Category: Interview Tips

PROPERTIES OF FLOWING CONCRETE AND SELF-COMPACTING CONCRETE WITH HIGH-PERFORMANCE SUPERPLASTICIER

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Tension & Compression on beams

Various beams react differently to the load acted on them, let us go through following 2 beams

  • Simply Supported beams & Continuous beams

simply-supportted-beam-civilmafia-in

For simply supported beams,

Compression acts on the top side whereas tension acts on the bottom side.
  • Cantilever Beams

cantilever-beams

Cantilever beams react differently than continuous beams,

In Cantilever beams, compression acts on the bottom side where as tension acts on the top side

The Properties Of Concrete In Plastic Stage

The Properties Of Concrete In Plastic Stage are:

Plastic stage of concrete is that stage where concrete can be transported easily,  moulded or poured into any place

  • Good Workability:

Workability is the most important property of concrete. It may be defined as ‘ The ease with which the concrete can be mixed, transported, placed and compacted. ‘ A workable concrete mix doesn’t results in bleeding or segregation.

  • Freedom from segregation :
A good concrete should be free from segregation. Segregation means separation of coarse aggregates from concrete in plastic stage.
  • Freedom from bleeding :

A good concrete should be free from bleeding.  The appearance of Water, along with some particles of cement and very fine sand on the surface of freshly placed concrete is known as bleeding.

  • Prevention from harshness :

The concrete mix which doesn’t give smooth surface with a certain amount of trowelling is known as harsh mix.

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USEFUL TIPS FOR CIVIL ENGINEERING INTERVIEW

USEFUL TIPS FOR CIVIL ENGINEERING INTERVIEW

GRADE OF CONCRETE:

M5 – 1 : 4 : 8

M10 – 1 : 3 : 6

M15 – 1 : 2 : 4

M20 – 1 : 1.5 : 3

M25 – 1 : 1 : 2


CLEAR COVER TO MAIN REINFORCEMENT:

Footings : 50 mm

Raft Foundation Top : 50 mm

Raft Foundation Bottom : 75 mm

Raft Foundation Side : 75 mm

Beam : 25 mm

Strap Beam : 50 mm

Column :40 mm

Slab : 15 mm

flat Slab : 20 mm

Staircase : 15 mm

Retaining Wall : 20 – 25 mm

Water Retaining Structures : 2 0- 30 mm


Maximum water absorption by bricks – 15%

Compressive strength of bricks – 3.5 N/mm2

Density Of Bricks- 1600-1920 Kg/m3

Minimum thickness of slab – 125 mm

Dimension tolerance for cubes – +2

Maximum free fall of concrete – 1.50 m

Lapping should not be used for the bars having larger dia than 36 mm.

Binding wire required for steel reinforcement – 8 kg per MT

3 samples should be taken for every 100 m2 in core cutting test.

Maximum chair spacing – 1 m.

Minimum dia should be used in dowels rod – 12 mm.

Hook for strriups (one side) – 9D

No. of strriups = (clear span/spanning) + 1

Length of main steel in cantilever anchorage – 69D.

Minimum no. of bars in square column – 4

Minimum no. of bars in circular column – 6

Minimum dia of main bars and distributors in the slab – 8 mm.

Maximum dia of  main bars and distributors in the slab – 1/8 of slab thickness.

All reinforcement should be free from mill scales, loose rust, and coats of paints , oil or any other substances.


SETTING TIME:

Initial setting time should not be less than 30 minutes.

Final setting time should not be greater than 10 hours.

REQUIRED CURING DAYS:

Super sulfate cement – 7 days

Ordinary portland cement – 10 days

Cement with minerals and admixtures – 14 days.

SLUMP VALUE (IS456):

Lightly reinforced concrete : 25 – 75 mm.

Heavily reinforced concrete : 75 – 100 mm.

Trench fill : 100 – 150 mm ( for in-situ & tremie).

