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POLYMER-BASED EMULSION (PBE) |
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Cementitious grouts, such as Ordinary Portland Cement (OPC) have historically been widely used for water control in underground structures such as mines and tunnels. Although cheap and readily available,
OPC exhibits performance limitations without additives. Chemical (or solution) grouts such as polyurethanes and acrylamides present with health and safety concerns during the mixing and application process. There is a third category of grouting materials, Polymer-Based Emulsion (PBE) that provide a cost-effective, non-toxic option.
PBE grout was developed in the 1970s and first used to seal high pressure, high-rate water inflows into deep subsurface South African mines. Since the 1980s, PBE has also been applied in mines in Namibia, the UK, Australia, Zimbabwe, Botswana, Zambia, the United States, Canada, Poland and Russia.
PBE has successfully sealed discrete inflows of 160 L/sec at pressures up to 20,000 kPa (2,900 psi), rendering it one of the few viable grout options for high-flow rate and high-pressure water leaks. In recent years, PBE has found application beyond its roots in mining in dealing with leaking subsurface infrastructure such as subway tunnels, stations and building basements that have benefited from the water-sealing properties of PBE.
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FAQS for Polymer-Based Emulsions |
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What are the optimal grout attributes for durable underground water control?
- A grout must exhibit low viscosity with very small particle size (suspension grouts) or no particles (solution grout) to permit deep penetration into water-bearing fractures; and
- The grout sets up as an insoluble, chemically inert, flexible or self-healing solid that maintains adhesion to wet rock surfaces and concrete despite recovering formation pressure and continued blasting or tunnelling, development induced subsidence and stress redistribution.
What is a polymer-based emulsion grout (PBE)?
Polymer-based emulsion is a stable dispersion of polymer particles suspended in an aqueous medium which promotes flow and adhesion. Essentially, it's a mixture where tiny polymer particles are suspended in water, creating a milky or cloudy liquid.
What is the difference between a PBE grout and a cementitious grout?
Polymer-based emulsion grouts use a water-activated polymer as the primary binder, providing superior flexibility, water resistance, and chemical resistance compared to cementitious grouts. Cementitious grouts are a blend of cement, water and additives that offer strong, stable, but less flexible bonds more suitable for general construction and equipment anchoring. PBE, as an emulsion, is a mixture of liquids as opposed to a cementitious, chemical or solution grout. A major difference between PBE and resinous solution grouts is in how the material sets from a fluid to a solid grout mass. Most resinous grouts require a chemical reaction between an agent and a reagent to set. Required reactions may be between a chemical solution and water, or between two to four components pre-mixed or injected simultaneously. In contrast, PBE can set solely by mechanical means (shearing action in flow); no chemical reaction is necessary. Because PBE activation can be achieved without a chemical reaction, grout set is non-exothermic.
How is a PBE grout different from a resin grout?
The key difference in between PBE and resinous chemical grouts is how desired set time is achieved. Set time for chemical grouts must be pre-determined and achieved by mixing a set proportion of catalyst in the resin prior to injection. Because PBE can be used as a single-component, self-activating grout, the need for a pre-determined set time is not necessary. Instead, set time is controlled based upon real-time field observations indicative of flow patterns/behaviour in a geologic formation or behind a liner system at any desired injection rate.
How does a PBE grout set?
PBE grout sets by internal shear as the grout passes through fractures or other voids in water-bearing media. Set time may also be controlled chemically with the use of activator or inhibitor to regulate spread. Still, PBE is differentiated from solution grouts, because it is a single-part grout which does not require a chemical reaction to set.
Why should I use a PBE grout?
Unlike cementitious grouts, a PBE grout is flexible and withstands washout; it can better withstand movement and shifting, reducing cracking; PBE grout offers excellent resistance to moisture and corrosive environments; PBE grout is highly durable and can provide a long-lasting seal.
What are the key attributes of a PBE grout that set it apart from a cementitious or resin grout?
PBE grout is designed to penetrate areas where other grouts cannot, making it effective in tight strata and challenging conditions (i.e. high flow and high pressure). Key attributes that set PBE apart from cementitious and solution grouts include:
- High penetration capability due to low viscosity and ultra small particle size.
- Activation without chemical additives, resistance to washout, and flexibility.
- Durability (>50 years) and environmental friendliness.
- Estimated product life of +125 years.
How long has PBE grout been used for underground water control?
With a proven success record of +50 years of use, across 400 projects in more than 40 countries on 5 continents, PBE has been referred to as the water brigade of the mining and tunnelling industry, particularly when used after other grouting efforts have failed. Those projects have included sealing leaks with flow rates up to 160 L/sec, pressures of 20 MPa and to depths of 1300m bgl.
Is NOH2O more expensive that a cementitious grout?
Like any specialty grout, the unit cost of PBE is higher than the unit costs for commonly used cementitious grouts such as OPC. However, total grouting program costs compare favorably with cementitious grouting programs. The primary reasons are that PBE requires fewer labour hours, less shut-down time and less drilling than traditional grouting, and PBE exhibits long-term durability. The penetrability of PBE contributes significantly to its cost-effectiveness for water-sealing. Because PBE is capable of spreading out over greater areas, the number of grout holes required (and therefore the labour required to drill and repair them) is greatly reduced.
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