CONCRETE PIPE Hydrokinetics (Infiltration and Exfiltration) As shown in the adjacent figure, Example 1, with water at equal pressure on both sides of a pipe wall, the concrete becomes saturated, stability is reached and no water movement takes place. In Example 2, there is a differential pressure, and, regardless of magnitude, a hydraulic gradient causes movement of water through the wall, along with whatever salts, alkalis, sulfates, and other chemicals are in solution in the water. Even though this movement may be imperceptibly slow, it will provide continuous replenishment of any chemicals that may be in solution. Direction of flow is highly significant. If the aggressive water were on the right of the wall, the movement of non-aggressive water through the wall would tend to mitigate any effect. In either case, with no exposure to the atmosphere, there is no concentration effect. Examples 3 and 4 have an evaporative surface condition. The water movement is due to either a hydraulic gradient or capillary action. In either case, there would be a concentration at or near the evaporative surface in solution. These considerations are not relevant to acid environments, attack is essentially confined to the exposed surface. They are significant, however, in evaluating severity of sulfate or chloride exposures. PAGE 56 LAFARGE PIPE eMANUAL