rick_rine
Link to Zolo
I want to make a pergola. I want 8 concrete columns, Greek style. I live in Tassie so shipping of precast columns is out of the question. I have Googled and tried to find form work to make my own without any luck. Does anyone have any ideas, where to buy, how to make, web sites to visit?
Thanks
Richard
KBs PensNmore
I saw where someone had made their columns from corrugated iron. A box was made for the base and top, shaped to suit. If you could make a sample of what was required, then make a split mold from it out of plaster of paris.
Kryn
rick_rine
Thanks Kryn but I would not try to use a plaster cast eight times on a 2.4 metre column as I doubt it would work. I appreciate the comment and had already thought along those lines. I think it , the mould, would have to be made of fiberglass or something similar. I am thinking of mini orb to curl around in an 180 mm column.
i will make the base and top separate from the column. I wonder if a plaster cast would last 16 times and how to make a nice pattern. I do not want a simple pattern. Ideally there would be leaves and more.
i am also keen to explore ideas for the roof beams, grape vines and such.
appreciate all ideas.
thanks Kryn.
Richard
Bushmiller
Richard
If you grab hold of an old carpenters book such as "The Australian Carpenter and Joiner" you may get some ideas there. In my copy of that publication there is a section on Boxing for a square column and I think you would have to make a modified version of that.
Pouring concrete into a vertical form is problematical.
1. There are tremendous pressures at the base if the column is a significant height and the structure has to be very strong, but with threaded rod it can be used many times.
2. You will need to prevent the concrete separating if it is poured from a height (2.4m ?). Baffles
3. You will need to be able to vibrate the mould to achieve a smooth finish on the column. The mould has to also be able to withstand that.
4. I would suggest a square form with packing to take something like a mini orb profile. The mini orb can be treated with a bond breaker to enable re-using and easy dismantling. It would have to be in two halves, but the corrugation lends easy mating of the halves.
5. Use a fine aggregate.
6. Reinforced cage (deformed bar) will be essential.
7. Cast the top and bottom separately.
8. It is not going to be an easy process.
Good luck
Regards
Paul
ian
mostly :whs:
what you want to do is doable, but problematic for the unwary/inexperienced
getting a good smooth finish (no holes, no exposed agregate) off the form is dependent upon your concrete mix, placement method, vibration, curing
you are probably looking at readymix, a concrete pump and 8 moulds -- not a cheap exercise
mixing yourself? well, you'll need around 4 portable mixer loads (2 cu.ft per load) per column and getting an invisible join between the mixer or barrow loads could be challenging
the finished colums will weight in the order of 200+ kg -- which suggests a crane to move them into position
maybe, shipping them in from a precaster will not be that expensive in comparision
Timless Timber
If you do make them, they would be far and away stronger load bearing, if they were "pre stressed", which means the reo bar reinforcement is put under longitudinal tension (like wire strainers) before the concrete is poured and tension not released until after the concrete is fully cured.
So the mould in addition to everything already described - should be devised such that its possible to add substantial tension to the reo bar by use of a straining mechanism that's secured to something immovable (buried in the ground) and capable of considerable tension (hydraulic jacking system or block and tackle for eg).
The weight bearing capacity of the column pre-stressed is far higher than un-stressed if that makes any sense.
Just to add to your woes! :wink:
Not saying it can't be done coz it can, just that it takes a well thought out & repeatable design is all.:2tsup:
Bushmiller
Richard
Another thought for a re-useable mould is to obtain a large diameter steel pipe (about 200mm) that the mini orb can be placed inside. The pipe would need to be cut in half lengthways and then provision made to bolt it together. You might be able to pick something up from a scrap metal merchant if you decided to go down that track.
Regards
Paul
Mobyturns
Check out building demolition material recyclers, as they may have some of the old concrete moulds lying around the place. In FNQ we used to hand mix and hand pour concrete columns in situ for highset houses using both timber and steel moulds into the 's. Most of those mould were nothing more than a square cross section with arised corners formed with a quad, tri-quad or ovolo section. Italian builders were quite adventurous with their sections.
rick_rine
I have calculated (http://www.calculator.net/concrete-calculator.html?slablength=5&slablengthunit=foot&slabwidth=2.5&slabwidthunit=foot&slabthick=5&slabthickunit=inch&slabquantity=1&holediameter=2.5&holediameterunit=foot&holedepth=6&holedepthunit=foot&holequantity=1&tubediameter=15&tubediameterunit=centimeter&tubeindiameter=1&tubeindiameterunit=centimeter&tubedepth=240&tubedepthunit=centimeter&tubequantity=1&circcal=Calculate) the weight of a column 150 mm x 2.4 m as being 90 kg and using .04m3 of concrete. This does seem low. I have a concrete vibrator but will just tap the formwork often. I will not worry about prestressing the reo as it is a garden ornament/feature so the structural integrety is not vital, if it cracks the reo will hold it together. I have bought a plastic mould from USA for $25 + $50 shipping. This features leaves and will be used for the top and bottom pads. I hope it lasts 12-16 times. maybe I could make a mold of a finished form...
The columns I think I will use 150 mm PVC sliced up one side. I don't think miniorb will work. Perhaps I will just have them plain.
I might make concrete beams to go from post to post to hold the wisteria but timber treated would be lighter and easier.
Thanks everyone and please post any more suggestions/ideas. I will not be doing the job until summer really sets in.
rick_rine
Richard
2. You will need to prevent the concrete separating if it is poured from a height (2.4m ?). Baffles
l
Hi Paul, I imagine you are referring to the cement separating, That is why I am concerned about using the mechanical vibrator. It did not occur to me that dropping the concrete in from a height would have the same effect but I think you might be right. Maybe do it on an angle and pouring the concrete down the sides would alleviate it.
rick_rine
I found a brass fireplace surround and used it for for work on a retaining area last week.
ian
If you do make them, they would be far and away stronger load bearing, if they were "pre stressed", which means the reo bar reinforcement is put under longitudinal tension (like wire strainers) before the concrete is poured and tension not released until after the concrete is fully cured.
So the mould in addition to everything already described - should be devised such that its possible to add substantial tension to the reo bar by use of a straining mechanism that's secured to something immovable (buried in the ground) and capable of considerable tension (hydraulic jacking system or block and tackle for eg).
The weight bearing capacity of the column pre-stressed is far higher than un-stressed if that makes any sense.
