Ultra high performance concrete

Ultra high performance concrete (UHPC) has six to eight times the compressive strength of traditional concrete. It is produced from a mixture of Portland cement, crushed quartz, sand, silica fume, superplas-ticiser, fibres and water with no aggregates larger than a few millimetres. Wollastonite (calcium silicate) filler may also be included in the mix. The fibres most frequently used are either high strength steel for maximum strength or polyvinyl acetate (PVA) of approximately 12 mm in length for lower load applications. The concrete can be cast into traditional moulds by gravity or pumped or even injection cast under pressure. When cast into traditional moulds, the material is self-levelling, so only slight external vibration of the formwork may be required to ensure complete filling. The material is designed for use without steel reinforcement bars.

Structural components in ultra high performance concrete may, after setting, be subjected to steam treatment for 48 hours at 90°C. This enhances durability and mechanical properties, eliminates shrinkage and reduces creep. The material does not spall under fire test conditions.

The enhanced compressive and flexural strengths of ductile fibre-reinforced ultra high performance concrete enable lighter and thinner sections to be used for structural components such as shell roofs and bridges, creating an enhanced sleek aesthetic. A high quality durable surface is produced from appropriate moulds (e.g. steel) coated with proprietary release agent.

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