Volume 2, Issue 5

The "Reials Col.legis de Sant Jaume i Sant Maties" (Tortosa, Catalonia) is one of the masteφieces of the Renaissance style and was built in the 16th century with dolostones and calcarenites relatively well preserved and which are coated by an orange to black continuous patina. By studying samples obtained from different rock substrate and orientations the building stones and the layers forming the patina have been characterized by using several techniques (XRD, SEM/EDS, optical microscopy). The data obtained allowed us to establish a common sequence for this patina which consists of two layers: one micritic and one gypsum-rich layer in which, occasionally, there is bioactivity present living in and on the patina and the underlying rock. An hypothesis of the development of the layers of the patina is proposed on the basis of their mineralogical and petrographical features.

In order to achieve a high quality in the field of conservation of natural stone surfaces it is most important to realize a high penetration depth of the conserving fluids on the besis of extensive laboratory research on the application of conserving fluids the relation between important factors such as quantity absorbed, duration of application, penetration depth, and selected practical relevant conditions has been established. With these results it was possible to develop a computer program which is able to predict penetration depth for a random choise of practical conditions of application. By the option of the comparision of stored real and predicted values of penetration depth destructive tests on the object are quite superfluous.

In order to get more information about the moisture transport through the interface of two capillary active materials, the capillary liquid transport for two types of layers of natural sandstone in ideal hygric contact was observed. The results show that the water absorption behaviour of the composite samples is strongly dependent on the sequence of its composition. This can be explained by the different water retention curves of the materials. Calculation shows in all cases good agreement between the measured and calculated values for the water absorption and for the moisture profiles. Examinations of the moisture transport between rendering and brick show that the moisture transport is reduced. Comparisons between measurement and calculation indicate that the introduction of a thin resistance layer between rendering (or mortar) and stone is necessary. With this layer the liquid transport through the interface can be simulated correctly.

Some surface treatments such as hydrophobing and realcalisation rely on capillary suction as the driving force. In this context, the critical admissible moisture content must be known. The porous structure of a series of different building materials has been characterized. The porosity and pore size distribution has been determined on 3 different types of autoclaved aerated concrete (AAC), on samples made of hardened cement paste with 3 different water-cement ratios, on natural sandstone and on burned brick. The sorption isotherm and at each equilibrium moisture content the remaining capillary suction has been measured on identical specimens. It can be shown that capillary suction of materials with a coarse porous structure such as sandstone or burnt brick depends slightly only on the moisture content Capillary suction of hardened cement paste with a fine porous system, in contrast, is drastically diminished with increasing moisture content and reaches negligible values near 100 % RH. Results presented in this contribution allow us to fix a critical admissible moisture content for different building materials. At the same time, building materials can be identified for which the moisture content has to be carefully controlled before surface treatment is to be applied It must be mentioned, however, that in critical cases the moisture profile must be determined up to the intended depth of the treatment instead of the surface moisture content.

A chemical risk assessment for the use of concrete admixtures was performed for the case of naphthalene sulfonate condensate (NS) which is a widely used supeφlastizicer. As a result of its use as a concrete admixture, NS and its degradation products in condensed naphthalene sulfonates can be emitted into the environment. In relation to other products such as detergents, the emissions of NS are classified as very low. The most important emissions of NS originate during its production and during the washing of concrete mixers when the wastewater is allowed to enter the sewers. Future emissions of naphthalene sulfonates are predicted for the case of storage/disposal of concrete waste, or the use of NS-containing concrete waste in road construction. The predicted concentrations of NS and naphthalene sulfonates in Switzerland (either on the regional or local scale) are expected to be below the predicted no-effect concentrations (PNEC values or "safe" concentrations).