Multi-scale pore structure characterisation of graphene-doped cement mortars

The presence of an internal pore structure is an intrinsic characteristic of all cementitious compounds, with pore sizes spanning from angstroms to millimetres. Investigating porosity is crucial to understand and predict the mechanical and transport behaviour of cement-based materials; however, no single experimental technique is capable of capturing the full range of pore sizes, making a multi-scale approach necessary. In this study, three types of cement mortar are examined: a control mortar with no additives (C), and two graphene-doped mortars containing 1 wt% of graphene technical grade (1TG) and 1 wt% of graphene oxide (1GO), respectively. Consistency, flexural and compressive strength, and capillary water absorption (CWA), previously reported, are correlated with the pore structure, characterized by nitrogen physisorption ( N2), mercury intrusion porosimetry (MIP), and x-ray microcomputed tomography ( mu-CT). Despite a considerable reduction in consistency, the doped mortars, 1TG and 1GO, do not show appreciable variations in compressive strength compared to mortar C, while they show a reduction in CWA of the 22% and 15% respectively. Morphological analysis was conducted on data collected by mu-CT: mortar C shows a significant contribution of low-sphericity pores associated with microcracks, 1GO is dominated by highly spherical pores consistent with entrapped air voids, and 1TG presents a broader distribution of sphericity. Overall, analysing and merging the pore size distribution data obtained from N 2, MIP and mu-CT, allowed us to cover a range of pore size from 2 nm to 10 mm and correlate the macroscopic behaviour to the internal pore structure of cement mortars.