Moscow, the largest city on the European continent, just had to be included in our City Collection.  Love or hate the idea of Russia and what it stands for, one cannot ignore the importance of Moscow when it comes to world history and art.

When I think of Moscow, I immediately think of the Red Square with the square box shapes of the Kremlin wall to the south of the square, in stark contrast to the round colourful towers of St. Basil’s cathedral right next to it.

It was these circular shapes of St. Basil’s cathedral that inspired the Moscow bollard.  This bollard is made up of circles interacting with each other creating a play of circles ‘cutting and filling’ along the height of the bollard.

Application

With its light facing directly down, it illuminates the concave concrete body of the bollard giving of a beautiful glow of light in a 180deg arc.  This makes the Moscow bollard great to use as edge lighting to define an area like a pathway, boundary wall, parking areas, or even your fire pit.

With the light source facing vertically down, the risk of the light source being disturbing is minimal making it ideal for use close to residential structures, walkways and next to driveways.

Features and Benefits

As with all our concrete products, the Moscow bollard is made from our high strength wet cast concrete.  Due to the wet cast process, each product is presented as it comes out of the mould with the timber mould details captured beautifully in the surface of the concrete.

Small air bubbles and slight mould bleed that are sometimes visible on the edges gives a unique and authentic appearance that only concrete can give, which is why we have been in love with concrete for so many years.

As with all our concrete products, our tried and tested two coat concrete sealant process gives this bollard a stunning, natural matt finish that will last for years.

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Johannesburg

Our City Collection would just not be complete without a Jo’burg tribute.  Johannesburg, with its rich history, cultural mix, and extremes bordering each other is a truly international city.  For me, it’s a smaller version of New York, which is exactly what our Jo’burg bollard is.

The Jo’burg bollard is versatile, durable, and very affordable which, combined with great aesthetics makes it ideal for almost any outdoor lighting application.

Application

The Jo’burg is one of the most versatile bollards in the City Collection series.  With its compact size and slightly angled light source, it projects light at an angle of 120° to form an oval pool of light in front of it.

It is ideal to light up pathways, circulation areas like a fire pit or open patio, and accentuate entrance areas.  Placing the bollard inside a landscaped area creates a stunning light effect with depth of field, where the light bounces off the vegetation in front of the bollard without taking anything away from the light emitted to the surrounding areas.

Features and benefits

As with all our concrete products, the New York bollard is made from our high-strength wet cast concrete.  Due to the wet cast process, each product is presented as it comes out of the mould with the timber mould details captured beautifully in the surface of the concrete.  Small air bubbles and slight mould bleed that are sometimes visible on the edges give a unique and authentic appearance that only concrete can give, which is why we have been in love with concrete for so many years.

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Introducing the new City Collection from Elemento.

But why a city collection, you may ask?  Well, the answer is simple and singular… Concrete!  Concrete is at the heart of any city; it is the essence of it.  Yes, there are steel and glass also, but without concrete, no city would exist.  Concrete is what gives a city its strength, its texture, its form, beauty, and longevity.  It is this same concrete that our City Collection is made of.  So, the thought of drawing life and inspiration from cities around the world for our new bollard collection became just too compelling to ignore.

New York

Many of us have never been to New York but have seen lots of photos of the city and watched lots of movie scenes playing off in its streets.  The one thing that has always struck me about this city is the needle-like appearance of the skyscrapers stacked so closely together.  I can just imagine what it must be like walking in between these tall thin structures with the sunlight peering in from the top, washing down the sides of these slender, tightly packed, skyscrapers.

It was with this image in mind that the New York bollard came to light.  This tall slender concrete structure with light peering in from the top, washing down the side of the structure, Illuminating and accentuating the concrete texture.  The thin sharp edges of the light recess speaking of the crispness that can be produced with concrete and of the strength thereof, being able to be formed in such slender elegance.

