Materials World Network: Effects of Precursor Nanostructure on Geopolymer Structure and Properties

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This project is co-funded by the Office of International Science and Engineering (OISE), the Division of Civil, Mechanical and Manufacturing Innovation (CMMI) and the Division of Materials Research (DMR).NON-TECHNICAL DESCRIPTION: Geopolymers are attracting considerable attention in the engineering community as a potential replacement for portland cement in making concrete, which is commonly used to make structures such as buildings and highways. Geopolymers are formed by reaction between clay, which has first been heated to make it more reactive, and an aqueous alkaline solution. The main reason that geopolymers are attracting attention is that their use in concrete may reduce considerably the amount of greenhouse gases associated with concrete production. The purpose of this research project is to explore whether geopolymers can be made using fly ash instead of clay. Fly ash is a waste material produced during coal combustion, for example to generate electricity, and is often used as a replacement for some of the Portland cement in concrete. Some types of fly ash have been used successfully in production of geopolymer, but Class C fly ash, common in the middle and western US, have not. The key intellectual objective of this research is to understand how the chemical composition and molecular structure of the fly ash control behavior of the geopolymer. This research involves collaboration with Prof. Lauren Gómez-Zamorano of the Universidad Autónoma de Nuevo León (UANL) in Mexico. Prof. Gómez's work is supported through the Consejo Nacional de Ciencia y Tecnología (CONACYT). A broad objective is to demonstrate whether geopolymer is effective as a binding material in concrete. Public support of such projects is vital to the development and implementation of new construction material systems, and new systems are critical to the nation?s progress towards controlling greenhouse gas emissions without sacrificing construction of buildings and highways. Finally, civil engineering students are seeking knowledge about new materials for sustainable construction, and research experience in such systems will enhance our ability to provide that knowledge. TECHNICAL DETAILS: Geopolymer is the name given to synthetic aluminosilicate polymers formed by chemical reaction between a solid precursor, such as metakaolin, and an alkali solution. Geopolymers are attracting considerable attention as a replacement for Portland cement in concrete for civil engineering applications, in part because they much reduce the production of greenhouse gas associated with concrete. The chemistry of geopolymer formation is similar to the chemistry of zeolite synthesis, but the geopolymers are amorphous. Most of the research on synthesis of geopolymers has used metakaolin as the precursor. However, additional environmental benefits would be realized by producing geopolymers from waste materials, so this research is focused on synthesis of geopolymers using Class C fly ash as the precursor. Fly ash is a by-product of coal combustion, and Class C fly ash is derived from subbituminous and lignite coals, commonly found in the middle and western US. The key intellectual merit of this research is to understand how the chemical and molecular structures of the precursor control behavior of the geopolymer. To meet this objective, composition and structure of the precursor and the geopolymer are being studied using XRD, XRF, DSC, MAS-NMR, TEM, and SEM/EDX, and therefore graduate students in engineering are trained to use these fundamental characterization techniques. A related objective is to demonstrate whether geopolymer is effective as a binding material in concrete, and engineering behavior of concretes made using geopolymers is also of interest. This research has important impact on the cement and concrete industries; these industries are under considerable pressure to reduce greenhouse gas emissions and so they are looking at geopolymers as a possible strategy.