PhD Oral Exam - Mohamed Ramadan, Civil 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

Calcined dredged clay (CDC) offers an opportunity to valorize dredged sediments and reduce reliance on ground granulated blast-furnace slag (GGBFS) by developing one-part alkali-activated binders. This thesis investigates the effects of CDC incorporation on one-part GGBFS–CDC shrinkage and examines existing mitigation strategies. First, the potential of CDC as a precursor was evaluated through comprehensive physical and chemical characterization. This was followed by an extensive experimental program that examined CDC replacement and activator dosage, and evaluated the efficiency of various mitigation strategies (including shrinkage-reducing admixture (SRA), internal curing with superabsorbent polymer (SAP), and their synergistic effect). The study integrates shrinkage and strength measurements with reaction kinetics, solution chemistry, internal relative humidity, microstructural characterization (MIP, XRD, and SEM), and life-cycle assessment (LCA). Results show that shrinkage in GGBFS–CDC binders is controlled by reaction development rate, internal moisture conditions, and pore microstructure. The thesis highlights CDC's high potential as a precursor and emphasizes the need to optimize mixture composition (i.e. replacement rate and activator dosage) to maintain adequate strength and dimensional stability. The thesis also highlights the distinct differences among conventional mitigation strategies. The SRA effect relies mainly on modifying pore-fluid conditions and surface tension, which are strongly influenced by CDC-released ions and the altered pore solution. In contrast, SAP and its water-release phenomena are strongly affected by CDC-induced changes in pore-solution composition. This directly influenced SAP efficiency in limiting self-desiccation. The synergistic effect of SRA and SAP aligned with the previous findings. However, the dominant mitigation strategy (i.e., SRA and SAP) will depend heavily on selecting the right dosages of each one and targeted performance. The thesis findings provide a framework for integrating shrinkage control with mechanical and environmental performance in high-CDC binders. Ultimately, this work advances dredged-clay binders toward construction use by reducing reliance on limited conventional raw-material resources and providing a beneficial-use pathway for dredged sediment that would otherwise require disposal.