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Building Materials

Interview Questions on Building Materials

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  1. Composition of brick earth –

Silica or Sand 50-60%– Prevent Shrinkage, Cracking and wrapping but too much quantity can make the brick brittle.

Alumina or Clay 20-30%– It make the brick earth plastic and provide the brick its hardness.

Lime and Oxide of Iron – Malt the sand grains and bind the clay particle when heated. Iron oxide provide the brick its red color.

Magnesia – Small quantity desirable but excess makes the brick yellow.

  • Burning Temperature – 800-10000C
  • Strength of 1st Class, 2nd Class and 3rd Class, Jhama bricks – 10.5N/mm2  7.5 N/mm2 5.5 N/mm2
  • Water absorption – First Class < 20% (Preferable below 15%) 2nd Class < 22% 3rd Class < 25%
  • Frog Size and Its position in masonry – 100x40x 10-20 mm

Frog acts as a key to the joint of brick and mortar.  

  1. Stones used in civil engineering and their strength –

Granite – Abutment and Pier of Bridge,

Stand Stone – Ashlar Masonry

Marble – Floor and Ornamental Work.

  • Why bricks are soaked before their use in brick masonry?

Dry brick absorb water and to prevent water getting absorbed from mortar and for better bonding with cement sand mortar.

  • Points to be supervised during brick masonry. –

No continuous vertical joint should be formed.

For brick masonry brick should be sufficiently wet before use.

Maximum height of construction should be limited to 1.5 m.

Verticality should be checked.

Proper curing should be done.


  1. Types- River Sand, Nallah Sand, Artificial Sand etc.

Sizes- Fine Sand, Medium Sand, Coarse Sand

Uses – Cement mortar, fine aggregate of concrete, Soil improvement, Plinth filling.

Bulking of sand The phenomenon of increase in volume of sand due to moisture in sand particle.

It’s Value – The volume may increase up to 45% corresponding to the water content of about 4.6%

What is FM of Sand – It’s an index number representing the size of sand particle.

FM -2.2-2.6 Fine Sand, 2.6-2.9 – Medium Sand, 2.9-3.2 Coarse sand.

 What does it indicate, what are their values?

It indicate the average size of the sand particles.


  1. Chief Ingredients – Limestone or Chalk (Calcareous materials), Shale or Clay (Argillaceous materials),
  2. Calcination temperature – 13000C – 15000C
  3. Bogue’s compounds –

Tricalcium Silicate – 3CaO.SiO2 (C3S)

Dicalcium Silicate – 2CaO.SiO2 (C2S)

Tricalcium Aluminate – 3CaO.Al2O3 (C3A)

Tetracalcium Aluminoferrrite – 3CaO. Al2O3 .Fe2O3 (C4AF)

Their functions – Tricalcium Silicate and Di Calcium Silicate are the two most important compound of cement responsible for strength development. Average C3S content is 45% and C2S is 25%. C3A flash set and to prevent flash set retarder like gypsum is added to the cement.C4AF is relatively inactive compound. C3S hardens early and develops early strength. C2S hydrates slowly and contribute to ultimate strength. C2S hydrate are much superior to C3S hydrate.

  • The Types of Cement and their uses in different locations –

Ordinary Portland cement – General purpose construction.

Portland Pozzolana Cement – Marine and hydraulic construction and mass concrete constructions.

Rapid Hardening Cement – Where formwork to be removed early, road repair works and in cold weather condition.

Portland Slag Cement –Underground construction and marine construction and at coastal regions and in mass concrete structure.

Sulphate resisting Cement – Concrete in foundation and basement where soil contains sulphates, fabrication of pipes, construction of sewage treatment plant and in marine environment.

Quick Setting Cement – Grouting operations.

Low Heat Cement – Mass concrete such as dams.

Super Sulphated Cement –Foundations where chemically aggressive condition exist marine environment and sewage pipe.

Coloured Cement –Decorative purposes.

Hydrophobic Cement – Remote locations where more storage time is required.

  • Initial Setting and Final Setting Time –

30 min 600 min for OPC.

  • What is 53 Grade Cement – Strength of the cement at 28 days is not less than 53N/mm2. (Tested as per IS 4031-1988)
  • How is cement tested at site –

Appearance of the cement should be greenish grey there should not be any lumps in the cement bags.

Smooth feeling is obtained in good cement when we take between our fingers.

If we insert our hand inside a bag of cement it should feel cool.

When a hand full of cement is thrown inside a bucket of water it should float sometime before sinking.

A cake made with stiff paste of cement when kept inside water for 24 hours should retain its shape and attain some strength.

