Fibre reinforced ultra‐high performance concrete – Rheology, fibre bond strength and flexural strength

Ultra‐high performance concrete (UHPC) is characterised by a high compressive strength, high durability, and a dense microstructure. The latter causes UHPC to fail in a brittle and sometimes explosive manner. For this reason, UHPC is reinforced with microfibre reinforcement. On the one hand, these lead to increased tensile and bending loads being able to be absorbed, but above all to ductile post‐fracture behaviour. The fibres used are mostly steel fibres.

An essential aspect of the fibre reinforcement is the bond strength between UHPC and metallic fibre. The bond is divided into chemical‐adhesive bond, form bond and friction bond. Depending on the shape, material and surface condition of the fibre, the individual types of bond have different effects on the concrete. To quantify these effects, fibre pull‐out tests are often carried out. These provide information about the bond strength between the fibre and the concrete. However, results of various studies show that the bond strength does not automatically correlate with the actual influence on the resulting tensile and flexural strengths of concrete components.