In order to support the vertical posts which will hold my solar panel mounts, I intend to set some cardboard
sono-tubes into the ground and fill them with concrete.
I have a question about mixing the concrete.
Will the following procedure work...
-Place my vertical poles into the son-tubes and support the poles in a vertical mode.
-Pour in a dry bag of redy-mix
-Add water and mix with a rod
-Pour in a dry bag of redy-mix
-Add water and mix with a rod
....repeat until the sono-tube is full.
For me this would be much easier than renting and transporting a cement mixer.
Anyone have experience doing this ?
Veggie
I've heard of folks around here setting fence posts by digging the hole and pouring in the bag of mix dry - no water added. The mix absorbs moisture from the soil and hardens, no mixing required! I'm not sure how long it takes or if that's a good method.
The bags are already mixed (cement/sand/gravel), you really only need to mix them enough to mix in the water, so I think your method is OK. Depending on how much space you have around the pole, you're also trying make sure there are no voids in the concrete. I personally like to add some cement to the mix because the bags are pretty poor with cement. I've also heard that the less water you use, the better - too much water causes the concrete to shrink a lot as it dries, which leads to cracks.
How big is the hole relative to the post?
You're not putting the sonotube all the way to the bottom of the hole, are you? I can understand using the sonotube near the surface where it forms up the concrete above grade for a nice appearance, but I wouldn't let it extend very far into the hole.
Hi Thob,
Thanks for the reply. Here in Canada we have to set the sono-tubes down to the 5ft. level in order to get below the frost line.
(So that they don't get pushed upward by the re-occurance of ground frost every winter)
The typical procedure here is to bore a 6 ft. hole and pour 1 ft. of gravel into the hole, then set the sono-tube onto the gravel and fill with concrete.
In this case the sono-tube ID will be 6" and the galvanized solar mount pole will be 2" OD.
Veggie
Good morning Thob
Also in Canada here, but in a warmer part. I used 6" diameter plastic sewer pipe as a form for my posts.
First we poured about 4" of concrete into the bottom of the 2 ft deep holes to give a mushroomed base, with a bit of rebar added.
While the mushrooms were still wet, I placed the pipe forms into the holes. they were already spaced and cross braced with the aluminium that I later used to build the racking. We held it all together with #10 screws while pouring the hand mixed concrete into the pipe forms. This method worked great, as I was able to use the aluminium for racking to correctly line up and space the forms, then tip the whole assembly into the holes,set them up level and vertical. After the concrete set up, we completely filled and tamped the holes, then removed the aluminium bracing. I used 3/4" threaded rod in the middle of the forms to make final adjustment of the racking a breeze after the concrete had set up.
The pipe forms were just left in place to make a neat installation, protruding about 2 ft above ground level.
Having used sonotubes before, I found this method far easier and quicker, and the sewer pipe does not get soggy in the rain. The thin walled sewer pipe was relatively inexpensive.
YMMV, but this method worked very well for us.
Cheers,
Hugh
Wow! 5 feet! Wow!
I've also heard of the sack in the hole and calling it hard candy in a week but I prefer to premix the premix and have found as I pour the sacks into the wheelbarrow that the three have separated from each other during shipping. I too throw in a couple of cups of Portland cement per bag as well.
I am challenged by the sono-tube or cheap sewer pipe all the way or near the bottom of the hole or putting plain gravel in as well. I'd more likely use a foot or two of concrete at the bottom and then do the upper part with 3/4 minus material. The minus material really packs in tight and as the fines migrate down the hole it gets a bit tighter with time.
I don't know how isolated you are but I've been known to buy a tool for a couple of hundred dollars on craigslist, use it at my leisure and then resell it for a couple of hundred dollars. The electric three sack units aren't really that tough to move if you have some child labor to help.
So how many panels? Stand alone or grid tie? Details veggie.
Casey
Hi Casey,
I have ten 220W Mono panels and a Magnum 4024 (kw, 24 volt) inverter with a small 550 amp battery bank.
The plan is to take key house circuits off the grid by using a transfer switch that can isolate individual circuits.
This gives the option to run those circuits (fridge, freezer, lights etc) on grid or off-grid with the flip of a switch. (see picture below)
I'm not really interested in grid-tie because I can't be bothered with the bureaucracy. ...and I don't have a grid-tie inverter of that size.
