Batch water. Batch water discharged into the mixer from municipal water supply, reclaimed municipal water, or water resulting from concrete production operations. This is the main source of mixing water in concrete.
Ice. During hot-weather concreting, ice may be used as part of the mixing water. The ice should be completely melted by the time mixing is completed.
Water added by the truck operator. ASTM C94 (AASHTO M 157) allows the addition of water on site if the slump is less than specified, provided the maximum allowable water-cement ratio is not exceeded and several other conditions are met.
Free moisture on aggregate. Free moisture on aggregate can represent a substantial portion of the total mixing water. It is important that any water brought in by the aggregate be free of harmful materials.
Water contained in admixtures. Water contained in admixtures must be considered part of the mixing water if the admixture’s water content is sufficient to affect the water-cementitious materials ratio by 0.01 or more.
Non-potable water and water resulting from concrete production operations can be used as mixing water in concrete provided the acceptance criteria given in ASTM C1602 are met. Water recovered from processes of concrete production includes: (1) wash water from mixers or that was a part of a concrete mixture, (2) water collected in a basin as a result of storm water runoff at a concrete production facility, or (3) other water that contains quantities of concrete ingredients. The solids content in recycled water generally ranges from 2.5 to 10 percent. The maximum permitted solids content for water to be used in concrete is 50,000 parts per million, or five percent, of the total mixing water and should be tested in accordance with ASTM C1603.
The National Ready Mixed Concrete Association has summarized the issues involving the revised mixing water requirements and use of the new standards. Click here.
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