Examining the impact of soluble salts on dolomite deterioration

Abstract

Salt weathering is known to be destructive to the historical buildings, which are constructed of porous stone materials. The study has the focus on salt weathering assessment on dolomite, a building stone that has been widely used in Anatolian monuments. The study is composed of laboratory analyses and non-destructive investigation techniques in order to better understand the causes and mechanism of decay. The artificially weathered dolomite samples by salt crystallization cycles were prepared at various states of deterioration, by exposing them to 5, 10, 15, 20, 25, 30, 35, 40 cycles of NaCl and Na2SO4 crystallization. Both fresh and artificially-weathered samples were examined in terms of their basic physical and physicomechanical properties, such as bulk density, effective porosity (total open porosity), ratio of fine pores, water absorption capacity, thermal dilatation coefficient, ultrasonic pulse velocity and modulus of elasticity. The thermal inertia characteristics of the samples were also determined by quantitative IR thermography (QIRT). The microstructural properties of the samples before and after the salt weathering cycles were investigated by means of stereomicroscope image analyses, XRD and SEM analyses. The state of deterioration or soundness of the samples were also defined by joint interpretation of ultrasonic and thermal inertia data. The results have shown that the change in durability characteristics in dolomite can be assessed accurately by monitoring their performance properties in terms of basic physical, physicomechanical and thermal properties. The data achieved is supported by microstructural properties of the fresh and artificially deteriorated samples. Deterioration of dolomite depending on salt crystallization cycles generally arises at the stone’s weak parts like impurities, veins and cracks within the stone. The XRD analyses of the impurities formed in the cracks as well as SEM analyses verified the presence of calcite veins, iron oxide and clay minerals in the cracks. Ultrasonic and thermal inertia values of fresh and deteriorated samples established the reference/control data that can be used for in-situ examination

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