Environmental Engineering Reference
In-Depth Information
Mineral water is groundwater with a minimum of 1 g of dissolved salt per liter,
but the salt can not be CaCO
3
or MgCO
3
.
●
Effects
Corrosive and incrusting water
causes the deterioration of underground metal piping and
geotechnical instrumentation and the clogging of drains and pyrometers. Indicators of a
high potential for corrosion and incrusting are given in Table 8.3.
Aggressive salts
attack concrete, causing its deterioration below the water table. The
chemical agents normally aggressive to concrete are CO
2
, chlorides, magnesium, sulfates,
and ammonia, with calcium and magnesium sulfates being encountered less frequently.
The value of the pH must also be considered since it also affects corrosion. Corrosion and
destruction of concrete are affected by the type of cement and aggregate used, the
water-cement ratio, the age of the concrete, and the geologic conditions to which it is
exposed. The action of sulfates in contact with concrete is summarized in
Table 8.4,
where
it is shown that concentrations higher than 1000 mg/L of sulfate in water can cause con-
siderable deterioration. The degrees of aggressiveness of pH and aggressive CO
2
are given
in
Table 8.5.
A case where moisture migrating upward through pyritic shales produced
sulfuric acid, which leached cement from a concrete floor, turning it into a “mush,” is
described in
Section 10.6.3.
Improvement of concrete resistance
is accomplished by mixing the concrete with chemical
additives, protecting the concrete from contact with aggressive waters by epoxy coatings,
or some other method of impermeabilization. Sulfate-resistant cements are available.
TABLE 8.3
Indicators of Corrosive and Incrusting Waters
Corrosive Water
Incrusting Water
A pH less than 7
A pH greater than 7
Dissolved oxygen in excess of 2 ppm
Total iron (Fe) in excess of 2 ppm
Hydrogen sulfide (H
2
S) in excess of 1 ppm,
Total manganese (Mn) in excess of 1 ppm in
detected by a rotten egg odor
conjunction with a high pH and the presence of
oxygen
Total dissolved solids in excess of 1000 ppm,
Total carbonate hardness in excess of 300 ppm
indicating an ability to conduct electric current
great enough to cause serious electrolytic
corrosion
Carbon dioxide (CO
2
) in excess of 50 ppm
Chlorides in excess of 500 ppm
Source:
From Cording, E. J., et al. Department of Civil Engineering, University of Illinois, Urbana, 1975. After
Johnson, E.E.,
Johnson National Drillers J.,
35, 1963.
TABLE 8.4
Effect of Sulfate Salts on Concrete
Degree of Attack
Sulfate in Water sample (mg/L)
Negligible
0-150
Positive
150-1000
Considerable
1000-2000
Severe
2000
Source:
After USBR,
Design of small Dams,
U.S. Govt. Printing Office, Washington, DC, 1973.
