Pozzolanic reaction of supplementary cementitious materials

This project investigated the effect of four different supplementary cementitious materials (SCMs) on the hydration of white Portland cement pastes. The studied SCMs were silica fume, metakaolin, microsit, and fly ash. The addition of the SCMS depended on the physical and chemical characteristics. The aim of this project was to extend the simplified Powers Model for pastes containing SCMs. Therefore, the following hydration properties of hardened Portland cement paste were measured on the cementitious materials: chemically bound water, gel water, calcium hydroxide chemical shrinkage, and degree of hydration.
Different microstructural characterization techniques were used to determine the mentioned hydration properties: thermogravimetric analysis (for chemical bound water and calcium hydroxide), X-ray diffraction (for calcium hydroxide and degree of hydration), dynamic vapor sorption (for gel water), desiccator method to determine sorption isotherms (for gel water), ²⁹Si Nuclear Magnetic Resonance (for degree of hydration of cement and SCMs), and chemical shrinkage. All the measurements were mathematically analyzed by the dispersion model developed by Knudsen.
The hydration of white Portland cement is described thoroughly in the document. The obtained results allowed to describe the CSH composition. An equation is proposed. In addition to this, the volumetric phase distribution was modeled by utilizing the simplified form of the Powers Model and computing the measured hydration properties.
Overall, the results showed that the pozzolanic reaction of the SCMs with the calcium hydroxide decreases the chemically bound water at later hydration age. It is believed that the pozzolanic reaction of SCMs physically binds water. The results also showed that the pozzolanic C-S-H gel produced by the silica fume and the calcium hydroxide has a tobermorite-like structure.
The extension of the simplified Powers Model for pastes made with different supplementary cementitious materials was possible under the assumptions and limitations that come with it.
It is concluded that even though the construction materials change over time due to manufacturing processes improvements, the Powers' Model continues describing the hydration of Portland cement accurately.