Just to add to your woes! :wink:
Not saying it can't be done coz it can, just that it takes a well thought out & repeatable design is all.:2tsup:this is not one for the faint hearted or the "she'll be right" brigade.
things to keep in mind if you go down that path
Pre-stressing needs a very strong mould (usually one made of steel) to push back against the force pulling the stressing wire
pre-stressing can easily induce a bow in the column
you don't want to be anywhere near a stressing wire if one lets go
Concrete properties for pre-stressed product tend to be rather tight in terms of mix ratios
pre-stressing can be an "inexact" science
I have calculated (http://www.calculator.net/concrete-calculator.html?slablength=5&slablengthunit=foot&slabwidth=2.5&slabwidthunit=foot&slabthick=5&slabthickunit=inch&slabquantity=1&holediameter=2.5&holediameterunit=foot&holedepth=6&holedepthunit=foot&holequantity=1&tubediameter=15&tubediameterunit=centimeter&tubeindiameter=1&tubeindiameterunit=centimeter&tubedepth=240&tubedepthunit=centimeter&tubequantity=1&circcal=Calculate) the weight of a column 150 mm x 2.4 m as being 90 kg and using .04m3 of concrete. This does seem low. I have a concrete vibrator but will just tap the formwork often. I will not worry about prestressing the reo as it is a garden ornament/feature so the structural integrety is not vital, if it cracks the reo will hold it together. I have bought a plastic mould from USA for $25 + $50 shipping. This features leaves and will be used for the top and bottom pads. I hope it lasts 12-16 times. maybe I could make a mold of a finished form...
The columns I think I will use 150 mm PVC sliced up one side. I don't think miniorb will work. I'm calculating just over 100kg per column.
the column will need to be well braced so it doesn't fall over
you will need a platform of sorts to stand on while you fill each column with concrete
also I think 150mm might look too slender for a "grecian" style column
to avoid spalling you want to make sure you have about 50mm cover to the reo -- which in a 150mm column translates to a something like a single bar up the middle
IMO round steel or timber posts are starting to look like a very viable option
Hi Paul, I imagine you are referring to the cement separating, That is why I am concerned about using the mechanical vibrator. It did not occur to me that dropping the concrete in from a height would have the same effect but I think you might be right. Maybe do it on an angle and pouring the concrete down the sides would alleviate it.Yes concrete will separate if just dropped into a mould.
tipping the mould to 45° doesn't aid much to avoid separation and your bracing now needs to support the entire length of the post.
to avoid unsightly voids, air bubbles and the like vibration should be vigorous and in the concrete itself
rick_rine
Thanks Ian for your comprehensive posts. It is clear you have a great deal of knowledge on the subject. I am now thinking of a 6 stage column, and yes treated timber would be easier and cheaper, but that is not what I want. So I will have a foundation, probably 4 bar trench mesh, 8-9 metres long. A square column base easily formed by myself with reliefs made on a scroll saw. This would be made do that black ply for form work. This would be 1.2 metres high. Then there might be the relief form from American 200 mm high and a custom orb column 1-1.2m high then another American bought ($50 for postage) form on top. Then I the treated pine or concrete frame for the top. It will all be tied together. These columns will weigh about 160 kg.
I appreciate your comment about the look of a thin column. It is something for me to consider but if it is only 1 or 1.2 m over a square pillar it might be okay. I must draw it up but I am only getting ideas together. My original post was really hoping to find retailers who sell for work but I am over that now. I think the ideas are coming together and I thank you all at WWF.
ps. Where in Sydney are you. I grew up in Hornsby (Mt Colah)
ian
ps. Where in Sydney are you. I grew up in Hornsby (Mt Colah)almost in the Harbour, I once joked that I was eying off the Opera House as a shed
DamianD
Hi Richard,
I used to do a lot of commercial formwork and often used farmatube for round columns. It comes in diameter 150mm+. Very easy and fast to use, all you have to do is secure the bottom and top making sure its plumb and pour the wet stuff in. Give it a tickle with the vibe or formies vibrator (slap it with your hammer a few times) and strip the tube off the next day :2tsup:. You could probably attach your reliefs after. Only thing is you can't reuse the tube.
Good Luck
Damo
rustynail
Split PVC pipe makes a good form, provided a good release agent is used. Whale oil is one of the best, but good luck with getting that. When making columns, we rip the pipe in half then use stainless steel split clamps to hold the two halves together. The closer the clamps are together the better the joint. The clamps with mounting feet are handy as they can be screwed to an available vertical surface, keeping the column upright during the pour.To overcome the problem of concrete separation a length of gal pipe down the centre of the form helps, provided the drop is not too great. The length you are talking would be fine. The steel pipe also gives some reinforcing to the finished column. It also gives a fixing point at both top and bottom of the finished column. Keeping agrigat size small also helps prevent separation, along with aiding a better surface finish. We have found external vibration to be more effective than internal on thin columns. It is most important to commence vibration from the start of the pour at the bottom of the column to help release trapped air and continue, up the column, right to the completion of the pour.By delaying vibration air pockets will develop and be unable to rise through the above layer of concrete.
Hope this helps and good luck.
rick_rine
Thanks Damian and Rustynails, I greatly appreciate your advice.
I am pretty excited. So far I have about 8 bases made and that is a learning experience. I now have 4" tubes inside to hollow them out. This, along with spray and cook, means they fall out of the mould after 24 hours curing. I was concerned about the 6" columns but have seen some on the local pub veranda and they don't look too small.
I am going to practice by firstly making a base for a garden ornament ( see photo) and then making a small pergola of the same di mentions but just one stage, in another part of the garden. This will be 2x2x2.3 high. The final one wil be 5 stages of 2x2 to make it 10 metres long by 2 metres wide.
I am now using the vibrator on the moulds. It won't reach down into the columns though so I will just tap them. The height of tghe columns alone will be about 1.9 metres. This will make the pergola about 2.4 m high. I don't want to go throught the trouble and expence of gal pipes. I can see the advantage. My plan is to use 10mm deformed bar tied into the 3 bar trenchmesh and this will protrude up 2.2m. just below the top of the column pvc formwork. When pouring I will concrete in gal strapping to hold on the 195mm treated pine beams. Perhaps the deformed bar will minimise the cement separation?
Thanks again every one. This post had me thinking about the concreting I have done over the years. I estimate that I have poured 60 cubic metres by truck and hand mixed the same amount! I must have some Italian in my blood. smile.
Bushmiller
Thanks Damian and Rustynails, I greatly appreciate your advice.
I am pretty excited. So far I have about 8 bases made and that is a learning experience. I now have 4" tubes inside to hollow them out. This, along with spray and cook, means they fall out of the mould after 24 hours curing. I was concerned about the 6" columns but have seen some on the local pub veranda and they don't look too small.
I am going to practice by firstly making a base for a garden ornament ( see photo) and then making a small pergola of the same di mentions but just one stage, in another part of the garden. This will be 2x2x2.3 high. The final one wil be 5 stages of 2x2 to make it 10 metres long by 2 metres wide.
I am now using the vibrator on the moulds. It won't reach down into the columns though so I will just tap them.
Rick
A quite passable concrete vibrator to be used externally is the cheapest, nastyist orbital sand you can find. We used such as this very successfully on pebble mozaic pavers like these
For those the sander was screwed to a base and turned on for three or four seconds. I think just holding it to the pipework mould would suffice. Cheapest sander you can find. I think we used an XU-1 brand. It's vibration you want :wink: .
