GeneralQ We have a school project in California. It is for a structure with shotcrete walls and a shotcrete dome roof shot with an inflatable form. There is disagreement on the nozzlemen qualification panels. One group says that a panel should be shot for each nozzleman for each position (three panels: one vertical, and two for different slopes of the dome) in a single layer with the most congested reinforcing bar in any single layer to simulate job conditions. A second group maintains that the same three panels should be shot, but they should be built up over a period of 6 days in gradual layers to represent the layering of the actual shooting. I think that the first group is correct and complies with the intent of ACI 506. Shooting one-layer panels with the most congested reinforcing bar to be placed in any one layer would best simulate the job placement conditions. I don’t see any added advantage in shooting qualification panels over a period of days in layers and seems to be reading too much into “simulating” jobsite conditions.
In construction of shotcrete dome roofs with inflatable forms, the structural thickness of the dome is built out in layers to prevent overloading the support offered by the inflatable form and foam. Thus, your nozzleman qualification panels should be representative of the dome construction methods. This would include shooting orientation (vertical and varying slopes), shooting procedures (layers), and with the most congested reinforcing. When shotcrete is applied in layers, all you need to do is wait for the first layer to stiffen sufficiently (usually called initial set), before applying the next layer. It is not necessary to wait for days before applying the next lift.
