Comportamento à tracção em flexão de betões de desempenho melhorado

A substituição parcial de cimento por cinzas volantes tem sido utilizada por razões económicas e de trabalhabilidade da mistura. O conhecimento acerca da influência da idade e da percentagem de cinzas no comportamento em flexão do betão, principalmente na sua capacidade de absorção de energia, é reduzido. O presente trabalho pretende dar um contributo nesta área

Flexural tensile behaviour of enhanced performance concrete

High-performance concrete is generally produced using carefully selected high quality materials. These materials increase significantly the initial costs, hence, limiting its use. In this research work the performance of concrete was enhanced through incorporating low cost untreated materials like fly ash and crushed aggregates. Thus, it can be produced enhanced or even high performance low cost concrete and, also, decrease significantly the use of cement and non-renewable natural resources (river/sea sand), contributing to the necessary sustainability of construction. From experimental program, the effect of replacing cement by fly ash (up to 60%) in the flexural tensile behaviour was evaluated, using control compositions without the addition of fly ash as a base of comparison. The results obtained demonstrate that it is possible to produce enhanced performance concrete with the selected materials replacing up to 40% of the cement by fly ash. In specimens of such mixtures, cured at least 56 days, the values of the compressive strength and the flexural tensile parameters were similar to the ones of the control mixtures

Avaliação do módulo de elasticidade de betões de elevado desempenho com cinzas volantes

Os betões de elevado desempenho (BED) geralmente recorrem a materiais e a processos de fabrico de custo mais elevado que o dos betões correntes. Este facto tem condicionado a aplicação destes betões a obras especiais, apesar dos benefícios mecânicos e físicos que resultam a longo prazo poderem superar o maior investimento inicial. Nos últimos anos tem-se desenvolvido BED de custo controlado, substituindo-se parte de cimento por cinzas volantes e adoptando-se materiais e procedimentos de fabrico correntes. Neste trabalho, o módulo de elasticidade dos BED desenvolvidos é determinado experimentalmente e comparado com o obtido com formulações regulamentares e aplicando modelos baseados na teoria dos materiais compósitos

Cutinase structure, function and biocatalytic applications

This review analyses the role of cutinases in nature and their potential biotechnological applications. The cloning and expression of a fungal cutinase from Fusarium solani f. pisi, in Escherichia coli and Saccharomyces cerevisiae hosts are described. The three dimensional structure of this cutinase is also analysed and its function as a lipase discussed and compared with other lipases. The biocatalytic applications of cutinase are described taking into account the preparation of different cutinase forms and the media where the different types of enzymatic reactions have been performed, namely hydrolysis, esterification, transesterification and resolution of racemic mixtures. The stability of cutinase preparations is discussed, particularly in anionic reversed micelles considering the role of hexanol as substrate, co-surfactant and stabilizer. Process development based on the operation of cutinase reactors is also reviewed