Thermodynamic calculations for the salt crystallisation damage in porous built heritage using PHREEQC
Thermodynamic calculations for the salt crystallisation damage in porous built heritage using PHREEQC
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DOI：
10.1007/s12665-015-4221-1
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发表时间：
2015-08-01
影响因子：
2.8
通讯作者：
Grossi, C. M.
中科院分区：
文献类型：
--
作者：
Benavente, D.;Brimblecombe, P.;Grossi, C. M.
这项工作考虑了最常见和最具侵蚀性的盐类的结晶机制，这些盐类由于环境条件的变化而在多孔建筑石材中产生应力。这些机制包括相对湿度下降和温度变化导致的盐结晶，以及在水合盐中，较低水合形式的溶解和随后水合盐的沉淀。我们提出了一种使用PHREEQC进行热力学计算的新方法，其中包括这些结晶机制。这种方法允许计算平衡相对湿度，以及溶解-沉淀转变的临界相对湿度和结晶压力的参数化。还评估了其他盐对盐结晶和化学风化效果的影响。我们回顾了单组分和多组分溶液中的硫酸钠、硫酸镁和氯化钠体系，并将它们与碳酸钠和碳酸钙体系进行了比较。还对结晶压力的变化、新矿物的形成以及其他盐的存在引起的化学溶解进行了评价。对于水合盐体系的结果表明，随着较低的水合盐溶解和更多的水合盐沉淀，高的结晶压力是可能的。温度降低也可能产生高应力，尽管这需要多孔材料长时间处于潮湿状态。其他盐的存在改变了盐转变的温度和相对湿度，如果以前有盐沉淀的话，这种转变会产生压力，而不是降低结晶压力。从所提出的方法中得出了几个实用的结论，并为自然保护者和建筑师提供了关于可溶性盐潜在风化活动的信息。此外，模型计算可能与对未来气候的预测相结合，以便更好地了解多孔石中盐类相变频率的可能变化。
This work considers the crystallisation mechanisms of the most common and aggressive salts that generate stress in porous building stones as a result of changing ambient conditions. These mechanisms include the salt crystallisation that result from decreasing relative humidity and changes in temperature and, in hydrated salts, the dissolution of the lower hydrated form and the subsequent precipitation of the hydrated salt. We propose a new methodology for thermodynamic calculations using PHREEQC that includes these crystallisation mechanisms. This approach permits the calculation of the equilibrium relative humidity and the parameterization of the critical relative humidity and crystallisation pressures for the dissolution-precipitation transitions. The influence of other salts on the effectives of salt crystallisation and chemical weathering is also assessed. We review the sodium and magnesium sulphate and sodium chloride systems, in both single and multicomponent solutions, and they are compared to the sodium carbonate and calcium carbonate systems. The variation of crystallisation pressure, the formation of new minerals and the chemical dissolution by the presence of other salts is also evaluated. Results for hydrated salt systems show that high crystallisation pressures are possible as lower hydrated salts dissolve and more hydrated salts precipitate. High stresses may be also produced by decreasing temperature, although it requires that porous materials are wet for long periods of time. The presence of other salts changes the temperature and relative humidity of salt transitions that generates stress rather than reducing the pressure of crystallisation, if any salt has previously precipitated. Several practical conclusions derive from proposed methodology and provide conservators and architects with information on the potential weathering activity of soluble salts. Furthermore, the model calculations might be coupled with projections of future climate to give as improved understanding of the likely changes in the frequency of phase transitions in salts within porous stone.