Performance of Cement-poor Concrete with Different Superplasticizers

• Concrete can be used for casting plugs in deep boreholes where fracture zones are intersected. They will be exposed to flowing groundwater and be in contact with very tight seals of smectite clay installed where the surrounding rock is tight. The cast concrete must be able to carry the clay segments placed over it after a few days. Its bearing capacity does not have to be very high after that since the clay soon adheres to the rock and carries itself. The concrete must be poor in cement for minimizing the risk of creation of voids caused by dissolution of the cement and it should have “inert” aggregate of quartz-rich material. Inorganic superplasticizers instead of conventional organic ones should be used for eliminating the risk of degradation and loss by formation of colloids that can carry radionuclides to the biosphere from holes bored in repository rock. The two concrete types discussed in the present study had Portland and Merit 5000 low pH cement as binders and crushed quartzite as aggregate. Talc mineral powder and ordinary organic Glenium 51 were used as superplasticizers for comparing their impact on the physical properties. The matrix of the cement-poor talc concrete gave ductile behaviour during initial hardening. The very dense matrix of either of the concretes would not lead to compression of the system even after complete loss of cement, which will happen over a longer period of time. The overall conclusion was that talc as superplasticizer and conditioner of the concrete can make the concrete sufficiently fluid for constructing seals at depth in boreholes, and react with cement to provide high strength with some delay. pH is much lower in Merit than in Portland concrete, which causes less impact on the clay seals. Portland concrete has five times higher strength than Merit concrete after a week but three times lower strength after 28 days.

Ämnesord

TEKNIK OCH TEKNOLOGIER  -- Samhällsbyggnadsteknik -- Infrastrukturteknik (hsv//swe)

ENGINEERING AND TECHNOLOGY  -- Civil Engineering -- Infrastructure Engineering (hsv//eng)

TEKNIK OCH TEKNOLOGIER  -- Samhällsbyggnadsteknik -- Geoteknik (hsv//swe)

ENGINEERING AND TECHNOLOGY  -- Civil Engineering -- Geotechnical Engineering (hsv//eng)

Nyckelord

Structural Engineering

Konstruktionsteknik

Soil Mechanics

Geoteknik

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