I may not need all the panels for this project, but I do have a solar PV powered greenhouse which would benefit from any left over panels.
This transfer switch can individually divert a circuit between grid and inverter (or generator) power.
I use the dry Quikcrete in the hole and tamp exclusively. It'll tamp in surprisingly tight, tighter than dirt and small rocks alone. I did the woodshed this way with 16 foot 4x6 posts and they were held plenty tight, then you have the bonus of the mix setting up. The stuff sets up 'way hard too, I think harder than when mixed with water. I can't give a timescale on how long the process takes because of the variables involved like humidity and ground moisture.
Ron.
With that large gap from the wall to the pole, I'd put a corkscrew of rebar in there, or wad up some mesh or chicken wire, to help the concrete hold together.
Fenceposts, I set with dry mix and water. PV mounts, I'd mix and pour. Maybe you can get a bag of reinforcing FIBER and add to the mix, and not need the rebar.
https://en.wikipedia.org/wiki/Fiber-reinforced_concrete
When I did my ground array i rented a tracked auger to bore my holes. I needed to bore to a depth of 6 feet with a diameter of 30" for my 4" schedule 40 steel pipe. our array has 7 uprights and required about 9 cubic yards of concrete. Needless to say i wasn't doing any mixing. The cement truck parked at the street and i used a motorized dump buggy to move the concrete to the holes about 300 feet away. It only took about 90 minutes to get the job done. The array is on a adjustable mount that can go from 60 degrees to 0 degrees to horizontal. The array consists of 56 200 watt panels for a total of 11.2 Kwh The array is 10 feet tall and 91 feet wide. It can be adjusted for seasons by one person as it is very well balanced. I did the install back in late 2009 and it has been performing great with no problems.
I keep forgetting about the ground freezing up north. Here the maximum frost depth is 6 inches, and I've never seen the ground freeze at all. But in a few years we're retiring to Wyoming and the frost depth is something like 4 feet there, so I'll need to keep that in mind. Water lines are 6 feet deep, so I definitely need to add a backhoe to the list of power tools I need to acquire. Good to know about using sonotube or pipe to keep away the frost heaves!
carlb. Have you tested tilt to evaluated change in output as a function of degrees from 90 to the sun?
didn't do a real study but the difference in winter from summer angles is quite substantial when i checked. if i move the panels from summer to winter position in the winter i gain about 30% and same when i move them from winter to summer in the summer. I move them 4 times a year and it takes about 10 minutes to change the angle.
fwiw, and having not read all the replies to your post...
and not knowing how many panels you have in mind, how many square feet of panels, and how strong of wind gusts you have in your local...
i personally would want the best foundation i could, especially for anything with more than just minimal sq/ft of panels
back in '83 a shop i worked at, a coworker and myself decided to enter a kite flying contest for the rededication of a ww2 airbase, there were several classes, the one we were going for was the delta design (big diamond shape)
our kite was 56lbs, 18ft tall and 12ft wide, and we used 3/8 woven nylon rope, and during testing we used a scout terra pickup truck with 5 guys in the back to try to get it up in the air... we also had 50ft of 3/8 tow chain for a tail (which was a horrible idea, but i digress)
the day of the contest, being mid august and as most know in the middle of the doldrums (absolutely no wind) we had to use a 1ton chevy tow truck with a 454cu/in and 4 speed manual trans.... we could get the kit up in low gear at about 14-15 mph, but could not shift to second as the kite would stop the truck dead in its tracks and put the driver up face first into the windshield. we did calculate the drag force at the time, but i don't recall any details other than it was a huge eye opener for all of us involved.
point being, panels are costly, so if you have many to mount (many sq/ft), and live in an area with brisk winds, if i were you i would err on the side of more and best concrete i could put down the hole.
remember the wind rules, double the frontal area, you square the forces, double the wind speed you cube the forces.
things can be pretty massive in some cases.
bottom line, just dumping the dry mix down the hole, while it works for fence posts will result in very low quality mix in my opinion. better off mixing by hand in a one time use framed up out of wood with a plywood bottom basin, using a hoe and shovel in my opinion. even if not perfectly mixed it will be far better than dry dumping and adding water i would think.
again fwiw, which ain't much these days
;)
bob g
Are these poles attached in a framework, or are they free-standing(each pole supports a standalone array)? Got the 6" tube 5' long with 2" pole. How many of these do you need to do? If my math serves me a 6" tube 72" long with a 2" pipe will take just over 1CU/FT of ConCrete(1800 CU/IN). An 80# plus a 60# bag = 1.05 CU/FT of CC. 5' of tube would probably be OK with 2 60# sacks. Got 10 of these to do, that's 20 sacks to mix?...
