Papers by Author: Carlos Alves

Abstract: The study of stone alterations in the Lisbon Metro stations allowed the discussion of the influence in the development of these alterations of stones characteristics and the actual conditions to which the stones are subjected. Alterations occur under what can be considered the usual conditions of use but also under abnormal situations that must be taken into account given its frequency. The diverse situations identified are considered in the discussion of possible recommendations bearing in mind the actual situations found at the stations.

Abstract: Lime mortars can suffer alterations when subjected to gaseous pollutants. Particulate air pollutants can also be deposited and incorporated to the mortar surfaces. Thus, they can be used as pollution tracers allowing us to measure deposition rates of pollutants to compare pollution loads. To calculate deposition rates the absolute age of the studied mortars must be known. Luminescence dating allows estimating the age of lime mortars but involves some partially unsolved problems. Luminescence yields the age of an object from the ratio between paleodose or cumulative radiation dose in the minerals of that object and the annual dose rate of ionizing radiation. The development of optically stimulated luminescence (OSL) in the last years and the application of statistical tools have resulted in the first dating of lime mortars. In this work mortars from old buildings and have been collected from two urban sites (A Coruña, Spain, and Braga, Portugal) to estimate their ages by luminescence. Thus, the mortars could be used as passive samplers to calculate deposition rates and relate these to different pollution loads. Results show partial successful estimates and some related problems in younger mortars are discussed.

Abstract: In this paper, an initial X-ray Computed Tomography study of sulphate salt degradation of two Portuguese Dimension Stones (“Semi-rijo” and “Mocacreme”) is presented, based on the Standard EN 12370 (1999). This study was performed using a high resolution X-ray Computed Tomography, a 3D X-ray microscopy non-destructive technique, in order to get representative digital information on 3D texture of the external surface and of the interior of visible light opaque objects for imaging and eventually measuring them, at resolutions in the m range. This will produce spatial quantitative information map on the density distribution of the scanned samples, usually associated to different mineral phases and voids’ textures constituting the natural materials. Both types of stones are also being investigated by the combined application of classic methods: Optical Microscopy, Scanning Electron Microscopy and Mercury Injection Porosimetry (MICP). Most of those classic studies use mainly traditional 2D imaging techniques, none of these being able to produce the 3D resolution details that X-ray micro-tomography enables. In order to achieve future better qualitative and quantitative integrated models, it will be important to combine its non destructive and 3D characteristics results with those of 3D MICP models obtained for such complex materials. This enables to qualitatively and/or quantitatively assess the evolution and decay potential of different phases and voids (pores + fissures) textures in different environmental interaction conditions. So, in order to set-up more efficient forecasts of their engineering properties behaviour in a given environment this study is an essential initial complementary step to compare and integrate in near future studies all the advantages and disadvantages of the application of these classic and new methods, based respectively upon visual examination of the samples’ exteriors and on micro-tomographic image models of the samples’ interiors and surfaces, to these geologic materials.

Abstract: Materials applied in buildings, sculptures and other civil engineering, architectural or artistic works can be affected by coatings of neoformation products, namely salts. Carbonate rich (typically calcite) coatings are common in recent constructions. They generally have a visual impact (frequently present a vertical streaking pattern and it could be argued that the aesthetic effect of white crusts on dark-coloured stones is similar to that of black crusts on light-coloured stones). The thickness and extension that can be achieved in some cases can be considered an important defacement process that develops in relatively small periods of time. There are evidences that in some situations the process might be recurrent with time. Its chromatic evolution with time could also contribute to increasing heterogeneity with aesthetic consequences. An interesting question regarding these crusts is the possible contribution of certain building materials to its formation, materials that will be, in this way, potential pollution sources that might affect other building materials.

Abstract: Several types of stones (igneous, sedimentary and metamorphic) are found applied in pavements, stairs and walls of the underground stations of the Lisbon Metropolitan System, Portugal. A field study based solely on non-destructive and non invasive visual inspection of these stations is presented, aiming to identify different transformations of applied stones and discuss its relation with the stone characteristics. This field study has pointed to relevant issues regarding durability of stone materials namely when used in pavements and stairs. The most striking aspect is the frequently marked variable behaviour of stones from a given rock type under the same use conditions, with heterogeneities and discontinuities that seem to cause irregularity from the early stages and further increase with time, having more accentuated consequences (in terms of intensity of surface irregularity) in some types of limestones. The observations collected could be relevant for the discussion of characteristics relevant for the quality control of these materials (namely at the quarry level), including the selection of stones for future substitutions. There is, therefore, the need for a more complete study comprising detailed petrographic studies and laboratory tests both from the applied stones and from the supplying quarries.

Abstract: Lime mortars have been commonly used in historical buildings since ancient times. The progressive deterioration of these mortars by air pollution and other environmental causes hinders the assessment of the original composition. The weakening of the mortar structure is due to dissolution and formation of calcium sulphate layers because of the interaction with SOx gaseous pollutants. Also, pollution particles can be incorporated to the mortar because of dissolution by rainwater or runoff. Scanning Electron Microscopy (SEM) studies allow us to distinguish allochthonous and autochthonous micro- and nanoparticles in order to identify original intact plasters. By comparing these intact to deteriorated mortars from both air polluted and non-polluted areas it is possible to indentify and preserve the original mortar composition as a key step to project future façade cleaning and restorations.