Strange mix

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NT

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Mar 16, 2012, 5:19:15 PM3/16/12
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While the guys were unloading supplies I looked at the recommended mix
ratios on a sack of mastercrete, abd was surprised to see recommended
a mix of 1 cement to just 1.5 sand! Plus 2.5 coarse aggregate. They're
taking the michael surely.


NT

charles

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Mar 16, 2012, 5:24:57 PM3/16/12
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In article
<e49a4c80-e52e-4f52...@d17g2000vba.googlegroups.com>,
That's 1 cement to 5 ballast - it's what I remember from my concrete mixing
days - over 30 years ago.


> NT

--
From KT24

Using a RISC OS computer running v5.18

TMC

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Mar 16, 2012, 6:53:11 PM3/16/12
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"charles" <cha...@charleshope.demon.co.uk> wrote in message
news:52718a08...@charleshope.demon.co.uk...
> In article
> <e49a4c80-e52e-4f52...@d17g2000vba.googlegroups.com>,
> NT <meow...@care2.com> wrote:
>> While the guys were unloading supplies I looked at the recommended mix
>> ratios on a sack of mastercrete, abd was surprised to see recommended
>> a mix of 1 cement to just 1.5 sand! Plus 2.5 coarse aggregate. They're
>> taking the michael surely.
>
> That's 1 cement to 5 ballast - it's what I remember from my concrete
> mixing
> days - over 30 years ago.
>
>
>> NT

Now my maths isn't brilliant but 1.5 + 2.5 = 4

so wouldn't that be 1 cement to 4 ballast?

That seems too strong for normal use

as coarse aggregate is specified I would be looking at about 1 cement to 5.5
ballast (2 sand 3.5 aggregate)

Regards


charles

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Mar 16, 2012, 7:02:36 PM3/16/12
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In article <UrGdnW0DUMfLWf7S...@bt.com>,
TMC <an...@nowhere.co.uk> wrote:

> "charles" <cha...@charleshope.demon.co.uk> wrote in message
> news:52718a08...@charleshope.demon.co.uk...
> > In article
> > <e49a4c80-e52e-4f52...@d17g2000vba.googlegroups.com>,
> > NT <meow...@care2.com> wrote:
> >> While the guys were unloading supplies I looked at the recommended mix
> >> ratios on a sack of mastercrete, abd was surprised to see recommended
> >> a mix of 1 cement to just 1.5 sand! Plus 2.5 coarse aggregate. They're
> >> taking the michael surely.
> >
> > That's 1 cement to 5 ballast - it's what I remember from my concrete
> > mixing
> > days - over 30 years ago.
> >
> >
> >> NT

> Now my maths isn't brilliant but 1.5 + 2.5 = 4

yes - too late at night - I woke at 4 this morning and couldn't get back to
sleep.

> so wouldn't that be 1 cement to 4 ballast?

> That seems too strong for normal use

What is normal?


> as coarse aggregate is specified I would be looking at about 1 cement to
> 5.5 ballast (2 sand 3.5 aggregate)

TMC

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Mar 16, 2012, 7:16:06 PM3/16/12
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"charles" <cha...@charleshope.demon.co.uk> wrote in message
news:527192f8...@charleshope.demon.co.uk...
> In article <UrGdnW0DUMfLWf7S...@bt.com>,
> TMC <an...@nowhere.co.uk> wrote:
>
>> "charles" <cha...@charleshope.demon.co.uk> wrote in message
>> news:52718a08...@charleshope.demon.co.uk...
>> > In article
>> > <e49a4c80-e52e-4f52...@d17g2000vba.googlegroups.com>,
>> > NT <meow...@care2.com> wrote:
>> >> While the guys were unloading supplies I looked at the recommended mix
>> >> ratios on a sack of mastercrete, abd was surprised to see recommended
>> >> a mix of 1 cement to just 1.5 sand! Plus 2.5 coarse aggregate. They're
>> >> taking the michael surely.
>> >
>> > That's 1 cement to 5 ballast - it's what I remember from my concrete
>> > mixing
>> > days - over 30 years ago.
>> >
>> >
>> >> NT
>
>> Now my maths isn't brilliant but 1.5 + 2.5 = 4
>
> yes - too late at night - I woke at 4 this morning and couldn't get back
> to
> sleep.
>
>> so wouldn't that be 1 cement to 4 ballast?
>
>> That seems too strong for normal use
>
> What is normal?

C20

Weatherlawyer

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Mar 16, 2012, 9:15:44 PM3/16/12
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On Mar 16, 10:53 pm, "TMC" <a...@nowhere.co.uk> wrote:
> "charles" <char...@charleshope.demon.co.uk> wrote in message
>
> news:52718a08...@charleshope.demon.co.uk...
>
> > In article
> > <e49a4c80-e52e-4f52-af9c-a97bc9375...@d17g2000vba.googlegroups.com>,

Weatherlawyer

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Mar 16, 2012, 9:29:22 PM3/16/12
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On Mar 16, 10:53 pm, "TMC" <a...@nowhere.co.uk> wrote:
>
> I would be looking at about 1 cement to 5.5 ballast
> (2 sand 3.5 aggregate)

If you were using brick sand, the people who are selling cement would
be about right, on the generous side. And I'd stick with it if the
gravel was river gravel not broken in a quarry's mill.

