About 6 months ago I have poured concrete in a plastic mould. The mould was plastic plinth for sun umbrella. It is usually filled with water but it cracked so I filled it with concrete. Before pouring I glued the cracks with generic cyanoacrylate glue.. I prepared concrete mix with coarse and fine sand, cement and PP fibers. I was aiming for 0.3 water to cement ratio. I added a superplasticizer based on 2-octyl-2H-isothiasol-3-on. The plasticizer was dark purple fluid with distinct smell.I used quite a lot of it, somewhere near the max of recommended dose. The concrete stayed soft for quite a while and I thought it would not harden at all. After a week it became warm and solidified. The surface at the opening where I poured it in (the top) was soft to the touch for a few weeks. You could scratch it with a fingernail. But now is rock hard. What I have noticed after a few weeks was dark purple excretion under the glued cracks. And I think it even softened the glue. It looked purple like plasticizer, smelled like plasticizer and had a stingy taste. The concrete itself is of normal color. Now, even after a few months a purple excretion leaches out of cracks in plastic. Is this really plasticizer leaching out? Is this normal?

Things to consider:
Final w/c somewhere around 0.3.
Max recommended dosage of plasticer.
On top of the mold is an empty cavity which I left filled with water to keep the concrete moist during curing. The surface of concrete underneath is hard.

  • $\begingroup$ Why add extra water? There are concrete additives to make concrete set under water $\endgroup$ – Solar Mike Nov 18 '18 at 5:33
  • $\begingroup$ @SolarMike It is not uncommon to cover curing concrete with water. It is a way to prevent drying out and giving it the water it needs. It is done after initial curing / hardening. In my case I have just filled a small cavity at the top. Think: top of the bottleneck. $\endgroup$ – o115208 Nov 18 '18 at 21:51

There are concrete additives to make concrete set under water. Yes, plasticiser can leach out of concrete as you have seen - one trick to help concrete “flow” was a squirt of washing up liquid but it only needs a small amount.

  • $\begingroup$ Ok, that washing up liquid idea is an old wives tale. Lol. It does nothing to improve concrete properties. $\endgroup$ – Rhodie Nov 20 '18 at 17:24
  • $\begingroup$ Seemed to work when I had to mix concrete by hand for the floor of my dad's house - the builders added it after the first mix or so to make it more workable - they noticed a difference.. But what do I know, I was on the blister end of the shovel... $\endgroup$ – Solar Mike Nov 20 '18 at 17:26

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