Carbonation of Portland Cement Studied by Diffuse Reflection Fourier Transform Infrared Spectroscopy

Abstract

Carbonation is a natural ageing process for cement. This study focuses on how the carbonation rate varies with selected hydration times and atmospheric conditions during the early stages of reacting dried cement paste. Diffuse reflection Fourier transform infrared spectroscopy is shown to be a suitable technique to monitor the formation of carbonates in cement. Combined with a previously developed freeze drying technique, carbonation can be studied at specific hydration stages. In ambient air both calcium hydroxide and calcium silicate hydrate (C-S-H) in cement are carbonated. Increased hydration time enhances the carbon dioxide uptake, which indicates that the calcium in the hydration products reacts more easily than the calcium in the clinker phase. In a humid CO 2 atmosphere, the carbonation process is so pronounced that it decomposes C-S-H into calcium carbonate and silica. In a moist N 2 atmosphere no carbonation occurs, but the sulfate chemistry of the cement seems to be affected due to the formation of ettringite.

Effects of CO2 and temperature on the structure and chemistry of C–(A–)S–H investigated by Raman spectroscopy

“…8,9 The carbonation process also degrades the C-S-H gel structure 10 and produces CaCO 3 , silica gel and water. However, the carbonation process is naturally a possible method to sequester CO 2 .…”

Heavy Metal Leaching, CO2 Uptake and Mechanical Characteristics of Carbonated Porous Concrete with Alkali-Activated Slag and Bottom Ash

“…This condition may act as a buffer for the decalcification of C-S-H phases in the OPC paste (Bakharev et al 2001). In addition, the carbonated products in an OPC matrix can create a protective area that can interfere with the diffusion of CO 2 , filling the pores with the carbonated products (Bernal et al 2014;Ylmén and Jäglid 2013). Thus, the formation of carbonates under the rich calcium condition can reduce the porosity of an OPC matrix (Bernal et al 2014;Bakharev et al 2001).…”

Carbonation of C–S–H and C–A–S–H samples studied by 13 C, 27 Al and 29 Si MAS NMR spectroscopy

“…For the C-S-H phase, valuable information about the structural changes that follow carbonation reactions has been obtained from transmission electron microscopy (TEM) [8][9][10], 29 Si MAS NMR [9,[11][12][13] as well as Raman and infrared spectroscopies [11,14,15]. Groves et al [9] investigated the C-S-H phase formed by hydration of tricalcium silicate (Ca 3 SiO 5 ) for 42 days and subsequently exposed to a continuous flow of CO 2 at a relative humidity of 72.6% by a combination of analytical TEM and 29 Si MAS NMR.…”