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

该项目由国际科学与工程办公室（OISE）、土木、机械和制造创新部（CMMI）和材料研究部（DMR）共同资助。非技术描述：地聚合物作为波特兰水泥的潜在替代品，在工程界引起了相当大的关注，而混凝土通常用于建造建筑物和公路等结构。地聚合物是由粘土和碱性水溶液之间的反应形成的，粘土首先被加热使其反应性更强。地聚合物引起人们注意的主要原因是它们在混凝土中的使用可以大大减少与混凝土生产相关的温室气体量。本研究项目的目的是探索是否可以用粉煤灰代替粘土制备地聚合物。粉煤灰是煤燃烧过程中产生的废料，例如发电，通常用作混凝土中一些波特兰水泥的替代品。某些类型的粉煤灰已成功地用于生产地聚合物，但在美国中西部常见的C类粉煤灰尚未成功。本研究的主要智力目标是了解粉煤灰的化学成分和分子结构如何控制地聚合物的行为。这项研究涉及与墨西哥Autónoma de Nuevo León大学（UANL）的Lauren教授Gómez-Zamorano合作。Gómez教授的工作得到了Tecnología国家科学委员会（CONACYT）的支持。一个广泛的目标是证明地聚合物在混凝土中作为粘结材料是否有效。公众对这些项目的支持对于开发和实施新的建筑材料系统至关重要，而新系统对国家至关重要。在不牺牲建筑和公路建设的情况下，美国在控制温室气体排放方面取得的进展。最后，土木工程专业的学生正在寻求有关可持续建筑新材料的知识，而这些系统的研究经验将增强我们提供这些知识的能力。技术细节：地聚合物是由固体前驱体（如偏高岭土）和碱溶液之间的化学反应形成的合成铝硅酸盐聚合物的名称。地聚合物作为波特兰水泥在土木工程中混凝土应用的替代品，正引起相当大的关注，部分原因是它们大大减少了与混凝土相关的温室气体的产生。地聚合物形成的化学性质与沸石合成的化学性质相似，但地聚合物是无定形的。大多数地聚合物的合成研究都是以偏高岭土为前驱体。然而，利用废旧材料生产地聚合物会带来额外的环境效益，因此本研究重点是利用C类粉煤灰为前驱体合成地聚合物。粉煤灰是煤燃烧的副产品，C类粉煤灰来源于亚烟煤和褐煤，常见于美国中部和西部。本研究的关键知识价值在于了解前驱体的化学和分子结构如何控制地聚合物的行为。为了实现这一目标，前驱体和地聚合物的组成和结构正在使用XRD， XRF， DSC, MAS-NMR， TEM和SEM/EDX进行研究，因此工程研究生被训练使用这些基本表征技术。一个相关的目标是证明地聚合物是否有效地作为混凝土的结合材料，以及使用地聚合物制成的混凝土的工程行为也是令人感兴趣的。本研究对水泥混凝土行业具有重要影响；这些行业面临着减少温室气体排放的巨大压力，因此他们正在考虑将地聚合物作为一种可能的策略。

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.