Dry stacked block column

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Dry stacked block column

Postby ajarnudon » Wed Sep 28, 2016 3:31 pm

Some time ago I read about a mortarless method for building a column using dry stacked blocks on top of a reinforced concrete footing pad. Large blocks 400 x 200 x 200 (or something similar are used) to build a nominal 400 x 400 column, each course set at right angles to the previous blocks. Shims are used to maintain straightness where necessary. From memory, after three courses the blocks are filled with concrete, and when it has slightly gone off, two 1200 lengths of 12mm rebar are driven down to the foundation in diagonally opposite openings, leaving 600mm of rebar exposed. The process is repeated, but this time the 1200 lengths of rebar are driven 600mm down the concrete in the other two openings. Repeat until the desired height is attained.
I thought I had read about this in CTH, but hours of searching haven't brought it to light. Can anybody point me to the post I am looking for, and/or has anyone had experience with this method?
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Re: Dry stacked block column

Postby ajarnudon » Wed Sep 28, 2016 3:56 pm

Should have looked for another half hour - just found the post by Rimtalay

viewtopic.php?f=41&t=4924#p64892

I am planning to build columns at the corners of my upcoming retaining/perimeter wall using this method. Any commets please?
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Re: Dry stacked block column

Postby Sometimewoodworker » Wed Sep 28, 2016 4:51 pm

ajarnudon wrote:Should have looked for another half hour - just found the post by Rimtalay

viewtopic.php?f=41&t=4924#p64892

I am planning to build columns at the corners of my upcoming retaining/perimeter wall using this method. Any commets please?

3,
first is, why?
The second is that they don't look to have much lateral strength, something that is essential in a retaining wall and desirable in the corner post of a perimeter wall.
Thirdly can you get them where you are building?
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Re: Dry stacked block column

Postby Roger Ramjet » Wed Sep 28, 2016 7:47 pm

ajarnudon wrote:From memory, after three courses the blocks are filled with concrete, and when it has slightly gone off, two 1200 lengths of 12mm rebar are driven down to the foundation in diagonally opposite openings, leaving 600mm of rebar exposed. The process is repeated, but this time the 1200 lengths of rebar are driven 600mm down the concrete in the other two openings. Repeat until the desired height is attained.

Why are you waiting for the concrete to go off slightly? The whole point of using rebar is so that the concrete bonds to it. This is sounding like another Rimtalay discourse on thermal mass! Are you trying to build a wall or are you trying to start that argument going again?
<slight edit, Dozer 02-Oct for off topic comment>
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Re: Dry stacked block column

Postby ajarnudon » Thu Sep 29, 2016 10:17 pm

Sometimewoodworker,
Thanks for your response. In the order of your comments:
1. Why? There appear to be several advantages, including speed of construction, savings on timber formwork, unskilled (but supervised) labour suffices for just the unmortared pillars, as well as additional sub-soil isolation of the rebar. One reason is experimental, as I might go with reinforced filled cavities for the wall with reinforced lintels as the top beam. If this was successful, then I would look at the possibility of continuing that method in the house construction. Here, I am planning cavity block walls for the living areas and bedrooms (the areas that will have air-conditioning), with CPAC blocks on the outside and AAC on the iner skin.
2. Lateral strength. This comes from the foundation as I would have it, with two Js coming from the cage up into the column 600mm, and a large footing cantileverd inside the wall and 1 metre below the undisturbed soil level. Lateral rebar into the vertically reinforced cavities of the adjacent wall blocks. Maybe I could up the rebar size on the corner columns. The maximum retention height of my retaining wall is only 1.2 m. I am thinking of a 1.2 m barbed wire fence for the perimeter wall on top, with a hedge planted both sides. OK, I'll have to buy a powered hedge trimmer, but this can be used for the topiary as well.
3. Local availability. Probably not. I work in BKK and normally fly back home to UTH, but I can bring enough blocks back in the pickup at Xmas to do one pillar, and following an assessment and costing, could organise a truck to bring up from BKK in one hit.
As a newbie to this forum, I appreciate your well considered questions - please feel free to come back. Once I start the job I will post in the My Construction forum.
By the way, I really enjoyed my first sakura trip to Japan in late March/early April this year. Took in Osaka, Kyoto, Fuji San and Tokyo. Want to go back, but probably after the build. Cheers, John.
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Re: Dry stacked block column

Postby Roger Ramjet » Thu Sep 29, 2016 11:08 pm

ajarnudon wrote: Lateral strength. This comes from the foundation as I would have it, with two Js coming from the cage up into the column 600mm, and a large footing cantileverd inside the wall and 1 metre below the undisturbed soil level. Lateral rebar into the vertically reinforced cavities of the adjacent wall blocks. Maybe I could up the rebar size on the corner columns. The maximum retention height of my retaining wall is only 1.2 m. I am thinking of a 1.2 m barbed wire fence for the perimeter wall on top, with a hedge planted both sides. OK, I'll have to buy a powered hedge trimmer, but this can be used for the topiary as well.

