Alkali-activated materials: Potential as alternative binders and use as extraterrestrial construction materials

Alkali-activated materials (AAM) are one of the most promising construction materials currently being studied for a variety of applications. The low carbon footprint of AAMs makes them a convenient, sustainable alternative to ordinary Portland cement, which has been one of the highest causes of CO2 emissions in the past few decades. On another scale, the availability of aluminosilicate regolith on the lunar and Martian surfaces makes AAMs one of the most promising extra-terrestrial construction materials that would not need transporting raw materials from the earth. The process of alkali-activation reaction is a fairly complex process that involves the transformation of one amorphous reactant (aluminosilicate precursor) into other amorphous products (N-A-S-H gel and/or disordered zeolite type phases). Despite this complexity, researchers in the past two decades have gained significant knowledge on the nature of this reaction at multiple scales. Understanding and developing a clear relationship between the alkalinity of the mix and the extent of reaction is of high interest for practical applications. However, detailed and thorough investigations into this vital relationship are limited. Here, in the first part of this study, we address this gap by systematically investigating a series of AAM samples with a wide range of Na/Al ratios (0.5 – 1.8) using 7 different yet complementary analytical techniques (isothermal calorimetry, FTIR, XRD, TGA, NMR, and Raman imaging). Applied in tandem, these tools reveal a clear but non-linear relationship between the Na/Al ratio and the extent of alkali-activation reaction, indicating diminishing returns at higher Na/Al ratios, where higher Na/Al ratios cause an increase in the degree of reaction until a certain point at which the increase in Na/Al ratio does not significantly affect the reaction kinetics, but may affect the gel polymerization. These findings could potentially aid decision-making for commercial applications of AAMs where the alkalinity of the mix is an essential parameter for performance as well as safety. The second part of this study evaluates the use of lunar and Martian regolith simulants as the aluminosilicate precursors for the alkali-activation process. Chemical and mineralogical composition analysis using XRF, XRD, and SEM-EDS showed the availability of aluminosilicate phases needed for alkali-activation, confirming the applicability of these simulants as precursors despite the presence of high amounts of crystalline structures. The activation reaction was also monitored using isothermal calorimetry and FTIR. Both showed an increase in the alkali-activation reaction with time, despite being a lot slower than other terrestrial precursors such as metakaolin. However, the reaction rate was considerably improved by heat curing. Finally, the porosity of the activated simulants was measured using helium pycnometry. It was found to be between 22% and 28%, suggesting a relatively low mechanical strength of these binders compared to alkali-activated metakaolin.

Name thesis:degree_name

M.S.

Level thesis:degree_level

Thesis

Discipline thesis:degree_discipline

Civil Engineering

Grantor

University of Illinois at Urbana-Champaign

Year dc:date

2023

Author dc:creator

• Abdelrahman, Omar Ahmed Moussa

Contributors dc:contributor

• Garg, Nishant

• Alkali-activated Materials
• Geopolymers
• Metakaolin, Extraterrestrial Construction, Isru

Statement dc:rights

• Copyright 2023 Omar Ahmed Moussa Abdelrahman

Language dc:language

en, eng

Handle dc:identifier

https://hdl.handle.net/2142/120580

OAI record oai:identifier

https://www.ideals.illinois.edu/oai-pmh?verb=GetRecord&metadataPrefix=etdms&identifier=oai%3Awww.ideals.illinois.edu%3A2142%2F120580