Artigos de Revista

The need for restoration of the built heritage increases the demand for new strengthening and rehabilitation techniques of structures. This paper discusses a rehabilitation system for timber beams, consisting of the replacement of the decayed parts by new ones of nearly the same material, connected to the sound parts by reinforced epoxy mortar plates. The use of this technique allows for lighter and less intrusive works, compatible with the normal building occupation during the rehabilitation process. The experimental analysis undertaken focused on the flexural bonding behavior with stainless steel, reinforcement steel, and glass fiber reinforced plastic bars being used as alternatives. A simple analytical model, based on the usual assumptions of the bending theory, is proposed, leading to a reasonable agreement with the experimental results. In spite of a reduction of strength when compared to the original elements, the safety level of the rehabilitated elements is high enough to comply with the Eurocode 5 requirements and is, therefore, suitable for actual works.

A aplicação de materiais reciclados é uma aposta a implementar com alguma urgência no quotidiano da construção. O material aqui apresentado como reciclável é o resíduo de tijolo da indústria cerâmica e da indústria da construção, para aplicação em argamassas de reboco. O desempenho a nível mecânico de argamassas de reboco incorporando resíduo de tijolo co-mo agregado foi testado experimentalmente e é analisado em pormenor no presente artigo.

A variabilidade da madeira é uma consequência da sua origem natural, podendo haver variações significativas do aspecto e das propriedades físicas e mecânicas dentro de cada espécie, nomeadamente em função das condições de crescimento das árvores, bem como ao longo do tronco. Importa por isso estabelecer critérios de selecção da madeira que permitam o fornecimento de lotes de material, tanto quanto possível homogéneo em termos de aspecto ou de comportamento, e com características conhecidas e fiáveis. A especificação da qualidade da madeira deverá assentar em parâmetros relevantes e objectivos, passíveis de verificação em obra, recorrendo-se quando possível a normas ou outros documentos que possam ser usados como referência. Para utilizações estruturais, pretendemos garantir o fornecimento de madeira com determinadas propriedades mecânicas mínimas. A “classificação de madeira para estruturas” (strength grading) agrupa assim a madeira de uma determinada espécie, ou grupo de espécies, em lotes (qualidades), aos quais é possível atribuir determinados valores de resistência mecânica e de propriedades elásticas.

The cryptic habits of subterranean termites impair studies of colony delimitation and the organization of foraging. Whereas feeding sites can be identified and the movements of foragers between them can be assessed using traditional mark-release techniques, the assignment of the termites found at feeding sites to their parent colonies remains problematical. Thus the extent and overlap of individual colony foraging territories are unknown. We used microsatellite markers to delineate colonies of R. grassei and compared the results with data from a mark-release-recapture study (Nobre et al., 2007)carried out in the same population and over the same period of time. The majority of colonies exhibited only a single-feeding site, but presented, even at a local scale, a high degree of variability in colony structure and no evidence of inbreeding. F-statistics for some colonies were consistent with pleometrosis. The population as a whole contained individual colonies that were separately identified as Mendelian, mixed family or pleometrotic families. Furthermore, microsatellite data suggest that what was represented by the MRR technique as a single foraging group could be drawn from more than one colony. Colony delineation is discussed as a tool for understanding overall population structure and termite feeding strategies.

