Graphene oxide’s regenerative acidity and its effects on the hydration of Type II Portland Cement

Incorporation of graphene oxide (GO) has been found to considerably improve the hydration process, strength and durability of Portland cement. However, the exact nature of its chemical interactions with the cement are unclear. In this study, GO of varying amounts of hydroxyl groups were synthesized to investigate the effects of these interactions on the hydration of an environment-friendly Type II Portland Cement. XPS, Raman, and FTIR analysis verified the functional group differences between the GO types, and SEM and AFM observations illustrated the existence of a hydronium layer coating the high-hydroxyl GO (HGO). The hydronium layer neutralizes small base additions as measured through titration, and regenerates via protonation of resulting water by HGO’s hydroxyl groups, confirmed via zeta potential analysis. In cement, HGO shows accelerated and greater early-age hydration, measured via heat of hydration and XRD. Finer microstructural density of HGO-cement was also observed from BET and microCT analysis. On the other hand, low-hydroxyl GO (XGO) cement ‘locks’ C-S-H on the GO sheet, preventing its propagation in the cement microstructure, as observed by Si-O bond changes during hydration. Lastly, HGO-concrete showed significantly improved workability (>40%), 28-day compressive strength (29%), and 28-day flexural strength (24%) with respect to control. Conversely, XGO-concrete showed reduced workability (−40%), and smaller 28-day strength improvements (compressive by 5%, and flexural by 8%). This research leads to new understandings of how GO may improve the strength, workability, and durability of concrete, with potentially less overall cement consumption and superplasticizer use.