Application

The New York is one of the most versatile bollards in the City Collection series.  With its relative height and slightly angled light source, it projects light at an angle of 120° to form an oval pool of light in front of it.

It is ideal to light up pathways, circulation areas like a fire pit or open patio and to accentuate entrance areas.  Due to its tall light column, placing the light inside a landscaped area creates a stunning light effect with depth of field, where the light bounces off the vegetation in front of the bollard without taking anything away from the light emitted to the surrounding areas.

Features and benefits

As with all our concrete products, the New York bollard is made from our high strength wet cast concrete.  Due to the wet cast process, each product is presented as it comes out of the mould with the timber mould details captured beautifully in the surface of the concrete.  Small air bubbles and slight mould bleed that are sometimes visible on the edges gives a unique and authentic appearance that only concrete can give, which is why we have been in love with concrete for so many years.

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To construct a 44.4m long raking, curved, off-shutter concrete roof for a curved passage linking living spaces for a very unique residential development.  The roof comprised two 16,5m and one 11,4m raking, curved sections with ends stacked on top of each other, and this whole stacked roof structure was suspended on slender 300mm concrete columns up to 4,9m high.  Each section of the roof also had a recess on top for planting, with all the necessary drainage installed in the 300mm concrete columns.

Options…

The first challenge with this roof was the columns.  Firstly, the columns had to be erected in the correct position, to the nearest millimetre.  Then, if a 4,8m high column is out of plumb by 0,1deg, the top of the column is off by 8mm.  By the time you are 0,3deg out of plumb, which you still cannot see with the naked eye, you are off by 24mm at the top…

The first option was to erect the columns as best as possible and then build the formwork for the roof with timber, by hand.  With this method, we would be able to compensate for any tolerance on the concrete columns but to construct curved, raking formwork, almost five meters up in the air for 44m long would take too long and the risk of getting it wrong, would just be too high.

Due to the complexity of the shape, I wanted to go with prefabricated steel formwork.  The benefit of the three, identical stacked roofs were that I could re-use the formwork three times, which brought the cost for the steel formwork within a justifiable price for the client.  The big benefit of the steel formwork was the speed with which we could erect the formwork and the accuracy we would have.  I just had to figure out how to allow for a degree of tolerance on the columns.

Getting the columns plumb

Obviously the first thing to focus on is how to get the columns as accurate as possible.  Due to the whole passage curving, no two columns lined up so to set up a reference grid was not going to work.  To survey each column after erection was going to be too expensive and time-consuming.  In the end, I decided to use a 1,6m long digital inclinometer (a fancy name for an electronic spirit level).  With this inclinometer, we could measure up to 0.1deg accurate, so we would get close, within the constraints of the steel column formwork.

I further had special brackets made up to attach push-pull props to the column formwork.  What made these brackets special was that the hole in the brackets for the push-pull prop pin, had a 0,2mm tolerance, so it was a very tight fit.  I wanted to be sure that there was no play between the formwork and props once the formwork was plumbed.

The second way in which we allowed for as much tolerance on the columns as possible, was to make the openings, where the columns would go through the steel formwork quite a bit bigger than what was required for the column diameter.  This would allow room to get the steel formwork to line up with the columns and the second benefit was that I had steel ‘compensation rings’ made up with which I could finish very tight up to the concrete columns and seal them, to prevent any concrete from the roof, leaking onto the columns.  Due to the complexity of the assembly, we would not have been able to get to the underside of the formwork to clean up any leakage after the pour and by the time we removed the formwork the damage to the columns would have been done, so I wanted to reduce the risk of leakage as much as possible.

Modular assembly

Although the profile of the three roof sections was the same, the length and ends of each roof section were different.  The symmetry in the design made it possible to fabricate the steel formwork to be completely modular making that all three roofs could be formed with one set of formwork with interchangeable parts.

While I figured out how to make the formwork modular, I want to give a big shoutout to the guys at Staluform who did a great job at designing the detail of the formwork.  It was very well thought out, well constructed and easy to work with.