  • Weight and volume of one Bag of cement – 50 kg weight and 0.0347 cum volume.
  1. How much temperature and heat are generated when cement is mixed with water?

After 7 days – 89-90 cal per gram.

After 28 days – 90-100 cal per gram.

Building Materials Uncategorized

What is the difference between formwork, shuttering, staging, centring and scaffolding?

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Formwork: As its name implies it is a temporary structure which gives form or shape to the poured concrete. It is a vertical or horizontal structure to keep the concrete in desired position until the concrete gains some strength. The cost of the formwork may be upto 20-25% of the cost of the structure in building work and even higher in bridges.
Shuttering: The formwork which supports the vertical arrangement is known as shuttering. The formwork used in columns, side of beam, footing and retaining wall is designated as shuttering.
Centring: The formwork which supports the horizontal members such as bottom of the beams and slabs are called centring.
Staging: The member which supports the formwork for centring or shuttering. Staging is generally done by bamboo props to support horizontal formwork.
Scaffolding: When the height of wall or column or other structural member of a building exceeds 1.5m, temporary structures are needed to support the platform where the workers can sit and carry on the constructions. Scaffolding is also needed for outside painting of a building or for repairs and demolition.

Building Materials

Admixture and their Properties

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 Definition
A material other than water, aggregate and hydraulic cement and additives like pozzolana or slag and fibre reinforcement used as an ingredient of concrete or mortar and added to the batch immediately before or during its mixing to modify one or more of the properties of concrete in the plastic or hardened state.

 IS Classification
i. Accelerating admixtures / Accelerator.
ii. Retarding admixtures / Retarder.
iii. Water reducing admixtures / Workability aid.
iv. Air Entraining admixtures.
v. Super plasticizing admixtures.
vi. Retarding super plasticizing admixtures.

 Special category admixtures
i. Grouting admixtures.
ii. Bonding admixtures.
iii. Damp proofing and permeability reducing admixtures.
iv. Air detraining admixtures.
v. Corrosion inhibiting admixtures.

 Function of admixtures
i. To accelerate the initial set of concrete i.e. to speed up early strength development.
ii. To retard the initial set i.e. to keep concrete workable for longer period.
iii. To improve workability.
iv. To improve penetration and pumpability of concrete.
v. To reduce segregation in grout.
vi. To increase the strength of concrete by reducing the water content.
vii. To increase the durability of concrete.
viii. To increase the resistance against chemical attack.
ix. To reduce heat of hydration.
x. To increase the bond between old and new concrete surfaces.
xi. To decrease the weight of concrete per cubic meter.
xii. To reduce the corrosion of reinforcement.

 Accelerator
These admixtures are added to concrete to –
a) Increase the rate of hydration of cement.
b) Shorten the time of set.
c) Increase the rate of hardening or strength development.

Thus these admixture are used when there is –
a) Earlier requirement of structure in service.
b) Earlier removal of formwork.
c) Earlier finish of surface.
d) Underwater concreting.
e) Coldwater concreting.

 Examples of accelerators

i. CaCl2 (Calcium Chloride)
 Dose
1.5 to 2% by weight of cement.
 Functions
Reduce setting time by 1/3 rd.
Increase 7 day compressive strength.
Increase flexural strength.
 Disadvantage
Exposed to alkali-aggregate reaction.
Sulphate attack.
Corrosion of reinforcement.

ii. Calcium formate.
iii. NaCl.
iv. Na2SO4.
v. NaOH.
vi. KOH.
vii. Fluoro silicates.

 Retarding Admixtures
These admixture are added to concrete to –
a) Delay the setting of cement paste.
b) Slowdown the initial rate of hydration of cement.

Thus these admixtures are used when –
a) There is requirement keep the concrete workable for longer period for transportation and placing.
b) To reduce the damaging effect during hot weather, low humidity and high wind velocity concreting conditions.
c) Ready mix concrete.

 Examples of Retarding admixtures
i. Sugar
 Dose
0.05 to 1% by weight of cement.
 Function
Delay initial setting time by 4 hrs.
ii. Starch.
iii. Dextrin.
iv. Zinc hydroxide.
v. Lead hydroxide.
vi. Calcium borate.

 Water reducing admixture
These admixture are added to concrete to –
a) Increase the workability of concrete without increasing water content.
b) Maintain wokability with reduced amount of water.
Thus these admixtures are used when –
a) There is faster requirement of concrete placement.
b) Heavily reinforced concrete sections.
c) Reduction of cement content.
d) Higher flowable concrete.

