PhD defence Jennifer Anette Canul Polanco

PhD defence Jennifer Anette Canul Polanco ”Pozzolanic reaction of supplementary cementitious materials”

Cement production is associated with high CO2 emissions. Therefore, alternatives to its use, like the replacement of cement by supplementary cementitious materials (SCM’s), are widely used to produce more sustainable concrete, and at the same time, more durable. The main reactions in the hydration of Portland cement are well known. However, the pozzolanic reaction of the supplementary cementitious materials with the calcium hydroxide is still a topic of discussion.

This thesis focuses on the pozzolanic reaction of four materials with different origins and chemical compositions: silica fume, metakaolin, and two fly ashes.

The development of the key hydration properties of cementitious pastes made with white Portland cement and different additions of SCM’s, such as degree of hydration, chemically bound water, gel water, chemical shrinkage, and calcium hydroxide consumption, have been determined by means of X-ray diffraction, thermogravimetric analysis, 29Si Nuclear Magnetic Resonance, sorption isotherms, and chemical shrinkage. The results were modeled by the dispersion model and furthermore analyzed with the classic approach of the Powers Model to describe the hydration process, leading to suggestions on how the SCM’s influence the hydration process of cement.

The results from the experimental program showed that although the Powers model was developed more than 50 years ago, it accurately describes the hydration of currently produced cements. The addition of SCM’s decreases the degree of hydration of the cement and changes the structure of the main hydrate product, the internal surface area, and increases the chemical shrinkage. All the studied SCM’s showed pozzolanic activity.