Pouring concrete against construction joint.

[egdad4]

How soon after stripping the form from a 12" base slab can you place concrete against the joint created. The jproposed oints in the slab have waterbars and reinforcement in them. Is there a reference that gives guidance?

 

[ptatohed]

How soon after stripping the form from a 12" base slab can you place concrete against the joint created. The jproposed oints in the slab have waterbars and reinforcement in them. Is there a reference that gives guidance?

I think the forms should not be stripped until the concrete sets to 75% of its maximum strength. I think you can pour up against it when the concrete sets to 100% maximum strength. Were samples taken/tested?

 

[IlPadrino]

How soon after stripping the form from a 12" base slab can you place concrete against the joint created. The jproposed oints in the slab have waterbars and reinforcement in them. Is there a reference that gives guidance?

I think the forms should not be stripped until the concrete sets to 75% of its maximum strength. I think you can pour up against it when the concrete sets to 100% maximum strength. Were samples taken/tested?

I don't have the ACI reference handy, but you can strip flatwork as soon as doing so doesn't cause the concrete to deform. Hours or days, not weeks.

 

[ptatohed]

How soon after stripping the form from a 12" base slab can you place concrete against the joint created. The jproposed oints in the slab have waterbars and reinforcement in them. Is there a reference that gives guidance?

I think the forms should not be stripped until the concrete sets to 75% of its maximum strength. I think you can pour up against it when the concrete sets to 100% maximum strength. Were samples taken/tested?

I don't have the ACI reference handy, but you can strip flatwork as soon as doing so doesn't cause the concrete to deform. Hours or days, not weeks.

This might be true for flatwork like C&G, sidewalk, ped ramps, but not necessarily for slabs, I don't believe.

C&G, sdwk, dwy, ramp, etc.forms should not be removed until the concrete has set sufficiently to hold its shape but should be removed in time to permit proper finishing.

Per the “GREENBOOK” Standard Specifications for Public Works Construction, 2009 Edition:

Section 307-8 discusses slabs and refers back to 303-1.4 for the removal of the forms.

Section 303-1.4, says the forms can be removed in 7 days after the concrete is placed.

 

[Dexman PE PMP]

It also depends on the governing agency's requirements. I've seen cold joints get established in hours...

 

[IlPadrino]

This might be true for flatwork like C&G, sidewalk, ped ramps, but not necessarily for slabs, I don't believe.

C&G, sdwk, dwy, ramp, etc.forms should not be removed until the concrete has set sufficiently to hold its shape but should be removed in time to permit proper finishing.

Per the “GREENBOOK” Standard Specifications for Public Works Construction, 2009 Edition:

Section 307-8 discusses slabs and refers back to 303-1.4 for the removal of the forms.

Section 303-1.4, says the forms can be removed in 7 days after the concrete is placed.

I assumed he meant slab-on-grade when he wrote "base slab", which is why I called out flatwork. If he's talking about a suspended slab with shoring, then he *really* needs to understand the requirements for removing shoring and reshoring; ACI 318M-11 reads:

6.2.2.1(b) No construction loads shall be supported on, nor any shoring removed from, any part of the structure under construction except when that portion of the structure in combination with remaining forming and shoring system has sufficient strength to support safely its weight and loads placed thereon;

and there is commentary relating to the sides of forms which reads:

Where the structure is adequately supported on shores, the side forms of beams, girders, columns, walls, and similar vertical forms may generally be removed after 12 hours of cumulative curing time, provided the side forms support no loads other than the lateral pressure of the plastic concrete.

I'm not familiar with the GREENBOOK. Can you share some of it? I don't know why it would require you to wait 7 days to remove vertical forms, even if it's a suspended slab. Thoughts?

 

[ptatohed]

I'm not familiar with the GREENBOOK. Can you share some of it? I don't know why it would require you to wait 7 days to remove vertical forms, even if it's a suspended slab. Thoughts?

Thanks for the ACI stuff.

Here is the book I am refering to. http://www.greenbookspecs.org/ I don't think it is CA specific. These Greenbook specs are the basis for the specs on nearly all projects (accept maybe Caltrans) that we work on. Since this is the real "Greenbook", it drives me nuts when people refer to the AASHTO GDHS as the "Green Book". We use the standard plans for public works construction if we need a standard that doesn't fit our City standards. But the Greenbook specs are used for every project.