ORCID Identifier(s)

https://orcid.org/0009-0001-6230-8911

Graduation Semester and Year

Summer 2025

Language

English

Document Type

Dissertation

Degree Name

Doctor of Philosophy in Civil Engineering

Department

Civil Engineering

First Advisor

Dr. Warda Ashraf

Abstract

Ancient Roman concrete is an extremely durable cement-based material, especially against seawater and alkali-silica reaction (ASR). Additionally, it is more advantageous than the Ordinary Portland Cement (OPC) for its lower carbon footprint and reduced freshwater consumption. Inspired by these attributes, a novel binder, Recreated Roman Cement (RRC), was developed by combining calcined clay and lime with seawater to replicate the cementation process of Roman concrete. While volcanic ash was primarily used as the source of pozzolanic materials in ancient Roman Concrete, such product is not abundantly available in the US at this time. Therefore, it was essential to identify an alternative source of pozzolanic materials to recreate ancient Roman concrete. On the other hand, natural clay deposits are abundant worldwide, making them a readily available pozzolanic material, and calcined kaolin possesses the highest reactivity. Medium-grade calcined clay was utilized as the pozzolanic material to broaden the applicability of the RRC binder.

The first thrust area of this study involves the durability performance evaluation of the RRC binder by assessing its durability in seawater, durability against ASR, and long-term durability in natural marine environments. Calcined clay mixes showed better chloride-binding capacity than OPC due to increased Friedel’s salt formation, leading to improved microstructure densification. These samples reached compressive strengths of 25 to 30 MPa, attaining 90% of their maximum strength within 28 days of curing. This binder also showed durability under alkaline conditions, with ASR-induced expansion in RRC samples limited to just 0.02% after two years of exposure. Following successful laboratory tests, RRC mortar and concrete samples were exposed to the Gulf of Mexico for one year. Among all binders tested, RRC exhibited the least visible cracking and achieved a compressive strength of 55 MPa, confirming its long-term durability. Notably, RRC also promoted substantial oyster colonization, highlighting its potential for use as an artificial reef substrate.

The second thrust area explores the performance enhancement of the RRC binder through CO2 sequestration and the incorporation of mineral aggregates to improve its self-healing capacity in a marine environment. Early carbonation led to calcite formation, which served as nucleation sites for C-A-S-H precipitation, resulting in a 36% increase in compressive strength in carbonated samples compared to non-carbonated ones after 28 days. Additionally, CO2 sequestration in RRC binders reduced the carbon footprint by 47−66% compared to OPC. Lastly, the incorporation of newly developed artificial mineral aggregates into the RRC matrix effectively demonstrated self-healing efficiency in marine environments. This was achieved by facilitating the binding of seawater ions (Cl⁻, SO₄²⁻, Mg²⁺) and promoting the formation of healing products, including ettringite, calcite, M–S–H, Mg–Al–Cl composites, aragonite, and brucite.

Overall, RRC offers a potential pathway for producing low-carbon cementitious materials primarily using calcined clay and specifically designed for marine applications. This study also underscores the importance of using naturally abundant resources, such as clay and seawater, to design durable and sustainable cementitious materials.

Keywords

Marine concrete durability, Low carbon binder, Lime-calcined clay, Artificial reef, Seawater, Concrete self-healing, Alkali-silica reaction

Disciplines

Ceramic Materials | Structural Materials

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