Le-Chatelier's Apparatus- Soundness Test of Cement - Theory, Procedure and Calculation Formula

• Aim: To find out the Soundness of Cement.
• Apparatus: Le- Ch-atelier's Apparatus, Weighing balance, measuring cylinder, trowel, mixing pans heater, thermometer.
• Standard Reference:  Test is performed as per IS: 4031 (Part - 1) - 1988,

• Theory: 

Cement of good quality does not contain the impurities like free lime, magnesia and sulphates, so this should be checked before use.

When it contains the impurities named above, it can expand after reacted with the water, which will result in the unwanted results like, cracking, unwanted expansion of the dimensions and lower strength. 

Le-Ch-atelier's Apparatus is the standard apparatus prescribed as per IS:5514 -1969 to check the presence of the impurities in cement.  Cement is said to be sound when the expansion is below 10 mm.

• Procedure: 

1. Prepare a cement paste of 78% of standard consistency of the cement, and fill it into the split brass cylinder.
2. Cover the top and bottom of the cylinder and put it in water at 27 degrees Celsius for 24 hours.
3. After 24 hours, measure the separation between the two indicators at their pointed ends.
4. Then heat the whole water and immersed cylinder with paste up to a boiling temperature in 30-35 minutes and then boiling  for 3 hours.
5. After cooling it down, again measure the separation between the two pointers.

• Calculations: 

Let the reading before putting the cement paste into the boiling temperature  = L1

After three hours of immersion in hot water, reading = L2                 then, Expansion = L2-L1

• Result: As the value of expansion is (Less/More)..... than 10 mm so the cement is .........(Sound/Unsound).

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Compaction Factor Test for Fresh Concrete - Theory, Procedure and Calculation Formula in brief

Hi,

• Aim: To find out the compaction factor for the given fresh mix of concrete.

• Theory: Workability of concrete is the ability/ease with which concrete can be mixed, transported and placed. This is a major factor which contributes to the other properties of concrete also. If concrete is workable enough then it can be compacted with less compacting effort.

 So there is a relation between the amount of work required to compact a given fresh concrete and the work-ability of the concrete. This relation is well suited for the concrete of the low water cement ratio. Slump cone test is also used to find out the work-ability of the concrete but only recommended for the concrete of higher work-ability. For less workable concrete(having less water cement ratio), compaction is standardized by various standards. 

• Apparatus: Compaction factor apparatus/machine, weighing balance, cow/mixing tray.

Compaction Factor apparatus

• Procedure:

1. Oil the inner sides of the top and bottom cone frustum.

2. Prepare a M15 concrete mix(1:2:4) using a water content of about 0.4-0.6 by weight of cement.

3. Fill the top cone frustum with the fresh mix of concrete and then open the gate and let the concrete fall on the second frustum.

4. Open the gate of second frustum and let it fall on the cylinder to fill up to top of cylinder. 

5. Measure the weight of the cylinder filled with the concrete(partially compacted) and then empty this.

6. Again fill the cylinder with the same sample of the concrete but this time, do the compaction using the mechanical vibrator to do the compaction. 

7. Again measure the weight of the cylinder filled with the concrete(Fully compacted).

8. Clean all the apparatus and put them at their places as before.

• Calculations: 

Let weight of the empty cylinder = W1

Let weight of the cylinder with the partially compacted concrete = W2

Let weight of the fully compacted(Using mechanical vibrator) concrete with cylinder = W3

Compaction Factor = Weight of the partially compacted concrete/ Weight of the fully compacted concrete

i.e., Compaction factor = (W2-W1)/(W3-W1)

• Result: The compaction factor of the given fresh concrete mix is .....

(Note: Relation between the compaction factor and work-ability is that higher the compaction factor higher is the work-ability. Theoretical maximum value of the compaction factor can be 0.96 to 1.0)

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Characteristics of Contours - Brief Theory

Hi,

Do you know what is a contour?
First, here are certain terms which are useful in understanding the contours.

• Contour -  Contour is an imaginary line on ground joining points of equal or constant elevations. contours are important to draw the topographical maps in which vertical distances are also shown using the contour lines.
• 
  
• Contour interval: Vertical distance between any two consecutive contours is known as the contour interval. It depends upon the scale of the map, nature of the ground and availability of the fund  and time.
• 
  
• Horizontal equivalent/ horizontal interval:  It is the shortest horizontal distance between the two consecutive contours. 
• 
  
• Contour Gradient: Imaginary line on the surface of the earth, maintains a constant angle to the horizontal. 

Characteristics of the contours:

1. Two contours of different elevation do not cross each other with only exception in the contours of a overhanging cliff.
2. Contours of different elevations do not combine or overlap to each other with exception in the contours of a vertical cliff.
3. When contours are drawn closer to each other, it shows a steep slope on the ground and when they are far apart it shows the gentle slope on the ground.
4. When contours are equally spaced they represent a uniform slope, and when they are parallel straight and equivalent they represent a plane surface. 
5. A contour is perpendicular to a line of the steepest slope.
6. A contour must close itself in the map or must go out of the boundaries of the map.
7. A set of ring contours with higher values of contour inside and lower values outside represents a hill and if the higher values are outside and lower values inside then it represents a depression like a pond.
8. When contours cross a ridge they form a V- shape across them. While if they cross a valley they form a u-shape or may a V shape also difference being, the concavity of the contour lines lies towards the lower contours in case of valley while it is convexity lying towards the another lower value in case of contours of a ridge.

