Using glass content to determine the reactivity of fly ash for thermodynamic calculations
Using glass content to determine the reactivity of fly ash for thermodynamic calculations
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DOI：
10.1016/j.cemconcomp.2020.103849
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发表时间：
2021
影响因子：
10.5
通讯作者：
D. Glosser;P. Suraneni;O. B. Isgor;W. J. Weiss
中科院分区：
文献类型：
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作者：
D. Glosser;P. Suraneni;O. B. Isgor;W. J. Weiss
普通硅酸盐水泥(OPC)的水化热力学模型通常能很好地预测生成的孔隙溶液和水化产物的组成。然而，对含有OPC和辅助胶凝材料(SCM)的胶凝体系的预测更具挑战性。由于飞灰的结晶成分一般不会在胶凝体系中发生反应，所以飞灰的整体化学成分不能充分反映材料的反应部分。仅使用飞灰的整体化学成分的热力学模型输入高估了火山灰和水力反应的程度。提出了另外两种方法来克服这一限制。在第一种方法中，飞灰的最大活性分数是通过将飞灰的每个主体相乘以反应程度(dor*)来计算的，该反应程度通过量热法进行了实验测量。在第二种方法中，通过测定飞灰的反应性(玻璃)分数来计算其反应性。在这种替代方法中，从使用X射线荧光(XRF)确定的整体氧化物含量中减去使用定量X射线衍射(QXRD)测量的结晶氧化物的分数，以建立用于确定热力学模型输入的每一相的反应程度(Dorph*)。通过将飞灰的反应性纳入到使用DOR*或DORPH*的计算中，热力学建模预测大大提高了。利用QXRD和XRF数据计算飞灰的反应相可作为当前计算反应性的量热方法的潜在替代方法。
Thermodynamic models for the hydration of ordinary portland cement (OPC) typically predict the composition of the resulting pore solution and the hydrates well. However, predictions for cementitious systems containing OPC and supplementary cementitious materials (SCM) are more challenging. The bulk chemical composition of fly ash does not sufficiently reflect the reactive portion of the material, as the crystalline components of fly ash do not generally react in cementitious systems. Thermodynamic modeling inputs using only the bulk chemical composition of fly ash overestimate the extent of both pozzolanic and hydraulic reactions. Two additional approaches are presented to overcome this limitation. In the first approach, the maximum reactive fraction of fly ash is computed by multiplying each bulk phase of the fly ash by a degree of reaction (DoR*) that is measured experimentally through calorimetric methods. In the second approach, the reactive (glass) fraction of the fly ash is determined to calculate its reactivity. In this alternative approach, the fraction of crystalline oxides measured using quantitative x-ray diffraction (QXRD) is subtracted from bulk oxide content determined using x-ray fluorescence (XRF) to establish a degree of reaction for each phase (DoRph*) to be used in the determination of the thermodynamic modeling inputs. Thermodynamic modeling predictions substantially improve by incorporating fly ash reactivity into the calculations using either the DoR* or DoRph*. The calculation of the reactive phases of fly ash using QXRD and XRF data serve as a potential alternative to the current calorimetric methods to calculate reactivity.