Adding More Water to Concrete

Not looking at all your options.

Did you pass slump test *way* over, or only just. Any difference offers room to add water.

At higher cost, but with less sacrifice of strength are admixtures designed for this purpose. Talk to your supplier about them, even the pump operator may have current information.

Back in the day - which means my experience is 20 years out of date - one of the things we used was a simple soap admisture. The entrained air helped things flow more smoothly. But even then there were proper admixtures we *should* have been using.

Too much water will definitely affect strength negatively.

Does "passed slump test" mean that it "just passed," or does it mean that it "passed by a large margin?" If your concrete will pass the slump test with enough added water so that you can pump it more easily, then use that much more water. Otherwise, the engineer who specified the grade 35 with a slump that can't be pumped either didn't foresee that it would need to be pumped, or he merely overlooked the problem.

Ask the engineer if you can substitute a higher strength concrete with more slump so that it can be pumped.

The slump test recorded 40mm, the design range is 25-80mm. I hope that answers your question. The RFP does not specify the addition of admixtures. Thanks for your help.

With a bottom of 28 you have room for water, but I would seriously look into better methods.

Air entrainment through admix will give you more bang for your buck (OK, more flow for your slump) at a cost, of course.

"With a bottom of 28 you have room for water, but I would seriously look into better methods."

The O.P. said range was 28 - 80 mm. Doesn't that mean that the mixture can settle as little as 28, or as much as 80 mm? If so, then the range available for added water is between the 40 [measured] and 80 [permitted maximum] mm slump. If water can be added until slump is, say 60 - 70mm, it should be possible to test pumping results without actually hitting the limit on slump. If this fully solves the pumping problem, great! If not, then admixtures are likely the only hope. The rule of thumb will still be, "Add as little water as possible" to maintain maximum strength. If it will pump at 50 mm slump, don't go to 60!

If possible, pose the question directly to the person who called out grade 35 concrete. They should know why they did so, and what results can come from violating that specification.

Thank you all out there for the assistance.Thanks again.

Adding water to concrete on the job only satisfies one person and that is the person who is laying down the concrete. It GREATLY reduces the strength.

Here is a real example: A few years ago residential contractor I personally know, installed about 2000 driveways. It was a very hot and dry summer. The concrete company sampled almost every load at the plant, which was only 15 to 30 min away. They all tested well within specs. which was about 3500 PSI. He had to replace 1500 driveways that year and wanted to know why. After testing several of the poured driveway it was discovered that the contracor had added about 5 gal of water per truck load on the job site. That's about 1/2 gal per CY.

This water did two things:

1) it lowered the strength to about 1200 PSI

2) it took out all of the air entrainment so there was no frost protection

In short it would have been better to have spent another $0.06 a CY and have added a water reducing agent to the mix and speced a stronger mix of say 4000 PSI instead of 3000 PSI. This would have made the mix thinner without sacrifising the strength.

DO NOT ADD WATER, for all the reasons stated here, you will change the Water-Cement ratio and your mix will be completely out of spec, and potentially dangerous and likely have to be replaced AT YOUR OWN COST!

If you are trying to pump, you'll need superplasticizer, it will increase the 'liquidity' ie. allow better flow. Even a horizontal pump can benefit from the superplasticizer.

Your mix will fail the slump test with the superplasticizer in, however that state is temporary, it will come back after it is pumped and will allow you to finish once it sets. Get your concrete supplier / contractor to recommend a dosage.

Ensure your tester understands it and tests the mix prior to the addition of it and that your specification allows it.