Selection of Colloidal Silica Grouts with Respect to Gelling and Erosion Behaviour

Abstract

Cembinder, Eka EXP36, and MEYCO MP320 are three colloidal silica materials that have been proposed for post-excavation grouting of deep tunnels in a radioactive waste repository. In this study, samples of these colloidal silicas were tested for their particle size distribution, gel induction time (t G ), gel time (T G ), and physical erosion, under mildly saline groundwater flow conditions. In order to achieve a desired gel time range, from 15 to 50 min, it is recommended that the colloidal silica is mixed with a NaCl accelerator at a 5:1 volume ratio. At 20 • C, the concentration range for the NaCl solution should be 1.5 to 1.7 M for MEYCO, 1.23 to 1.38 M for Eka EXP36, and 1.3 to 1.47 M for Cembinder. The physical erosion of the set silicas remained steady during a 10 h flow cell experiment, when grouts were subjected to 0.05 M NaCl at a superficial velocity of 2.2 × 10 −5 m/s. For these test conditions, the results show that MEYCO has the highest average erosion rate (0.85 mg/h) of the three grout materials, as well as the greatest variability in this rate. Cembinder performed best with the lowest silica removal rate. Extrapolation of the measured erosion rates suggests that grout fracture dilation would not be significant under natural quiescent groundwater flow conditions, but would be high if there was hydraulic communication between the geosphere and the repository.

Stabilization of Sand with Colloidal Nano-Silica Hydrosols

“…Examples are CemSyn manufactured in India, Meyco MP320 manufactured in Sweden and MP320T manufactured in Germany. The main difference between these commercial products is their silica content and particle specific surface area values [57].…”

Grouting of Waste of the Baikal Pulp and Paper Mill to Reduce the Technogenic Impact to the Baikal Lake Ecosystem

“…Sludge lignin from existing drive cards was also attempted to be disposed of in the same way as the newly formed sludge lignin. However, gaseous anaerobic decomposition products were found in the sludge lignin from the sediment accumulators, and the proposed disposal method was considered unsuitable (Shen et al, 2017).…”

Silica sol as grouting material: a physio-chemical analysis

“…The time it takes for the silica sol to reach the non-flowing state from the introduction of accelerator is taken as the gel time. A modified version of this method exists where a needle is inserted into the gel and the point at which the needle does not move upon tipping the gel is taken as the gel time [ 77 ]. Although this method is very easy to use it is not considered to be very scientific.…”

“…This would suggest that even though the visual method is not considered very scientific the results produced by the method are close to the results that would be produced by the more scientific rheological method. Given the visual method’s ease of use it is understandable that many scientific groups choose this method when determining the PoG [ 38 , 53 , 58 , 77 ].…”

“…The choice of accelerator can also impact the gel time and often silica sols are supplied with a suggested mixing ratio and therefore a suggested gel time. Shen et al have reported dissolution and erosion behaviour of gels made from three different sols; namely Cembinder, Eka EXP36, and MEYCO MP320 [ 77 ]. These sols have different particle size distributions and were tested with gel times suggested by the supplier.…”