Concrete for foundations

steamjetjoe

Hello,

Could someone please tell me the difference between 25N & 30N concrete for foundations.

Its for a block wall about 6 foot high. Party wall

smashey

It's to do with the srength of the concrete.

Have a look at this.

steamjetjoe

Cheers Smashey,

One other question.... I hope to be able to fit the readymix truck up the side of the house. Now taken into account that the founds will be dug it only leaves 8 foot 7 inches to play with for the truck to fit, Plus the wheel will be right on the edge of the trench, whick is not a clever idea.

1. Can anybody tell me the with of these trucks ( its a 8 cubic metre load truck)

2. Any suggestions on how to get aroung the problem if the truck cannot fit.

I did ask the company but the woman simply hadn't a clue if the truck would fit or not.

Mellor

A few lads and a few wheel barrows. Fill at the front run down the side pour.

steamjetjoe

Mellor wrote:

A few lads and a few wheel barrows. Fill at the front run down the side pour.

Yes but 8 cubic metres of readymix will be back breaking.

I found out the width of a truck, its 8 foot. So I might just get away with it.

muffler

If you tell them its tight they can send a lorry with a good chute on it.

ircoha

steamjetjoe wrote:

Yes but 8 cubic metres of readymix will be back breaking.

I found out the width of a truck, its 8 foot. So I might just get away with it.

I dont think so as the driver will not risk the trench collapsing.
It is a double axle at the back with some serious load: see below.

I have posted elsehwere that if u rent a small CONCRETE vibrator it will ease the moving of the concrete along the trench and help to level it also.
The other consideration is that if doing by hand, the truck may not wait that long.
8 cubic meteres is the guts of 20 tonnes so perhaps a pump might be worth looking at.
The other option is to look at what is called mini-mix trucks: they mix on site and may wait around longer.

Avns1s

Had a similar situation to the OP recently with concrete for foundations and the driver was suggesting using a garden rake to move it along the trench. Also, it's just foundations for a wall so mix it up with plenty of water, it'll "flow" a bit easier. Still very heavy stuff though!!!

ircoha

Avns1s wrote:

Had a similar situation to the OP recently with concrete for foundations and the driver was suggesting using a garden rake to move it along the trench. Also, it's just foundations for a wall so mix it up with plenty of water, it'll "flow" a bit easier. Still very heavy stuff though!!!

Mixing water seriously reduces the design strength of the concrete and should not be suggested on such a forum: there are enough cowboys/shoddy practices without the DIY-ERs getting into it

Johnniep

ircoha wrote:

I have posted elsehwere that if u rent a small CONCRETE vibrator it will ease the moving of the concrete along the trench and help to level it also.

Sorry ircoha, but OP, do NOT do this. Moving the concrete in a trench using a poker will cause segregation of concrete!!!! Never good.

The idea of driving a fully laden concrete truck that close to an open trench sets off alarm bells! Just think of the damage the truck could cause if the trench collapsed and if this is your site, you are responsible!!!

If you are just doing mass concrete strip footings, a 20N20 (or even a 25N20 mix would suffice). The important thing for concrete below ground is durability which is directly related to the cement content of the concrete and not necissarily the strength (although they are directly linked)

Hope this helps.......

Avns1s

ircoha wrote:

Mixing water seriously reduces the design strength of the concrete and should not be suggested on such a forum: there are enough cowboys/shoddy practices without the DIY-ERs getting into it

The Op has said that the concrete is for a 6' high wall. Unless it is almost totally water, it will be perfectly adequate for the job in hand. You could kindly keep your insults to yourself! It is not a shoddy practice for the job in hand and the post was to try and help the OP. :mad: I don't wear a hat!!

smashey

Right people. Calm down or the ban stick will make an appearance.

steamjetjoe

Ill sort something out. Delivery is not till next tuesday so I have a bit of time to sort it. Thanks to all for the help.

ircoha

Avns1s wrote:

The Op has said that the concrete is for a 6' high PARTYwall. Unless it is almost totally water, it will be perfectly adequate for the job in hand. You could kindly keep your insults to yourself! It is not a shoddy practice for the job in hand and the post was to try and help the OP. :mad: I don't wear a hat!!

From the link posted by smashy

The addition of extra water to either increase workability
unnecessarily or to restore workability to concrete left
unused for extended periods weakens the cement ‘glue’
and reduces the overall performance of the concrete.

Suggesting bad work practices is never acceptable in my book: there was never any intention to insult anyone but if that happens as a result of condeming bad practice then tough:D

If u want to encourgae bad practise: do it by PM

Avns1s

What's the PARTY you inserted in my post got to do with it??

