Moulding Concrete in Plastic Tubes
Discussion
Have a look at this site. May give practical tips.....
https://castawaymoulds.com.au/how-to-guides/guide-...
https://castawaymoulds.com.au/how-to-guides/guide-...
Equus said:
R_von_S said:
Equus said:
The other problem you will have is that it will be difficulty to consolidate any voids in the concrete. When you're casting 'proper' concrete of any depth, you use a poker vibrator (no sniggering at the back!), to settle out the voids, but this will be difficult to do, in a long thin tube. Suppose you could try pouring gradually, while shaking/tapping the tube as you go.
You can apply the vibrations from the outside on something of that size, it'll be just as effective. fnarr...More seriously, just tap repeatedly on the outside of the form, at this scale you're just trying to encourage some of the (relatively) free fluid to flow into all of the gaps to improve the surface finish.
shtu said:
I'd be going to the local merchant and seeing what paving edging they have. Probably less than a fiver each and no troubles with finish, strength, appearance, etc.
eg https://www.jewson.co.uk/landscaping/garden-paving...
Thanks. Trouble is that it has to follow an s-shaped curve.eg https://www.jewson.co.uk/landscaping/garden-paving...
sospan said:
Have a look at this site. May give practical tips.....
https://castawaymoulds.com.au/how-to-guides/guide-...
Cheers. https://castawaymoulds.com.au/how-to-guides/guide-...
So as it's only 300mm long section, you might be able to just use a relatively normal concrete mix and fill the pipe (vertically) in 4-5 layers tamping each layer very well as you go to ensure compaction. It might well work, particularly if you use a piece of rebar for reinforcement and some fibres for crack control too.
But for a more interesting/geeky method...
You're essentially trying to create a highly fluid, self-compacting concrete to fill the pipe form. In commercial construction applications this is used where vibrator access is not achievable or if there is a complex form/reinforcement congestion to fill.
In precast concrete manufacturing i.e. lintels, fence posts (pouring concrete into moulds) this would be achieved through carefully controlled concrete mix design, vibrating tables/moulds and the use of superplasticisers - chemicals that make the concrete much more fluid for a given water content.
As best you can try to recreate this, I'd suggest:
10mm max aggregate would be better for the dimensions you are filling.
2:2:1 or 2:3:1 (4-10mm coarse aggregate : 0-4mm sand : cement) mix would be best. Self-compacting concretes make use of much higher fine(s) aggregate and cement content than traditional mixes.
You will want to add water to make your mix more fluid. Keep in mind more water in concrete = less strength and more shrinkage (cracking).
Aim for maximum 0.5 water : cement ratio i.e. if you're using 400kg/m3 cement, use 200kg/m3 of water.
If you can find an off the shelf concrete plasticiser from DIY store you'll need to use this to obtain the additional fluidity in the concrete mix (up to max recommended dosage on the bottle) you need rather than adding extra water. This keeps the w/c ratio low but consistency high.
Add a reinforcement bar. Glass or polypropylene fibres will help with shrinkage control too (but offer little benefit in tensile strength).
The gentle vibrating of the pipe with power tools that someone else suggested is not a bad idea and should help with getting rid of air pockets and voids in the pipe.
Of course it would be easier to just buy a precast concrete lintel etc (but not in the spirit of the challenge!) but if you really want to cast it yourself to your required dimensions and don't want to try and create the mix, use this pre-bagged highly fluid concrete https://www.uk.weber/files/gb/2018-03/04.020_Five_... - Weber Five Star Repair Concrete, it will do a far better job at filling the form than anything that could be made diy.
Probably much more information than you wanted.
Good luck!
But for a more interesting/geeky method...
You're essentially trying to create a highly fluid, self-compacting concrete to fill the pipe form. In commercial construction applications this is used where vibrator access is not achievable or if there is a complex form/reinforcement congestion to fill.
In precast concrete manufacturing i.e. lintels, fence posts (pouring concrete into moulds) this would be achieved through carefully controlled concrete mix design, vibrating tables/moulds and the use of superplasticisers - chemicals that make the concrete much more fluid for a given water content.
As best you can try to recreate this, I'd suggest:
10mm max aggregate would be better for the dimensions you are filling.
2:2:1 or 2:3:1 (4-10mm coarse aggregate : 0-4mm sand : cement) mix would be best. Self-compacting concretes make use of much higher fine(s) aggregate and cement content than traditional mixes.
You will want to add water to make your mix more fluid. Keep in mind more water in concrete = less strength and more shrinkage (cracking).
Aim for maximum 0.5 water : cement ratio i.e. if you're using 400kg/m3 cement, use 200kg/m3 of water.
If you can find an off the shelf concrete plasticiser from DIY store you'll need to use this to obtain the additional fluidity in the concrete mix (up to max recommended dosage on the bottle) you need rather than adding extra water. This keeps the w/c ratio low but consistency high.
Add a reinforcement bar. Glass or polypropylene fibres will help with shrinkage control too (but offer little benefit in tensile strength).
