Research Center for Safety and Durability of Structures and Materials

Madrid, Spain

Research Center for Safety and Durability of Structures and Materials

Madrid, Spain
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Galan I.,Research Center for Safety and Durability of Structures and Materials | Glasser F.P.,University of Aberdeen | Andrade C.,Research Center for Safety and Durability of Structures and Materials
Journal of Thermal Analysis and Calorimetry | Year: 2013

Calcium carbonate decomposes under well-defined conditions giving CaO (solid) and CO2 (gas). The process kinetics are known to be strongly influenced by the CO2 partial pressure and temperature. In dynamic conditions, as in thermogravimetric analysis (TG) and differential thermal analysis (DTA), kinetics influence the observed heat effect and mass losses, as was shown in semi-static studies by Hyatt et al. (J Am Ceram Soc 41:70-74, 1). However, differing DTA and TG curve shapes are reported in the literature even under supposedly comparable conditions. The differences are attributed in part to the design of the equipment and in part to differing crystalline states of the precursor calcium carbonate. To resolve these uncertainties, the TG has been performed at different heating rates and at different but controlled partial pressures of CO2. The results are reported and critically evaluated in the light of the data obtained, and the kinetic parameters as reported by Hyatt et al. (J Am Ceram Soc 41:70-74, 1) are re-evaluated. © 2012 Akadémiai Kiadó, Budapest, Hungary.


Galan I.,Research Center for Safety and Durability of Structures and Materials | Andrade C.,Research Center for Safety and Durability of Structures and Materials | Castellote M.,Research Center for Safety and Durability of Structures and Materials
Journal of Thermal Analysis and Calorimetry | Year: 2012

Cement paste carbonation, i.e., the reaction between CO 2 and the hydrated cement phases, mainly calcium hydroxide or portlandite, can lead to a pH decrease, which in turn can give rise to steel corrosion in reinforced concrete. At the same time, the carbonation reaction contributes to combine CO 2 and fix it as calcium carbonate. It is a crucial phenomenon from the point of view of structure durability and also for cement-based materials sustainability. Cement paste specimens with two w/c ratios and eight types of cements were submitted to different environmental conditions for 4 years and the evolution of calcium carbonate formed or carbon dioxide bound was followed by TG performed in inert atmosphere. The amounts of calcium hydroxide, evaporable and C-S-H gel water were also measured. The CO 2 bound follows the same trend in all samples and environments: at the beginning there is a sharp increase followed by a very slow stretch and reaching a maximum after less than 2 years in most cases. The calcium hydroxide amounts evolve very differently in each environment. While outside it is almost consumed after 1 year, inside there is a decrease in the first year, but an increase in the next 3 years. The behavior of the C-S-H water in both environments is similar to that of the portlandite inside. The evaporable water diminishes in all cases to 1 %. From the data obtained by TG, the quantification of the C-S-H gel as well as the calculation of the Ca/Si ratio and the hydration of the gel formed by different type of binders has been possible. © 2012 Akadémiai Kiadó, Budapest, Hungary.

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