And tonight´s star is ………(ba-dum -tssss). Concrete. We have been waiting for his visit a long time and finally he found some time in its busy schedule to tell us some interesting facts about itself.
As we all know, concrete is a mixture of three basic components; aggregate, cement and water. The aggregate is of two types; fine(sand) and coarse(different sizes of gravel and stones).
The basic process of making concrete involves mixing all the components together in a specific ratio, which influences properties of finished concrete. Once you mix components together, you have to be quick, because concrete slowly hardens. Because of the liquid nature of fresh concrete, you can essentially sculpt anything you can imagine if you have the right formwork.
The concert hall of Santa Cruz de Tenerife. Designed by the architect Santiago Calatrava
And now beware my reader, because now I will get all educational so leave immediately if you are bored because it will get worse, I will describe in detail all the components and its types, so it will get very nasty soon. I warned you.
Cement is a general name for a material that binds other materials together, so yes, it is kind of another name for glue. In construction industry we commonly speak about Portland cement, which is the most usual type. When water is added to the cement, it sets off chemical reactions and the cement starts to harden. Portland cement is a basic component in concrete, mortar and stucco.
Most of the production of Portland cement in Denmark is carried out in Aalborg. We can choose from standard general purpose cement which is suitable for walls/columns/beams and foundations. Another type is rapid cement, which is more resistant to cracking and is used mostly for floors. Then we have special mortar cement and white cement, which is more expensive and therefore used only for decorative purposes.
We can normally use standard drinking water for most uses and we can also use sea water. If sea water is used, the concrete develops white powdery surface, but unfortunately also quickens the corrosion of used steel, so it is generally not suitable for most uses.
In Denmark, particles smaller than 4mm are classed as fine aggregate. Choosing the right sand is essential. The usual demands are uniformity of shape, round or cubical, and also appropriate strenght. Best sand also has a wide range of sizes (from tiniest through medium sized to “biggest” 4mm). Because of these demands, sand used is either specifically crushed stones in a factory environment or river sand. Other types (desert, beach or pit sand) are for one or another reason unsuitable.
Stones have smaller impact on the quality of concrete than sand, nevertheless, they should be hard, clean and durable. Sizes of these should not exceed one-fifth of the thickness of the wall we are pouring. Usual sizes are 19 to 25 mm.
Once you mix these, you can see our star driving around in its limo. (I would kill to be able to drive this baddass piece of machinery)
And once it arrives on a construction site. It is poured into the formwork.
Fun fact nr. 18. Since concrete quickly hardens, pouring the concrete must be exceptionally well organized, when pouring concrete on bigger projects, there are dozens of baddass vehicles arriving and leaving the construction site in cca. 15-30 minutes intervals. On exceptionally big projects, the concrete on one side might be already hardened and on the other side, a fresh batch is being poured. Also on huge projects, the concrete is actually being pumped around. See the picture below.
Well, I guess those of you who made it this far are already showing symptoms of brain-dripping-out-of-the-ear syndrome, so I am going to stop myself, since you are educated enough for today. Hope you at least found something useful.