It is well-established that aqueous carbonation of recycled concrete paste produces calcium carbonate and an amorphous alumina-silica gel as the main products. However, sparse information is available about the structure and composition of the gel. This work focuses on these properties by carbonation of synthesized C-S-H (Ca/Si = 1.75) alone and blended with portlandite and ettringite. Wet carbonation of pure ettringite results in an alumina gel with the approximate composition, Al₂O₃·7.4H₂O, and including two distinct octahedral Al sites. For carbonated blends of C-S-H with ettringite, this phase is observed along with the alumina-silica gel. Increasing ettringite contents lead to significant changes in the structure of the alumina-silica gel and to increasing Al/Si ratios approaching the maximum of Al/Si = 1.0. For the blended samples, portlandite and ettringite carbonate independently and faster than the C-S-H phase, and both additional Ca and Al slow down the carbonation rate for the C-S-H phase.

中文翻译：

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Ca/Si 和 Al/Si 比值对合成的 C-S-H 与硅酸盐和钙矮石共混湿碳化形成的氧化铝硅胶的组成和结构的影响

众所周知，再生混凝土浆料的水碳化产生碳酸钙和无定形氧化铝硅胶作为主要产品。然而，关于凝胶的结构和组成的信息很少。这项工作的重点是通过单独碳化合成的 C-S-H （Ca/Si = 1.75） 并与硅酸盐和钙矾石混合来研究这些特性。纯钙矾石的湿碳化产生氧化铝凝胶，其成分近似为 Al₂O₃·7.4H₂O，并包括两个不同的八面体 Al 位点。对于 C-S-H 与钙矾石的碳酸混合物，该相与氧化铝-硅胶一起观察到。钙石含量的增加导致氧化铝-硅胶的结构发生显着变化，并导致 Al/Si 比率增加，接近 Al/Si = 1.0 的最大值。对于混合样品，硅酸盐岩和钙矾石碳酸盐独立且比 C-S-H 相更快，额外的 Ca 和 Al 都会减慢 C-S-H 相的碳化速率。