Influence of temperature and salt concentration on the salt weathering of a sedimentary stone with sodium sulphate
Matthieu Angeli, Ronan Hébert, Beatriz Menéndez, Christian David, Jean-Philippe Bigas, 2010. "Influence of temperature and salt concentration on the salt weathering of a sedimentary stone with sodium sulphate", Natural Stone Resources for Historical Monuments, R Přikryl, Á Török
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The aim of this study is to evaluate how the ambient temperature and salt concentration affect the salt decay of a sedimentary stone. Samples of a detritic limestone which have experienced cycles of accelerated ageing at 5, 25 (room temperature, RT) and 50 °C with brines which had different sodium sulphate concentration were analysed. The weight of the samples and of the pieces fallen off during the cycles was monitored. The results show that the damage is more important at 5 °C than at RT. The samples at 50 °C were intact at the end of the experiment. Second, the size of the pieces fallen from the samples is significantly smaller for low temperatures: at 5 °C, the decay produces a fine powder; at RT, the pieces fallen off are of millimetre to centimetre scale. The weathering patterns are therefore different at these two temperatures: fine crumbling at 5 °C; coarse crumbling and contour scaling at RT. The salt uptake seems quite similar for a given concentration whatever the temperature. The decay also seems to be of a different kind for each concentration at RT: crumbling at low concentration, contour scaling at high concentration. Crystallization seems to take place deeper inside the porous network of the stone when the concentration of salts in the brine is higher, that is to say when the brine viscosity is higher.
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Natural stone is considered to be a versatile, durable and aesthetically pleasing building material. From the beginning of civilization, important structures and monuments have been built from, or based on, natural stone. Until the end of the nineteenth century, the use of local stone resources was mostly in balance with the local environment. Strict environmental legislation has resulted in the closing of many long-standing quarries in industrialized countries, which has led to a shortage of traditional stone varieties. This has caused problems for restoration practice. Cheap, imported stone from less industrialized countries has become more widely available in recent years.
Some of the issues related to built stone conservation and restoration covered by this volume are: the establishment of inventories of possible replacement stones; understanding the decay mechanism and use of preventive conservation methods for slowing down decay processes; evaluation of the properties of natural stone; and assessing the risks of using replacement stones of different qualities.