Landfilling

Calcium sulphate halite construction material for dumpsites and radwaste depositories

This project aims to develop a construction material with sufficiently adhesive, leak-tight and workable properties for use in subterranean dumpsites and radwaste depositories in salt rock strata. The basic substance herefor shall be a mixture of hemihydrate, calcium sulphate and halite.

 

Summary

In order to dispose of radwaste permanently and in an ecologically sound manner, it is deposited observing a multi-barrier concept: besides the rock strata as a geological barrier, artificially raised barrier structures play a key role as geo-technical barriers. The material to be disposed of is installed in a previously excavated chamber and the access route is closed off using a structure with long-term durability. The research project's aim was to develop a workable construction material suitable for use on an industrial scale and to test this material for the following properties on the floor level of the Asse research mine: setting capacity in large-volume monolithic blocks even at high temperatures in the saliniferous formation, swelling power, adhesion to the salt rock strata and suitability for pneumatic projection. Over the course of testing, approx. 250 tonnes of the developed construction material (mixture of alpha-hemihydrate (CaSO4 * ½ H2O), anhydrite (CaSO4) and halite) were installed.

Results:

  • Maximum temperature during the hydration phase was 41.75°C. Moisture after hydration lay at 8 mass percent and dropped to 5% by the end of the test period (15 months).
  • The core samples taken from the structure display an average density of 1.98 g/cm3. They display strengths between 5.23 MPa and 13.74 MPa. This validates setting capacity of a large monolithic block at the ambient temperatures prevalent in the saliniferous formation.
  • Reliable swelling power for connection to the roof was not observable; the examinations of shrinkage tendency showed a longitudinal expansion of only 0.23‰.
  • Connection and adhesion to the salt rock strata were verified during demolition of the barrier structure.
  • Suitability for pneumatic projection and for dry-mix projection was verified.
  • Due to the lacking swelling power and the lack of verification of leak-tightness against fluids, the construction material examined is suitable for creation of liquid-tight barrier structures only to a limited degree.
  • Overall, a technically simple, formwork-free and cheap process for construction of barriers is available. However, the process still requires optimisation for industrial use.

Project Participants

Implementing Institution

http://www.ptka.kit.edu/english/wte/385.php

More Project Informations

Project title: Untersuchungen an Calciumsulfat-Steinsalz-Baustoffen für Dammbauwerke in Unter-Tage-Deponien und Endlagern

Project number: 02C1134

Project period: 2004 - 2008

Project region: Germany (Lower Saxony)

Project contact:

Herr Prof. Dr. Langefeld

View Publication

Source: German National Library of Science and Technology Hannover (TIB)