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Damage to porous materials in heritage buildings caused by salt mixture crystallization is driven by the surrounding environmental conditions. To understand the crystallization behavior of a mixed salt solution as a function of changing climatic conditions (i.e., relative humidity and temperature), excluding factors such as the internal pore structure, the thermodynamic model ECOS/RUNSALT is the only freeware available that requires simple input and includes the most relevant ions for heritage buildings and solids. We suggest the use of specific terminology and describe how to use the model and how to interpret the output, with emphasis on key limitations for which solutions are provided. When used correctly, the model output can be trusted, specifically when it is used to inform preventive conservation (e.g., environmental conditions in which salt crystallization cycles should not occur). However, salt mixture kinetics and the internal pore structure remain crucial parameters that are not considered in the model. These aspects need further attention to develop a better understanding and correctly model salt damage in relation to climatic changes. [ABSTRACT FROM AUTHOR]

Salt weathering is one of the most important causes of deterioration in the built environment. Two crucial aspects need further investigation to understand the processes and find suitable measures: the impact of different climatic environments and the properties of salt mixture crystallization. We demonstrate the importance of kinetics in quantifying crystallization and dissolution cycles by combining droplet and capillary laboratory experiments with climate data analysis. The results proved that dissolution times for pure NaCl are typically slower than crystallization, while thermodynamic modelling showed a lower RHeq of NaCl (65.5%) in a salt mixture (commonly found in the built heritage) compared to its RHeq as a single salt (75.5%). Following the results, a minimum time of 30 min is considered for dissolution and the two main RHeq thresholds could be applied to climate data analysis. The predicted number of dissolution/crystallization cycles was significantly dependent on the measurement frequency (or equivalent averaging period) of the climatic data. An analysis of corresponding rural and urban climate demonstrated the impact of spatial phenomena (such as the urban heat island) on the predicted frequency cycles. The findings are fundamental to improve appropriate timescale windows that can be applied to climate data and to illustrate a methodology to quantify salt crystallization cycles in realistic environments as a risk assessment procedure. The results are the basis for future work to improve the accuracy of salt risk assessment by including the kinetics of salt mixtures. [ABSTRACT FROM AUTHOR]

Salt crystallization is recognized as a major cause of damage to porous building materials, threatening the sustainable preservation of our valuable built heritage. Unfortunately, the crystallization behavior of the detected salt mixtures is complex and not fully understood. While the deliquescence points of single salts are well documented, this is not the case for salts in a mixture where one is confronted with the presence of different cations and anions. In this paper the salt content of the murals and the limestone tracery of the main entrance porch from the sixteenth century church of St. James in Liège, Belgium is investigated and related to the climatic conditions of its environment. Concerning the salt load, the research consists of hygroscopic moisture content measurements, quantitative ion analyses, and the prediction of phase equilibria using the thermodynamic model ECOS/RUNSALT. This model can predict the salt crystallization sequences of a particular ion mixture. The output is mathematically evaluated with collected temperature and relative humidity data, which enables the calculation of the number of salt crystallization–deliquescence cycles. The results show that even small amounts of salts can cause damage over a long period of time when the environment causes frequent cycles of crystallization–deliquescence over time. It is shown how a mixture of small amounts of (double) salts, including hygroscopic ones, can have a significant effect on the decay of historic building materials in the case of daily changing climatic conditions and periods of extreme drought. As a result, the crystallization of double salts and hygroscopic salts such as calcium nitrate cannot be ignored. The scientific method and the results are described. [ABSTRACT FROM PUBLISHER]

The rehabilitation of historic buildings is a practice that aims to turn a historic property into a state of contemporary comfort for private or commercial use, while preserving its historic, architectural and cultural value, respecting items of authenticity, compatibility and sustainability. What once was a modest use of locally fired brick and mortar has become the subject of ambitious rehabilitation campaigns conforming to the rules of comfort and hygiene of the twenty-first century. A pre-investigation concerning the diagnosis of damage phenomena and the risk assessment of interventions is a crucial aspect for the success of a restoration campaign. The question of 'How to optimally preserve a monument within its current conditions' is replaced by 'How can a monument optimally perform in the conditions suited to the assigned rehabilitation project'. Today historic farms and their surroundings, after being abandoned for several decades, are the subject of different types of private or commercial rehabilitation projects. An example of such a project is the farm 'Hof De Pleyne' in Loppem (West-Flanders, Belgium). The project intended to integrate a restaurant kitchen into the former animal barn. The limits of salt content with respect to the desired rehabilitation facilities while respecting safety regulations are presented. [ABSTRACT FROM AUTHOR]

