Friction and Pressure Drag on a Moving body

 Civil Engineering Study with Vk

Friction and Pressure Drag on a body moving through fluid

• A body moving through fluid experiences a drag force, which is usually divided into two components:
• frictional drag, and 
• pressure drag.

• Frictional drag comes from friction between the fluid and the surfaces over which it is flowing. 
• This friction is associated with the development of boundary layers, and it scales with Reynolds number.

• Pressure drag comes from the eddying motions that are set up in the fluid by the passage of the body. 
• This drag is associated with the formation of a wake, which can be readily seen behind a passing boat, and it is usually less sensitive to Reynolds number than the frictional drag. 
• It depends on the shape of the body.

• Frictional drag is important for attached flows (that is, there is no separation), and it is related to the surface area exposed to the flow. 
• Pressure drag is important for separated flows, and it is related to the cross-sectional area of the body.

• For streamlined bodies (like a fish, or an airfoil at small angles of attack), frictional drag is the dominant source of air resistance. 
•  For a bluff body (like a brick, a cylinder, or an airfoil at large angles of attack), the dominant source of drag is pressure drag.

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Rajasthan Public Service Commission (RPSC) Rajasthan RPSC State and Sub. Services Combined Competitive Exam 2023 - Job and Vacancies

#Opportunitis and Vacancies

 
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Rajasthan Public Service Commission (RPSC)  Rajasthan RPSC  State and Sub. Services Combined Competitive  Exam 2023 
 
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Find Initial and Final Setting Time of Cement

Type of cement	Initial Setting Time (min)	Final Setting Time (min)
Ordinary Portland Cement	30	600
Portland Pozzolona Cement	30	600
Quick Setting Cement	5	30
Rapid Hardening Cement	30	600
High Alumina Cement	30	600
Sulphate Resisting Cement	30	600
Super Sulphated Cement	30	600
Portland Slag Cement	30	600
Hydrophobic Cement	30	600
Low Heat Cement	60	600
Masonry Cement	90	1440

How to Find Initial and Final Setting Time of Cement
Setting Time Test of Cement

What is initial and final setting time of cement?

Setting time of cement is an important property to knowing the time limit for handling, transportation and placing of concrete. Setting time of cement is divided into two types-

Initial Setting Time of Cement.Final Setting Time of Cement.

But before discussing these types let's understand what is a setting of cement is?

What is the setting of cement?-

When water is added to cement it reacts with water and forms a paste. This cement paste is in a plastic state and can be moulded to any shape. After some time this cement paste starts losing its plasticity and starts to set. This entire process is called the setting of cement.

What is Initial Setting Time of Cement?

Initial setting time is a time from the moment water is added to the cement, to the time that the paste starts losing its plasticity.

Initial setting time of ordinary portland cement (OPC) is 30 minutes.

What is Final Setting Time of Cement?

The time from when water is mixed with cement to the time when cement paste loses completely its plasticity and became hard is called the final setting time of cement.

Final setting time of ordinary portland cement (OPC) is 600 minutes.

Significance of Initial and Final Setting Time of Cement –

Initial setting time of cement gives us an idea about the time limit for handling, transportation and placing of cement on site.After placing cement on site it should not be disturbed up to the period of final setting time of cement.The final setting time of cement plays an important role in the formwork removal period of any structural member.

How to Calculate Initial Setting Time and Final Setting Time of Cement-

We are going to do a setting time test on cement using VICAT Apparatus as per IS 4031(Part 5):1988

APPARATUS-

VICAT Apparatus conforming to IS : 5513-1976.

VICAT mould

Measuring Cylinder of 200ml

Weighing balance with 1g accuracy

Stopwatch

Trowel

Apparatus for initial and final setting time test of cement

Procedure to Find Initial Setting Time of Cement –

1) Take 500g of cement in-tray.

2) Add the amount of water (which is calculated using the formula given below) to cement to make cement paste and start the stopwatch. ( Stopwatch should be started from the moment water is added to the cement).

Amount of water to add = 0.85P % of the weight of cement.

Where P = Percentage of water required to make a cement paste of standard consistency.

3) Pour this cement paste into the Vicat mould using a trowel within 2-3 minutes from water added to cement and level the top surface properly.

4) Then place this mould on the Vicat apparatus under the square needle.

5) Move the needle slowly downwards until the needle touches the top surface of the mould.

6) Then released the square needle and allow it to penetrate into the mould.

7) Now note down the reading on the Vicat scale, initially, it shows zero reading because the needle completely penetrates into the mould.

8) Repeat this procedure at 2 minutes intervals until the Vicat scale shows a reading of 5mm (which means the plunger should stop penetrating 5mm from the bottom of the mould).

9) Now note down the time shown on the stopwatch. This time from the moment water was added to cement to the time needle penetrated the cement mould 5mm from the bottom is theinitial setting time of cement.

Procedure to Find Final Setting Time of Cement –

1) Replace the needle of Vicat apparatus by needle with angular attachment.

2) Move the needle slowly downwards until it touches the top surface of the mould gently.

