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Shotcrete is concrete (or sometimes mortar) conveyed through a hose and pneumatically projected at high velocity onto a surface, as a construction technique. Shotcrete is usually an all-inclusive term; gunite is a term sometimes used for some dry-mix types. Shotcrete undergoes placement and compaction at the same time due to the force with which it is projected from the nozzle. It can be impacted onto any type or shape of surface, including vertical or overhead areas.
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| Shotcrete swimming pool under construction in Northern Australia. |
Dry Mix Process
Batching and Mixing
Aggregate and cementitious materials shall be batched by mass. Equipment for batching by mass shall be capable of the accuracy specified in ASTM C94. The mixing equipment shall be capable of thoroughly mixing materials in sufficient quantity to maintain placing continuity and be capable of discharging all mixed material without any carryover from one batch to the next.
Delivery Equipment
The equipment shall be capable of discharge the aggregate-cement mixture into the delivery hose and delivering a continuous smooth stream of uniformly mixed material to the discharge nozzle. The discharge nozzle shall be equipped with a manually operated water injection system (water ring) for directing an even distribution of water through the aggregate-cement mixture. The water valve shall be capable of ready adjustment to vary the quantity of water and shall be convenient to the nozzleman. The water pressure at the discharge nozzle shall be sufficiently greater than the operation air pressure to ensure that the water is completely mixed with the other materials. If the line water is inadequate, a water pump shall be introduced into the line. The water pressure shall be steady (non-pulsating). The delivery equipment shall be thoroughly cleaned at the end of each shift. Equipment parts, especially the nozzle liner and water ring shall be regularly inspected and replaced as required.
Wet Mix Process
Batching and mixing
Batching and mixing shall be accomplished in accordance with the applicable provisions of ASTM C94. The mixing equipment shall be capable of thoroughly mixing the specified materials in sufficient quantity to maintain continouous placing. Ready-mix shotcrete complying with ASTM C94 may be used.
Delivery Equipment
The equipment shall be capable of delivering the premixed materials accurately, uniformly and continuously through the delivery hose. Recommendations of the equipment manufacturer shall be followed on the type and size of nozzle to be used and on cleaning, inspection, and maintenance of the equipment.
