PhD Oral Exam - Dulani Pankaja Abeysing Kodippili, Building Engineering

When studying for a doctoral degree (PhD), candidates submit a thesis that provides a critical review of the current state of knowledge of the thesis subject as well as the student’s own contributions to the subject. The distinguishing criterion of doctoral graduate research is a significant and original contribution to knowledge.

Once accepted, the candidate presents the thesis orally. This oral exam is open to the public.

Abstract

Nano-silica (NS) is one of the most widely used nanomaterials in the cement industry, the addition of which delivers many advantages in improving the properties of hardened cement. It has been proven that NS can increase the strength, reduce the permeability, increase the durability, and reduce the CO2 emissions by lessening the usage of cement. However, the associated problems such as the agglomeration of NS and uneven dispersion of NS in the cement pastes limit its potential benefits.

These problems were addressed in this research by optimizing the method of NS incorporation. NS was synthesized by the sol-gel method and was utilized in cement as a suspension of calcium hydroxide. The hydration of cement with the sol-gel derived NS was studied using various techniques such as isothermal calorimetry, differential scanning calorimetry, mercury intrusion porosimetry, scanning electron microscopy, non-evaporable water content measurements, and X-ray diffraction with Rietveld refinement as well as mechanical properties. The optimum amount of NS was determined to be approximately 4% and perhaps as low as 2% if ultra sonification is utilized. It was shown that the NS synthesized by this method increased the rate of hydration by 12% in two days in terms of energy. Calcium hydroxide consumption and refinement of the microstructure and pore structure improved until this optimum amount. Moreover, the mechanical strength was improved up 35% in two days and 50% in seven days. The limitations of the NS usage can be minimized by this novel approach of NS incorporation.