Durabilidade de argamassas de base cimentícia reforçadas com fibras sintéticas

O presente artigo apresenta os resultados obtidos num programa experimental de caracterização de três argamassas de matriz cimentícia reforçadas com diferente tipo de fibras, nomeadamente, fibras de poliacrilonitrila (PAN), vidro (GF), polipropileno (PP) e de álcool polivinílico (PVA). A avaliação do desempenho das fibras como reforço efetivo de materiais de matriz cimentícia, foi realizada com ensaios de avaliação das propriedades reológicas, mecânicas (compressão e flexão) e de durabilidade (absorção de água por capilaridade e permeabilidade ao ar e à água). De modo a comparar e analisar os resultados obtidos, foram também realizados os mesmos ensaios com uma argamassa comercial de base cimentícia. Os ensaios são descritos e os principais resultados obtidos são apresentados e discutidos.Esta investigação foi realizada no âmbito do projeto InoTec - Material inovador de ultra elevada ductilidade para a reabilitação do património construído, promovido pela Empresa CiviTest e pela Universidade do Minho e financiado pelo COMPETE / QREN / FEDER (NORTE-07-0202 FEDER-023024). O primeiro autor agradece a bolsa de investigação atribuída ao abrigo deste projeto. Um especial agradecimento à empresa Owens Corning pelo fornecimento das fibras de vidro, à Exporplas pelas fibras de polipropileno, à Sika pelo superplastificante, à Secil pelo cimento, à CHRYSO pelo VMA e à S&P Clever Reinforcement Ibérica pelo fornecimento da argamassa comercial

Trypsin immobilisation on zeolites

This work compares different types of zeolites (NaA, NaX and NaY) as potential carriers for trypsin immobilisation. Silica was also used as a traditional carrier. Covalent attachment to the carriers was tested using glutaraldehyde. The efficiency of immobilisation and activity, operation and storage stability of free and immobilised enzyme on the three supports were studied. Optimum value of operation temperature was determined for trypsin immobilised on the best zeolite. Trypsin was most successfully immobilised on NaY by covalent attachment using glutaraldehyde. Though the best efficiencies were still obtained with silica, promising results were achieved with zeolite NaY. The ratio of immobilised protein achieved was very high, especially with silica, NaX and NaY. However there was a significant loss of enzyme activity with the immobilisation of trypsin. Optimal temperature obtained with immobilised enzyme was ca. 60 ºC, higher than the correspondent temperature for free enzyme (50 ºC).Fundação para a Ciência e a Tecnologia (FCT) - POCTI/2000/QUI/36452.European Social Fund (ESF)

Argamassa de ultra-elevada ductilidade para reabilitação: comportamento mecânico e durabilidade

Foi desenvolvida uma argamassa de ultra elevada ductilidade reforçada com fibras (FRCC) para uma nova técnica de reforço de estruturas existentes. São apresentados os estudos de caracterização do material, do ponto de vista mecânico (compressão e flexão), durabilidade (absorção de água por capilaridade, permeabilidade ao ar e à água, retração por secagem) e aderência ao suporte. É ainda apresentado um estudo da aplicação de diferentes tipos de conetores a empregar na técnica de reforço proposta, cujo desempenho foi determinado pela realização de ensaios de push-out.Fundação para a Ciência e a Tecnologia (FCT) FEDER - Programa Operacional do Nort

Durability of steel fiber reinforced self-compacting concrete

Publicado em "Proceedings of the 5th International Conference on The Concrete Future", ISBN 978-981-07-6067-0For conventional concrete without steel fibers, although still an aspect under discussion, there are some commonly used durability indicators. However, for steel fiber reinforced self-compacting concrete (SFRSCC) literature is sparse and the aspects of durability, particularly corrosion resistance, still deserve deeper research, mainly the corrosion of the fibers, since its influence on the appearance and on the serviceability limit states of a SFRSCC structure can be a concern. Therefore, in the ambit of an ongoing research project dealing with the development of SFRSCC sandwich panels, durability tests were executed to compare the performance of SFRSCC and self-compacting concrete (SCC) specimens. Nine different tests were performed, applied to SFRSCC and SCC in order to characterize their mechanical properties (elasticity modulus, compressive strength and flexural behaviour) and to evaluate its durability indicators normally used for plain concrete, namely: water absorption by immersion and by capillarity, permeability to air, electrical resistivity, chloride diffusion by migration under nonsteady state and carbonation. The results for the different concretes and curing times up to 28 days are presented and analyzed.(undefined