Uses of Contours:

1.  To study the general character of the tract of the country without visiting the ground. With the knowledge of characteristics of contours, it is easy to visualize whether country is flat, undulating or mountainous.
2. To decide the sites for engineering works such as reservoirs, canals, roads and railways etc. on the basis of the economy.
3. To determine the catchment area of the drainage basin and hence capacity of the proposed reservoir.
4. To compute the earth work required for filling or cutting along the linear alignment of the projects such as canals, roads, etc.
5. To find out the inter-visibility of the points.
6. To trace out a contour gradient for road alignments.
7. To draw longitudinal and cross- sections to ascertain nature of  the ground.

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References and Books:

Surveying Vol-I  by Dr. B. C. Punmia

   

A Brief Theory of Plane Table Surveying

Hi,

A short introduction to Plane Table Survey- A graphical method of Surveying.

Plane Table Survey:

Plane Table Survey is a method of plotting the plans on the sheet, in which field work and the office work are done simultaneously. It is also known as the graphical method of Surveying. Therefore the main characteristic of the map is that, there is no need of carrying a field book to note various readings.

List of Instruments used in Surveying:

1.  Plane Table
2. Alidade
3.  Plumbing fork and Plumb bob
4. Spirit Level
5. Chain or Tape
6. Rain roof cover for the plane table
7.  Compass
8. Ranging Rods
9. Drawing Sheets
10.  Drawing equipment.

Procedure: 
To perform the plane table survey one has to follow the following procedure at every plane table set-up at various stations.

(a) Fixing the plane table to the tripod stand
(b)Setting up and temporary adjustments:

1.   Leveling the plane table with the help of spirit level
2.  Centering with the help of plumbing fork
3.  Orientation by trough compass or by back sighting

• (c) Sighting the points with the help of Alidade

Methods of plane tabling:

1. For locating details: 

(a) Radiation Method: 
With the help of Alidade, a ray is drawn towards the point. Then using the Chain or Tape the horizontal distance is measured from the Plane Table to the point. Then using the scale of plotting, this point is located on the sheet.

(b) Intersection Method: 
In this method no chain or tape is needed, just two instrument stations are needed. Intersecting rays are drawn from these two stations whose location is already plotted on sheet(by measuring the distance between them). The point of intersection of the two rays is the location of the point of interest.

2. For locating Plane Table Stations: 

(a) Traversing: In this method the location of the Plane Table station is located in the following manner:

(1) At previous station a ray is drawn in the forward direction(toward next station) and point is plotted by measuring the horizontal distance and plotting it to scale.

(2) Instrument is shifted to next station(which is just located in first step) and the previous station is back-sighted to orient the plane table.

(b) Resection: 
Resection is the process/method of finding the position of a station where plane table is placed. Sights are taken towards the known and visible points and rays are plotted.

Procedure :

First of all the plane table is oriented correctly by one of the four given methods:

(1) Orientation by trough compass

(2) Orientation by back sighting

(3) Orientation by two point problem

(4) Orientation by three point problem

Then afterwards point is located.

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Note: If reader want details of any of the topic please, leave a comment below.

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Tacheometry (Surveying) - Theory and Formulae

Hi,

Tacheometry is the branch of Surveying in which we determine the horizontal and vertical distances between points by taking some angular measurements with the help of an instrument caled Tacheometer. 

       

This is not so accurate method of finding the horizontal distances as the Chaining is, but it is most suitable for carrying out the surveys to find the distances in the hilly area where other methods are quite difficult being carried out. It is generally used to locate contours, hydrographic surveys and laying out routes of highways, railways etc.

The instruments required for carrying out the Tacheometric survey are:

(1) A Tacheometer 
(2) A Stadia Rod.

• Tacheometer: Tacheometer is more or less a Theodolite installed with  a stadia diaphragm. Stadia diaphragm is equipped with three horizontal hairs and one vertical hair. So we can take three vertical staff reading at the same instruments setting, lowermost hair reading, central hair reading and the top hair reading. The difference between the lower hair reading and the upper hair reading gives the staff intercept(s).

The Tacheometer with the analactic lens are famous because their additive constant is zero. There is one concave lens introduced between the eyepiece and the object piece to eliminate the additive constant of the instrument. It simplifies the calculations.

Methods of Tacheometric Survey:

(A) Stadia Hair Method

1. Fixed Hair Method
2. Movable Hair Method

(B) Tangential Method

(A)Stadia Hair Method: 

• As the name suggests in this method theodolite with the stadia diaphragm is used to find out the staff intercept between the lower and upper hairs and also the central hair reading is noted.

Principle of Stadia hair method is that the ratio of the length of perpendicular to the base is constant in case of similar triangles.

