Artigos de Revista

This study examines the potential of zinc hydroxychloride cement pastes as a fill material for the conservation of damaged historic tiles. The scope for modifying various properties was investigated by the preparation of numerous versions of the basic formulation in which the ratio of the three principal constituents – zinc oxide powder, an aqueous solution of zinc chloride, and a mineral aggregate – was varied. The importance of adjusting these variables for optimal performance was confirmed. The concentration of the zinc chloride solution was also found to be an important factor as this affected the useful working time before cementation occurred. The resultant reaction products were examined by x-ray diffraction in several cases. Compressive and flexural strength tests were undertaken on a number of the variants and on a commercial formulation (Lithos Arte). Observations of the cement-tile interface (using optical and scanning electron microscopy) were made. In addition, adhesion was assessed by means of a shear-stress test.

The evolution of the materials used in Portuguese interior wall coatings since the Roman occupation, namely the binders, is investigated using XRD in order to build a preliminary systematic database to contribute to the design and study of compatible products for conservation and repair. The results show that lime was the main binder until the end of the 18th century, with gypsum overcoming its use in the 19th century. A relationship is established between the results and several influencing aspects, namely other cultures, the neighbouring countries and their traditional construction techniques, the availability of raw materials, the purposes/techniques of application and the geographical location.

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Volcanic rocks have been found to be potentially alkali-reactive in a number of countries, including Japan, New Zealand, Iceland and Turkey. In order to characterize the potential reactivity of the volcanic rocks in Azores a project is being carried out, under the support of the Azores Government: the ReAVA Project—“Characterization of Potential Reactivity of the Volcanic Aggregates from the Azores Archipelago: Implications on the Durability of Concrete Structures”. This project comprises mainly: (1) petrographic assessment of the aggregates, (2) assessment of their performance in expansion tests and (3) site inspection of existing large concrete structures. This study has also the support of the IMPROVE Project—“Improvement of Performance of Aggregates in the Inhibition of Alkali-Aggregate Reactions in Concrete”, aiming to minimize the occurrence of alkali aggregate reaction (AAR) in Portugal. The Azorean rocks used as aggregates are mainly basalts and some trachytes. The reactivity of this kind of rocks is usually associated with the presence of volcanic glass, altered minerals and SiO2 content of the rock. The petrographic examinations of the rocks confirmed that one of the basaltic samples contains volcanic glass. The occurrence of microcrystalline quartz as a secondary product filling the interstices of the trachyte sample was confirmed by scanning electron microscope. The results of the concrete expansion test RILEM AAR-3 showed an increasing expansion starting on 140 days and continued to grow after 2 years of laboratory testing, but below the limit of 0.05 % recommended for this method.

In this paper we provide an overview of recent research work that contributes to clarify the effects of non-linear dynamic interaction on the seismic response of soil foundation-superstructure systems. Such work includes experimental results of seismically loaded structures on shallow foundations, theoretical advancements based on improved macro-elementmodeling of the soil-foundation system, examples of seismic design of bridge piers considering non-linear soil-foundation interaction effects, and numerical results of incremental non-linear dynamic analyses. The objective of this paper is to support the concept of a controlled share of ductility demand between the superstructure and the foundation as a key ingredient for a rational and integrated approach to seismic design of foundations and structures.

Lime coatings are frequent in the architectural heritage. Previous research showed that they can accelerate the drying of porous materials, such as stone and mortars, which could help control the endemic problems of dampness of these constructions. Here, we investigate the effect lime coatings have in presence of soluble salts. The work is based on evaporation tests performed on one lime coating applied on five materials contaminated with solutions of NaCl or Na2SO4. Conclusions could be drawn about: (i) the behavior of the coating; (ii) the salt decay process. It was observed that the coating can, in few cases, still enhance drying when salts are present. However, in comparison to pure water, the drying kinetics is slower, more irregular and shows higher dispersion. Also, it sometimes diverges among specimens of the same material subjected to similar experimental conditions. These chaotic variations are in agreement with the decay patterns and suggest that soluble salts amplify the effects of the natural heterogeneity of porous materials.

This paper discusses the thermal influence on long-distance and noncontact measurement of suspension bridge three-dimensional displacement by the use of an optical system composed of a digital camera, infrared active targets, and computational support. ln this type of measurement method, the optical propagation path of light through the air can range from 250 m up to 750 m, making its measurement accuracy strongly dependent on atmospheric refraction and turbulence, phenomena that are linked to the vertical temperature gradient between the camera and targets. ln addition, the adopted measurement geometrical configuration can lead to a height difference between these two elements (camera and targets) above 50 m. The paper describes the experimental setup and procedure followed for the determination of local temperature vertical gradients in the 25th of April Bridge in Lisbon (Portugal), where an optical measurement system was applied. The obtained thermal measurements are presented and applied in the evaluation of the systematic refraction vertical deviation, based on appropriate mathematical models mentioned in the paper, and for the identification of stable or unstable observation thermal conditions related to turbulence.

Railway tracks degrade faster at transition zones to railway bridges. In modern lines, back

This paper is focused on the study of an earthquake protection system, the tuned liquid damper (TLD), which can, if adequately designed, reduce earthquake demands on buildings. This positive effect is accomplished taking into account the oscillation of the free surface of a fluid inside a tank (sloshing). The behaviour of an isolated TLD, subjected to a sinusoidal excitation at its base, with different displacement amplitudes, was studied by finite element analysis. The efficiency of the TLD in improving the seismic response of an existing building, representative of modern architecture buildings in southern European countries was also evaluated based on linear dynamic analyses.