Ground water attack

Pourbaix Diagrams. Plots of equilibrium pH vs electrochemical potential E describe the effects of aqueous corrosion on borosilicate and silicate glasses. They are applicable to weathering studies and to ground water attack on nuclear waste glasses. The diagrams display any immune zone between active corrosion... 

The resistance to attack by aggressive liquids which would commonly be chlorides from marine environments or de-icing salts and sulfates from ground water. 

Other kinetically allowed mechanistic models, i.e. hydroxide ion attack on the monoanion, can be rejected on the grounds that the required rate coefficients far exceed that found for alkaline hydrolysis of phosphate triesters. At pH > 9 two new reactions appear, one yielding a 1,6-a.nhydro sugar by nucleophilic attack through a five-membered transition state of the 1-alkoxide ion upon C-6 with expulsion of phosphate trianion. The second is apparently general-base catalysis by 1-alkoxide of water attack on C-6 or phosphorus through greater than six-membered cyclic transition states. 

Brick masonry, even though susceptible to acid rain attack, owes its deterioration mainly to the crystallization of the soluble salts produced in that reaction or from other, more important, sources of soluble salts the inherent vice in bricks and ground water salts. The capability of a given masonry structure to resist deterioration will be directly related to its resistance to water penetration, which is the main single agent responsible for the decay process by salt crystallization. 

The input to the combined system occurs on the potentiometric highs in the form of rainfall containing minor amounts of total dissolved solids. Initial changes in water chemistry occur within the soil zone where the water is charged with large amounts of CO2 gas. This C02-rich water percolates into the ground-water system where the C02 attacks the carbonate minerals. This is an irreversible chemical process whereby the C02 in the water reacts with the minerals and brings them into solution. 

Where concrete is exposed to chemical attack from natural soils and ground water as given in Table 3.3, the exposure shall be classified as given below. The classification of seawater depends on the geographical location, therefore the classification valid in the place of use of the concrete applies. ... 

The hydrated components (C-S-H, portlandite, sulfoaluminates) in the cement matrix of concrete are in equilibrium with the pore liquid that is characterized by a high pH, due to the presence of OH (balanced by Na and K ). When concrete comes into contact with acid solutions, these compounds may dissolve at a rate that depends on the permeability of the concrete, the concentration and the type of acid. In soil with acidic ground water, the rate of refreshing is important Acids that can attack concrete are sulfuric acid, hydrochloric acid, nitric acid, organic acids such as acetic acid and humic adds and solutions of CO2. The rate of attack on the cement matrix depends on the solubility of the salts that are formed... 

Table 3.3 Limiting values for exposure classes for chemical attack from natural soil and ground water, according to EN 206 [4]...

The sulphate attack has been known from a long time, and already in 1858 Vicat [247] studied the chemical causes of hydraulie eompounds corrosion in sea water [247]. Bied [248] invented the teehnology and developed the production of calcium aluminate cement, as a remedy for rapid destmetion of concrete in France, caused by the sulphate ground water attaek, from the dissolution of gypsum and anhydrite. 

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