CUBE SAMPLES:

1 – 5 m3 : 1 No.

6 – 15 m3 : 2 No..

16 – 30 m3 :3 No.

31 -50 m3 : 4 No.

Above 50 m3 : 4 + 1 no. of addition for each 50 m3.

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Quantity Estimation for Brickwork

Lets calculate the rate analysis for 5 CuM Brickwork

Standard size of brick = 9 cm X 9 cm X 19 cm

Size of brick with cement mortar on both sides = 10 cm X 10 cm X 20 cm

No of Bricks in 5 CuM =        5 / ( 0.1 X 0.1 X 0.2 ) = 2500 Bricks

Mortar Required for 1 Cum = 5 – (2500 X 0.09 X 0.09 X 0.19) = 1.153 CuM

Mortar volume increases for frog filling, brick bonding & wastage by 15 %

So the volume of wet mortar becomes = 1.153 + (1.153 X .15 ) = 1.325

for Dry volume of mortar mixing we will have to consider 1/3 rd of more of wet volume

Therefore Volume = 1.325 + ( 1.325 / 3 ) = 1.766 CuM 

Considering the mortar ratio as 1:4

Cement Quantity =  ( 1 X 1.766 ) / ( 1+4 ) = 0.353 CuM

Cement Quantity in Bags of 50 Kg = 0.353 / 0.035 = 10.08 Bags

Sand Quantity in CuM = (4 X 1.766) / (1+4) =  1.41 CuM

 

 

 

Types of Covers in Civil Engineering

There are 2 Types of cover provided to reinforcement in Civil Engineering

1.Clear Cover

clear-cover

Clear Cover is the length between outer end of reinforcement to outer edge of concrete.

2. Nominal Cover 

Nominal cover is the length from center of reinforcement to outer edge of concrete.

nominal-cover

Stress Strain and Young’s Modulus

  • Stress–  Force applied on a body per Unit area is called as stress.stresscivilIt can be denoted by Stress= Force/Area.
  • Strain– When a body is subjected to tensile force, the body undergoes change in length.

Change in length of the body to the original length is known as Strain.

Strain = Change in Length / Original Length

sttraincivil

  • Modulus of Elasticity / Young’s Modulus

Modulus of elasticity is the ratio of stress to the strain induced in a body

Young’s modulus is denoted by E

E= Stress / Strain

Why Steel is used in Concrete for RCC structures ?

Below are the Reasons why steel is used in RCC structure not some other Metals, Non-metals or Alloys

  1. It is cheap and Easily available
  2. It possesses very high Tensile strength & elasticity
  3. It develops good bond with concrete
  4. Coefficient of expansion(12.6 X 10^-6) of steel is nearly equal to the same of concrete (14 X 10^-6) which means concrete and steel expand and shrink with almost same volume change when exposed to heat or cold.

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Density of Materials used to batch concrete

Have you ever been asked for density of Cement, Sand, Aggregates & Water along with density of concrete in an job interview ?

If not you were lucky because here are the densities of all


  • Density of Concrete – 2400 Kg/m3

  • Density of Cement – 1440 kg/m3

  • Density of Water – 1000 Kg/m3

  • Density of Dry Sand – 1600 Kg/m3

  • Density of Wet Sand – 1850 Kg/m3

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  • Density of 20mm Aggregate – 1600 Kg/m3

  • Density of 10 mm Aggregate – 1700 Kg/m3

  • Density of Fly Ash – 750 Kg/m3

Workability of concrete

What is Workability  ?

Workability of concrete is the ease with which it can be mixed, transported & placed in position in homogeneous state.

tips-for-pouringlaying-down-concrete

Workability of concrete can be found out by performing following tests 

 

  1. Slump Test
  2. K-Slump Tester
  3. Compacting Factor Test
  4. Flow Test
  5. Kelly ball test
  6. Vee Bee Consistometer Test

Links will be provided soon for the above tests **Stay tuned ©Civilmafia.in