strongest mix for a concrete head

JMSE

I have a 3m wide garage doorway to build a gable on top of and the best solution for me is to mix at home and pour my own concrete into a form set in place on top of the door. I'd want it to bond to the walls below it on either side so there wont be a membrane inside the form to keep the mix wet so it will probably dry out very fast. Anybody suggest the strongest mix possible for hand mixing and should I worry about it drying too fast and cracking?

CJhaughey

With a 3m span, I would think that a RSJ or similar would be a better and safer bet.
How are you going to reinforce the concrete? You will have to build all the rebar in place inside the form and fix it so that it doesn't move during the pouring process.
all in all this will be quite a complex job if you intend on casting in place.

Cheiftan

Or why not just buy a concrete lintol, for a 3 metre opening i would imagine a lintol say 3.8 would be more than enough.

De_man

as cheiftan suggested a concrete lentil...you can get "heavy duty" lentils
(extra rebar etc) specifically for this job ask your building products supplier if they stock them (don't let them pawn off a "normal" lentil)

if the opening was wider well then you might have to cast or use /rsj

imho a heavy duty lentil is a much better job for that

R33F

Cheiftan wrote: »

Or why not just buy a concrete lintol, for a 3 metre opening i would imagine a lintol say 3.8 would be more than enough.

The thickness of the lintel will become the determining factor at that length. What are you using above the door head ? If blockwork, you could possibly need a half cut or similar ?

Just a thought.

JMSE

Thanks for the ideas so far. Yes there will be blockwork above the head, cavity blocks maybe 5 or 6 courses high up to the apex but altogether maybe only 40 blocks or less.
I originally bought and placed a 3.6m head but changed my mind coz you could see the lighter head just wasnt right. Its still there. I tried the local steel stockist (McAleese's in Dunboyne) and they didnt have a beam with a 9" flange. I think what I want is a steel beam or a 9"x9" head.

The reason I'm going for a cast in place is that I dont have the time to go and get a heavy duty one due to work commitments and even if I did it would surely need to be lifted into place by a teleporter or something which I dont have.

The form is made and just needs to be put up on the walls, the steelwork is no big deal, I've lots of long mesh offcuts from the floorwork and 4 lengths of rebar running through the form should do the trick I'd say.

So....is my idea nuts (entirely possible) and if not, what tips to dya have for the mix?

bakerbhoy

I am using an insulated steelite lintel (3.5m) over my garage door (2.7m ope), not sure how many courses are going on it ,but it is a low ridge height . May be an option.

Mellor

JMSE wrote: »

Thanks for the ideas so far. Yes there will be blockwork above the head, cavity blocks maybe 5 or 6 courses high up to the apex but altogether maybe only 40 blocks or less.
I originally bought and placed a 3.6m head but changed my mind coz you could see the lighter head just wasnt right. Its still there. I tried the local steel stockist (McAleese's in Dunboyne) and they didnt have a beam with a 9" flange. I think what I want is a steel beam or a 9"x9" head.

The reason I'm going for a cast in place is that I dont have the time to go and get a heavy duty one due to work commitments and even if I did it would surely need to be lifted into place by a teleporter or something which I dont have.

The form is made and just needs to be put up on the walls, the steelwork is no big deal, I've lots of long mesh offcuts from the floorwork and 4 lengths of rebar running through the form should do the trick I'd say.

So....is my idea nuts (entirely possible) and if not, what tips to dya have for the mix?

Its not just a case of making a form and pouring some concrete on top of rebar. It would take a decent knowledge of insitu concrete to do this as a self build. It is was me i'd be looking at a steel lintel or a precst one.
For reference a heavy duty lintel is for increased loading, not large spans.

muffler

JMSE wrote: »

and even if I did it would surely need to be lifted into place by a teleporter or something which I dont have.

A lot of the delivery lorries would pop this on with a grab providing you have someone there to help out

JMSE

Mellor wrote: »

For reference a heavy duty lintel is for increased loading, not large spans.

But then why do they make large span heavy duty lintels? McComish concrete told me today they do a 3.6m 9x9 head for 127+vat

Ok I'm seeing the light, the main reason being that I would probably have to leave the 'cast in place lintel' there for a month for it to gain the strength to support anything.

Mellor

JMSE wrote: »

But then why do they make large span heavy duty lintels?

For large spans with high loading. If it was for large spans alone then all long lintels would need to be heavy duty. It should be easy enough to calculate the load if the blocks are known, and I think you can get prices online.

JMSE

Mellor wrote: »

For large spans with high loading. If it was for large spans alone then all long lintels would need to be heavy duty. It should be easy enough to calculate the load if the blocks are known, and I think you can get prices online.

Ive worked out that there should be 35 cavity blocks altogether (allowing for half blocks etc.) sitting above the opening. Can you calculate the load from that basic information?

Mellor

35 cavity blocks @ 24.5KG = 875.5KG
Some places might give loading in newtons, so the total there is 8.6 KN
So that might help with pricing, BTW 127+vat seams very reasonable

JMSE

Mellor wrote: »

35 cavity blocks @ 24.5KG = 875.5KG
Some places might give loading in newtons, so the total there is 8.6 KN
So that might help with pricing, BTW 127+vat seams very reasonable

great thanks !