Microstructure development and mechanism of hardened cement paste incorporating graphene oxide during carbonation

In this work, the carbonation mechanism of cement paste containing graphene oxide (GO) was examined by evaluating its electrochemical, kinetic, and microstructural characteristics under accelerated carbonation, corresponding to a 20% concentration of CO2, a temperature of (30 +/- 1)degrees C, and a relative humidity of 65%-70%. Transport properties of the composites were studied using a non-destructive electrochemical impedance spectroscopy (EIS) technique, while their carbonation kinetics was investigated via thermogravimetric analysis (TGA). The obtained EIS results indicated that the ion diffusion and transport resistance increased after the incorporation of GO, while TGA results revealed that the carbonation of portlandite (CH) and calcium-silicate hydrate (C-S-H) was significantly inhibited during early ages of carbonation due to the increased degree of hydration. In addition, the hybrid GO/hydration products from the carbonation process were characterized, and the formation of a hydrated phase coated with a carbonated layer was observed via scanning electron microscopy and energy dispersive spectroscopy. Porosity variations of the studied materials during carbonation were also evaluated using a mercury intrusion porosimetry method. The porosity of the OPC decreased more significantly during the initial carbonation period as compared to the effect observed for the GO cement-based material.