If part of an interconnected frame, the frame can provide the rigidity, so the legs merely need to be restrained by the weight of the CC around the legs in the holes. With a plate attached to the bottom of the pole you could probably fill the tubes with tamped crushed rock which would provide the necessary weight to restrain the legs... Havn't used CC for fence posts for years, crushed rock drains better so the posts last longer.
If freestanding posts, the issue becomes withstanding lateral force. For this you need that base to be bonded throughout. Since the powdered CC resists the transmission of water, and proper wetting is necessary to fully fire the CC chemical reaction, just putting the dry mix in the hole and wetting will make for an inconsistent mix. The sonotubes will also restrict the dry mix from absorbing moisture from the earth. If I recall correctly a 60# sack of quickrete takes about 2 quarts of water to activate properly. But mixing throughly with that little water by hand is laborious. Using more water is a problem as the more fluid mix will separate as it falls into the hole, with the aggregate settling to the bottom. The cement glued to the agregate spread evenly thru the mix is what gives it it's strength. With a proper mix, the sonotube helps the mix retain the moisture and cure properly.
Depending on how many of these posts you have to do you can mix it by hand in a tub or wheelbarrow, just resist the urge to add more water... Way easier to throw 2 sacks into a mixer, start it up and add 4 measured quarts of water. This way it gets mixed properly and evenly with the proper ammount of water. As soon as you see it fully wetted, tip it down the hole, repeate as necessary... With a small mixer you could probably do 10 posts in under 2 hours as it goes very fast...
CC only really needs re-enforcement(rebar/mesh) when placed in tension. Not any real tension loads associated with a pole/post in CC, so no re-enforcement necessary... that is why crushed rock typically works well for posts.
Last month we had a bit of a blow. So I notice the tent roof over the tractor and farm truck tried to run away but was still there as were the 1" conduit pipes set in about 5 gallon poured pads (6). This is a kite that measures out to about 20' by 30'. "Wow!" mumbles me as I fire up the tractor for some mission or another. Two women and I got it replaced in about two hours. Ok, the two women got it replaced in about two hours but I provided important supervision. The weather service reported 40 mile an hour gusts.
As I putted by MEL, Menehune Energy Laboratory and not Melvin, I noticed the metal roof had curled up on one side and was caught against the ridge cap. "Holy Wow" or something like that. Five minutes later I'm up there with a jar of screws and screw driver. "Holy Shit" I had forgot to put most, yes - MOST, of screws in the leading steel roof panels on BOTH sides. The South side has 30 solar panels! Yeah the unit has paid for its self but now is the sweet part of solar panels. The decade plus of nearly complimentary power generation. 40 - 60 screws later and I'm sleeping better.
So how does this tie into this thread? How much concrete do you need and what is it's mission? I escaped catastrophic consequences on the tent building because the sides of the tent material ripped loose and allowed much of the force to escape. There are no walls so there wasn't any entrapment going on either. OK, this is the way I usually know it's time to replace the roof. I got three years out of this one while I normally get only two. The even better news is that I'm ready to go for the wet season that starts next month if the plants are lucky.
The second part is there's more to building the greatest brick out house in the county if you don't secure the roof because you're too pooped to think straight. Relying on luck is not always the best plan but be thankful when she stops by and gives you a hand
Casey
Quote from: veggie on March 16, 2017, 08:52:47 AM
In order to support the vertical posts which will hold my solar panel mounts, I intend to set some cardboard
sono-tubes into the ground and fill them with concrete.
I have a question about mixing the concrete.
Will the following procedure work...
-Place my vertical poles into the son-tubes and support the poles in a vertical mode.
-Pour in a dry bag of redy-mix
-Add water and mix with a rod
-Pour in a dry bag of redy-mix
-Add water and mix with a rod
....repeat until the sono-tube is full.
For me this would be much easier than renting and transporting a cement mixer.
Anyone have experience doing this ?
