (Fig. 2e, f). Very thin sheets were positioned on the surface of the cement particles and had a wrinkly appearance that was analogous to the morphology shown in Fig. 2e. Additional methods of characterization indicated beyond a shadow of a doubt that glucose was effectively transformed to graphene. The X-ray diffraction (XRD) patterns of the GC composite (Fig. 3a) revealed a new peak around 27° representing as-formed graphene sheets. According to the Raman spectra of the GC material, two additional peaks were discovered at 1578 and 1360 cm−1, corresponding to the G-peak and D-peak of graphene, respectively. These peaks are found at these specific frequencies. The development of graphitic carbon was further supported by the G-band of the samples’ 532 nm Raman spectra (Fig. 3b), which was located at 1578 cm−1. The sample displayed a wide D-band with its center at 1360 cm−1, which was indicative of nanoscale graphite particles and chemically modified graphene flakes. The center of the band was at 1360 cm−1. This property, representing the existence of disorder as well as the boundaries of graphene domains, was detected with high-resolution SEM. The results of the studies suggested that the GC composite was composed of cement and graphene. Additionally, the results indicated that the graphene was equally distributed throughout the cement matrix and was confirmed by the fact that the GC material passed the GC test.

Fig. 2
Six images of G C material. a, Microscopic image of the G C material. b, c, and d, E D S images with Calcium K alpha 1, Carbon K alpha 1, 2, and Silicon K alpha 1. e, Microscopic image of a graphene sheet with a dashed rectangle. f, A F M image with a signal height of 1.1 nanometers.

Microscopic shape and structure of graphene, cement, and graphene–cement (GC) composite. a SEM image of fabricated GC composite in this study. b–d EDS of GC material. e High-resolusion SEM of GC material. f AFM of fabricated graphene sheet. AFM, atomic force microscopy; EDS, energy dispersive X-ray spectroscopy; SEM, scanning electron microscopy

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Fig. 3
Two graphs depict 3 fluctuating curves for graphene-cement, graphene, and cement from top to bottom. a. Intensity, arbitrary units, versus 2 theta, degree. b. Intensity, arbitrary units, versus Raman shift per centimeter. The highest peaks of the top and bottom curves are obtained at 1000.

a X-ray diffraction results, b Raman results of graphene, cement and graphene–cement composites

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3.2 Mechanical Properties of GC Material

After being cured for 28 days, the compressive strengths of GOP paste, GP-0, GP-1, GP-3, and GP-6 were evaluated, and the results are depicted in Fig. 4. When calculating each reported compressive strength, the average of three duplicate specimens was used as the basis for the calculation. The compressive strengths were affected by the different content of the reinforcing materials. The compressive and flexural strengths of the GC paste were superior to those of GP-0 and GOP. The compressive strength of GC paste increased in direct proportion to the graphene content. The GP-3 group demonstrated the strongest compressive strength of all of the groups. In comparison with the GC paste, GOP had a somewhat lower compressive strength. After curing for 28 days, the compressive of GP-3 rose by 38.18% in comparison with GP-0. In contrast, after curing for 28 days, the compressive strength of GOP fell by almost 0.75%, as shown in Fig. 4.

Fig. 4
A bar graph depicts the compressive strength in megapascals of G P 0, G P 1, G P 3, G P 6, and G O P on the left and the increase in G P 1, G P 3, and G P 6 on the right. The bars follow a bell-shaped trend. The highest value is 70 megapascals for G P 3.

The 28-day compressive strength tests of GP-0, GP-1, GP-3, GP-6, and GOP and corresponding rising rates of the samples compared with pure cement paste after 28 days

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3.3 Dispersion Effect

The large-scale SEM study of GP-3 and GOP, as well as the related element scanning tests, were carried out as shown in Fig. 5 for the purpose of confirming consistent distribution of the graphene. The carbon element distribution map of GCP-3 is shown in Fig. 5b, d, and the element distribution map of GOP is shown in Fig. 5f, both at the same scale as Fig. 5b. As can be seen in Fig. 5f, the aggregation of GO resulted in the formation of carbon element facula. On the other hand, graphene with uniform dispersion does not create an aggregation zone at the same scale (Fig. 5b), which demonstrated that the graphene was uniformly disseminated throughout the cement matrix.

Fig. 5
Three microscopic images with 3 E D S maps. a and b, The appearance of G P 3 with scale bars of 250 micrometers. c and d, Well-distributed graphene sheets with scale bars of 50 micrometers. e and f, Aggregation of G O sheets with scale bars of 50 micrometers.

Microscopic morphology and structure of GP-3 and GOP samples. a, c SEM image of GP-3 with different magnification. b EDS map of (a). d EDS map of (c). e SEM image of GOP. f EDS map of (e). GOP

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4 Conclusions

By heating a mixture of glucose powder and cement powder, a new in-situ growth approach has been devised with the goal of successfully dispersing graphene throughout the cement matrix in a homogeneous manner. In order to manufacture high-quality graphene in situ, glucose was used as the carbon source because it reduces the overall cost of the process. This recently developed synthetic technique is extensible to the rational design of additional cement-based materials, and it has already been done. The in-situ growing process that was developed may produce a low-cost product and improve the dispersion effect of graphene sheets in the cement matrix. This in turn improves the mechanical properties of cement paste and makes it more amenable for graphene-based reinforced cement composites to be used in civil engineering.