Regards
Paul
rick_rine
I have 3 bar 11 mm trench mesh in my test project. I will use 12 mm deformed bar going up inside a 150 mm PVC tube. The starter bar will be tied into the trenchmesh. I would appreciate some ideas on how to keep the 12 mm bar in the centre of the PVC. The PVC tube will be about 1.9 m high.
the foundation formwork allows for footings 0.32 m wide and about 0.2m deep. Under the columns footings are about .3 x .3 m x .3m.
rustynail
Rick,
We found deformed bar in thin columns was a real problem. Smooth bar or pipe has far less "shattering" as the concrete is poured. The distance between the form and the bar is only 120mm or so, which means the bar has a pronounced separating effect on the mix as it goes down. Also, black steel protruding from the ends of the columns is a rust starter.
The method we use to keep the pipe in the centre of the column is a base board with a hole for the pipe and a routed groove circle for the form tube. Another options would be blocks holding the form tube central on the board.At the top, the pipe is held with a legged ring clamp which attaches to the same vertical surface as the ring clamps holding the form tube.
rick_rine
Thanks Rustynails. Today I poured the first column, I was happy with the way it went but I won't know how good it is until I pull off the PVC in a day or two. I had already bought deformed bar so tried to minimise its affect by inserting a 50 mm PVC conduit over it and tried to pour the concrete down that. It did not work that well. I forgot to get rid of the air bubbles often and had poured in one mix, about point eight metres height, before I remembered.
the reason for this post is my surprise at how the concrete shrunk quickly, I assume because of the water content. I had levelled it off at the top of the PVC tube but thirty minutes later it was down by thirty mm. I am glad I am making a practice project.
ian
Today I poured the first column, I was happy with the way it went but I won't know how good it is until I pull off the PVC in a day or two.
snip
the reason for this post is my surprise at how the concrete shrunk quickly, I assume because of the water content. I had levelled it off at the top of the PVC tube but thirty minutes later it was down by thirty mm. I am glad I am making a practice project.I think it more likely that what caused the settlement was either air working it's way out of the form, or free water being absorbed back into the mix.
out of interest how "sloppy" was your mix
rick_rine
Hi Ian. The gravel I am using is finer than standard and is very hard to get the mix right. It is as if the mix is a bit dry and you add one cup of water and it goes sloppy. The mixes have been wetter than I would prefer but I think it is going to work. I had a sneak-peek at yesterdays column, peeled it back a tad, and it looks okay so far. I did another column today and it also sunk by 30-40 mm. Not surprising when I think about it, it's only 2% of the length, but it was something I did not foresee. Using the 50 mm PVC has I think aided in the removal of air bubbles as when it is pulled out I jiggle it to settle the concrete. I have not been too aware of cement coming to the top excessively.
ian
Rick
from this distance it's a little difficult to suggest much in the way of mix design
Given the small diameter of the columns, a 10mm coarse aggregate is probably where you should be looking -- and a rounded rather than angular stone.
Then for fine aggregate you probably need some 5mm and sub 2mm sand.
Cement content (for the fines) should probably be up around 20% of the total mix (including the water), unless you can get some graded fly ash in which case you could swap about 1/3 of the cement for fly ash.
I'd start with around no more than 450mm of water for every 1 litre of cement -- maybe start with as little as 400ml of water and add addditional water at the rate of 50mm per litre of cement -- I think you should be aiming for a water:cement ratio of about 50%. Maybe a bit more, maybe a bit less.
You will want a plastic rather than a sloppy mix.
Also, I suggest that rather than climbing a ladder to cast trial columns, you should cast some trial blocks. These could be stripped 36 hours after pouring to get a look at how they turned out.
Keep notes of the mixes you're using to find the one that will work best for your project
On reflection, the concrete dropping down from the top of the form is most likely due to settlement, which suggests uneven vibration -- some areas within the column are more dense than others
rustynail
Thanks Rustynails. Today I poured the first column, I was happy with the way it went but I won't know how good it is until I pull off the PVC in a day or two. I had already bought deformed bar so tried to minimise its affect by inserting a 50 mm PVC conduit over it and tried to pour the concrete down that. It did not work that well. I forgot to get rid of the air bubbles often and had poured in one mix, about point eight metres height, before I remembered.
the reason for this post is my surprise at how the concrete shrunk quickly, I assume because of the water content. I had levelled it off at the top of the PVC tube but thirty minutes later it was down by thirty mm. I am glad I am making a practice project.
Rick,
A 30mm slump does not surprise me at all, particularly if the mix is very wet. Slump is a percentage of height so you would be looking at only about one percent. Just top it up while the concrete is still wet.
It would seem you are working alone. Thats unfortunate as continuous vibration during the pour is critical to achieve consistent results.
I am a little concerned that the conduit over the reo bar may cause more problems than it solves. It will restrict the column diameter too much for easy concrete flow. Also, when the conduit is drawn out, it will allow air right to the bottom of the column and then all the way to the top as it is drawn out, with only fall-in of the concrete to fill the void. May be better to do away with the conduit and lube the bar instead.
When using fine agrigate, the amount of water in the mix requires far more care. For consistency, it would be better to use containers for each of your ingredients ie buckets or drums.
Dont leave the PVC formwork on too long as you may get sticking, particularly towards the top, due to the release agent being rubbed off during the pour.
Once stripped, column must be kept wet 7days to prevent surface cracking.
Your form work looks good. Show us a pic of the stripped column, no matter how it turns out, so we can make any recommendations if necessary.
rick_rine
Thanks Rustynail and Ian.I pulled the formwork off the first column today. I am quite happy with the result. The attached photos make it look much worse than it is. The mix was 10 sand/gravel to 2 cement. I did not then measure the water. The sand/gravel is quit fine with the gravel being no larger than 5 mm. It is not sharp but it is not round and smooth either. The bottom of the column, where I forgot to tap the formwork, is actually very good. The top of the column is not as smooth and the middle has the most air bubbles. I can see what you are saying rusty about the PVC. I agree with you but think next I will try much smaller PVC, 20 mm. I think it might help with the jiggling action. In the main project I will use smooth round bar as suggested and not use any PVC inside. Ian I don't really have much choice in aggregate mixes and to be honest, if this column is strong enough, I am quite happy with the result so far. My main regret is that I had the clamps 280mm apart. It is clear that at least down the bottom they need to be no more than 140 mm apart.( I ordered a dozen from blackwoods 10 days ago but they still have not arrived :~ ) This is shown in the 4th photo where there is the gap between the clamps. Where the clamps were there is no problem. I ran out of whale oil last week so until my next trip with the Japanese I am using vegetable oil. It worked well. It seems strange as it must get wiped off as the concrete is poured down the tube. The columns are 150 mm in diameter. Being curious I gave it a very, very gentle push. It did wobble a tad. I was hoping to build the pergola with a flat top. This however would give no diagonal bracing. I am a bit concerned that the structure, the main one, might not be strong enough.
