Announcement distributed 9 days in advance of defense with approval from Institute and CEE Associate Chair for Graduate Programs.

School of Civil and Environmental Engineering

Ph.D. Thesis Defense Announcement

Innovations in Characterization and Design of Durable Sustainable Cementitious Systems Utilizing Pozzolanic Materials

By Connor Szeto

Advisor:

Dr. Kimberly Kurtis

Committee Members:  Dr. Susan Burns (CEE)

Dr. Lauren Stewart (CEE)

Dr. Fred Meyer (CEE)

Dr. Russell Gentry (ARCH)

Dr. Weston Straka (IMS)

Date and Time:  October 31, 2025.  2:30-4:30 PM EST

Location: Mason 5134

Teams Meeting ID: 215 253 086 765 4

Passcode: cS2iE7vx

Abstract
This dissertation investigates how pozzolanic materials influence both the microstructural and macrostructural properties of cementitious systems, with the overarching goal of advancing the design and implementation of sustainable, durable concretes. Through a combination of experimental, analytical, and microstructural characterization approaches, this work provides new insights into the design of these low-clinker systems, the performance of reclaimed ashes as a supplementary cementitious material (SCM), and the long-term mechanisms of durability observed in ancient Roman concrete.Low water-to-solid ratio limestone–calcined clay cement (LC3) systems were designed using a particle packing approach to link packing density with hydration, strength development, and environmental efficiency. Strong early-age correlations between the particle packing index (PPI), compressive strength, and an Environmental Performance Indicator (EPi) confirm particle packing as a predictive framework for designing high-performance, low-impact mixtures.
Reclaimed coal ash was evaluated as a sustainable SCM alternative to conventional fly ash, focusing on mitigation of alkali–silica reaction (ASR) and sulfate attack. For ASR mitigation performance, reclaimed ashes outperformed inert fillers, but they did not match Class F fly ash, indicating that higher replacement rates may be required. MicroXRF analysis revealed key differences in alkali transport among standard ASR test methods, supporting the 56-day AASHTO T380 as a representative evaluation protocol. To investigate sulfate attack, LC3-based engineered cementitious composite (ECC) incorporating reclaimed ashes was assessed using both mechanical expansion tests and microXRF imaging. These low-clinker, fiber-reinforced systems demonstrated superior resistance to external sulfate attack compared to portland cement controls, owing to the combined effects of LC3’s dense matrix and fiber-induced crack-width control. MicroXRF provided spatially resolved quantitative data on sulfate penetration and diffusivity, revealing very low diffusion coefficients and confirming the excellent durability of these systems.
The final component of this work applied a novel, non-destructive analytical approach of combining microXRF and solid-sample XRD to a 2000-year-old Roman concrete sample. This technique preserved spatial resolution while enabling phase identification and compositional mapping across the heterogeneous microstructure. The findings point towards the use of seawater and “hot-mixing” of the lime and support the interpretation that Roman concrete durability arises from progressive phase development over time, creating an impermeable microstructure, while also enabling potential post-pozzolanic reactions and self-healing to occur.
Collectively, this thesis provides both design methodologies and analytical frameworks for developing durable, low-clinker cementitious systems. The particle packing approach offers a quantitative guide for sustainable mixture design; reclaimed coal ashes expand the resource base for SCMs; and spatially resolved characterization techniques reveal fundamental relationships between composition, microstructure, and durability. From the ancient Romans, use oflocally available materials, allowance for chemical evolution over time, and harnessing material-environmental interactions to the benefit offer a strategy for enhancing the durability and sustainability of modern concretes.