Veggie
I think your basic technique would work. If you substitute standard ready mix for rapid set you will be good to go. Some fence installers just pour it in dry and add water. Personally I use 2 bags of standard mix at a time, a wheelbarrow, and a hoe it's cheaper and I think the well mixed standard mix is stronger.
My two cents, also in canada, and having hand mixed more concrete in hard to access spots then I care to remember :)
Best Regards, David Baillie
As has been mentioned, pre-mix is very low on cement. Fine for non critical stuff but I would not use it to hold up expensive panels. Pre-mix is also relative expensive compared to combining the individual bits yourself. Fine for small quantities but a bad choice if you need any quantity. I would suggest to look at getting in a concrete truck - better concrete, a hell of a lot easier on your back and you might be surprised if you calculate the total cost of getting it delivered vs bags.
The stuff delivered with the concrete truck is a known quality and will give you peace of mind when you got some bad weather coming in!
I have dug out and broken up foundations which have used both bagged concrete and the "proper stuff" mixed before pouring into the hole. Chalk and cheese - the bagged stuff just crumbles off with the 1st smack of a maul but hell, the real stuff takes a good pounding to release from the piles.
1 cubic yard = 27 cubic feet. I've heard that those 60 pound bags only have 1/3 of a cubic foot of finished concrete in them. 80 bags of concrete might set you down to think but for small jobs they sure are handy. The first yard or two that come out the back of a truck are not cheap either. Really, really handy but not cheap.
Casey
Yep, and the truck dosn't give you all day to off-load it either... A lot of redimix plants won't even talk to you untill you are planning at least a few yard or more for delivery.
I have seen some of the rental places with 1/2 yard towable mixers(United Rentals used to do this). They pre-mix it for you, you pick it up, tow it to the site, add the water and pour, then flush out the drum and return it. Cool little units and way easier to maneuver than a full sized truck to dump less than a full yard of CC...
I've done a few trailer loads from the rental place, and my advice is DON'T, unless you live really close. The aggregate settles to the bottom and water/cement floats to the top if you travel a few miles. The result is you can't even open the gate and dump the load without mixing it by hand first, which is a lot of work! There's a reason they haul that stuff in mixers that constantly mix.
And yes, most places around here charge for a full truck load (9 yards?) as the minimum. There is also a service here that has trucks with dry materials, they mix on-site and will do small batches but I haven't checked out their prices.
Well mixed premixed bags of concrete should meet their specs. How many people actually read the bag though? Or measure the water. If you can get a truck in by all means but for a few piers you will pay dearly for small quantities. Is quality is an issue add a shovel of cement per two bags and increase your strength...
Best regards, David Baillie
QuoteHow many people actually read the bag though?
Wow David! There are actually instructions on the bag? Again, my reason and purpose for attending this blog is learning. Grinning aside; I too put some extra portland cement into the mix and do mix up the premix before pouring. I've also measured the water, cement, sand and gravel when doing repeated mixes in a small mixer.
I'll be reading that bag on the next project for sure. Thanks for the tip.
Casey
Quote from: Thob on March 23, 2017, 03:12:55 PM
I've done a few trailer loads from the rental place, and my advice is DON'T, unless you live really close. The aggregate settles to the bottom and water/cement floats to the top if you travel a few miles. The result is you can't even open the gate and dump the load without mixing it by hand first,
The ones I am talking about WERE a drum mixer on a big trailer. Gas powered, with a water tank. Looked like the back half of a cement truck, downsized, with a trailer hitch where the cab should be:). No handmixing on these badboys.
I wouldn't want to tow mixed CC in a trailer that wasn't mixing for the very reasons you mentioned. Over agitation/consolidation is as bad as under consolidation. One separates the materials, and the other leaves voids...
Quote from: David Baillie on March 23, 2017, 05:20:11 PM
Well mixed premixed bags of concrete should meet their specs. How many people actually read the bag though? Or measure the water. If you can get a truck in by all means but for a few piers you will pay dearly for small quantities. Is quality is an issue add a shovel of cement per two bags and increase your strength...
