Abstract
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.
Highlights
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
The mechanism of salt precipitation and consequent weathering forms are controlled by the petrographical characteristics of the limestone, as well as the dominant environmental conditions, e.g. air temperature and relative humidity [7,8,9], the type of salt and its concentration are affected factors
A commonly used method for understanding the mechanics of natural deterioration is the simulation, under controlled laboratory conditions, of salt weathering dynamics, by subjecting samples to various environmental regimes and carrying out imbibitions-drying tests [2, 12, 13] and the environmental cabinets which allow the accurate control of temperature and humidity cycles and by testing the resulted samples using different t echniques, this may give us more details about salt crystallization and its relation to deterioration of the natural stones
Summary
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. A commonly used method for understanding the mechanics of natural deterioration is the simulation, under controlled laboratory conditions, of salt weathering dynamics, by subjecting samples to various environmental regimes and carrying out imbibitions-drying tests [2, 12, 13] and the environmental cabinets which allow the accurate control of temperature and humidity cycles and by testing the resulted samples using different t echniques, this may give us more details about salt crystallization and its relation to deterioration of the natural stones In this specific case, solutions were imbibed by capillarity, without applying any external pressure, as this is one of the main mechanisms for solution transport in the built environment. The location of crystallisation is mainly controlled by the dynamic balance between three rates which are: the rate of moisture loss through evaporation, the rate of moisture ingress by capillary flow and the rate of ion back diffusion due to the concentration gradient established within the salt solution [16]
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