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"Too much" plasticizer vs cracking?

"Too much" plasticizer vs cracking?

"Too much" plasticizer vs cracking?

(OP)
A contractor claims that too much plasticizer caused cracking of the finished product aftre a change in mix design.  Dry Proportions - kg/m3.  The placticizer complies to ASTM C494
                  Before              After
Cement             295                305
Fly Ash            126                131
Water (litres)     185                187
Coarse aggregate   1100               1110
Fine aggregate     610                584
Plasticizer        2530               1743

I don't work with these materials often and this is my first stab at trying to find out what the next step should be.  The concrete supplier is well established and respected and I would be surprized if the amount of placticizer is the problem.  In addition, I am aware of Abedkayrouz's reply to Vickeyb, suggesting that there are no general upper limits for plasticizers, and that trial mixes (which I believe was done)is the way to go, taking the specific material properties into account. Anny suggestions?

RE: "Too much" plasticizer vs cracking?

In general the concept of plasticizers is that they have a limited life and die out after the concrete is placed and finished, but before it has any set. There are low mid and hi range plasticizers which refer to the relative life of the additive.
Looking at your mix, the first thing is the plasticzer amount must be a typo. -not that I can type at all.
Second doing some rough math (and bearing in mind that I converted to work english units) I have a w/c of .61 which is kind of high. Also the cement  wt per yard is a little rich. Thse things can lead to cracking.
Third if you use plasticzer, it should be used in accordance with the manufactures direction. If there is a question about the plasticzer,I would talk to the engineering department at the manufacterer. They ussually have pretty good people whose job is to help answer these questions.
Last, many things can effect cracking besides the mix. Finihing techniques are very important. Constenntly bleeding waterto the top or conntiually "blessing" the slab can lead to a very weak suface that can cause cracking. Vibration or distubance during curing can lead to crackig. Proper curing, esp for slabs is extremely important. So don't just focus on the mix.
However, for an opinion on the mix, thry the concrete supplier. They  also ussualy have a knowledgable enginner responsible for QA/QC who could provide insight.
Good Luck

RE: "Too much" plasticizer vs cracking?

(OP)
Sorry, I forgot to add the units for the amount of plasticizer, it is millilitre (ml).
I greatlty appreciate the insight provided by DRC1, and will follow these suggestions.

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