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Influência do método de ensaio nos valores da extensão total na força máxima em varões de aço para betão armado
No full textNo presente trabalho discute-se a influência do método de ensaio na determinação da
extensão total na força máxima em varões de aço para betão armado. Apresenta-se uma análise comparativa entre os valores da extensão total na força máxima obtidos em varões de diferentes tipos, com vários diâmetros e produzidos por diversos fabricantes. São também analisadas as diferenças entre os valores desta característica mecânica, obtidos por diversas entidades e através de diferentes métodos de ensaio para varões do mesmo lote.
Com base nestas análises comparativas discute-se o impacto das incertezas associadas ao método de ensaio na dispersão dos valores desta característica, bem como a influência de outros parâmetros alheios ao ensaio.15pDE/NC
Results comparison of alkali-reactivity tests for same aggregates, using a kinetic model
No full textA kinetic based comparison between expansion tests for alkali-aggregate reactivity was carried out deriving critical rates from test criteria, in an earlier paper. The present paper checks the assumptions and models of that earlier comparison against results with real aggregates varying in alkali reactivity. Using the same approach, for each aggregate, expansion rates for three expansion tests were estimated, corrected for alkalinity and depicted as an Arrhenius plot. The relationship used data from NF P18-590, ASTM C 1260 and ASTM C 227 expansion test-methods and shows linear Arrhenius plots for several aggregates, aligned almost parallel to the line obtained for test criteria. Aspects related to the different experimental conditions on test-methods and their effects are discussed. The proposed conclusion is that both standards and aggregate results, in the given conditions, are not inconsistent from the kinetic point of view. Some suggestions are made for improving the accuracy of the relationship obtained.498-505pp.The authors are grateful for the financial support provided by Fundação para a Ciência e Tecnologia (FCT), through the projects EXREACT (PTDC/CTM/65243/2006) and IMPROVE (PTDC/ECM/115486/2009).Volume 634DM/NMMKey Engineering Material
Diversas opções para os espaços da habitação ou Zonas domésticas: propostas organizativas – II
No full textDesenvolvimento de matérias associadas a um leque de propostas organizativas para as zonas domésticas, sob o ponto de vista de diversos autores especialistas nestas matérias, apontando-se, desde já, a importância deste tipo de reflexões, designadamente, quando aplicadas a soluções habitacionais espacialmente muito condicionadas, como é o caso das soluções de habitação de interesse social.1 fig5 pInfohabitar, Ano X, n.º 493DED/NUTRevista Infohabita
Traditional methods of timber protection against bio-deterioration
No full textTimber, as a construction material, has played an important role in the history of architecture and construction since is very beginning. Naturally, the concerns about its durability and resistance are equally old and have been registered throughout history on building treaties and writings that can date as far as the Old Testament. Being a natural material, bio-deterioration is one of wood’s main weakness. Early attempts to deal with this issue included the resource to simple techniques as charring, immersion on saltwater and painting with natural oils and tar. On the 19th century the timber preservation industry was born and new methods and chemical preservatives were introduced. Presently most of those methods are known to be harmful to the environment and over the past decades the banned substances list has progressively increased urging the timber preservation industry to research for new sustainable methods. The study presented in this paper consists of a survey of traditional preservation products and technics and was conducted based on a historical bibliographical research. The results obtained were compiled into a database. This study, revealing a great deal about past construction methods, provides a valuable insight to the conservation of antique wood elements and allows understanding the timber elements condition when inspecting and rehabilitating old buildings. This insight can also be useful to the ongoing research on sustainable timber protection as the principles behind past methods can be the base to develop new improved solutions.410ppDE/NCE201419 a 21 de març
Influence of red mud addition on rheological behavior and hardened properties of mortars
No full textThis experimental research evaluates the individual and combined influence of red mud particles (RM)
and water/binder weight ratio (W/B) on the fresh–hardened properties and durability of cured mortars
up to 360 days. Samples containing up to 40 wt% RM and 0.47–0.58 W/B were prepared keeping the
workability constant. Samples with similar workability showed distinct rheological behavior along time.
