Chalk as a base? Concrete expansion joints?

2 questions for the wise ones out there?

New road going in for a residential house - acquired about 500 m3 of chalk, best quality I have seen for a while. Planning on using it for a base followed by a few inches of road Plainings whacked down hard ready for a tarmac cap in the future. Will chalk @ maybe 300mm be enough / work at all? It's a substitute for hard core which is getting expensive!

Secondly, re concreting yards, 8 inch with re bar. I know I need to put expansion joints in, thinking ever 6 m. Current plan is to pour every other then when it sets fill in the others. Question is I think you can buy expansion kits, otherwise it's cut out and fill with mastic / resin. What would people recommend?
 
I always cut expansion joints in feet, 2-3 times the slab thickness, so your 8" concrete would have a cut every 24 foot. You only need to cut your joints about 25% of the slab thickness, you're only controlling where the concrete will expand. Depending what your slabs for you might not need to fill the joints with mastic bit if I'm on a job where the joints need filling I put two disks in the floor saw then fill the gab with concrete sealant
 

Greenasgrass

Member
Location
N Ireland
They are called expansion joints but they are actually to control contraction / cracking as the concrete drys out. Expansion / construction joints are only needed every 40m so it's unlikely that you need to pour your bays hit and miss. You need to stop your reinforcement back 50mm either side of your saw cut position. As above cut min 25% depth of the slab to control the crack. It's important to put anti crack bars at 45 degrees to any sharp projection - 4 corners of a manhole, at the corner of a building. Correct positioning of saw cuts are the secret to preventing cracking. That and curing the concrete properly. Concrete likes to crack out from the point of a gable return or corner of a manhole or such like.
 

Greenasgrass

Member
Location
N Ireland
Every 40m? If the pads 40m square at 200mm deep that means you'd pour 320 cube without an expansion joint?
Provided that you are able to physically handle the concrete - yes. As i said contraction is the main reason that concrete cracks not expansion. So encouraging it to crack where you want it to crack is the secret - i.e. at the saw cuts which in theory should be the weakest point.
 

Wombat

Member
BASIS
Location
East yorks
We use chalk for most of our bases and tracks, it's fairly cheap here ( 2/3 price of hard core) and with a roll will go down very hard especially after a rain on it
 

Derky

Member
Location
Bucks/oxon
If your doing it in every other 6 metre bays then put dowels through the shuttering, then when you concrete the next bay push on some joint onto the dowels and concrete, by far the tidiest way.
 

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