1. Fixed Hair Method: In the fixed hair method the cross hairs of the diaphragm are kept at a constant distance apart and the staff intercept varies with the horizontal and vertical position of the staff with respect to the Theodolite.
2. Movable Hair Method: In this method the staff intercept between the lower hair and the upper hair is kept constant by moving the horizontal cross hairs in the vertical plane.

Formula to carry out calculation works:

Case:  

(a) Staff held vertical:

Tacheometry -Staff held vertical

             D = (f/i).s+ (f+d)

   where, f/i = multiplying constant

               s = staff intercept between the bottom and top hair

               f+d = Additive constant

              D = Horizontal distance between the staff station and the observer's position

(b) Inclined sights staff held vertical:

            D = (f/i).s. cos^2A + (f+d) cosA

            V = {(f/i).s.} .[{sin(2A)}/2] + (f+d) sinA

                Where A is the angle of elevation or angle of depression.

(c) Inclined sights upwards, staff held normal:

    D = [(f/i).s+ (f+d)]cosA - h.sinA  ;    V= [(f/i).s+ (f+d)].sinA

     h= central hair reading.

R.L. of staff = H.I. + [(f/i).s+ (f+d)].sinA - hcosA

(d) Inclined sights downwards, staff held normal:

  D = [(f/i).s+ (f+d)].cosA - h.sinA  ; 

 V= [(f/i).s+ (f+d)].sinA ;

 R.L. of staff = H.I. + [(f/i).s+ (f+d)].sinA - h.cosA

(B)Tangential Method:

In Tangential method only central hair reading is noted down and generally two angular observations are taken to calculate the horizontal and vertical distances.

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List of the Surveying Minor Instruments

Hi,
There are some instruments used for the rough surveys, which are not used for the precise surveys. These instruments are also known as minor instruments. 

 These are the following.

•  Hand Level:

It is a compact instrument used for locating contours, taking cross sections in reconnaissance surveys.

• Clinometer:

It is a light, compact instrument used for measuring vertical angles, finding out the slope of the ground, and for locating points on a given grade. There are three commonly used forms of clinometers:

 (i) Abney's level

(ii) Tangent Clinometer

 (iii) Ceylon Ghat Tracer

• Box Sextant: 

It is a reflecting instrument capable of measuring up to 120 degrees with an accuracy of one minute. It is one of the most precise hand instruments.

• Pantograph: It is used to reduce or enlarge the given figure.

• Planimeter: It is used to measure the area of the given figure.

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Error and Correction for the Curvature of the Earth, and Refraction (Surveying)

Hi,

Finally, today I thought to write about this particular topic, which is important to study when we are talking about Geodetic Surveying.

As we know, in Geodetic Surveying we have to consider the error due to the curvature of the earth and the refraction as well. Reason is that larger areas are surveyed in Geodetic Surveying, more than about 256 km2 and therefore one can not ignore the curvature of earth. In such large areas, the error due to curvature of the earth has to be considered to calculate the linear distances and also in case of the angular measurements.

We have to consider the refraction error too, because here we are dealing with the large distances and in order to get the correct results we have to apply these correction.

• What is the Error due to Curvature? 

To understand this simple concept of error due to curvature of the earth, first you have to understand the shape of the earth and the methods and instruments which we employ for calculating these distances.

When we do leveling with Theodolite or Autolevel, the line of sight first is set horizontal. Then we measure the vertical angle to the target and by applying some trigonometrical formulae we can calculate the vertical distance of the target from that horizontal line.

Error due to curvature comes into play, because in the cases of long distances, the horizontal line and level line do not coincide. Level line is a curved line, parallel to the level surface, but the horizontal lines goes straight.

This means that the vertical distance of that target from the level line is going to be larger than the distance which we calculate from the horizontal line. Please refer the figure given above, the amount of correction depends upon the magnitude of the horizontal distance between the target and the instrument station.

• What is Error due to Refraction?

Error to refraction can be understood easily once you understand the phenomenon which takes place when light passes from one density system to another density system. Refraction is nothing but the phenomenon by which when light travels from a denser media to the lighter media, it deflects away from the normal to the plane of the media.

Phenomenon occurs vice-versa when light travels from lighter media to denser media. This phenomenon has to be considered in the calculation of the distances in case of Geodetic Surveying. Suppose a man is taking the observation of the top of a hill from a point, which is at a considerable down far vertical distance from it to change the density of the air.

We know that density of air decreases with the height, this will effect your line of sight. The line of sight of a person who is taking observation to a point at a quite higher distance, will be a curved path, because light will continuously change its direction due to the continuous change in the density of the air.

Imporant question to ask is, how does it effect our observations? Well, the observed angle will be to high in case of taking the observation of an elevated object and the observed angle will be small in case of taking observations to an object in depressions.

• Correction for the Error due to Curvature and Refraction:

There are a numbers of textbooks, which explains the procedure to calculate the correction for the refraction and curvature.

Formulae:

Curvature correction, Cc = - 0.07849.D^2 meter

Refraction Correction, Cr = 0.01121.D^2 meter

Combined Correction C = Cc+Cr= -0.06728. D^2  meter;  
 here D is in kilometer

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