How long for this quantity of concrete to go off?

[gcol]

I'm gonna be making a concrete foundation (set in a lawn) for a decorative lamp post about 8 feet high and weighing about 25kgs. It just has 4 fixing holes and will just bolt down onto a flat surface.
Ok so I was gonna dig a hole about 15" in diameter and about 30" deep then fill it with concrete. Maybe drive a few pieces of angle iron into the side of the hole for extra stability too.
My question is, how long should I expect it to take for this quantity of concrete to go off before I can fix through-bolts to it? Also is there any minimum temperature that concrete should be laid in? Finally, will a concrete mix of 1 part cement, 1 part sand and 4 parts aggregate be ok for this depth?
Thanks in advance,
Gcol

 

[PFE]

see here :
http://www.pavingexpert.com/concmix1.html

for loads of info on concrete.

Don't concrete when frost is likley.

I'd leave at least a week before drilling any fixing hoes (if thats what you meant?)

A better solution (drilling concrete can be a B*****d) would be to cast some threaded bar into the concrete, using a wooden template to ensure they are in the right place, then when the concrete has gained sufficient strength simply drop the lamp column onto the protruding bars and fix down with nuts.


P

 

[2scoops0406]

And if you use the threaded bars, I guess using stainless ones would aid longevity.

 

[gcol]

Hey that's not a bad idea PFE. I'll price up some threaded bar and give it some thought.
Thanks for replying,
Gcol

 

[empip]

Try bolts .. longish ones.. then you have the hex head buried, remember you will need to anchor the bolts, otherwise they will turn in the concrete when you inevitably over tighten the nuts on fixing.
You need think about anchorage a little more...
Stainless is good idea.

Perhaps use wooden pegs of the right diameter correctly placed in the concrete, remove when mix has set to enable fitting rawlbolts?

 

[masona]

Use 2 long threaded bar, bend it to a U-shape & wire it together in the middle of the U-bend, push it through the lamppost base holes temporary, support the lamppost and cement it in one go, tighten nuts when cement is hard.

 

[gcol]

Well the job is done. Concreted in place with an octagonal flag on the top to finish. Not sure what you meant with the u shaped bars masona. But anyway, it's gonna get drilled out and rawl bolted in place in the new year - my makita will make short work of that.
All went smoothly except for cracking the flag in half trying to get it level with the rubber mallet. Grrrrrrr. Wasted an hour sat in traffic going to get another. I think the hole I drilled in the middle for the cable to pass through weakened it somewhat.
Thanks all,
Gcol

 

[masona]

Not sure what you meant with the u shaped bars masona.

Example a long treaded bolt say 600mm long, bend it in the middle like a U-shape and put it through the base holes and cement it in one go. Tighten nuts when concrete is set. No drilling this way.