Historical mortars from sixteenth to seventeenth century military forts located at the mouth of the Tagus River in Lisbon have been characterized by polarized light microscopy (PLM), thermal analysis (TG/DTA), X-ray diffractometry (XRD) and scanning electron microscopy ? energy dispersive spectroscopy (SEM ? EDS). The results indicate that the mortars used were all hydraulic lime-based. The presence of well-rounded lime lumps indicates a limited use of water during the lime hydration process. The detection of hydrated calcium chloroaluminate and carboaluminate compounds mostly at binder-aggregate interfaces provides evidence for the onset of pozzolanic reactions during mortar production as further confirmed by the presence of ceramic fragments in the aggregate fractions intentionally added by the fort builders to increase the hydraulic properties of the mortars. The higher mechanical strength and greater resistance to degradation processes imparted by these pozzolanic compounds could explain why, despite the extreme proximity of the investigated sites to the sea, salt weathering processes do not appear to have significantly affected the studied mortars.

Alentejo's religious buildings reflect undoubtedly the history and character of this southern Portugal region. Conservation of these buildings requires a deep knowledge of their masonry and renders' lime mortars to evaluate correctly their state of conservation, to avoid progression of pathologic situations, and to plan efficient interventions, with repair and substitution materials with similar characteristics. This article presents a synthesis of the main results obtained in the mortar characterization of religious buildings from Alentejo, which include E´vora and Elvas Cathedrals, Me´rtola Mosque, and the Church of Amieira do Tejo. For each monument, several samples were collected from different sites and a set of tests was carried out, including chemical, mineralogical, and micro-structural tests, as well as physical and mechanical tests. The tested mortars correspond to different phases of construction and interventions on the buildings, comprising mainly origin periods from the twelfth to the eighteenth centuries; hence exhibited significant differences in composition and in application techniques. The obtained results of composition have given important information about the provenance of the materials used, including binder and sand types, and also about decay products and their correlation with the mortar's conservation state, which gave important clues on the repair strategy to adopt.

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The study of old mortars composition, using physical-chemical, mineralogical and microstructural characterization has an important role in the preservation of architectural heritage, allowing a deep knowledge about the materials used, construction techniques, possible repairs and degradation processes.

).Mortars are common and essential elements of masonry historical buildings [1] and are composed by a binder, aggregates and eventually, some additives. The binder provides consistency to this composite material, and until the emergence of Portland cement in the 19th century, lime was the main binder used. The aggregates are normally sand or rock fragments with variable sizes. The whole set is morphologically very similar to a sedimentary clastic rock with carbonate cementing. Following an old tradition of microscope use in this kind of rocks, it is not surprising the application of optical microscopy to mortars [2] as also happened with concrete. The focus of the study was three 16th/17th century buildings in the Tagus estuary access, the forts of S. Bruno, Bugio and S. Julião da Barra ( fig. 1). The S. Bruno Fort is located at the confluence of Barcarena river with Tagus River, near Caxias (Oeiras County). The Fort was ordered by King D. Joao IV in 1647. It is a small fortress with a typical star typology. The S. Julião da Barra Fort is located in Oeiras on the right side of the mouth of Tagus River and facing the sea. Its construction started in the 16th Century by order of King Joao III. During the Filipine Dinasty it was used as state prison and under D. Joao IV was amplified to the present size in order to augment its defensive power. The Bugio Fort is located in a small sand islet (Cabeça Seca Island) at the middle of entrance of Tagus river mouth and is an example of military renascence fortress with circular typology. Its construction started in 1590 by order of King Filipe I and was concluded in 1657. During the 18th Century was used as a prison and a lighthouse was installed to aid navigation. Each sample was collected under supervision of the Portuguese Institute of Architectural Heritage in sites defined by the conservation technicians. The size of each sample was the minimum that could guarantee the success of the analysis and the confirmation for future studies. The mortars were thoroughly observed in laboratory using an Olympus stereo-zoom microscope and carefully disaggregated to avoid breaking the existing aggregates. Thin sections and polished surfaces of the mortars were prepared by vacuum impregnation with an epoxy resin. Optical microscopy observations were performed in an Olympus petrographic microscope while scanning electron microscopy (SEM) observations were performed in a JEOL JSM-6400 microscope in polished surfaces and thin sections after carbon sputtering and complemented with energy dispersive X-ray Spectrometry (EDS) by an Oxford Inca X-Sight EDS Si(Li) detector. The lime nodules are easily identifiable. Its presence is compatible with a minimum use of water during the slacking process. The carbonate binder is optically very similar to a very fine carbonate rock. The aggregates are homogeneously distributed in the binder, configuring a carbonate cement sandstone texture like ( fig. 4 IIIa, IVa, IVb). Occasionally the binder is cut by fractures filled with secondary carbonates. Thi...