Casting concrete beams

[John LawsonParticipant @johnlawson61116]

[John LawsonParticipant @johnlawson61116]

Does anyone have any experience of casting steel reinforced concrete beams, we wish to replace the wood beams on our raised track with something more stable and would welcome any guidance as regards mix, casting etc.

 

Thanks

John

[Peter TuckerParticipant @petertucker86088]

Hi John,

 

What size are your beams and what loading are they going to have?

 

Peter.

[brickyParticipant @bricky]

Hello John.

The size of the beam and the length is a factor.

If you have access to a machine to lift the beams then they can be cast in shuttering on the ground.If not they will need to be cast in situ in a supported shutter. 

The mix for concrete for beams (shovels)10 gravel 5 Sharp sand 2 cement or if it is mixed ballast I use 7 ballast 1 cement.

The reinforcing bar needs 2 longitudal rods top and bottom with bar bent into a square at 300mm centres tied with wire to the 4 rods to form a cage.Keep the cage 25mm up from the bottom/side&top .Hire a vibrating poker to remove the air .Hope this helps

Francis  

[Nicholas FarrParticipant @nicholasfarr14254]

Hi John, Francis mix seems a little weak to me. The info I have gives a general purpose mix of ballest otherwise knowen as pre-mix of 4 to 1, however if it is out in the weather it would want to be a paving/driveway mix of 3.5 to 1. I have not got any info on a structual beam, but I would think it would have to be at least as strong as a driveway.

 

Regards Nick.

[BrianParticipant @brian]

Sounds like a lot of hard graft to me.

This link http://www.mexboroconcrete.com/brochures/ebeamsbrochure1.pdf may solve the weight and construction time problem for the straight section of trackway.

This would leave the curved section to be cast insitu, but it could cut out a lot of back breaking work.

 

Just a thought.

 

Regards Brian

 

No connection with this company, Honest. 

[John LawsonParticipant @johnlawson61116]

Hi Paul

As the beams are a direct replacement for the existing raised track they are 1.8mtr long 200mm wide and we proposed to make them fishbellied shape from 100mm at the ends to 200mm in the centre with 2 lengths of rebar in the bottom section.

As for loading ? how many fat people can you get on the 1.4mtr free span.

We will cast these on site and lift them in so we can keep the track available for use we have about 100 to produce.

 

John

Edited By John Lawson 1 on 03/11/2010 10:49:55

[DMBParticipant @dmb]

Do you have to have concrete beams? Many tracks have A shaped support pillars topped by all sorts of beams including wood. Worthing Model Engineers use 2 channel steel sections laid on sides with the `bottom` of the channels back to back. I dont know how the beams were bent. The passenger car bogies (cast ali. – frem) have an outboard steel drop – arm bolted on with a right – angled stubby bar which travels inside the channel, but not normally touching it. This arrangement serves as a very effective anti – tip device. I am anformed that the track was not originally planned in this way and that  a member responsible for devising the anti – tip thought up this simple brilliant solution.

Solving the channel bending prob. would make a simple system for other tracks without recourse to many additional bars and tubes of steel added on under the track with the increased difficulty in grass cutting under the track.

Just a thought but hope it helps someone.

John.

[DMBParticipant @dmb]

Sorry, can spell! Previous post said “cast ali. frem” but this was meant to be “frame”,

[Jeff DaymanParticipant @jeffdayman43397]

Just FYI For the strongest possible concrete I have found a mix as below works best:

 

3 parts crushed 3/4″ stone

2 parts sharp sand

1 part cement

 

Use minimum possible water. If you can get some chemical plasticizer and air entrainer it will increase workability while using less water.

 

Good luck. JD

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