The gentle vibrating of the pipe with power tools that someone else suggested is not a bad idea and should help with getting rid of air pockets and voids in the pipe.
Of course it would be easier to just buy a precast concrete lintel etc (but not in the spirit of the challenge!) but if you really want to cast it yourself to your required dimensions and don't want to try and create the mix, use this pre-bagged highly fluid concrete https://www.uk.weber/files/gb/2018-03/04.020_Five_... - Weber Five Star Repair Concrete, it will do a far better job at filling the form than anything that could be made diy.
Probably much more information than you wanted.
Good luck!
Edited by T1547 on Monday 19th August 21:22
T1547 said:
So as it's only 300mm long section, you might be able to just use a relatively normal concrete mix and fill the pipe (vertically) in 4-5 layers tamping each layer very well as you go to ensure compaction. It might well work, particularly if you use a piece of rebar for reinforcement and some fibres for crack control too.
But for a more interesting/geeky method...
You're essentially trying to create a highly fluid, self-compacting concrete to fill the pipe form. In commercial construction applications this is used where vibrator access is not achievable or if there is a complex form/reinforcement congestion to fill.
In precast concrete manufacturing i.e. lintels, fence posts (pouring concrete into moulds) this would be achieved through carefully controlled concrete mix design, vibrating tables/moulds and the use of superplasticisers - chemicals that make the concrete much more fluid for a given water content.
As best you can try to recreate this, I'd suggest:
10mm max aggregate would be better for the dimensions you are filling.
2:2:1 or 2:3:1 (4-10mm coarse aggregate : 0-4mm sand : cement) mix would be best. Self-compacting concretes make use of much higher fine(s) aggregate and cement content than traditional mixes.
You will want to add water to make your mix more fluid. Keep in mind more water in concrete = less strength and more shrinkage (cracking).
Aim for maximum 0.5 water : cement ratio i.e. if you're using 400kg/m3 cement, use 200kg/m3 of water.
If you can find an off the shelf concrete plasticiser from DIY store you'll need to use this to obtain the additional fluidity in the concrete mix (up to max recommended dosage on the bottle) you need rather than adding extra water. This keeps the w/c ratio low but consistency high.
Add a reinforcement bar. Glass or polypropylene fibres will help with shrinkage control too (but offer little benefit in tensile strength).
The gentle vibrating of the pipe with power tools that someone else suggested is not a bad idea and should help with getting rid of air pockets and voids in the pipe.
Of course it would be easier to just buy a precast concrete lintel etc (but not in the spirit of the challenge!) but if you really want to cast it yourself to your required dimensions and don't want to try and create the mix, use this pre-bagged highly fluid concrete https://www.uk.weber/files/gb/2018-03/04.020_Five_... - Weber Five Star Repair Concrete, it will do a far better job at filling the form than anything that could be made diy.
Probably much more information than you wanted.
Good luck!
Good stuff. Cheers. But for a more interesting/geeky method...
You're essentially trying to create a highly fluid, self-compacting concrete to fill the pipe form. In commercial construction applications this is used where vibrator access is not achievable or if there is a complex form/reinforcement congestion to fill.
In precast concrete manufacturing i.e. lintels, fence posts (pouring concrete into moulds) this would be achieved through carefully controlled concrete mix design, vibrating tables/moulds and the use of superplasticisers - chemicals that make the concrete much more fluid for a given water content.
As best you can try to recreate this, I'd suggest:
10mm max aggregate would be better for the dimensions you are filling.
2:2:1 or 2:3:1 (4-10mm coarse aggregate : 0-4mm sand : cement) mix would be best. Self-compacting concretes make use of much higher fine(s) aggregate and cement content than traditional mixes.
You will want to add water to make your mix more fluid. Keep in mind more water in concrete = less strength and more shrinkage (cracking).
Aim for maximum 0.5 water : cement ratio i.e. if you're using 400kg/m3 cement, use 200kg/m3 of water.
If you can find an off the shelf concrete plasticiser from DIY store you'll need to use this to obtain the additional fluidity in the concrete mix (up to max recommended dosage on the bottle) you need rather than adding extra water. This keeps the w/c ratio low but consistency high.
Add a reinforcement bar. Glass or polypropylene fibres will help with shrinkage control too (but offer little benefit in tensile strength).
The gentle vibrating of the pipe with power tools that someone else suggested is not a bad idea and should help with getting rid of air pockets and voids in the pipe.
Of course it would be easier to just buy a precast concrete lintel etc (but not in the spirit of the challenge!) but if you really want to cast it yourself to your required dimensions and don't want to try and create the mix, use this pre-bagged highly fluid concrete https://www.uk.weber/files/gb/2018-03/04.020_Five_... - Weber Five Star Repair Concrete, it will do a far better job at filling the form than anything that could be made diy.
Probably much more information than you wanted.
Good luck!
Edited by T1547 on Monday 19th August 21:22
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