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manufacturing of concrete

Concrete usually are mixed at concrete plants and delivered to field by concrete trucks. concrete can be mixed at the field, but it is not recommended to produce concrete at field especially for a large concrete pour, concrete produced at the field will lack for the required quality compared to concrete plants, producing concrete at plants may have some advantages such as:
  1. producing concrete with high quality due to strict quality measures followed in concrete plants.
  2. concrete plants can produce concrete in large quantities, suitable for mass concrete.
  3. using the concrete supplied from concrete plants will reduce the required manpower, also it will reduce noise and pollution.
  4. reduce the cost of producing concrete
  5. reduces the area required for storing raw materials for concrete at field

ASTM C94 / C94 M-09a provide guidance for the quality requirement in concrete plants. for batching plants:
  • a sufficient number of pins should be available with compartments for storing each size of coarse and fine aggregate. the mechanism should be designed to minimize segregation of aggregates during the process of discharging aggregates to weighting hopper
  • scales should be tested to verify the efficiency and accuracy of the used scales.
  • the devices used for measurement of water for concrete mix shall provide an accurate reading within 1% of the measured mixing water without being affected by the pressure variation in the water supply line. 
Mixers and Agitators:

  • stationary mixers should be equipped with plates in which plainly marked the speed of drum or paddles and the capacity in terms of the volume of mixed concrete. also, it should be equipped with a timing device that will not allow the discharging of the mix until the specified time elapsed. 
  • stationary mixers should be able to produce a homogeneous concrete mix within the specified time and revolutions, the product mix should meet the requirement shown in the table below.

Table 1
  • truck mixers or agitators should be equipped with plates that marked the speed of the drum, paddles, blades and the capacity in terms of the volume of mixed concrete. the volume of mixed concrete shall not exceed 63% of the total volume of the mixer for shrink mixing, in shrink mixing concrete is partially mixed in a stationary mixer then mixed completely in the truck. for central mixing in which concrete mixed totally at the stationary mixer, the concrete volume should not exceed 80% of the truck total capacity. 
  • agitator or mixer trucks should maintain the concrete homogeneous and uniform from the time of loading to time of placing concrete.
  • the mixer should be tested by their mass frequently to determine if there is any accumulation or concrete residual, also blades should be checked for wear, a proof test should be done for mixers with extensive changes that may affect the performance of the mixers. 

Figure 1


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