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Author Topic: Construction Q/Concrete for Mast Support/Cold Weather  (Read 6037 times)
WB4CMB
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Posts: 39




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« on: February 08, 2013, 10:45:18 AM »

I realize this may be way off but I've seen other Qs that are "off" too. 
     I'm hoping some of you have construction experience, amateur or professional. I'm wanting to pour some concrete to set a 4 X 4 in a hole. Hole is approx 6 in in diameter and 3 ft deep.  The purpose is to use the 4 X 4 as a support for a mast used to support a vertical ham radio antenna.  See, I told you this Q was off. 
      I'm wondering about concrete seting up in cold weather.  Altho we have had some days lately in 50s, the lows get into freezing down into the teens at night.  I have heard that concrete generates heat when curing??  Aren't there additives for the concrete mix to aid in this?  I don't want the concrete to freeze or crack and have a big mess on my hands.
Thanks     Ray 
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W0FM
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Posts: 2056




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« Reply #1 on: February 08, 2013, 11:24:18 AM »

Hi Ray,

Your question is not off topic.  Guys have planted 4x4's for years to support their masts or vertical antennas.  Make sure you use treated wood for longevity.  Yes, there are addatives you can mix with concrete to accomodate various climate and soil conditions, although most would not bother.  If you are very concerned about this, I'd suggest you stop by your local redi-mix concrete company and talk to the dispatcher.  Concrete contractors order all sorts of different concrete mixes to allow them to pour concrete in all kinds of weather.  They only make money when they pour concrete, so it's essential.  Let us know what they tell you.  Good luck with the project.

73,

Terry, WØFM
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K2DC
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« Reply #2 on: February 08, 2013, 11:50:07 AM »

Ray,

   Pouring concrete at those temperatures should be no problem at all.  The curing of concrete is not just a physical reaction (drying), it is also a chemical reaction, and it's exothermic - it gives off heat.  I don't have any construction experience.  But I know this because many years ago as a EE student I worked on a project to remotely monitor the curing of concrete by measuring and transmitting the internal temperature of poured cement.  As it turns out, there are curves to relate the internal temperature to the strength as it set up.  We were told of a pour that went in at an air temp of -5F.  The mud went in at 55F, and peaked at 105F the next day.  After peaking, the internal temp will decay for (depending on the mix) up to 13 years.
    So - Pour away.

73,

Don, K2DC
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KH6DC
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Posts: 643




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« Reply #3 on: February 08, 2013, 01:15:14 PM »

Ray,

   Pouring concrete at those temperatures should be no problem at all.  The curing of concrete is not just a physical reaction (drying), it is also a chemical reaction, and it's exothermic - it gives off heat.  I don't have any construction experience.  But I know this because many years ago as a EE student I worked on a project to remotely monitor the curing of concrete by measuring and transmitting the internal temperature of poured cement.  As it turns out, there are curves to relate the internal temperature to the strength as it set up.  We were told of a pour that went in at an air temp of -5F.  The mud went in at 55F, and peaked at 105F the next day.  After peaking, the internal temp will decay for (depending on the mix) up to 13 years.
    So - Pour away.

73,

Don, K2DC

You got it correct.  Also if using bagged concrete, check the writing on the package as there should be a temperature range.  Good luck

73, Delwyn KH6DC
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73 and Aloha,
de Delwyn, KH6DC
VE3FMC
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« Reply #4 on: February 08, 2013, 01:42:01 PM »

Another way to go is to pour some quick set in the hole, minus the 4X4. About a foot in the hole will do. Let it set up over night. Then set the 4X4 in the hole and fill the hole with pea stone gravel, tamp it down as you go. That will hold the post in place and allow the water to drain away.

That is how my brother in law sets deck poles. The benefit of this method is it allows you to square up the post.

If you do not want to do it that way I would still use quick set cement. It will harden quickly so the weather will not effect it.
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AE5QB
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« Reply #5 on: February 08, 2013, 02:24:40 PM »

You may want to check out this video.  http://youtu.be/hkhz1RY0cY8

If you are just going to attach a light duty mast and a vertical antenna, you really don't need a huge amount of support.  Unless you have access to a 40 foot 4x4 then you may want to reconsider.  But just as support, you should be good with the above procedure.  Bury it about 4 foot in the ground and it isn't going anywhere.  You may have problems with warping though, depending on how long you decide to go with.

73

Tom/AE5QB
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N4JTE
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« Reply #6 on: February 08, 2013, 06:20:46 PM »

I've used 4x4 pt poles for years to hold up 50 ft rohn push ups and other types of poles with no failures. As long as the hole is deep enough and post holed, there really is no need for any sackrete or other bag goods unless you are sure it will be permenant installation.
If  gravel or small rocks are jammed/ tamped in to the small space around the the pole your good to go, it will take an 80 +mph sustained wind to break a 4x4, if 1/3 of the length of the 4x4 is in the hole.
Bob
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WB4CMB
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Posts: 39




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« Reply #7 on: February 08, 2013, 08:49:00 PM »








Today, 01:40 AM#11



 
WB2WIK




 Premium Subscriber


Join Date: Jan 2000Posts: 58,099






 I agree concrete isn't needed if the "hole" is just right.
 
Utility poles 50' tall buried 4-5' underground don't have any cement, but the hole is drilled with an auger and the pole is a tight fit.


A government which robs Peter to pay Paul can always depend on the support of Paul.
 
