Gas CO2 foaming and intermixing in portland cement paste to sequester CO2

Abstract

In this study, concentrated CO₂ gas was used to create foamed cement paste, and concentrated CO₂ gas was intermixed in fresh cement paste to produce regular cement paste materials that were not foamed. The potential of both methods to form CaCO₃ from calcium ions that would form Ca(OH)₂ was investigated. After curing the materials for different ages, the Ca(OH)₂ and CaCO₃ contents were measured using thermogravimetric analysis; the large void size distributions, dynamic modulus, and compressive strength were tested and compared against Control (no gas added), and N₂ foamed and N₂ intermixed specimens. A 10% increase in dynamic modulus and compressive strength was measured in CO2 foamed specimens compared to N2 foamed specimens. The increase in mechanical properties was the result of both a narrow void diameter distribution and CaCO3 formation in place of Ca(OH)₂. The CO₂ foamed cement generation method shows the potential to sequester 0.06 ton of CO₂ for every ton of cement which is a CO₂ emission reduction of 7.0% of the CO₂ production associated with cement production. For the CO₂ intermixing method, the void content, compressive strength, and dynamic modulus results were consistent between the Control and CO₂ intermixed specimens while the N₂ intermixed specimens showed a decrease in compressive strength and dynamic modulus. The CO₂ intermixing method showed potential to sequester 0.04 ton of CO₂ for every ton of cement or a 4.7% CO₂ emission reduction of the total CO₂ production associated with cement manufacturing. The reported CO₂ emissions are not based on life cycle assessment and do not account for emissions associated with CO₂ collection, transportation, and intermixing. The present paper does not investigate the mechanisms of hydration under CO₂ intermixing.