concrete confusion 4

[sag04]

BS 5328 'concrete' replaced with BS EN 206-1 and BS 8500
In new code slump is reported to the nearest 10mm - in BS 5328 it was 5mm.
More confusing is in BS EN 206-1 the the slump is defined by class; as S2,S3,S4 and consistence is workability in BS 5328.
What about S1 class?.
How we specify the slump to redy mix supplier?
Please comments on this subject....... I will be obliged

 

[iandig]

I've got some useful slides I did as part of a presentation I wrote for a previous company. If you woud like me to send them accross to you I will. In my previous job, I actually went round to lots of companies in the UK to help explain this, so please feel free to contact me at: ian@geotechnical.co.uk
Anything I can do to help, please let me know

 

[BigH]

sag04 - I know the feeling - used to use 3inch slumps - right? Now we use the metric so it is 75mm. But, 75mm not permitted as it doesn't meet round-off - so have to specify 70 or 80mm. Ah, life, ain't it sweet . . . . . ??

 

[iandig]

Ok, brace yourself, I have dug out some of the info you were asking for.
The specified classes for slump include an S1, and go up to S5. The way the new system works is that is reccomends the use of slump classes, as opposed to the previous method of target slump - please note reccomends.
When it comes to what each slump must meet when measured, it depends on who you are, if you are the producer doing confirmity testing, you have a tighter range than for the user doing identity testing on site. The idea behind this new method, is a reflection of moving from British Standards to European Standards, and it is reflected in ALL the NEW BS EN, not just concrete, but soils, aggregates, kids toys, condoms etc....
Below is a summary of each class, target slump, conformity range and Identity range:
Class/target/conformty range/identity range
S1/20mm/0-60mm/0-70mm
S2/70mm/40-110mm/30-120mm
S3/120mm/90-170mm/80-180mm
S4/180mm/150-230mm/140-240mm
S5/>210mm/>210mm/>200mm
The're the numbers but you also need to be aware of the principle behind the change, and this is the crux of it all.
The leading people behind the production of ready mix concrete lay a significant proportion of blame for concrete failure at the door of consultants. They feel that what has become common practice to specify a minimum water:cement ratio, and target slumps of 50mm has resulted in a high proportion of concrete being delivered to site which is too stiff to place and which has then resulted in the site adding water to increase workability, thus having a detrimental effect on the water:cement ratio. If you have seen concrete placed in the UK you will have noted that it had become common practice to add water on site before placement -THIS IS BAD YOU MUST NOT DO IT!!!!
So, under the new system when you specify what you want, you tell the ready mix supplier the information you know and can control, this should include:
Design life of structure - guidance in BS EN 206/BS 8500
Exposure conditions - guidance in BS EN 206/BS8500
Target Strength - Structural design requirements
Maximum aggregate size (reference to reinforcement being used)
Concrete consistence class - Slump or flow in UK, sufficiently high to prevent the need to add additional water.
Any other relevant info to do with specific part of structure, allowable/required use of admixtures etc..
Things to do with cement type and blend, water cement ratio required use of admixtures etc.. will be under the control of the ready mix supplier, they know hao to make concrete and they should be able to guarantee that the concrete will meet the site requirements. They have to use high levels of confirmity testing to control this, and the site can/may use identitiy testing to check what has been delivered is what the supplier said he was going to deliver. This IS different to the old system, and is quite difficult to summarise here.
There is lots of info out there if you know who to ask, please do, you don't want to get bitten. The new system could mean that if concrete fails, it is always the designers fault if he doesn't understand the system!

 

[BigH]

iandig - for a well noted submission. Does make you wonder if going to EuroStds are worth it - I'm thinking of geotechnical engineers here. Whilst I do not work in UK, I will be contacting you about your kind offer above. In India here, I see for blinding concrete that the standards want the w/c ratio to be, like no higher than 0.5 - which is why 10MPa blinding concrete is testing out at 22MPa at 7-days!! Again, a nice discussion!

 

[iandig]

BigH - There is a real change in mentality under the new EN system, you need to get your head round their way of thinking, and also to the fact that there is a REAL difference between inferred and implied language. The easiest way to explain it is that in the UK if it say you will do X, then legally you must do X. Yes this is a legal obligation in the UK, the standards cover CE marking and it is a criminal offence to mis-lable goods with a CE marking. The principle is that ANY material covered by a EN can be CE marked, and in the UK our Government has adopted this as law. The ready mix industry are covering the provision of concrete by stating that their suppliers are supplying materials to the new BS EN and are CE marked, therefore the concrete they produce does not have to be, otherwise if it failed, it would be breaking the law!!. This may all sound a bit dramatic, but it does provide a bit of background to the implication of the new standard in the UK. OK now for the rest of Europe, their attitude is a bit more along the inferred understanding, which tends to go along the lines - "yes thats what the standards says, and we would do it if we used to do it, but we don't so we won't"
This is probably over simplified and very cynical, but it is a real problem, and a worry, and no one is really sure how it will pan out. We have already introduced the new standards for Concrete, aggreagtes and earthworks materials started from June this year, asphalt is to follow shortly - boy am I glad I changed jobs!

 

[BigH]

iandig - I might actually be coming to London for 4 days in October - home leave from India to US. I might be in touch to ask a few questions. I especially want to buy Eurocode 7 - and it scares me to think what is in it!

 

[iandig]

BigH, please feel free to contact me, if you let me know before you get here, I will forward my contact details

 

[sag04]

Hi jandig...great discussion and good summerization. Thanks a lot. belated one (sorry I was on 40 days vacation from work & subject..). It will be helpfull to me if you send me the slides.Thanks in advance.
regards

saleemangilath@hotmail.com