Important Properties Of Fluid

• Viscosity

It is defined as the property of a liquid which offers resistance to the movement of one layer of liquid over another adjacent layer of liquid.

The viscosity of a liquid is due to cohesion and interaction between particle.

Viscosity is also known as Absolute Viscosity or Dynamic Viscosity.  

• Kinematic Viscosity

It is defined as the ratio of dynamic viscosity  to the density of liquid.

• Compressibility 

It is that property of liquid by virtue of which liquids undergo a change in volume with the change in pressure.

The compressibility is the reciprocal of bulk modulus of elasticity, which is defined as the ratio of compressive stress to volumetric strain.

• Surface Tension

The tensile force acting on the surface of a liquid in contact with a gas or another immiscible liquid.

The contact surface behave like a membrane.

• Capillarity

It is defined as a phenomenon of rise or fall of a liquid surface in a small vertical tube held in a liquid relative to the general level of the liquid. 

• Symbols & Units

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Classification Of Bricks

• Introduction

Bricks are the most important construction material.It is mainly made up of Clay but with the advancement of technology,now Fly Ash is also used to manufacture Bricks. 

• Types of  Bricks

On the basis of classification bricks are classified in various categories.

This Classification are very Important for competitive exams.

1. First Class Bricks -

     These bricks are well burnt having smooth and even surface with perfect rectangular shape and uniform radish colour.

2. Second Class Bricks -

    These bricks are slightly over burnt having rough surface and not perfectly rectangular in shape.

3. Third Class Bricks -

    These Bricks are not properly burnt ( under burnt ) in the kiln ang hence these are 

soft and can easily be broken.

4. Jhama Bricks -

     These bricks are over burnt with irregular shape.These bricks are dark bluish in colour.

• Important Points on Bricks

1. The standard size of bricks are 19cm x 9cm x 4cm  or  19cm x 9cm x 9cm.

2. Specific Gravity of bricks is about 2.

3. The no of bricks required for one cubic meter of brick masonry are 550.

• Some Special Types of Bricks

1. Squint Bricks - These bricks are used in construction of acute and obtuse                                                           squint quoins.

2. Refractory Bricks -A good refractory brick should have the capability of                       withstanding high temperature and low coefficient of expansion and contraction.

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Chemical Oxygen Demand

• Introduction

COD stands for Chemical Oxygen Demand.

Waste water consist many harmful ingredients like organic or inorganic wastes which are very harmful for human health and other creatures, to remove this matters we have to oxidised these materials  for oxidation we have need oxygen if these oxygen is provided by using Chemical Oxidising Agent ( Like K2Cr2O7 ).

So in case of COD in spite of  organic Oxygen we use Chemical Oxidising Agents.

• Definition

Amount of the Chemically combined  Oxygen required to oxidised the Organic  (Biodegradable) matters as well as inorganic ( Non-Biodegradable ) matters to make the water pure , is known as Chemical Oxygen Demand ( COD ).

• Some Important Points

1. In COD Potassium Dichromate ( Like K2Cr2O7 )  is used as Oxidising Agent.

2. COD removes both Biodegradable & Non-Biodegradable matters.

3. COD test take three days.

• Difference Between  BOD & COD 

1. BOD removes only Biodegradable Matters but COD removes both Biodegradable &              Non-Biodegradable matters .

2. BOD consumed Organic Oxygen but COD consumed Chemically combined oxygen.

3. BOD test takes 5 days but COD Test Takes 3 days.

4. COD > BOD. COD to BOD ratio range between 1.25 to 2.5  .


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Bogue's Compounds ( Concrete Technology )

• Introduction

Bogue's compounds are the main components of cement.After the application of water in cement these compounds starts reacting with water, those reactions are known as hydration reaction and the phenomenon is known as hydration of cement.

Due to this hydration cement paste become hardened and get strength. List of the Bogue's compounds are given below -

• Discussion

C3S ( Alite ) - 

1. It  is  responsible for early strength of cement.

2. First 7 day strength of cement is due to C3S.

3. It produce more heat of hydration than C2S.

4. Cement with more C3S content is preferred in cold Countries.

C2S ( Belite ) -

1. C2S take part in Hydration reaction after 7 days.

2. It hydrates slowly and gives strength after 7 day.

3. C2S is responsible for ultimate strength.

4. It produce less heat of hydration.

C3A - 

1. C3A reacts first with water and produce huge heat of hydration which results in quick setting of cement which is known as Flash Setting.

