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2016WinterShotcreteEMag

Goin’ Underground Enhancement of Shotcrete Performance with a Pozzolanic- Based Rheology Control Agent By Ezgi Yurdakul and Klaus-Alexander Rieder In underground applications such as mining and tunneling, shotcrete is widely used for structural support of permanent openings, linings, and rock stabilization. Considering the performance that shotcrete plays on the quality of these applications, the following properties are often assessed: • Pumpability—the mixture should have an adequate flowability for the ease of pumping; • Sprayability—viscosity, cohesiveness, and stickiness is desired for minimum rebound; • Early-age strength—the mixture should have sufficient early-age strength to ensure required structural support is provided to the ground within the first few hours; • Later-age strength—the mixture should meet the specified long-term strength to ensure no strength loss is occurring over time that may compromise the service life of the structure; and • Durability—the mixture should be durable to ensure the longevity. Because silica fume improves many of these properties, the use of silica fume became common in shotcrete in the last few decades.1 However, due to various concerns about the health and safety, variation in quality, availability, and costefficiency of silica fume, there is a need to use alternative materials, which could provide equal or superior performance while eliminating any potential risks. The Need for Replacing Silica Fume with Pozzolanic-Based Rheology Control Agent What is pozzolanic-based rheology control agent? Pozzolanic-based rheology control agents (for example, TYTRO® RC 430) are suspension of fine amorphous silica particles in a stable liquid form. It consists of nonporous, spherical, nonaggregated, nanometric particles dispersed in water free from chlorides and with low alkalinity. Which Applications is Pozzolanic- Based Rheology Control Agent Used For? A pozzolanic-based rheology control agent can be used in any shotcrete mixture to replace cementitious materials such as silica fume, metakaolin, fly ash, or slag cement within a certain limit. Typical applications include but are not limited to the following areas: • Mining; • Tunnel linings; • Rock slope stabilization; • Pools and recreational structures; • Domes; • Retaining walls; • Water-retaining structures; and • Repair and rehabilitation of concrete structures. Reason 1—Health and Safety There is a concern that silica fume is a potential hazard to workers who add the material to the concrete or shotcrete mixers. Any dust generation can be a nuisance; and the lifting and dumping of bags presents their own health and safety risks with respect to back injuries, pinching, and straining. Because the pozzolanic-based rheology control agent is a liquid product, it can be automatically dispensed, and thus problems associated with handling powder-based silica fume can be eliminated. The facilities required for storing and dispensing admixtures are less expensive than those for silica fume, and require less maintenance and attention. 48 Shotcrete • Winter 2016


2016WinterShotcreteEMag
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