Concrete @ your Fingertips

High strength concrete

High strength concrete (HSC) may be defined as concrete with a specified characteristic cube strength between 60 and 100 N/mm², although higher strengths have been achieved and used. Strength levels of 80 to 100 N/mm² and even higher are being used for both precast and in-situ work in the USA, France, Norway and some other countries. The main applications for HSC in-situ concrete construction are in offshore structures, columns for tall buildings, long-span bridges and other highway structures. The main advantage is the reduction in size of compression elements and/or the amount of longitudinal reinforcement required.

The methods and technology for producing high strength concrete are not substantially different from those required for normal strength concrete. The target water/cement ratio should be in the range 0.30–0.35 or even lower. HSC can be produced with all of the cements and cement replacements (additions) normally available in the UK. A wide range of aggregates can be used though crushed rock aggregates (of suitably high crushing value) are preferable, but can increase the total water content.

Superplasticisers / high range water reducers are essential to achieve maximum water reduction, although plasticisers may be adequate for lower strength HSC (C50/60 to C55/67). Silica fume (microsilica) or metakaoline can be used to enhance the strength at high levels (C60/75 and above).

The terms high performance concrete and high strength concrete are often taken to mean the same thing. However, as indicated, high performance strictly relates to a concrete that has been designed to have good specific characteristics, such as high resistance to chloride ingress or high abrasion resistance. As a result it may also have a high strength, but this is not the main consideration.

Acknowledgement: The Concrete Society

Concrete Bookshop - Members receive 40% discount on Concrete Society publications

TR49 Design guidance for high strength concrete