Cracked New Concrete

[SJM]

Laid a 600m2 pad of concrete within panelled walls outside mid September. Within 2 weeks this was the extent of the cracks.

In terms of preparations, clay floor vibration rolled within a inch of its life, plastic sheet, A393 mesh with steel chairs at 1m spacing. Concrete pumped in and pokered as it was laid. Plastic sheet over it that night and expansion joints cut every 6m within 24hrs.

Worked together with a groundworker/concrete chap to prep it then he laid it. Concrete supplier saying it’s not structural even though they haven’t been out.

What would you do? Accept it’s not structural or get a independent structural engineer out? Not sure what way to turn with it. TIA

 

[Yorkshire lad]

Have you laid it directly onto clay

 

[SJM]

Not directly. Was a plastic sheet but no stone under that as clay was very hard

 

[Dian Landman]

Not directly. Was a plastic sheet but no stone under that as clay was very hard

That is the problem i reckon. The clay will still expand and contract. The plastic is not enough. Needed a layer of gravel or sand between clay and concrete

 

[Lazy Eric]

It just looks like shrinkage/ surface cracking.

 

[SJM]

Will it get worse as time goes on or is that the extent of it?

 

[Lincs Lass]

For an out side concrete pad ,you really should have dug out the clay atleast 12 inches ,,layed a geotex membrane ,hardcored atleast 6 inches and compacted it solid ,then poured the concrete another 6inches thick with either rebar mesh or fibres ,,no need for the visqueen sheet .
Then cut the expansion joints

 

[kill]

Has it been over pokered? Looks bleady awful.

 

[SJM]

Maybe just one of life’s expensive lessons about not putting stone down then! We had dug down over 5m to get to this level as it was a bank before and brought it down to yard level. Clay really was very hard

 

[SJM]

Has it been over pokered? Looks bleady awful.

Wasn’t aware it could be? Agree it looks awful!!!

 

[milkloss]

Maybe just one of life’s expensive lessons about not putting stone down then! We had dug down over 5m to get to this level as it was a bank before and brought it down to yard level. Clay really was very hard

not a comment regarding your concreting, just a general question. Can ground heave once it’s had that much weight taken off it?

 

[kill]

Wasn’t aware it could be? Agree it looks awful!!!

Over pokering will settle concrete out so chippings at bottom and just cement and water will ride to the top and will give a very shiny finish to concrete but it's very weak

 

[Mc115reed]

Laid a 600m2 pad of concrete within panelled walls outside mid September. Within 2 weeks this was the extent of the cracks.

In terms of preparations, clay floor vibration rolled within a inch of its life, plastic sheet, A393 mesh with steel chairs at 1m spacing. Concrete pumped in and pokered as it was laid. Plastic sheet over it that night and expansion joints cut every 6m within 24hrs.

Worked together with a groundworker/concrete chap to prep it then he laid it. Concrete supplier saying it’s not structural even though they haven’t been out.

What would you do? Accept it’s not structural or get a independent structural engineer out? Not sure what way to turn with it. TIA

Who was in charge of the planning ? I’d never dream of laying concrete direct onto anything other than a hardcore membrane.... if it was your decision then it’s a bit of bad luck really but if the groundswork guys told you to do that I’d expect them too answer too it tbh ... it’s just surface cracking but those cracks will hold water and gradually get worse over time

 

[spin cycle]

could you not in effect use that as a base and put another 'finishing' screed over the top?....not an expert BTW

 

[Pennine Ploughing]

What mix spec was it,
A pump mix should have more cement in it due to the slump value of it being low,
Or was it just a R 35 watered down, if you ask for more water in the mix on site, you have to sign for it, and it can , if to much water is added void the spec, and no come back on concrete suppliers
Was it a hammered down price and lower spec

 

[RWG Contracts]

Looks like extreme plastic shrinkage. Should still be structural though if there’s mesh in there

 

[Sharpy]

We had something very similar in a shed 20 years ago, laid with a vibrating beam. Still fine today. I would say too much vibration and too much water addition leading to aggregate sinking. Your clay base will have bugger all to do with this, although you may hit problems if water wants to move under the concrete.

 

[RWG Contracts]

We had something very similar in a shed 20 years ago, laid with a vibrating beam. Still fine today. I would say too much vibration and too much water addition leading to aggregate sinking. Your clay base will have bugger all to do with this, although you may hit problems is water wants to move under the concrete.

I wouldn’t say it’s to much vibration, just far to wet

 

[Sharpy]

I wouldn’t say it’s to much vibration, just far to wet

Just ours had 3 goes with the screed, only difference from all the rest of the concrete we laid with a wooden beam.

 

[RWG Contracts]

Just ours had 3 goes with the screed, only difference from all the rest of the concrete we laid with a wooden beam.

ive never seen concrete separate from over vibrating So I just presumed you’d have to go mental for separation to happen