Mechanism of graphene oxide inducing the orderly growth of CaCO3 and C-S-H seed crystals in cement slurry-solid transition: Application in CCUS cementing

In the geological storage and utilization wells of CO2, the cement paste will undergo an early carbonization reaction with supercritical CO2 at the liquid-to-solid transition stage during the injection process. In the early stages of the hydration-carbonation synergistic reaction, liquid cement slurry exhibits high porosity and inadequate mechanical properties. In this work, the early carbonization reaction rate of the liquid cement paste is accelerated by adding graphene oxide (GO) to refine the pores of the cement and optimize the microstructure. The results show that GO can enhance the predominance of the hydration reaction in the cement paste during the synergistic process of early hydration and carbonation. This effect leads to an earlier appearance of the peak relative content of Ca(OH)2, a hydration product generated by the reaction, and shifts the peak time from 16 to 12 h. 29Si NMR spectra show that GO can increase the degree of polymerization of C-S-H, with the average chain length increasing from 5.79 to 6.53. SEM-EDS and μ-CT results show that in the early synergistic reaction between hydration and carbonation (4–72 h), GO induced the orderly growth of CaCO3 and C-S-H seed crystals through the "carbon dot effect", forming a large number of flower-like structures, which reduced the porosity of cement from 2.15 % to 1.22 %. •GO accelerates the hydration-carbonization synergy rate of cement slurry in the liquid-solid transition stage.•The "carbon dot effect" of GO causes the hydration and carbonation products to take the form of flower clusters.•Flower clusters of hydration and carbonization products refine the cement pores.•GO increased the polymerization degree and average chain length of C-S-H during supercritical CO2 intrusion into cement.