PROJECT RESULTS / Annual Technical Results
Year 2 : ESDRED TECHNICAL RESULTS to January 2006
Module 4 : Low pH Cement for Shotcrete and Sealing Plug Construction Technology
Summary :
During the past year the feasibility of constructing, under realistic repository conditions, a low-pH shotcrete plug in an underground disposal drift has been demonstrated. A one meter long shotcrete plug was constructed by AITEMIN during November 2005 in an ad hoc 1.85 meter diameter drift. This drift had been previously excavated by SKB on the minus 220 m level of the Äspö HRL using a horizontal push-reaming system. The concrete formula used for the shotcrete plug was designed by IETcc in compliance with the Functional Requirements established in the project Deliverable D1. The plug has been constructed in such a way that it can be loaded to study the mechanical behaviour and so gain very valuable information for the designers.
Work completed :
- Definition of “Input Data and Functional Requirements”
- Design and selection of low-pH cements
- Design of low-pH concrete for the construction of shotcrete plugs
- Shotcreting technique development and field testing - view pictures
- Shotcrete plug design
- Test site preparation - view pictures
- Shotcrete plug construction - view pictures
Microscopic view of cement paste B.1.2 after 90 days of curing
B.1.2 concrete formula selected and properties
Work Underway :
- Shotcrete plug testing at failure under axial loading
- Analysis of the plug behaviour and model calibration
- Discussion on the construction of a “long-term” testing plug under “natural” conditions
- Design and testing of concrete formulas suitable to be used for rock wall shotcrete structural support
Important Events Planned for 2006 :
During the spring of 2006 the plug will be loaded up to failure. The axial hydraulic pressure applied to the inner end of the plug, the radial mechanical pressure transmitted form the plug to the rock, the displacements in the outer face of the plug and “noise” induce by fracturing (acoustic emission) will be monitored on line. Concrete samples will be collected for laboratory testing (mechanical, chemical and hydraulic determinations). The test results will be analyzed and used for model calibration/validation. Conclusions will be drawn and recommendations regarding further testing of this disposal component made.
Use of low pH cement in shotcrete applied to rock walls for rock support will be planned and tested in situ at the Äspö underground laboratory in Sweden.