Impact of graphene oxide and highly reduced graphene oxide on cement based composites

Abstract

This study examines and compares the performance of two specific forms of graphene nanomaterials in the cement based composite, namely graphene oxide (GO) and reduced graphene oxide (rGO). A typical forms of GO with the average C:O ratio of 54:46 and a rGO with the average C:O ratio of 82:18 were used in the cement based paste composites. rGO was treated with superplasticizer to improve its dispersibility in water. Both GO and rGO were used as 0.02, 0.04, 0.06 wt% of cement. The effect of GO and rGO on workability, early age hydration, microstructure, mechanical and transport properties was determined. Different characteristics of GO and rGO such as molecular structure, functional groups, d spacing, size and physical strength influenced the properties of the cement based composites. The workability and final setting time of composite gradually decreased compared to 100% PC (control) with higher dosages of GO up to 0.06 wt% (of cement), which is due to the dominant oxygen functional groups and the hydrophilic nature of GO. To the contrary, the workability and final setting time increased in the rGO composites compared to the control mix due to the almost hydrophobic nature of rGO and the presence of superplasticiser. The XRD and TGA quantification of the hydration products shows that GO composites have a greater content of Ca(OH)2 and C-S-H compared to rGO composites measured at 1, 7 and 28 days. Micropores (smaller than ∼10 µm) in GO composites were observed to be filled with calcium silicate hydrate (C-S-H) gel and crystalline compounds. Random pore filling nature was observed in rGO composites and ettringite was more common element in those pores. Meso and gel pores (<2 nm) related to C-S-H show increasing trend in the GO and rGO composites compared to the control mix in dynamic vapour sorption (DVS) analysis. Compared to the control mix, the 28-day compressive strength increased by ∼10% and ∼15% in 0.06 wt% of GO and rGO in the composites. However, the highest flexural strength was increased in the 0.04 wt% of GO and 0.06 wt% rGO composite, and the enhancement was 75.7% and 33.7%, respectively, compared to the control mix. The electrical resistivity value increased with the incorporation of GO and rGO. The water sorptivity coefficient of 28-day GO and rGO composite reduced 24.8% and 4.7%, respectively, compared to the control mix.