Cold

[dig dug dan]

AH! the most expensive property there!

[dodger41]

AH! the most expensive property there!

Technically speaking yes, but also needs the most money spent on it !!! :;):

[Noony]

pretty much the same luton, stopped us in tracks on thurs, so came home for weekend hoping monday be warmer?? might not be that way by looks of things!!

[lutonlagerlout]

the forecast looks a total bollix

went to a funeral today but need to get some shifts in

LLL

[hondacrm]

looking for a bit of advice here.

my builders are meant to be starting work on a garage next week. I think it will take 2/3 days to demolish existing wooden structure, excavate for foundations and soakaway.

With next week's weather forcast as it is, what criteria should i use regarding tempertures to be comfortable with concreting the foundation? Ground is hard, sandy type soil.

Also, would forst/frozen ground also cause problems?

I really don't want this to wrong.

thanks.

[lutonlagerlout]

i am sure brucie can give a definitive answer but foundation concrete is pretty much bullet proof
cover with hessian if hard frost/sub zero temps are forecast
3 degrees and rising is a must for brickwork/blockwork
again cover with hessian every night when frost etc is forecast
and plenty of tea :;):
LLL

[Carberry]

This time of year I would be covering it with polythene, 4" of straw then another layer of polythene to insulate it.

[Brucieboy]

hondacrm - I assume you're using ready mixed concrete? On the basis the plant isn't frozen up, most suppliers will pass the responsibility onto the customer when the air temperature is 2 degC or lower (this policy will vary somewhat from supplier to supplier - less so for the volume batch guys who mix at site). Some suppliers will also overstamp the delivery tickets confirming it's your responsibility - for others it may be in the small print. Also be aware that a lot of suppliers record telephone conversations to cover them if something goes pear-shaped.

What mix are you using? Typical foundation concrete for low rise buildings (unreinforced) varies between GEN 1 (C10) and GEN 3 (C20). Most suppliers will push for a blended cement, CIIIA (pronounced "c three a" - which is typically 50% ggbs) or CIIB-V (prounounced c two b v - which is typically 30% pfa), depending on which replacement material they stock.

Technically, concrete should not be placed if you cannot maintain its temperature at 5 degC until it's hardened sufficiently to withstand frost damage. However, if it's absolutely essential it goes ahead next week, I would beef up the mix to at least C30 or C35 (ask for an RC30 or RC35 which have definitive minimum cement contents and maximum water/cement ratios) and dictate CEMI (pronounced "cem one" which is 100% Portland cement) stressing you do not want a blended cement. This will harden much quicker than the first lot of mixes/cement types given above thus minimising the risk of early age frost damage. As LLL says, cover the top surface of the foootings with as much insulation/hessian as you can once placed. Avoid wetting up the mix on site. Ask for the correct workability in the first place - minimum S3 (this is slump class S3 which has a target slump of 120mm). The supplier will add extra cement to cover the higher slump - much better than adding water on site. This mix may cost a bit more than a GEN 1 CIIIA etc, but I can assure you it's worth it to give peace of mind.

Personally, if it's really cold, i.e. zero or below throughout the day, I'd leave it until the weather warms up a bit. Some will take a chance and get away with it, others won't be so lucky!! It's your choice.

[Brucieboy]

ps - I'd go with Carberry's recommendations for insulation if you can.

[Brucieboy]

pps - S3 slump is required if you're straight tipping the concrete, i.e. the mixer can get close to the footings. If you're barrowing it in, tell the supplier. They will then send it at 50mm slump or possibly S2 (target 70mm slump) plus the driver will know and not get a*sed off if he's only just been told when he turns up.

[hondacrm]

Brucie,

I assuming the supply will be ready mix using a mini mix truck which might just be able to gain access on the driveway. The spec on the drawing states 30N/mm2 concrete but no mention of slump, cement content or type of cement.

It is not essential for the work to go ahead next week but the guys will probably want to get on with it.

Thanks for the info and insulation recommendation from Carberry.

I will discuss all of the points raised with builders when they turn up next.

PS: For my information, why would the concrete supplier want to have varying cement types in the mix?

[lutonlagerlout]

PS: For my information, why would the concrete supplier want to have varying cement types in the mix?

cost

ggbs and pfa are byproducts of heavy industry
and therefore the cost is low
whereas portland cement is made specifically for what it does
cheers LLL

[Brucieboy]

LLL - the price differential now between CEMI and ggbs/pfa is not as great as it was in the 70's and 80's. Granted blended cements are a still bit cheaper per tonne than CEMI but bear in mind that for straight designed strength mixes with no specified minimum cement content or maximum free water/cement ratio, the actual batched cement contents will generally be 5-10% higher.

The main driver for using blended cements now is "sustainability". The construction industry is under increasing pressure from architects/specifiers to supply concrete with "green" credentials. CEMI has quite a high CO2 footprint in comparison with by-products such as ggbs and pfa, hence their common use. In addition, architects/specifiers are now demending we use more and more recycled aggregate rather than virgin aggregate. However, many don't appreciate that unless you have a readily available supply on the doorstep, the cost of transporting it (in terms of CO2) outweighs the benefit of using it.

This pressure has resulted in all of the plc's and a few of the smaller independent ready mixed suppliers being certified to BES 6001 (Building Research Establishment Environmental Standard 6001) - Responsible Sourcing of Construction Products. Go onto the "Greenbooklive" website to find out if a supplier is certified or visit their individual website. Among other criteria, this standard demands you measure CO2 emissions with the aim of trying to reduce them. We are now starting to see this standard as well as ISO 14001 (Environmental Management System) being specified as a mandatory condition of supply - basically, if you're not certificated, you cant supply the job.

Gone are the days when we only supplied bog standard mixes such as 1:2:4 or 21 N/mm2.

Sorry to go on and on, but like you and many of the other guys on this forum, I'm passionate about what I do.

[lutonlagerlout]

interesting stuff bruce , load of tosh really(by them) as we all know that to make cement you must drive all of the c02 out of chalk ,which involves kilns
its one of those industries that is never going to be green,no matter how they dress it up
LLL

[Mikey_C]

any body ever tried this stuff to help protect against frost, I didn't see till after I had actual gone out and brought some hessian, for this very purpose.