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What Is Jobsite Addition Of Water?

Simply, it’s adding water — usually a small amount of the mix design water — to ready mix concrete inside the mixer truck after it arrives on the job site.

Why Is Water Added At A Jobsite?

Adding water to concrete on site brings the slump up to an acceptable or previously specified level. It’s crucial to only add as much water as necessary since deviation above or below the design mix allowance or specification generally has an adverse effect on the ability to place the concrete.

Water can be added when the truck arrives on site provided the exact slump and/or cement-water ratio isn’t exceeded. Adding water should always follow ASTM C 94, Standard Specification for Ready Mixed Concrete.

What Are The Effects Of Too Much Water In Concrete?

Concrete provided by a ready mix supplier is designed under industry standards specific to its intended purpose. Adding too much water reduces overall strength and causes the concrete to be more susceptible to future cracking.

Can I Request More Water Be Added To The Concrete?

Yes, but as the buyer, you’re assuming the responsibility for the resulting concrete quality. Instead of adding more water, it’s recommended to use a water reducing admixture or superplasticizer as two solutions for how to increase concrete slump. Then, as long as segregation is avoided, using admixtures to increase the slump usually won’t greatly alter the concrete properties.

How To Add Water At A Jobsite

Specify Maximum Allowable Slump

Use the specified nominal slump plus tolerances for determining the maximum allowable slump.

Estimate Or Determine Actual Slump Before Discharge

Measure the slump using a sample taken from the first quarter cubic yard of discharged concrete. The result should be used as a consistency indicator and not an acceptance test. All acceptance tests should be taken following ASTM C 172.

Add Water To The Entire Batch

By adding to the entire batch, you’ll know the volume of the retempered concrete. Generally, a rule of thumb is to use one gallon of water per cubic yard for a one-inch slump increase.

Measure & Record Added Water

All water added at the job site should be measured and recorded.

Increase Revolutions After Adding Water

An extra 30 mixer drum revolutions, at mixing speed, are required under ASTM C 94 after adding water to the concrete. If the truck can mix at 20 revolutions per minute or more, 10 revolutions are sufficient.

Control The Amount Of Water

Any amount of water added to the concrete should be controlled as to not surpass the maximum slump and/or water cement ratio.

Prohibit Extra Water On-Site

Further addition of water at the job site is prohibited once the appropriate slump and/or water cement ratio has been reached.

Establish Proper Procedures Before Pouring

It’s recommended to establish proper procedures before pouring the concrete, such as who has the authorization to request more water and to define the documentation method for any added water.


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