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

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 physicalmixtures 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
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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.