When the air content of portland cement concrete is below the specified level by more than the allowable tolerance, the supplier may use additional air entraining admixture if the following conditions are met:

1. The admixture is the same brand and type as originally introduced at the concrete plant unless otherwise permitted by the Engineer.
2. The admixture, if liquid, is measured into a bucket containing 1 gallon of water. The admixture, if prepackaged powder, is added according to the manufacturer's recommendation.
3. The admixture, if liquid, is thoroughly mixed with the water and the mixture is then directed to the front of the drum (end nearest truck cab) with the drum momentarily stopped.
4. The maximum allowable water-cement material ratio of the concrete is not exceeded with the addition of water and admixture solution.
5. The concrete is then mixed 30 revolutions at mixing speed.
6. A record is kept by project personnel of the brand, type, and quantity of admixture and of water added and clearly noted on the sample card and batch ticket.

This policy should apply only to trucks already on site and enroute. However, air adjustments may be necessary on subsequent loads due to variations in raw materials at the ready mix plant. Concrete plant personnel shall monitor and adjust admixture proportions at the plant in an effort to produce concrete with air contents that meet specification requirements.

Air entraining agent may be added on site up to twice per truck. If, after the second addition of the concrete fails to meet air content and/or slump specifications, the concrete shall be rejected.