CHAIN’S & TYPE’S OF CHAIN’S

                                CHAIN’S & TYPE’S OF CHAIN’S

Chains are the measuring instrument used in SURVEYING formed by the 100 links of 4mm galvanized mild steel wire. These links are joined by 3 circular or oval wire rings. These rings provide the flexibility to the chains. Every aspect of the life requires some measuring units. Measurements are used to do the work precisely and accurately. Let it be from kitchen to office, everywhere measurements are used. So as in engineering calculation or measurements holds a very greater role in construction or surveying or any other aspect. There are various units of measurements such as meters, centimeters, feets, inches, acre, yards and the list goes on. Same as units there are various instrument used in the measurements of any entity. One of the instruments used in measurement are chains. 

Parts of Chains used in Surveying

The chain consists of many small parts used for handling or reading the measurements. 

• At the ends chain is provided with brass handle with swivel joint so that it can be easy to roll or unroll the chain without twisting and knots.

• At every 1 M is provided with a tally of one tooth, 2 M with a tally of two teeth and so on till 4 M. This is provided for the easy reading of measurements. At the 5 Meter of the chain is provided with a circular tally used for easy reading.

Types of Chains used in Surveying

Depending upon the length of the chain, these are divide into following types, 

1. Metric chain 

2. Steel band or Band chain

3. Gunter's chain or surveyor’s chain Engineer’s chain

4. Revenue chain

5. A. Metric chains

Metric chains are the most commonly used chain in India. These types of chains comes in many lengths such as 5, 10, 20 and 30 meters. Most commonly used is 20m chain. Tallies are provided at every 2m of the chain for quick reading. Every link of this type of chain is 0.2m. The total length of the chain is marked on the brass handle at the ends. 

B. Steel band or Band chain

These types of chain consist of a long narrow strip of steel of uniform width of 12 to 16 mm and thickness of 0.3 to 0.6 mm. this chain is divides by brass studs at every 20cm or instead of brass studs, band chain may have graduated engraving as centimeter. For easy use and workability band chains are wound on steel crosses or metal reels from which they can be easily unrolled. These steel bands are available in 20m and 30m length and the width of about 12-16mm. 

C. Gunter's chain or surveyor’s chain

Gunter chain comes in standard 66ft. 

This chain consists of 100links,

Each link being 0.66ft or 7.92inches. 

The length 66ft is selected because it is convenient in land measurements.

10 square Gunter’s chains = 1 Acre 

10 Gunter chains = 1 Furlong 

80 Gunter chains = 1 mile 

D. Engineer’s chain

This chain comes in 100ft length. 

It consist of 100 links each link being 1ft long.

At every 10 links a brass ring or tags are provided for indication of 10 links.

Readings are taken in feet and decimal. 

E. Revenue Chain

The standard size of this type of chain is 33ft. 

The number of links is 16, 

Each link being 2 ft.

This chain is commonly used in cadastral survey. 

Testing and Adjustment of Chain

As the chain is a metal made, it may undergo many changes due to temperature effect or human error and etc. So for all lengths of chain a tolerance is given, 

5m chain = + or – 3mm 

10m chain = + or – 3mm 

20m chain = + or – 5mm 

30m chain = + or – 8mm 

Chain length shorten due to

1. Bending of links.

2. Sticking of mud in the rings

Chain length increases due to 

• Opening of small rings.

• Wearing of surfaces.

Chains may be tested with respect to 

• Steel tape

• Permanent test gauge

• Pegs driven in the field at required distances

• Permanent test gauge made with dressed stones

• 

If chain is found long, then 

• Close the joins of the rings

• Reshape the elongated rings

• Remove one or two rings Replace worn out rings

• If chain is found short, then 

• Straighten the links

• Replace the small rings with big one

• Insert additional rings

• Flattening the circular rings

Errors in chain Surveying

Errors in chaining may be classified as: 

• Personal errors

• Compensating errors, and

• Cumulating errors.

Personal Errors

Wrong reading, wrong recording, reading from wrong end of chain etc., are personal errors. These errors are serious errors and cannot be detected easily. Care should be taken to avoid such errors. 

Compensating Errors

These errors may be sometimes positive and sometimes negative. Hence They are likely to get compensated when large number of readings are taken. The magnitude of such errors can be estimated by theory of probability. The following are the examples of such errors: 

• Incorrect marking of the end of a chain.

• Fractional part of chain may not be correct though total length is corrected.

• Graduations in tape may not be exactly same throughout.

• In the method of stepping while measuring sloping ground, plumbing may be crude.

Cumulative Errors

The errors that occur always in the same direction are called cumulative errors. In each reading the error may be small, but when large number of measurements is made they may be considerable, since the error is always on one side. Examples of such errors are: 

1. Bad ranging

2. Bad straightening

3. Erroneous length of chain

4. Temperature variation

5. Variation in applied pull

6. Non-horizontality

7. Sag in the chain, if suspended for measuring horizontal distance on a sloping ground.

Errors (i), (ii), (vi) and (vii) are always +ve since they make measured length more than actual. 

Advantages and Disadvantages of Chains in Surveying

Advantages of Chains in Surveying

• Chain survey is simplest and commonest method used in surveying exercises

• The equipment used to conduct chain survey are simple to use,

• The equipment used in chain survey can easily be replaced. For example measuring rods can be replaced with measuring tape.

