Frequently on construction projects, project specifications require “No addition of water to be added to the concrete onsite.” Why is this specified? There are a few good reasons this may be beneficial to the project and the contractor, but often contractors believe this is a hindrance to their production and finishing methods. In turn, this can lead to a conflict between the contractor and the onsite quality control.
Limiting the addition of water to concrete onsite can benefit the contractor in a couple of ways. The first good reason being, it can better protect the contractor in the event of a concrete failure. If you haven’t noticed, there is fine writing on the back of most well written batch tickets to protect the ready mix company. Often within the fine print writing, it generally states that the ready mix company is not responsible for the concrete once water or admixtures are added onsite. In general, the minute you start making adjustments, “You own it.”
Contractors frequently get frustrated with the “no water onsite” specification because it hinders placement production and finishing. However, this actually is not the case. There is much time wasted by adding water to the concrete onsite and achieving the specified ready mix truck revolutions. Consider this, if you placing 500 yards with each truck containing 8 yards, that is just over 62 trucks. If done properly per ASTM C 94, each truck should take approximately 2 minutes. If each truck had water added, that is over 2 hours of wasted time.
Adding water prior to arriving to the project generally benefits the project by increasing the chance of meeting the project specifications. If water is added at the plant, it is more likely that the mix will be within the mix design tolerances. If the mix design tolerances are met, it saves the developer, the design engineer, and contractor from many headaches. When project specifications are not achieved, it can lead to RFI submittals, RFI reviews, non-destructive and destructive testing, etc. Overall, this leads to wasted time and money.
Obviously, this isn’t a perfect world and sometimes adjustments need to be made onsite. Actually, ASTM C 94 allows a one-time addition of water provided that it does not exceed the maximum water content established on the approved mix design. Ideally, you want to reduce the likelihood that the addition of water is needed.
In a perfect world, a consistent concrete can be achieved with a team effort between the quality control and the concrete contractor. The quality control should always report results immediately to the contractor so that the contractor is able to call the plant to make adjustments. Once the adjustments have been made, its more likely that the concrete will be suitable for direct placement and will in turn reduce the amount of time wasted and reduce concrete specification deviations.
