Is sodium sulphate invariably effective in destroying any type of rock?
Sodium sulphate has been implicated as one of the most destructive weathering agents in many field observations and numerous laboratory studies. We hypothesize however, that sodium sulphate would not be invariably effective on any type of rock. To verify the supposition, a laboratory cyclic impregnation–drying experiment was undertaken. In addition to sodium sulphate, two other destructive hydratable salts, magnesium sulphate and sodium carbonate, were used to attack eight types of rock. In all three salt attacks, rock breakdown occurred only during immersion due to the exertion of higher crystallization pressure driven by the greater supersaturation reached after dissolution of the crystals precipitated during drying. Sodium sulphate was the most destructive salt in six out of the eight rocks tested, and even granite was substantially disintegrated. However, although probability is small, sodium sulphate indeed manifested its impotency against a relatively weak rock (Tago Sandstone). Contrary to its modest damaging power on other rocks, magnesium sulphate destroyed Tago Sandstone which could resist sodium sulphate attack. Sodium carbonate was the least destructive of the three hydratable salts. The general damage mechanism of hydratable salts, the process of damage of Tago Sandstone by magnesium sulphate and the possible reasons behind the impotency of sodium sulphate against Tago Sandstone are all investigated.
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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.