X-ray computed tomography-based characterisation of graphene nanoplatelets re-agglomeration in hardened cement composites

Graphene Nanoplatelets (GNPs) have been found to be an effective additive for enhancing the mechanical strength of cementitious materials, attributed to the role they play as nucleation sites. However, there is not a direct correlation on the enhancing effect of graphene with increasing graphene dosage, resulting in different optimal dosages for different binders and mix designs. This study aims to develop a method to clarify the governing factor that determines the optimal graphene dosage in mortar mixes. X-ray computed tomography (XCT) was used to identify the size, surface area and distribution/re-agglomeration of graphene nanoplatelets in the prepared mixes. Compressive strength tests and TGA analysis were carried out to evaluate correlations among the total surface area of graphene nanoplatelets, mechanical performance, and cement hydration. Out of the three graphene dosages (0.035, 0.07, and 0.1 wt% by mass of cement) used in this study, samples with 0.07 wt% graphene revealed the highest total surface area of graphene nanoplatelets, hydration degree, and compressive strength. Results revealed that the enhancing effect of graphene addition in cement-based mixes was associated with the total surface area of the graphene nanoplatelets. A larger surface area contributed to stronger mechanical reinforcement by providing an increased number of nucleation sites in the pore solution.