-- George Bernard Shaw


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Today, 01:52 AM#12



 
K8ERV




 Ham Member


Join Date: Jan 2004Location: Beautiful Downtown Colorado. (Montrose, SW corner)Posts: 23,764






 




Originally Posted by WB2WIK

I agree concrete isn't needed if the "hole" is just right.
 
Utility poles 50' tall buried 4-5' underground don't have any cement, but the hole is drilled with an auger and the pole is a tight fit.
 Who climbs up to the top with a BIG hammer?
 
TOM K8ERV Montrose Colo

Reply  Reply With Quote        .

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Today, 02:32 AM#13



 
N4JTE




 Ham Member


Join Date: Oct 2001Posts: 38






 Asked and answered on eham.net, why the double posting?


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Today, 03:26 AM#14



 
KC9UDX




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Join Date: Jun 2011Location: Look it up on QRZ...Posts: 1,554






 I'm still trying to think how to calculate the Q of the construction.


Nach Feineinstellung mit der Hand. Lauschen wir dem Morse Band. Elektronenklange aus dem Radioland.
 
-------------------------------------------------------------------------------
  I have an 8 ft, 3in diameter galvanized pipe that I could use instead of the 4 X 4.   I would have to be a bit more careful about vertical alignment. Actually wanted 6 ft above ground so I would be 1 ft short I also just noticed it will be getting down in the very low teens for a low for a few days. 11 deg one night. Think I'll hold off.     Thank!    Ray
 
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AJ3O
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« Reply #8 on: February 09, 2013, 06:03:18 AM »

Temperature DOES affect the cure in concrete. Unless you are pouring a substantial thickness, the top can freeze and this could cause cracking and or spalling later. Yes there are additives. But I highly doubt that you want to pay for a 3-5 yard minimum for a two bag hole....

If you pour in this type of weather, get yourself a thermal blanket from a local construction rental supplier for any type of slab. BUT,  in this case 4 to 6 inches of straw or batt insulation over the hole and covered with an old towel should be good enough as the concrete is below ground. If you bring the concrete to the top of the hole about 1/2 inch above ground and slope it down and away from the post. This will make it easier to trim the grass around the post later.
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WB4CMB
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Posts: 39




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« Reply #9 on: February 14, 2013, 07:51:58 PM »

Now you folks really have got me to thinking. I also want to put up a directional antenna. I am not locked into anything but was thinking of something lightweight such as a hex or a spiderbeam. I have seen plans for tilt overs in the old antenna handbook, prob 35 yrs old. I would definitely use two supports, prob make them metal and have them longer (higher so I could get a higher pivot point for better leverage) I'm limited to 25 ft without a Colorado Engineer to sign off on plans. The City of Aurora, CO has no requirements or permits required if I stay under 25 ft. I can only go 35 ft even with engineer's approval.
 Used towers of any kind around here are about as scarce as hen's teeth, availability from 0 to minus 10. Wish I was wrong on that but it seems I am not.
 A new tower is out of the question financially, at least for now as I am an older ham trying to get back up on the air and as of yet don't even have a radio. I do have a decent retirement and I am thankful for that but just can't afford too much right now. And the next expense for the divorce lawyer after 52 1/2 yrs of marriage really would be costly. I also have a personal thing going on here too. I have to keep enough in reserve to be able to purchase my sister's half of a farm we own jointly, she has mental problems and has to pay for Assisted Living and on occasion a Nursing Home. When her money runs out and the government comes for the farm, I need to be prepared.
 Don't get me wrong, I have no significant debts and am in good shape financially, just can't purchase a tower now.
 Thanks Ray
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WB4CMB
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Posts: 39




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« Reply #10 on: March 02, 2013, 08:01:36 PM »

Decided to and used Quikrete Fast Set today. Temp was supposed to get to 62deg. Was prob about 50 when I finished. Dug hole 36in.
Used exactly as much water as recommended. They recommended one gallon of water per bag after pouring dry.I did hand mix a small amount so I could build up about 3 in over ground level at the base to help in water run off. All the water did soak in after a long time (maybe an hour)but it took many applications pouring a bit at a time. Hope it doesn't get too cold tonight. They rate it as 400 lbs/sq in after a couple hours and 1000 after 24 hrs. I drilled my holes in the 4 X 4 before doing concrete so as to not disturb leveling and/or set(now or later).
Hope it works! Ray
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WB4CMB
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« Reply #11 on: March 04, 2013, 12:30:52 PM »

I did enlarge hole to approx 10 in and belled out the bottom, a
lot. Post seems to be holding well and is still "level" I am still keeping it
braced on 4 sides, however. We are expecting winds of 25 mph today. This Fast
set stuff is supposed to set so you only have 20 minutes "working" time. It
looks pretty well set up on top but of course can't tell about down in the hole.
It's been since about 5pm Saturday.
Guess it's a bit late for asking, but has anyone had experience with "Fast Set" Quickrete?
 I have some layers of cloth plus a raincoat covering it now to keep it fm getting wet and maybe
provide a bit of insulation. It was up into the high 50s yesterday but is snowing now, typical Colorado weather. Later, I plan to waterproof the top. I understand that you should not waterproof for quite a few days, prob to allow it to "set" better.
 Thanks Ray
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W9FIB
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Posts: 787




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« Reply #12 on: March 05, 2013, 11:46:41 AM »

Insulating it is fine. But you don't need to waterproof it. It is not going to dissolve once mixed and hardened. Actually, if the soil is really dry, the added moisture will allow the crete to cure harder.
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