 Benefits of water reduction in hardened state of concrete.
i. Increased strength.
ii. Density.
iii. Durability.
iv. Volume stability.
v. Abrasion resistance.
vi. Reduced permeability & cracking.

 Water reducing admixtures are also termed as plasticizing admixtures. The mechanism involved are (i) Dispersion (ii) Retarding effect.

 Dispersion
When plasticizers are added thy get absorbed on cement particles. The absorption of charged polymer creates repulsive force, which results in deflocculation and dispersion. Thus increases the fluidity of concrete.

 Retarding effect.
On addition of plasticizers the following mechanism takes place –
a) Reduction in surface tension of water.
b) Induce electrostatic repulsion between particles of cement.
c) Lubricating film between cement particles.
d) Surface hydration of the cement particles, leaving more water to fluidify the mix.

 Examples of water reducing admixtures
i. Derivatives of lignosulphonic acids and their salts (e.g. Calcium Lignosulphonate).
(Reduce water requirement by 8 to 15 %. Dose 0.1 to 0.2 % by weight of cement. )
ii. Hydroxylated carboxylic acids and their salts.

 Air Entraining Admixtures
These admixtures are added which causes –
Air to be incorporated in the form of minute bubbles in concrete usually to increase workability and resistance to freezing and thawing and disruptive action of de-icing salts.

These admixtures are used when –
a) High workability is desired.
b) Freezing and thawing condition.
c) Cellular concrete.
d) Light weight aggregate concrete.

 Mechanism
These admixture when added acts as surfactants which are absorbed on to the cement particles. These surfactants forms bubbles on agitation which stabilize as microscopic spheres which increases mobility of concrete. These air entrainment bubbles reduces capillary forces in concrete. During freezing these bubbles produce extra space for expansion of ice and again regain their original size during thawing.
Thus segregation and bleeding is also reduced due to formation of homogenous mix. However increase of air entrainment reduces compressive strength.

 Properties effecting due to addition air-entrainment admixtures –
i. Segregation, bleeding get reduced.
ii. Improves permeability.
iii. Reduces aggregate alkali action and chemical attack.
iv. Reduction of sand and water content.
v. Lowers unit weight.
 Examples of Air Entraining Admixtures
i. Natural wood resins.
ii. Vegetable fats and oils.
iii. Olive oils.
iv. Stearic and oleic acids.

 Superplasticizing Admixtures
These admixtures are used to impart –
a) Very high workability.
b) Large decrease in water content for a given workability.

These admixtures are principally surface reactive agents. They confer negative charge on individual cement particles such that they are kept in a dispersed or suspended state due to interparticle repulsion. Thus they confer high mobility to the particles.

 Uses of Superplasticizers
i. Produce flowing concrete (Slump ≥ 200mm) without causing segregation and bleeding.
ii. Produce concrete with very low water cement ratio maintaining same workability.
iii. Produce high performance concrete.
iv. Produce concrete mix with reduced cement content.

 Examples of Superplasticizing Admixtures
i. Sulphonated Melamine Formaldehyde (SMF)
(3% by weight of cement)
ii. Sulphonated Naphthalene Formaldehyde (SNF)
(e.g. Poly B-nepthalene, imparts longer period of workability retention)
iii. Modified Lignosulphonates (MLS)
(Greatest workability retention)
iv. Carboxylated Acrylic ester Co-polymers (CAEC)
(Produce concrete with lower slump loss)

 Retarding Superplasticizing Admixtures
These admixtures imparts prolonged workability and retards setting.
e.g. SNF and MLS.

 Requirements of Admixtures.
Admixture in general sence should be avoided. If used its suitability or conformance to specified requirements should be compared with identical concrete without the admixtures under the following requirements.
i. Percentage reduction in water content.
ii. Slump.
iii. Initial and final setting time deviation.
iv. Deviation of compressive strength.
v. Deviation of flexural strength.

 Tests to be performed on fresh concrete
i. Tests of workability (Slump and C.F. test)
ii. Loss of workability on standing (45 mm and at 2hrs.)
iii. Test for air content.
iv. Test for time of setting.
v. Test for bleeding (Absorbtion of aggregates)
vi. Test for water content.
(Water absorption of aggregate, W/C ratio, Mass of cement/ Unit volume)
 Tests to be performed on hardened concrete
i. Compressive Strength.
ii. Flexural Strength.
iii. Test for length change.

 Information required for selection of a admixture
a) Physical state. (Liquid or Solid and Colour)
b) Generic type. (Lignosulphonate, Organic hydroxyl carboxylic)
c) Dry material content.
d) Ash content.
e) Relative density of liquid admixture.
f) Chloride ion content.
g) Recommended storage conditions, maximum storage time etc.
h) Recommended dosage.
i) Effect of under dose and overdose.
j) Expiry date.

