Formwork of reducing thickness due to loading of slab cast in-situ

A method of forming a concrete slab to be supported on a top surface of one or more load bearing members, wherein the formwork used to support the concrete when poured includes a support element having a support surface onto which concrete is poured to form the concrete slab, the method comprising:

• providing a load bearing member to support the slab when cured;
• providing a formwork including a support element having a layer of active material that compresses progressively under the load exerted by the concrete over a time it takes for the concrete to cure;
• covering a space around the load bearing member, including under the concrete slab when poured, with the support surface of the support element facing towards where the slab will be formed;
• sealing any space between a top surface of the load bearing structure and the support surface to form a continuous surface onto which concrete can be poured;
• and
• pouring the concrete over the continuous surface, wherein
• the providing of the load bearing member comprises providing a load bearing member comprising at least part of a base isolation device, and
• a surface of the base isolation device forms the top surface of the load bearing member.