Bushmiller
RR
I thought your concrete mix might be a little light on with cement and Ian has mentioned that aspect is important. My take on concrete (but I am no expert) is that the finer your aggregate the higher content of cement you require. The reasoning behind this is that in an ideal world every particle of aggregate needs to be completely coated with cement. As fine aggregate occupying a given volume had a larger surface area than a coarse aggregate it becomes clear that you require more cement.
I would be reluctant to say exactly what the cement component should be and others may be able to advise. If not a call to the Cement and Concrete Association may be of help. However my memory is that they man the phones on a volunteer basis and may only be there during mornings for example.
The project looks as though it has potential. Good for you for trying.
Regards
Paul
rick_rine
RR
I thought your concrete mix might be a little light on with cement and Ian has mentioned that aspect is important. My take on concrete (but I am no expert) is that the finer your aggregate the higher content of cement you require. The reasoning behind this is that in an ideal world every particle of aggregate needs to be completely coated with cement. As fine aggregate occupying a given volume had a larger surface area than a coarse aggregate it becomes clear that you require more cement.
Thanks Paul. That makes sense.
Regards
Richard
ian
The mix was 10 sand/gravel to 2 cement. I did not then measure the water.
The sand/gravel is quit fine with the gravel being no larger than 5 mm. It is not sharp but it is not round and smooth either. The bottom of the column, where I forgot to tap the formwork, is actually very good. The top of the column is not as smooth and the middle has the most air bubbles. I can see what you are saying rusty about the PVC. I agree with you but think next I will try much smaller PVC, 20 mm. I think it might help with the jiggling action. In the main project I will use smooth round bar as suggested and not use any PVC inside. Ian I don't really have much choice in aggregate mixes and to be honest, if this column is strong enough, I am quite happy with the result so far. Hi Rick
as alluded to by Paul, you need enough fines in the mix to completely fill the voids between the aggregate particles.
In your case filling the voids is less about strength and mainly about the surface appearance -- the right mix design and enough vibration will give you a nice smooth column without any surface voids.
rick_rine
[QUOTE=
Cement content (for the fines) should probably be up around 20% of the total mix (including the water), unless you can get some graded fly ash in which case you could swap about 1/3 of the cement for fly ash.
I'd start with around no more than 450mm of water for every 1 litre of cement -- maybe start with as little as 400ml of water and add addditional water at the rate of 50mm per litre of cement -- I think you should be aiming for a water:cement ratio of about 50%. Maybe a bit more, maybe a bit less.
You will want a plastic rather than a sloppy mix.
Keep notes of the mixes you're using to find the one that will work best for your project
s[/QUOTE]
thanks Ian, today's column was measured accurately. I used 2 water, 3 cement and 12 aggregate. I could not use less water. So although it is what I would call a 4:1 mix in fact the cement is not 20% of the total mix. It is in fact only 17.6% if I understand you properly. If I make 2:3:10 that would satisfy the requirement and that is what I will do on the fourth and final trial post. The water to cement ratio is much lower than you suggest. Do you think this matters? I would think the less water the better. The posts do look a bit on the thin side. At least 200 mm would be better but I could not find any fancy formwork on line except the one I bought. Perhaps I should have tried harder but it will be okay. On the main project I am thinking of making the distance between the post 1.5 m x 2 m wide.
Rustynail, I used smaller PVC today but I will take your advice for the final post and lubricate the bar instead.
I think for the main project I will put in three bars of reinforcing, one 12 mm and two 6 mm.
black woods have still not got the clamps so I modified the arrangement and I believe it will be better.
To to minimise the flex in the posts if I am too concerned I could go back to the idea of having the posts sit on a square pillar, say .4 x .4 x 1 metre high. Then the columns would only be 1 metre high.
just to clarify, although I am calling this a test project it will still be a pergola, just smaller and in a corner of the garden that cannot be seen from the house. It is behind the trees. The main one 10 m x 2 m will be in front of the dam, easily seen from the house.
rustynail
If you are short of clamps, just use a doubled piece of fencing wire in the form of a bushmans twitch. If you put a clamp every 400mm and then a twitch in between each clamp that should be plenty, I trust you know what I mean by a bushmans twitch.
I dont think there will be much advantage in putting in extra reo. It will make it hard to get the concrete down. The rods would require ties to stop them bellying in or out during the pour. These ties would then load up with concrete in such a small area.
A bit of bicol in the water may help eliminate those small surface voids. Burt most importantly, plenty of external vibration,from the bottom up, during the pour.
I'd up the cement content too.
ian
Hi Rick
thinking back on the big pours we did in the past, the mix had around 330kg pf cement and 150kg of fly ash per cubic metre, and a water:cement ratio of under 0.45 = less than 150 litres per cubic metre. For some pours we dropped the water cement to 0.38, but the dry mixes were real bastards to place.
these were road pavement slabs and if the mix was too wet the concrete would run down the cross-fall. we needed the high fines content to get a durable and void free surface
for your mix you need plasticity so it stays together as it drops down the form,
lots of fines to avoid surface voids
and lots and lots of vibration to get the air out
if the form is a tending to wobble or bulge, stiffen it with a timber battern on one or two sides
rustynail
Rick, you may be making life hard for yourself with such thin columns. If you increased the size to 200 or 300mm it would give more pressure against the form, which would assist with air escape during vibration.
rick_rine
Hi Rustynail. The columns are looking pretty good. I would have liked to make them thicker but I could not find suitable moulds. To anyone reading this post, if you know of any please tell me. This is actually why I started this thread. I would prefer they were 200-250 mm .
Having said that, the project is looking as good as I could have hoped for. I am very pleased thanks everyone. The final column was poured today with the help of my eight year old son who tapped and tapped with me. I had been wary of tapping too much as I was concerned about the cement separating. I am not so concerned now as all the WWF advice has been to tap, tap and tap, also I have heaps of cement in the mix and I have not experienced the cement seperating in this job so far. The mix has been increased to 1:2:6 water, cement, aggregate. This, to me, is a 1:3 mix. Twice the strength of my normal, general purpose, concreting. The posts are very flexible and I am slightly concerned about this. I might need to put diagonal bracing on the structure, but it is just to hold up a vine.
I think the posts are too high and with the major project I think I will lower it by 150 mm.
ian
Hi Rick
I won't say "looking good" till I see the surface finish on your last post :)
re flexibility, I presume you mean the posts are prone to wobble on their bases.
This is to be expected until you tie the tops together to create a portal frame. For safety -- no one wants to be hit on the sconce by a concrete post -- you should continue to brace each post till the portal beams go in and are connected
rick_rine
Thanks Ian. No the posts are secured to the bases with the reinforcing rod coming through from the trench-mesh and there is no wobble on the base The concrete post actually bends slightly as it is pushed. I have seen this before on a 6" thick suspended slab. A builder jumped up and down on the fully cured slab that was cantilevered and unsupported where he stood and it bounced, or flexed, quite a lot.
rustynail
Rick,
Pipe rather than bar will give you more rigidity. If you are concerned about having a void down the middle of the post with pipe, just fill it with concrete at the end of the pour.