3) Then released the needle and allowed angular attachment of the needle to make an impression on the top surface of the mould.

4) Now repeat the same procedure at some time intervals until the angular attachment of the needle is failed to make an impression on top of the mould.

5) Note down the time shown on a stopwatch. This time from the moment water is added to the cement to the time at which the circular attachment of the needle failed to make an impression on the surface of the mould is called the final setting time of cement.

Calculations –

Weight of cement sample = …….. gms.

Water required to make cement paste of standard consistency = P = …….. %.

Quantity of water added = 085P = ……. ml.

Sr.NoTimeReading(mm)

The initial setting time of the cement sample is ………..

The final setting time of the cement sample is ………….

Precautions –

Lumps should be removed from the cement sample.Test should be performed away from any vibrations and disturbance.The room temperature should be maintained at 27 ± 2°C at the time of conducting the initial and final setting time of the cement test.The relative humidity of the laboratory should be 65 ± 5%.The needle should be released gently.

FAQs on Initial and Final Setting Time of Cement-

What is the initial and final setting time of ordinary portland cement(OPC) of different grades?

OPC Grade -IST FST
Grade 33     30  600
Grade 43     30  600
Grade 53     30  600

Which IS CODE is used to find initial and final setting time of cement?

The initial and final setting time of cement is calculated using the VICAT apparatus as per IS 4031(Part 5):1988.

What is the difference between the setting and hardening of cement?

The setting of cement is the stiffening process of cement paste. When we add water to the cement sample it forms a paste. This cement paste is in a plastic state. The transformation of the cement paste from a plastic state to a solid state is the setting of cement.

After the setting of cement, it starts to gain strength, this strength gaining process is called the hardening of the cement.

Table of Contents

• What is initial and final setting time of cement?
• What is the setting of cement?-
• What is Initial Setting Time of Cement?
• What is Final Setting Time of Cement?
• Significance of Initial and Final Setting Time of Cement –
• How to Calculate Initial Setting Time and Final Setting Time of Cement-
• APPARATUS-Procedure to Find Initial Setting Time of Cement –
• Procedure to Find Final Setting Time of Cement –
• Calculations –
• Precautions –
• Initial and Final Setting Time of Cement of Different Grades –
• FAQs on Initial and Final Setting Time of Cement-
• What is the initial and final setting time of ordinary portland cement(OPC) of different grades?
• Which IS CODE is used to find initial and final setting time of cement?
• What is the difference between the setting and hardening of cement?
• initial and final setting time of cement?

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Kerala Public Service Commission (KPSC) invites the application Online Form for various recruitment - Jobs & Opportunities

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Dear Student 
Kerala Public Service Commission (KPSC) 
invites the application Online Form for various 
recruitment 
 
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Assistant Engineer/Head Draftsman 
 
DISCPLINE 
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Chain Survey - Introduction and Condition for its use - Civil Engineering

Chain Survey - Introduction and Condition for its use 

Chain Survey

• Chain surveying is the simplest method of surveying.
• Measurements for this survey are taken on the field and other supplementary works like plotting and calculations are carried out in office.
• The measurements in chain surveying are linear.
• Chain, tape, ranging rod, arrows and, cross staff are the tools required for chain surveying.
• It is used when plans are required on a large scale.

It can be used if the area meets the following conditions:

• 1. The area shall be fairly small.
• 2. The ground is fairly levelled and open with simple details
• 3. The area needs to be open.

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Temporary Adjustment of SURVEYING Instrument in Civil Engineering

Temporary Adjustment of SURVEYING Instrument in Field

• The adjustments to be made at every setting of the instrument are called temporary adjustments.

• Following are the five temporary adjustments are required:

• 1. Setting up: Tripod stand is set on the ground firmly so that its top is at a convenient height.

• 2. Centering: It is done to place the vertical axis exactly over the station mark

• 3. Levelling: The levelling is done to make the vertical axis of the instrument truly vertical or to make horizontal plate truly horizontal

• 4. Focusing the eye piece: The eye piece is focused to make the cross hairs distinct and clear

• 5. Focusing the objective: This is done to bring the image of the object in plane of the cross hairs

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Surveyor compass versus Prismatic Compass -  Compass used in Surveying

COMPASS USED IN SURVEYING

Parameter	Surveyor’s  Compass	Prismatic Compass
Magnetic Needle	Edge bar needle is  used and it act as index	Broad needle is used  and it is hidden below the aluminium ring  and does not act as index.
Graduation	Graduated ring is attached  to the box and ring rotates with box. Graduations vary from 00 to 900  in the four quadrants.  Zero points are marked with N and S.	Graduated ring attached to the needle and remains stationary. Graduations vary from  00 to 3600 clockwise  with zero at south end.
Sighting Vanes	Readings are taken by directly looking  through the glass  and reading the north end of needle.	Readings are taken  through the vertical  side of the prism provided  at the eye vane.
Reading	Sighting and reading are done separately  and that too from different positions. After sighting the object,  the observer move around and takes the reading at North end of needle.	Sighting and reading  are done simultaneously.
Support-Requirement	Tripod is compulsory.	Tripod may or may not be used.

