The low-pH shotcrete plug was completed at the Grimsel Test Site in March 2007. The aim of the full-scale set-up is to demonstrate the support capacity of such a sealing plug under realistic conditions. The necessary pressure is applied by a swelling bentonite buffer at one side of the plug.

The low-pH concrete used for the construction of the plug must meet two key requirements:
  • Its pH has to be as low as possible (below 11) in order to minimise any chemical interaction of the plug with the bentonite and the surrounding geological medium.
  • It must be suitable for emplacement with the shotcrete technique.
Appropriate concrete formulations were developed and a short low-pH shotcrete plug was constructed in the framework of one of the earlier full-scale demonstrations for ESDRED at the Äspö URL. Based on the results and lessons learned, a full-scale low-pH plug was constructed at the Grimsel Test Site with the shotcrete technique.
The second step has been to test and monitor the plug‘s support capacity under the realistic conditions of a filled emplacement gallery, i.e. in a gallery of appropriate diameter, with an actual granite-shotcrete interface and with the load of a swelling bentonite buffer at one end. An artificial hydration system in the buffer has accelerated the saturation process and imposes a pore-water pressure in the bentonite. The plug is monitored by a network of sensors for total pressure, water pressure and water content.

Construction of the bentonite backfill (left) and hydration system in vertical mats (right)

Esdred Plug - Shotcrete
Completion of the plug with a shotcrete robot