Bushmiller
Thanks Ian. No the posts are secured to the bases with the reinforcing rod coming through from the trench-mesh and there is no wobble on the base The concrete post actually bends slightly as it is pushed. I have seen this before on a 6" thick suspended slab. A builder jumped up and down on the fully cured slab that was cantilevered and unsupported where he stood and it bounced, or flexed, quite a lot.
RR
I think you have just discovered the reason for reinforcing in concrete.
Concrete has little tensile strength (but extremely good compressive strength). The reinforcing is there to make up the deficiency in tensile strength.
In a column there is also the problem of resistence to sideways force. Fortunately the main force will be compression and probably not very much of that either; Just the roof.
I agree with Rustynail that you would make life easier for yourself by increasing the diameter of the column.
Regards
Paul
ian
The final column was poured today with the help of my eight year old son who tapped and tapped with me. I had been wary of tapping too much as I was concerned about the cement separating. I am not so concerned now as all the WWF advice has been to tap, tap and tap, also I have heaps of cement in the mix and I have not experienced the cement seperating in this job so far. The mix has been increased to 1:2:6 water, cement, aggregate. This, to me, is a 1:3 mix. Twice the strength of my normal, general purpose, concreting. The posts are very flexible and I am slightly concerned about this. I might need to put diagonal bracing on the structure, but it is just to hold up a vine.
I think the posts are too high and with the major project I think I will lower it by 150 mm.
re flexibility, I presume you mean the posts are prone to wobble on their bases.
This is to be expected until you tie the tops together to create a portal frame. For safety -- no one wants to be hit on the sconce by a concrete post -- you should continue to brace each post till the portal beams go in and are connected
Thanks Ian. No the posts are secured to the bases with the reinforcing rod coming through from the trench-mesh and there is no wobble on the base The concrete post actually bends slightly as it is pushed. I have seen this before on a 6" thick suspended slab. A builder jumped up and down on the fully cured slab that was cantilevered and unsupported where he stood and it bounced, or flexed, quite a lot.
Hi Rick
from this distance, I think the wobble has two sources
1) the concrete is still very green -- it will probably take another 2 weeks to develop near full strength
2) the mix used for the first few columns is too weak. From recollection the tensile strength of concrete is less than 1/10th the compressive strength. I think you said that your first few mixes were 1 cement to 5 gravel/sand and pretty wet. At a guess this would give a compressive strength in the range of 10-15 MPa, with a corresponding tensile strength possibly <1 MPa. The mix with the much higher cement content probably has a tensile strength around 3.5 MPa. I can't tell from nearly km away, but I fear that your first few columns may not be durable.
I think the higher cement content mix will fix the wobble -- you shouldn't need additional reinforcing.
However, I'd keep at least one decent size bar down the centre to act as a tie down rod for the column and eventual pediment
rick_rine
I have finished. The columns do look pretty good. I am very happy and thanks for all the advice. I will make some changes when I make the big project.
ian
hi Rick
you can't leave it like that
you have to tell us how the last column compars to the first -- surface voids, wobble, etc
rick_rine
Hi Ian. The last post was tapped a great deal, almost constantly. I did not see much difference. It still had many air bubbles. It was the strongest and did not wobble as it was a 1:3 mix. The one with the least air bubbles was the first post which was made of wet mixes, ones that I was unhappy with as I thought the mixes too sloppy.
If I build the big project I will 1) make mixes 1:3 2) make the mixes a bit wet. 3) mount the posts on square pillars about 900 mm high to reduce wobble. 4) make the posts mm apart. 5) tap constantly.
ian
Hi Ian. The last post was tapped a great deal, almost constantly. I did not see much difference. It still had many air bubbles. It was the strongest and did not wobble as it was a 1:3 mix. The one with the least air bubbles was the first post which was made of wet mixes, ones that I was unhappy with as I thought the mixes too sloppy.
If I build the big project I will 1) make mixes 1:3 2) make the mixes a bit wet. 3) mount the posts on square pillars about 900 mm high to reduce wobble. 4) make the posts mm apart. 5) tap constantly.
Hi Rick
diagnosing from a distance is always tricky ...
1) It looks like a 1:3 mix is the choice in respect to eliminating "wobble"
2) given your vibration technique -- external taping of the form -- a wet mix is preferred to a dry one
3) there's no reason to have short columns -- I rather like your slender trial columns -- the wobble is mostly due to a mix with too little strength
4) I can't comment on the column spacing -- with the right strength concrete this will mostly be an issue of aesthetics
rick_rine
Put points on the beams. I had half a dozen cans of interior paints in the shed with a bit left in them. Mixed them all together to make four litres and sprayed it today. Looks great. Yes I know it is interior and inferior paint. I'm not worried. The vine will cover it.
I am very proud and thanks for your help and support people.
rick_rine
rick_rine
Having trouble uploading photos but I thought I would share my new test pergola. This one has an 800 mm high square base which will reduce the sway in the posts. Also the posts are closer at 1.5 m centres. I reverted to standard gravel and sand mix 3:1 gravel:cement. I used a mechanical vibrator in the posts and in the base. One thing I overlooked was to tie down the base. What happened to the first one is that the concrete lifted the formwork up off the foundation. This oversight was easily fixed with the remaining posts. There is a photo of the first pergola as it is now and the work in progress on the new one. There are more air pockets in these posts, probably because, as I said, I reverted back to standard gravel instead of the fine stuff but it could also be because I used the mechanical vibrator and did not tap the concrete as often when I placed it in the PVC pipe.
rwbuild
I know we come from the land down under but can us locals get a photo that we can relate to?
rick_rine
I am enjoying building the third and main pergola. I estimate that I have laid 100 cubic metres of concrete in my handyman life but this has been the ultimate in learning about this fantastic, malleable material. The mould I bought from America was stated to last 16 pours. I have made over 30 and have about 16 more to go so hope it lasts the distance.
Beside the practice/test pergolas I have made lots of tests columns and moulds.
There will be just under 9 ton of concrete in this pergola if I build the cross bars from concrete which I am seriously considering. I will then be able to curve the arches.
I have been very worried about lining up all the columns but am very pleased so far.
It is a great project both physically and mentally.
Mini-orb has been used form the columns.
I can't post the pictures properly. Sorry.
