Aggressive Index

Published: October 4, 2018 | Last updated: July 5, 2023

What Does Aggressive Index Mean?

The aggressive Index is a part of Standard C-400 established by the American Water Works Association (AWWA). It relates to the corrosive tendency of water and to its effect on asbestos cement pipe. This corrosion index uses a formula that's calculated from the water's pH – whether the water is more acidic or more alkaline, the water's hardness, or how much calcium the water contains, and the alkalinity of the water.


Trenchlesspedia Explains Aggressive Index

To make the calculation one needs to know the alkalinity, hardness and the pH of the water. These are the factors that make water corrosive to a cement-asbestos pipe. The pH is the pH of the water determined by a litmus test. The hardness of the water turned by a water mineral content test.

The formulae used in the aggressive Index is stated as AI = pH + log (A * H). In this statement, "AI" represents the aggressive Index. "A" is the alkalinity of the water. "H" is the hardness of the water.

Neither the alkalinity nor the pH of the water is a whole number, so the first step is to multiply the logarithm of the alkalinity by the logarithm of the hardness of the water. Add this to the pH of the water and the result is the aggressive Index of that water sample.



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