Jump to content

Concrete explanantion


Vijay

Recommended Posts

Morning guys,

 

Having a little issue with finding a concrete supplier who will give me the exact spec I require, which is:

 

DESIGNATED CONCRETE to external walls

  • Designation: RC32/40.
  • Fibres: Not required.
  • Aggregates:

- Size (maximum): 10 mm.

- Coarse recycled aggregates: RCA permitted.

- Additional aggregate requirements: Rounded coarse aggregate.

  • Special requirements for cement/ combinations: CEM 1
  • Consistency: S2 slump range with an ideal slump to around 80mm
  • Chloride class: Normal.
  • Admixtures: Waterproofing admixture below d.p.c. to wall system manufacturer's

approval or a high cement concrete to BS8007 with minimum cement content of 325kg/cu.m and water cement ratio of 0.5.

 

 

Just looking for some help with what things mean.

 

Firstly, the RC32/40 - is that the strength of the concrete? From other posts, I believe the R stands for reinforced as it will have rebar in it?

 

I've been assured that having a minimum cement content of 325kg pcm and water cement ratio of 0.5 will give me a waterproof concrete without the stupid expense of waterprrof additive, but has anyone come across this before as I'm a little worried about that?

 

Vijay

Link to comment
Share on other sites

Ask the person who specified that why it's so difficult to find and can it be relaxed. Yes 32/40 relates to the strength.

 

http://www.grabtrucks.com/ready-mix-concrete/mix-design/

 

Quote

RC32/40

"Designated Mix" achieving 40 Newton/28 day strength. Consists of a minimum cement content, 4-20mm stone, graded sand and water. Can be supplied with 10mm stone for specialist applications, subject to a cost premium. A water cement ratio mix to a 0.55 value.

 

Ask if it's essential the stone be <10mm.

 

I'm not sure I would rely on concrete being waterproof but perhaps you are adding braces to your belt.

 

 

 

 

Edited by Temp
Link to comment
Share on other sites

@Vijay, I have learned one thing about concrete: what is specified is often not what gets delivered. I say this on the basis of about five deliveries (or so), and having bought several lots of cheap concrete from a lets say 'informal' supplier.

 

Our main builder explained that, unless you know the production and delivery companies - the real people on the end of a phone - then you are likely to get generally strong concrete, or middling concrete or weak concrete.

 

Here are a few factors affecting what actually gets delivered

  • How do you know you arent getting the tail end of someone else's delivery - to a different spec - topped up with your spec?
  • How well do you know the company dispatcher (for the lorries)? Not at all? He'll smell it and might well take advantage of that
  • Is the concrete going to be pumped? If so more cement is added to make it 'slippier' in the pipes
  • Is the concrete going to be tested? If not, lie and tell everyone that samples will be taken.
  • Trying to squeeze prices? By accident I saw some cheap concrete being mixed. I lost some (more) hair that day. All the locals have subsequently warned me only to order from that person when the quality doesn't matter

This board  is full of people who have forgotten more than I'll ever know about the subject. But one thing is sure. Concrete is fascinating. Really fascinating. 

Link to comment
Share on other sites

1 hour ago, Temp said:

Ask the person who specified that why it's so difficult to find and can it be relaxed. Yes 32/40 relates to the strength.

 

http://www.grabtrucks.com/ready-mix-concrete/mix-design/

 

 

Ask if it's essential the stone be <10mm.

 

I'm not sure I would rely on concrete being waterproof but perhaps you are adding braces to your belt.

 

 

 

 

 

Thanks for that link, really helpful!

 

The mix is specific so it falls into the ICF properly and sets at the right rate, so not to cause bursts. 

Link to comment
Share on other sites

17 minutes ago, recoveringacademic said:

@Vijay, I have learned one thing about concrete: what is specified is often not what gets delivered. I say this on the basis of about five deliveries (or so), and having bought several lots of cheap concrete from a lets say 'informal' supplier.

 

Our main builder explained that, unless you know the production and delivery companies - the real people on the end of a phone - then you are likely to get generally strong concrete, or middling concrete or weak concrete.

 

Here are a few factors affecting what actually gets delivered

  • How do you know you arent getting the tail end of someone else's delivery - to a different spec - topped up with your spec?
  • How well do you know the company dispatcher (for the lorries)? Not at all? He'll smell it and might well take advantage of that
  • Is the concrete going to be pumped? If so more cement is added to make it 'slippier' in the pipes
  • Is the concrete going to be tested? If not, lie and tell everyone that samples will be taken.
  • Trying to squeeze prices? By accident I saw some cheap concrete being mixed. I lost some (more) hair that day. All the locals have subsequently warned me only to order from that person when the quality doesn't matter

This board  is full of people who have forgotten more than I'll ever know about the subject. But one thing is sure. Concrete is fascinating. Really fascinating. 