How to form a curving soffit ?

The soffit was formed using resin face board.  What worried me when I drew out the formwork (I always do a board layout for concrete soffits) was that the joint lines on square boards, would not follow the curve of the roof.  With the small infill pieces that would be required and the joint lines being almost random to the soffit lines, it just looked wrong.

So I worked out the angle with which the perpendicular line to the curve would change with each board, which was 1,54deg per board and then had all the resin face boards waterjet cut at a 1,54deg angle on one side with the other side remaining square.  The result was that the joint lines on the soffit of the slab were always perpendicular to the edge of the curved roof.

Creating the planter on top

Creating the planter recess on top of the roof required a ‘flying shutter’ which followed the curve of the roof.  To form this, I had lugs welded to the top sides of the steel formwork at around 400mm intervals to which 114×50 SAP runners were bolted.  To these runners, we fixed a 170mm wide steel flat bar which we could bend to form the ‘flying shutter’.

Unforeseen problems…

As with any construction project, regardless of how much thought and planning you put into a project, there are always surprises along the way.

One of these was with the very tall, slender columns.  Upon stripping the first two columns we placed, we found horizontal cracks around the circumference of the columns at certain intervals.  Something I have never encountered before.  After some investigating and careful demolition of the first column, we saw that these were segregation cracks that formed at the stirrups as the concrete was setting.

So we demolished the two columns and tried again, with an altered concrete mix with a higher segregation resistance.  Upon stripping the formwork, the same cracks were still present.

The only alternative now was to negotiate with the engineer to increase the rebar cover from 25mm to 60mm to give the concrete space to settle between the rebar and the side of the formwork.  The engineer eventually agreed, and so we set off, re-bending 386 stirrups to the smaller diameter.

After the third try and four demolished columns, we finally had our first two columns poured.  Thereafter everything went pretty much as planned.  The tolerance we built into the steel formwork for the columns was pushed to the maximum in one of the roof sections, but we always had enough play to work with that the steel formwork fit around the columns.

Construction progress

Fresh out the mould as the formwork is being stripped

The end product

As can be seen from the photos, the only patching we had to do was around the columns to remove the marks left by the ‘compensation rings’.

To finish off these passages, we moulded custom copings to accommodate sectional glazing that went from floor to ceiling with stiffening webs in between each section of glazing.  I will cover my process of making custom concrete copings on-site in a separate blog, so keep a lookout for that.

Conclusion

Although there was nothing really out of the ordinary with this build, I hope you learned something about working with tolerances, planning soffit board layouts, and enjoyed seeing the finished product, as much as I enjoyed building it!

Should you require any assistance with your next concrete project or would like to get more information about our moulded concrete solutions, feel free to contact me at anton@elemento.net.za

The post Constructing a Raking, Curved Off-Shutter Concrete Roof appeared first on ELEMENTO.

“You employ stone, wood and concrete, and with these materials you build houses and places.  That is construction.  Ingenuity is at work.  But suddenly you touch my heart, you do me good, I am happy and I say:  This is beautiful.  That is architecture.  Art enters in.” – Le Corbusier

The Brief

A few years ago I had the privilege of building my own house and, being true to my love for concrete, I just had to have an off-shutter concrete fireplace in my living room.  By this time I’ve done several off-shutter projects but never had to form a ‘window’ type opening in a concrete structure.

And that was exactly what the challenge with the fireplace was.  How do you get the concrete to fill up to the underside of this ‘hole’ that you ‘box out’, right in the middle of the formwork?

Constructing the fireplace by doing it in two pours to first finish the bottom of the opening, would work and be quite easy to do, but I refused to accept any horizontal joints in my ‘Piece-de-Resistance’ fireplace… and patching the concrete afterwards where the second pour would join the first was just not an option.  The opening had to be created in one pour, while filling the mould perfectly all around the opening.  So, I set off, trying to find a solution to cast the perfect opening in an off-shutter concrete structure.

