Estimating geochemical behavior of concretes to be placed at Yucca Mountain

The interactions of J-13 water with cementitious materials were examined at 25 degrees C using the geochemical code EQ3NR/EQ6. Results of the modeling suggested the following conclusions: (1) Solution chemistry for calcium-rich concretes was similar to that for silica-rich concretes. (2) Solution pH was strongly buffered by J-13 added concrete. For larger amounts of concrete the pH was dominated by the concrete and typically had values near 12. (3) If ettringite or excess portlandite are present, their decomposition opens the concrete structure. Excess silica reacts with hydrogarnet to tighten the concrete structure. (4) The permeability changes for the limited conditions discussed here are small