Compass surveying

 TRAVERSE 

In traverse  surveying  the direction of  survey  lines are  fixed by  angular  measurements  and not by  forming a network of triangles as  is done  in chain surveying. 

A traverse  may  be 

(a) Closed or 

(b)  Unclosed. 

(a) Closed Traverse 

             A traverse  is  said to  be  closed  when  a complete  circuit  is  made, i.e. when it  returns to  the starting  point forming  a closed  polygon as in  (Fig. 1), or  when it begins and  ends  at points whose positions on plan  are known (Fig. 2). 

It is particularly  suitable  for locating  the boundaries  of lakes,  woods, etc, and for  the survey of  moderately  large  areas. 

1. Closed traverse 

2. Link traverse

          

(b) Unclosed or open traverse

                       A traverse  is said to  be  open  or unclosed  when it  does not  form  a closed polygon.  It  consists of a series of  lines  extending in  the  same  general direction  and not returning to  the  starting point. 

3. Open traverse

Tests on bricks

 To know the quality of Bricks, various tests are performed. They are

1. Compressive  strength  test 
2. Water Absorption  test 
3. Efflorescence test 
4. Hardness  test 
5. Size, Shape  and Colour   test 
6. Soundness  test 
7. Structure test 

1. Compressive strength test

              This  test  is  done  to know  the  compressive  strength of  brick.  It  is also called crushing strength of  brick. Generally  5  specimens  of  bricks  are  taken to laboratory for  testing and tested  one  by  one.  In this  test  a  brick specimen is  put  on crushing  machine  and applied  pressure  till it breaks.  The  ultimate  pressure  at which  brick  is  crushed  is  taken  into account.  All  five brick  specimens  are  tested  one  by  one  and  average  result  is  taken  as  brick’s compressive/crushing  strength. 

2. Water absorption test

          In this  test  bricks  are  weighed in dry  condition and let  them immersed in fresh  water  for  24  hours. After  24 hours  of  immersion those  are  taken  out  from water  and wipe  out  with cloth. Then brick is  weighed in wet  condition. The  difference between weights  is  the  water  absorbed by  brick.  The  percentage  of  water  absorption is  then calculated.The less  water  absorbed  by  brick  the  greater  its  quality.  Good quality  brickdoesn’t absorb more  than 20%  water  of  its  own weight. 

3. Efflorescence test

          The  presence  of  alkalies  in  bricks  is  harmful  and  they  form  a  grey  or white  layer  on brick surface  by  absorbing  moisture. To find out  the  presence  of  alkalis  in bricks  this  test  is  performed.  In this  test  a  brick  is  immersed in fresh  water  for  24 hours  and then it’s  taken out  from  water  and allowed  to dry  in shade.If  the  whitish layer  is  not  visible  on surface  it  proofs  that  absence  of  alkalis  in brick.  If  the  whitish layer  visible  about  10%  of brick  surface then  the presence of  alkalis  is  in  acceptable  range.  If  that  is  about  50%  of surface then  it  is  moderate.  If  the  alkalies’  presence is  over  50%  then  the brick  is  severely affected  by  alkalies. 

4. Hardness test 

            In this  test  a  scratch is  made  on brick surface  with a  hard thing.  If  that  doesn’t left  any  impression on brick then that  is  good quality  brick. 

5. Size,  shape  and  colour  test

                In this  test  randomly  collected 20 bricks  are  staked along lengthwise,  width wise  and height  wise  and then those  are  measured to know  the  variation of sizes  as  per  standard.  Bricks  are  closely  viewed  to  check  if  its  edges  are  sharp  and  straight and uniform  in shape.  A  good quality  brick  should have  bright  and uniform  colour throughout. 

6. Soundness test

               In this  test  two bricks  are  held by  both hands  and  struck  with one  another.  If the  bricks  give  clear  metallic  ringing  sound  and don’t  break  then those  are  good quality bricks. 

7. Structure  test

In this  test  a  brick is  broken or  a  broken  brick  is  collected  and  closely observed.  If  there  are  any  flows,  cracks  or  holes  present  on that  broken face  then that  isn’t good quality  brick. 

Constituents of good brick earth

   In order to get  a  good quality  brick, the  brick earth should contain the  following  constituents. 

1. Silica 
2. Alumina 
3. Lime 
4. Iron oxide 
5. Magnesia 

1. Silica

• Brick  earth should contain about  50 to 60 %  of  silica. 
• It  is  responsible  for  preventing  cracking, shrinking and warping  of  raw  bricks. 
• It  also  affects  the  durability  of  bricks. 
• If  present  in  excess,  then  it  destroys  the  cohesion  between  particles  and  the brick becomes  brittle.

2. Alumina 

• Good brick earth should contain about  20%  to 30%  of  alumina. 
• It is  responsible  for  plasticity  characteristic  of  earth,  which  is  important in  moulding operation. 
• If  present  in excess, then the  raw  brick shrink and  warp during  drying. 

