British standards - Revamped page

[Brucieboy]

LLL - not sure what you mean by "pavemix". Some volumetric and ready mixed concrete companies use proprietary names to describe some of their concretes - Cemex being one. If it's a C30 (technically it should be described as C25/30) with fibres, it should be fine. BS 8500 specifies a GEN 2 (C16/20) and GEN 3 (C16/20) for house and garage floors respectively that are unreinforced, i.e. contain no embedded metal. For reinforced floors, the minimum grade should be C25/30 unless something higher is specified by design.

To be clear, you only need air entrainment if the concrete is an external slab exposed to the elements, e.g. house drive, car park etc. However, if you do need it, the possible problem with a volumetric truck is the very short mixing time - this may not be enough to entrain the volume of air required to provide resistance to frost damage of the hardened concrete. The only certain method is to carry out an air test on site using a special pressure meter - generally only available on request - if you're lucky!! QSRMC and BSI certified companies (see below) have to test for air content routinely to ensure it falls within BS limits. If the air content is excessively high, it can be just as bad as having no air entrainment at all.

For info, with regard to the volumetrics (and some of the smaller ready mixed concrete companies), they can only supply designated (not to be confused with designed) concretes prefixed with GEN, RC, PAV and FND if they are third party certified by QSRMC (Quality Scheme for Ready Mixed Concrete) or kitemarked via BSI (British Standards Institution). They are, however, entitled to supply alternative designed concretes such as C16/20, C25/30 etc. QSRMC and BSI certified companies are subject to regular visits by external assessors who check the whole quality system from start to finish.

If you are powerfloating in the winter and assuming it's ultimately an internal slab , I strongly recommend you specify a C28/35 with a minimum cement content of 330 kg/m3 CEMI (100% OPC) or a higher grade if it's industrial use. Do not use blended cemnents containing ggbs or pfa such as CIIIA or CIIB-V. Finally, most of the big powerfloat boys specifically ask us NOT to include an admixture such as a plasticiser/water reducer as they can retard the set in the winter (as can ggbs / pfa) - they don't like working till 2 or 3 am the following morning. An 8 am start is ideal as long as it's not too cold. Cover with hessian if necessary - generally not done by the big boys.

Sorry to go on a bit (as usual)!!

[lutonlagerlout]

its a 150mm slab for a timber garage
we are using 2 layers of mesh @50 and 100mm
the volumetric fellas we use are licensed to work on the Motorway and they have been doing loads there,so i guess they are ok
custom concrete
i have done ground beams in c.35 and they dry up looking well
LLL

[Brucieboy]

The mix I've suggested above is fine for the floor for the timber garage in question. Generally, powerfloating with much less won't give a decent finish.

As for Custom Concrete - their website doesn't display either the QSRMC or BSI logo. However, if they're not certified, this doesn't mean to say you shouldn't use them. If you're happy with their quality, then fine.

Be aware though, if you are doing one of the bigger jobs, it's often written into a specification or BOQ that the concrete supplier must have a quality system to BS EN ISO 9001 (yet another standard!!!) certified by either QSRMC or BSI. Generally, not a problem if ignored until someone in high authority finds out or there's a quality issue such as cube failures.

[lutonlagerlout]

i think there is more info on their invoices
the weird thing is that C35 only costs £20 a metre more than leanmix
I think most of the cost is in haulage and plant cost
i find the volumetric drivers to be far more amenable than cemex driver who fell out of the ignorant tree and hit every branch on the way down :;):
LLL

[Brucieboy]

The price differential is not too far adrift - however, if you go for the C28/35, mcc 330 kg/m3 CEMI (without admixture), it's likley to be a few quid more (plus a bit more for poly-fibres if you want to use them).

I take your point about the volumetrics. They have, in some areas, gained a significant advantage over the ready mixed guys for the reason you state. The latter don't like hanging around for fear of missing out on the next load which could be a 5 miniute straight tip.

[lutonlagerlout]

IME the ready mix drivers only want straight back up and pours
I have paid £60 extra for barrow time and they still overfill the barrows and basically make a mess
the volu guys can do 6 metres in barrows without 1 drop on the pavement
and they only get paid per metre too
will ask for that spec cheers bruce
LLL