[C M Dordi]

MECHANISATION OF CONCRETING 
PART 1- BATCHING, MIXING AND TRANSPORTING
Taken from : Ambuja Technical  Literature Series -12

Concrete construction methods need to be changed drastically in our country. Modern construction equipment are used only on very few construction sites. In our country the conventional concreting methods are preferred to the modern mechanized concreting methods which are generally used in all developed countries and in several developing countries. 

Sites using modern construction equipment's are lie oasis in the desert of conventional construction sites. Often modern construction equipment's are adopted in combination with conventional methods. This results in inefficient use of these equipment's, poor quality of work and ultimately the modern equipment's and methods are given up.

It is essential that the entire method of construction practice undergoes a change if modern construction equipment's are to be used. If computerised concrete production plants are used they should be supported by equally fast and modern transporting and placing equipment's. Similarly reinforcement work and formwork must be completed fast and have to be of good quality, adequately designed and capable enough to suit the modern placing methods. Equally capable compacting and finishing equipment's also have to be deployed. Ultimately, curing also has to be done properly so that concrete strength and durability are not effected. Every step needs a change and modern thinking. It is not only essential to produce concrete with excellent quality but also necessary to produce it with speed and economy. It adequate precautions are taken costly time consuming repairs and future maintenance problems can be avoided thereby giving an overall economy.

The suggestions given by Schwing GmbH, Germany and Putzmeister AG, Germany are also incorporated in this revised booklet. We are grateful to them for the same We hope that computerised equipment for batching and mixing and modern equipment for transporting and placing concrete become more and more popular in our country and ultimately result in durable concrete structures constructed with speed and economy.


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[Manish Jain]

BATCHING AND MIXING PLANTS 
The principal functional elements of every stationary concrete production Plant comprises of the following

• Storage of materials Silos, containers and bins
  
• Batching arrangement
  
• Measuring and recording equipment
  
• Mixing equipment
  
• Control systems
  
• Electrical, hydraulic and pneumatic drives
  
• Conveying systems (belt / screw conveyors)
  

STORAGE OF RAW MATERIALS

CEMENT

Cement is generally stored in silos. The loading of cement is done with the help of pneumatic blower systems either installed on bulk carriers  or a separate system available at the plant. If baggage cement is used then the cement is loaded using a compressed air loader (See Figure 2) and a splitter unit. Cement is weighed separately, and is transported from the silo into a

mechanical or electro mechanical weighed by mens of a screw conveyor .

WATER

Water is generally stored in tanks located close to the plant. It is accurately measured by a water gauge and microprocessor controlled system.

The modern plants have new litronic MFM 85 moisture recorders . These recorders actually measure the moisture present in sand while the entire batch flows past. A recording unit calculates the average moisture value of the sand and passes on the information to the batching control unit to allow corrective action to be taken. The system operates to an accuracy of as low as 0.2% relative moisture.

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 MECHANISATION OF CONCRETING FD.pdf

[Manish Jain]

SPECIAL TRANSIT MIXERS

Transit mixers are further modified or changed for specific usage as given below:

Fluid concrete equipment - This equipment has a admixture pressurised system which can add admixture in the mixing drum in 50 seconds.
Mortar equipment - This equipment is devised with an attachment to remove the oversized particles and mixing spirals are modified to handle mortar
mixing.
Foam concrete equipment- This equipment is used to produce and transport foam concrete. The mixer drum is well suitable for mixing extremely light additives (foam) into specifically heavy concrete or mortar. The plastic foam is prepared by simple foam generator and fed deeply into the mixing drum. With this equipment a homogeneous concrete/mortar for structures having a very high heat-cold insulation factor can be produced on site shortly before placement and within a short period.
Tropical condition equipment - This equipment has metal shields over the mixer drum and water tank. The drum is also encased in jute and water
sprinkled on it to keep it cool and moist. This shielding and evaporative cooling effects appropriate reduction of temperature.
Low temperature equipment - This equipment has well insulated water tank and drum. For very cold temperatures electrically heatable water line is also provided .

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 MECHANISATION OF CONCRETING FD.pdf