Preventing unintended carbonation in hardened cement paste powder during thermogravimetric analysis

Unintended carbonation of hardened cement paste (HCP) powder samples during thermogravimetric analysis (TGA) can compromise the accuracy of carbonation-related studies in cement-based materials. To prevent the CO₂ absorption of HCP samples during prolonged standby on the auto-sampler of the TGA device, this study proposes and evaluates five countermeasures: no treatment, platinum cover, alpha-alumina powder coverage, styrene monomer injection, and 2,6-dimethyl-4-heptanone injection. Among these, 2,6-dimethyl-4-heptanone effectively inhibited carbonation, maintaining the stable amount of Ca(OH)₂ and CaCO₃ in samples over ten hours. Fourier transform infrared spectroscopy (FTIR) analysis confirmed that 2,6-dimethyl-4-heptanone was physically adsorbed in HCP pores without forming chemical bonds, while proton nuclear magnetic resonance (¹H NMR) relaxometry revealed a correlation between micropore volume and physical adsorption. Additionally, nitrogen sorption results confirmed that the pore structure of HCP remained unchanged by the 2,6-dimethyl-4-heptanone. Despite minor challenges in quantifying bound water, this method enhances the reliability of TGA-based carbonation-related studies by eliminating background carbonation effects. These findings provide a practical solution for accurate CO₂ absorption assessments in cementitious materials, contributing to sustainable carbon capture and storage strategies in the construction industry.