Ultra-high performance concrete (UHPC) and Ultra-high performance fibre reinforced concrete (UHPFRC)

Ultra-high performance concrete

Ultra-high performance concrete (UHPC) is a class of concrete developed since the 1980s to provide improved strength and durability over traditional concretes. Performance of this concrete can be further enhanced by including fibres, i.e. as ultra-high performance fibre reinforced concrete (UHPFRC).

Cement contents of UHPC and UHPFRC are higher than in traditional concretes and concrete mix designs typically include various admixtures or replacement fillers of very small particle size (such as silica fume and ultra-fine silica powders) that increase the wet packing density. This reduces the potential size of voids or pores and hence gives improved compressive strength and durability performance as well as a degree of ductility. 

Compressive strengths for UHPC and UHPFRC

Typical cube sample compressive strengths for UHPC and UHPFRC are in the range 120–200N/mm², so are outside the scope of BS EN 1992 ‘Eurocode 2: Design of concrete structures’. Such concretes also fall outside the scope of associated concrete mix design standards typically used in the UK, i.e. BS EN 206 ‘Concrete – Specification, performance, production and conformity’ and BS 8500 (Parts 1 and 2) ‘Concrete – Complementary British Standard to BS EN 206’.

Limited use of UHPC and UHPFRC in the UK

To date, the use of UHPC and UHPFRC has been extremely limited in the UK, with much of the materials’ development and practical experience from design through production and to execution being abroad. There are known German technical guidelines (at least in draft) and French National Standards that govern UHPC/UHPFRC use in those specific European countries, but limited expertise exists from any UKAS Accredited Certifier or professional consultancy within the UK.

There are therefore no UK recognised design standards, codes of practice or industry guidance that cover UHPC and UHPFRC, or, just as importantly, the manufacture of products or components using them and their interaction with other products or components, for example fixings.

On this basis, NHBC does not currently accept applications using ultra-high performance concrete (UHPC) or its fibre reinforced variant (UHPFRC) under Technical Requirement R3, for materials either in the manufacture of panels for external walls and façade claddings or for load-bearing elements.