Influência de polímeros superabsorventes na retracção de argamassas

Hoje em dia, o desenvolvimento dos superplastificantes permite a produção de betões com menor razão água/cimento. Ao usar razões água/cimento mais baixas, os materiais científicos apresentam maior tendência para fissurar devido à retracção autogénea. Este trabalho apresenta um estudo sobre a utilização de polímeros superabsorventes (SAP) no controlo da retracção. O uso de SAPs em materiais comentícios atenua a retracção autogénea pois estes produtos permitem o fornecimento interno de água. Estes produtos podem também afectar outras propriedades, afectando as características mecânicas e a trabalhabilidade. Para análise do efeito dos SAP foram estudadas argamassas com várias concentrações deste produto, tendo como referência argamassas semelhantes sem SAP, determinando-se as retracções autogénea e total, a resistência à compressão e o módulo de elasticidade. Além de SAP, foi também utilizado um agregado leve, um outro tipo de introdutor de água, para comparação com os polímeros em estudo. /ABSTRACT: This work presents a study on the use of superabsorbent polymers (SAP) in the control of shrinkage. The use of SAPs in cementitious materials reduces the autogenous shrinkage because these products enable the internal supply of water. These materials can also affect other properties such as mechanical properties and workability. To analyze the effect of SAP, mortars containing various concentrations of this product were studied, in comparison with reference mortars without SAP. The tests performed were autogenous and total shrinkage, compressive strength and modulus of elasticity. Besides SAP, it was also used a lightweight aggregate, another type of internal supply of water, for comparison with the polymers under study.

Novos desenvolvimentos para a deteção de leveduras e bactérias presentes em argamassas

The development of simple and rapid new approaches for analysing microbial communities colonising Cultural Heritage materials is pivotal for its safeguard. Fluorescence in situ hybridisation technique using ribosomal RNA directed probes (RNA-FISH) has demonstrated a great potential for this purpose. A protocol for analysing filamentous fungi in mortars has been already developed in previous studies. In this work this protocol has been adapted for detecting bacteria and yeasts. Good results have been obtained for the analysis of suspensions of isolates. In this way, the optimized protocol was applied in microsamples from synthetic mortar artificially inoculated with yeast and bacterial isolates. Promising results have been obtained for the ex situ analysis of yeast and bacteria thriving in mortar microsamples.

19th c. Coloured stuccos and plasters from Grilos' Church (Oporto, Portugal): Materials and techniques employed

The Oporto's St. Lourenço Church of the Jesuit College is locally known, since the St. Augustin Barefooted Eremites occupation (1779/80), as Grilos' Church. The Oporto's siege laid by D. Pedro and D. Miguel (1832/33) succeed in the college abandonment by Grilo's Friars. Throughout Augustin Friars presence period, the white plasters of the nave (end of 18th c.) were executed and it was constructed the Holly Sacrament Chapel (early 19th c.) with neoclassic coloured stuccos and plasters, influenced by Robert Adam, Luigi Chiari and Teixeira Barreto ornamental motifs. Pigments were added to the external layer to imitate the marble and to achieve the “base” colour of the panels. This study of the blue, rose and white stuccos and plasters of H.S. Chapel of Grilo's Church allows carrying out useful database on the original mortars composition by the use of different analytical techniques, important to select the most adequate solutions for restoration interventions. Optical microscopy, XRD, TG-DTA, SEM-EDS, XRF analysis results were considered to identify the composition of different layers and to provide mineralogical, microstructure and chemical characterization of the mortars components and to quantify the binder content in those mortars. These results were compared with collected information on compositions from other sources. This study allowed the identification of the decay causes of decorative stuccos and plaster, suggesting that water retention in the masonries and wooden laths structure of the dome of the chapel is the main factor.