# Multifunctional Graphene-Concrete Composites: Performance and Mechanisms
## 3 Results and Discussion
### Microstructure of Concrete  
As illustrated in Figure 7, the cross-sectional morphology of ordinary concrete exhibits significant roughness and pronounced cracking at both 200 \(\upmu\)m and 20 \(\upmu\)m scales. At a higher resolution (2 \(\upmu\)m scale), the hydration products display a predominantly loose and disordered sheet-like structure. In contrast, graphene-modified concrete demonstrates a smoother cross-section with no observable cracks and a denser microstructure at the same magnification levels (200 \(\upmu\)m and 20 \(\upmu\)m). At the 2 \(\upmu\)m scale, the graphene-modified specimens reveal a higher abundance of well-defined plate-like crystals and a reduced  
Figure 5: **(a)** TEM image of graphene. **(b)** XRD diffraction image of graphene. **(c)** Raman spectrum of graphene (The D peak, G peak and 2D peak are the most important characteristic peaks, which respectively reflect the structure, defects and layer number information of graphene).  
presence of unbound hydration products. These observations collectively indicate that graphene incorporation enhances the interfacial bonding between coarse aggregates and cement paste, thereby improving the microstructural integrity and compactness of the composite material.  
As shown in Figure 8a, the thermogravimetric analysis reveals distinct weight-loss stages for concrete specimens within specific temperature ranges, consistent with previous studies [37]. Between 150 and 400 \({}^{\circ}\)C, the primary mass loss originates from the dehydration of calcium silicate hydrate gel (C-S-H), the dominant hydration product of cement. Subsequently, from 400 to 600 \({}^{\circ}\)C, the decomposition of calcium hydroxide (CH) accounts for the observed mass reduction, while the decarbonation of calcium carbonate (CaCO\({}_{3}\)) predominates between 600 and 1000 \({}^{\circ}\)C. The residual mass analysis demonstrates that graphene-modified concrete exhibits higher proportions of both CH and C-S-H compared to ordinary concrete, indicating enhanced hydration product formation and a denser microstructure. Figure 8b further illustrates that at a cement-to-graphene mass ratio of 0.006, the derivative thermogravimetry (DTG) peak intensity decreases most significantly, suggesting graphene's inhibitory effect on localized rapid pyrolysis induced by microcrack propagation. The DTG curve exhibits a prominent peak near 600 \({}^{\circ}\)C, confirming graphene's substantial influence on the thermal stability of concrete. The shift in peak characteristics underscores graphene's role in modulating the decomposition kinetics of concrete at elevated temperatures. In summary, microstructural characterization reveals that graphene-modified concrete exhibits a denser microstructure and a higher abundance  
Figure 6: (**a**) Graphene XPS superposition spectrogram. (The C1s, O1s and N1s peaks respectively correspond to the electronic binding energy information of carbon, oxygen and nitrogen elements, which can reveal the chemical composition, bonding state and possible doping or functional group modification of graphene.) (**b**) Spectrum of O element in graphene. (**c**) N spectrum in graphene. (**d**) Spectrum of C element in graphene.  
of hydration products compared to conventional concrete, as evidenced by comprehensive analytical techniques.  
Figure 8: (**a**) TGA curves of concrete with different cement and graphene mass ratios. (**b**) DTG curves of concrete with different cement and graphene mass ratios.  
Figure 7: Scanning electron microscopy (SEM) images were acquired to investigate the microstructural characteristics of concrete specimens incorporating varying graphene contents, with observations conducted at multiple magnification scales.