J.L. García Calvo

Development and application of low-pH concretes for structural purposes in geological repository systems

Abstract: Several construction concepts of underground repositories for high-level waste (HLW) consider the use of low pH cementitious materials and different aspects related to their development are exposed in the present chapter. The general functional requirements and the special characteristics implied in the development and production of low-pH concretes are described, mainly focused on the design of a specific application: a low-pH concrete plug using the shotcrete technique. Considering the long life expected in HLW repositories, parameters related to the durability of the low-pH concretes are analysed, such as the interaction of low-pH cementitious materials with groundwaters and the risk of corrosion if reinforcements are needed.

Round Robin Test for Defining an Accurate Protocol to Measure the Pore Fluid pH of Low-pH Cementitious Materials

The present research belongs to an international project where several of the main nuclear waste management agencies have been involved. The main objective is the development of agreed procedures or protocols for measuring the pH value using low-pH cementitious products (LopHC). Pore Fluid Expression (PFE) identified as Reference method and Ex situ Leaching methods (ELS) with two variants (filtering and without filtering the suspension made) identified as Routine methods have been employed. Both methodologies are based on the extraction of the pore solution of the concrete before pH determination. The protocols employed were based on a broad literature review and in fitting the more critical parameters, such as the sample size, the carbonation affection, the leaching of cement hydrates during the measurement, etc. Moreover, the routine methods were validated with respect to the pore fluid expression results. According with the obtained results, the selected measuring methods were proposed. The proposed methodologies show very promising results having low deviations and high reproducibility when applied to LopHC materials that have given the possibility to develop agreed simple protocols for pH determination considering the chemical requirement in the construction of high nuclear waste repositories.