Concrete Strength

[BigH]

Does anyone have the real strength required of the concrete for picking up NJ type barriers by the hooks. Maybe 20MPa is specified but normally these barriers are moved within a day or two so the actual strength would be in the order of 5MPa or so?
Thanks -

 

[jdonville]

BigH,

I suppose that you could look at the pullout resistance of the hooks/bars used to lift the barriers, and the strength required of the concrete to maintain its integrity during lifting.

Jeff


Jeffrey T. Donville, PE
TTL Associates, Inc.

http://www.ttlassoc.com

The views or opinions expressed by me are my own and do not necessarily reflect the views or opinions of my employer.

 

[PEinc]

I would call a barrier precaster and ask that question.

 

[jheidt2543]

BigH

I called a local precaster that produces New Jersey style concrete barriers to the State of Illinois DOT Spec. He said they use a mix design that requires a 28 day strength of 4,500 psi. The barriers they cure in the forms (not steam cured) are stripped in two days. They don't do a strength test to determine the concrete strength at stripping, they've been doing it so long they "know" they have the strength to handle the units.

That's all I've found so far!

 

[BigH]

Thanks Jim. I can't see where they need anymore than 1000 to 1500 psi to 'lift' and move the units. In our case, all units were moved at two days of casting without any problems - it is just that the 28-day strengths were low and the construction guy wants to throw back on the designer that it is safe to handle given the 2700 psi strengths we had at 28-days. With 4500psi concrete - the strength at 2-days would be only about 1800 psi - so if they can be moved at that strength, then I am okay since any subsequent handling of the units would have sufficient strength. I might throw it back on construction that this all depends on their records to ensure the hooks were properly placed! b- and they don't have any records!