Robotic Application of a 50 mm Thick Sprayed Concrete Fireproofing Layer

Summary

The design of the tunnels at Crossrail’s Bond Street Station (C300/C410) includes a final sprayed concrete fireproofing layer. This layer covers any protruding steel fibres in the secondary lining and provides passive fire protection to the tunnel structure.

The ability of this regulating layer to limit spalling in the event of a fire was verified by a programme of testing in accordance with Crossrail’s KT24 specification. This testing proved that a dosage of 1 kg/m³ of polypropylene fibres and a layer thickness of 50 mm would be sufficient to limit spalling, based on exposure to a EUREKA fire curve. To ensure the application on site represented the test conditions, it was imperative that the minimum thickness of 50 mm could be achieved in a single operation.

This paper looks at the practical application of this 50 mm thick layer within SCL caverns up to 10 m in diameter, by means of a state of the art spraying robot with the ability to scan the profile and automatically apply a uniform layer of concrete. This paper shows that once the spraying parameters were determined, the required minimum layer thickness could be consistently achieved while working under tight tolerances specified by the designers.
Nevertheless, in order to provide further assurance and assist with the development of the correct parameters for the spraying robot, BFK developed an innovative and bespoke point cloud based survey system for checking thicknesses in the field. This provided an instant independent check of the spraying robot and allowed areas of inadequate thickness to be rectified without the risk of cold joints.