Deep research about the mechanisms of graphene oxide (GO) aggregation in alkaline cement pore solution

Abstract

In order to understand the fundamental mechanisms beneath the aggregation of Graphene Oxide (GO) in cement pore solution, deep research about the differences in the dispersion behavior of GO in Ca(OH)2, CaCl2, and NaOH solutions has been done. The results showed that the prime factor responsible for the immediate aggregation of GO in cement paste is the complexation of Ca2+, rather than the deoxygenation of GO in the alkaline environment. GO could disperse uniformly in NaOH solution (pH = 12.9) for a few hours. However, with the gradual deoxygenation of GO, small agglomerates formed after 6 h due to the weak electrostatic repulsion and less hydrophilic nature. The analysis of X-ray photoelectron spectroscopy (XPS) and hydration heat measurement showed that GO maintained a large number of functional groups (especially carboxyl groups), which could act as growth sites for hydration products and interact with them. Moreover, the dispersion capacity of GO in the alkaline environment with the presence of polycarboxylate superplasticizer (PC) was also studied and the results revealed that PC could adsorb on GO surface due to the entropy gain and delay the aggregation of GO through steric hindrance effect.