3. Lime

• The percentage of  lime  should be  in the  range  of  5%  to 10%  in a  good brick earth. 
• It  prevents  shrinkage  of  bricks  on drying. 
• It  causes  silica  in clay  to melt  on burning  and thus  helps  to bind it. 
• Excess  of  lime  causes  the  brick to melt  and brick looses  its  shape. 

4. Iron  oxide 

• A good brick earth should contain about  5%  to 7%  of  iron oxide. 
• It  gives  red colour  to the  bricks. 
• It improves  impermeability  and  durability. 
• It  gives  strength and hardness. 
• If  present  in excess, then the  colour  of  brick becomes  dark blue  or  blakish. If  the  quantity  of  iron oxide  is  comparatively  less,  the  brick becomes  yellowish colour 

5. Magnesia

• Good brick earth should contain less  a  small  quantity  of  magnesia  about 1%
• Magnesium in  brick  earth  imparts  yellow  tint to  the  brick. 
• It  is  responsible  for  reducing  shrinkage 
• Excess  of  magnesia leads  to  the decay  of  bricks. 

Bricks

 Brick is the most commonly used construction material. 

• Standard size : 190mm x 90 mm x 90mm
• Nominal size  : 200mm x 100 mm x 100 mm

On the basis of manufacturing and preparations,

1. First class bricks
2. Second class bricks
3. Third class bricks
4. Fourth class bricks

1. First class bricks

• Table moulded and burnt in kilns
• Standard shape, edges are sharp, square, smooth and straight
• Used for superior work of permanent nature

2. Second class bricks

• Ground moulded and burnt in kilns
• Surface is rough and shape is irregular 
• Edges are not sharp and uniform
• Used at places where brick work is to be provided with a coat of plaster

3. Third class bricks

• Ground moulded and burnt in clamps
• Rough surface with irregular and distorted edge
• Used for unimportant and temporary structures

4. Fourth class bricks

• Over burnt bricks
• irregular and dark colour
• Used as aggregate for concrete in foundations, floors, roads etc 

Timber: Structure of Trees

 From  the visibility  aspect, the structure of a tree can be divided into two categories 

1. Macro structure 

2. Micro structure 

1. Macro structure:  

         The structure of wood visible to the naked eye or at a small magnification is called macro structure. Figure shows the macro structure of exogenous tree.

Image source: http://4.bp.blogspot.com

(i) Pith:  

     The innermost central portion or core of the tree is called pith  or medulla 

(ii) Heart wood: 

    The inner annual rings surrounding the pith is known as heart wood. It imparts rigidity to tree

(iii). Sap wood:  

      The cuter annual rings between heart wood and cambium  layer is known as sap wood 

(iv) Cambium layer:  

      Thin layer of sap between sap wood and inner bark is known as cambium  layer 

(v) Inner bark:  

        The inner skin or layer covering the cambium  layer is known as inner bark  

(vi) Outer Bark:  

       The outer skin or  cover of the tree is known as outer bark 

(vii) Medullary rays:  

       The thin radial fibres extending from  pith to  cambium  layer are known as medullary rays

2. Micro strructure:  

      The structure of  wood apparent only at great magnifications is called micro structure under micro scope, it becomes evident that the wood consists of living and lead cells of various sizes and shapes. 

Timber: Classification of Trees

 Depending upon their mode of growth trees may be divided in the following two categories 

(i) Endogeneous trees:

 These trees grow inwards and fibrous mass is seen in their longitudinal sections. Timber from these trees has very limited engineering applications Ex: bamboo, cane , palm  etc 

(ii) Exogeneous trees:  

These increases in bulk by growing outwards and used for engineering purposes. Exogeneous trees are further sub divided into two groups   

      a) Conifers or evergreen trees:

These trees having pointed, needle like or scale like leaves and yield soft wood

        b) Deciduous trees: 

The trees having flat broad leaves and leaves of those trees fall in autumn and new ones appear in spring season. Timber for engineering purpose is mostly derived from  deciduous trees. These trees yield hard wood. 

Eg.. ash, beach, oak, sal, teak, shishum and wallnut 

Bulking of sand

        The presence of moisture in sand increases the volume  of sand. This is  due to fact that  moisture causes film  of water around the sand particles  which result in  the increase of volume  of sand. For a  moisture content of 5 to 8  percent, the increase in  volume may  be about 5 to 8 percent, depending upon the grading of sand. The finer the  material, the  more will be the increase in volume for a given moisture content. This  phenomenon is known as bulking of sand.  

         When  moisture content  is  increased by  adding  more water, sand particles pack near each other and  the amount of bulking of sand is decreased. Thus the dry  sand and the sand completely  flooded with  water have  practically  the same  volume.

Grading of sand

      According to the state of  grains, sand is classified as fine, coarse and gravelly 

     Sand passing through a screen with clear opening of 1.5875mm  is known as fine sand. It  is generally used for masonry works. 

     Sand passing through a screen with clear openings of 7.62mm  is  known as gravely sand. It is generally  used for plastering. 

