The Brew Cabin

Posted: **Wed May 18, 2011 12:51 pm**

Hi,

I hope someone can help here. I had some ready-mix concrete delivered yesterday and it just doesn't seem right. It's very gravelly and as you can see from the pictures it looks aweful cosmetically, despite being compacted and rollered. Trowelling didn't make any difference either.

The slab is 10' x 10' for an 8' x 8' hot tub weighing around 2,500kg. This will have decking round it and a timber building over that, both of which will extend beyond the concrete slab. The slab is therefore taking the weight of the tub, plus some of the decking & building weight.

The ground was dug out to firm earth with a geotextile underneath 4" of MoT type 1 sub-base, then a 1000g damp-proof membrane and 4" of Drivecrate (supplied by Aggregates)

I ordered 1 cubic metre and they delivered around 1.5, which makes me think 50% too much gravel was added. It certainly looks that way. The remainder was dumped in a skip I have on my driveway.

My concern is the strength and integrity of the slab. For instance, the pile in the skip can be broken up by hand. It's also now been a day and I can break stones off the surface of the slab with my fingers. Will it eventually crack & crumble with the hot tub, decking & building on top?

The company are investigating the mix for me, but I'd like an independant opinion. Will this slab be strong enough for its intended purpose, or do need to pull up this concrete and get a new lot delivered?

Would appreciate any advice, pictures are below...

Many thanks,
Avann.

Posted: **Wed May 18, 2011 4:59 pm**

Looks like a dry mix, should have added more water when it came off the mixer.

Posted: **Wed May 18, 2011 6:02 pm**

looks way too dry
what slump did you specify?
also looks like there are no fines in it
at best it needs latexing ,but personally i would accept concrete like that for a base
IMHO
LLL

Posted: **Thu May 19, 2011 8:23 am**

Thanks guys. The company have offered a full refund and a free replacement load. I'm taking that as the uncertainty will always play on my mind.

We dug it up last night and some areas were nicely bound, but mostly it just crumbled as there was loads of air in it.

Thanks again for the replies.

Posted: **Thu May 19, 2011 10:11 am**

Make sure you specify when you order like gen 1-3 or c20-40 etc

The higher the number the more cement content and ergo more strength and expense I'd have said a gen 1 or c20 would be fine and trowel up nice.

See the first barrow full then get the driver to add more water and wet it up, seanandruby will say that wetting it up affects it's structural strength but he works on terminal 5 etc for your hottub it will be fine. Wants to be creamy.

Posted: **Thu May 19, 2011 3:59 pm**

GB_Groundworks wrote:seanandruby will say that wetting it up affects it's structural strength but he works on terminal 5 etc for your hottub it will be fine. Wants to be creamy.

lol

Posted: **Thu May 19, 2011 5:02 pm**

you need fat to work concrete,which is cement and water
without that you have no hope
LLL

Posted: **Thu May 19, 2011 5:19 pm**

Giles I was going to say that you should not add water too the mix, it should arrive as it left the plant. not cooked it the jager

Posted: **Fri May 20, 2011 8:34 am**

if you order the right slump in the first place you won't need to add any water from the lorry. the stuff they have delivered looks total wrong. read the pages on this website about concrete and try to talk to someone technical and the suppliers your using so you can spec the right concrete.

Posted: **Fri May 20, 2011 10:20 pm**

aye, no amount of adding water will bring it back to the consistency you require if the batch has been overdosed with 50% excess coarse agg. kick off with the supplier and demand removal and replacement

Posted: **Sat May 21, 2011 7:24 am**

I'm the same as the next man when it comes to holding your dick and making a drink sign with the hands m8, on a big pour when concrete isn't spreading as easy as you would like. On these 2.5billion pound jobs the concrete is ordered to a set slump and neither i, nor God can change it. There is an engineer permanently stood by the pump etc: only he has the discretion to add a set amount of water, which will be in the lower litres. On a slab you can just about get away with it but on a wall where there is a chance of separation of the agg etc it needs to be up to spec. On a wall too much water becomes apparent with the drag lines and larger blow holes, making for a boney finish. Even secondary pokering doesn't help much. Apologies for doing my job right G B and D N ??? Back to main topic. I would expect the spec i ordered to be delivered, if the company has f***** up, then i'd expect them to put it right with no expense to me.

The Brew Cabin

Concrete quality - Do i have a problem with this concrete?