• This method does not involve complicated mathematical calculation. I know this is the relief to those who are afraid of mathematics

• In chain survey few people are needed to conduct the survey. Normally chain survey team has three people Booker, leader and follower.

Disadvantages of Chains in Surveying

• Simple chain survey cannot be conducted in built up areas and large areas.

• Simple chain survey is subject to several chances of errors of accumulation which may cause by problem of chain. The chain linkage may fail to stretch up properly and result in inaccurate data. Also clogging of chain may read to error in reading.

• It is time consuming

• It may not be conducted in areas with steep slopes or water logged areas. Chain survey is usually conducted in dry areas with gentle slopes. It becomes more complicated when survey is conducted in areas that are too wet.

• Chain survey becomes more complicated method when there are raised points (obstacles) in between areas to be surveyed

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Cement Ingredients of cement

       Cement 

Cement is manufactured through a closely controlled chemical combination of calcium, silicon, aluminum, iron and other ingredients. Common materials used to manufacture cement include limestone, shells, and chalk or marl combined with shale, clay, slate, blast furnace slag, silica sand, and iron ore.{ The most important raw materials for making cement are limestone, clay, and marl. These are extracted from quarries by blasting or by ripping using heavy machinery.}

                      Ingredients of cement
The main ingredients used in the manufacturing of cement are lime, silica, alumina and other oxides. A brief discussion about the contribution of different ingredients in cement is below:

Lime

About 60 - 65 % of cement constitutes of lime which contributes to the strength. Proper care should be taken in proportion to make the cement sound and strong, as an excess of lime makes the cement unsound and causes the cement to expand and disintegrate. In case, if lime is deficient, the strength of the cement is reduced and sets quickly.

Silica

Silica consists of about 17 - 25 % in cement, which also contributes to the strength of cement due to the formation of dicalcium and tricalcium silicates. Excess presence of silica increases the cement strength but prolongs the setting time of cement.

Alumina

The percentage of alumina is 3.5 - 9.0 in cement, which imparts quick-setting quality to the cement. Surplus amount of alumina presence in cement leads to the reduction of strength.

Iron Oxide

Iron oxide is present about 0.5 - 6.0 % in cement, which provides colour, hardness and strength to the cement.

Magnesium Oxide

The correct quantity of magnesium oxide imparts hardness and colour to the cement, and the required amount is about 0.5 - 4.0 %. Presence of excess quantity seriously affects the soundness of cement.

Sulphur Trioxide

It is present in small quantities of about 1 - 2.0 % to make the cement sound. Excess of sulphur trioxide causes the cement to become unsound.

Alkalis

Alkalis like soda or potash should be present only in small quantities up to 0.4 - 1.3 %. Excess quantity of these materials cause efflorescence and straining while using in concrete or mortar.

Top 10 Requirements for Quality Cement:

1.   It should possess a uniform colour.

2.   It should be free from lumps.

3.   It should be smooth as it should get sink completely if thrown in the water.

4.   The ratio of percentage of alumina to that of iron oxide should not be less than 0.66 in cement.

5.   The total sulphur content in cement should not be greater than 2.75%, and Magnesia content should not exceed    5% by weight.

6.   Insoluble residue in cement should not exceed 1.5% by weight.

7.   When heated, cement should not lose its weight more than 4%.

8.   The specific surface of cement as from the fineness test should not be less than 2,250 mm² / gm.

9.   The initial setting time of cement should be about 30 minutes and the final setting time should be about 10 hours.

10.   Cement should not expand more than 10 mm in a soundness test.

Different Types Of Cement

• Ordinary Portland Cement (OPC) 

• Portland Pozzolana Cement (PPC) 

• Rapid Hardening Cement.

• Extra Rapid Hardening Cement

• Low Heat Cement.

• Sulfates Resisting Cement. 

• Quick Setting Cement

• Blast Furnace Slag Cement

                                 Portland cement 

Is used in concrete for bridges, walls, culverts, floors, pavements, sidewalks, pipe, railway structures, reinforced concrete buildings, tanks and reservoirs, as well as for masonry units and other precast products.

Some harmful constituents of cement:

The presences of the following two oxides adversely affect the quality of cement.

1. Alkali oxides K2O and NaO2.

2. Magnesium oxide MgO.

If the amount of alkali oxides exceeds 1 percent, it leads to the failure of concrete made from that cement. Similarly, if the content of magnesium oxide exceeds 5 percent, it causes cracks after mortar or concrete hardens.

It is due to the fact that magnesium oxide, burned at a temperature of about 1500 °C, Slakes very slowly, when mixed with water.

Must Read Other Powerful Articles

• Properties of Cement 

• Types of Cement

• Composition of Cement Clinker

• Hydration of Cement

• Products of Hydration of Cement

• What is Cement?

• Various Tests on Cement

• Ordinary Portland Cement (OPC)

• Manufacturing of Cement By Dry and Wet Process

• Raw Materials of Cement

• History of Cement in Civil Engineering

• Composition of Cement Clinker

• Ordinary Portland Cement (OPC)

• What is Concrete with Definition & History