Options… Options…

After some consultations with concrete and formwork specialist, I considered the following options:

• External concrete vibration. The first problem with this option was the cost of external vibration units.  They are quite a bit more expensive than a normal concrete poker and drive unit assembly and with limited application, it just could not justify spending that kind of money for only a fireplace.  I could also not find one for hire, which sort of proved the point that they probably cost too much for the limited application options.

Another aspect of using external vibration that I was not happy with, was that there would be no visible way to see that the concrete-filled to the underside of the box-out formwork properly.  You would have to vibrate and hope that the concrete-filled the formwork… and hope is not a plan!

• Self-Compacting Concrete (SCC). SCC was an option, but back in 2013 (when I built this fireplace), SCC was not as readily available as it is today and once again, an expensive option.

One other consideration with SCC is the high hydrostatic pressure due to the high slump flow associated with SCC, which adds considerable load to the formwork.  I was going to use a brick-built kicker and not a concrete kicker, to save cost and time.  So, building formwork that’s strong enough for the hydrostatic pressure, on a brick-built kicker looked like quite a risk to take.

Don’t get me wrong, there definitely is place for SCC in off-shutter concrete construction which I will cover more in future blog posts.

Working through these options, I realized I knew what I wanted and what the concrete needed.  By not using SCC, it meant the concrete would have to be vibrated.  I also wanted to be able to visually see that the concrete has filled to the underside of the box-out formwork.  Eventually, after a lot more thinking and talking to various experts, the solution started to take shape.

The Plan

The concept started with the idea of creating openings, through the opening box-out, to drop conventional concrete pokers through, with which we could vibrate the concrete in, directly under the box-out formwork.  After considering some options, the idea of putting PVC pipes through the box-out was born.

The final plan was actually quite simple…  Place 75mm PVC pipes in strategic positions, through the box-out, which would allow concrete pokers to be dropped through to vibrate the concrete into the underside of the box-out.  While placing and vibrating the concrete, it would be possible to see through the 75mm pipes that the concrete is filling in below the cavity under the box-out.

So, it all sounds great, but what about the concrete-filled pipes going through the opening when everything is said and done?  My ‘get out of jail free’ bit, with the concrete-filled pipes in the final opening was that the pipes could be placed in an area of the opening that would be covered by the fireplace.  So after cutting out the concrete-filled pipes, the marks where the pipes were, would be closed by the fireplace.

So with a carefully crafted plan, we set off building the box-out for the opening and the rest of the formwork.

Funny how, with all the focus on technical stuff, the practical often gets left behind… I still remember the frantic phone call from site to my wife as we were doing the final assembly of the formwork; ‘So dear, how high from the floor do you want your fireplace to be?’

40MPa Concrete !?

With that resolved, the final assembly was completed, ready for an early afternoon pour.  I ordered a 40MPa concrete mix with a 120 slump.  With the fireplace clearly not bearing any load, you would wonder why 40MPa with 120 slump concrete?  There are a few reasons for this:

• A 40MPa concrete mix contains more fines so it gives a much smoother finish showing more of the formwork detail.
• Also because of the higher paste content, it ‘seals’ better in the formwork joints, making it less prone to leakage, which is one of the causes of honeycombing in concrete.
• I also like the high early strength of a 40MPa mix which make it less prone to damage when the formwork is removed.
• When doing off-shutter concrete, I always order a 120-slump mix. It costs a bit more but the additional flow that you get, helping to fill the formwork as good as possible, is fully justifiable compared to all the other costs incurred to get a good ‘off-shutter’ finish.

Ok, so enough of the technical stuff and on to the pour.  The truck arrived on time, slump test was spot on, and we were ready to go.  Since we were only placing 3.5m³ concrete, we placed with buckets by hand.  Everything went great.  The concrete-filled the sides of the mould and as we went up with the concrete level, we started vibrating through the 75mm pipes.  I could clearly see how the concrete levelled out under the box-out until it filled to the underside of the box-out and into the pipes… And then disaster struck!

