Stone decay acidity

Sulfur-oxidising bacteria convert inorganic sulfur compounds to sulfuric acid that can cause severe damage to mineral material. Thiobacillus species have been implicated with concrete corrosion in the Melbourne and Hamburg sewer systems due to sulfuric acid formation. However, a role in stone decay is less certain since sulfuric acid and calcium sulfate in stone can originate from the direct action of atmospheric pollution and acid rain. 

BACKGROUND AND LOCAL CONTRIBUTIONS TO ACIDIC DEPOSITION AND THEIR RELATIVE IMPACT ON BUILDING STONE DECAY ... 

Uses. For arresting decay and disintegration of stone for manufacture of weatherproof and acid-proof mortars and cement... 

Damage to stone occurs also for the corrosion of metallic bars used for anchoring blocks of stone with each other and with the structural framework. Oxidation of iron produces the mineral limonite (FeO-OH) which has greater volume than the parent iron. This volume increment generates stresses sufficient to disintegrate the stone. The presence of SO2 and other acid components decidedly accelerates the decay phenomenon. 

OTHER COMMENTS used in the manufacture of weatherproof and acid-proof mortars and cements, refractory bricks, heat-resistant and chemical-resistant paints, lacquers, and protective coatings for industrial buildings and castings also used in hardening stone useful in arresting decay and disintegration. 

Dissolution and precipitation occur both within us and around us. Tooth enamel dissolves in acidic solutions, for example, causing tooth decay, and the precipitation of certain salts in our kidneys produces kidney stones. The waters of Earth contain salts dissolved as water passes over and through the ground. Precipitation of CaC03 from groundwater is responsible for the formation of stalactites and stalagmites within limestone caves. 

In addition to the chemical composition, several other properties of the stone determine its actual rate of decay. These properties relate to the porosity and pore structure which govern the transport of water and chemically active gases into the stone. Also, the aspect of exposure influences the decay rate. Therefore, determination of the carbonate-acid reaction in reaction-kinetic studies yields only partial information on the actual weathering rates. 

Yet, controlled studies of weathering promise the generation of data usable,not only for the determination of weathering rates> but also for the reconstruction of the history of the acidity of precipitation. As shown earlier in the introduction, the absence of nitrates and sulfates in the weathered rock indicates that GO is the cause of decay this reveals that the pH of the precipitation has been nearly 5.6. Since the presence of NO2 and SO2 considerably reduce the pH of the precipitation, the occurrence, quantities, and the depth to which the weathered products have penetrated in dated stones (e.g. monuments in graveyards) may form bases for determinations ofactual acidity when the pH of the precipitation is below 5.6. It will, however, be necessary to determine the reaction rates in laboratory conditions at known acidity levels and correlate them with reaction rates in ambient conditions,both for stones which are directly exposed to precipitation and those which weather due to acid aerosols while protected under the dome. 

Keeping teeth clean requires toothpaste, a mixture of detergents and abrasives, which are hard substances that help remove unwanted materials on the tooth surface. The structure of tooth enamel is essentially that of a stone composed of calcium carbonate (CaCOj) and calcium hydroxy phosphate [apatite—GajQ(PO )g(OH)2], Despite being the hardest substance in the human body, tooth enamel is readily attacked by acids. Because the decay of some food particles produces acids, it is important to keep teeth clean. 

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