Best regards, David Baillie
I agree for the most part. The bags should be fine and plenty strong if mixed properly. I have a front step I did with bags of sackrete about a decade ago, mixed with wheelbarrow and hoe, Still solid as a rock, no flaking or chipping with square corners and edges all intact. I did a walkway from driveway to that front step using a stepping stone mold form(1 60# sack per mold) and those are all intact and walked on daily for that same decade... Don't overwater, mix throughly and don't over consolidate and it is plenty strong for domestic/residential use...
More cement won't necessarilly make it stronger. Only if it was lacking in cement content in the first place. Most of those bags are rated to produce a 2500-4000 PSI mixture, and most of that probably depends on the ammount of water that is used and how throughly it is mixed... Cement by itself is not very strong. It is the aggregate that makes CC strong with just enough cement and sand to bond it together. Adding cement will only reduce the ammount of aggregate per CU/FT. Just as too much water will make the mix fluid enough that the sand and gravel will be able to separate more easilly during the pour and consolidation with the force of gravity before the cement chemically fuses...
i just did a 1 yd pour of 5k psi mix, for a base to install an 8k dollar washing machine that spins out to 400g's
we checked into bags of premix and found that it would take around 200 bucks worth of bags and a lot of work and even then i was unsure of the quality of the finished product with cold joints and such, let alone what psi the stuff would be good for if all was done perfectly, which it never is.
i called a concrete plant 20miles away and they would deliver 4 yds or more at the regular price of 105 bucks/yd of 5kpsi mix
when i asked for 1.5 yd (had a small side project to do at the same time) they told me that they would deliver a 5 gallon bucket of mix for 40 bucks... hmmm 40 bucks! why not?
it is common thinking at least for me, that small quantities are horribly expensive, well i guess that is not the case?
i guess "horribly expensive" is a relative term?
all i know is i will never mix concrete again! at least for anything over a couple bags of premix.
bob g
https://www.google.com/search?q=log+pole+building+round&tbm=isch&tbo=u&source=univ&sa=X&ved=0ahUKEwiY8Zb3lPjSAhWKjFQKHfEUAa4QsAQIHw&biw=1098&bih=527&dpr=1.75#imgrc=--oQ09jCLw0d9M: (https://www.google.com/search?q=log+pole+building+round&tbm=isch&tbo=u&source=univ&sa=X&ved=0ahUKEwiY8Zb3lPjSAhWKjFQKHfEUAa4QsAQIHw&biw=1098&bih=527&dpr=1.75#imgrc=--oQ09jCLw0d9M:)
Give it a minute. Interesting illustrations.
I Don't understand all the concern for the strength of the concrete.
It's not going to be like a floor or anything that holds significant compression loading and that's what concrete strength is all about. This is more going to be about surface area and the ability of the surrounding soil to hold the concrete in place. Anything that set up properly is going to do this job, it's very low demand and the soil and the post is going to be the weak link rather than the cement.
I'd be doing as suggested, Digging the hole bell shaped at the bottom to get more purchase on the soil rather than worry about the strength of the cement.
Looking at it the other way, if you were trying to push these over or pull them out, I'd guarantee either the 2" posts or the soil is going to give way before any properly prepared cement from bags or other wise gives way.
The weak point is going to be where the post meets the cement because that's the point of most force/ leverage on the pole. No bagged cement is going to break away from that!
Those posts are not that strong as I have well seen helping out a mate with a road sign business. Never seen the cement break away from the posts but I have seen plenty ripped out of the ground with the cement still attached and just as many posts bent like pretzels..... Usually with the concrete still attached perfectly to the pole but with soil movement. If the ground is wet, you can push the posts over with surprising ease even with 100Kg of concrete attached. For signs they always use bagged mix unless it's one of those huge things hanging over the road where the structure is 8" box section and you need a mixer full for all the anchor points anyway.
It's the leverage on the posts and soil that is the problem, not the strength of the concrete.
You'd be better off with larger posts and deeper holes with crappy cement than you would with the best cement out there and lesser poles in not so deep quality cement.
Probably better off still with no cement at all and just pile driving the posts.
Aloha glort,
I pretty much agree with you but I found the thread interesting and informative. The different approaches are always fun. Sometimes we're confronted with building code or the challenges brought out by isolation not to forget that old adversary: being under capitalized.
Casey
Quote from: glort on March 28, 2017, 09:43:30 AM
I Don't understand all the concern for the strength of the concrete.
