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

本研究将提高我们对波特兰水泥混凝土中控制粉煤灰反应性的基本因素的理解，从而建立更准确的性能预测模型，从而计算出粉煤灰/水泥混合料设计的最佳水泥替代系数。主要的创新是使用模拟的整个粉煤灰，它与真实粉煤灰的所有主要特性相匹配，作为系统地研究控制其反应性的单个因素的模型系统。这些主要性能包括玻璃相组成、惰性质量分数和组成以及粒径分布（PSD）。每一种模拟飞灰都是几种合成玻璃颗粒的混合物，这些玻璃颗粒的化学成分与真实飞灰的化学成分相匹配。这些成分将基于使用计算机控制的扫描电镜对单个粉煤灰颗粒的分析。在模拟粉煤灰中，PSD、玻璃化学组成和惰性分数会独立变化。固体颗粒的混合将使用新型共振声混合方法来确保均匀化。这项研究结合了三种测量技术来测量不同长度尺度下的反应性：湿化学、热重法和标准的工程性能测试，如抗压强度和耐久性。此外，凝胶水化产物的分子结构将用固体核磁共振表征。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函数的玻璃成分，PSD和惰性分数。它将加速粉煤灰在混凝土工业中作为波特兰水泥的替代品的使用。在经济效益方面，粉煤灰用量的增加将降低混凝土结构的成本。环境效益包括减少了处理粉煤灰所需的垃圾填埋场的数量，以及减少了波特兰水泥生产的能耗和二氧化碳排放。这项合作计划将加强两所院校对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.