Proportioning of Cement-Based Grout for Sealing Fractured Rock-Use of Packing Models

Abstract

Fractured, very permeable rock hosting repositories for radioactive waste will require grouting. New grout types of possible use where long-term performance is needed should have a small amount of cement for minimizing the increase in porosity that will follow from the ultimate dissolution and erosion of this component. They have to be low-viscous and gain strength early after injection and packing theory can assist designers in selecting suitable proportions of various grout components. Optimum particle packing means that the porosity is at minimum and that the amount of cement paste needed to fill the voids between aggregate particles is very small. Low porosity and microstructural stability must be guaranteed for long periods of time. Organic additives for reaching high fluidity cannot be used since they can give off colloids that carry released radionuclides and talc can be an alternative superplasticizer. Low-pH cement reacts with talc to give high strength with time while Portland cement gives early but limited strengthening. The clay mineral palygorskite can be used for early gelation because of its thixotropic properties. Once forced into the rock fractures or channels in soil it stiffens and serves as a filter that prevents fine particles to migrate through it be lost. However, its hydrophilic potential is too high to give the grout a high density and high strength. According to the experiments carried out, most of the investigated grouts are injectable in fractures with apertures down to 100 μm.

Enhancement of Workability of Cement-Poor Concrete by Optimizing Paste Content

“…This powder, termed Norquartz 45, was delivered by the Sibelco Nordic, Lillesand, Norway. The specific density, granulometry and chemical compositions of Norquartz 45 are shown in Table 2 [3]. Finely milled substance called "talc" manufactured by VWR International Company UK, which was used as superplastisizer and conditioner.…”

“…The concrete seals to be cast in boreholes should have a minimum amount of cement for minimizing the mutual chemical impact on the contacting clay seals [2]. This can be achieved by keeping the cement/aggregate ratio very low, using aggregate material with high internal friction after maturation, and also by using low-pH cement [3]. The bearing capacity of the concrete must be sufficiently high in order to carry the clay seals, which consist of perforated tubes filled with compacted smectite-rich clay.…”

Rheological Properties of Cement-Based Grouts Determined by Different Techniques

“…A fundamental requirement for bringing grout deep into rock fractures or leaks in earthen dams is that it must be very finegrained and be effectively forced into them. Two types of cement were used in this study, Portland cement and Merit 5000 low-pH cement, the latter for sealing rock containing boreholes with interacting seals of concrete and clay [11]. Long-lasting grouts require chemical integrity, which is provided by selecting quartzite as aggregate.…”

“…This technique is novel and used in pilot tests of talc-based grout [11] [26]. A glass tube with an inside diameter of 3.3 mm is filled with grout to one meter height with the valve being closed at the bottom (Figure 9).…”

“…For the measurement, the valve is opened and the grout allowed to flow down by 10 cm while measuring the time. The viscosity is evaluated by use of Poiseuille's law [11] [26], the flow rate being the cross section area of the tube multiplied by the flow length 10 cm, divided by the flow time.…”