Concrete freezing during curing period 1

[JJD1]

I have been involved with placement of cold weather structural concrete, such that the heated curing blankets lost power overnight after 10PM, placement of the concrete was complete the same day at approximately 1:30PM (recorded concrete surface was 55-60 degrees, ambient temp was 20 degrees at 10PM) and discovered the following morning the power went out and the concrete surface temp was 20 degrees. The power was restored and temperatures resumed for the balance of the curing period. The opposition is claiming the concrete should be removed without perfroming any in place testing. The concrete test cylinders attained the proper strength. We have recommended swiss hammer and windsor probe testing with the opposition's claim being the future durability of the concrete is suspect. The concrete installation is on a bridge. Coring the concrete is unlikely due to its location and proimity to embeded structural components

I am looking for information to convince the parties that the in place concrete, with evidence of non-destructive testing represents strength and durability of the concrete.

 

[DTGT2002]

To validate the NDT, you will undoubtedly need some coring. Even small cores can tell quite a story.

Was there any instrumentation of the slab, maturity meters etc?

How large was the placement?

 

[Ron]

Core the slab if you can. It will give the most accurate data. The Swiss Hammer should not be used to assess strength. It's fine for uniformity, but not strength, no matter what the ready mix supplier or testing lab tells you. The ASTM standard for using the Swiss Hammer specifically warns against it.

As DTGT2002 noted, correlate the core strengths with a non-destructive method, either pulse velocity or Windsor Probe.

I would have petrographic examination of a core done as well. That will tell you the damage from the freezing and will clearly show if microcracking is evident.

 

[JJD1]

TO DTGT2002:

NO, THERE WAS NO INSTRUMENTATION OF THE CONCRETE.

THE TOTAL VOLUME OF CONCRETE WAS AT 3 SEPERATE LOCATIONS APPROXIMATELY 1.5CY AT EACH LOCATION.

 

[PEinVA]

Such small amounts of concrete, why not just replace it as requested by the "opposition".

The testing and time spent fighting about it, will no doubt, cost similar as if it was jsut fixed in the first place due to contractor/inspector error.



RC
All that is necessary for the triumph of evil is that good men do nothing.
Edmund Burke

 

[dik]

If concrete is plastic (ie. still a fluid) then freezing it will not likely harm it. If it is in the process of setting up and freezes, but has a compressive strength of approx 5 MPa, then freezing will not likely harm it. If it has a strength less than 5 MPa, then the concrete is generally damaged.

If only slightly below freezing, the matrix may not have frozen.

As Ron notes, it is a matter of taking cores and doing a petrographic study. If it is part of a bridge and a small quantity, then it's probably cheaper to replace it.

Dik

 

[dik]

On one of my projects, I was informed yesterday of a 3-day break strength of 0.7 MPa... (100 psi) The lowest I've ever encountered! The one specimen fell apart when they tried to sawcut it to cap it for compression testing.

Dik

 

[Ron]

dik...that's worse than soil-cement!! How did they manage that one?

 

[dik]

From what I understand, they had problems with their batch plant... it was noticed that something was different when they placed it.... go figgur... no analytical testing, they are simply removing the offending concrete. The lowest, ever...

Dik