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Is it Safe to Add Water to Concrete at the Job Site?


It is not unusual for a contractor to request more water to be added to the concrete being poured at the job site. Water makes the concrete more workable, and concrete loses slump as time passes, decreasing the workable consistency. Only a minimal amount of water is required to create the final form of concrete that flows out of the chute. However, there are instances when additional water is needed to make the concrete more workable for easier placement. However, increasing the amount of water changes the mix design and could result in weaker concrete that could require repair or replacement over time. How does a contractor determine how much water can be safely added?

The ASTM (American Society for Testing and Materials) C94 recognizes the need for water to complete mixing and make slump adjustments at the job site. However, the standard cautions “not to exceed the maximum water content for the batch….” Unfortunately, the maximum water content for a batch is not likely known and difficult to measure as adjustments are made onsite.

The best solution for a contractor is to use a superplasticizer. Adding a superplasticizer to a concrete mix produces workable, high-strength concrete without increasing water or weakening the concrete strength. Superplasticizers can reduce the need for water by 30%. This means that a contractor can be confident that they can obtain the desired workability and flow without sacrificing strength.

Not every pour will require a superplasticizer. It is up to the contractor to determine whether a superplasticizer is necessary for a specific project. Superplasticizers often reduce the amount of “bleed water” at the surface, allowing the contractor to begin finishing sooner. While superplasticizers have many benefits, keep in mind that they only work for 30 to 60 minutes. Finishing problems can occur. Some contractors find concrete treated with a superplasticizer is sticky and challenging to trowel.

Superplasticizers are not a cure-all and are not needed on every pour, but they can be used to make the contractor’s job easier and faster and produce stronger concrete. All Garden State Concrete trucks are equipped with superplasticizers for your use. Ask our dispatcher or driver for pricing.


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