Mechanisms of carbonation of calcium silicate hydrate phases in hydrothermal hardened aerated building materials

• Applicant: Professor Dr.-Ing. Thomas Matschei, since 12/2023
• Subject Area: Construction Material Sciences, Chemistry, Building Physics
• Term: since 2020
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 445500601

The strengthening phase 11Å-tobermorite is decomposed to silicate gel and calcium carbonate by carbonation of autoclaved aerated concrete (AAC). Until now, the main influencing factors regarding carbonation of AAC have not been completely understood. Investigations of Lohaus et al. have shown that after storage for 58 months in case of some products of AAC only minor amounts of tobermorite have reacted, whereas in case of one product no tobermorite was remaining in combination with a high loss of strength. The question is why the crystalline phase tobermorite partially strongly reacts with CO2 and partially nearly is inert, respectively. The main aims of this research proposal are the elucidation of the carbonation mechanism of AAC and the determination of the carbonation velocity. For elucidating the carbonation mechanism the two internal influencing factors crystallinity and porosity in combination with the sulfate content should be investigated initially. For this, AAC products with two bulk density classes and varying sulfate contents should be produced in cooperation with an industry partner. External factors like temperature, relative humidity and CO2 concentration should be kept constant. For analysing the internal influencing factors the results of chemico-mineralogical investigations and mechanical-physical investigations should be correlated. By chemico-mineralogical research methods like chemisorption, NMR, SEM, TEM and XRD the microstructure and the reaction process should be analysed. With these methods the reactivity of tobermorite with CO2 should be investigated, inter alia. By determining the compressive strength, the elastic modulus, the bulk density and the shrinkage behaviour the changes on macroscopic scale should be analysed. For determining the carbonation velocity a carbonation profile in function of time should be prepared for the selected AAC products. In conclusion a model should be developed which shows the carbonation of tobermorite in AAC in function of time.

• DFG Programme: Research Grants
• Ehemaliger Antragsteller: Dr. Holger Nebel, until 11/2023