Batch mixer-A type of mixing machine in batching plant, which mixes concrete in batches and releases each batch of materials separately.
2 Batch mixer types in Batching plant
The following are the 2 batch mixer types:
- Tilting batch mixer
- Non-Tilting batch mixer
Tilting batch mixer
The following are the primary points of this type of concrete mixer adopted in construction.
- In massive construction projects, this type of tilting mixers is utilised.
- The particles size greater than 75 mm can also be used in this type and all the elements are rolled down into this mixer.
- For dry concrete, this mixer delivers pleasing results.
- The sizes of this mixers are:200 T,140 T,100 T, where T = tilting, Number =Nominal volume of concrete mix in litres.
Non-Tilting batch mixer
The following are the primary points of this type of mixer.
- In small construction projects, this type of mixers is practised.
- The particle size of less than 75 mm are utilised and all the elements are raised, rolled and dumped into the mixer.
- The sizes of this mixers are:800 NT,400 NT,280 NT,200 NT,140 NT, where NT=Non-tilting.
Tolerances in Batching Plant
The following are the three categories these batching plants are available.
- Fully automatic
The following are the ingredients tolerances used in cumulative and individual batches in construction.
If tare control of materials is used.
- Cement, cementitious materials: Tolerance +/- 1% of required materials weight or +/- 0.3 % of scale capability, whichever is higher is considered.
- Aggregates: Tolerance +/- 2% of required material weight or +/- 0.3 % of scale capability, whichever is higher is considered.
- Water: Tolerance +/- 1% of required material weight or +/- 0.3 % of scale capability, whichever is higher is considered.
- Admixtures: Tolerance +/- 3% of required material weight or +/- 0.3 % of scale capability or 45.4 kg minimum cement dosage rate, whichever is higher is considered.
If tare control of materials is not used.
- Cement, cementitious materials: Tolerance +/- 1% of required cumulative materials weight or +/- 0.3 % of scale capability, whichever is higher is considered.
- Aggregates: Tolerance +/-12% of required cumulative material weight or +/- 0.3 % of scale capability, whichever is higher is considered.
- Admixtures: Tolerance +/- 3% of required cumulative material weight or +/- 0.3 % of scale capability or 45.4 kg minimum cement dosage rate, whichever is higher is considered.
Types of equipment for compacting concrete
The following equipment are used for compacting concrete:
The process of compacting concrete with the use of A-rod or hand tool by inserting and moving up, down for removing air bubbles out of the concrete is called tamping.
A rod of 150 mm is used for RCC works and 300 mm rod is used in mass concrete.
The following are the vibrators and other methods used for compacting concrete.
- Form Vibrator
- Needle vibrator
- Vibrating table
- Surface vibrator
- Air jets method
- Vibropressing method
- Centrifugation method
- Jolting or Shock method
This form vibrators are utilised in small concrete regions and densely reinforced regions where needle vibrator is able to enter into the concrete.
For this needle vibrator a vibrating head is attached to the long flexible tube and it also consists of power unit.
With the help of this vibrating head, it will compact concrete very quickly. This vibrator is more useful in mass concreting works.
For preparing prefabricated elements,when concrete mix is harsh or still,this vibrating table is used.
It is mostly used for preparing laboratory samples only.
This Surface vibrator is termed as pan or screed vibrator. It is utilised when screeding is done and it works excellent within the concrete depths of 150 mm to 200 mm.
Compaction of concrete is achieved by eliminating air in concrete with the help of air jets, then all particles will come closer and gets compacted.
In this method, by vibrating form the bottom and applying external pressure from the top, compaction of concrete is performed.
This type of compaction is used for mostly in preparing of paving stones and concrete kerb stones.
In this method, the compaction of concrete is done by placing concrete in the mould and rotating the mould at great speed for eliminating water from it.
This centrigual compaction method is manufacturing of concrete water supply pipes and sewage pipes.
Jolting or shock method
In this method, the compaction of concrete is done by constraining the concrete mould to shock with the cooperation of cams.
Batch mixer Concrete finishing and Curing
Screeding is the finishing method of batch mixer concrete. It is done by eliminating excess concrete from the top surface until a proper grade is achieved.
Removal of irregularties from surface of concrete after screeding is called floating.Using woodden float this floating is performed.
Curing is the method of achieving complete hydration by controlling moisture content and humidity by utilising water to concrete which is placed freshly.
The following are the curing objectives:
- To obtain the highest concrete compressive strength.
- To reduce concrete shrinkage effect.
- To improve weather resisting quality.
- To increase the impermeability and durability of concrete.
Batch mixer Hoisting equipment
The batch mixer in batching plants and other areas for Lifting and placing of the loads from one place to another place is done by hoisting equipment.
The following are the hoisting equipments:
- Chain hoists
This hoisting equipment works in a union of clutches, brakes, gears and guided by a set of levers.
This equipment in general used for railway gates lifting.
In Pully wire ropes and chains are used for lifting heavy objects.
Cranes in construction are divided into two types
- Tower cranes
- Mobile cranes
These tower cranes in very limited area provide high lifting height and better radius for working in construction field.
These tower cranes are used for shifting concrete in drums and for concreting in high raised building construction.
These of two types:Bottom Slewing and( top slewing) fixed tower cranes.
In the bottom slewing tower, the jib assembly and tower revolve at the base and also have swing circle at the base.
But in fixed tower cranes whirl circle is positioned at the top and enable tower top, jib assembly and operator cabin to rotate.
The following are the types of mobile cranes:
- Heavy lift cranes
- Telescoping boom truck mounted cranes
- Crawler cranes
- Lattice boom truck-mounted cranes
Heavy lift cranes
These heavy-lift cranes have capacities varies from 600 tons to 2000 tons.
It consists of counterweight, boom, each positioned on self-supporting crawlers which are connected by a string.
Telescoping boom truck mounted cranes
These cranes can move on public places on its own power and can assemble with minimum dismantling.
Due to its easy setup and ease of movement, first preference will be given to this crane.
On a pair of consecutive parallel crawler tracks, this crane is positioned and these crawlers help this crane for easy transportation while executing the jobs.
Due to its large ground surface area,the soil with low bearing capacity can get failure.
Lattice boom truck mounted crane
On a multi axle truck carries this crane is mounted and have full revolving superstructure and it is light weight.
But for dismantling and transporting this type of crane is very difficult.
The above mentioned 2 batch mixer types are used in the construction field for mixing concrete and above-mentioned tower cranes are used for placing batch mixer concrete in high raised buildings construction works.