Concrete for hardcore base?

[BillieJNR]

I want to slightly alter the shape of my drive. This means paving an extra strip only 6-12" wide. As it doesn't seem practical to get a wacker plate into such a narrow strip, is it worth using concrete for the base? I'm assuming concrete would consolidate much easier than dry limestone?

[84-1093879891]

You could do that, I suppose. There's not much point in bringoing in a lot of kit to pave such a small strip, so a concrete bed/base would be the logical method. You could bed the blocks directly onto 100mm or so of a C20 equivalent concrete, and haunch the outer edge with the same.

[BillieJNR]

I had planned to use concrete as an alternative to hardcore and put sand over the top. All concrete sounds easier, except that I'll have to get it right pretty much first time! It's for a drive and there's a risk of getting a HGV on the new paving. I've excavated 150mm. Will the all concrete method survive an occaisional HGV? Thanks very much for your advice.

(Edited by BillieJNR at 4:44 pm on May 19, 2003)

[84-1093879891]

HGV?? For pavements carrying such heavy loads, the usual method is to use 80mm thick blocks and lay them on a 35-50mm sand bed over a 150mm concrete base, but, as yours is so narrow and at the edge of the pavemnt, laying on sand is not feasible, so that's why I suggest laying directly onto concrete. However, the depth of the concrete should be at least 150mm, given the loads you anticipate, and the haunching will need to be very strong, at least 150mm wide.

What's the construction of the existing driveway?

[BillieJNR]

Existing construction is standard: Roco Cobble Setts over sand and hardcore. Quite a decent job, done by the buliders, Seddons. HGV's will be whatever delivery vehicles have to come to us. No problems so far, including large brick wagon on a couple of occaisions and many sixteen tonners

[68-1093879172]

Please excuse me for latching on to someone else's query, but my D-I-Y question is related.

I want to extend my existing driveway, currently Marshall's Driveline 60. I would use their Driveline 50 and appreciate that there may be some colour difference.

The easiest way seemed to be to lay the new blocks directly on top of an existing 150mm thick concrete slab (40 sq metres). To keep the levels right for drainage, this would mean setting them on a 15mm - 30mm concrete bed on top of the slab rather than on compacted sand. I asked Marshall's advice and they strongly recommended against this, saying that I must have at least a 35mm sand bed on top of the concrete slab. I didn't ask why.

I don't really want to break up and dispose of such a big area of concrete. The drive extension is most unlikely to be used for anything other than cars. Is it really necessary to lay on compacted sand?

[84-1093879891]

The reason why the blocks should be laid on a minimum 35mm bed of compacted grit sand is that they have been specifically developed for flexible paving and laying them onto a rigid bed could cause problems. Obviously, it could all go swimmingly well, but if Marshalls were to suggest that such a laying method was suitable, they open themselves to all sorts of legal problems.

I suggested directr bedding to the previuous query because it is such a relatively small area - not much more than an extra soldier course, but for larger areas, I have to agree with Marshalls amd say the blocks really should be laid on a sand bed over a suitable base or sub-base. You could lay the blocks on sand over the existing concrete (see the Laying over an Existing Base page) if the situation is suitable, which would do away with the problem of breaking up all that concrete, but have a read of that page first, and see if it's possible.

[68-1093879172]

Tony, thanks very much for your prompt and helpful reply. You should be extremely proud of your website & forum and the help they have given so freely to so many people.

I can now see that laying over the existing concrete base is not the right way so I will be hiring a breaker and skip for a few days!