Microstructure and Hydration of Cement-based Materials Incorporating Calcined Clay and Calcium-silicate-hydrate (C-S-H) Seed
Date
2020-07-22
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Abstract
The production of concrete is estimated to account for around 5 to 8% of the global anthropogenic CO2 emissions. The use of supplementary cementitious materials (SCMs) to partially substitute Portland cement in concrete is the most effective and practical approach to reduce such emissions. Calcined clays have great potential to be used as SCMs due to their abundant distribution in the earth crust. In particular, metakaolin (MK), obtained from the calcination of kaolinitic clay, possesses high pozzolanic reactivity which enables it to react with calcium hydroxide (CH) derived from cement hydration to form additional calcium-silicate-hydrate (C-S-H). Such extra hydrates can contribute to the mechanical properties and durability of concrete. Pure MK, however, is expensive due to the competitive uses in other industries. It is therefore of great interest to explore calcined clays with lower grades of MK as SCMs in concrete. A seeding approach using C-S-H seed was also investigated to improve the properties of cement-based materials incorporating high volumes of calcined clay. Analytical techniques including thermogravimetric analysis (TGA), quantitative X-ray diffraction (QXRD), scanning electron microscopy-energy dispersive spectroscopy (SEM-EDS) and X-ray photoelectron spectroscopy (XPS) were used to investigate the hydration and microstructure of two types of cementitious systems: I. Cement paste made with calcined clay: A locally available calcined clay with ~40 wt.% MK content was used to replace cement with increasing substitution levels (10‒40 wt.%). Strength test and microstructural analysis showed that cement paste with up to 40 wt.% replacement level generated good mechanical properties, which was linked to the refinement of microstructure due to the incorporation of the calcined clay. II. Cement paste made with calcined clay and C-S-H seed: Based on the results obtained in Part I, a C-S-H seeding agent was introduced to systems with selected replacement levels (20 and 40 wt.%) to improve the properties of the cement paste. The results demonstrated that the C-S-H seed was able to compensate for the strength of cement paste specimens even those made with high replacement levels. The combination of these two materials represents a promising approach to produce more sustainable concrete with lower embodied carbon.
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Zhao, D. (2020). Microstructure and Hydration of Cement-based Materials Incorporating Calcined Clay and Calcium-silicate-hydrate (C-S-H) Seed (Master's thesis, University of Calgary, Calgary, Canada). Retrieved from https://prism.ucalgary.ca.