Gerard Brood, Senior Quality Officer and Concrete Technologist at Byldis: “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.”
Two examples
Gerard explains based on two projects: Project Overhoeks De Jakoba and project Kunstwerf Groningen. 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.
1. 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!
2. 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. 😊
Read more about Gerard Brood and his passion for his work in his blog "Concrete chunks".
