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.

UHPC is an advanced cementitious material able to meet the current construction industry challenges regarding structural safety and durability. However, new UHPC formulations with limited shrinkage are still being pursued to reduce residual tensile stresses in the UHPFRC layers, for rehabilitation/strengthening applications. This investigation estimates the durability of a non-proprietary UHPC incorporating a by-product originated by the oil refinery industry (ECat), as an internal curing agent. Direct and indirect transport properties measurements as well as the carbonation assessment and evaluation of dimensional resilience to potential deleterious reactions revealed that the new UHPC possesses an excellent durability performance, typical of these materials. These results combined with its self-compacting ability, low autogenous shrinkage and high compressive strength confirm the belief in the role of this new UHPC towards a high-tech construction.

UHPFRC has become one of the most promising cement-based materials for the next generation of infrastructures because of its good workability, outstanding mechanical properties, and excellent durability. A promising field of application is the rehabilitation and/or strengthening of existing reinforced concrete structures, in which a new layer of UHPFRC replaces the deteriorated concrete (cracked, carbonated, chloride attack, etc.). The combination of the UHPFRC as protective layer, which can be reinforced, provides a simple and efficient way of increasing the durability (extending the service life), the stiffness and structural resistance capacity while keeping compact cross sections. A study was carried out to test a non-proprietary UHPC mix containing equilibrium catalyst to determine whether this new mix is a viable option for rehabilitation/strengthening applications. Several mechanical properties and durability were assessed, such as early age E-modulus development and autogenous shrinkage, compressive strength evolution in time, uniaxial tensile strength, water absorption by capillarity, chloride ion penetration, alkali-silica reactivity and sulphates attack resistance. Test results show that new UHPC developed present equivalent performance to other UHPCs cured under normal curing conditions.

The main goal of the current paper is to optimize ultra-high performance cementitious material (UHPC) mixes incorporating the spent equilibrium catalyst (ECat) to mitigate autogenous shrinkage. Design of experiments approach was used to optimize mixtures targeting different engineering properties, namely, self-compactibility, low early-age shrinkage and cracking risk, improved durability and high mechanical performance. The statistical models established indicated that ECat exhibits a strong positive effect on the autogenous shrinkage mitigation of UHPC attributed to the water absorbed in the porous of ECat particles. The proposed optimal UHPC mixture represents the best compromise between low autogenous shrinkage – 32% of reduction – and high resistivity at 28 days without impairing self-compatibility and compressive strength. This optimal UHPC combined with 3% high-strength steel fibres (l_f/d_f = 65) proved to be comparable to other Ultra High-Performance Fibre Reinforced Composites (UHPFRC), in terms of mechanical behaviour, and more eco-friendly and cost-efficient than UHPCs reported in the literature.