You can make concrete a lot weaker. It all depends on what you are
using it for. And how much trowelling up you are going to give it.

The more you mess with the concrete the more likely the fat is to come
out of the mix. Tamping it and leaving it will be OK with a weaker mix
but if you are going to tamp it then float it...

But I think I'd go for a coarse sand, replacing half a shovel of that
with gravel: 2 cement 3 coarse sand 8 mixed size aggregate.

harry

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Mar 17, 2012, 4:01:06 AM3/17/12
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The ultimate strength of concrete depends on the aggregate. So adding
more cement to a weak aggregate is of no help.

If you look at broken concrete, the fracture line is through the
aggregate ,not between.

A lot of todays aggregates are dredged and hence of all sorts of
mixed up shit.
The best aggregates are quarried stone, crushed and graded.
The best stone is stuff like basalt, quartz and granite, which you
don't often see nowadays.

NT

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Mar 17, 2012, 3:38:57 PM3/17/12
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Can we drop that ino the wiki somewhere?


NT

Bolted

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Mar 17, 2012, 5:19:03 PM3/17/12
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There is nothing wrong with good quality gravel and it would be really
stupid for some-one in the South-East to go chasing after crushed
granite for concrete. Flint pebbles are hard as, err, nails, well
harder than nails then. And, with a crushed aggregate (rather than a
naturally rounded gravel) you need to up the cement ratio to get the
same strength of concrete.

Bolted

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Mar 17, 2012, 5:56:27 PM3/17/12
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On Mar 16, 9:19 pm, NT <meow2...@care2.com> wrote:
That's C35 - good enough for a road.

The Natural Philosopher

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Mar 17, 2012, 8:34:47 PM3/17/12
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good enough for a nuclear bunker probably.


--
To people who know nothing, anything is possible.
To people who know too much, it is a sad fact
that they know how little is really possible -
and how hard it is to achieve it.

harry

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Mar 18, 2012, 3:00:44 AM3/18/12
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On Mar 17, 7:38 pm, NT <meow2...@care2.com> wrote:
> NT- Hide quoted text -
>
> - Show quoted text -

The aggregate you use depends on what you want the concrete for.
For most purposes dredged gravel is OK.

But it is very variable, if you buy readymixed concrete, the providers
make constant checks by analysing samples.

Proper paving stones are often made with granite as they can be made
thinner.

The point was that adding cement beyond a certain level is useless if
the aggregate is weak.

Bolted

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Mar 18, 2012, 4:50:35 AM3/18/12
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On Mar 18, 7:00 am, harry <haroldhr...@aol.com> wrote:
> On Mar 17, 7:38 pm, NT <meow2...@care2.com> wrote:
>
>
>
>
>
>
>
>
>
> > On Mar 17, 8:01 am, harry <haroldhr...@aol.com> wrote:
>
> > > On Mar 16, 9:19 pm, NT <meow2...@care2.com> wrote:
>
> > > > While the guys were unloading supplies I looked at the recommended mix
> > > > ratios on a sack of mastercrete, abd was surprised to see recommended
> > > > a mix of 1 cement to just 1.5 sand! Plus 2.5 coarse aggregate. They're
> > > > taking the michael surely.
>
> > > > NT
>
> > > The ultimate strength of concrete depends on the aggregate.  So adding
> > > more cement to a weak aggregate is of no help.
>
> > > If you look at broken concrete, the fracture line is through the
> > > aggregate ,not between.
>
> > > A lot of todays aggregates are dredged and  hence of all sorts of
> > > mixed up shit.
> > > The best aggregates are quarried stone, crushed and graded.
> > > The best stone is stuff like basalt, quartz and granite, which you
> > > don't often see nowadays.
>
> > Can we drop that ino the wiki somewhere?
>
> > NT- Hide quoted text -
>
> > - Show quoted text -
>
> The aggregate you use depends on what you want the concrete for.
> For most purposes dredged gravel is OK.

A quick google gave some examples of purposes for which dredged gravel
was OK - Sizewell B and the Dartford bridge being the two most
memorable ones.

I think it'll be ok for the slab I am pouring today in my garden. I
am not sure whether it is marine or pit sourced, but it would be
ridiculous to care.

Weatherlawyer

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Mar 18, 2012, 10:32:52 PM3/18/12
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On Mar 17, 9:19 pm, Bolted <boltm...@mailbolt.com> wrote:
>
> And, with a crushed aggregate (rather than a
> naturally rounded gravel) you need to up the cement ratio to get the
> same strength of concrete.

