Powder Characterisation of ZincModified Synthetic Calcium Silicate Hydrate (C-S-H)
Tutor / Supervisor
Morales Melgares, Anna
Student
Sola Blasco, Arnau
Document type
Master thesis
Date
2022
rights
Open Access
Publisher
Universitat Politècnica de Catalunya
UPCommons
Abstract
Despite being one of the most abundant materials in the world, several aspects of C-S-H still remain unknown. It has been shown that minor additions of zinc enhance the early age strength of the cement's clinker as it increases C-S-H reactivity, but the mechanisms behind this are still unclear. As C-S-H is the main hydration product of cement, understanding the effect of zinc on it's growth can help improve cement's properties and thus lower its CO2 emissions by partially substituting it with SCMs. In this project, high Ca:Si ratio (>1.5) C-S-H and Zn-modified C-S-H have been successfully synthesized by a dropwise precipitation method. Samples were preliminary characterised through XRD, which confirmed that zinc was incorporated into the structure of C-S-H and no new phases were formed. TGA quantified the bound water, carbonation and portlandite losses. It also showed that portlandite formation did not have a significant impact in the corrected Ca:Si ratio. TEM micrographs showed the nanofoil morphology of both C-S-H and Zn-modified C-S-H. Particle size distributions (PSD) were studied using laser diffraction., concluding that C-SH was agglomerating into particles that are 1-20 µm. PSD frequency plots also showed the formation of two main agglomerates families of 4.9 and 6.6 µm, regardless of the amount of zinc. SSA values, obtained through N2 adsorption experiment and using the BET model, oscillated between 133 and 325 m2 /g. When both values from PSD and SSA were used, an agglomeration factor FAG could be calculated. It ranged from 110 to 171, which concludes that the C-S-H is a very heavy agglomerated powder. Also, zeta potential results indicated that positive Na+ and Ca+2 ions adsorbed from the dispersion media onto the C-S-H surface, with a preference for the latter when both were competing. Also, when supernatant was used as the dispersion medium, zeta potential values decreased for Zn-modified C-S-H. This supports the current Zn-modified C-S-H atomistic structure theory, which points to zinc substituting silicon and calcium atoms in CS-H surface.
Entitat col·laboradora
École polytechnique fédérale de Lausanne
Participating teacher
- Morales Melgares, Anna