Graduation Semester and Year

Fall 2025

Language

ENGLISH

Document Type

Dissertation

Degree Name

Doctor of Philosophy in Civil Engineering

Department

Civil Engineering

First Advisor

WARDA ASHRAF

Abstract

Alkali-activated materials (AAM) are considered a more sustainable alternative to OPC concrete. GGBFS-based AAM concrete has lower CO2eq. emissions and superior mechanical and durability properties than OPC concrete. However, additional CO2 sequestration in this type of composites is not viable due to their poor resistance to carbonation. There is growing interest in identifying new materials and techniques to enhance the mechanical strength and durability of AAM systems while minimizing CO2-induced degradation. This research will explore innovative approaches to address these issues.

The first part of this study focuses on the study of atmospheric and accelerated carbonation resistance of matured AAS incorporating bio-inspired additives such as cellulose nanofibers and biomimetic molecules. For this part of the work, matured AAS composites were exposed to CO2 rich environment. It was observed that CNF fibers formed a nanocomposite-like structure with calcium carbonate polymorphs, thereby increasing the structural pore refinement, which contributed to the increase in compressive strength while also increased the CO2 sequestration. Another approach to mitigate carbonation-induced degradation involves the stabilization of CaCO3 polymorphs using bio-inspired molecules derived from natural biological systems. The results show that the addition of biomimetic molecules significantly decreases the amount of carbonation by stabilizing vaterite in the alkali-activated slag (AAS)-based system. This strategy effectively mitigated the carbonation-induced degradation and enhanced the compressive strength of AAS under carbonation exposure. However, the incorporation of such molecules during the mixing time was found to have negative effects by delaying the alkali-activation.

The second part investigated the potential pathways of incorporating CO2 sequestration at the early stage of AAS composite formulations. The accelerated carbonation curing method serves as an effective strategy for integrating bio-inspired additives into an AAS system. Therefore, one approach is to use biochar, a carbon-rich by-product from wood, which can sequester higher CO2 during curing. Furthermore, biochar can promote permanent sequestration of CO2 as carbonates while simultaneously improving the compressive strength of the AAS system. The second approach is to use L-Aspartic acid (L-Asp) on the wet carbonation of slag for performance enhancement and CO2 capture. By using L-Asp, the mechanical performance of the AAS system can be enhanced by stabilizing the metastable CaCO3 polymorphs.

Overall, this study highlighted potential pathways for carbon sequestration in AAM via accelerated and natural carbonation without compromising their mechanical performance. This approach of reducing the carbonation degradation of AAM enables further reduction of their carbon footprint.

Keywords

Alkali-Activated Slag, Accelerated Carbonation, Carbonation curing, CO2 sequestration, Cellulose nanofibers, L-Aspartic acid, Biochar, Wet carbonation, Carbon-neutrality, CaCO3 polymorphs

Disciplines

Civil and Environmental Engineering | Civil Engineering | Other Civil and Environmental Engineering | Structural Engineering

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