Fire protection options for circular tunnels: spray and boards option

Spray system

The reason why the spray system was considered but disregarded is that the pre-cast concrete segments contained a curing agent, which has the (side) effect of causing very dense and non-permeable concrete at the surface. As a result any cement based spray-on passive fire protection material would suffer from bonding issues. The application of a spray system could have been technically justified if (1) the concrete aggregate would have been exposed by means of hydro-milling, causing environmental issues or (2) a structural metal lath would have been installed to the concrete lining to create proper mechanical bond to the concrete. Both means were judged not to be feasible or economical for this project.

Post curved board systems

Calcium silicate aluminate boards come as flat sheets and can be post curved on site to match the tunnel radius, depending on the required thickness and the radius. The board is pushed into the radius by means of manpower. The required thickness in the case of the Port Of Miami Tunnel was 22mm using the Promat®-T/PROMATECT®-T board. This system was considered but disregarded because the system was judged to be less forgiving during installation, due to the multiple compound horizontal and vertical curves of the alignment, potentially opening up gaps between the boards. This is a project specific judgment that needs to be made for every project on a case-by-case basis.

Facetted board system

This system consists of fire rated boards with backer strips at all joints, both the circumferential and the longitudinal joints between the main panels.