Simultaneous wetting/drying, freeze/thaw and salt crystallization experiments of three types of Oya tuff
Chiaki T. Oguchi, Hayato Yuasa, 2010. "Simultaneous wetting/drying, freeze/thaw and salt crystallization experiments of three types of Oya tuff", Natural Stone Resources for Historical Monuments, R Přikryl, Á Török
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An abandoned subsurface Oya tuff quarry in Japan had abundant salt efflorescence in winter. Besides salt weathering, freeze-thaw weathering and slaking were likely to occur because of winter temperatures below 0 °C and the presence of swelling clays in the rock. Field surveys were performed to collect salts. Thenardite and gypsum were detected by X-ray diffraction (XRD) as the main salts, along with zeolites as secondary minerals. Oya tuff is categorized into three types for practical usage. To investigate petrophysical differences among the three types of Oya tuff, mercury intrusion porosimetry and tensile strength tests were performed. To determine the influence of petrophysical properties on salt weathering, freeze-thaw weathering and slaking (wet-dry weathering), all three types of Oya tuff were used for experiments. Prismatic specimens, the bases of which were sunk into distilled water, were used for the freeze-thaw and slaking experiments and Na2SO4 saturated solution was used for the salt-weathering experiment. The results show that the specimens subjected to salt weathering were the most severely damaged. The coarse-type Oya tuff sustained the most severe damage, whereas the fine type received the least. There was a large amount of debris in the coarse type, but less in the fine type. The weathering susceptibility index WSI was also calculated from the results of the pore size analyses and tensile strength. The index decreases with increasing weathering cycles representing resistant rocks. The phenomena of weathering of Oya tuff were explained by three weathering experiments on three kinds of tuff. The WSI may be useful as a practical indicator of rock weathering.
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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.