If we take an example of a soil that contains about 25% clay and a pH of 7, than you can expect the following:
After you test have concluded that the soil is suitable for making blocks, you take about 1 wheelbarrows (ca. 100 litre) of dry soil and put it in the crusher (which is accommodated with a sieve at the input, to keep out the rocks). The soil and clay will be crushed so you get a homogeneous mass, so it will be more easy to mix with the cement.
Secondly, you put the soil in the mixer and add in 5kg of cement which is 5%. If there is little clay in the soil (between 15% to 20% ) you add a bit more cement, so you reach the dosage of 6%.Make sure that this is mixed well in the soil. Than you also mix about 5% to 40% of sand in, this depends on the clay content within the soil. Furhtermore you add and mix the dosage of Block Rapid in a bucket of water. In this case with 100 litres of soil you mix about 0,03 litre in a bucket of water and then slowly poor it in the mixer, equally divided over the soil. This is necessary to bring the soil to the Optimum Moisture Content, so you can shape the blocks perfectly. If everything is mixed well it is time for the next step.
The mixture will get out of the mixer and you shovel it in a bucket and take it to the block pressing machine. When the mould is filled up, you can close the mould and start pressing. The machine will press till about 200 bar, from the bottom side as well as from the top side, so you get a smooth surface once the block is pressed. Sometimes you see that these kinds of blocks are only pressed from one side (top or bottom), but this results in cracks and uneven parts at the other end of the block. An additional advantage is that with two sided pressed blocks, the bearing capacity increases as well.
If the block is pressed and you will take it out, make sure that you treat the blocks carefully, because it is still porous. The blocks need to dry slowly for appr. 3 weeks to hard out and become as solid as a rock. You store the blocks under a plastic cover and spray some water over them daily, so it has the chance to dry slowly from the inside. Hereunder you find a table which will help you out on the right doses. But in praxis you will only use this as a guide, and you will learn by doing, how easy it is to do this.
|Clay content||Dosage liter / m³||Cement dosage||Sand dosage|
For the above mentioned table we have different amount of water/Block Rapid mixture before bringing to Optimal Moisture Content:
Clay content 15% till 30%: Block Rapid should be mixed with 10% water => than bring to OMC.
Clay content 30% till >45%: Block Rapid should be mixed with 14% water => than bring to OMC.
Keep in mind following requirements:
- Make sure that the initial soil is dry;
- First dry-mix;
- Add the mix and water slowly;
It is possible to add (fine) aggregate for stronger blocks.