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Daily Archives: September 25, 2018

Building Materials

Cement the binder of new World of Structures

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Cement is the most widely used materials in construction industries from decades. In India cement plants were established way back in 1904

Manufacturing of Cement –

The main raw materials for manufacturing of Portland cement are –

Lime stone and Clay – that is Calcareous and Argillaceous materials.

Cement are mainly manufactured by two process –

  • Dry Process
  • Wet Process.

Now a day’s mostly wet process of cement manufacturing is found which is superior to dry process.

The steps of manufacturing are as follows –

  • Grinding of raw materials

Grinding of raw materials and mixing is done in the wet process as in wet condition, so finer particle and uniform mixing could be done yielding superior quality clinker. Although more fuel is consumed in wet process than in dry process.

  • Mixing them in certain portion according to product required.
  • Burning them in kiln at 1400 to 1500 degree Celsius temperature.
  • Cooling the obtained material known as clinker and mixing it with about 2 % gypsum.

 

Chemical Composition of Raw Materials of Cement –

The chemical composition of raw materials used for manufacturing of cement consist of Lime, Silica, Alumina and Iron Oxide.

These compounds react chemically at high temperature in the kiln to form complex compound of cement.

Raw materials of Portland cement consists of the following chemical composition –

CaO – 60 -67%

SiO2 – 17-25 %

Al2O3 – 3-8 %

Fe2O3 – 0.5 to 0.6 %

MgO – 0.1 to 4.0

Alkalis ( K2O and Na2O ) – 0.4 to 1.30 %

SO3 – 1.0 to 3.0 %

 

The formed compound after chemical reaction are as follows –

 

Tricalcium Silicate – 3CaO SiO2 – C3S – 54.1 %

Dicalcium Silicate as 2Cao Sio2- C2S -16.6%

Tricalcium Aluminate – 3Cao Al2O3 – C3A – 10.8%

Tetra Calcium Alumino Ferite – 4 Cao Al2O3 Fe2O3 – C4AF – 9.10%

So it’s found that C3S and C2S are the main constituent and forms 70-80 % of cement.

 

The specification of Portland cement is specified in IS 269 –

 

Hydration of Cement –

When water is added to the cement the compound reacts with water and the liberating heat this process is known as hydration of cement.

C3S and C2S reacts with water and produces calcium silicate hydrate and Calcium Hydroxide.

Calcium Hydroxide is not a desirable product of cement as it is dissolved in water and may leach out from the concrete making small pores.

C3S reacts with water at more rapid pace and produces more heat and provided early strength.

C2S reacts slowly and produces less heat of hydration and is responsible for later strength of concrete.

The hydrated product of C2S are found to be more superior as they are denser.

The reaction of C3A with water is very fast and that may lead flash set to prevent this gypsum is added to cement.

C3A does not contribute to the strength of cement and makes it prone to sulphate attack.

Hydrated product of C4AF also does not contribute to the strength of cement and their hydrated product are resistant to sulphate attack.

 

Types of Cement –

  • Ordinary Portland cement
  • Rapid Hardening Cement
  • Extra Rapid Hardening Cement
  • Sulphate Resisting cement
  • Blast Furnace Slag cement
  • Quick setting cement
  • Super Sulphate Cement
  • Low Heat cement
  • Portland Pozzolona Cement
  • Air entraining cement
  • Hydrophobic cement
  • Masonry cement
  • Expansive cement
  • Oil Well cement
  • High strength cement
  • Redieste cement
  • High Alumina Cement

 

Classification of cement –

IS classification –

  1. 33 Grade OPC – IS 269 1989
  2. 43 Grade OPC – IS 8112 1989
  3. 53 Grade OPC – IS 12269 of 1987

Grade number refers to the minimum compressive strength after 28 days.

 

Test of cement –

Field test

The colour should be greenish grey but it may depend upon the types of cement. No visible lumps should be there.

When hand is inserted inside the cement the hand may feel cool.

Take a pinch of cement and it should give smooth feeling

When some quantity are thrown in a bucket of water they must float for some time before they sink.

Make a cube of cement paste with about 100 gm of cement. When the cake is inserted into a bucket of water after 24 hours the cake should retain its shape.

 

 

Lab Testing of Cement

Fineness Testing

Standard Consistency Testing

Setting Time Test

Soundness Test

Heat of Hydration Test

Chemical Composition Test.

Building Materials

Lime and Limestone Characteristics and Uses

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Lime is used for construction works since ancient times lime is also used to manufacture cement and other construction products.

