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NaCl-related weathering of stone: the importance of kinetics and salt mixtures in environmental risk assessment

Godts, S; Orr, SA; Desarnaud, J; Steiger, M; Wilhelm, K; De Clercq, H; Cnudde, V; (2021) NaCl-related weathering of stone: the importance of kinetics and salt mixtures in environmental risk assessment. Heritage Science , 9 (1) , Article 44. 10.1186/s40494-021-00514-3. Green open access

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Abstract

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.

Type: Article
Title: NaCl-related weathering of stone: the importance of kinetics and salt mixtures in environmental risk assessment
Open access status: An open access version is available from UCL Discovery
DOI: 10.1186/s40494-021-00514-3
Publisher version: https://doi.org/10.1186/s40494-021-00514-3
Language: English
Additional information: © 2021 BioMed Central Ltd. This article is licensed under a Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/).
Keywords: Sodium chloride, Salt mixture, Weathering Crystallization, Porous materials, Damage prediction, Built heritage
UCL classification: UCL
UCL > Provost and Vice Provost Offices > UCL BEAMS
UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of the Built Environment
UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of the Built Environment > Bartlett School Env, Energy and Resources
URI: https://discovery.ucl.ac.uk/id/eprint/10126050
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