There are a number of details you haven't considered, if you are driving rebar into the soil it will rust within a month or so, There is a chart showing what the lateral forces will be from wind against your 1.2 metre wall. If you decide to place barbed wire on top with a hedge planted either side then it would be far cheaper and stronger to have pins driven into the soil and attach normal concrete posts (900 Baht each) to the pins. The hedge of course will add more lateral force, but I think the calculations were done up to 2 metres when the wind is horizontal.
Max and Bee in Chiang Mai put in similar corner posts, but they put down foundations before they did the fence, which was made out of bamboo and concreted in posts, it was an exercise in futility as the fence was blown down in various places and the corner columns had to be torn down and rebuilt.
Why are you driving rebar into partly cured concrete, it defeats the whole purpose of using rebar in any structure?
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Re: Dry stacked block column

Postby Roger Ramjet » Thu Sep 29, 2016 11:20 pm

You might like to look at the solutions: https://www.google.co.th/search?q=later ... BrIQsAQINA
I might add none are based on your "concept" at all.
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Re: Dry stacked block column

Postby Sometimewoodworker » Fri Sep 30, 2016 2:21 am

ajarnudon wrote:I am planning cavity block walls for the living areas and bedrooms (the areas that will have air-conditioning), with CPAC blocks on the outside and AAC on the iner skin.

Hi John.

That seems the exact opposite of what you want. Regular concrete blocks, yours or normal, are a heat sink. AAC insulate (night storage heaters are concrete blocks)

So with your plan your house becomes nice and toasty.

AAC on the outside lets the thermal properties of concrete work for you by retaining the colder temperature you want avoiding heat buildup.

We have accidentally proved this point with our storage/security room. It is a solid concrete construction almost entirely within an AAC shell and it is noticeable cooler inside than any other room. This wasn't intended but is welcome.
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Re: Dry stacked block column

Postby Andyfteeze » Fri Sep 30, 2016 3:17 am

I agree with sometimewoodworker. He has hit on something i have been looking at for some time.
You need to think carefully about what you are trying to acheive as far as thermal insulation goes. Thermal mass can be used to stabilise the inside temperatures of the house. No thermal mass means its quick to cool and quick to heat. Too much and it can stay hot for long periods.

Why do you want a cavity wall? I ask this question because you started with the proposition .
If you use concrete, cement blocks or bricks a cavity is needed because they are porous materials. If you use AAC blocks with an acrylic render, a cavity is not needed or it can be filled with an extra insulator. Unless you plan a feature wall, have another think.
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Re: Dry stacked block column

Postby ajarnudon » Fri Sep 30, 2016 3:01 pm

Thanks for your responses guys. Starting with the columns and wall: I was probably a little misleading when I spoke initially of a retaining/perimeter wall. I need a retaining wall on three sides, above ground height starting at close to zero on the street side, gradually rising to be about 1.2 m at the rear boundary. The wall itself will have no wind factor as it will be laterally supported by fill on one side (yes, with the proper drainage) and with cantilevered foundations. In lieu of a perimeter wall I am thinking about a concrete post/barbed wire fence on top of the retaining wall, covered up with a hedge. In respect of the columns, these will be built on very substantial reinforced footings, so when driving rebar through the fresh concrete it will only go down to the top of the foundation, not into soil. And yes, there is probably no reason not to drive in the steel as soon as the blocks are filled. 600mm into the concrete in a relatively small block cavity should keep it stable enough to manoeuvre the next three blocks over the protruding rebar.
As far as the house goes, the external walls will be doubled skinned block. The wall cavity has several useful purposes including a duct for serevices, an air gap preventing direct thermal transmission to the internal surface, and allowing air to come in at the bottom (weep holes) and convection cooling with the hot air rising up the cavity into the very high, insulated and ventilated roof space. A car port keeps the sun off most of the southern-side wall, while the rest of the southern side and the west will be sun-protected by trees. My idea of using the AAC block inside is to prevent heat transfer in the air conditioned rooms.
Cheers
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Re: Dry stacked block column

Postby Sometimewoodworker » Fri Sep 30, 2016 3:17 pm

ajarnudon wrote:As far as the house goes, the external walls will be doubled skinned block. The wall cavity has several useful purposes including a duct for serevices, an air gap preventing direct thermal transmission to the internal surface, and allowing air to come in at the bottom (weep holes) and convection cooling with the hot air rising up the cavity into the very high, insulated and ventilated roof space. A car port keeps the sun off most of the southern-side wall, while the rest of the southern side and the west will be sun-protected by trees. My idea of using the AAC block inside is to prevent heat transfer in the air conditioned rooms.
Cheers


As I said concrete block on the outside provides a good heat storage system, venting the gap doesn't change that it just means that you have nice walm air for most of the night. Also if the blocks are prevented from getting hot by an AAC skin there's not a significant heat transfer anyway.

