[C M Dordi]

MECHANISATION OF CONCRETING
CONCRETE MATERIALS AND QUALITY CONTROL
Taken from : Ambuja Technical  Literature Series -14

MATERIALS FOR MECHANISED CONCRETING
The success of Mechanised Concreting is greatly dependent on the quality of concrete materials used and efficiency with which they are batched and
mixed at the production plant and transported as concrete to various sites. While it is absolutely necessary to have efficient and automatic equipment to
assure good quality concrete, it is equally important to have very dependable and consistent quality of concrete material supply at the production plant also.
This is an important factor which requires to be studied before the production plant is set up. It is important to identify the material suppliers well in advance so that they can deliver materials of desired quality and quantity. 

Alternatively the production plant can be set up at the material source itself by the concrete producers. As aggregates (coarse and fine) are the maximum requirement weightwise it is often observed that plants are generally located at the aggregate source itself and the processed aggregates are  transferred to the production plants by means of series of conveyors.

WHAT IS QUALITY ?
Traditionally quality is related to cost and performance. In concrete too 'quality' means high performance concrete and generally good quality concrete materials too are available at a higher cost. 
In concrete, specifiers give their requirement for temperature, workability, pumpability, strength, durability and any other specific requirement. Hence,
quality is attained when the concrete supplied at site meets these specifications. As far as the material component of concrete production is concerned it is essential to do proper checks on the input material first and later proper check on the output material i.e. concrete.

for more details download ..... 

MECHANISATION OF CONCRETING PART 3 FD.pdf Size: 3.89 MB  Downloads: 0

[Manish Jain]

CHECKS ON INPUT MATERIALS AND CONCRETE MIX

Generally, the checks on input materials of mechanized concrete production and conventional site produced concrete are more or less identical. The
requirements are clearly specified in the Bureau of Indian Standards (BIS) for all materials. The testing procedures and sampling methods too are available in form of BIS standards published from time to time. 

In mechanized concreting it must be clearly understood that the concrete, at times, has to be transported for a longer duration or distance than conventional concrete. In hot weather (generally prevalent in our metropolitan cities) it is very important to select all materials which do not cause drop in workability or require larger quantity of water for concrete workability to be maintained for a longer duration.

The basic requirements for designing a good conventional concrete mix are also applicable for pumpable concrete mix designs. Additional attention has
to be given to cohesion , workability, slump retention and aggregate grading (See Figure 1 ). The mix should have an optimum quantity of fines to avoid segregation due to lack of fines or high frictional resistance due to excess fines, (See Figure 2). The workability should
be such that target slump is 75 ± 25 mm. 

Concrete mix for a mechanized concrete supply has to take care of different requirements for different consumers. The concrete specification will keep varying for different usages. Some of the following factors will generally be specified by the consumer
or their consultant. 

• Concrete Grade.
  
• Workability (slump) when received at Site (minimum 50 mm)
  
• Minimum cement content or maximum water/cement ratio (durability).
  
• Types of Cement (OPC, PPC, PBFS or SRC).
  
• Types of Cement substitution additives (Slag, Flyash or micro silica).
  
• Temperature of concrete at the time of delivery.
  
• Initial setting time of concrete (in case of massive continuous pours).
  

for more details download ..... 
 MECHANISATION OF CONCRETING PART 3 FD.pdf