Recycled aggregates, especially the fine (0–4 mm) fraction, are often contaminated with sulfates coming from gypsum residues on demolition sites. When these aggregates are used in concrete, the sulfates can induce internal sulfate attack which causes expansion of the concrete. European standard EN 206:2013 sets the water-soluble sulfate limit at 0.2% by weight of the aggregate, but other studies suggest this limit could be safely increased. In addition to the sulfate content, other parameters, such as the porosity and alkalinity of the mix, have been shown to influence the swelling results. In this study, different proposed sulfate limits were evaluated on concrete made with 100% fine recycled aggregates (FRA). It was also researched whether the mixing parameters could change the swelling amount regardless of the sulfate content. The results showed that the incorporation of FRA with sulfate contents up to 0.8 wt% is safe when combined with coarse natural aggregates. If coarse recycled aggregates are used in the mix, the sulfate content of FRA can be up to 0.3%. The swelling caused by these sulfate levels was not high enough to be influenced by the porosity or alkalinity of the mix.

中文翻译：

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由于细再生骨料被石膏污染而形成二次钙矾石而导致混凝土膨胀

回收骨料，尤其是细粒（0-4 毫米）部分，经常受到拆除现场石膏残留物中的硫酸盐的污染。当这些骨料用于混凝土中时，硫酸盐会引起内部硫酸盐侵蚀，从而导致混凝土膨胀。欧洲标准 EN 206:2013 将水溶性硫酸盐限量规定为骨料重量的 0.2%，但其他研究表明可以安全地提高这一限量。除了硫酸盐含量外，其他参数（例如混合物的孔隙率和碱度）也已被证明会影响溶胀结果。在本研究中，对采用 100% 细再生骨料 (FRA) 制成的混凝土评估了不同的拟议硫酸盐限值。还研究了混合参数是否会改变溶胀量，而与硫酸盐含量无关。结果表明，硫酸盐含量高达 0.8 wt% 的 FRA 与粗天然骨料结合时是安全的。如果混合料中使用粗再生骨料，FRA的硫酸盐含量可高达0.3%。由这些硫酸盐含量引起的膨胀并没有高到足以受到混合物的孔隙度或碱度的影响。