Building Materials

Aggregate and their properties

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Some kind of filler materials are used in Concrete or mortar to increase its volume, these are termed as aggregates. They may be naturally obtained, manufactured in plant or by-product of other industries. Aggregate are main mass composition of concrete and posses about 70-80% of concrete.


Aggregates may be Natural or Artificial depending upon their geologic origin.

But mainly what we are used to classify them is according to their Size.

They may be Coarse aggregate and Fine Aggregate as per their size-

Aggregate having size greater than 4.75 mm to 80 mm are coarse aggregate. Usually for concreting 20 mm and 10 mm size aggregate are used as coarse aggregate.

Aggregate having size less than 4.75 mm but not less than 0.06 mm are fine aggregate. Fine aggregate are also classified as Fine, Medium and Coarse fine aggregate.

IS: 383 specifies four zones of  grading according to the size of fine aggregate.


On the Basis of shape – aggregate are of round, angular, flaky and etc.








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.

Building Materials

Brick as Building Material and its Properties.

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Bricks are made out of clay, clay is moulded to desired shape and size to make sun dried or burnt brick . The clay of brick contain iron oxide, lime iron pyrites pebbles of stone and gravel  alkalies etc.
Iron oxide gives red colour to the brick. Lime binds the particles while burning and reduces shrinkage although excessive lime melts the brick.
The sequence of making brick are – Digging – weathering – blending – tempering – moulding – drying – and burning .
Pug mill is used for tempering the brick earth, then hand moulding or machine moulding is done. Bricks are dried in sun or in controlled room environment then they are burnt in kilns or clamps
Kiln burnt brick are of superior quality. Widely used kiln are Bull trench and Hoffman’s kiln.

Well burnt with uniform red colour crack free brick are good quality brick, they produce clear ringing sound when they are struck against each other . Water absorption should be limited to 15 by weight when kept in water for about 24 hours. Crushing strength should be more than 55 kg/cm2
Brick may be of different types, bricks which withstand high temperature are refractory bricks alumina content is more in these bricks.

They are different sizes of bricks in India, Is bricks is 19cmx9cmx9cm and with mortar it becomes 20cmx10cmx10cm. Different pwd uses different sizes of bricks.
Perforated bricks hollow bricks and coping bricks king closer bricks Queen closer bricks are some types of bricks.

Test on Bricks –

For testing the suitability brick may be tested for –

Dimensional Tolerance.

Compressive Strength.

Water Absorption.

Efflorescence etc.

Building Materials

Stone as Building Material.

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Stone is one building material which is being used from primitive time. Their strength and availability made them so popular but now a days they are mainly replaced by brick and concrete. Stone are obtained from rocks and the process is called as quarrying. The rocks are broken into suitable pieces by means of blasting, wedging, excavating etc.

After quarrying their faces are made smooth and regular and that process is termed as dressing.Engineers widely use stone like marble, granite (flooring materials), basalt and trap (as railway ballast) , lime stone, sand stone, laterite etc.

Before uses for any purposes we need to know how they are constructed and their constituents. Rocks may be classified according to their geological, physical or chemical properties.

Geologically they may be –

(1) Igneous  –  Molten magma from volcano is forced up to surface and solidifies as rock.

When they are solidifies at earths surface at rapid rate basalt and trap rock are formed, if the solidification takes place below the surface of earth at slower pace then granite is formed.

(2) Sedimentary – Sand, silt and debris are deposited and subjected to overburden pressure sedimentary rocks are formed.

(3) Metamorphic – Due to high temperature and heavy pressure texture and composition of  sedimentary rocks and igneous rocks are changed, these rocks are termed as metamorphic rock.

The following are the few example of metamorphosis of rock –

Granite ——–Gneiss,

Sand Stone  ——— Quartizite,

Lime Stone ——— Marble,

Shale ——— Slate.

Physically they may be of  – (1) Stratified – The rocks show distinct layer of stratification and may be split into layers like slate, marble, lime stone etc.  and (2) Unstratified  – No such stratification is found and cant be split in layers like granite basalt and trap.

Chemically rocks bay be of  – (1) Argillaceous – When the main constituent of rock is clay mineral they are argillaceous rock by chemical nature, examples are Slate and Laterite .

(2) Calcareous – When the main constituent is lime or calcium then they are calcareous by chemical nature, like Lime Stone and Marble Stone.

(3) Silicious – If the principle constituent of rock is silica then they are silicious rock, examples are quartzite and granite.