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CE2307-CONCRETE-AND-HIGHWAY-ENGINEERING-LAB--->View question


Asked On2017-05-20 20:05:22 by:scribed

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Steps of manufacturing of concrete

 BATCHING


 MIXING


 TRANSPORTING 


 PLACING 


 COMPACTING


 CURING


 FINISHING

BATCHING Batching is the process of measuring concrete mix ingredients by either mass or volume and introducing them into the mixer . To produce concrete of uniform quality, the ingredients must be measured accurately for each batch. 

 Volume batching 

 Weight batching 

 Volume batching 
• This method is generally adopted for small jobs .
• Gauge boxes are used for measuring the fine and coarse aggregate. 
• The volume of gauge box is equal to the volume of one bag of cement. 

4.  Gauge bow are also called as FARMAS 
 They can be made of timbers or steel. 
 They are made generally deep and narrow 
 Bottomless gauge boxes are generally avoided. 
 While filling the gauge boxes the material should be filled loosely,no compaction is allowed.  Weigh Batching 
• Batching by weight is more preferable to volume batching ,as it is more accurate and leads to more uniform proportioning. 
• It does not have uncertainties associated with bulking. It’s equipment falls into 3 general categories :
 I. Manual, II. Semi automatic, III. Fully automatic. 
 1) In case of manual batching all weighing and batching of concrete are done manually. It is used for small jobs. 

 2)Semi automatic In case of semi automatic batching the aggregate bin gates are opened by manually operated switches . And gates are closed automatically when the material has been delivered. This system also contains interlock which prevents charging and discharging. 

3)Fully automatic In case of automatic batching the material are electrically activates by a single switch and complete autographic record are made of the weight of each material. The batching plant comprises 2,3,4 or 6 compartment bins of several capacitie. 

Over the conveyer belt the weigh batchers discharging are provided below the bins 

8. Mixing The mixing should be ensure that the mass becomes Homogeneous , uniform in colour and consistency . Methods of Mixing : 
• 1.Hands(using hand shovels) 
• 2.Stationary Mixers 
• 3.Ready mix concrete 

9. Hand Mixing 
• Mixing ingredients of concrete by hands using ordinary tools like, hand shovels etc. This type of mixing is done for Less output of concrete.

10. Stationary Mixers 
• Concrete is sometime mixed at jobsite in a stationary mixer having a size of 9 cubic meter . • These mixers may be of : 
1. Tilting type , 

2. Non-Tilting type , 

11. Tilting type mixer 
• It consist a conical drum which rotates on an inclinable axis. 
• It has only one opening. 
• The drum charged directly and discharged by tilting and reversing the drum. 

12. Non tilting type mixer 
• The mixing drum is cylindrical in shape and revolves two – horizontal axis. 
• It has opening on both sides. 
• The ingredients are charged in from one opening. 
• For discharging concrete chute is introducing to other opening by operating a lever. 

13. Ready Mixed Concrete Ready mixed concrete is proportioned and mixed off at the project site and is delivered to the construction area in a freshly mixed and unhardened state. It can be manufactured by any of the following methods: 

 1.Central-mixed concrete 

 2.Truck-mixed concrete . Central Mixed Concrete

 • Central-mixed concrete 

 mixed completely in a stationary mixer
 • delivered in  Agitator Trucks A non-agitating truck 

 Agitator Trucks
 • A vehicle carrying a drum or agitator body, in which freshly mixed concrete can be conveyed from the point of mixing to that of placing, the drum being rotated continuously to agitate the contents.

  Advantages: Operate usually from central mixing plants
  Watch for: Timing of deliveries should suit job organization. Concrete crew and equipment must be ready onsite to handle concrete. 
 Used for: Transporting concrete for all uses. Haul distances must allow discharge of concrete within 1½ hours. 16. Agitator Trucks 17. Non-agitating Trucks 
 Used for: Transport concrete on short hauls(small distance) over smooth roadways.
  Advantages: Cost of non-agitating equipment is lower than that of truck agitators or mixers. 
 Watch for: Slump should be limited. Possibility of segregation. Height upon discharge is needed 

. Truck-mixed concrete 
 Used for: Intermittent (periodic) production of concrete at jobsite, or small quantities.  Advantages: Combined materials transporter and batching and mixing system. One-man operation. 

 Transporting 
• 1) Mortar Pan : Concrete is carried in small Quantities 20. Transporting 
• 2) Wheelbarrows and Buggies : Short flat hauls on all types of onsite concrete construction 21. Transporting 
• 3) Belt Conveyors : Conveying concrete horizontally or higher/lower level. 

Transporting 

• 4) Cranes and Buckets : Used forWork above ground level , Buckets use with Cranes, cableways, and helicopters. 

Transporting

 • 5) Pumps : Conveying concrete from central discharge point to formwork.

Transporting 

• 6) Transit Mixer : used for transporting the concrete over long distance particularly in RMC plant . 

Compaction of concrete
• Compaction of concrete is process adopted for expelling the entrapped air from the concrete 
• In the process of mixing , transporting and placing of concrete air is likely to get entrapped in the concrete .

 • It has been found from the experimental studies that 1% air in the concrete approximately reduces the strength by 6%. 

• If we don’t expel this air, it will result into honeycombing and reduced strength 26. Different Methods Of Concrete Compaction 

1) Hand Compaction Rodding Ramming Tamping 

2) Compaction by Vibration Internal vibrator Formwork Vibrator Table Vibrator Platform vibrator Surface vibrator . 

 Hand Compaction

 • Hand compaction is used for ordinary and unimportant structures. Workability should be decided in such a way that the chances of honeycombing should be minimum. The various methods of hand compaction are as given below: 

Rodding It is a method of poking with 2m long, 16 mm dia. rod at sharp corners and edges. The thickness of layers for rodding should be 15 to 20 cm. 28. Ramming • It is generally used for compaction on ground in plain concrete. It is not used either in RCC or on upper floors. 

Tamping 

• It is a method in which the top surface is beaten by wooden cross beam of cross section 10 cm x 10 cm. both compaction and leveling are achieved simultaneously. It is mainly used for roof slabs and road pavements. 

Compaction by Vibration

 • Vibration is imparted to the concrete by mechanical means. It causes temporary liquefaction so that air bubbles come on to the top and expelled ultimately. Mechanical vibration can be of various types as given under.

  Internal Vibration It is most commonly used technique of concrete vibration. Vibration is achieved due to eccentric weights attached to the shaft. The needle diameter varies from 20 mm to 75 mm and its length varies from 25 cm to 90 cm. the frequency range adopted is normally 3500 to 5000 rpm. The correct and incorrect methods of vibration using internal vibration needles are shown below. 30. External Vibration

 • This is adopted where internal vibration can’t be used due to either thin sections or heavy reinforcement. External vibration is less effective and it consumes more power as compared to the internal vibration. The formwork also has to be made extra strong when external vibration is used

 Table Vibration 
• It is mainly used for laboratories where concrete is put on the table 

 Platform Vibration
 • t is similar to table vibrators but these are generally used on a very large scale 

 Surface Vibration

 • These are also called screed board vibrators. The action is similar to that of tamping. The vibrator is placed on screed board and vibration is given on the surface. It is mainly used for roof slabs, road pavements etc., but it is not effective beyond 15 cm depth.

Answerd on:2016-03-22 Answerd By:metaphor

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