Influence of water vapour and carbon dioxide on free lime during storage at 80°C, studied by Raman spectroscopy

Abstract

10Micro-Raman spectroscopy has been used to follow the reaction of free lime (CaO) exposed 11 for 24 hours to moist air at 80 °C under conditions of different relative humidities (10 -80 % 12 RH). X-ray diffraction and SEM imaging were applied as complementary techniques. The 13 conversion of lime to calcium hydroxide and its subsequent carbonation to various calcium 14 carbonate polymorphs was found to strongly depend on the relative humidity. At low RH (10 15 -20 %), only Raman spectroscopy revealed the formation of early amorphous CaCO 3 which 16 in the XRD patterns was detected only at ≥ 40 % RH. However, XRD analysis could identify 17 the crystalline polymorphs formed at higher relative humidities. Thus, between 20 and 18 60 % RH, all three CaCO 3 polymorphs (calcite, aragonite and vaterite) were observed via 19 XRD whereas at high relative humidity (80 %), calcite was the predominant reaction product. 20The results demonstrate the usefulness of Raman spectroscopy in the study of minor cement 21 constituents and their reaction products on air, especially of amorphous character. 22 23

Investigation of the carbonation mechanism of CH and C-S-H in terms of kinetics, microstructure changes and moisture properties

“…It is noteworthy that in a recent study [76] authors have investigated the effect of water vapor and CO 2 on portlandite by Raman Spectroscopy and have shown the presence of amorphous CC if RH < 20%, metastable vaterite and aragonite if 20% < RH < 80% and calcite for higher RH-values.…”

Alkali-activated slag cements produced with a blended sodium carbonate/sodium silicate activator

“…The formation of aragonite or vaterite rather than calcite in the early stages of the reaction may be associated with an intermediate relative humidity reached within the sample (Dubina et al, 2013) or a high concentration of magnesium present in the pore solution at early times of curing. Magnesium has a significant influence on calcium carbonate precipitation, and can stabilise amorphous carbonates, aragonite and/or vaterite when its concentration is sufficiently high (Falini et al, 1996;Loste et al, 2003).…”

Micro‐Raman spectroscopy investigation of the carbonation reaction in a lime paste produced with a traditional technology

“…In the complex system of Portland cement studied by Corvisier et al , all three calcium carbonate polymorphs (calcite, aragonite and vaterite) were detected and their distribution along the main CO 2 diffusion direction was mapped at the millimetric scale. The formation of crystalline CaCO 3 polymorphs in lime paste was found to be strongly dependent on relative humidity . The concurrently formation of calcite, vaterite and aragonite was observed between 20 and 60% RH at 80 °C .…”

“…It is well known, that reactions conditions (e.g. temperature, pH, humidity, presence of additives) play a crucial role in the precipitation of the CaCO 3 polymorphs . In the complex system of Portland cement studied by Corvisier et al , all three calcium carbonate polymorphs (calcite, aragonite and vaterite) were detected and their distribution along the main CO 2 diffusion direction was mapped at the millimetric scale.…”