Carbonation resistance of different types of calcium silicate hydrates

Carbonation is a natural process and occurs in all building materials based on cement or lime. Re‐carbonation of cement‐based materials is an eco‐friendly process, but this process cannot proceed too fast. Autoclaved aerated concrete is a type of concrete produced using the autoclaving process. Due to the fact that other C‐S‐H phases can be formed under hydrothermal conditions in comparison to the standard hydration process in natural conditions, the durability of those phases, mainly tobermorite, should be higher, which was a subject of many studies. Different raw materials and different Cao/SiO₂ ratio of the fresh concrete mix is used to produce different densities. Using different CaO/SiO₂ may result not only in different amounts of tobermorite in AAC phase composition but also in different morphology of those crystals. This research program concerns the correlation between CaO/SiO₂ and the source of the raw materials used on tobermorite formation under hydrothermal conditions and its resistance to re‐carbonation. The different CaO/SiO₂ molar ratios used are reflected in the formulas of different class densities of AAC with different cement‐to‐burnt lime ratios. The impact of CO₂ in a climate chamber on the phase composition were tested for all samples. The phase composition test was conducted using the XRD method and a SEM analysis with EDS system.