Correlation between microstructural characteristics and weight loss of natural stones exposed to simulated acid rain.
The correlation between stone microstructural characteristics and material degradation (in terms of weight loss), in given environmental conditions, was investigated. Seven lithotypes, having very different microstructural characteristics, were used. Four acidic aqueous solutions were prepared to simulate acid rain (two adding H(2)SO(4) and two adding HNO(3) to deionized water, in order to reach, for each acid, pH values of 5.0 and 4.0), and deionized water at pH=5.6 was used to simulate clean rain. Stone samples were then immersed in such aqueous solutions, the surface alteration being periodically inspected and the weight loss periodically measured. After 14 days of immersion, a good correlation was found between weight loss and the product of carbonate content and specific surface area in the starting materials. This was explained considering that this product accounts for the weight loss owing to the sample's fraction actually composed of calcite (the most soluble fraction) and the effective surface area exposed to dissolving solution (which depends on stone porosity and pore size distribution). Such correlation between stone microstructure and degradation may be useful for comparing the durability of different lithotypes, in given environmental conditions, and quantitatively predicting the weight loss of a lithotype, compared to another one. Hence, the correlation found in this study may be used to specifically tailor to various stone types, with different microstructural characteristics, some results that have been calculated in literature for specific stone types and then proposed as possibly representative for a broad category of stones with similar characteristics.
Dipartimento di Ingegneria Civile, Ambientale e dei Materiali, Università di Bologna, via Terracini 28, 40131 Bologna, Italy. elisa.franzoni@unibo.it
Elisa
E
Franzoni
Enrico
E
Sassoni
D015258:Acid Rain / Q000009:adverse effects*; D000397:Air Pollution / Q000009:adverse effects*; D002119:Calcium Carbonate / Q000737:chemistry; D003252:Construction Materials / Q000032:analysis*; D004784:Environmental Monitoring / Q000379:methods*; D017942:Nitric Acid / Q000737:chemistry; D012822:Silicon Dioxide / Q000737:chemistry; D013464:Sulfuric Acids / Q000737:chemistry; D014961:X-Ray Diffraction
D015258:Acid Rain; D013464:Sulfuric Acids; D017942:Nitric Acid; D012822:Silicon Dioxide; D002119:Calcium Carbonate; C033158:sulfuric acid