Accelerated carbonation of hardened cement paste: Quantification of calcium carbonate via ATR infrared spectroscopy

Abstract

In context of carbon capture and storage in cement and concrete industry, there is a strong demand for fast, reliable, and low‐cost CO2 quantification methods. Attenuated total reflection infrared spectroscopy (ATR‐IR) in conjunction with multivariate calibration via partial‐least‐squares regression was applied to quantify CaCO3 in carbonated hardened Portland cement pastes, as this method shows great potential in the field of process control. Thermogravimetric analysis coupled with infrared spectrometry for the detection of the evolving gases was used as a reference for quantification. Three methods for the quantitative analysis with different partial‐least‐squares parameters were developed on a series of ground physical mixtures of slightly carbonated and highly carbonated hydrated cement pastes that had absorbed up to 77% of the theoretical capacity for CO2. Additional samples for optimization and validation of the method were prepared by accelerated carbonation of cylindrical slices of hardened cement paste as a function of exposure time. In these experiments, the major CO2 uptake occurs in the first 60 min until the formation of CaCO3 layers limits the diffusion of CO2 and Ca2+ ions. The developed partial‐least‐squares models provided low estimation errors of max. 1.5 wt% and high correlation coefficients above 99.5%. The validation covers a concentration range of 20–48 wt% of CaCO3. Limitations of the method are discussed.