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2014FallShotcreteEMag

Shotcrete FAQs Question: I have a 24 in. (610 mm) thick concrete dome that Answer: Multi-layer buildout of shotcrete sections is very serves as an enclosure to protect extremely sensitive and common and has decades of successful performance in existing important equipment that needs to withstand high impact structures. Shotcrete applied to a properly prepared, existing demands such as tornados or missiles. The contractor is proposing hardened concrete substrate (such as a previously shot shotcrete to use the shotcrete method with the following sequence: shoot layer) develops an excellent bond. The high-velocity impact approximately 1 in. (25 mm) (to achieve reinforcing bar cover); of shotcrete on the surface is in effect like sandblasting, and let stand for 8 hours; then place a reinforcing mat; then shoot opens up the receiving surface immediately before exposing it the majority of the dome thickness; let stand for 8 hours; then to the fresh cementitious paste. Cores taken through multiple place the other mat of reinforcing; then shoot the remaining layered shotcrete sections exhibit no signs of reduced bond. concrete cover. Often it is nearly impossible to identify where one layer stops I am concerned that, with an 8-hour duration between and the next starts. concrete placements, the three layers of concrete will not be Incremental placement of reinforcing bars in layered application adequately bonded such that they behave monolithically. In is also common. Proper shotcrete consistency, nozzleman particular, I would be concerned that the aggregate of the technique, and air velocity will force fresh cement paste around concrete that is shot onto a mat of reinforcement will not be able the back of the bar and fully encase the reinforcing bar, even to make its way “behind” the bar’s deformation, thus causing voids. when in contact with the previous hardened concrete surface. Please let me know your thoughts on the aforementioned Shooting a 24 in. (610 mm) thickness at one time with two concerns, whether it would be reasonable to shoot a 24 in. layers of reinforcement in the mostly overhead orientation of (610 mm) dome with a minimum of two layers of reinforcement a dome would require use of special concrete mixture designs all at once, and whether any of the ACI codes or standards with chemical accelerators, and would be very difficult to speak to shotcrete joints parallel to reinforcement. execute with consistent quality. Also, depending on the Over 30 years of experience, nationwide service.... American Concrete Restorations, Inc. Amerconcrete@aol.com www.americanconcreterestorations.com Phone: 630-887-0670 Fax: 630-887-0440 Restoring America using the Shotcrete Solution Interstate 80 - Joliet, IL Shotcrete • Fall 2014 63


2014FallShotcreteEMag
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