Abstract
In this study, the formulation of alkali-activated grouts based on Callovo-Oxfordian argillite, with a long setting time (up to 24 h) and a moderate pH value (10–11), is investigated. The first step was to select the reference mixture based on calcined argillite (650 °C) and metakaolin. The selected binder presented an initial setting time of 11 h and a pH value of 12.7. In this mixture, the addition of 2.5 %weight boric acid produced a 24-h setting time. The pH value decreased to 12.4 and 12.3 with the incorporation of boric acid and sodium tetraborate, respectively. Finally, samples cured at 90 °C (the high-level waste disposal cell temperature under operating conditions) are studied. The high temperature leads to a decrease in the pH value down to a minimal value of 11.1. Analysis of the cured samples reveals a reorganization of the geopolymer network during the treatment. The formation of zeolite phases in the network, which can trap alkaline cations, is considered and can explain the pH value decrease.
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