Filling in steep driveway center.

[MikeT]

Hello,

I've got a driveway with two concrete strips and dirt in the middle - which I'm about to fill in. It's really steep (use low range in the ute). Although it's 1.5m3 which would ordinarily warrant a truck - It's 20m long so I don't reckon I can get that all levelled in one go (given the steepness - and how long it's been since I've laid a slab). So are planning on getting cement bags and aggregate and sand (about to check the prices - assuming that it's cheaper buying it seperate) - and will do it in 4 strips mixing myself.



So a couple of questions:
-I would like as high a slump as I can and still have it workable, but not really sure how to go about that, have only ever mixed concrete for standard applications (have helped lay a real steep driveway before but it was trucked concrete).
- how much quicker is using a mixer - have done both barrow and mixer but it's been a while. Setting up a mixer on the drive is another matter.
- haven't checked out the reo sizes but was planning on using around 50mm*100mm squares - given it's not real wide (750mm)

Cheers,
Mike.

[addo]

Mixer should be about twice the speed of barrow mixing. I batch using 20 litre buckets, and would suggest 20mm aggregate.

Two full buckets of aggregate, two 2/3 buckets of sharp sand and two 1/3 buckets of off-white cement. Water will vary with sand and aggregate wetness, but from 9-13 litres. That will give you a pretty full barrow - more than you can mix in one go with a shovel. Say 0.1m³...

For 750mm - unless you're planning to load it up - I would just go about 80-90mm thick and skip the reo. Joint it across every 3' or so, and cut every 2nd joint with the trowel before it goes off.

[Terrian]

Hello,

So a couple of questions:
-I would like as high a slump as I can and still have it workable, but not really sure how to go about that, have only ever mixed concrete for standard applications (have helped lay a real steep driveway before but it was trucked concrete).

higher the slump, the wetter the mix, just add more water to get a higher slump/

- how much quicker is using a mixer - have done both barrow and mixer but it's been a while. Setting up a mixer on the drive is another matter.

Lots quicker, lots less backbreaking as well.

- haven't checked out the reo sizes but was planning on using around 50mm*100mm squares - given it's not real wide (750mm)

non standard reo, personally I would just buy a sheet of f52 (yeah, pretty light, but no going to have much load on the center of the driveway) and cut that into strips.

[MikeT]

Thanks Addo and Terrian - thought as much with the slump (except I meant I wanted as low a slump as possible so it doesn't flow)

With the reo - I don't think I could not put any in - besides that I always have to overdo things (which you can afford more to do if doing it yourself) the drive isn't totally straight and so wheels often venture into the dirt center strip. I've actually had a 5 tonne truck venture down to drop off some plasterboard which if you could see the drive is quite a feat - he was down before I could say no.

I was going to do it in strips the same length as the current strips - but as each side varies and ones 5.5m - I might shorten them somewhat. Unfortunately one side has a change in steepness at a different point than the other so I'll have to do a little jiggery pockery around there.

[Terrian]

Thanks Addo and Terrian - thought as much with the slump (except I meant I wanted as low a slump as possible so it doesn't flow)

yeah, I thought that is what you meant

With the reo - I don't think I could not put any in - besides that I always have to overdo things (which you can afford more to do if doing it yourself) the drive isn't totally straight and so wheels often venture into the dirt center strip. I've actually had a 5 tonne truck venture down to drop off some plasterboard which if you could see the drive is quite a feat - he was down before I could say no.

buy a sheet or two of f72 if you are expecting heavy traffic, cross drill holes into the existing concrete and slide in some y12 reo rod, will help tie all the slabs together.

I was going to do it in strips the same length as the current strips - but as each side varies and ones 5.5m - I might shorten them somewhat. Unfortunately one side has a change in steepness at a different point than the other so I'll have to do a little jiggery pockery around there.

have fun...

