Euradwaste '08 - EU Bookshop - Europa

1. Bonding material: cement (CEM I 52.5N HSR LA), and powder CaCO3 type Carmeuse
2. Calibrated river sand with grain size between 0 and 4 mm
3. Superplasticizer Glenium®, a polycarboxylate ether-based material
Alternative backfill solutions are still being considered by O/N. A materials survey, accompanied
by pre-testing using the dry-gun projection technique (August 2005), rendered the following list of
granular material for possible use as backfill: pure sand (SiO2), pure bentonite (MX-80), sandbentonite
mixture (25/75), sand-cement mixture (90/10), and bentonite-cement mixture (85/15).
Reduced-scale mock-up testing (grout)
On June 30 th 2006, the grout injection backfill technique was tested on a 5 m long, reduced-scale
(2/3 rd scale) mock-up of a disposal cell. The centre of the mock-up was equipped with a heater,
representing the waste, locked in a steel tube filled with sand to simulate the Supercontainer and its
thermal inertia. The initial average temperature of the tube surface was a stable 40°C. It took
about 100 minutes, at a target rate of 5 m 3 /h, to fill up the annular void. After the setting of the
grout, the result was investigated by means of taking borehole samples and cutting a slice of the
mock-up (see Figure 3.2.2). It was noticed that a 100% void filling with a homogeneous backfill
had been achieved. Based on the above, it was concluded that the test had been a success.
The following characteristics of the backfill were measured on the borehole samples:
• density: 2190 kg/m 3
• thermal conductivity: 3 W/°C-m (if 9% water content), 1.6 W/°C-m (if dried)
• compressive strength: 12 MPa
Figure 3.2.2: Reduced-scale mock-up for grout backfill testing, after slice-cut (Nov. 2006)
Reduced-scale mock-up testing (dry granular materials)
The projection of dry granular materials with a dry-gun was tested on a similar 5 m long, reducedscale
mock-up, but without a central heater. The projection nozzle was mounted on a vehicle, running
on rails, and specially designed for mechanical robustness (see Figure 3.2.3). All selected
backfill materials were tested between June and October 2006. Borehole samples were taken from
the resulting backfill. It was observed that the machine operated without failure under mechanically
very harsh conditions, and achieved a linear pace of about 2 to 3 m/h. No problems with dust
generation or water runback were encountered. The annular void was 100% filled with a backfill
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