 

Depending upon the calcium Oxide content lime may be of three types.

  • FAT Lime
  • Hydraulic Lime and
  • Poor Lime

Quick lime contains about 95% calcium oxide. Quick lime is obtained from stone containing Calcium Carbonate the stones are heated to drive out Carbonate as CO2 leaving Calcium Oxide. The burning is done at kiln and is known as Calcination After slaking the quick lime increases its volume 2 to 2.5 times and its known as Fat lime.

 

Hydraulic Lime is obtained from burning limestone containing lot of clay material along with the calcium carbonate. This lime has setting property that means it can set lime cement and that is known as hydraulicity. It can set under water. Setting property depends upon the amount of clay and its property.

Its further subdivided into three category-

Feebly Hydraulic Lime – Less than 15% Silica and Alumina

Moderately Hydraulic Lime – 25 to 30%

 

Poor Lime – The lime which contains more than 30 % clay material and slakes very slowly and does not dissolve in water. This lime has setting property but it set and hardens very slowly.

 

Lime is classified according to IS 1973 as various classes namely –

Class A – Eminently Haudraulic lime

Class –B Semi Hydraulic lime

Class C – Fat Lime

Class D – Magnesium Lime

Class E – Kankar Lime

Properties of Lime –

  1. Lime is easily workable.
  2. Lime has good plastic properties.
  • It can withstand moisture.
  1. It imparts good strength if used as mortar.
  2. Masonry lime is more durable due to its low shrinkage.
  3. Good adhering properties with stone and brick similar to cement.

Uses of Lime –

There are a lot of use of lime in construction industry following are the few examples-

  • Limestone Extensively used for manufacturing of cement.
  • Its used as binding material in mortar and in cement.
  • Extensively used as plastering material.
  • Sometimes used as an aggregate.
  • Used fro base coat and distempering of wall.
  • Used as flux material in many industry.
  • Lime is used for soil stabilization.
  • It is used to improve soil property for agricultural purposes (for controlling pH of soil).
  • Used in fish culture.
  • Used in sewage treatment process.
  • Used in glass manufacturing.
Building Materials

Timber as Building material

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Bradly wood is the hard material which retina underneath the bark of the tree. Timber is the main portion of wood which can retain its structure.

Timber is the natural material obtained from wood. The wood may be chemically and mechanically treated to create synthetic wooden materials which has superior quality than the timber, plywood, compressed wood fibre boards are the examples.

Wooden materials are widely used as door, window frame, partition walls and for form work of construction works.

Wood has good property of absorbing shock and thermal, sound and electrical resistance is very good, wood is also less prone to chemical attack.

 

Wood are obtained form –

Exogenous and Endogenous trees – Exogenous trees grows outwards and they made good structural element. They are further sub divide in to – Deciduous and Conifers trees –Deciduous have flat and broad leaves and annular rings are indistinct in these trees. Examples are – oak, maple, shisham etc.

Conifers trees are evergreen throughout the year and they have pointed needle like leaves their annular rings are distinct. Their wood has long and soft fibre with resinous substances. Examples are – deodar, chir,  pine etc.

 

Timber is classified according to IS : 399 and IS 6534

According to IS 6534 Timber may be classified by grade A,  grade B, grade C and grade D method. Grade D method being used internationally.

On the basic of modulus of elasticity (E) timbers are of –Grade A, Grade B and Grade C-

Grade – A E >12.5 KN/mm2,

Grade B E>9.8 <12.5 KN/mm2

Grade B E>5.6 KN<9.8 KN/mm2

 

On Basis of Durability they are classified as –

High Durability > 120 months life span.

Moderate 60 months to 120 months life span.

Low durability – life span being less than 60 months

 

How to know if a timber is of good Quality.

The principal properties of a good timber are-

  1. Annular rings should be spaced closer, more closer being greater strength.
  2. Medullary rays should be compact.
  3. Colour and uniform texture.
  4. Sweet smell when cut fresh.
  5. Free from any defects.
  6. Good metallic sound  should be produced when struck with any object.
  7. Good unit weight.

 

What is seasoning of Timber –

The timber from fresh cut tree has a lot of moisture in it and is not suitable for using as building materiel so its moisture content is reduced to desired level.

The process of reducing the moisture content to desired level is call seasoning of timber.

Seasoning reduces the shrinkage and warping after its placement,

Reduces its tendency to split and decay due to fermentation.

Make timber suitable for painting

Reduces unit weight of timber.