UFC 3-570-06
JANUARY 31 2003
Potential drop is measured across probes inserted into the soil. The resistivity is
calculated using constants furnished with the particular size of soil box being used. Due
to the disturbance of the soil during sampling and possible drying out of the soil during
shipment, this method of soil resistivity measurement is less likely to represent true, in-
place soil resistivity than an actual field test. To minimize drying out of samples, they
should be placed in plastic bags and sealed prior to shipment.
Figure 7-29. Soil Resistivity Measurement Using a Soil Box
C
2
P2
C
1
P1
7-12
pH TESTING PROCEDURES. The pH of an electrolyte is a measure of the
acidity or alkalinity of the electrolytic solution. pH ranges from 0 to 14 with 0 to 7 being
acidic, 7 being neutral and 7 to 14 being alkaline. pH can be measured using several
methods. The pH of an electrolyte--the state of active acidity or alkalinity--is a major
factor that determines the rate at which metals will corrode. Acid solutions have more
hydrogen (H+) ions than hydroxyl (OH-) ions. The electrolyte pH is tested for planning,
design considerations, and leak surveys. For steel, the corrosion rate remains fairly
constant, from a pH of about 4.5 to a pH of about 10.5. At a pH below 4, the corrosion
rate for steel is drastically accelerated. Also, above a pH of 11, the corrosion rate for
steel is drastically lower, except for a sharp rise when the pH approaches 14 (not shown
in Figure 7-30). For aluminum, acidic corrosion rates are similar to steel, but unlike iron
and steel, aluminum also shows accelerated corrosion attack in alkaline electrolytes
(above a pH of 8.5) because of a reaction of Al+ ions with OH- ions (see amphoteric,
Glossary).
7-45
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