Curing tank issue

[TDAA]

I have come across a new problem that I have not seen before. We are getting a thin film over the top of the water surface in our curing tanks. The film is sort of off-white/translucent, and is like a thin crust.

The one tank had been used for holding buckets for sodium sulfate durability testing, and I am sure some of the solution had dripped into it. The water was removed, and the tank "cleaned" and resealed with roofing compound at the seams. After lime was added to the tank, the surface film started to form.

Has anyone seen this? Do we have a reaction between materials, bad lime, etc.? Any way to salvage?

 

[Ron]

Your water is oversaturated with lime.

 

[TDAA]

Isn't that the intent of the 3g/L?

I have no issues taking some out, but we put it in (at least I calculated it) to the standard.

 

[Ron]

The intent of the lime saturation is so that lime is not leached from the concrete. Temperature variations in the water affect the saturation point for lime. Are your water temperatures consistent?

It's a bit odd that you have a surface encrustation. There might be some other factors working here. Usually when there's just too much lime, it precipitates and settles out.

 

[TDAA]

Yes, I expected the precipitate, just not the surface encrustation. That is why I was concerned there may be a reaction with something left in the tank (and should not have been put in the tank in the first place).

 

[kelowna]

disclaimer - No experience/knowledge at all on this issue

Wild guess - Could the lime be reacting with some of the minerals in the water? lime plus hard water could form calcium carbonate.