Different grouting and repair mortars were developed and evaluated for the conservation and restoration of fragmented bricks in the walls and floors of the remaining cellars underneath the Aula Magna, the palace's main banqueting hall, and to fill the lacunae and perform edge repairs of red and blue-grey ceramic floor tiles in the remaining cellars underneath the chapel of the former Palace of Coudenberg in Brussels, Belgium. To prevent the deposition of lime bloom at the surface of the masonry and to achieve an acceptable colour match of the grout in harmony with the bricks of the Aula Magna, the effect of brick powder added to natural hydraulic lime was studied. The pozzolanic properties and colour match of several historic and modern powdered bricks were investigated. Surprisingly, ancient bricks do not seem to possess higher pozzolanic properties than the more modern ones, although it is supposed that they were fired at lower temperatures. Additional evidence for the pozzolanic reaction of the different brick powder materials was obtained from a simple visual observation of stored samples. After eight weeks all of the samples containing brick powders, fired at low and high temperatures, added to putty lime had hardened under water and were transformed into a remarkably tough material. These results are important, as modern bricks are readily available in large quantities and different colours, which are hence in favour of being used instead of historical material from the site. For the repair of the ceramic floor tiles different mortars were investigated with mixtures containing talcum, stone or brick powder, pigments, and chalk added to an epoxy binder. The mortars were tested in the laboratory and in situ for their workability and resemblance with the historic floor tiles. The finished mortars showed excellent aesthetic properties with the tiles in situ and good properties to prevent further loss due to human interaction. [ABSTRACT FROM AUTHOR]

Archaeological sites are essentially submitted to decay phenomena inherent on their history as well as the environment to which they are exposed after excavation. The history of such archaeological sites is particularly related to their long-term underground conservation conditions during which they were subject to salt migration into the architectural remains. It is well known that soluble salts present in building materials can cause damage, mainly by producing stresses in the substrate. A lot of research has been done in the past concerning the behaviour of salts in built constructions. However, most studies include single salts, of which the deliquescence points are well documented, while in situ one mostly finds complex salt mixtures, which makes the conservation strategy much more intricate. The environmental conditions to minimize damage of salt-laden porous building materials can be modelled using a computer program ECOS capable of predicting the crystallization behaviour of salt mixtures. To use the model data of quantitative salt analyses are required as input. The program is then able to predict from a thermodynamic point of view which minerals will exist in the solid state under specified climatic conditions. This paper deals with the results of a systematic investigation of the salt contamination of the building materials of the Coudenberg site and a prediction of the behaviour of the salt mixture related to the actual climate, as part of the environmental assessment. [ABSTRACT FROM AUTHOR]

The characterization of historic mortars by means of a concise methodology of material analyses can provide crucial information with regard to the origin of the raw materials and the ancient mortar technology. For the analysis of the historic mortars of the Coudenberg archaeological site, the methodology consists of optical and scanning electron microscopy, simultaneous thermal analysis, and an acidic treatment. These analyses were carried out on a total of seventeen samples lifted from various areas in the site, in function of the building chronology resulting from a historic built investigation. The type of binder and aggregate as well as their volumetric ratio were determined. Both binder and aggregate present distinctive features, which made it possible to identify the probable geological provenance of the raw materials. The observations are verified with available historical records regarding the construction of the main banqueting hall — the Aula Magna — and the use of raw materials such as limestone and sand for the production of lime and construction purposes. [ABSTRACT FROM AUTHOR]

The excavation and valorization of subterranean archaeological remains, and eventually opening a site to the public, required a proper management and conservation strategy. This strategy was based on the evaluation of the delicate balance between the requirements for public health and safety, and the protection of the archaeological remains from future degradation. Controlling the climate can be essential for a preventive conservation strategy, which can be defined as an indirect action to increase the life expectancy of the archaeological remains, and by doing so keeping them in a preferred state of conservation to mitigate damage and/or deterioration. Potential risks and possible interventions are outlined to avoid climatic conditions which are in conflict with the requirements for the visitors' comfort while preventing damage phenomena to the materials. [ABSTRACT FROM AUTHOR]

• A procedure for accumulating salts at the surface of porous materials is proposed. • Most of the salt is concentrated in the first millimetres of the subsurface. • The measurement of the salt distribution is crucial in salt crystallisation tests. The RILEM TC ASC-271 is developing a new laboratory test to assess the durability of porous building materials to salt crystallisation. The test encompasses two phases: salt accumulation and damage propagation. This paper focuses on designing a procedure for the accumulation phase; this is considered successful when salts crystallise at the material's evaporative surface (common situation observed on site) without the occurrence of damage. Two procedures were developed and tested on two limestones with different porosity: (1) capillary absorption of a salt solution followed by drying, and (2) continuous capillary absorption. Sodium chloride or sodium sulphate solutions were used. Several methods for assessing the salt distribution were employed: ultrasonic pulse velocity, drilling/scratching resistance, hygroscopic moisture content, ion chromatography, scanning electron microscopy, and micro X-ray fluorescence. The results enabled the selection of the most effective protocol for the salt accumulation phase. [ABSTRACT FROM AUTHOR]

Archaeological sites are essentially submitted to decay phenomena inherent on their history as well as the environment to which they are exposed after excavation. The history of such archaeological sites is particularly related to their long-term underground conservation conditions during which they were subject to salt migration into the architectural remains. This paper describes the results of drill resistance measurements using a drill resistance measurement (DRMS) device to evaluate the mechanical damage resulting from salt crystallization pressures. Further tetraethoxysilane (TEOS) was applied on powdered bricks of often moist archaeological remains. It was noticed that TEOS serves as potential nutrient for present moulds. The mechanical consolidation effect was evaluated by comparing the hardness profiles after treatment with the reference ones. Bricks used for the construction of the Aula Magna, situated underneath the Royal Square, are characterized by severe patterns of fissures for which the damage diagnosis was built up. [ABSTRACT FROM AUTHOR]