Percorrer por autor "Matos, Ana Mafalda"
A mostrar 1 - 5 de 5
Resultados por página
Opções de ordenação
- Comparison of response models from full, fractionated and small central composite design of experiments in cement-based mortarsPublication . Cangussu, Nara; Matos, Ana Mafalda; Maia, LinoExperimenters often do not have adequate time, resources or budget to carry out large number of experiments. DOE based in factorial designs are a powerful tool for designing and optimizing advanced cement-based materials, such as high performance self-compacting mortars, where many constituents raw-materials are employed (binder phase, granular materials, and admixtures) and several engineering as aesthetics requirements. The objective of this work was to compare response models from full, fractional, and small Central Composite Design of experiments applied to mortars properties.
- Modelling and Predicting Self-Compacting High Early Age Strength Mortars Properties: Comparison of Response Models from Full, Fractioned and Small Central Composite DesignsPublication . Cangussu, Nara; Matos, Ana Mafalda; Milheiro-Oliveira, Paula; Maia, LinoThe mixture design of cement-based materials can be complex due to the increasing num ber of constituent raw materials and multiple requirements in terms of engineering performance and economic and environmental efficiency. Designing experiments based on factorial plans has shown to be a powerful tool for predicting and optimising advanced cement-based materials, such as self-compacting high-early-strength cement-based mortars. Nevertheless, the number of factor interactions required for factor scheduling increases considerably with the number of factors. Con sequently, the probability that the interactions do not significantly affect the answer also increases. As such, fractioned factorial plans may be an exciting option. For the first time, the current work compares the regression models and the predicting capacity of full, fractionated (A and B fractions) and small factorial designs to describe self-compacting high-early-strength cement-based mortars’ properties, namely, the funnel time, flexure and compressive strength at 24 h for the function of the mixture parameters Vw/Vc, Sp/p, Vw/Vp, Vs/Vm and Vfs/Vs for the different factorial designs. We combine statistical methods and regression analysis. Response models were obtained from the full, fractionated, and small plans. The full and fractionated models seem appropriate for describing the properties of self-compacting high-early-strength cement-based mortars in the experimental region. Moreover, the predicting ability of the full and fractionated factorial designs is very similar; however, the small design predictions reveal some concerns. Our results confirm the potentiality of fractioned plans to reduce the number of experiments and consequently reduce the cost and time of experimentation when designing self-compacting high-early-strength cement-based mortars.
- Numerical Design and Optimisation of Self-Compacting High Early-Strength Cement-Based MortarsPublication . Cangussu, Nara; Matos, Ana Mafalda; Milheiro-Oliveira, Paula; Maia, LinoThe use of SCC in Europe began in the 1990s and was mainly promoted by the precast industry. Precast companies generally prefer high early-strength concrete mixtures to accelerate their production rate, reducing the demoulding time. From a materials science point of view, self-compacting and high early-strength concrete mixes may be challenging because they present contradicting mixture design requirements. For example, a low water/binder ratio (w/b) is key to achieving high early strength. However, it may impact the self-compacting ability, which is very sensitive to Vw/Vp. As such, the mixture design can be complex. The design of the experimental approach is a powerful tool for designing, predicting, and optimising advanced cement-based materials when several constituent materials are employed and multi-performance requirements are targeted. The current work aimed at fitting models to mathematically describe the flow ability, viscosity, and mechanical strength properties of high-performance self-compacting cement-based mortars based on a central composite design. The statistical fitted models revealed that Vs/Vm exhibited the strongest (negative) effect on the slump-flow diameter and T-funnel time. Vw/Vp showed the most significant effect on mechanical strength. Models were then used for mortar optimisation. The proposed optimal mixture represents the best compromise between self-compacting ability—a flow diameter of 250 mm and funnel time equal to 10 s—and compressive strength higher than 50 MPa at 24 h without any special curing treatment.
- Numerical modeling and optimization of self-compacting mortars: central composite design approach withPublication . Cangussu, Nara; Matos, Ana Mafalda; Maia, LinoThe current work developed Statistical models to reach high-performance self compacting cement-based mortars for structural purposes. A central composite design approach was employed to describe mortar fresh and hardened properties (mechanical strength) in function of key mortar mixture design parameters. The fitted models allow to model and predict flowability and viscosity properties and find a range where self-compacting behavior existed. Sand to mortar volume ratio exhibited the main effect on flowability and viscosity, with a positive effect, which is explained by decreases in paste volume. As expected, the water to cement volume ratio had the highest effect on both flexure and mechanical strength of mortars.
- Quartz Powder Valorisation in White Self-Compacting Concrete: Mortar Level StudyPublication . Matos, Ana Mafalda; Maia, Lino; Coutinho, Joana SousaQuartz powder (QP) from mining exploration has increased, and valorisation solutions are sought. QP incorporation in structural concrete is an exciting strategy for the growth and sustainable development of the concrete industry, waste management and environmental protection. This work addresses the valorisation of QP from a Portuguese company on powder-type self-compacting concrete for architectural and structural purposes, combining the light colour of quartz with white cement. As such, QP was used as a partial cement replacement, acting as a filler on self-compacting white mortars (SCWM) and pastes (SCWP). Firstly, the QP was characterised by chemical, physical and morphological properties. Afterwards, SCWM with 10% of the white Portland cement with QP were produced and, with 10% cement replacement by limestone fillers, commercially available, for comparison purposes. The following engineering properties were evaluated, flowability and viscosity, electrical resistivity, porosity and mechanical strength. In equivalent pastes samples, the heat of hydration was accessed. Finally, an architectonic element prototype was produced using SCWM-QP, and colour and aesthetics were evaluated. All SCWM reached adequate deformability and viscosity for self-compaction. In the hardened state, compressive strength, electrical resistivity and water-permeable porosity presented similar results for mortars incorporating quartz powder and limestone fillers. The isothermal calorimetry in equivalent pastes revealed a slight desacceleration of hydration for SCWP incorporating QP. The major findings of this study confirm the feasibility of SCWM with QP, meeting the required performance while reducing resource depletion in the concrete industry and adding value to a by-product.