Anybody know anything about building slipways?

Robert Wilson said:
Great thread, answers nearly all my questions for a similar job,.
BUT

My drive is steep (1:3 in places?) and I need to get an eight-wheeler(16 tonne?) loaded with a 3.5tonne boat up and down it.

What sort of thickness of concrete would I need? Any ideas?

Thanks in anticipation
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It’s not the concrete that has the strength - its the steel that is held rigid and hence much stronger than if allowed to twang. I would be happy with two 4’s mesh’s on that. Well, ok, i used one and sometimes two here and there. 6 inch thick minimum please. Depends on what’s underneath, a bit. If that could yield or sink , the concrete will become a bridge - and hence yerknow, two steel meshes under 6inceh of concrete minimum
 
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tcm said:
i would set plywood “stairs” in the slope, to reduce slumping from potential big scale to a series of small ones. In fact, er that;s the right way to do it - then you just a a series of short slopes. I’d jet blast the existing surface, put a 2-4 inch mesh down, then ply shuttering either side at the level of the final slope, and ply at various heights, perhaps supported being with a bit of rebar. Do the stairs first, then bog around with the slope on final pass, and this means you CAN use the tamping machine and I win the Best Answer prize :-)
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Not really following this... are you suggesting ply goes under the concrete? Which would be rather odd to say the least!
Also I've never heard of jet blasting the ground first. Is the idea there to scour away all traces of soft material until you hit bedrock? The soil here has rotten rock underneath it so removing that would be a chore and, IMHO, completely unnecessary. But maybe I'm misunderstanding something.
 
No the idea is to divide the slope up into smaller err slopes so the weight of the concrete does not slump big time.Personally I would do sections one at a time but then you would have to forgo the cement delivered by lorry..... or maybe not
 
14 m cube is a hell of a lot of concrete. You will need beefy assistance, and possibly a power float. You can make up a beam screed to leave the surface with a pattern for drainage and grip.

It would certainly be worth talking with the supplier about doing the work in three or more stages, and also asking for their view on re-inforcing fibres, and two layers of mesh. It's much bigger than anything I have done.
 
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sarabande said:
14 m cube is a hell of a lot of concrete. You will need beefy assistance, and possibly a power float. You can make up a beam screed to leave the surface with a pattern for drainage and grip.

It would certainly be worth talking with the supplier about doing the work in three or more stages, and also asking for their view on re-inforcing fibres, and two layers of mesh. It's much bigger than anything I have done.
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I shall definitely discuss with the supplier. He is also a local builder so I may get him to quote for the work.
I was also thinking of doing it in three or more stages. Definitely two layers of mesh.
Methinks this will become an expensive solution to keeping the boat in the drive!!
 
Yes concrete will set quite happily under water. Setting is a chemical reaction not a drying process. But if the water is moving due waves or current this could wash the cement paste out of the concrete before it has time to set.
 
DJE - I understood that the Romans had a cement which set underwater, some 2000 years ago. I believe it used volcanic ash. How did that work, please ?
 
Rick_A said:
Fine Tar planing's and a road roller. 40 tonne lorry's run on 2" of them in the forestry commission roads. Far cheaper, easier to lay and once rolled has a good finish.
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It's still essentially a loose surface, not a bound one. What sort of limit is there on gradient with planings? And how susceptible to water damage would it be?

I was quoted £30/ton for planings so it didn't seem especially cheap, but obviously still much cheaper than even concrete would be.
I also heard that quality is variable depending on how 'tired' the stuff is. So you might end up with lots of stones and not much actual bitumen.
 
Kelpie said:
It's still essentially a loose surface, not a bound one. What sort of limit is there on gradient with planings? And how susceptible to water damage would it be?

I was quoted £30/ton for planings so it didn't seem especially cheap, but obviously still much cheaper than even concrete would be.
I also heard that quality is variable depending on how 'tired' the stuff is. So you might end up with lots of stones and not much actual bitumen.
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Once rolled in, it is a hard wearing surface suitable for a driveway, and unless it has a small river flowing over it it will survive heavy rain, but it needs to be fine planing's to be rolled in tight. Cost depends on location for getting it to you. I pay £6/ton in a 20 tonne load but it come from less than 10 miles from me. Also its not prone to flaking off when salt is put on it in the winter like concrete is.
 
What about gradient limitations?
I've seen the stuff used on forestry roads before (there were old cats eyes mixed in with it) and you could scuff it with your foot. It didn't appear any different to well trafficed type one in terms of how 'together' it was.
 
sarabande said:
DJE - I understood that the Romans had a cement which set underwater, some 2000 years ago. I believe it used volcanic ash. How did that work, please ?
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Don't quote me on the details - concrete chemistry is complicated. But basically in a modern cement kiln you put in clay and limestone, grind it up fine and heat it (it needs lots of fuel). This produces a finely ground mixture of strong alkaline chemicals (mainly calcium and aluminium oxides and silica IIRC). When you add water to this mixture it reacts fairly vigourously and forms calcium and aluminium silicate crystals which cause the cement paste to solidify. The reaction continues long after the initial set and strength continues to increase for months and years. (Traditionally strength is measured 28 days after casting).
I assume that the heat in the volcanos whose ash the Romans mined produced similar effects to those in the modern kilns. Setting is not a drying out process - in fact the cement absorbs water. Drying causes concrete to shrink so it is to be avoided until the paste has gained enough strength to resist cracking. As long as there is no current or waves washing out the paste then underwater is just about the ideal place for concrete to set and cure. Standard test cubes are stored underwater at 20 degrees C for 28 days before they are crushed in a testing machine to prove the strength of the concrete.
More on volcanic cements here:- https://en.wikipedia.org/wiki/Pozzolan
 
Sarabande, look up Pozzolanic mortars. From memory, it originally referred to a certain type of volcanic ash which aided setting of lime mortars, discovered by the Romans and still used in a similar way in traditional lime mortars still use today. It also refers to additives in modern portland cement.

To the OP - I carry out small civil engineering projects of this nature, and the story of trying to shift a large quantity of rapidly-setting concrete on a hot day is only too familiar. Had you contemplated the use of interlocking concrete pavers? They're capable of taking the type of load you talk about and you can take your time over laying them, and as a semi-flexible surface they'll not fail catastrophically even under heavy load, unlike concrete.
 
Which os why I prefer to use the volumetric guys instead of readymix! The only time pressure is if they have another job to go to. Works out cheaper for the 4-5cu that I think I'll need.

Hadn't thought of using pavers, my worry would be ensuring that the ones at the lower end were well enough anchored in place that they wouldn't be at risk of slipping. I'll look into it though.
 
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