DropSaw
Hi rick_rine,
i spent 30 odd years making molds
statues column's retaining walls fountains pots
all out of concrete i used fibreglass to make the outer casting.
iv worked for BGC concrete in
perth for 12 months before getting sick of that.
ideally you want the thickest concrete possible
and use a plasticizer, this is an additive to make
your concrete go from 30 slump to 100 slump the additive last for about 15/20 min so you need to work fast
before the concrete returns to 30 slump or what ever it was before adding plasticizer, we used it all the time for tilt up walls were high strength was needed. The less water you add to concrete the less shrinkage you'll get.
rick_rine
The columns have been made with mini orb and look great. In the columns I used 10 mm reinforcmnt and a 4-1 gravel cement mix. In the beams I have used nylon fibres and two six mm reinforcment bars. It has been over two years in planning but looks amazing. Mostly mixed by hand. Poured in-situ. Almost perfectly straight and level surprise. I am using 4 concreting gravel, 3 bickies sand, and two cement for the crossbeams. They are 3 metres long with a span between the posts of two metres, they are .1 wide and 0.14 high. The supporting beams are 0.1 x 0.18. The posts are on a 0.3 x 0.3 base with 0.15 diameter columns moulded with mini orb. No scaffolding was needed as they sat up right and I poured the concrete in with a garden pot.
rick_rine
The he pergola is twelve metres long, two metres wide, has 18 columns and has taken six months about so far to build. I am thinking of a clematis or wisteria. I got the idea when I was in Italy a few years ago. One of a kind! No one else would have one of these in their backyard, and probably no one else would want one either &#;
Bushmiller
Rick
Seeing those columns immediately made me think Appian Way and Aqueducts. It looks extremely impressive!
An amazing project.
Regards
Paul
Concrete construction is a common activity found on most jobsites throughout the world, one of the critical activities that goes into making sure that the concrete ends up where it needs to be is formwork. This Guide provides information on designing, erecting, using and dismantling formwork.
Formwork means the surface of the form and framing used to contain and shape wet concrete until it is self-supporting.
Formwork includes the forms on or within which the concrete is poured and the frames and bracing which provide stability. Although commonly referred to as part of the formwork assembly, the joists, bearers, bracing, foundations and footings are technically referred to as falsework.
Formwork construction may involve high risk activities like operating powered mobile plant like cranes, working at height and excavating foundations.
If the work involves high risk construction work, a SWMS must be developed in consultation with workers and their representatives who are carrying out the high risk construction work as defined under the Work Health and Safety (WHS) Regulations.
A safe work method statement is a document which outlines the steps in which a task needs to be performed and the hazards and controls necessary to help make the work safe.
The design of the final concrete structure can have a major effect on the ease of formwork construction and the health and safety of people during construction. Generally the more basic and simple the final concrete structure, the safer it is to construct, erect and dismantle the formwork.
An experienced formwork designer should be consulted during the design of in-situ concrete structures to enable the health and safety risks during formwork construction and dismantling to be considered in the design.
The formwork designer must be competent in formwork design including documenting temporary work platforms and special equipment needed for safe formwork construction on-site.
A designer may use a technical standard or a combination of standards and engineering principles relevant to the design requirements as long as the outcome is a design that meets regulatory requirements.
Want more information on concrete column formwork? Feel free to contact us.
Formwork should be:
Formwork drawings should include details of:
The formwork designer should determine the vertical pour rates for walls, columns and other vertical concrete elements before completing the formwork design.
Details of the construction method and erection sequence should be included on the formwork drawings where appropriate. Where special methods like external vibration are involved the formwork design should allow for any resulting additional structural loads.
Where formwork is to be re-used, the formwork design should ensure form strength is retained after allowing for the deterioration of materials through use, handling and storage.
All formwork drawings should be certified as complying with applicable laws. Components from different formwork systems should not be mixed unless a competent person, for example an engineer, has authorised the component use. Variations to a design of a system should be checked and verified in writing by a designer, engineer or other competent person.
The design of the permanent structure affects the risk of injury from slips trips and falls (and from falling objects) during formwork construction and use. While often not reasonably practicable, permanent structure design measures that can reduce these risks include:
The design of formwork systems can also reduce the risk of slips trips and falls by providing adequate safe access and fall and falling object protection.
The design of formwork systems can reduce the amount of manual handling required in formwork activity. To reduce manual handling risks use:
The safety of workers erecting, using and dismantling the formwork should be considered when choosing a formwork system for a particular job. In particular consider stability, strength and the risk of falls, falling objects and manual tasks. The best proprietary systems have integrated safety features to help control the risk of falls and hazardous manual tasks.
Traditional formwork systems (plywood formwork) are typically constructed on-site from timber or plywood and supporting elements like scaffolding.
When using a traditional system, a standard formwork frame with a known tested loading capacity should be used wherever possible. Standard frames can minimise the risk to workers erecting and dismantling the formwork and handling and storing materials.
Modular formwork systems (aluminum formwork / steel formwork) are specially designed and manufactured off-site. Modular systems usually have proprietary formwork components and rated load calculations set out by the manufacturer and are often made from hardboard, plastics, steel and aluminium products. Most formwork systems use two or more materials, for example plywood facing to steel frames for wall panels.
Modular systems are often lighter weight and require less physical effort than traditional systems. This minimises the risk of injury resulting from manual tasks. However because of their lighter weight, modular systems may be more susceptible to falling over when erecting the system due to factors like wind loading. Generally this will only be an issue before placement of the formwork deck on the modular system. To effectively control this issue the modular formwork system should be progressively braced in accordance with the suppliers instructions during its erection.
Wall and column forms should be designed to withstand wind loading before, during and after the concrete pour. The bracing and forms should not be removed from the cast element until it can safely withstand potential impact loads and wind loads.
Lateral support can be provided to vertical elements in a variety of ways including horizontal and angled braces and structural connections to other parts of the building. A bracing element design should be completed by a competent person.
The bracing element should also be able to resist both tensile and compressive loads that may be applied by the wind. Anchors for braces should preferably be cast-in type anchors or &#;through-bolts&#; extending through both sides of the anchoring medium. Drill-in anchors of the following type may be used provided they are installed in accordance with the manufacturer&#;s instructions:
Note: Some jurisdictions may not accept these types of installations, so check with your WHS regulator.
Drill-in anchors should be installed in accordance with the manufacturer&#;s instructions.
They should have their torque set using a torque wrench or other reliable method to verify the torque, for example a calibrated &#;rattle gun&#;. Written records verifying the setting torque for drill-in type anchors should be available at the workplace.
Suitable access should be provided for wall and column forms and may include:
Edge protection should be provided on the access platforms. Preferred methods of entry to platforms include stair access systems or if this is not practicable secured industrial ladders.
The entry method should allow room for a person and be positioned at a height and distance from the form to minimise a person&#;s effort and movement. The concrete pouring system should permit enough space for a person to stand with edge protection provided. Where stair access passes a formwork deck, joist or bearers should not protrude over the stairs.
Platforms should also be designed to resist loading that may be applied during a concrete pour to ensure the platform does not collapse or overturn. They may need to be tied in or counter weighted, particularly aluminium scaffolding which may not have the self-weight to prevent overturning.
Mobile work platforms should have their castors locked, except when relocating the mobile platform.
The designer should ensure a trailing access system can support the loads that will be applied to it including wind conditions and an emergency evacuation situation. Both the system itself and the form should be able to withstand applied loads from the access system.
Wall and column forms should be provided with designed lifting points. Design drawings should confirm this. Cutting holes in the form in-situ is not recommended as this can damage the form, be inadequate lifting points and make it difficult to safely attach lifting gear.
