Alkali-silica reaction (ASR) - Investigation of crystallographic parameters of natural sands by backscattered electron diffraction

abstract: This study involved analyzing several natural sands to ascertain the possible causes for distress due to ASR. The analyses were performed using the following techniques: X-ray diffractometry, accelerated mortar bar tests (AMBT), electron backscattering diffraction and elementary chemistry analyses, by FEG-SEM/EBSD/EDS. These experiments allowed identifying the presence of several mineral composites (such as microcline, anorthite, among others), as well as the microstructural-crystallographic planes of quartz (such as the Dauphiné type). From the results it could be inferred that the multiple techniques used, especially the FEG-SEM / EBSD, proved to be promising in the analysis of the ASR potential of sands for use in Portland cement mortars and concretes.摘要：本研究对多种天然砂展开分析，旨在明确碱骨料反应（Alkali-Silica Reaction，ASR）引发材料劣化的潜在成因。研究采用以下技术手段开展测试：X射线衍射法、加速砂浆棒试验（AMBT）、电子背散射衍射以及元素化学分析，具体通过场发射扫描电子显微镜/电子背散射衍射/能谱仪（FEG-SEM/EBSD/EDS）完成。实验结果表明，样品中存在多种矿物组分（如微斜长石、钙长石等），同时观测到石英的微观结构-晶体学平面特征（如道芬双晶结构）。基于上述结果可推断，本次研究所采用的多种分析技术，尤其是场发射扫描电子显微镜/电子背散射衍射（FEG-SEM/EBSD），在评估用于硅酸盐水泥砂浆及混凝土的天然砂的碱骨料反应潜力方面，展现出良好的应用前景。