Stable phase composition in novel cementitious systems: C-A-S-H
Description: Concrete is the world's most durable, reliable and economical construction material, essential for the basic infrastructures that make our societies function smoothly. However, the production of cement, the key binding element in concrete, is responsible for roughly 5-8% of global man-made CO2, due to the very large use of concrete to build houses and infrastructures. For every tonne of Portland cement produced, 650-900 kg of CO2 is emitted amounting to more than 2 million tonnes worldwide The largest potential for CO2 reduction lies in (a) reducing the clinker content e.g. by the addition of limestone or (b) using supplementary cementitious materials (SCMs). The use of SCMs such as blast furnace slags resulting from steel production or fly ash from coal combustions, represent a viable al-ternative to Portland cements and are means to utilize by-products of industrial manufacturing proc-esses. The use of such SCMs is hindered by the fact that novel, low-CO2 cementitious materials will inevitably have different chemistry and will form different solids during hydration than Portland ce-ments and therefore perform and behave differently in concrete. The single most important phase in cements based on silica-rich SCMs is the calcium silicate hydrate phase (C-S-H). The C-S-H in such systems is dramatically different to C-S-H in Portland cements; it will exhibit a low Ca/Si ratio, will have different space filling properties and also show an increased incorporation of ions such as aluminum (C-A-S-H) or alkalis. This is critical for the mechanical properties and durability of the concrete. Our knowledge about the structure, composition and the properties of such a low Ca/Si C-A-S-H is insuffi-cient. This project aims to understand the change in properties of silica-rich C-S-H in presence of silica-rich supplementary cementitious materials. We will develop a thermodynamic model for C(-A)-S-H, N/K-A-S-H gel in cementitious systems based on i) the structural information and surface properties of C-(A)-S-H from atomistic simulations, ii) experimental data on solubility of C(-A)-S-H in the presence of al-kali, iii) experimental data on solubility of C(-A)-S-H in the presence of sulfate, carbonate and chlorides and iv) detailed spectroscopic characterization and investigation of the homogeneity of the solid phases.We will apply the thermodynamic model to predict the stable phase assemblage, its volume properties and porosity in cement. The development of such generic thermodynamic models is an indispensable step toward a better fundamental understanding of cementitious systems based on SCMs.
Amount: CHF 919,100
Funding type: research
Funder scheme: Sinergia
Start date: 2010-11-01
End date: 2014-10-31
Investigator: Lothenbach, Barbara
Institution: Swiss Federal Laboratories for Materials Science and Technology – EMPA
Funded outputs count: 6
Funder award ID: 130419
OpenAlex ID: G1925741385