Your point about not intending to insult is noted.

Your ongoing assertion that the addition of water for this purpose is shoddy practice is not accepted though.

Perhaps we should leave it at that.

smashey

Perhaps you should take it to the thunderdome.

Final warning. Stop bickering.

Cheiftan

Johnniep wrote:

Sorry ircoha, but OP, do NOT do this. Moving the concrete in a trench using a poker will cause segregation of concrete!!!! Never good.

The idea of driving a fully laden concrete truck that close to an open trench sets off alarm bells! Just think of the damage the truck could cause if the trench collapsed and if this is your site, you are responsible!!!

If you are just doing mass concrete strip footings, a 20N20 (or even a 25N20 mix would suffice). The important thing for concrete below ground is durability which is directly related to the cement content of the concrete and not necissarily the strength (although they are directly linked)

Hope this helps.......

Ehh quick one for you there but it is impossible to over vibrate concrete, impossible. Segregation happens if conc is dropped from a height greater than 1.5 metres ( well thats what any spec I've ever read tells me ) or if pumped ( and its not pump mix ) or if you use a chute thats too long. If a pump is too expensive , I personnally would get a few guys with barrows, failing that smaller loads( though you will more than likely incur part load charges)

What concrete to use?

Simple ans to a simple question , use 25 n concrete , 100 slump , put 2 layers of A393 mesh in , bingo , job done.

fatboymsport

i hope to be starting mine in the morning and the lad doing it is a engineer and he wont let anything under 35n near the foundations and also using 2 layers of a393

there is only 4 euros a meter difference between 25 and 35 anyway

Johnniep

Cheiftan wrote:

Ehh quick one for you there but it is impossible to over vibrate concrete, impossible.

It is not only possible, but it does happen on site, I have seen it (can't locate a pic, but I will try and dig it out) Have a look here

OP there are three possible solutions, depending on distance,

You could get a truck with a convayer belt - it will go about 10 metres - maybe enough for you the "rake" it the rest of the way.

concrete pump - expensive.

Dumper truck, easier than wheelbarrows.

As for the truck getting too close to the trench - well I had one cause some shifting in the trench wall when he was one metre away from it, rapidly followed by some quick digging!:eek: it had rained a few days previously.

Cheiftan

Johnniep wrote:

It is not only possible, but it does happen on site, I have seen it (can't locate a pic, but I will try and dig it out) Have a look here

Johniep , What site does it happen on ? where ? what you have linked to there is an american publication on precast concrete , we here are dealing with insitu concrete , different animal , anyway your link says

"Over-consolidation, however, is normally not a significant concern and rarely occurs in the precast industry. In fact, in cases in which the appearance of the concrete surface is important, it is common to double the normal vibration time to ensure a smooth, defect-free finished surface."

We're going slightly off topic I think, but having worked as an Engineer on site for going on 12 years under vibration is the problem and i stand by my earlier post.

Fatboymsport , your right minimal difference in price with 25n v 35n. Go for 35n , however for a 6ft high wall 25n would be more than good enough.

Cheiftan

http://www.concrete.ie/concrete_pra.asp

If you don't wanna believe me believe these guys:D have a nice weekend people

smashey

Cheiftan wrote:

http://www.concrete.ie/concrete_pra.asp

If you don't wanna believe me believe these guys:D have a nice weekend people

Good link.

Knocking off at this time of the day? Pffft. Part timer.

billy_beckham

A 6' wall.........35N concrete and TWO layers of steel!!!
OTT in my opinion...

muffler

billy_beckham wrote:

A 6' wall.........35N concrete and TWO layers of steel!!!
OTT in my opinion...

Thats what I would have thought unless of course he's building on quicksand.

ircoha

Avns1s wrote:

What's the PARTY you inserted in my post got to do with it??

Your point about not intending to insult is noted.

Your ongoing assertion that the addition of water for this purpose is shoddy practice is not accepted though.

Perhaps we should leave it at that.

Truce agreed: I inserted the word party to highlight the fact that if something went wrong it might affect an innocent party other than the OP or his family and leave him woefully exposed. I get paranoid when it comes to this stuff with garden walls/kids/neighbours/etc. It allows me sleep well:)

Keep well.

muffler

ircoha wrote:

It allows me sleep well:)

Vodka does the trick for me

steamjetjoe

Breakdown of prices so far for a 145 foot wall, 6 foot high

readymix = 560
minidigger = 199
1058 4 inch solids = 600