Salt crystallization represents one of the major causes for the degradation of building and ornamental stone. As such, it has attracted the attention of researchers, who over the years have progressively unraveled most mechanisms involved in salt damage. Despite this mechanistic understanding, many questions subsist about how to quantitatively predict damage or its progression, and in particular how to relate performance on site to that in laboratory tests. In this context, a new RILEM TC 271-ASC has been started with the objective of defining laboratory tests that deliver more reliable predictions of field behavior. One deliverable of this TC is to provide a theoretical insight into this question based on recent progress on the understanding of salt damage. This paper presents a summary of this work, highlighting key aspects relating to crystallization pressure, chemo-mechanics and mass transport. Implications are discussed in relation to the most used accelerated salt crystallization tests in an attempt to better define which field exposure conditions that these tests best represent and may be used for, or define effective test procedures representing specific field conditions. A simple conceptual model for the development of salt damage is introduced. During an initial "induction" phase, transport of ions and accumulation of salt in the porous materials occurs without causing detectable damage until a critical point, termed "damage onset" is reached. Beyond this point, during the "propagation phase", the material degrades, typically losing strength and cohesiveness. The implications of these two phases are discussed in relation to the selection of appropriate salt weathering tests and conservation interventions.

This research deals with the characterization of black crusts collected from several historical buildings in the city of Venice. This city suffers from pollution from the industrial area of Marghera, as well as from the maritime traffic. Black crust can be considered as a passive sampler of pollutants, with particular reference to heavy metals. For this reason, in order to fully characterize those samples, several techniques were used, including scanning electron microscopy, thermogravimetric analysis, laser ablation inductively coupled plasma mass spectrometry, infrared spectroscopy and ion chromatography. This integrated approach allowed us to gain information about the mineralogical phases and the elements within the crusts giving the possibility to identify the pollution sources causing the stone decay within the buildings, as well as the variability in composition depending on the exposure of the analyzed

Limestone is one of the most frequent building stones used in monuments in Egypt from ancient Egyptian times and salt weathering is one of the main threats to these monuments. During this work, cylindrical limestone samples (2 cm diameter and approx. 4 cm length) from Mokattam group, one of the most frequent materials in historic Cairo, were subjected, in a purpose-made simulation chamber, to laboratory salt weathering tests with a 10% weight NaCl solution at different temperatures (20, 30, 40 °C). During each test, temperature was kept constant and salt solutions flowed continuously imbibing samples by capillary rise resembling the way they get into building stone in many real cases. Air temperature, relative humidity inside the simulation chamber and also samples weight were digitally monitored and recorded. Results show the influence of temperature and the ratio between imbibitions and evaporation on the dynamics of salt crystallization in the samples. RESUMEN: La influencia de la temperatura en un ensayo simulado de deterioro por sales mediante absorción capilar en la caliza de mokattam.Los monumentos egipcios se construyeron frecuentemente con caliza desde la antigüedad y uno de sus principales agentes de deterioro son las sales. Por ejemplo, en la zona histórica de El Cairo son frecuentes las calizas del grupo Mokattam. Cilindros (2 cm de diámetro y aproximadamente 4 cm de altura) de esta caliza se sometieron a ensayos de deterioro por sales en una cámara experimental específicamente diseñada. Se utilizó una solución salina (10% en peso de NaCl) a diferentes temperaturas (20 °C, 30 °C, 40 °C) que se mantuvieron constantes en cada ensayo. La solución fluía constantemente embebiendo las muestras por capilaridad, simulando lo que ocurre en casos reales. La temperatura del aire, humedad relativa en la cámara y peso de las muestras se monitorizaron con sensores digitales. Los resultados muestran la influencia de la temperatura y del balance entre imbibición y evaporación en la dinámica de la cristalización de sales en las muestras.

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This study presents five different lithotypes of limestone containing stylolites and commonly used as dimension stones in Egypt, Hungary and Israel. All the studied limestones are generally hard, dense, with high degree of cementation and have high strength and low porosity. Stylolites are small tooth-like irregular surfaces most often developed on the carbonate-rich stones. Insoluble particles, i.e., organic matter, oxides and clays are usually incorporated within the stylolitic planes. The presence of stylolites and their filling materials generally has a large effect on the physical and mechanical properties of the host stones. The main aim of this study is to evaluate the damage mechanism of different stylolitic limestones and to understand the role of the clay in the deterioration of these stones. Hundred cube samples (2 cm) of all the studied limestones were subjected to 500 thermal cycles (10-70 °C) and 20 cube samples (3 cm) of a grey Israeli limestone with high open porosity were subjected to multiple wet/dry cycles. The changes in mass, strength, and ultrasound V p velocity, were measured to follow any damage that happened due to cycling. The thermal cycling was proved to be an effective deterioration mechanism of both Egyptian and Hungarian lithotypes. The response of Israel grey lithotype to the wet/dry cycling was clearly shown by the splitting of the tested samples through the stylolite planes and the sharp decrease of their strength.