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Assessment of the Glassy Phase Reactivity in Fly Ashes Used for Geopolymer Cements

机译：用于地质聚合物水泥的粉煤灰中玻璃态反应性的评估

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Geopolymer cements have not found widespread use as a Portland cement replacement, in part because of the difficulty in proportioning mixtures in a reliable manner. Unlike Portland cements, which are manufactured materials with relatively consistent compositions, geopolymers are made from natural or waste aluminosilicate powders that come from a variety of sources and have highly variable compositions. These powders are mixed with caustic solutions, which must be selected carefully to optimize strength and durability. Geopolymer cement can be designed by tailoring caustic solution composition to the reactive phase composition of the solid component of the mixture; however, assessing which phases are reactive is challenging for complex and heterogeneous solids, such as fly ash. The work presented here focuses on applying a scanning electron microscopy and multispectral image analysis (SEM-MSIA) method to identify and quantify the reactive glassy phases in fly ash and to determine how these phases dissolve over time in a caustic activating solution. The fly ash was selected based upon its oxide contents and was analyzed for phase content using X-ray diffraction and Rietveld analysis (RQXRD) and SEM-MSIA, which identified multiple glassy phases in the fly ash. Next, the fly ash was suspended in 8 M NaOH, and tested at various time intervals with SEM-MSIA to track changes in the amounts of each individual glassy phase initially identified in the fly ash. The results showed that an aluminosilicate glass (C-A-S) with a moderate amount of calcium appeared to be the most reactive between 0 and 28 days for a Class F fly ash. Other phases that were identified in the fly ash included a high-Ca C-A-S glass, two aluminosilicate glasses with different S/A ratios, two alkali-modified A-S phases, and an iron-containing glass.
机译：地聚合物水泥尚未广泛用作波特兰水泥的替代品，部分原因是难以以可靠的方式对混合物进行配料。不同于波特兰水泥，波特兰水泥是具有相对一致组成的人造材料，地聚合物是由天然或废弃的铝硅酸盐粉末制成的，这些粉末的来源多种多样，而且组成变化很大。这些粉末与苛性溶液混合，必须仔细选择苛性溶液以优化强度和耐久性。可以通过将苛性溶液成分调整为混合物中固体成分的反应相成分来设计地质聚合物胶结剂。但是，对于粉煤灰等复杂且非均质的固体而言，评估哪些相具有反应性具有挑战性。本文介绍的工作重点是应用扫描电子显微镜和多光谱图像分析（SEM-MSIA）方法来鉴定和量化粉煤灰中的反应性玻璃态相，并确定这些相在苛性活化溶液中如何随时间溶解。根据粉煤灰的氧化物含量选择粉煤灰，并使用X射线衍射和Rietveld分析（RQXRD）和SEM-MSIA进行相含量分析，确定了粉煤灰中的多个玻璃相。接下来，将粉煤灰悬浮在8 M NaOH中，并用SEM-MSIA在不同的时间间隔进行测试，以追踪粉煤灰中最初鉴定出的各个玻璃态相的量变化。结果表明，对于F类粉煤灰，钙含量适中的铝硅酸盐玻璃（C-A-S）在0至28天之间具有最高的反应活性。粉煤灰中发现的其他相包括高钙C-A-S玻璃，两个具有不同S / A比的硅铝酸盐玻璃，两个碱改性的A-S相和含铁玻璃。

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