Designing Buildings - User contributions [en]

Ballast

2019-11-27T16:50:50Z

Humayoon: Created page with "BALLAST & TYPES OF BALLAST Ballast: Ballast is material like broken stone, gravel or any other granular material spread and packed below and around sleeper. It provides go..."

BALLAST & TYPES OF BALLAST

Ballast:

Ballast is material like broken stone, gravel or any other granular material spread and packed below and around sleeper.

It provides good drainage for the track structure, It provides weed of greed, It holds sleepers in correct position by preventing movements caused by lateral load therefore ballast is used in the railway track.

Types of ballast is as follows:-

i) Broken stone

ii) Kankar

iii) Gravel

iv) Moorum

v) Brick ballast

vi) Blast furnaces slag

vii) Sand

viii) Ashes/cinders

ix) Selected earth

Broken sand:-

These are obtained from hard stones and it should be strong, hard, tough, durable, angular and does not flake when broken and hence Indian Railway adopt it very frequently.

Advantages:-

* They are strong, durable and provide maximum stability to track.
* These are mostly used for high speed track in India.
* These types of ballast are cheaper in long run.

Disadvantages:-

* The main disadvantages of this type of ballast is that its initial cost is more.

Moorum:-

It is normally used as an initial ballast in new construction. It is of red or sometimes yellow in color. It is Suitable for station yards.

Advantages:-

* It is cheaper.
* It may serve as soiling when stone ballast is spread afterwards.
* Drainage property is good.

Disadvantages:-

* It may turns into powder under heavy loads.
* It may produces dusty track.
* Maintenance of track with this type of ballast laid is difficult.

Sand:-

Coarse sand is generally used as ballast and is a moderate material to use as ballast.

Advantages:-

* It is cheap material
* It is easily available
* It has good drainage property
* It produces less noisy track.
* It will not allow vegetation to grow on track
* It is used on temporary and unimportant track.

Disadvantages:-

* Maintenance of tracks laid by these ballast is difficult
* Sand may blown by wind or may washed by rain
* It may spread due to vibrations and thus maintenance is difficult
* It may leads to wear if it gets into the moving part of train

Kankar:-

Kankar are also used as ballast where other chief material for ballast is not easily available.

Advantages:-

* It is cheap
* It has got good drainage property
* Used for M.G. and N.G. tracks having light traffic

Disadvantages:-

* It is soft and hence it may convert into powder under heavy load.
* It may have corrosive action on rails
* Maintenance of track is difficult

Brick ballast:

It is generally in form of broken over burnt brick

Advantages:-

* It is cheap material for use as ballast
* It is drainage property is good
* It prevents growth of vegetation
* It is easily available

Disadvantages:-

* It may have adverse effects on rails and metal sleepers as it may corrugate them
* Maintenance of track laid with this material as ballast is difficult
* It may produce dusty track as it turns into powder under heavy load

Ashes:

These are residue obtained from coal. It is also used as ballast.

Advantages:-

* It is cheap and very economical as it is by product of every railway
* Available in abundant quantity
* It has very good drainage property

Disadvantages:-

* It has got corrosive property and hence affect the rails and metal sleepers
* It may laid track dusty as it gets easily reduced to powder under heavy load

Gravel:-

It is one of the best material used as ballast next to broken stone consisting of smooth round shaped material obtained from riverbed.

Advantages:-

* It is cheaper than broken stone
* It's drainage property is good
* It is useful for main line

Disadvantages:-

* Due to rounded shape, it can easily rolls down due to vibrations and results in loosening of sleepers
* Washing is required if gravels are obtained from pits
* Screening is required as there is variation in size and quality
* In short, uniform grading of gravel is required

Blast furnaces slag:

A byproduct obtained from manufacture of iron can also be used as ballast.

Advantages:-

* It is cheap
* It has good drainage property
* It is strong and holds track in correct gauge and alignment

Disadvantages:-

* It is not available in large quantity

Selected earth:

These are indurate clay and decomposed rocks. These are used as ballast when tracks to be laid on new formation. After consolidation, the surface becomes hard then good type of ballast is laid.

Advantages:-

* It prevents loss of good ballast on new formation
* It may be used on sidings and tracks.

<Humayoon Sial>

<humayoonsial.civil@gmail.com>

[[Category:Articles_needing_more_work]] [[Category:Conservation]] [[Category:Definitions]] [[Category:Education]] [[Category:Projects_and_case_studies]] [[Category:Publications_/_reports]] [[Category:Research_/_Innovation]] [[Category:Theory]] [[Category:Standards_/_measurements]] [[Category:Construction_management]] [[Category:Construction_techniques]]

Concrete compaction

2019-11-27T14:13:44Z

Humayoon:

= [https://worl.data.blog/2019/04/09/compaction-of-concrete/ COMPACTION OF CONCRETE] =

Compaction is a process of expelling the entrapped air. If we don’t expel this air, it will result into honeycombing and reduced strength. It has been found from the experimental studies that 1% air in the concrete approximately reduces the strength by 6%.

DIFFERENT METHODS OF CONCRETE COMPACTION

There are two methods of compaction adopted in the field as given below.

* Hand compaction
* Mechanical Compaction

(A) 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.

1. 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.

2. RAMMING

It is generally used for compaction on ground in plain concrete. It is not used either in RCC or on upper floors.

3. 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.

(B) MECHANICAL COMPACTION

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.

1. 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.

2. 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 form work also has to be made extra strong when external vibration is used.

3. TABLE VIBRATION

It is mainly used for laboratories where concrete is put on the table.

4. PLATFORM VIBRATION

It is similar to table vibrators but these are generally used on a very large scale.

5. 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.

<Humayoon Sial>

<humayoonsial.civil@gmail.com>

[[Category:Conservation]] [[Category:Definitions]] [[Category:Education]] [[Category:Theory]] [[Category:Construction_techniques]]

Concrete compaction

2019-11-27T14:12:07Z

Humayoon: Created page with "= [https://worl.data.blog/2019/04/09/compaction-of-concrete/ COMPACTION OF CONCRETE] = Compaction is a process of expelling the entrapped air. If we don’t expel this air, it w..."

= [https://worl.data.blog/2019/04/09/compaction-of-concrete/ COMPACTION OF CONCRETE] =

Compaction is a process of expelling the entrapped air. If we don’t expel this air, it will result into honeycombing and reduced strength. It has been found from the experimental studies that 1% air in the concrete approximately reduces the strength by 6%.

DIFFERENT METHODS OF CONCRETE COMPACTION

There are two methods of compaction adopted in the field as given below.

* Hand compaction
* Mechanical Compaction

(A) 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.

1. 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.

2. RAMMING

It is generally used for compaction on ground in plain concrete. It is not used either in RCC or on upper floors.

3. 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.

(B) MECHANICAL COMPACTION

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.

1. 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.

2. 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 form work also has to be made extra strong when external vibration is used.

3. TABLE VIBRATION

It is mainly used for laboratories where concrete is put on the table.

4. PLATFORM VIBRATION

It is similar to table vibrators but these are generally used on a very large scale.

5. 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.

<Humayoon Sial>

[[Category:Conservation]] [[Category:Definitions]] [[Category:Education]] [[Category:Theory]] [[Category:Construction_techniques]]