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Development of an accurate methodology for measuring the pore fluid pH of low-pH cementitious materials

低アルカリ性セメント材料の精密なpH測定手法の開発

Alonso, M. C.*; Garc$'i$a Calvo, J. L.*; Pettersson, S.*; Cu$~n$ado, M.*; Vuorio, M.*; Weber, H.*; 植田 浩義*; 内藤 守正; Walker, C.

Alonso, M. C.*; Garc$'i$a Calvo, J. L.*; Pettersson, S.*; Cu$~n$ado, M.*; Vuorio, M.*; Weber, H.*; Ueda, Hiroyoshi*; Naito, Morimasa; Walker, C.

低アルカリ性セメントの開発において基本的なことは、pHの目標値を決定づける配合の量と品質を確保するために正確かつ信頼できる方法でpHを測定することである。本件の目的は低アルカリ性セメントのpHを測定するための標準的な手順を開発することである。文献調査により4つの方法を出発点に検討を開始し、その結果、圧搾法をレファレンスに、浸出法を通常の方法として2つのタイプを選定した。これらについて、pHに影響を与える固液比などのパラメータを変えて手順の検討を行い、同じサンプルを用いて7か国8機関でそれぞれ測定を試みたところ、ばらつきは小さく、高い再現性を有することが示された。

Low pH cementitious (LopHC) materials are expected to be used in the construction of an underground repository for the geological disposal of high level radioactive waste (HLW). A fundamental aspect of the development of LopHC is the accurate and reliable measurement of the pore fluid pH in order to qualify and help quantify mix designs to achieve specific pH targets. The main objective of the current research is the development of an agreed protocol for measuring the pH value of LopHC. There are four different methods described in the literature for characterizing the pore solution of cementitious materials: (1) Pore fluid expression; (2) Leaching methods, including both in-situ and ex-situ techniques); (3) Percolation methods; and (4) Embedded pH sensors. In a first step, different parameters that may affect the measured pH values were evaluated, including the solid/liquid ratio, fineness, carbonation, time, and the results obtained from a pH meter in comparison with an OH titration. Based on the results obtained from the first step, selected protocols were proposed and tested for reproducibility and repeatability in 8 laboratories of 7 countries using the same LopHC sample. The proposed methodologies showed very promising results with low deviation and high reproducibility and have allowed the development of an agreed set of simple protocols for the determination of pH in LopHC.

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