Carbon dots as a superior building nanomaterial for enhancing the mechanical properties of cement-based composites

Carbon nanomaterials, such as graphene and its derivatives can act as a significant building nanomaterial for ameliorating the various properties of cement-based composites, but their poor water solubility lead to unevenly dispersed in the cement pore solution, and limits their effective application in cement-based materials. Moreover, the high price of these nanomaterials restricts the practical use in industry. Herein, in this study, the carbon dots (CDs), which was prepared by the improved microwave pyrolysis method, is demonstrated to own the superior performance in the enhancement of the cement-based composites mechanical properties for the first time. The X-ray powder diffraction (XRD), High-resolution transmission electron microscopy (HR-TEM), X-ray photoelectron spectroscopy (XPS) and related structural characterizations are performed to prove the successful synthesis of CDs, and the compressive strength of cement-based composites increased by 16.8% after curing 28 days at the 0.08 wt% CDs dosage in comparison to the blank samples. Through thermogravimetric analysis (TGA), scanning electron microscopy (SEM) and mercury intrusion porosimeter (MIP) and XRD, it is proved that: i) the small nanometer size and good water solubility of carbon dots promote them easily filling into the pores of cement as a result of increasing its compactness; ii) the carbon dots act as much more nucleation sites to make the hydration products superimposed in a more dense room; iii) the surface of carbon dots possess many hydrophilic groups, including carboxyl and amide, these groups produce a strong adsorption on the cement particles and then affect the formation of hydration products. These joint effects effectively enhance the compressive mechanical strength for cement-based composites. Besides, the simple preparation of CDs with a low price is suitable for the industrial application. The CDs as the superior alternative nanomaterial for heightening the properties of cement-based composites show a great potential, and is significant for the exploitation of building nanomaterial with outstanding performances for cement.