Shotcrete

Introduction and History
• The shotcrete process has grown into an important and widely used construction technique.
• In 1910, a double chambered cement gun was introduced to the construction industry.
• The sand-cement product of this device was given the proprietary name Gunite.
• In the ensuing years, trade marks such as Guncrete, pneucrete, Blastcrete, Blocrete, Jetcrete, and the terms pneumatically applied mortar and concrete, were introduced to describe similar processes.
• The early 1930s saw the generic term “shotcrete” introduced by the American Railway Engineering Association to describe the Gunite process.
• In 1951, the American Concrete Institute (ACI) adopted the term shotcrete to describe the dry-mix process.
• Shotcrete is now applied to the wet-mix process and has gained universal acceptance in the United States.
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Definition Of Terms /References
• Gunite / Mortar: Maximum aggregate size = sand
• Shotcrete : Maximum aggregate size = 3/8” typical (1/2” max)
• AKA: Sprayed Concrete (Europe)
• Relevant ACI Publications
     • 506R-90 Guide to Shotcrete
     • 506.3R-91 Guide to Certification of Shotcrete Nozzlemen
     • 506.4R-94 Guide for the Evaluation of Shotcrete
     • 506.2-95 Specification for Materials, Proportioning and Application of Shotcrete
     • 506.1R-98 State of the Art Report on Fiber Reinforced Shotcrete
Component Materials
• Aggregate
      • Fine = 60 - 70% of combined weight of aggregates
      • Coarse = 30-40% of combined weight of aggregate
• Portland Cement
      • Types I, II = 6.5 - 9.0 sack (611 - 846 lb/yd3)
• Water (potable)
      • Target W/C = 0.33 - 0.45
• WRA
      • Objective = workability with reduction of W/C ratio
• Microsilica
      • Typical range = 5% - 15% by weight of cement
• Latex Modifier
      • More commonly used in thin layer repair work than in ground support
• Accelerator
      • Silicates
      • Aluminates
      • Dosage = 2 - 5% by weight of cementitious material
Strength Developement of Shotcrete
Shotcrete Applications
• Sealing of Ground Mass Interface
    • Prevent erosion and/or air slaking (crumbling)
    • Deter exfiltration/infiltration
• Component of Excavation Support System
    • Sole Support
    • Rockbolt / shotcrete system
    • Rockbolt / shotcrete / lattice girder system
• Final Lining
     • Practical, functional or esthetic considerations do not require formed concrete
• Repair Work
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