Wall and column forms should only be lifted with a positive lifting system, for example lifting lugs or by slinging the lifting slings around the form so the form cannot slip out of the slings. Purpose designed lifting lugs should be used instead of slinging the load because there is less risk of the load becoming inadvertently disconnected from the crane hook.
Where lifting lugs are attached to the form they should be attached in accordance with the design.
Formwork frames should be erected progressively to ensure the installers&#; safety and the stability of the overall structure.
Braces should be attached to the frames as soon as practicable and designated access ways should be indicated by using bunting or by other means.
If side bracing or other edge protection is installed progressively on formwork frames other control measures to prevent a fall occurring may not be required.
Many conventional formwork frames consist of diagonal braces that cross in the middle. While these braces are not considered to be suitable edge protection for a completed formwork deck, they may provide reasonable fall protection during frame erection. This is only the case where braces are installed in a progressive manner as soon as the frames are installed.
As the height of formwork frames increase there is a greater need to provide lateral stability to the frames. Ensure framing, including bracing, is carried out in accordance with on-site design documentation and manufacturers&#; instructions. People erecting formwork must be trained to erect formwork using safe methods.
The risk of internal falls while erecting frames can be controlled by fully decking each lift of the formwork decks and false decks. This involves:
During dismantling of a lift, decking should be removed while standing on a fully decked platform immediately below.
Where the next formwork deck would require people to stand at heights of 2 metres or more above the finished formwork deck to install bearers and joists for the next formwork deck, a continuous &#;false&#; deck, which is a full deck the same area as the floor being formed, should be provided.
This deck should be provided both inside and between formwork frames and typically consist of formply, scaffold planks or modular platform sections.
A protected entry opening can be left in the deck to enable materials to be lifted. Using a captive platform system is preferable to lapped planks because a captive system cannot be accidentally dislodged. Lapped planks may only be used if secured against uplift and slipping.
The false deck should be constructed so there are no large gaps and gaps only exist where a vertical member of a frame passes through the deck (see Figure 1). Gaps should not exceed 225 mm in width.
A false deck should be able to support the expected load of workers and materials during construction and people or objects that could fall onto the deck. Access should be provided to each of the false decks.
When considering the design of the deck for erecting, altering or dismantling formwork, the weight of the false deck and live load should be applied to the formwork support structure.
The height between the false deck and the pouring deck should allow entry for a person during stripping. Workers must take reasonable care for their own safety by not climbing the framework.
Where the potential fall distance is less than 2 metres, an intermediate work platform can be provided that is at least 450 mm wide (see Figure 2).
Bearers are the primary horizontal support members for a formwork deck that are placed on top of formwork frames. They are usually timber but are sometimes metal. They should be placed in position by people located on a secure platform no more than 2 metres below them.
Bearers should be positioned so they will not fall off the top of the frames. The usual method to do this is by placing the bearers in U-heads on top of the frames and by minimising cantilevers. U-heads should be used where two bearers abut. Where only single bearers are placed in the U-head, the bearer should be placed centrally in the U-head unless a formwork designer, engineer or other competent person states otherwise. This can be achieved by rotating the U-head or by using timber wedges.
Where the top of the supporting member consists of a flat plate, the bearer should be nailed or otherwise effectively secured to the plate. Flat plates should only be used where specified by a formwork designer, engineer or other competent person.
Where a false deck is provided at 2 metres or less below a worker, joists may be spread on the bearers with the worker standing on top at bearer level.
If the height of the formwork deck being constructed is more than 2 metres above a continuous deck or surface below it, joists should be spread from a platform located within 2 metres of that surface, underneath the deck being constructed (see Figure 2). This work platform should be a false deck but an intermediate platform may be used.
A person should be provided with a working platform at least 450 mm wide (two planks) when the potential fall distance is less than 2 metres. It is not acceptable for a person to work from a single plank or bearer.
One example of a work system that may be used to do this is as follows:
A formwork deck should be laid in a progressive way so people will be provided with a method to prevent them from falling below the deck.
This control measure is particularly important in situations where a false deck has not been provided within 2 metres below the level of the deck to be laid. In this situation formply may only be spread on the joists provided:
1.8 metres (see Figure 3). Therefore, if a person falls they will fall onto the joists and should be prevented from falling further. In some situations, there may be a possibility of a person falling through the joists if the joists spread as the person&#;s body makes contact. This
is more likely to be a potential hazard when the person falls onto the joists in the same direction as the joists. Implementing controls to minimise sideways movement of joists will minimise this possibility.
Where a leading edge is involved and the distance below the deck being constructed is greater than 2 metres the SWMS must detail how work will be completed to control the risk.
Cantilevered bearers, joists and ply sheets can be hazardous when left unsecured. The weight of material or a person standing on the cantilever may make the timber see-saw and cause the person or material to fall. When designing the formwork system, the use of cantilevers should be kept to
a minimum. In some situations using cantilevered sections is unavoidable. In these cases, a formwork designer should consider the potential for people and stored materials to cause cantilevers to pivot.
Wherever the weight of a person will cause a cantilever to pivot, the formwork design should include
measures to secure the cantilevers so this will not occur. This may include temporary propping, nailing, bolting or another effective method. If nailing is used the formwork design should specify the nailing detail and this should be followed. This may include the use of purpose designed or proprietary brackets. Materials should not be stacked or stored on a cantilever section unless the section has been designed to carry the load. Temporary working platforms cantilevered from shoring frames are a form of cantilevered scaffold. Where a person or object could fall more than 4 metres from a scaffold, workers involved in erecting, altering or dismantling them must hold a scaffolding licence. The minimum licence class for this type of work is Intermediate Scaffolding.
Open penetrations like stairwells or penetrations to allow for services create hazards for people on the deck, for example a fall through a larger penetration, stepping into a smaller penetration or an object falling through the opening onto people below. A penetration where there is a risk a person or an object could fall through should be guarded.
Protect open penetrations with edge protection like handrails or by securely covering them so no one can fall through them. Penetrations in concrete slabs may include cast-in-mesh as a back-up system. The mesh should be of a small aperture, for example 50 x 50 mm mesh size or smaller and made of material capable of withstanding the potential imposed loads. Where mesh or other physical fall protection material is to be provided for larger penetrations this should be included in the slab design specifications to ensure it can withstand potential loads including those applied by people, equipment and material.
Where holes are cut in the mesh for services to pass through the hole should be cut to the profile of the service so the mesh remains in the penetration and the load carrying capacity of the mesh is not reduced below design specifications.
Using plywood covers alone is not a satisfactory risk control because:
Plywood covers should be structurally graded, painted in a bright colour and marked with wording, for example &#;Danger penetration below&#;. The cover should be firmly secured to the concrete and designed for potential loads that may be applied, for example workers, materials or plant that may travel over the cover.
Before stripping formwork, cover the penetration that will be exposed as the formwork is stripped or protect the penetration before starting the stripping operation.
Penetrations are also hazardous before the deck is laid. Joists placed up to the edge of the penetration should be secured so the timbers cannot spread if a person falls on them.
