Browsing by Author "Nunes, Sandra"
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- Durability of an UHPC containing spent equilibrium catalystPublication . Matos, Ana Mafalda; Nunes, Sandra; Costa, Carla; Aguiar, JoséUHPC 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.
- Multi-level study on UHPFRC incorporating ECatPublication . Abrishambaf, Amin; Pimentel, Mário; Nunes, Sandra; Costa, CarlaThe 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.
- Numerical optimization of self-compacting mortar mixture containing spent equilibrium catalyst from oil refineryPublication . Nunes, Sandra; Costa, CarlaAs the oil refining industries continue to grow, the production of waste catalysts generated in that process is expected to also increase. It would be of great value both economically and ecologically if these wastes could be reused as an addition in self-compacting concrete (SCC). This paper uses statistical factorial design approach, namely a central composite design, to conduct a proper experimental plan to design SCC mortar mixtures incorporating spent equilibrium catalyst (ECat), a waste generated by the oil refinery industry. The mathematical empirical models derived (which were also experimentally validated) revealed the influence of mixture design parameters, and their coupled effects, on the mortars' properties namely, deformability, viscosity, compressive strength, resistivity and ultrasonic pulse velocity. A numerical optimization technique was applied to the derived models to select the best mixture, which maximizes simultaneously durability and eco-efficiency and minimize cost, while maintaining self-compactability. The current study revealed that ECat can be successfully applied in SCC mortars, as a high volume cement replacement material (up to V-Ecat/Vp = 19.7%) due to its high pozzolanic activity. Nevertheless, for powder-type SCC5, cement/ECat blends must be combined with other finer additions to complete the powders distribution curve increasing the viscosity and stability of paste phase, in the fresh state.
- Spent equilibrium catalyst as internal curing agent in UHPFRCPublication . Matos, Ana Mafalda; Nunes, Sandra; Costa, Carla; Aguiar, J. B.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.
- Tailor-made SCC incorporating spent equilibrium catalyst from oil refineryPublication . Nunes, Sandra; Costa, CarlaThe spent equilibrium catalyst (ECat) is a waste generated by the oil-refinery industry with very high pozzolanic activity and, therefore, has a great potential as an addition in SCC. This paper describes research on the use of factorial Design of Experiments (DoE) approach to design SCC mortar mixtures incorporating ECat. As such, a central composite design was carried out to mathematically model the influence of mixture parameters and their coupled effects on deformability, viscosity, compressive strength, resistivity and ultrasonic pulse velocity. Thereafter, a numerical optimization technique was applied to the derived models to select the best mixture, which simultaneously maximizes different engineering properties and eco-efficiency, while maintaining self-compactability.