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硝酸塩がセメント水和物の溶脱挙動へ及ぼす影響

The Influence of nitrate on dissolution behavior of cement hydrates

藤田 英樹*; 根岸 久美*; 大澤 勉*; 本田 明

Fujita, Hideki*; Negishi, Kumi*; Osawa, Tsutomu*; Honda, Akira

普通ポルトランドセメントペースト硬化体を用いた通液試験により硝酸ナトリウムがセメント水和物の溶脱へ与える影響を評価した。純水に比べ1mol dm$$^{-3}$$硝酸ナトリウム溶液を通液した場合では水酸化カルシウムの溶脱が1.5倍程度促進された。硝酸ナトリウム濃度を変えながら活量を補正し、水酸化カルシウムの平衡濃度を計算した結果、硝酸ナトリウム濃度が1mol kg-1付近でCa濃度が最大となり、純水の約1.5倍と評価され通液試験結果と整合した。試験後の供試体の物性は純水に比べ、圧縮強度の低下,劣化部の空隙率増大が起こった。硝酸ナトリウム溶液通液中は透水係数は低下し、空隙率の結果と一見矛盾するものであったが、劣化部に高濃度に存在したNaが関連している可能性が示唆された。

The influence of sodium nitrate on dissolution of cement hydrates was investigated by flow through experiment. Dissolution of portlandite was accelerated in NaNO$$_{3}$$ solution of 1 mol dm$$^{-3}$$ than in ion exchanged water. The acceleration of portlandite dissolution attributed to impact of ionic strength on the activities of aqueous species, because Ca concentration in 1 mol kg$$^{-1}$$ NaNO$$_{3}$$ solution equilibrated with portlandite was estimated to be 1.5 times as high as that in pure water. After flow through experiment, compressive strength fell down and porosity was higher than blank test using pure water. However low permeabilities were contradictory kept during NaNO$$_{3}$$ solution flowing. Dense existence of Na was possible to cause the low permeability during NaNO$$_{3}$$ solution flowing.

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