Effects of steel fibres on dynamic strength of UHPC

• Ultra-high performance concrete with various steel fibre addition is developed.
• Uniaxial compression and split tensile tests are carried out to obtain material static strength.
• SHPB tests are carried out to investigate the dynamic performance of the material and dynamic increase factors are obtained.
• Influence from fibre aspect ratio and volume fraction is discussed.
• Comparison DIF of UHPC is made with that of normal strength concrete.

In modern civil engineering, steel fibres are widely used as reinforcement in the design of high performance concrete material. The addition of steel fibres in the concrete matrix can greatly improve the material ductility and durability as well as the impact and abrasion resistance. The performance of steel fibre reinforced concrete changes with varying concretes, fibre geometries, distribution, orientation and densities. In the recent study, an innovative ultra-high performance concrete (UHPC) material with nano-material addition is developed. In the mix design of this UHPC material, steel fibre is taken as an important composite. Great improvement of static compressive strength and split tensile strength had been obtained. In the current research, Split-Hopkinson-Pressure-Bar (SHPB) tests are conducted on this UHPC material to investigate its dynamic properties. Different types of steel fibres including two kinds of micro fibres and two kinds of twisted fibres are mixed in the UHPC. In total, 80 UHPC samples were tested in Swinburne University of Technology in 2011 and 190 specimens were tested in the Central South University of China in 2013. The influence of steel fibre addition on the dynamic strength of UHPC is experimentally investigated. It is found that steel fibre additions have prominent influence on the concrete dynamic strength, however, Dynamic Increase Factors (DIF) of steel fibre reinforced UHPC are constantly lower than that of conventional concrete material.