Formwork Removal Time for RC walls 1

[Ganesh Persaud]

Hello everyone,

What’s the allowable period to keep formwork in place for a rc wall before adding fill and compacting. In this instance my wall is 4ft in height and 6 inches thick.

Thank you
Ganesh Persaud

 

[MotorCity]

As long as it takes to achieve the required strength. Compare your cylinder breaks to the required strength at the time of form removal.

Some people impose a minimum time such as 3 or 7 days, but that alone is not sufficient. Poor concrete at 3 or 7 days could still be poor concrete at 28 days.

 

[SlideRuleEra]

There can be several answers depending on whats the Contractor wants to do:

1) If the forms are needed for reuse on a different length of wall, forms can be removed the day after concrete placement. However, the day old concrete should be covered and kept wet for a total of seven days so that it can continue to cure.

2) If the forms are left in place to provide the protection for concrete curing, forms can be removed after seven days.

3) For adding fill, wait until concrete reaches 90% of design 28 day compression strength.

4) For compacting fill, wait until concrete reaches 100% of 28 day design compression strength.

These are typical numbers based on my interpretation of DOT requirements for bridge construction. Other members may have different recommendations.

http://www.SlideRuleEra.net

 

[skeletron]

@SlideRuleEra: are those DOT backfill suggestions specifically for R/C walls?

 

[SlideRuleEra]

skeletron - Not walls specifically, but highway bridges and cast-in-place culverts (walls are about half of a box culvert concrete). The pages used for my interpretation, extracted from the South Carolina DOT Standard Specification, are attached.

http://www.SlideRuleEra.net

 

[skeletron]

Great! Thanks for the reference. It's funny that it mentions "piers" because of a recent issue with a contractor. Contractor wanted to form the pier (bolting a casing down to the mat) and backfill, <24 hours after pouring the mat. He was pretty adamant that he could easily do it with no issues. My answer was still "no". Anyways, back to the original topic. Sorry for the digression...

 

[SlideRuleEra]

skeletron - Glad the info was helpful. My understudy and I wrote a series of limited "mini-specs" based totally on DOT standards. Examples like a mini-spec for timber pile driving, another for steel piling, and a third for concrete piling; also reinforced concrete, structural steel, excavation and backfill, etc. We used these for in-house projects where, as the Owner, we did both design and construction management. Eliminated a lot of "boiler plate" and unnecessary language that did not apply to get Contractors to focus on what was important.

http://www.SlideRuleEra.net

 

[oldestguy]

Hell, I see housing contractors here "getting away" with next day strip of basement wall forms and within a week are filling, but no compaction, no wetting of concrete either. Darn walls stay up. Not recommended, but who knows how close to failure they go. Of course in my many years I have seen them lean also, but rarely.

 

[Lomarandil]

SRE, if you're interested in trading your hard work for little purple stars, I for one would love to see those mini-specs.

----
just call me Lo.

 

[SlideRuleEra]

Lo - We did those mini-specs in the 1990's (pre-computer, for us) and never digitized them. I'll see if I can track down paper copies... if so, will be happy to make them available.

http://www.SlideRuleEra.net

 

[racookpe1978]

SlideRuleEra:

Good points for fill and compacting fill (sideloads) for a thin "wall" apparently comparable to the OP's questions.

I would recommend using the same criteria for points loads or embedded foundations in that wall: A handrail (sideways load for example) or structural columns on that wall for a roof or second floor need to be based on the concrete strength and surroundings at the specific time after pour the forms are removed or the structural attachment made. NOT the final 28 day geometry complete with adjacent walls and floors and supports, nor the 28 day cure strength.

 

[SlideRuleEra]

Lo - Apparently did not keep a copy of any of our mini-specs when I retired. Did the next best thing, put together an updated draft of one as a sample... chose steel H-pile driving as typical (attached). We did a number of small projects from time to time that required just a few piling. Three examples:

pipe bridge for polyethylene pipe lines, 8 piling, (photos included)
conveyor foundations, 12 piling
transformer foundation, 4 piling

http://www.SlideRuleEra.net

 

[robyengIT]

one more mini-spec to be added : "when You retire remind to keep a copy of all the mini-specs done all over the years"