Major codes of practice around the world are still based on experimental and theoretical results derived from investigations on normal strength concrete, high strength concrete and fibre reinforced concrete. Ultra high performance concrete (UHPC) poses enhanced mechanical properties and hence exhibit different failure mechanism compared to other concrete. The evaluation and definition of the stress-strain relationship of concrete are required to perform sectional analysis. To understand the same, stress strain behavior and toughness of UHPC is evaluated by carrying out uniaxial monotonic compression tests on cylinders. Experimental studies have been conducted with different fibre volume and aspect ratio of steel fibres (2.5%, 2% of 13m and 6 mm length fibres with diameter of 0.16 mm) on UHPC specimens. The inferences from the stress strain relationships have been evaluated and a new stress strain model has been proposed for UHPC under compression.

Keywords: Ultra high performance concrete, Fibre volume and aspect ratio, Stress strain model.