Holding Back Water From Concrete - Potential Issues? 1

[jseng9]

A concrete supplier on our project has been holding back water at the plant and not adding water on site. This obviously means that we aren’t hitting the target w/c but concrete will have higher strength. GC has stated the concrete is perfectly workable. This concrete is for spread footings and walls. The cylinders taken on site have reached 100% f’c in 7 days. Are there any potential issues with the quality of the concrete? I’m wondering how big an issue this is.

 

[r13]

Strength wise, I couldn't think of any problem, if it is workable, and flows (to remold) by vibration, so no honeycombs will result. Watch out for the vertical wall faces though, that may require extra external vibration to avoid surface defects. What was the measured slump?

 

[Eric C.]

If the concrete meets strength requirements, durability requirements(% entrained air, for example) and can be placed and consolidated effectively then there should be no issues.

It could be that the concrete plant is adjusting the water based on the moisture content of the coarse and fine aggregates. Have you checked the batch yield?

 

[BUGGAR]

I thought it was common to hold back some of the design water to allow tempering on site. The truck ticket has to say how much was held back. This should be covered in the specs.

 

[jseng9]

Thanks everyone for the responses. I really appreciate it. Apparently the truck tickets are showing the water held back and the field reports show no water added on site - they are supposed to balance. As suggested we will keep a close eye on the slump, air content, and temperature to make sure they meet the requirements. I will also be on the look out for any issues relating to the finish. Thanks!

 

[hokie66]

It sounds to me like you have a good concrete supplier and good GC. The less water, the better.

 

[Ron]

Agree with hokie66...not an issue. Be thankful. Usually goes the other way!

 

[STrctPono]

I'm confused, what's the problem!? I wish more concrete suppliers were like this. You say that you "aren't hitting the target w/c ratio". W/C ratio should not be thought of as a "target" number. It should be thought of as a maximum allowable number. Being below the w/c ratio is a good thing so long as the Contractor can place and get proper consolidation. Trust me, you will still have plenty of free water in the mix for hydration. The only negative thing it affects is slump. In the world of chemical admixtures this is really a problem of the past. High range water reducing admixtures allow us to pour 0.35 w/c ratio mixes in the field. This is something that would never have been achievable prior.

Please don't mess this up for the rest of us and start complaining to the ready mix supplier for not having enough water! Too many of us fight every day for the complete opposite...