2. To prevent flash setting 2 to 3% of Gypsum is added to cement during grinding operation gypsum act as retarding agent.

3. Hydration of C3A does not contribute in strength of cement.

C4AF - 

 

1. C4AF hydrates rapidly.

2. It dose not contribute in strength of cement.

• Some Important Points For Competitive Exams

1. C3A Reacts with water first after adding water into cement.

2. C3S is responsible for 7 day strength.

3. C2S is responsible for 28 day strength.

4. Maximum heat of hydration is produced by C3A.

5. C3A is responsible for flash setting.

6. Gypsum ( CaSO4,2H2O ) is a retarder it prevent Flash Setting. 

Important Properties Of Soil

Here is Some Important Properties of Soil -

• Specific Gravity - Specific Gravity  ( G ) is defined as the ratio of the weight of a given volume of soil at a given temperature to the weight of equal volume of distilled water at that same temperature.

• Void Ratio - Void Ratio (e) of a given soil is the ratio of volume of void to the ratio of  soil solid in a given soil mass.

• Porosity - Porosity (n) of a given soil sample is the ratio of volume of void to the total volume of given soil mass.

• Degree of Saturation - Degree of saturation (S) is defined as the  ratio of volume of water present in a given soil mass to the total volume of voids in it.

• Percentage Air Voids - It is defined as the volume of air voids to the total volume of soil mass.

• Some Relation Between Above Parameters -

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Consistency Limits of Soil

• Introduction

Consistency denotes the firmness of soil, which may be termed as soft,firm,stiff or hard.

Soil has different different states depending upon its water content such as -

1. Solid

2. Semi Solid

3. Plastic State

4. Liquid State

There are some definite water contents which are decide the state of the soil. This specific water contents are known as consistency limits.

Consistency limits also known as Atterberg limits.

• Definition

Consistency limits are the water contents at which soil may pass from one stage to another.

We classify the consistency in three limits-

1. Liquid Limit.

2. Plastic Limit.

3. Shrinkage Limit.

• Discussion

1. Liquid Limit - It is defined as the minimum water content at which soil is still in Liquid state.

It is the arbitrary limit between Liquid and Plastic state.

2. Plastic Limit - It is the minimum water content at which a soil will just began to crumble when it is rolled into  a thread approximately 3 mm in diameter.

It is the arbitrary limit between Plastic state and Semi-solid state.

3. Shrinkage limit - It is defined as the maximum water content at which a reduction in water content will not cause a decrease in volume of a soil mass.

It is the minimum water content at which soil can still be completely saturated.

See the graph of consistency -

• Some important Indices with their Formula

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Earth Pressure

                        

• Introduction

Earth Pressure, you can understand from the word it is one kind of pressure produced by the Earth (Earth mean soil).This topic is related with Retaining wall.

Retaining wall is a special type of wall which is constructed to retain some material it may be soil or sand(which is called Back fill).You can see this kind of wall in culverts or in metro projects,where wall of concrete are constructed to support the side soil surface.

• Definition

It is the pressure exerted on the retaining wall by the soil which is retained.

• Discussion

Earth pressure is of two type-

1. Active earth pressure (Pa).

2. Passive earth pressure (Pp).

                                                         Pp > Pa

All the theories and mathematical experiments on earth pressure was done by Rankine in 1860,thats why it is known as Rankine's earth pressure theory.

1. Active earth pressure-

It is the pressure exerted by the back-fill on the retaining wall.it is happen when back-fill has more strength than the retaining wall.It is the minimum pressure.

In this case retaining wall move away from back-fill.

2. Passive earth pressure-

It is the pressure exerted by the retaining wall on the back-fill.This happen when back-fill is week such as loose sand.It is the maximum pressure.

In this case retaining wall move towards back-fill.

See the graph for better understanding-

• Numerical Formulas

Active Earth Pressure-

Passive Pressure-

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