Salt crystallization is accepted to represent 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, 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 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 transport. Implications are more specifically discussed in relation to existing accelerated tests in an attempt to better define the type of field exposure that they may best represent. 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 increasingly. The implications of these two phases are discussed in relation to the selection of appropriate salt weathering tests and conservation interventions.

© 2015 CSIC. 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.Peer Reviewe

This study was concerned at a limestone quarry located southeast of Helwan city, Egypt, in order to investigate the effect of hydric swelling on the geomechanical aspects of limestone rocks. The Volume of Egyptian limestones change due to the presence of clay minerals (swelling/shrinking). These changes in volume induced by changing environmental conditions, high temperature and fluctuation of the relative humidity, causes accelerated physical deterioration of limestone. The rainfall is infrequent, and it is usual for the area to have no precipitation for successive months. There is a remarkable variability in daily temperature between summer and winter. The hot and arid environment that controls the geological development can affect the engineering behavior of local sedimentary stones. Petrographic investigation by scanning electron microscopy (SEM) of Helwan limestone (biomicritic limestone) revealed the existence of smectite and glauconite within the stone. The clay fraction extracted from Helwan limestone is equal to 10 % by weight. The analysis of oriented clay mounts by X-ray diffraction (XRD) confirmed the dominance of smectite in the clay fraction. To study the effect of the clay content on the mechanical behavior of Helwan limestone, hydric swelling tests were performed at first by using a displacement sensor, afterwards, the effect of a sequence of wetting/ drying cycles on the stone strength was determined by the unconfined compressive strength (UCS) test. Results confirmed that the strength loss of the limestone is directly proportional to the degree of swelling of the clay, as expected. This highlights the importance of this parameter for selecting stones in new construction or for replacing purposes, and for establishing preventive measurements to minimize this damage in historic buildings.  

The tomb of Cyrus the Great, founder of the Persian Empire, is considered one of the most important monuments of Iran. Its advanced state of deterioration motivated the need to carry out a study focused on analyzing the possible damage caused by the presence of soluble salts, and to assess the suitability of an electrokinetic treatment for their extraction. Preliminary diagnostics carried out on stone samples taken from the tomb confirmed that it is affected by the action of soluble salts, and especially by the presence of nitrates and sulfates. The effectiveness and possible harmful effects caused by electrokinetic treatment were evaluated, under laboratory conditions, using the same limestone that makes up the tomb. The obtained results show that this treatment, in a short period of time, reduces the ionic content, reaching high percentages of anion extraction, without causing any damage, which indicates that it is suitable for this type of stone.