It’s the little things in life...

VELDHOVEN - blog #5 Tuesday 23 March 2021

In this fifth blog, Gerard talks about just good, clear mid-rise projects that always include a special design element. And about the projects Overhoeks De Jakoba and Kunstwerf Groningen; two mid-rise architectonic concrete projects that each have their own focus, and the difference in concrete applications.

We have a mutual understanding – a project in the precast factory is in its final phases – a final concrete element is being poured and the space that will become available in the hall will be filled with the next challenge.

The feeling at the end of a project always conjures up words like; "It was a serious puzzle at the start, but now it’s almost a shame that the project is coming to an end for us.”

Just good, clear mid-rise projects that always include a special design element

Sometimes months or even years before this, steps have been taken to plan the follow up to the current project in the concrete factory. Long before the first concrete element is made, there have already been lots of meetings and conversations about how to make the concrete puzzle pieces that will ultimately bring the building to life. At Byldis these are often large, complex objects, or to use my neighbour’s words: “How tall is the tower going to be, again?”

“I’ll tell you something, neighbour – we can certainly handle larger projects, but we traditionally make good old mid-rise projects that always contain a special element of design and for which all facets of our club are keen use collaboration and craftsmanship to give the building its desired character”. All projects are equal – we do not distinguish between a project from a prize-winning architect or one from a young architect’s firm that wants to make a difference in the construction world. Of course, one is more experienced than the other, but we maintain the same focus on each and every project.

As a concrete technologist I focus on all the properties of concrete, from its fluid state to its fixed, solid destination in the concrete element. As well as with the standard self-compacting concrete, my passion lies in the architectonic concrete composition and the final appearance of the finished product. The great thing is that this kind of concrete effect can become the calling card of the building in the “smaller” projects. All it needs from us is personal attention, because it is not only concrete, but also the engineering – work preparation – mould construction – the reinforcement – compaction technology – the post-processing – the aftercare on site - completion with aluminium frames and glazing via Byldis Facades and careful loading onto a transport vehicle before it leaves through the gates. If we assemble it ourselves, there is another team waiting to put the puzzle together at the other end. It only ends when we see the photos of a festive opening on social media.

Two mid-rise architectonic concrete projects that each have their own focus

Every colleague plays his or her part, and without belittling the others I would like to highlight three of these activities that closely influence my aspect of concrete. The best way of doing this is to take you on a journey through the factory that is current focusing on the Overhoeks De Jakoba building project and the Kunstwerf Groningen project. Two mid-rise architectonic concrete projects that each have their own focus. They are completely different from each other, but each receives personal attention and gets exactly what is required.

Overhoeks, building 'De Jacoba' project

De Jakoba has a decorative concrete composition with a pistachio, light green colour and, after blasting, the green-black aggregate material with a slight shine becomes visible. A concrete that is based on a self-compacting concrete but adjusted to a low-compaction version so that we can compact the specially curved shaped using vibration.

Stability is important because the vertical deposits will also be polished or blasted. If you continue vibrating for too long, or the mixture is too wet, a “porridge” layer develops on the finishing side. This is not immediately a problem with concrete that remains smooth but blasting or polishing will reveal a poorly mixed finish.

It is purely aesthetic, but the concrete pourers and finishers pay attention right until the very last drop in order to prevent potential problems for their colleagues further down the process. The mixture is created in the concrete mixer at the concrete plant. All kinds of sensors give digital information, but the mill manager sees each and every decorative concrete batch in his mixer by actually physically looking into the mixer before it is emptied into the container. You will often see me, or my concrete laboratory colleague, there because that’s where you can still do something about the cohesion. Sensors are good tools, but the craftsmanship of a mill manager is what makes concrete!

Kunstwerf Groningen project

Completely different aggregates are used to mix the dark grey and white concrete mortar for the Kunstwerf Groningen project. The dark grey is based on basalt and from the start is a traditional vibrate mixture – a mixture that is compacted through vibration in elements that are sometimes 50cm thick, while the walls are smooth and white, made using a semi-self-compacting concrete mixture that is further deaerated by the slow shaking of the mould table.

The same operations are always carried out with these mixtures, in the same mixer, but with different starting values. Remember that concrete consists of constantly differing natural aggregate materials and a sand with grains varying from 0 to 4 mm cannot be distributed evenly; sometimes it is finer, sometimes coarser. 

…And then there’s the concrete technologist who wants to make a stable mixture using 0-1 mm sand and coarse 8-15 mm aggregate because it fits best with the architect’s vision... What a great job I have. 😊

Post-processing creates the final appearance

Mixing and pouring is one thing, but there is also post-processing. This is what creates the final appearance that was approved in advance based on all kinds of samples. Both De Jakoba and the Kunstwerf projects include concrete surface elements that require blasting and polishing.

Concrete blasting is a technique that cannot be done mechanically, but rather using a pressurised blasting grit that is blown from the nozzle of a blasting hose, controlled by a colleague in a protective “moon suit” (see photo).

The concrete elements are expertly loaded onto a blasting trolley the day after pouring, so that they can be moved inside along rails into a custom-lit, enclosed space where the blaster treats the surface using exact, manual movements. We call this “colouring” the elements.

De Jakoba is particularly challenging because it involves blasting a curved surface, instead of a straight, vertical one. It is blasted with the finest grit at a relatively low pressure which makes it even more difficult to keep it even. The dark grey Kunstwerf enters the same blasting cabin just a few hours after the Jakoba elements. A different concrete – a different pressure with a different grit – a deeper blasting depth.

Each element is laid exactly flat using measuring sensors

The concrete, which is removed from the mould the day after pouring, is not equally hard every day, just like the temperature does not stay at a constant 20 degrees every day. The blasting operator assesses the elements when they arrive and must make a new estimation every day about the hardness of the concrete surface. No digital sensors – just good craftsmanship.

Two weeks after the elements have been poured and blasted, they have developed the correct advanced compressive strength and are brought back to the polishing area. There are sections that must be polished to match the previously approved sample. This applies to both De Jakoba and Kunstwerf. It is not a question of laying the element flat and pressing a button. Once again, it is precision work – even programming the machinery demands time and expertise. Each element is laid exactly flat using measuring sensors, to make sure that the polishing stones grind the element to the exact required finish.

Polishing work carried out by the hands of a polisher are competing against the automatic polishing machine, and the outcome is always a tie. The polishing machine is very precise and manual polishing is a specialised craft, so I dare to say that the manual polisher still wins on points. Compare it to a chess player who uses his last move to put the most advanced chess computer in checkmate. You understand - craftsmanship.

Digital design wishes come to life in a collaboration between modern and traditional technology

During an initial inspection of the first concrete products ready for transport, a client and/or architect assesses what he/she had in mind and whether it corresponds with the agreements made and the animation on the digital screen. The first positive critical words are spoken, which is exactly as it should be. Because whether it’s a bicycle shelter or a 200-meter-high residential tower, only honest mutual communication can lead to the right adjustments.

Digital design wishes anno 2021 come to life in a collaboration between traditional and modern technology. It feels like I am writing a commercial, but with a smile on my face I write the final words in this blog and it surprises me in a nostalgic way that even these old words are still up to date:

“A project big or small – Byldis does it all!”

Written by: Gerard Brood, Senior Quality Officer and Concrete Technologist at Byldis 

But wait... there's more! 

In "Concrete chunks", Gerard Brood talks about his work as Senior Quality Officer and Concrete Technologist at Byldis. As well as a passion for his work, he also loves describing his observations. Want to read all the blogs? Go to: all concrete chunks.

Photography: Danny Fiers