Sprayed Concrete for Repair of Structures
Sprayed concrete can be defined as mortar or concrete pneumatically projected into place’.
Sprayed concrete is used widely in the repair of deteriorated structures, because of its ease of application in situations where it is virtually impossible to use formwork to recast, and because it can be applied in thin layers maintaining good bond to the existing material let it be concrete, steel, brick or stone or meshing.
Spraying of concrete is a continuous process. Best use is made of this technique where there is a reasonable amount of continuous work. Spraying is less appropriate for a large number of small areas needing repair. Where the reinforcement to be encased is highly congested or for confined or highly profiled areas spraying will be inappropriate.Nearly all sprayed concrete repair work at site is carried out using the dry process with aggregate size of less than 10 mm.
High volume wet process technology is not normally compatible with the low volumes and frequent stoppages which characterize sprayed concrete repairs.
Sprayed Concrete Repair Considerations
Prior to repairing, there are many important considerations to be made, including
- determining the cause of the problem;
- deciding on the preparation work;
- designing and detailing the repair;
- specifying the material;
- high standard of workmanship;
- Sensible supervision by the engineer.
Among the initial design considerations it is particularly important to ensure that the repaired structure acts as it should, by reflecting the original joint pattern together with the movement joints which the structure itself has determined in the form of cracks. Not allowing for these will result in failure of the new sprayed-on part of the structure, in the form of cracking along the lines of the underlying joints.
Applications of Sprayed Concrete
Repairs have been carried out with sprayed concrete on many different types of structures, including:
- bridges soffits, beams, parapets and abutments;
- steel and RC framed buildings;
- cooling tower shells;
- industrial chimneys;
- water-retaining structures including dams;
- tunnels with various linings, and
- jetties, sea walls and other marine structures.