Collaborative Research: Investigation of the Effect of Fly Ash Variability on Cement Paste Microstructure and Mechanical Properties Using Simulated Fly Ash

这项研究将提高我们对控制粉煤灰在波特兰水泥混凝土中的反应性的基本因素的理解，导致更准确的性能预测模型，这将使最佳水泥替代因素的计算粉煤灰/水泥混合设计，。主要的创新是使用一个模拟的整个飞灰，它匹配的所有主要性能的一个真实的飞灰，作为一个模型系统的调查控制其反应性的各个因素。这些主要性质包括玻璃相组成、惰性质量分数和组成以及粒度分布（PSD）。每个模拟飞灰将是几种类型的合成玻璃颗粒的混合物，其特征化学成分与真实的飞灰相匹配。这些成分将基于使用计算机控制的SEM对单个飞灰颗粒的分析。PSD，玻璃化学成分和惰性分数将独立地在模拟飞灰之间变化。固体颗粒的混合将使用新的共振声混合方法进行，以确保均匀化。本研究使用三种测量技术的组合来测量不同长度尺度下的反应性：湿化学，热重分析和工程性能（如抗压强度和耐久性）的标准测试。此外，凝胶水合产物的分子结构将用固态NMR表征。 这种多尺度方法提供了从单个粒子数据到宏观工程特性的桥梁。这项研究的结果将导致一个模型的反应性作为一个功能的玻璃组成，PSD和惰性组分分数。 它将加速粉煤灰作为混凝土行业波特兰水泥替代品的使用。在经济效益方面，增加粉煤灰的使用将降低混凝土结构的成本。环境效益包括减少处理飞灰所需的垃圾填埋场数量，以及减少波特兰水泥生产的能源消耗和二氧化碳排放。这个合作项目将加强两个机构之间的本科生和研究生的研究和教育。

This research will improve our understanding of the fundamental factors controlling the reactivity of fly ash in Portland cement concrete, leading to more accurate predictive models of performance that will enable the calculation of optimum cement replacement factors for fly ash/cement mix design,. The major innovation is the use of a simulated whole fly ash, which matches all the major properties of a real fly ash, as a model system for investigating systemically the individual factors that control its reactivity. These major properties include the glassy phase composition, the inert mass fraction and composition, and the particle size distribution (PSD). Each simulated fly ash will be a mixture of several types of synthetic glassy particles made with characteristic chemical compositions that match those of real fly ashes. These compositions will be based on analyses of individual fly ash particles using Computer Controlled SEM. The PSD, glass chemical composition and inert fraction will be independently varied among the simulated fly ashes. The mixing of the solid particles will be done using the novel Resonance Acoustic Mixing method to ensure homogenization. This research uses a combination of three measurement techniques to measure the reactivity at different length scales: wet chemistry, thermogravimetry, and standard tests of engineering properties such as compressive strength and durability. Also, the molecular structure of the gel hydration products will be characterized with solid state NMR. This multiscale approach provides a bridge from individual particle data to macroscopic engineering properties. The results of this research will lead to a model of the reactivity as a function of the glass composition, PSD and inerts fraction. It will accelerate the usage of fly ash as a replacement for Portland cement by the concrete industry. In terms of economic benefits, the increased use of fly ash will lower the cost of concrete structures. The environmental benefits include the reduction in the number of landfills otherwise needed for fly ash disposal, as well as reduced energy consumption and lower CO2 emissions from Portland cement manufacture. This collaborative project will enhance the research and education for undergraduate and graduate students between two institutions.