[ian]

I've got a driveway with two concrete strips and dirt in the middle - which I'm about to fill in. It's really steep (use low range in the ute).
So a couple of questions:
-I would like as high a slump as I can and still have it workable, but not really sure how to go about that, have only ever mixed concrete for standard applications (have helped lay a real steep driveway before but it was trucked concrete).

it's nearly 20 years since I supervised a concrete pour in a situation like the one you describe.
We used a mix that contained about 350kg of cement per cu.m plus 150kg of fly ash (that's 500kg of dust sized fines per cu.m — which is 20% of the mix) plus water reducing and air entraining additives so that it could be mixed in the truck. I don't recall what the coarse medium and fine aggregate proportions were but the minimum slump that could be hand placed was 40-45mm — and that was a lot of work, the crew preferred to work with 50–60mm slump. One problem we didn't forsee was that with a mix that stiff we couldn't order a full truck load because if we did the transit mixers would arrive on site with a partially mixed load.

I was going to do it in strips the same length as the current strips - but as each side varies and ones 5.5m - I might shorten them somewhat. Unfortunately one side has a change in steepness at a different point than the other so I'll have to do a little jiggery pockery around there.

even if you have to angle your joints have them line up either side. otherwise the risk of the centre slab cracking in line with the joints one side which then leads to cracks in the other wheel path is too great.

[MikeT]

Ian,

With making the joins line up. This will result in one of the joins been at about 45degrees. If I match it with a straight line it'll result in corners that I would've though would break off. I could pull it back an inch or two each side to pull back the angle or - now this is getting cute - use a bit of thin ply and make it curved (I actually like that idea). Should the lengths of each section be the same or would it be fine to split them up into two center slabs to one side (to make it easier for me to pour)

And the concern with cracking makes me think that tieing the center slabs in with the sides might tend to prompt the same. The centre may settle or shrink or whatever and then affect/be affected by the sides. My original plan was to just key them in to the ground and maybe tie them in to the slab just laid down the hill.

cheers,

and I hope everyones had a good chrissy

[ian]

With making the joins line up. This will result in one of the joins been at about 45degrees. If I match it with a straight line it'll result in corners that I would've though would break off. I could pull it back an inch or two each side to pull back the angle or - now this is getting cute - use a bit of thin ply and make it curved (I actually like that idea). Should the lengths of each section be the same or would it be fine to split them up into two center slabs to one side (to make it easier for me to pour)

what you want to avoid is the situation where the joint/crack in one wheel path translates through the centre slab and induces a crack in the other wheel path.
Lining the joints up will help prevent this
tieing the three slabs together may promote this

as to your 45° join, the way to handle this is to come in from the edges at about 70° for about 300mm and then head to the other end of the join


ian

[MikeT]

Another quick question - expansion joints. It seems as if the current slabs don't have any - unless they are hidden underneath a little concrete. Not sure how much concrete expands but I would've thought it'd cause a problem. Perhaps they were left out because having them there would allow the slab to slide down the hill somewhat (which is a concren of mine). The expansion joints I've used before are about 10mm wide.

As I said before I am planning on keying the slabs into the ground with a small trench anyway. Is it possible to get thinner expansion joints - or just use a couple of strips of old tyre rubber - which I have plenty of.

I'm also considering tieing each slab with the one down the hill but are concerned this would mess up any independent expansion (I've read you can get ones that allow movement but can't find them anywhere).

Just tell me if I'm getting too concerned with detail here - the ground should be pretty stable - incidentally - the gradient at the steepest is over 1/3.

[Terrian]

Another quick question - expansion joints. It seems as if the current slabs don't have any - unless they are hidden underneath a little concrete. Not sure how much concrete expands but I would've thought it'd cause a problem. Perhaps they were left out because having them there would allow the slab to slide down the hill somewhat (which is a concren of mine). The expansion joints I've used before are about 10mm wide.

As I said before I am planning on keying the slabs into the ground with a small trench anyway. Is it possible to get thinner expansion joints - or just use a couple of strips of old tyre rubber - which I have plenty of.

I'm also considering tieing each slab with the one down the hill but are concerned this would mess up any independent expansion (I've read you can get ones that allow movement but can't find them anywhere).

Just tell me if I'm getting too concerned with detail here - the ground should be pretty stable - incidentally - the gradient at the steepest is over 1/3.

you are getting too concerned, have a look at other concrete drives in the area and see what others have done.