Concrete batch tickets typically have the water added in the plant neatly printed on the ticket. What may surprise you is that there are actually multiple sources of water. For the total water content in the concrete to be correct, the concrete producer must carefully control and document each source. Here are eight potential sources of water:
- Water from cleaning the drum after the prior load: Some batch software programs let users input the amount of water in the drum prior to batching. However, measuring this water accurately is a challenge. So, in most cases, the driver should reverse the drum after washing and before loading to empty out the remaining water.
- Aggregate free moisture: Aggregate free moisture can account for 10 to 40% of total water. That’s why aggregate moisture measurement is crucial.
- Batch water: This water is measured by volume or weight. It may be heated or chilled. Given all the other water sources, it accounts for only 60 to 90% of total water.
- Admixtures: Most admixtures contain water in addition to their active ingredients. Given typical volumes of admixture, this water content is very small, but easily and accurately accounted.
- Ice: One pound of ice = one pound of water.
- Wash down water: After batching, the driver needs to clean any material that got on the hopper and the top of the drum during batching. This prevents material from building up and hardening on the truck. The driver simply “washes down” this material into the drum. Usually only a few gallons of water are needed.
- Driver water: If the slump after batching or at the site is less than target, the driver may add water. This water can be measured with an electronic meter, or more commonly with the sight tube on the truck water tank. However, don’t assume that the sight tube shows all water added. Some water may be used for other purposes—such as washing the truck. Any water added before the tank is filled will be missed on the sight tube. Water can also be added from a fixed hose at the plant used to wash the truck.
- Contractor water: The contractor may request a higher slump than ordered. When this happens, it’s actually not uncommon for the contractor to walk over to the truck and open the water valve leading to the drum, sometimes without the driver or inspector even seeing.
Submitted by Eric Koehler, Vice President of Verifi. Verifi helps concrete producers control these sources of water and provide documentation to inspectors, engineers, and owners. Learn more at VerifiConcrete.com.