The yield stress was the best rheological parameter to represent such variations. The maximum values of
exothermic peak reduced when the Portland cement was replaced by RM. Deeper negative changes in the
apparent porosity, water absorption, compressive strength and carbonation extent were also observed
changing the W/B ratio from 0.47 to 0.58 in the 20RM-containing mortars. In fact, the compressive
strength of mortar 20RM + 0.47W/B reduced 13% in comparison to RM-free mortar at 360 days, while
20RM + 0.58W/B reduced 46%. Although the extra voids created in the matrix by using 0.58W/B implied
in a positive effect to the alkali–silica reaction, adjusting a dosage of water similar to the one of RM-free
mortar makes RM an attractive alternative without compromise the materials’ properties studied in this
work.The authors acknowledge the financial support of the Brazilian
Council for Scientific and Technological Development (CNPq) and
the Portuguese Foundation for Science and Technology (FCT) under
the projects PTDC/CTM/65243/2006 and PDTC/ECM/115486/2009.
The authors also thank Alcoa (Spain), Weber and BASF – SE (Portugal)
for providing raw materials.9484-91pp65DM/NMMConstruction and Building Material
Dynamics of exchanges between the Ria Formosa and the ocean: role of environmental forcings
No full text128pDHA/NEC201412 a 16 de mai
Modelling beach morphological changes during episodic erosion-recovery events: preliminary results
No full textEpisodic and seasonal beach-dune system erosion, unlike long-term erosion, are, in general, followed by natural beach-dune recovery. This study, developed based on numerical modelling, is focused on the wind driven waves onshore and offshore induced sediment fluxes and resulting beach-dune morphological evolution, particularly on the underlying physics not yet fully understood, during episodic events of erosion-recovery. The objective is to improve the prediction capacity of the short to medium-term morphodynamic numerical model XBeach, particularly in what concerns the beach recovery phenomenon, and thus contribute to its credible application.31233-236DHA/NEC201424-26/junho/201
Fortes das Linhas de Torres – O testemunho dos materiais e das técnicas construtivas
No full textAs construções históricas são testemunhos físicos da história de um País mas também repositórios de conhecimentos científicos e técnicos e, em muitos casos, exemplos do gosto e da arte de uma época. O estudo dos materiais e das técnicas empregues desvenda informações importantes sobre a história construtiva e as condições em que ocorreu a sua evolução no tempo.
No caso dos Fortes das Linhas de Torres os estudos experimentais realizados incidiram sobre os principais materiais de construção: argamassas e terras. Trata-se de materiais porosos e heterogéneos, com características dependentes não só das matérias-primas mas também dos processos de execução e alteráveis sob a ação do clima, do ambiente, do homem; por isso esses materiais evolutivos guardam uma “impressão digital” do seu percurso no tempo, apenas parcialmente legível por quem a saiba interpretar.
As argamassas foram usadas principalmente nas zonas dos Fortes que exigiam maior resistência mecânica, segurança e durabilidade, como é o caso dos paióis. Os resultados dos ensaios realizados revelaram que se trata em todos os casos de argamassas de cal aérea, terra e agregados siliciosos e por vezes também calcários. Apesar da semelhança geral dos materiais, as argamassas são bem diferenciadas de Forte para Forte.
As terras recolhidas das muralhas e dos través revelaram o uso de materiais locais e em alguns casos variação textural vertical, relacionada com os recursos terrosos disponíveis e mais facilmente escaváveis.
Os estudos realizados permitiram conhecer as estratégias usadas na construção dos Fortes, e poderão ser mais desenvolvidos em futuras colaborações com as entidades envolvidas na recuperação e/ou manutenção e na valorização e divulgação das estruturas das Linhas de Torres.1pDM/NM
The effect of dune morphology longshore variation in the beach-dune system resilience
No full textThe present study consists on the analysis of the effect of the longshore variation of the frontal dune morphology in the beach-dune system morphodynamics during erosion events. Despite the predominance of the cross-shore component of the coastal processes under storm conditions, it is important to understand how the longshore gradient of such processes can affect the cross-shore component. The lack of field or laboratory data is an obstacle to the understanding of the underlying physics. Thus, this investigation is developed with a 2DH process-based numerical model. The morphology of the study zone is simplified in order to limit the complexity of the underlying physics and to be able to identify the driving processes more clearly. Initially, the bathymetry is uniform and only the frontal dune height varies alongshore. However, in time, as the dunes erode, only the topography above the foreshore becomes non-uniform, despite the volume of sediment extracted from the dune face which is transported seaward being higher for the highest dunes. Such sediment is stirred by the longshore current to the adjacent areas in front of the lowest dunes protecting these against erosion.60237-240DHA/NEC201424-26/junho/201
Water demand profiling as a decision support system for network operation and planning
No full text1pApresentação em PosterDHA/NES201421 a 26 de setembr