06-16-2022, 12:16 PM
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.
for more details download .....
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MECHANISATION OF CONCRETING PART 3 FD.pdf
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