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Types of Chain and its length for Surveying work in Civil Engineering

TYPES OF CHAIN FOR SURVEY WORK AND CIVIL ENGINEERING STUDENTS

TYPES OF CHAIN

S.No.	Type of chain	Length	No. of links	Length of links
1	Meter Chain	20 m or 30 m	100 or 150	20 cm
2	Engineering Chain	100 ft	100	1 ft
3	Gunter Chain	66 ft	100	0.66 ft
4	Revenue Chain	33 ft	16	2116$\mathrm{2 }\frac{\mathrm{1/}}{16}$ ft

(As 1 foot = 0.3048 m)

66 feet = 0.3048 × 66 m = 20.11 m

 Gunter’s chain is 20.12 m long.

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Properties of First class brick

Properties of First class bricks

Properties of first-class bricks are given below:

• Dry first-class bricks should not absorb water more than 20% of their own weight when immersed in water for 24 hours.
• No impression should be left on the brick when a scratch is made by finger nail.
• They emit a clear ringing sound when two bricks are struck by each other.
• First-class bricks are table molded and they are burnt in Kilns.
• These are well burnt in kilns.
• The surface of the first-class brick should be smooth and rectangular.
• The edges of the brick are perpendicular (Make an angle of 90°) to the adjoining edges.
• They are regular in shape and size with sharp edges and corners.
• They shall be of uniform deep red color.
• They should be free from any cracks.
• They should be free from chips, efflorescence, flaws, and lumps of any kind.
• The average compressive strength of the first-class bricks should not be less than 100 kg/cm2 and not more than 125 kg/cm2.

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Storage of Cement Bags on Site, How to -

Storage of Cement How to Store Cement Bags on Site

Storage of Cement Bags on Site

Storage of cement bags on site should be done in a proper way. Because cement is climate-sensitive material and it reacts with moisture from the atmosphere and starts the hydration process which makes cement hard.

So there are some precaution should be taken for bulk storage of cement as per IS code 4082: 1996 as follows –

1) Sheds for storage of cement –

2) Arrangement of Cement Bags –

3) Storage Duration –

4) Protection in Rainy Season –

5) Handling of Cement Bags –

6) Use of Cement Bags –

1) Sheds for storage of cement –
On construction site storage of cement should be done in a proper way so they are not exposed to the atmosphere and can be stored for a long time before being used in construction.

Bulk Storage of cement bags on site should be done in buildings or closed sheds whose floor, roof, and walls should be dry, leakproof, and moisture-proof.

The building or shed should have a minimum number of windows and doors. The windows of these sheds are must be small in size and the door should be airtight and kept these doors closed as far as possible.

Proper drainage should be provided for the drainage of water in any case.

2) Arrangement of Cement Bags –

Before the storage of cement bags on site ensure that the shed is completely dry from inside.

Dampness is also responsible for the moisture in cement.

So, the cement bags should be stored on wooden pallets in such a way that as to keep about 150mm to 200mm above the ground level.

Wooden Pallet

Cement bags should be arranged one above the other in a cross arrangement in length-wise and cross-wise fashion to minimize the danger of toppling over.

The arrangement of cement bags should be closed to each other to avoid air circulations.

Cement Bags Arranged on Wooden a Pallet

Stacked bags should be at least 600mm away from the external walls.

These stacked cement bags should not be more than 10 bags in height to prevent the possibility of lumping up under pressure and the width of the stack should not be more than 4 bagsor 3 meters.

Different types of cement should be stored separately.

Different types of packaging bags should be stored separately such as paper bags, gunny bags, and polyethylene bags, etc.

A passage width of 600mm should be provided for easy access.

Section of Shed

Plan of Shed

3) Storage Duration –

Time is also an important factor in the storage of cement. Because the strength of cement is decreased with time.

The table below shows the percentage of decrease in strength of cement with time –

So, Cement should be used before 3 months from the date of manufacturing.

If cement is stored for more than 3 months duration then it is recommended to cement should be tested before using it on site.

4) Protection in Rainy Season –

During monsoon season extra moisture is present in the atmosphere which required extra precautions for the storage of cement.

In the rainy season, cover the stack cement bags with plastic sheets or tarpaulins to protect them from moisture and an accidental sprinkle of water.

5) Handling of Cement Bags –

Do not use hooks while handling cement bags in loading and unloading.

Do not drop cement bags from height as this can damage the packing of cement.

Handle cement bags with care to avoid split of bags and damage of packing.

6) Use of Cement Bags –

Cement bags should be used on a first in first out basis. This means cement bags that are stored first in sheds should be used first for the construction.

A label of the date of receipt of cement should be put on each stack to know the age of cement.

FAQ on storage of cement bags on site –

How long cement can be stored?

It is recommended that cement should not be store for more than 3 months.

How much area required for storage of cement?

Approximately, in 1 cubic meter, 20 cement bags of 50kg each can be stored

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