Disaster !

I got a frantic shout from one of my workers Patrick, next to me.  ‘Eish boss, hy’s vas!’.  ‘What do you mean?’ I replied.  ‘Die poker boss, hy’s vas, ek kry hom niks los nie!’ (the poker is stuck, I can’t get it out!).  After some inspection, I realised that a poker, going through one of the 75mm pipes, twisted below the box-out and got stuck, and no amount of pushing and pulling was getting it to come loose.

To add insult to injury, Patrick, in a state of panic, decided to turn the drive unit off, with cries of ‘NOOO!’ coming from the others as they saw this.

So, the way to get a concrete poker to vibrate is to start the drive unit and then give the poker a good shake or bump, which makes it start to vibrate.  Our only hope of getting this poker out was that is would vibrate itself loose.  But with the poker stuck and now turned off, that was sure not going to happen…

It’s crazy how many thoughts can go through your head in a moment of crisis…  ‘All this planning and hard work, gone!’,  ‘Do I break open the formwork before the concrete sets and start again?’,  ‘What will my fireplace look like with a concrete poker right through the middle?’, ‘How do I explain this to my wife?!’.

Thomas to the rescue

After, what felt like forever, one of my trusted workers, Thomas said, ‘Moenie worry boss, ek maak ‘n plan!’ (don’t worry, I have a plan!).

In a moment of clarity, Thomas dropped a second poker down the side of the box-out until he could push it up against the now, dead stuck poker.  (PS, always have a spare poker and drive unit at hand when placing concrete!)  From there he pushed and poked and pushed and poked until he got the stuck poker started, which also made it come unstuck!

This situation had the franticness of an accident scene where a patient is receiving CPR, everyone watching, holding their breath in anticipation. And then, the relief when the patient gives a gasp of breath again!

The rest of the pour went without incident.  I left the formwork in place for around 36 hours and then stripped.  I immediately cut the, now concrete-filled 75mm PVC pipes out using a normal masonry cutting disc.  You don’t want to leave it in place to later cut through 40MPa concrete.  That will be a proper waste of a diamond-tipped blade.

The final product

As you can see from the photos, after a lot of sweat and almost tears, I got my perfect opening!   Well almost… If you look closely at the top of the opening, you will notice a slight bow where the box-out deformed under the weight of the concrete.  Lesson learned; the next box was built strong enough!

The concrete was cured by wrapping it in plastic.  I left the concrete wrapped for approximately three months, other than for the opening I had to cut to install the fireplace.  I will cover my views on concrete curing in a separate blog, so keep a lookout for that.

That Concrete-Will

Over the years, I have learned that concrete does what concrete wants to do.  It has a will of its own.  But you can get to learn this ‘concrete-will’ over time, and by working with this ‘concrete-will’ and not ignoring it, by guiding it into what you want to create with it, amazing results can be achieved.

Have you had experiences with creating openings in off-shutter concrete?  Do you have other ideas of how to create great-looking openings in concrete?  Let me know in the comments below.

Should you require any assistance with your next concrete project or would like to get more information about our moulded concrete solutions, feel free to contact me at anton@elemento.net.za

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“What’s nice about concrete is that it looks unfinished” – Zaha Hadid

Concrete is all about being creative.  But your creativity does not have to stop with the design of the concrete structure…

I have always been fascinated with the process of forming 3-dimensional shapes using 2-dimensional elements.  Inspired by works like Cirrus by Zaha Hadid, I came upon the idea to construct formwork for a vaulted concrete roof using the ‘flat-pack’ concept.  In this first blog in my new Concrete Blog Series, I go through the process of how I built this vaulted concrete roof using ‘flat-pack’ formwork.