Steel fixers, plumbers and electricians often follow closely behind the formwork erection. The formwork zone should be large enough to ensure these people are clearly separated from the form workers.
A &#;formwork only&#; zone should be maintained behind the leading edge. This zone should be clearly marked by signs and a mesh barrier. Figure 4 shows the &#;other work&#; zone, the &#;formwork&#; zone and the area retained as edge protection&#;four joists spaced mm beyond the laid deck.
Temporary walkways laid across reinforcement mesh can be used to control the risk of slips and trips when multiple trades are entering large areas where reinforcement mesh has been laid behind formworkers.
A physical barrier should be provided and maintained to separate the formwork work zone from other workers. This barrier should be rigid, capable of maintaining its integrity in an upright position and capable of supporting signage if required.
Formwork decks are rarely flat across the entire floor, generally due to deep beams or &#;drop downs&#; sometimes called &#;capitals&#; around columns. Uneven floors introduce fall hazards.
These hazards are most effectively managed by ensuring formwork supports and the deck are progressively constructed for the lower parts of the deck before work starts on the higher- level areas of the deck.
During formwork construction the structure is constantly changing so continual modification of fall protection measures is also necessary.
When there is only one leading edge where the other edges are provided with scaffold edge protection or safety screens, providing fall protection on the leading edge is relatively straightforward. However, where there are multiple leading edges or the deck is not at one consistent level, fall protection may be difficult to implement.
Where the design of the formwork is complex, it may be impractical to provide edge protection on leading edges because the profile of the deck is constantly changing and constructing leading edge protection would create more hazards than it would control. For example, the people installing the edge protection could be exposed to risks when installing the edge protection.
In some situations it may be necessary to provide perimeter edge protection on edges of the formwork deck.
Examples where edge protection should be installed are:
Perimeter containment screens or a scaffold are effective means of edge protection on a completed formwork deck. Scaffolding should be erected before the formwork and prevents workers falling off the completed deck. The main advantage of these systems is people
are not required to install edge protection on the perimeter of the formwork deck and are therefore not exposed to a risk of falling. The other advantage is edge protection for people installing the final perimeter formply sheets is already in place.
Where suspended, cantilevered, spur or hung scaffold, or any scaffold from which a person or object could fall more than 4 metres from the platform or the structure is used, any erection, alteration or dismantling of the scaffold must be carried out by licensed scaffolders. Cover gaps between a completed floor and scaffold after the formwork is stripped if there is a risk of a person or materials falling through the gap.
In some situations it may be impractical to provide perimeter containment screens or scaffolding. Use a work system to install perimeter edge protection on the deck which eliminates or minimises the risk of a fall.
Harness systems should not be used because they do not provide a practical control for the risk of a fall from height from the perimeter of formwork.
If required, edge protection can be substituted with an alternative measure provided this measure prevents a person falling from the edge. One alternative is providing a barricade
1.8 metres back from the edge with clearly visible warning signs.
Perimeter containment screens are protective structures fixed to the perimeter structure or working platform to prevent objects and people falling outside the work area. This significantly minimises the risk of injury to other workers and the public.
Screens should be used throughout the whole construction process especially while erecting or stripping formwork. They are usually sheeted with timber, plywood, metal or synthetic mesh.
Screens may be supported by the building or structure or by a specifically designed scaffold. The screens can also act as perimeter fall protection on a top working platform and should extend at least 2 metres above the working surface to provide protection for the public and workers outside the contained work area.
When selecting containment screens consider:
Containment screens should remain in position from the start of the formwork being erected until soffit stripping is complete to prevent objects falling throughout the process.
To prevent material from falling below, gaps between perimeter screens and the formwork deck or floor should not exceed 25 mm.
Inspection and certification processes each contribute to controlling risks during the construction of formwork and falsework.
Inspections and clearance to load should occur at key stages during the construction of formwork including when formwork is being loaded, for example with formwork components, equipment or pre stressed tendons and prior to its completion.
A separate certification process should occur when the formwork is complete and prior to concrete being poured.
A competent person such as an engineer with experience in structural design (certifying engineer) should inspect and certify that completed formwork meets the design specifications and is structurally sound before it is loaded. Generally certification will not be required for formwork and falsework in housing construction work.
The certifying engineer should complete and provide a Formwork Structural Certificate
to the person with management or control of the formwork, often the principal contractor. An example is at Appendix A.
Where a scaffold is being used there are specific requirements to control entry to the scaffold and for inspection and certification prior to use.
The formwork should not be subjected to a load until it is confirmed as meeting the design specification, for example by completing a pre-pour inspection before placing concrete.
Loads should not exceed the design loading specified by the designer.
To maintain stability of the forms the placement of concrete should not exceed the maximum calculated pour rate and the inboard part of formwork should be placed before proceeding to any cantilever section.
Hoisting, pumping and other equipment should not be attached to the formwork unless specifically allowed for in the formwork design.
Formwork should be monitored as it is loaded to check for indications of potential failure or collapse and that vertical and horizontal movements do not exceed specifications.
A competent designated observer should continuously monitor the formwork assembly during concrete placing operations and be provided with an appropriate communication system to alert others in case an emergency arises.
Other than a designated observer, no person should be underneath a formwork deck during concrete placement. An observer should not stand directly underneath an area where wet concrete is being placed into the forms.
Competent persons should be available during concrete placement to carry out any emergency adjustments or repairs. The concrete placement should cease during adjustments and repairs.
Once the concrete is cured and before starting the stripping operation a competent person, for example an engineer with experience in structural design should provide written confirmation the permanent structure is self-supporting and the formwork can be removed. The certification should be based on the design specifications for the structure, the verification of the strength of the concrete mix and the time period elapsed since the pour.
Documentation from the concrete supplier verifying the concrete specification should be available on request. A concrete sampling and testing procedure should be in place to verify the concrete meets its design specification.
A competent person should also provide input into the SWMS on formwork stripping to ensure the permanent concrete element will not fail and result in structural collapse.
As with formwork erection, the stripping operation should be carried out in an orderly, systematic and progressive manner, considering the risks of falls, falling objects and manual task hazards in the now enclosed space.
When assessing the risks from stripping formwork consider:
Formwork removal should be carried out in a systematic way so the deck is gradually removed as the support system. Formply may be removed by partially lowering the support system and then dropping the segment of the deck (sheet) onto the support system. This eliminates the need to manually lift sheets of ply from ground level.
Stripping formwork is easier when the strength of the bond between the form material and the concrete is reduced. The bond will be dependent on the material characteristics and the smoothness of the form material. A liquid bond breaker can be used on wall and column forms to reduce the strength of the bond but use on floor forms is not encouraged because it can cause a slip hazard.
&#;Drop stripping&#; describes the method used when all of the formwork support system is removed and the formply is then allowed to drop to the level below either by its own weight or by people levering it off.
Drop stripping should not be used. It can be very hazardous because the formply is likely to fall uncontrolled and can hit people in the vicinity of the work.