[ox]

Looking for info regarding a large concrete pour. I am setting up two ham radio towers in a remote area (no ready mix access on this project). I have a mixer that will work in this situation but not sure on technique. 4x4x6 foot hole has to be filled as a base for the towers. Wondering if there is a good method of doing this without compromising integrity.

Any leads appreciated.

 

[copperkid3]

That's a LOT of concrete to hand pour; that's roughly 3.55 cubic yards doing the math in my head.

Not sure what you're hinting at regarding "integrity"...... are you concerned for the
costs involved, the time and labor or that you might have to pour over a period of
days, instead of hours? I'm thinking more along the last than the others, but will
try to address them in order of importance. The costs are going to be pretty fixed
as far as mixing your own, as to bags of portland cement needed,and sand and gravel
delivered. However, if you have access to clean, solid (river) rocks of various sizes,
they can be used in the footing without compromising the 'integrity' and will go along
ways towards filling up the space and conserving some of the other ingredients.
The time and labor are going to still be there, but if you can enlist some help from others,
it will certainly help make the task go easier. The last problem is getting the pour completed
in a timely manner. Ideally, you would want to get it finished at one time......so the entire mass
can cure at the same pace. But with a portable mixer only capable of small amounts being processed at a time,
it's unlikely that you'll be able to do so without having more than one machine going at the same time.
Hence the reason to get more help and get it finished as quickly as possible. I'm assuming that you are
going to just dig a hole with those dimensions and not place any forms?

Anyway, hope this gives you some ideas to consider further.

 

[Harry Chickpea]

Sounds about the size of the base my dad poured for his 50' mast with a 2 meter on top. It was a premix pour. One thing you can do to cut down on the amount of concrete is to make the forms so that the base is a truncated pyramid, with only about 6" outside of the lags. You could save up to 1/3 doing it that way.

What I would do is rent a second mixer and hire three or four day laborers so that the pour was semi-continuous once started and there could be reasonable rest periods. I would also look to rent a vibrator or breaker that would accept a rod so that the bubbles could be worked out around the rebar frame.

You are still going to guy wire it, right? Get those dogs set at the same time.

 

[bigjon]

set rebar (verticle)then start pouring.that should hold it all together

 

[Ozarks Tom]

Without knowing the distance from road access, or the terrain you're dealing with my suggestion might not work. If possible I'd use a front end loader ferrying premix from the truck to the hole, specifying a wet mix.

 

[fordy]

...............On the Ham tower projects I've worked on we would cut all the rebar , tie it all together and lower it into the hole and suspend it with 2x4's or any thing that had sufficient strength to withstand concrete being poured into the hole .
................I'd put 6 inches of pea gravel in the bottom of the hole so that any moisture condensing on the inside of any tubular legs extending into the concrete can have a place to go . If the soil is clay the pea gravel will allow the moisture to be slowly absorbed so it doesn't build up in the tubular legs , thus facilitating rust . , fordy

 

[arnie]

have your sand ,gravel water ,and cement close to your mixer and your wheel barrel route ready once you start pouring the concrete you hae to keep steady mixing and filling your forms keeping it as a continuios pour having a few helpers say one sholveing and gradeing viberating or jabbing at the hole one wheel barrel man one or two feeding the mixer should work I hope you have a good sized mixer not one of those little hand crank ones .mine is a 1/2 bager with a 8 horse power engine keep the mix cosistant I always count the shovels of ingredints as they go in the mixer 4 of gravel three of sand one of Portland . if you don't have much experience working around a mixer use caution . those moveing parts belts gears are powerfull and dangerious . and you will be loading ,and unloading it while every thing is moveing . try a few trial runs filling with gravel and dumping in the wheel barell pushing to the hole and dumping to make sure all will go smoothly conctere is very heavy . lets do some math a 4 x4 x6 foot hole will take 3.5 cubic yards of concrete to fill and you will want about 5 bags of Portland per cubic yard ;so you are looking at around 18 90lb bags plus the sand and gravel which wii be about 1.5 cubic yard of sand and 2 of gravel . I welcome any one to add any corrections to my math or mixing ratios .

 

[Darren]

I'd use something like Masterset Delvo to retard setting time. That ensures you won't have issues with part of the concrete setting before the last is placed and creating a cold joint. I would not use a real wet mix. That's a common error that limits strength. Add enough water to get a uniform mix color but not enough to turn the concrete into soup.

Vibrate the concrete. Do not vibrate the rebar. That weakens the bond.

 

[Nimrod]

The math is good. I question your ability to have sand and gravel hauled in if a cement mixer can't get in.

A cement mixer would be ideal. It would cost a bit more but save a lot of labor and could do the pour all at once to preserve integrity. If it's a question of getting the cement mixer close enough to the hole, you could have a half a dozen manned wheelbarrows and move it that way from the cement mixer to the hole. Also, I did a pour where the truck had a 30 foot long boom to deliver the concrete so it didn't have to be as close to the site.

If you have to use the premixed bags of concrete, each 60 pound bag nets you 1/2 cubic foot of concrete. A cubic yard is 27 cubic feet so 3 1/2 cubic yards is 94 1/2 cubic feet. Two bags per cubic foot times 94 1/2 cubic feet equals 189 bags of premix.

You might have to mine rocks and gravel on site to mix with straight Portland cement. From what I hear they need to be washed first or the concrete will be weaker.

Good luck