A Talc-Based Cement-Poor Concrete for Sealing Boreholes in Rock

Roland Pusch^*, Laurence Warr, Georg Grathoff, Alireza Pourbakhtiar, Sven Knutsson, Mohammed Hatem Mohammed

Geography & Geological Department, Greifswald University, Greifswald, Germany.
Luleå University of Technology, Luleå, Sweden.

DOI: 10.4236/eng.2013.53036                

Abstract

Deep investigation boreholes in crystalline rock for site selection of repositories for high-level radioactive waste are proposed to be sealed by installing a series of dense concrete and clay plugs. These should prevent radionuclides from leaking canisters at depth to migrate to the biosphere through the holes. The concrete seals will be installed where the holes intersect water-bearing fracture zones to serve as stable and low-permeable supports for adjacent clay plugs. Low porosity and microstructural stability must be guaranteed for many thousands of years and ordinary Portland cement with organic superplastizer will not fulfill the requirements since the high pH will cause degradation of contacting clay and the organic additive can produce colloids with a capacity to carry radionuclides up to the biosphere. Very cement-poor concrete (<8%) based on low-pH cement and with talc as plasticizer is an option but it matures more slowly, which requires that the construction of seals is made so that sufficient bearing capacity for carrying overlying clay seals is reached.

Keywords

Clay; Concrete; Ductility; Strength; Superplasticizers; Talc

Conflicts of Interest

The authors declare no conflicts of interest.

References

[1]	N. Bockgard, “Hydraulic Effects of Unsealed Boreholes. Numerical Groundwater Flow Modelling of the Forsmark and Laxemar Site,” Report of Sub Project 2 of Borehole Sealing Project Phase 4, Svensk Karnbranslehantering, 2011.
[2]	R. Pusch and G. Ramqvist, “Borehole Sealing Project,” Final Report of Phase 3, SKB, 2007.
[3]	Ch. Svemar, “Cluster Repository Project (CROP),” Final Report of European Commission Contract FIR1-CT-2000, Brussels, 2005.
[4]	L. N. Warr and G. H. Grathoff, “Sealing of Investigation Boreholes: Mineralogical and Geochemical Borehole Plug Analyses,” SKB Report, Ernst-Moritz-Arndt-Universit?t, Greifswald, 2010.
[5]	R. Pusch and R. N. Yong, “Microstructure of Smectite Clays and Engineering Performance,” Taylor & Francis, New York, 2006.
[6]	R. Chaplow, “Review of Requirements for Sealing Investigation of Boreholes,” Nuclear Decommissioning Authority Radioactive Waste Management Directorate, Robert Chaplow Associates Ltd., Oxfordshire, 2011.
[7]	R. Pusch, G. Ramqvist, N. Bockgard and L. Ekman, “Sealing of Investigation Boreholes Phase 4,” Final Report, SKB, 2011.
[8]	T. C. Powers, “Structure and Physical Properties of Hardened Portland Cement Paste,” Journal of American Ceramic Society, Vol. 41, No. 1, 1958, pp. 1-6. doi:10.1111/j.1151-2916.1958.tb13494.x
[9]	A. Pourbakhtiar, “Pilot Study of Method for Constructing Concrete Seals and Fracture Grouts in Deep Boreholes and Cementitious Backfills in Tunnels, Drifts and Shafts in Crystalline Rock,” Master Thesis, Lulea University of Technology, Lulea, 2012.
[10]	G. K. Batchelor, “An Introduction to Fluid Dynamics,” Cambridge University Press, Cambridge, 1967.
[11]	D. Hillel, “Soil and Water: Physical Principles and Processes,” Academic Press, New York, 1971.
[12]	L. M. Arya, F. J. Leij, P. J. Shouse and M. van Genuchten, “Relationship between the Hydraulic Conductivity Function and the Particle-Size Distribution,” Soil Science Society of America Journal, Vol. 63, No. 5, 1999, pp. 1063-1070. doi:10.2136/sssaj1999.6351063x
[13]	Y. Mualem, “A New Model Predicting the Hydraulic Conductivity of Unsaturated Porous Media,” Water Resources Research, Vol. 12, No. 3, 1976, pp. 513-522. doi:10.1029/WR012i003p00513
[14]	K. Kosugi, “General Model for Unsaturated Hydraulic Conductivity for Soils with Lognormal Pore-Size Distribution,” Soil Science Society of America Journal, Vol. 63, No. 2, 1999, pp. 270-277. doi:10.2136/sssaj1999.03615995006300020003x
[15]	T. Vogel, M. Th. van Genuchten and M. Cislerova, “Effect of the Shape of the Soil Hydraulic Functions near Saturation on Variablysaturated Flow Predictions,” Advances in Water Resources, Vol. 24, No. 2, 2000, pp. 133-144. doi:10.1016/S0309-1708(00)00037-3
[16]	P. Paulini, “A Through Solution Model for Volume Changes of Cement Hydration,” Elsevier Science, Cement and Concrete Research, Vol. 24, No. 3, 1993, pp. 488-496. doi:10.1016/0008-8846(94)90137-6
[17]	F. Locher, “Cement, Principles of Production and Use,” Verlag, Berlin, 2006.
[18]	A. W. Jenike, “Storage and Flow of Solids,” Utah Engineering Experiment Station, University of Utah, Salt Lake City, 1970, Bulletin No. 123.
[19]	J. Ravenet, “Silo Problems,” Bulk Solids Handing, Vol. 1, No. 4, 1981, pp. 667-679.