Pouring a concrete ramp at the waters edge.

[Renze]

My friend in Finland uses hot water and quick curing compound to pour concrete in the winter. And boy it does freeze over there !

 

[Streetcar]

The way I've seen it done, is they pour the slab, then push it into the water as far as the can after it cures, then they pour another slab next to that one. This was with a full sized 4x4 backhoe. I don't know what it weighed or how much power it takes to push a slab down hill into the water, but it sure looked pretty easy when I saw it being done.

You would need a heavily reinforced slab because you are not likely to have good bearing from soil on slab.
What kind of soil was at the lake and how big was the slab?

 

[Streetcar]

I forgot to ask how much wave action at the lake.
I would pour 7" slab with reinforcement 12" on center

 

[dstig1]

You would need a heavily reinforced slab because you are not likely to have good bearing from soil on slab.
What kind of soil was at the lake and how big was the slab?

Yeah - I agree with this. Steel is cheap for that size slab. Go overboard given the questionable bearing soils in a lake (plus wave erosion). 1/2" rebar at 12" centers or more. It is best to keep it below the center line of the slab as steel in a slab works in tension, really, so you want it on the tensile side of the loading (the bottom of the slab). But it needs to be fully embedded in cement too. That is hard to do in a 4" slab. If you went thicker, you could do it more easily, but of course that costs more. Mostly it is just material costs as the placing and finishing work do not change much from 4" to 6", for example. Good idea to put rock around the edges for erosion.

 

[oosik]

The only concrete boat ramps I've seen around here were constructed by DNR(Dept of Natural Resources). They are not a "pour in place" operation. They first grade the ramp area and lay down a layer ( looked like 6" to 8") of crushed basaltic lava. The lava rock was what I would call 2" screened. Then here comes the precast concrete ramp pieces. They were 6' x 20' x 8". They were lifted from a large semi truck and set using a rather large crawler backhoe. Each piece had cast in place tie lugs. So as each piece was set, it was linked to the previous one with a large bolt thru the tie lugs. There were three tie lugs on each side of each piece.

The result looked like a large grey track off a crawler tractor with a 6" gap between each piece. The supervisor said one of the advantages is if one of the pieces became damaged - it was simple to pull the bolts and replace that piece. The other neat thing was the crawler backhoe just walked out the ramp to set the next piece out in the water. The limit to this operation was - how far out in the water the crawler backhoe could deposit and level the initial crushed basaltic lava base.

 

[ajmaxham]

In a 6'' slab should the rebar be at the center line. The force of frost will come from the bottom side of the slab. The weight of truck and boat will come from the top. Should the rebar that will be under water for part of the year be a corrosion resistant epoxy coated rebar?

 

[check]

I forgot to ask how much wave action at the lake. I would pour 7" slab with reinforcement 12" on center

Not much wave action at all. The ramp will be at the "back door" of a 50 foot long boathouse.

 

[check]

The way I've seen it done, is they pour the slab, then push it into the water as far as the can after it cures, then they pour another slab next to that one. This was with a full sized 4x4 backhoe. I don't know what it weighed or how much power it takes to push a slab down hill into the water, but it sure looked pretty easy when I saw it being done.

Interesting idea, but it won't work in my application. As I mentioned earlier, the lake rises and falls to even as much is 4 feet over the course of the season. Right now the lake is down 31" from the average Summer level. So, if I poured now, the slab will be under plenty of water when I put the boat in and take it out. The slope of the slab will be a drop of about maybe 2 feet over a total length of 30 feet. And then it will be Rocky/Sandy at the end of the ramp. Should be no problem.

 

[deere36]

We poured one like EddieWalker said here in Mississippi 20'x12' slab wire & rebar pushed in with mini-excavator, then poured a second slab to match. Left about 3 feet wire & rebar out of first slab to connect second slab for stability, this was in 2007 & have launched full size bass boats with ease.

 

[Streetcar]

In a 6'' slab should the rebar be at the center line. The force of frost will come from the bottom side of the slab. The weight of truck and boat will come from the top. Should the rebar that will be under water for part of the year be a corrosion resistant epoxy coated rebar?

Rebar in the center of the slab will only help to hold the cracked concrete from spreading. It adds very little to the strength of the slab.
For fresh water I would not worry about epoxy rebar. Almost every structure I have built in fresh water used black steel. In brackish or salt water use epoxy steel