Samples were collected from a 20-year-old concrete suffering alkali-silica reaction for examination using scanning electron microscopy. The concrete was also exposed to cycles of freezing and thawing in service. The old concrete was processed and used as recycled concrete aggregate in new concrete tested under lab conditions. The study shows that backscattered electron imaging, energy dispersive x-ray analysis and x-ray mapping are helpful tools to identify the presence of alkali-silica reaction products. X-ray mapping was found helpful to confirm the presence of reaction products in cases where the products or the cracking are not very clear in the collected image. The study shows the presence of ettringite in the air voids of the concrete. The formed ettringite is believed to have no direct effect on the expansion due to the alkali-silica reaction as they form in an empty space without causing swelling pressure on the concrete. The effect of the ettringite formed in the air voids on the resistance to freezing/thawing was not confirmed in this study. Recycling the old affected concrete as aggregate in new concrete was found to cause significant expansion under lab conditions.

中文翻译：

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碱硅反应影响混凝土中钙矾石的存在及其作为再生骨料的潜在用途

从一个 20 岁的混凝土中采集样品，使用扫描电子显微镜进行检查。混凝土在使用中也经历了冻融循环。在实验室条件下对旧混凝土进行加工并用作新混凝土中的再生混凝土骨料。该研究表明，背散射电子成像、能量色散 X 射线分析和 X 射线映射是识别碱-二氧化硅反应产物存在的有用工具。在收集的图像中产物或裂纹不是很清晰的情况下，发现 X 射线映射有助于确认反应产物的存在。研究表明在混凝土的空隙中存在钙矾石。形成的钙矾石被认为对由于碱-二氧化硅反应而导致的膨胀没有直接影响，因为它们在空旷的空间中形成，而不会对混凝土造成膨胀压力。本研究未证实在空隙中形成的钙矾石对抗冻融性的影响。发现在实验室条件下回收旧的受影响混凝土作为新混凝土中的骨料会导致显着膨胀。