Concrete is the resulting mixture between water, cement and mineral fillers, such as sand and gravel of different grain sizes. The cement is the binder. With this formulation, something important has already been indicated; namely, that concrete does not dry, but passes a chemical process! This chemical process alters the crystal structure of the cement and only this allowes to harden the whole conglomerate. The longer the time to harden, the better the concrete! The concrete is light duty after about 1-2 days, it has standard hardness after a month, but final hardness after more than half a year !
In our smaller construction works we mostly use premixed concrete, delivered in sacks. The 25 to 40Kg portions are easy to transport and only need to be mixed with water. The grain size of the silica is in a maximum of 8 mm, so that an universal material is produced. It is therefore perfectly suitable to put in paving stones, to create natural stone terraces or for concrete fence posts. Likewise, for small repair work. The normal mixing ratio for coarse concrete is 1 part cement and 3 parts additives (sand or gravel). Then of course you do not need to pay more attention to the pre-mixed screed concrete. Only the amount of water is important.
If the concrete is to be used on, or in the soil, it is mixed slightly dry! A flabby mass, as one would expect, is completely unsuitable and can not be handled without problems. Such a mixture sticks to the tools, can not be shaped and not be compacted. The semi-dry mixture, however, is the best and is quality gets even higher. The reason ist that concrete is hygroscopic and attracts all the moisture it needs from the soil. The chemical process therefore takes place slowly and continuously.
The mixing process of a 40-kilo sack begins once you have chosen the correct container. Depending on the space available, one can choose a wheelbarrow or other containers. Fill in the dry concrete the container carefully, because the fine dust is toxic !
In order to achieve exactly the right consistency for 40Kg dry weight, you only need about 4 liters of water. This small amount is a little astounding, but will produce the perfect cosistancy. Now the water is poured in intervals into the concrete and gets mixed with a flat shovel or spade. Stick your shovel into the mass, turn it over, so that the blade is pointing downwards. Now you stick the shovel repeatedly in the mass and move the blade thereby forwardly. On the way back you pull down the little pile, which has been formed in front of the blade. This whole process is quite stressful and can sometimes take a lot longer than five minutes. It is easier to take half a sack and about 2 liters of water. When the mixture (see the video ) finally trickles loose, it's perfect !
Garten Trick :
Too wet concrete, but also dry cement makes ugly stains that you might never get clean again on pourous surfaces. If you work on a precious floor, you should cover it because there always something goes wrong!
Garten Trick :
The semi-dry mixture has another advantage. Where it is used, it is weepable! This is absolutely not possible with wet concrete mixtures.
Garten Trick :
When concrete is prpared in the summer, be cautionous. If in the mixture the water evaporates more rapidly as the chemical process is activated, it will just dry out ! Then no chemical reaction takes place and the concrete will be nothing more than a crumbly mass. In the summer fresh concrete must be covered or remoistened !