Why not use AAC on both skins? It is cheaper than the standard block both in itself, in the glue needed to fix it and the time taken to lay the blocks.

Take a look at my build for an example.

7.5cm blocks can be sourced for 15baht each
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Re: Dry stacked block column

Postby ajarnudon » Sat Oct 01, 2016 7:59 pm

Might be a case of overkill, but apart from the roof insulation there will also be reflective foil in the wall cavities.
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Re: Dry stacked block column

Postby pipoz » Sat Oct 01, 2016 9:23 pm

ajarnudon wrote:Might be a case of overkill, but apart from the roof insulation there will also be reflective foil in the wall cavities.


I used a double skin block wall (150mm superblock on indise & 70mm block on external) with 30-40 mm air gap in between the two skins.

Have no problems with heat transfer from outside to inside and no cracks in walls. "Udon Thani Happy House". Also have Black Tiles on the roof

As you indicated, a lot depends on which direction you face your house (for those main evening living/bedroom area and also how you protect the southern wall faces from the sun.

I put my day-time main living area in the center of the house, so it gets minimal direct sun on the external wall areas - the doors leading to that living area are open during the day, most of the time, so the inside living room temperature runs at the outside ambient temperature of the day and my Helicopter fans justmoves the air around.

In the evening when cooler, we close the doors to the living room and run the AC for an hour or two, then retire to the cooler bedroom areas (also with Mr Ken fans). It all works fine for me.

Re Lateral strength. This comes from the foundation as I would have it, with two Js coming from the cage up into the column 600mm, and a large footing cantileverd inside the wall and 1 metre below the undisturbed soil level. Lateral rebar into the vertically reinforced cavities of the adjacent wall blocks. Maybe I could up the rebar size on the corner columns. The maximum retention height of my retaining wall is only 1.2 m. I am thinking of a 1.2 m barbed wire fence for the perimeter wall on top, with a hedge planted both sides. OK, I'll have to buy a powered hedge trimmer, but this can be used for the topiary as well. -

I drilled & epoxied 8mm plain bar starters/ties into my 250x250mm concrete column, tied my block wall inner skin to that column, plus concrete filled with vertical 12mm reo some mid span area of the block wall (i.e. midway between footing), tied my concret lintels to the blcok over windows & doors. Some of my block wall sections between column actually span their length and self support themselves to a large degree, from column to column - "She ain't going to fall down" :lol: :D

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Re: Dry stacked block column

Postby ajarnudon » Sat Oct 01, 2016 10:45 pm

Back to the original topic. The land is a parallelogram (not quite square) measuring 27 m on each side. I have decicided to go with the dry stacked block pillars - one on each corner with four intermediate pillars on each side to provide the necessary lateral support from the cantilevered foundations. The pillars will be almost as far below ground level as above.
Have just about settled on the floor plan - external dimensions will be:
Width: 10.4 m plus a 4 m tandem car port/laundry/workshop.
Length: 12.25 m plus front and rear patios taking the total length out to 20.6 m. Don't want to get too far off topic, so I will save the rest for 'My Construction'.
Before closing, my final words about beating the heat. I am convinced that the No.1 factor in keeping house temperatures down is to protect the building from sun exposure. I have downloaded tables (courtesy of the US Navy) which give accurate hourly solar azimuth and elevation data for any given day of the year. Using this I have been able to produce a design that ensures windows never allow sun into the interior on any day of the year. In my case and alignment, 1.2 m eaves keep most of the sun from the external walls. As the azimuth is predominantly to the south (9 months of the year) this is where I have built-in most solar protection. Apart from the building design, tall trees will be planted along the southwest and western boundaries - with foliage trimmed up to the three metre level to preserve the pleasant rural outlook. The trees will shade the walls and a good portion of the roof.
The proof of the pudding will be in the living comfort once we move in, but if not entirely successful first off, there are plenty of remedies available. These include shade sails, large vertical season-adjustable metal louvres mounted clear of the walls, and dual-sensor auto switching powered (from solar cells) roof cavity ventilation. And as mentioned earlier, the living area and bedrooms will be air conditioned (sparsely used I hope).
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Re: Dry stacked block column

Postby ajarnudon » Sat Oct 01, 2016 10:53 pm

Hi Pipoz
I had already writen my last post before I saw yours, so I let it go up anyhow. It seems that we think along similar lines, and what you say makes a great deal of sense to me. My build will be in a village called Ban Thuam, go 13 kms north of Udon then 13 kms west towards Ban Phu. I will get to have a look at your construction posts soon, and if you are around it would be good to have an eyeball sometime - maybe around Christmas when I have holidays (work in BKK). Thanks for your response, John.
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