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

Alonso, M. C.*; Garca Calvo, J. L.*; Pettersson, S.*; Cuado, M.*; Vuorio, M.*; Weber, H.*; Ueda, Hiroyoshi*; Naito, Morimasa ; Walker, C.

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.