The Brief

The brief was simple, build a 7.5m x 5m library with a vaulted concrete roof, on a property down a panhandle, with trees big enough that it probably dates from my grandfather’s youth, in the middle of Sandton.  So access was limited to say the least.  With no overhead space for a crane or a concrete pump, everything had to be taken to site by hand only.

Problems!

Initially, I went the traditional route, without thinking about it too much, until I received the first proposal from a formwork supplier, and I realized that maybe I have a problem.

The best offer I could get from a formwork supplier was pre-built panels, of which the smallest section would weigh 175kg.  There was just no way I would be able to get the formwork into position by hand and even getting a small crane in was out of the question.  I considered assembling this formwork in position on top of a formwork deck but due to the complexity of assembling formwork like this, it was just not an option.

Then there was the cost.  The total cost for supply only of this ‘traditional’ formwork was R 82 000.  For a small project like this, the formwork cost would have made it completely not viable.  At this point, nothing was working out and I knew I had to start thinking out of the box to come up with a solution.

Getting Creative

With my fascination with ‘flat-pack’ furniture and ‘ribbed’ architecture, I began wondering if it would be possible to form the vault with a ‘flat-pack’ ribbed structure.  After a few hours of playing around with concepts, I came up with a structure that looked like it could work.

At this point, I had a solution for the internal structure, but concrete needs a closed mould, or so I thought.  I decided to contact a friend of mine who is a concrete technologist for one of the big ready-mix suppliers.  After some head-scratching and tossing ideas around I suddenly saw his face lit up as he announced; “Let’s pack it like a swimming pool!”, and the rest was history.

It took some convincing to get the project engineer on board but eventually, he bought into the concept, and I set out designing the system.

The Design

The success of the system was going to be dependent on getting two main things right.  The first was the assembly of the formwork in terms of accuracy and ease of assembly.  To achieve this, the ‘flat-pack elements’ were slotted in such a way that with the use of spacers, the structure could be assembled without even the need for a tape measure.  So the accuracy and ease of assembly were designed into the flat-pack boards.  Assembly was literally ‘plug and play’.

The second was to be able to pack the concrete accurately on top of this vaulted tube to an even thickness throughout and to a proper half-circle shape to the outside of the dome.  To achieve this, templates were cut with the rest of the structure elements, to be used as guides during the placing of the concrete.

The following diagram shows how the ‘flat-pack’ would be assembled and cladded to form the vault formwork.  The material that was to be used was a normal grade 19mm shutter board for the ribs and spacers. 76×50 SAP profiles were to be inserted into pre-cut slots to work as ‘purlins’ for the fixing of 0,8mm galvanised sheets for the final cladding.

Construction

The first step was to cut the shutter board profiles.  This was done using water jet cutting.  Shutter board survives this process quite well provided the boards are allowed to dry out properly after cutting.  Below is the cutting layout that was used to cut the boards.

The base of the vaulted formwork was shuttered with boards as for a normal roof slab with the vaulted formwork erected on top of the flat shuttered surface.  A picture is worth a thousand words so without any further explanations, follow the rest of the construction process through the following photos.

What happened with the budget problem?

The total cost for the ‘flat-pack formwork’ came to R 22 500 including the water jet cutting which was a 75% saving on the cost for ‘traditional’ formwork.  Other than the cost-saving on the formwork, since there were no cranage and concrete pumping involved, this resulted in further cost savings.

So, what will you do?

My purpose with this blog is to illustrate what can be done using alternative formwork methods.  And illustrating that the possibilities do not stop with just using alternative formwork but also with what can be achieved by using different concrete mixes.

I hope this blog inspires you, when you design your next amazing concrete structure, to think of new forms, new applications, and new solutions for old problems.

Let me know in the comments below of alternative applications for ‘flat-pack formwork’ that you can think off.

Should you require any assistance with your next concrete project or would like to get more information on our moulded concrete solutions, feel free to contact me at anton@elemento.net.za

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