The synergic effects of metakaolin and polycarboxylate-ether on dispersion of graphene oxide in cementitious environments and macro-level properties of graphene oxide modified cement composites

Abstract

Studying the effects of pozzolanic materials such as silica fume, fly ash, and metakaolin (MK) on dispersion of graphene oxide (GO) in cementitious environments has attracted interest in recent years. In this research, the potential of MK particles as an impediment against GO agglomeration in high alkaline environments is investigated. Despite the exhibited results in previous studies that the particles of pozzolans can inhibit the agglomeration of GO in cementitious environments by consuming Ca(OH)2 besides the mechanical separation of GO sheets, the results of the present study revealed that MK particles alone could not prevent GO nanosheets from clustering, physically or chemically. However, based on UV–vis spectroscopy and SEM-EDS analysis results, the incorporation of MK particles with Polycarboxylate-ether (PCE) significantly ameliorates the dispersion and time-dependent stability of GO nanosheets in simulated cement pore solution. Indeed, in this case, the anchoring characteristic of the negative surface charge of MK particles besides the steric hindrance effect of PCE’s side chains can reduce the possibility of the interaction between GO nanosheets and calcium ions in cementitious environments. Moreover, the improved stability of MK-PCE modified GO suspensions ensures the permanence of the desired dispersion of GO in the alkaline medium of cement composites, which is advantageous for enhancing the mechanical and transport properties of cement composites. In this research, the results of compressive strength, flexural strength, flexural modulus, toughness, and ultrasonic pulse velocity tests on MK-GO incorporated cement paste samples after 28 days of curing showed an enhancement by 27.6%, 36.3%, 49.8%, 42.0%, and 5.0%, respectively compared to the reference sample. This improvement is primarily due to the beneficial effects of MK-PCE to make GO play a better reinforcing role in cement composites.