Concrete plants incorporate planetary mixers available on models P250, P375, P560, P750, P1125, P1500, P2250.
The characteristics required to design a concrete plant are:
- Mixer: The size will be determined by the size of the machine vibro compressor.
- Number of aggregates: According to the blocks we manufacture: One layer, double layer... Minimum two aggregates.
- Hoppers cannot be placed underground, we install a charging system.
- The quality of blocks depends largely on the aggregate, its proportion and its good mixing.
- The aggregate hopers must be covered to avoid that rain can change the humidity level of the mixture.
The selection of aggregates is very important to get a good quality of the final product. The aim of the precast concrete manufacturer is to get a hard block with the minimum consumption of cement.
The main characteristics of aggregates are:
These properties will be achieved if we choose good aggregates, and a good dosage between them.
The weight of the piece has to be usually the minimum, to facilitate road transport and installation on site.
The mixture should be as homogeneous as possible, to achieve this we have to make a good dosage of aggregates and cement. But the most important is the amount of water.
The amount of water changes the aggregates and therfore, the behavior of he producer machine : mold filling and block compression.
DOSAGE OF AGGREGATES:
The dosage of the aggregates can be done in two ways:
• Weight: By weighing the desired amount of agregates.
• Volume: By regulating the feeding time for each aggregate. This is a much more simple system.
The big drawback is also the variation of moisture content of aggregates, because the unit weight changes.
To get a block that meets our needs in hardness, finish, weight and dimensions, we need to select the best aggregates.
The classification of the aggregates granulometry is:
Fine aggregates: grain size below 0.1 mm.
Sand: grain size between 0.1 and 5 mm
Gravel: grain size between 5 mm and 8 mm
Aggregates can not be larger than one-third the thickness of the walls.
For a good dosage we need three hoppers with aggregates of different granulometries although the minimum recommended is two hoppers.
A recommended mix to achieve a compromise between all the properties would be:
• 45% of medium aggregate
• 40% of big aggregate
• 15% of fine aggregate
Importance of DUST: aggregates may not be washed, which means free of dust.
Dust is needed in the dosage of the aggregate to help the cement to form a paste and attach perfectly all grains. Without dust we will have to increase the amount of cement and water, but on the other hand, iwith to much dust we would not get a resistant block.
The amount of dust cannot exceed the 5% by weight of total aggregates