Concrete Spraying Process

Concrete Spraying Process

Dry spray process 

In the low build dry spray process (blown delivery), the semi dry (earth moist) base mix is pumped using compressed air, then water is added at the nozzle together with an accelerator (as required) and this mixture is spray applied.

The inherent moisture content of the aggregates in the base mix should not exceed 6%, as the effective flow rate is greatly reduced by clogging and the risk of blockages is increased.

Cement content

For 100 liters dry mix

28 kg of cement is added to 80 liters of aggregate.

For 1250 liters dry mix

350 kg of cement is added to 1000 liters of aggregate.

Wet spray process

There are two different wet spray processes, namely “thin” and “dense” stream pumping. In the thin stream process, the base concrete is pumped in a dense stream to the nozzle with a concrete pump, then dispersed by compressed air in a transformer and changed to a thin stream. The accelerator is normally added into the compressed air just before the transformer. This ensures that the sprayed concrete is uniformly treated with the accelerator.

With thin stream pumping, the same base mix is pumped through a rotor machine, as with dry spraying, with compressed air (blown delivery). The accelerator is added through a separate attachment to the nozzle with more compressed air.

Assuming that the same requirements are specified for the applied sprayed concrete, both processes – dense and thin stream application –require the same base mix in terms of granulometry, w/c, admixtures, additives and cement content.