Radiation Containment Facility

Hospital Oncology Unit

The brief was to contain radiation caused by X-Ray in the Oncology unit of a public hospital in Australia. The designers had prepared documents using very thick walls (1.2 m) and a thick roof slab (1.8 m). The walls and roof were very heavily reinforced using conventional rebar - in excess of 200 kg/m³ - to control cracking. Very small cracks were not permitted as tests on previous units had demonstrated excessive radiation leakage due to cracks in the concrete. The oncology unit was located in a tropical climate, so heat of hydration was also a major concern with respect to cracking.

The builder wanted to explore an alternative solution and we proposed using steel fibre, thus eliminating virtually all the rebar. We also proposed using precast panels as formwork for the walls which would form part of the wall thickness. The advantages were;

Reduced construction time as there were no reinforcing bar cages to build and install
Reduced number of workers on site as there was no formwork nor rebar to install
Reliable concrete pour and compaction as there were concerns about ensuring sound concrete towards the bottom of the heavily reinforced walls

The ready-mix concrete supplier developed an excellent mix that enabled 40 kg/m³ of hook-end steel fibre 65/60 to be added. To control heat of hydration and obtain a dense concrete mix a high proportion of non-cementitious binder was used together with cement.

The project was a successfully completed and tested using radiation detection equipment. The new oncology unit easily met the stringent requirements of the client. This project was completed in 2009 and set a precedent. We understand that all new oncology units constructed in Australia since then have adopted fibre reinforced concrete.

It should be noted, very thick walls and slabs constructed of fibre reinforced concrete would not only contain radiation but would also be highly resistant to blast forces and severe impact loads. This is due to the high energy absorption capacity of FRC compared with conventionally reinforced concrete.

Oncology plan — **Plan view of the oncology unit**

This diagram shows the maze-like nature of the oncology unit to avoid radiation leakage through openings.

Oncology preparation of walls — **Wall preparation**

A view of the top of the walls about to be poured. The precast panels acting as lost formwork for the walls and roof slab are visible. Props have been placed at the top are propped at the top and mesh has been placed over the openings as a safety measure to prevent accidental falls and equipment being dropped.

Oncology wall pour — **SFRC being poured in walls**

This is the first wall that was poured. All pours were completed during night-time hours to avoid the heat of daylight hours in the tropical climate.

Oncology preparation of roof — **Preparation of the roof slab**

As the roof slab is very thick there was no need for any conventional reinforcement, nevertheless a bottom layer of light mesh was adopted to ease any concerns about tension capacity of the concrete.

Oncology roof pour — **Roof pour under way**

A boom lift was utilised to deliver the pumped concrete and apply compaction equipment. As the SFRC had plasticizer the slump was quite low and did not require a great deal of compaction. The "tide marks" on the walls indicate the concrete staging adopted by the builder.

Oncology finished roof — **Finished roof slab**

Water was applied to help with curing

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