 

From my foundation pour I would agree with you and the pump bloke was really annoying with wanting to add more water to things. It was a smaller company and they really want my ICF concrete business, so are working to get it right. I've already warned them that any tickets for wrong concrete will be turned away and I will have a slump cone for random tests ;)

Link to comment
Share on other sites

9 minutes ago, Vijay said:

 

 

 

Hello mate - was it you pumping up the hill then?? ;)

It was - I'll  check the paperwork when I get home but think we ended up with a 120mm slump,  but that was for running through a two inch line pump over 35metres. 90mm should be fine for a boom. 

 

 

Link to comment
Share on other sites

10mm is pump grade - anything bigger and the pump guy may hate you.... sanded and extra cement to make it flow. 

 

And I've never heard of concrete being certified waterproof without an additive. Small price to pay it is wrong ... 

Link to comment
Share on other sites

22 minutes ago, PeterW said:

10mm is pump grade - anything bigger and the pump guy may hate you.... sanded and extra cement to make it flow. 

 

And I've never heard of concrete being certified waterproof without an additive. Small price to pay it is wrong ... 

 

Is that 100% right? The only reason I ask is the concrete supplier who was originally gonna supply my foundation concrete who knew it was gonna be pumped, has said he cannot do the ICF mix as he doesn't supply concrete with 10mm aggregate.

 

Small price to pay - is that said with a touch of sarcasm???? ;)

Link to comment
Share on other sites

Think we used r35 120mm sump through the boom (can't remember the aggregate but 10mm rings a bell).

 

Maybe slightly of topic but we have used 3 different pumps from 3 different companies at various stages. The best one was a 35m boom from a national company due to them having a shut of valve at the end of the boom so it was very quick to stop which was a major help for running up the gables. They also had the smallest nozzle for easiest control. 

Link to comment
Share on other sites

The 'R' doesn't mean it will have rebar - as long as you give the prescribed spec, they will worry about how to make it up. 

 

Interested in the water proof concrete part tho - why is this needed? If it's below DPC there is no reason for it that I'm aware of but would be interested to know if there is a specific reason?. 

Link to comment
Share on other sites

 Yep. Nudara icf. Learned on job from rebar to concrete it was a real learning curve. Made a few mistakes but will be doing a eps passive slab and icf again on second build so pretty happy with build up to now. 

Was meant type c35 concrete not r35. 

I think waterproof additive to concrete is more for used for basements constructed with icf but biggest problem I see with this is the concrete sealing around the plastic ties but that is a other topic.

I am a bit wary of your 80mm sump, who has spec'd that? How high are you pouring? 

Link to comment
Share on other sites

38 minutes ago, jamiehamy said:

The 'R' doesn't mean it will have rebar - as long as you give the prescribed spec, they will worry about how to make it up. 

 

Interested in the water proof concrete part tho - why is this needed? If it's below DPC there is no reason for it that I'm aware of but would be interested to know if there is a specific reason?. 

Yeah, it's for up to DPC. 

Link to comment
Share on other sites

30 minutes ago, Alexphd1 said:

 Yep. Nudara icf. Learned on job from rebar to concrete it was a real learning curve. Made a few mistakes but will be doing a eps passive slab and icf again on second build so pretty happy with build up to now. 

Was meant type c35 concrete not r35. 

I think waterproof additive to concrete is more for used for basements constructed with icf but biggest problem I see with this is the concrete sealing around the plastic ties but that is a other topic.

I am a bit wary of your 80mm sump, who has spec'd that? How high are you pouring? 

80mm slump was quoted by Polarwall. Height will be up to and including gables but obviously separated at each floor

Link to comment
Share on other sites

Obviously go with what the manufacturer says but the three icf manufacturers I looked at in detail was nudara, quadlock and amvic. They all quoted sump between 120-150mm  and use a poker especially around rebar (on second thoughts can't remember if amvic quoted a poker) .  

 

Link to comment
Share on other sites

But we need need some sort of damp proofing to stop rising damp even with ICF don't we?

 

Obviously I wouldn't want to pay for the crazy price of a waterproof additive and was told that just having a minimum cement content of 325kg pcm and water cement ratio of 0.5 will give me a waterproof concrete.

 

Link to comment
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
×
×
  • Create New...