It's not going to be like a floor or anything that holds significant compression loading and that's what concrete strength is all about. This is more going to be about surface area and the ability of the surrounding soil to hold the concrete in place. Anything that set up properly is going to do this job, it's very low demand and the soil and the post is going to be the weak link rather than the cement.
I'd be doing as suggested, Digging the hole bell shaped at the bottom to get more purchase on the soil rather than worry about the strength of the cement.
Looking at it the other way, if you were trying to push these over or pull them out, I'd guarantee either the 2" posts or the soil is going to give way before any properly prepared cement from bags or other wise gives way.
The weak point is going to be where the post meets the cement because that's the point of most force/ leverage on the pole. No bagged cement is going to break away from that!
Those posts are not that strong as I have well seen helping out a mate with a road sign business. Never seen the cement break away from the posts but I have seen plenty ripped out of the ground with the cement still attached and just as many posts bent like pretzels..... Usually with the concrete still attached perfectly to the pole but with soil movement. If the ground is wet, you can push the posts over with surprising ease even with 100Kg of concrete attached. For signs they always use bagged mix unless it's one of those huge things hanging over the road where the structure is 8" box section and you need a mixer full for all the anchor points anyway.
It's the leverage on the posts and soil that is the problem, not the strength of the concrete.
You'd be better off with larger posts and deeper holes with crappy cement than you would with the best cement out there and lesser poles in not so deep quality cement.
Probably better off still with no cement at all and just pile driving the posts.
+1 Ron
Quote from: LowGear on March 28, 2017, 10:46:36 AM
Aloha glort,
I pretty much agree with you but I found the thread interesting and informative.
As they always are here! :0)
I have an offer in on a place atm. Pretty sure the agent is BS ing me about other offer's, ( what a surprise!!!) Trying to get my offer up. I can pay what the owner is asking, I'm just not of the opinion the place is worth it going on what I have seen others in the area go for. Maybe the Mrs and I looked a bit too exuberant with it ( which we were) but at the end of the day I won't let heart rule head.
If by some some miracle of Miracles we do get it, I might look at doing a solar farm of my own.
It's one acre with a lot of trees that will be introduced to a chainsaw and a LOT of hedge trimming as well. The expansive roof of the buildings faces an off direction so I would look at Putting some panels on frames myself and making a bit of an outdoor area under them. Could expand the existing outdoor area on the house but it would also be facing the wrong direction. A lot of places we have seen are very clear but the one we like best has to be heavily wooded doesn't it? :0(
I have read that tracking seasonally here adds 15% to the efficiency and tracking east west movement adds another 15%. At this stage I think I'll dial in for winter if I do something fixed like making a shelter of some sort. If I do a frame setup then I will make that adjustable. Might be able to do that with something like a Hydraulic Jack and locking pins or counter balancing.
Rotation may not be that bad either. I picked up a Huge bearing from a truck repair place today. Think it might be out the gearbox. I grabbed it for the man cave along with a piston but maybe could be put to use for a solar frame?
The used panels seem to have become more plentiful the last couple of weeks. Lots of people removing them to knock down places and re build Duplexes or apartments. Many are still asking stupid money and showing how clueless they are about things but I have had a couple come back now after realising how far wide of the mark they are. I'm going to stick to +200W panels now. As the new panels are going over 350W at the top end, I don't think the older ones are worth worrying about. Too much time and cost to erect them in the first place.
If the weather holds, I have negotiated to get a full 1.7 Kw system with inverter, panels, rails etc for $350. have to remove myself but that's OK. Won't have to worry about some clown just cutting the connectors off the panels or other stupidity. I bought the tools for the job a while back so might get to put them to use. All depends on the weather now which unfortunately is not predicted to be good.
From there will be difficult to get hold of but anyway.
The place I am looking at has 3 phase power. Not really sure why. It has no pool, just a couple of split AC units and solar water heating with gas appliances. Not really a big draw household. In any case it might be bit of a pain to back feed each phase. I'll have to see where each circuit goes or just move everything onto one circuit and back feed that. Didn't think to check in the garage if there was 3 phase connected there in a socket but I can't see myself being that lucky. If I am then I can run the Lister with my 3 phase motor and back feed each phase individually to balance the draw out. Putting a 3 phase socket in would be handy but also not cheap giving where it would have to be run.
Looking forward to giving that a permanent home and finally getting it sorted. :0)