"Too much" plasticizer vs cracking?

[DrAWH]

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?

 

[DRC1]

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

 

[DrAWH]

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.