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2016SpringShotcreteEMag

Technical Tip The nozzleman can tell whether there is sufficient impact velocity and plasticity when the face of the reinforcing steel will glisten and remain clean. Reinforcing bar deformations will be visible and a ridge, rather than a valley, of material will develop behind the bar. Mineral Additives The use of thixotropic mineral additives in recent years has allowed suppliers and applicators to have slumps of 6 to 7 in. (150 to 175  mm) without sacrificing stability. When added to the fluid 7 in. (175 mm) slump, the additive stabilizes the mixture while at rest. But when energy is applied, the mixture becomes fluid again. The result is a 5 in. (125 mm) slump that acts like the 7 in. (175 mm) slump under shear or stress. The additive is very effective at preventing shadowing because the nozzleman can have a very fluid mixture that will flow nicely behind the reinforcement yet remain stable enough to not sag or slough. The additive’s thixotropic properties also add other benefits, such as reduced rebound, increased cohesion, and improved finishability. There are many ways to prevent shadowing from occurring and causing headaches on the jobsite. Nozzle placement and a small dosage of a mineral additive are just a couple of easy ways to eliminate these problems and provide the industry with high-quality structural shotcrete that customers will continue to ask for. Joey Bell, Business Development Manager, Active Minerals International, grew up on a farm in Tennessee and received his BS in Concrete Industry Management from Middle Tennessee State University, Murfreesboro, TN. Bell travels the world developing new customers through technical support, product demonstrations, and field sales support for the Acti-Gel® 208 concrete additive. Along with shotcrete, his role at Active Minerals has furthered his knowledge in other applications, such as lightweight concrete, precast, slipform paving, RCC, and concrete block. Bell is Active Minerals’ corporate member representative for ASA and also a member of the Pool and Recreational Shotcrete Committee. Fig. 2: Nozzleman shooting at a proper angle Fig. 3: Proper impact velocity and reinforcing bar encasement Shotcrete • Spring 2016 41


2016SpringShotcreteEMag
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