The suitability of a recently developed ultra-high performance fibre reinforced cementitious composite (UHPFRC) incorporating Spent Equilibrium Catalyst, ECat, for structural applications is investigated through a systematic multi-level investigation across micro, meso and composite levels. Scanning electron microscopy, isothermal calorimetry, thermogravimetric analysis, and mercury intrusion porosimetry tests were performed to evaluate the microstructure of the composite. At the meso-level, the mechanical properties of fibre to matrix ITZ were characterised by single fibre pullout tests on fibres embedded with various fibre orientation angles. At the composite level, specimens with 3% fibre content and different fibre orientation profiles were prepared to determine uniaxial tensile behaviour. The relation between the tensile fracture parameters and fibre structure parameter was assessed. In each level, the results are compared to a conventional ternary UHPFRC mixture and point towards the suitability of the newly developed mixture for structural applications.

This paper presents and discusses experimental results on the tensile mechanical performance of a newly developed ultra-high performance cementitious material, UHPC, incorporating spent equilibrium catalyst (ECat), a waste generated by the oil refinery industry, as a supplementary cementitious material. The results are compared to a previously developed conventional UHPC. The influence of ECat on the heat of hydration in UHPC is evaluated by isothermal calorimeter under a constant temperature of 20 ℃. To determine the evolution of the tensile behaviour with time, a series of uniaxial tensile tests are performed on the specimens at different ages, i.e. 1, 3, 7, 28 and 91 days after casting. Afterwards, the fibre to matrix interfacial bond properties were characterized by executing a series of single fibre pullout tests at the age of 28 days on the steel fibres embedded in UHPCs with 0°, 30° and 60° orientation angles. The results confirmed the adequate performance of the new developed UHPC for the structural application.

A simple model is proposed to predict the uniaxial tensile behaviour of ultra-high performance fibre-reinforced cementitious composites (UHPFRC) based on a meso-level description of the involved mechanics. The model relies on quantifiable material properties of the both matrix and fibres, on basic information concerning the fibre structure (such as fibre volumetric fraction, fibre orientation and geometry) and on three model parameters. Pullout tests on short fibres embedded in ultra-high performance cementitious matrix with different orientation angles and embedded lengths were developed for estimating the representative value of the average fibre-to-matrix bond-strength to be adopted, as well as for defining the fibre efficiency function describing the effects of fibre orientation on the pullout force. The model performance is validated against a series of uniaxial tensile tests on UHPFRC specimens covering a wide range of tensile behaviours. It is shown that the tensile response of UHPFRC can be well reproduced both in the hardening and softening stages with a single set of model parameters, and for a significant range of fibre contents and orientation profiles.