Sprayed concrete is a concrete which is delivered to the point of installation in a sealed, pressure-resistant hose or pipe, applied by ‘spraying’ and this method of application also compacts it simultaneously.
Sprayed concrete has a wide application range due to its high flexibility, good economics and good physical properties. However, the sprayed concrete method is requiring a high degree of mechanization and well trained nozzle operators. Nevertheless, the advantage over conventional concreting methods is outstanding: the application of concrete without any formwork.
Sprayed concrete is mainly used in the following applications:
- Excavation stabilization in tunneling and mining
- Trench and slope stabilisation
- High performance linings
- Repair and refurbishment works
The lion's share of sprayed concrete is employed today in tunnel construction. Particularly here in deep mining, early strength development plays a central role. Sprayed concrete should be applied quickly in thick layers, including overhead. As a result the strengths of freshly-applied sprayed concrete are divided into three classes: J1, J2 and J3 (EN 14487).
Class J1 sprayed concrete is appropriate for application in thin layers on a dry substrate. No structural requirements are to be expected in this type of sprayed concrete during the first hours after application.
Class J2 sprayed concrete is used in applications where thicker layers have to be achieved within short time. This type of sprayed concrete can be applied overhead and is suitable even at difficult circumstances, e.g. in case of slight water afflux and immediate subsequent work steps like drilling and blasting.
Class J3 sprayed concrete is used in case of highly fragile rock or strong water afflux. Due to it’s rapid setting, more dust and rebound occurs during the application and therefore, class J3 sprayed concrete is only used in special cases.