Regular readers of our InTransit email have seen the “In the Field” graphic showing averaged data across all Verifi equipped trucks. Let’s explore two of the numbers from that report and learn more about concrete water additions.
Average Water Available for Verifi to Add (3.8 gpy for Dec. 1 – 15). This is the maximum water allowed in the mix less all water added during batching, including aggregate moisture. For instance, if the mix is designed with 30 gal/yd3 and only 27 gal/yd3 is added at batching, then 3 gal/yd3 is available for Verifi to add. As explained in a previous article, concrete producers add less than the maximum water at batching so that some water is available to adjust slump during transit or at the jobsite. Verifi interfaces with batch software to obtain this value and can be programmed to stop adding water after reaching the maximum.
Average Water Added by Verifi (0.5 gpy for Dec. 1 – 15). This is the total water added by Verifi, as recorded by a Verifi water meter on each truck. Although drivers or contractors may find ways to add water outside of Verifi, increases in slump recorded by Verifi are indicative that water has been added and can be used to flag unauthorized water additions.
The average amount of water added by Verifi is less than the average amount available for Verifi to add. What are the implications?
Concrete producers design mixes to account for water added in transit and at the jobsite. This allows additions after batching without exceeding the maximum water-to-cementitious materials ratio for the mix.
The numbers represent averages, so there are some loads where the maximum water content is reached. Verifi can be programmed to stop water additions in these cases.
Producers need to design mixes for the maximum expected amount of water, not the average amount. They need to consider the maximum expected slump, haul time, temperature, and other factors. Thus, in the average concrete delivery, less water than the maximum water will be needed.
By adding superplasticizer with Verifi, concrete producers can design for the average case, rather than the worst-case conditions. This enables producers to save superplasticizer, cement, or both. For example, producers can add all water and less superplasticizer during batching, then add superplasticizer to maintain slump until discharge. In the case with the maximum slump, haul time, etc., the amount of superplasticizer used may be the same as before. But in every other case with lower slump, shorter haul time, etc., the amount of superplasticizer used will likely be less.