Spent-grains and zeolites as potential carriers for trypsin immobilisation

Trypsin is a widely used enzyme for protein hydrolysis and can be used to improve functional and nutritional properties of foods. The immobilization of enzymes on solid supports can offer several advantages over free enzymes including easy handling, recovery from the reaction medium, reuse and operation in continuous reactors. Traditional carriers include porous silica, porous glass and cellulose derivatives. Zeolites are porous alumino-silicates available in a wide range of particle size and porosity and can also be used as carriers. Spent grains are a brewing by-product with a high content in cellulose and can also be interesting as carriers for enzyme immobilization because, besides having the necessary conditions (as stability, rigidity, low mass transfer limitations, for instance), they are cheap and food grade. This work proposes the use of spent grains and zeolites as alternative carriers for trypsin immobilization and compares them with a traditional support (silica). Physical adsorption, ionic attachment and covalent attachment to the supports were tested. The efficiency of immobilization and activity, as well as the operation and storage stability of free and immobilized enzyme on the three supports were studied. Trypsin was most successfully immobilized on the supports by covalent attachment using glutaraldehyde. Though the best efficiencies were still obtained with silica, promising results were achieved with both spent grains and zeolite.Fundação para a Ciência e a Tecnologia (FCT) - project POCTI/2000/QUI/36452.European Social Fund (ESF)

Processamento de imagem digital com MatLab : uma aplicação em ambiente industrial

Fundação para a Ciência e a Tecnologia (FCT

Influence of the concentration of locust bean gum on the gelling ability of whey peptic hydrolysates

The gelling ability of whey proteins can be changed by limited hydrolysis and by the presence of other components such as polysaccharides; depending on the environmental conditions it can either be improved or impaired. In this work the effect of LBG on the heat-set gelation of aqueous whey protein hydrolysates (10 % w/w) from pepsin was assessed at pH 7.0 by small deformation rheology. Whey protein concentrate (WPC) and hydrolysates with a degree of hydrolysis (DH) of 1.5, 2.5 and 4.9 % were used. Different LBG concentrations were tested: 0, 0.1, 0.3 and 0.55 % (w/w). The behaviour of gels from whey proteins or whey protein hydrolysates towards the presence of LBG was very similar. The evolution of the viscous and storage moduli followed the general behaviour reported for many biopolymer heat-set gelation processes including whey proteins gelation. The increase in the LBG concentration generally led to a decrease in the gel strength. However, for whey proteins a small amount of LBG (0.1 %) leads to a big enhancement in the gel strength probably due to an increase in the protein concentration of the protein enriched phase. Further increases in the LBG concentration led to a decrease in the gel strength. The gelation process is very sensible to environmental conditions and to processing and often leads to rather coarse data. The factorial planning used allowed validating conclusions using fewer experiments than those needed if no planning had been used, while still getting statistical significance out of the results. However, as many factors are involved, the modelling of the process was not straightforward

Durability of steel fiber reinforced self-compacting concrete

Durability is one of the most important aspects of concrete due to its fundamental incidence on the serviceability working conditions of concrete structures. Research on the durability of steel fiber reinforced self-compacting concrete (SFRSCC) is still scarce, particularly in the aspects of corrosion resistance, which did not yet demonstrate clearly whether the corrosion of steel fibers may or may not lead to cracking and subsequent spalling of the surrounding concrete. For conventional concrete, without steel fibers, there are some widespread used durability indicators, which applicability to SFRSCC and its common values are practically unknown. For this purpose, an experimental work with SFRSCC and self-compacting concrete (SCC) specimens was carried out in order to characterize their mechanical properties and evaluate durability indicators. The results showed that the addition of steel fibers to SCC was very effective in terms of increasing the post-cracking flexural resistance and the energy absorption, and did not affect significantly the selfcompacting requisites and the durability indicators of SCC.The study reported in this paper is part of the research project QREN number 5387, LEGOUSE - Development of cost competitive pre-fabricated modular buildings, involving the Companies Mota-Engil, CiviTest, the ISISE/University of Minho and PIEP. The authors wish to acknowledge the support provided by Maccaferri and Radmix for the supplying of the fibers, Sika for the superplasticizer, Secil for the cement and Omya Comital for the limestone filler. The first author acknowledges the research grant under this project