Artigos de Revista

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This work reports a study carried out on the design and performance of galvanic and polarization resistance sensors to be embedded in concrete systems for permanent monitoring of the corrosion condition of reinforcing steel, aiming to establish a correlation between the galvanic currents, Igal, and the corrosion currents, Icorr, estimated from the polarization resistance, Rp. Sensors have been tested in saturated Ca(OH)2 aqueous solutions, under a variety of conditions, simulating the most important parameters that can accelerate the corrosion of concrete reinforcing steel, such as carbonation, ingress of chloride ions, presence or absence of O2. For all the conditions, the influence of temperature (20 to 55 ºC) has also been considered. From this study, it could be concluded that the galvanic currents are sensitive to the various parameters following a trend similar to that of the Rp values. A relationship between the galvanic and the corrosion current densities was obtained and the limiting values of the Igal, indicative of the state condition of the reinforcing steel for the designed sensor, were established

Among the different types of tidal inlets, wave-dominated inlets have been subjected to few quantitative studies, so that the physical processes controlling their dynamics are not fully understood. This study presents the application of a coastal area morphodynamic modeling system to a wave- dominated inlet (O´ bidos Inlet, western coast of Portugal), in order to investigate the physical processes responsible for channel development during fair weather conditions and shoaling during periods of larger waves. The modeling system was able to reproduce reasonably well morphological changes at the O´ bidos Inlet and subsequent tidal amplitude evolutions inside the lagoon over a period which includes 3 months of fair weather conditions, followed by 2 months representative of winter conditions. The inlet development during fair weather conditions was attributed to the strong ebb-dominance of the main channel without waves, enhanced by the combination of shallow channels and a meso-tidal range. The inlet infilling during the maritime winter was attributed to three main wave-induced mechanisms: (1) the onshore component of wave radiation stresse gradients, which is not fully compensated by the wave-induced setup in front of the inlet; (2) the acceleration and convergence of longshore transport toward the inlet, due to the presence of a strong lateral gradient in free surface elevation on both sides of the inlet, and, to a smaller extent, to wave refraction around the ebb-delta; and (3) the increase in mean water level inside the lagoon, which reduces tidal asymmetry and subsequent ebb-dominance.

This paper tackles the problem of establishing prioritization of alternative waterrehabilitation investment plans. In mature systems, the planning department is often facedwith the problem of selecting investment proposals submitted by different departments, all ofthem contributing to meet the strategic and tactic corporate objectives, but none of thembeing critical to meet the service or legal requirements in the short term. This was the frameof the applied research project described herein. In this context, a conceptual model andworksheet-based operational prototype were developed and tested, incorporating the keyobjectives, assessment criteria and performance measures. A whole-of-life risk-basedapproach was adopted, including direct, indirect and external costs. A Business RiskExposure (BRE) technique was used to quantify the main technological and operational risks.The investment benefits are assessed subtracting the global costs of each investmentscenario from the corresponding costs of the statu quo. Given that this decision support toolshould be applicable to assets of different types (e.g., pipes, pumping stations, storage tanksand treatment facilities), sensitivity analyses were carried out in order to identify, for eachasset type, the main cost items to be considered, as a minimum set, in simplified applicationsof the developed model. Comparisons between alternative investment proposals require thata single period of analysis is adopted. The selection of this period is not obvious whendifferent asset types, each with different expected useful lives, are involved. Sensitivityanalyses were carried out in order to get a better insight of this problem. Finally, alternativeprioritization criteria were explored, concluding that investment prioritization should be basedon a simple ranking of the total direct relative benefits (i.e., total benefits/capital investment);however, indirect benefits should always be taken into consideration in the final decision.

A influência da pressão dos resíduos na migração de fluidos através de orifícios na geomembrana (GM) foi estudada mediante a realização de ensaios laboratoriais. Simulou-se um sistema de confinamento de fundo de um aterro de resíduos, constituído por uma GM com um orifício circular, um geossintético bentonítico (GCL) e uma camada de solo argiloso compactado (CCL). Mediu-se o fluxo que migra através do orifício na GM. Com base no fluxo final, obtido em regime permanente, estimou-se a transmissividade da interface entre a GM e o GCL, através de retroanálise. Os ensaios foram conduzidos com seis pressões de confinamento: 25, 50, 75, 100, 150 e 200 kPa. Os resultados obtidos sugerem que o aumento da pressão dos resíduos sobre o sistema de confinamento tem uma influência reduzida sobre o fluxo e sobre a transmissividade da interface, para a gama de pressões utilizada.

Adhesive bonding technology has played an essential role in the development and growth of the rehabilitation and repair of timber structures. The ability of a structural joint to maintain satisfactory long-term performance, often in severe environments, is an important requirement of a structural adhesive joint, as the joint should be able to support design loads, under service conditions, for the planned life time of the structure. A number of factors determining the durability of structural adhesive joints have been identified and can be grouped in three categories: environment, materials and stresses. The environment is dominated by temperature and moisture. The materials category includes the adherend, the adhesive, and the inter-phase between them both. The last category refers to the stresses to which the bond is subjected during or after exposure to service environment, affecting both longevity and residual strength. Since this subject in relation to timber bonding is very disperse within the literature, this paper will focus briefly on each of the aforementioned factors, thus providing a general understanding on the factors that influence the durability of bonded timber joints.

The quantitative forecasting of corrosion development remains difficult, limiting the development of validated preventive maintenance strategies. Difficulties come from the spatial variability of material properties, the temporal variability of the environment and the sensitivity of non destructive measurements to changing environmental conditions. The reinforced concrete Barra Bridge, Portugal, has been thoroughly investigated, and on site data have been used for modelling the development of corrosion and its variability. A model has been derived from additional laboratory experiments, which enables to account for the influence of environment and to support the decision process regarding the corrosion state and the forecasting of its evolution.