I find it difficult to believe that rounded gravel can interlock they
way sharp edged stuff can.

harry

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Mar 19, 2012, 3:55:21 AM3/19/12
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We're not talking about glueing.
The range of aggregates is in a concrete formulated so that the
smaller stuff fills the voids between the bigger. Angular aggregates
just need a different formulation because the voids are smaller.
There is no problem in getting the cement to "stick" to the
aggregate.
When concrete fails the aggregate fractures and also the crack runs
through any voids arising through bad aggregate formulation or
segregation that has occurred in the handling of the product..

Bolted

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Mar 19, 2012, 6:21:21 AM3/19/12
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On Mar 19, 2:32 am, Weatherlawyer <weatherlaw...@gmail.com> wrote:
You need to add more water to crushed, angular, aggregate to get a
workable mix. More water in the mix = weaker concrete, so you need to
add more cement to compensate.

harry

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Mar 19, 2012, 3:05:52 PM3/19/12
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What you need is a vibrator.

Bolted

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Mar 19, 2012, 7:28:51 PM3/19/12
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It doesn't work like that. You still need more water to get it
plastic, with or without vibration. Add the poker, and the gravel mix
still wins as you can reduce the water in that too. So you pay extra
(as a DIYer) in poker hire, and some extra for additional cement on
top. Still not a winner.

harry

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Mar 20, 2012, 1:09:07 PM3/20/12
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> top.  Still not a winner.- Hide quoted text -
>
> - Show quoted text -

We have established that adding cement doesn't necessarily make it
stronger.

Bolted

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Mar 20, 2012, 1:50:03 PM3/20/12
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On Mar 20, 5:09 pm, harry <haroldhr...@aol.com> wrote:
> We have established that adding cement doesn't necessarily make it
> stronger.

Like for like, it does. Go and do some reading, you are wrong (and
boring me).

The Natural Philosopher

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Mar 20, 2012, 4:18:25 PM3/20/12
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harry wrote:

> We have established that adding cement doesn't necessarily make it
> stronger.

No you simply stated it as a fact with zero supporting evidence, harry.
That is not the same as establishing it as a fact.

harry

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Mar 21, 2012, 3:33:31 AM3/21/12
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On Mar 20, 8:18 pm, The Natural Philosopher <t...@invalid.invalid>
wrote:
> harry wrote:
> > We have established that adding cement doesn't necessarily make it
> > stronger.
>
> No you simply stated it as a fact with zero supporting evidence, harry.
> That is not the same as establishing it as a fact.

This common knowledge to anyone in the construction business with even
half a brain.

Part of my previous job was laying concrete.
If you want your concrete more fliud/workable you can add/have added
chemicals without affecting quality..
Adding superfluous cement is not helpful and expensive.
Or for small amounts you can buy the dry cement with the suff pre-
added.

http://en.wikipedia.org/wiki/Plasticizer#For_concrete

The Natural Philosopher

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Mar 21, 2012, 5:29:37 AM3/21/12
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harry wrote:
> On Mar 20, 8:18 pm, The Natural Philosopher <t...@invalid.invalid>
> wrote:
>> harry wrote:
>>> We have established that adding cement doesn't necessarily make it
>>> stronger.
>> No you simply stated it as a fact with zero supporting evidence, harry.
>> That is not the same as establishing it as a fact.
>
> This common knowledge to anyone in the construction business with even
> half a brain.
>

No, it isn't. Its well known that you can make a porous and weak mix
with lots of airgaps by using less cement. Its called in the limit a
screed.

Its common knowledge that increasing the cement to remove those airgaps
leads to a stringer more frost resistant mortar or concrete.

Its called a 'strong' mix, by all the people in the trade.



> Part of my previous job was laying concrete.

No wonder you got fired.

> If you want your concrete more fliud/workable you can add/have added
> chemicals without affecting quality..

That much is at least true.

> Adding superfluous cement is not helpful and expensive.

No one was talking about adding 'superflous' cement. The ideal mix is
where the interstices between the ballast grains are just fully filled
with cement and the final mix is fully waterproof.

That's why you ideally need a graded ballast of shingle, larger stones
and sand, of varying grades. Ultimately its a composite where the cement
fills the gaps between the ballast fully - that's as good as it gets
without steel added.

Adding extra cement beyond that doesn't weaken the mix much but reducing
it below that does - simply because of the porosity.

And, finally, I believe it was your assertion that the ballast was in
fact weaker than the cement and would give first. I dont ncesessarily
believe that is the case with granite or flint, under non shock loads,
but if that IS the case then it directly contardicts your assertion that
cement is weaker than the ballast and more cement will make it even weaker.


> Or for small amounts you can buy the dry cement with the suff pre-
> added.
>
> http://en.wikipedia.org/wiki/Plasticizer#For_concrete


stuart noble

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Mar 21, 2012, 5:49:28 AM3/21/12
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IME plasticiser improves all mixes, and it's truly amazing how little is
required (considerably less than the recommended dose usually).
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