Four different PVC formulations, designed for outdoor applications, in the form of calen dered films, were submitted to artificial accelerated ageing under different radiation sources, with and without water spray, and also to natural exposure. The influence of the different photo-oxidation conditions was evaluated by means of surface analysis using X-ray photoelectron spectroscopy (XPS) and infrared spectroscopy. The photo-oxidation of PVC is well monitored by FTIR measurements by following the formation of oxidation products of the carbonyl type, which are due to radical attack on the double bonds in the molecular structure of PVC, and enhanced by radiation and temperature. Results show that relative rates of PVC degradation reactions are different under different photo-oxidative conditions. XPS results show that, in technical PVC formulations, the fraction of chloride ions trapped in the inorganic filler is a better parameter to measure the PVC degradation (measured by the yellowing index variation) than the total remaining (or lost) chlorine in the surface. When the ageing method includes water jets, the top superficial layers made from the inorganic filler and the organic products from the PVC degradation are removed and leave behind a much more homogeneous layer which is more resistant to ageing than the ‘‘as processed’’ one that contains defects introduced by the calendering process. XPS also makes clear that zinc–calcium additive is a better thermal stabilizer than dibutyltin-maleate, and the presence of tinuvin P retards the PVC degradation. The best simulation of the natural weathering of such PVC materials under laboratory conditions needs to consider, besides the light, the intervention of water jets and/or humidity as well as the existence of light and dark periods.

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As esculturas de exterior em liga de cobre, sem a aplicação de medidas de protecção, podem mostrar aceleração da degradação devido à corrosão, agravada pelo aumento da poluição atmosférica associado ao desenvolvimento industrial e social do último século. Da corrosão resulta a alteração cromática da superfície das estátuas, com a formação de patinas de cor verde e preta, cujas características definem níveis de risco de degradação e, consequentemente, o tipo de intervenção a que a escultura deverá ser submetida para a sua conservação. Neste artigo abordam-se os processos de corrosão mais comuns em estátuas de ligas de cobre expostas no exterior e descreve-se a formação, composição e estrutura das patinas resultantes dessa corrosão. Referem-se ainda alguns aspectos sobre a conservação deste tipo de obras de arte

Portugal is one of the European countries in which built heritage is a testimony of its history. In this context, the legacy of the decorative glazed tile coatings of facades must be preserved and restored. This research is dedicated to the conservation of such facades in the city of Ovar, considered an example due to its rich heritage in glazed tiles, a high percentage of which requires a deep intervention. Therefore, this work is focused on the study of lime renders, serving as a support for this type of tile facades. For this, samples were collected from several buildings in the city, targeting their mechanical and physical study with the aim of producing compatible mortars to be used for application of detached tiles in these buildings and generally for the repair of the facades with glazed tile coatings. For this purpose, four mixtures of lime mortars with different volumetric ratios were composed. The aggregates used were: ordinary river sand and a local gravel. In three of the mixtures metakaolin, was added, with the intention of acting as an artificial pozzolan and thus improving the performance of these mortars. The use of a pozzolanic addition promotes hardening of lime mortars in cases when the ingression of carbon dioxide is low as is the case of mortars placed below glazed tile coatings. These mortars were also tested in the laboratory taking into account their physical and mechanical characteristics. The mechanical characteristics determined were: modulus of elasticity (E) by two different methods, compressive strength and flexural strength. In turn, the physical characteristics determined were: water vapour permeability and water absorption by total immersion and capillary action. The best mechanical behaviour (compressive and flexural) was observed in the mortar with pozzolanic additions. Similarly, the value of the modulus of elasticity was better in mortars with pozzolanic additions. The performance of these mortars was also adequate in terms of water behaviour. The mortars revealed suitable characteristics for application in building conservation situations concerning coating with glazed tiles.

Digital preservation aims at maintaining digital objects anddata accessible over long periods of time. The emerging context of e-Science imposes new scenarios and new requirements for digital preser-vation. This paper presents the main issues, current solutions and promi-nent projects for digital preservation and e-Science data management. Fi-nally, it presents the problem to be addressed, the solutions to explore,the proposed methodology and expected contributions of the associatedPhD work.

Digital preservation aims at maintaining digital objects anddata accessible over long periods of time. We propose the use of dedicatedor surplus storage resources of data grids to build frameworks of digitalpreservation. In this paper we focus on the problem of digital preservationin two scenarios: a national digital library and a repository of scientificinformation for dam safety. We detail the scenario of dam safety dataand provide an analysis of an existing data grid solution that can be usedfor this purpose.