Forum: Other Pavings
Topic: Joints in concrete slab(s)
started by: TheRealAleman

Posted by TheRealAleman on 15 Aug. 2019,15:19
Hello all,

What a great resource this place is ... Just one little question though.

I am in the process of laying a driveway, and replacing the council laid paving slabs forming our original pathway along the side of the house. My intention is to do so with exposed aggregate concrete, using the Surfaced dressed method, and do the vast amount of work myself (Although I do have a son to do a chunk of the heavy work :D )

The 'main' slab will be 6.1 by 3.6m with a 8.5 by 1.2m 'path' down the side of the house. As the lay of the land is downhill from the road to our house, I'm laying acodrain about .75m from the house across the width of the 'drive' slab, and along the side of the 'path' slab, which will output into the existing storm water drain. So far I have dug down 250mm and laid 120-150mm deep type 1 MOT sub base which has been compacted with a whacker. My initial thoughts were to have the slab laid in one piece, but then I woke up when I realised that for a 100mm thick slab will be 3.5 cu metres of concrete, PLUS the decorative agg, and as an amateur is probably a bit much to lay in one go, plus a monolithic slab will almost certainly crack.

So according to Tony's formula I need expansion joints every 3 to 3.5m which  means that I can have a go at this over two days. It's easy enough to splt the main slab into 4, but I'm concerned about the path ... I seem to recall reading somewhere that when the slab is 'narrow' the standard formula doesn't necessarily apply, and you need to reduce the spacing of the joints ... but I can't find the page now :( So should I reduce the gap between joints down to say 1.5 or 2m for the 'path' slab?

The other question is simply should I reinforce the joints, although I have a firm sub base down, the ground here is clay, and what I don't want is the individual mini slabs moving or settling?

Posted by Tony McC on 17 Aug. 2019,12:30
Narrow labs of concrete impose awkward stresses, so we move away from the usual 'rule of thumb' spacing for movement joints, and, instead, look at never having sections greater than 3:1 in plan dimensions.

So, your 1200mm wid epath could have movement joints at up to 3600mm centres, but that would leave you with an odd 1300mm lenth at one end or in the middle. In that situation, I'd simply split the path into three roughly equal length bays of 2850mm.

Posted by TheRealAleman on 19 Aug. 2019,11:22
Thanks Tony, oddly enough that is exactly what I was planning to do.

Suppose I should stop prevaricating, and get the decorative agg ordered. ... put the form work down ... and have a chat with the local barrow mix boys :D

Posted by Tony McC on 27 Aug. 2019,12:49
Take photies and let us see the results....... :D
Posted by TheRealAleman on 27 Aug. 2019,14:05
Will do, Shifted 2 tonne of decorative agg over the weekend, using an idiot stick and barrow, Getting levels and Shuttering fitted, and ACO Drain is bedded in, should be ready for the concrete next week.

As I'm going for Alternate Bay construction, and pouring a couple of days apart, I'm going to use FillCrete FillaBoard for the joints which should take care of expansion issues, I'm going with Fibre mix in the concrete (As recomended by the concrete guy), Do I need to reinforce the joints, and should I allow for contraction as well as expansion? If so how do I 'debond' one side of the reinforcement rods?

Posted by jwill on 28 Aug. 2019,06:50
Idiot stick ha love it
Posted by Tony McC on 31 Aug. 2019,18:19
No need to worry about contraction in our climate and on such a relatively small scheme.
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