Concrete Forming in the intertidal zone

[eriks]

Hi
I was wondering if anyone has experience in forming a concrete footing in the intertidal zone. Can regular 3/4” plywood be used or does it have to be marine plywood? Is the plywood form left on for 7 days before removing?
Any advice or tips would be greatly appreciated. Thx

 

[seachicken]

Cheapest 3/4 plywood you can find, forms can be stripped 24 hours after, usually 48 though. Easy to chip the concrete in the first 48 hours.

 

[eriks]

Cheapest 3/4 plywood you can find, forms can be stripped 24 hours after, usually 48 though. Easy to chip the concrete in the first 48 hours.

thanks for the response. What if I do the forming and pour concrete two days later? The forms will be completely submerged at mid tide onwards. If this happens for two days will it wreck the plywood?

 

[salmonkiller01]

thanks for the response. What if I do the forming and pour concrete two days later? The forms will be completely submerged at mid tide onwards. If this happens for two days will it wreck the plywood?

Plywood should last all of that. It will be one use anyways

 

[Marley]

If you are using rebar I recommend epoxy coated (green). Also increase your concrete cover over the rebar to 3” to help protect against the chlorides. There is specific concrete that’s should be used when exposed to salt water but I am not sure how technical you want to get.

 

[Brett83]

Crown 43 forming plywood might last a little longer under saltwater. Plus the finish will look smother.

 

[WHO DAT]

Anchor your forms well, I've witnessed them floating away due to tidal action. Best Regards

 

[eriks]

If you are using rebar I recommend epoxy coated (green). Also increase your concrete cover over the rebar to 3” to help protect against the chlorides. There is specific concrete that’s should be used when exposed to salt water but I am not sure how technical you want to get.

I spoke to a concrete supplier who said they add fly ash for those applications. I know that I may also need a plasticizer too if the bottom of the form is in the water.
I’d love to hear any advice you have on what concrete should be ordered.

 

[Marley]

I spoke to a concrete supplier who said they add fly ash for those applications. I know that I may also need a plasticizer too if the bottom of the form is in the water.
I’d love to hear any advice you have on what concrete should be ordered.

Mix design can vary dependant on supplier but the category of concrete should be C1 as shown in the link https://atlanticconcrete.ca/images/Concrete-Exposure-Classes-2013_0.pdf

Concert prevents chlorides (salt) from getting to and corroding the rebar. The salt moves slowly through the concrete and will eventually reach the rebar. This is why you see crews removing the concrete off bridge decks and sand blasting the rebar before it can corrode. They remove the concrete before the road salt reaches the rebar. In your case the epoxy coated rebar will provide protection when the salt eventually reaches the bar and will help prevent corrosion and spalling of the concrete.

Also giving more cover (3” from bar to the edge of form) and using the concrete designed for the salt water application will give you a much longer service life.

It is also important to ensure that the concrete mix has air entrainment for the freeze thaw cycles.

If you discuss your application with your supplier they will help you out.

 

[eriks]

Mix design can vary dependant on supplier but the category of concrete should be C1 as shown in the link https://atlanticconcrete.ca/images/Concrete-Exposure-Classes-2013_0.pdf

Concert prevents chlorides (salt) from getting to and corroding the rebar. The salt moves slowly through the concrete and will eventually reach the rebar. This is why you see crews removing the concrete off bridge decks and sand blasting the rebar before it can corrode. They remove the concrete before the road salt reaches the rebar. In your case the epoxy coated rebar will provide protection when the salt eventually reaches the bar and will help prevent corrosion and spalling of the concrete.

Also giving more cover (3” from bar to the edge of form) and using the concrete designed for the salt water application will give you a much longer service life.

It is also important to ensure that the concrete mix has air entrainment for the freeze thaw cycles.

If you discuss your application with your supplier they will help you out.

Thanks for the long and informative response. It’s greatly appreciated.

 

[eriks]

Should I be using 5/8 fiberglass rebar or epoxy coated?

 

[Flashman]

Depending on what you're building, budget etc there are options for galvanized, or fiberglass rebar. If it's not a heavily loaded structure might even be able to use chopped strand fiberglass reinforcing.

Epoxy coated rebar helps slow corrosion but it's not a miracle cure. You need to be careful about damaging the coating. If you're doing the work yourself, not a big deal but most rebar crews are not known for their finesse.

 

[Marley]

Depending on what you're building, budget etc there are options for galvanized, or fiberglass rebar. If it's not a heavily loaded structure might even be able to use chopped strand fiberglass reinforcing.

Epoxy coated rebar helps slow corrosion but it's not a miracle cure. You need to be careful about damaging the coating. If you're doing the work yourself, not a big deal but most rebar crews are not known for their finesse.

That’s a good point. If you damage the coating or cut epoxy bar it will corrode. I believe you can touch it up.

Fibreglass bar is available but it can’t be bent so if you need hooks or bent bar it needs to be ordered rather than done on site or by the building supply. Galvanized bar is a good solution as well. Many options that depend on budget and type of structure you are building.

Dependant on what you are building the bar size will change. 15 M or 5/8” bar is standard for a lot of residential work but can increase in size if more force is applied to the structure.

 

[Bifmalibu]

What are you building? What is it supporting?

 

[eriks]

A footing for the end of a bridge and start of a counterweighted ramp down to a dock. Our neighbor has a 6’x6’x3’ footing for the end of their bridge/approach. Something that size won’t tip over. Piles were quoted at $25K for 2 pcs and $50K if they need to be screw piles, so that’s out. We have a very rocky foreshore (debris field with some huge boulders) so just pouring a big footing seems to be the most cost effective method I think. If anyone has other suggestions, please let me know. I’m grateful for everyone’s input.

 

[tubber]

Do you have approvals from neighbours, municipality, regional district, DFO, MOE, and the three FNs with overlapping land claims?
Night pour?

 

[terrin]

Do you have approvals from neighbours, municipality, regional district, DFO, MOE, and the three FNs with overlapping land claims?
Night pour?

Sad reality. Unless your Chip.

 

[eriks]

Do you have approvals from neighbours, municipality, regional district, DFO, MOE, and the three FNs with overlapping land claims?
Night pour?

Yes.

 

[WHO DAT]

How will you be placing the Concrete? Boom pump , Line pump, truck on a barge ?Clearances from power lines.