Aging of concrete and removal of formwork!
Aging of concrete and removal of formwork!
(OP)
Hi,
Is there a section in ACI that talks about the percentage compressive strength gaining of concrete over time? As I know 7 days strength is about 70-80% of 28 days compressive strength. Also, how quickly can we remove the form-works and shoring in an elevated slab (not post tensioned slab) per ACI? I would appreciate your help.
Is there a section in ACI that talks about the percentage compressive strength gaining of concrete over time? As I know 7 days strength is about 70-80% of 28 days compressive strength. Also, how quickly can we remove the form-works and shoring in an elevated slab (not post tensioned slab) per ACI? I would appreciate your help.






RE: Aging of concrete and removal of formwork!
Section 6 of ACI318 talks about the removal of forms and shoring.
Generally the notes will say something like:
ALL SHORING TO REMAIN IN PLACE UNTIL CONCRETE HAS ATTAINED 75% OF ITS 28-DAY COMPRESSIVE STRENGTH.
Refer to this written faq about concrete:
FAQ507-1572: what do i need to know about concrete
thread581-120179: Stripping RC Beam Forms
Some engineers say shoring can be removed after 14 days, other engineers say 21 days. Personally 21 days is better for the design of the slab because it reduces the contribution of creep and shrinkage to the longterm deflections because the time of first loading has been delayed.
To say they must remain in place until the concrete has attained 75% of it's design strength is ambiguous. It would require and additional cylinder test to ensure the concrete has attained it's particular strength.
Remember to give rowingengineer a good review for the FAQ.
RE: Aging of concrete and removal of formwork!
Forms can be safely removed in as little as three days, assuming perfect curing conditions and immediate re-shoring which, in turn, must be maintained until the concrete has gained its 28 day strength.
BA
RE: Aging of concrete and removal of formwork!
RE: Aging of concrete and removal of formwork!
RE: Aging of concrete and removal of formwork!
RE: Aging of concrete and removal of formwork!
RE: Aging of concrete and removal of formwork!
That seems an unusual requirement to me. It would serve to lessen the short term slab deflection, but whether it helps to prevent wall distress depends a lot on the sequence and speed of construction. I think a more common requirement is to require the removal of shoring prior to construction of supported masonry above the slab. That way, the masonry and the slab deflect together as the masonry is constructed.