Sandra Nunes

Robust SCC Mixes through Mix Design

AbstractOne of the main obstacles to a wider use of self-compacting concrete (SCC) is its sensitivity to small variations of the constituent materials, mix proportions, and other external factors. The main objective of this paper is to illustrate how to evaluate and compare the robustness of SCC mixtures optimized according to various economic criteria while maintaining the water/cement ratio and fresh state target properties. The optimization is derived from numerical models, and a central composite design is developed to mathematically model the influence of mixture parameters and their coupled effects on deformability, passing and filling abilities, and compressive strength. The strategies to increase the robustness of SCC mixtures and the existing methodologies to assess it are presented and discussed. By applying these methodologies, it is shown that robustness can be enhanced by changing only the proportions of materials in mixtures. Minimizing the superplasticizer dosage and, consequently, increasi...

Durability Enhancement Of SCC With Waste Glass Powder

Self compacting concrete (SCC) requires a large quantity of fine materials compared to common concrete. In this work waste glass powder was used to replace (50%) of filler required. Two types of SCC were manufactured, a control SCC type (CTL) using cement and limestone filler and another with glass powder replacing 50% of the filler. Mechanical and durability properties, namely, compressive strength, resistivity, chloride ion penetration, carbonation, capillary water absorption and oxygen permeability were assessed on both SCC types. It could be concluded that waste glass powder can be used successfully in SCC improving chloride penetration and water absorption by capillarity and maintaining strength levels. The potential risk of alkali-silica observed on mortar was mitigated when incorporating glass powder.

The Effect of Fibre Orientation on the Uniaxial Tensile Response of UHPFRC: Experimental Evaluation and Analytical Modelling

The tensile strength of Ultra-High Performance Fibre-Reinforced cementitious Composites (UHPFRC) depends primarily on the properties of the matrix and fibre’s length and geometry, but can also vary significantly according to the fibre orientation. In this study an experimental campaign is developed involving 22 uniaxial tensile tests on UHPFRC specimens with varying fibre content (1.5% and 3% in volume) and fibre orientation profiles (well oriented, randomly oriented and poorly oriented). The different fibre orientation profiles were obtained using a magnetic setup for orienting the fibres along a pre-defined direction during casting. The fibre orientation profiles were quantitatively analysed using image analysis algorithms, allowing the determination of fibre orientation angle distributions and other scalar fibre orientation indicators.

Caracterização das propriedades do betão em elementos produzidos com BAC e betão convencional

Resumo The present paper deals with comparing properties of hardened SCC cast during first full-scale tests in a precast factory and similar conventional concrete currently used in the same factory. The main goal was to evaluate viability of replacing the C45/55 conventional concrete, in use at the precast factory, by a SCC of the same class of resistance and maintaining the constituent materials. A wide number of specimens (cubes, cylinders, prisms) and full size precast elements were cast with both SCC and conventional vibrated concrete to enable comparing different properties of both types of hardened concrete. In order to implement SCC in this precast factory, suitability of actual current processes involved in production, mixing, transport and placing had to be evaluated. SCC exhibited improved mechanical behavior, higher resistance to fluid ingress and a more uniform strength along the full-size element due to a combination of proper mixdesign together with controlled mixing and placing on site.

Betão auto-compactável com resíduo agroindustrial

Os autores agradecem o programa EBW+ pela bolsa concedida, o CONSTRUCT/LABEST / FEUP, a engenheira Paula Silva e o tecnico Claudio Ferraz pelo suporte nos testes laboratoriais, o PPGECIV / UFSCar, o Instituto de Pesquisas Tecnologicas de Sao Paulo –IPT e a empresa Raizen pela doacao da ACBC. Este trabalho foi financiado por: Projeto POCI-01-0145-FEDER-007457- CONSTRUCT – Instituto de I&D em Estruturas e Construcoes – financiado pelo Fundo europeu de Desenvolvimento Regional (FEDER), atraves do COMPETE2020 – Programa Operacional Competitividade e Internacionalizacao (POCI) e por fundos nacionais atraves da Fundacao para a Ciencia e a Tecnologia I.P.

Modelling and Experimental Characterization of the Tensile Response of Ultra-High Performance Fibre-Reinforced Cementitious Composites

In this research, an experimental programme is developed to investigate the influence of fibre orientation on the tensile behaviour of UHPFRC from micro-mechanics to composite level. The micro-mechanical aspects of fibre reinforcement are analysed by performing single fibre pull-out test on the short fibres embedded in an ultra-high performance cementitious matrix. The influence of fibre embedded length (\( l_{f} /2 \) and \( l_{f} /4 \), l f being the fibre length) and fibre orientation (0°, 30° and 60°) on the pull-out behaviour are appraised. At the composite level, uniaxial tensile tests (UTT) on UHPFRC specimens with varying fibre contents (1.5%, 2.3% and 3.0% volume fractions) and fibre orientation profiles (parallel to the loading direction, randomly oriented and perpendicular to the loading direction) are performed. The different fibre orientation profiles were obtained using a magnetic setup for orienting the fibres along a pre-defined direction during casting. An image analysis technique is employed to determine the fibre orientation angle distributions and other scalar fibre orientation indicators. The results of this experimental programme clearly evidence the effect of fibre orientation not only on the tensile strength, but also on the development of the hardening branch that is typical of this type of cementitious composites.

Determination of the Tensile Response of UHPFRC Layers Using a Non-Destructive Method for Assessing the Fiber Content and Orientation

A procedure is developed for estimating the representative tensile response of existing thin Ultra-High Performance Fiber-Reinforced cement Composite (UHPFRC) layers. The procedure relies on non-destructive (NDT) measurements and on a previous tensile characterization campaign of the composite material, thereby avoiding the extraction of samples from the real structure. Two reliable indicators of the fiber content and fiber orientation within the UHPFRC layer are derived from the NDT measurements along two orthogonal directions. It is shown that these two indicators can be directly correlated to the parameters of a mechanical model providing the tensile response of the composite. The procedure is applied for the prediction of the peak stress of 36 Double-Edge Wedge Split tests and of the structural behavior of slab strips strengthened with a UHPFRC layer.