     Sand passing through a screen with clear opening of 3.175mm  is  known as coarse sand. It is generally  used for masonary  work

Functions of ingredients of cement

 1. Lime:

 Lime is the important ingredient of cement and its  proportion is to be  maintained carefully. Lime in excess  makes the cement unsound and causes the cement to expand and disintegrate. On the other hand, if lime  is  in  deficiency  the strength  of the cement is  decreased and it causes cement to set quickly 

2. Silica: 

This also an important ingredient of cement and it gives or imparts quick setting property  to imparts strength to cement. 

3.Alumina:  

This ingredient imparts quick setting properly to cement. Express alumina  weakens the cement.   

4. Calcium Sulphate: 

This ingredient is in the form  of gypsum  and its function is to increase the initial setting time  of cement. 

5. Magnesia: 

The small amount of this ingredient imparts hardness and colour to cement. 

6. Sulphur: 

A very  small amount of sulphur  is useful in making sound cement. If it is in excess, it causes the cement to become  unsound. 

7. Alkalies: 

Most of the alkalies present in  raw  material are carried away by  the flue gases during heating and only  small quantity  will be left. If they  are in excess in cement, efflorescence is caused.

Ingredients of cement

•  Lime  (Cao)        ------------ 62% 
• Silica (Sco2)        ------------ 22% 
• Alumina (Al2O3)------------ 5% 
• Calcium  Sulphate (CaSo4) – 4% 
• Iron Oxide (Fe2O3) --------- 3% 
• Magnesia (MgO) ------------- 2% 
• Sulphur & Alkalies -------------- 1% each 

Tests for Bricks

 A brick is generally  subjected to following tests to find out its suitability  of the construction work.

1) Absorption:  A good should not absorb not  more than 20 percent of weight of  dry  brick 

2) Compressive strength:  crushing or compressive strength of brick is found out by  placing it in compression testing  machine. It is pressed till it breaks. Minimum  crushing strength of brick is 35kg/cm2  and for superior bricks, it  may  vary from  70 to 140 kg/cm2. 

3) Hardness:  No impression is left on the surface the brick is treated to be sufficiently  hard 

4) Presence of  soluble salts: The bricks should not show any grey or white deposits after immerted in water for 24 hours 

5) Shape and  size:  It should be standard size and shape with sharp edges 

6) Soundness: The brick should give clear ringing sound struck each  other 

7) Structure:  The  structure  should be homogeneous, compact and free from  any  defects

Constituents of Bricks

 Following are the constituents of good brick earth.

 1. Alumina: 

It is the chief constituent of every  kind of clay. A good brick earth should contain 20 to 30 percent of alumina. This constituent imparts plasticity  to earth so that it  can be  moulded. If alumina is present in excess, raw bricks shrink and warp during drying and burning. 

2. Silica:

A good brick earth should contain about 50 to 60 percent of silica. Silica exists  in clay either as free or combined form.  As free sand, it is mechanically mixed with clay  and in combined form;  it exists in chemical composition with alumina.  Presence of silica prevents crackers shrinking and warping of raw bricks. It  thus imparts uniform  shape to the bricks. Durability  of bricks depends on the proper proportion of silica in brick earth. Excess of silica  destroys  the cohesion between  particles and bricks become brittle. 

3.Lime:

A small quantity of lime  is desirable in finely  powdered state to prevents shrinkage of raw bricks. Excess of lime  causes the brick to melt and hence, its shape is last due  to the splitting of bricks. 

4. Oxide of iron:

A small quantity  of  oxide of Iron to the  extent of 5 to 6 percent is desirable in good brick to imparts red  colour to bricks. Excess of oxide of iron makes the bricks dark blue or blackish. 

5. Magnesia: 

A small quantity  of magnesia  in brick earth imparts yellow tint to bricks, and decreases shrinkage. But excess of magnesia decreases shrink leads to the decay  of bricks. 

Grading of Aggregates

      Grading of aggregates  consists  of proportionating the fine  and  coarse  aggregates in  such a  ratio, so  as  to  get strongest  and  densest  mix  with  the least amount  of cement. Grading the aggregates  is so graded as  to have  minimum voids when mixed  with all ingredients, and  water  should render a  concrete  mass of easy  workability. 

The  grading  of aggregates are  done by  the following  methods 

(i) By trail

        In this  method, proportionating  of aggregates as to give  heaviest weight for same volume,  yield the densest concrete

(ii) By finesse modules method (sieve analysis method): 

        In this  method, the  samples of  both  coarse  and  fine aggregates  are  passed  through  a set of  nine standard  sieve and the percentage of sample retained on  each of  the  said sieves is determined.  The total  of these percentages divided  by  100 gives  the  finesses  modulus of sample 

(iii) By  minimum  voids method: 

      This method is  based on the fact, that so  obtain dense concrete the  quantity  of cement should  also  be  slightly  in excess  of  voids  more  that the fine aggregates. In  this method the voids in  the  fine  and coarse  aggregates  are separately  found out with  the help  of graduated  cylinder  and water. The percentage  of  voids I aggregate,  “X” given by  the  equation. 

                  X =  (V1 – V2)  V2  x 100 

Where v1,  volume  of water filled

             v2,  volume  of aggregates.  

(iv) By  arbitrary  standards: 

            It  is  a  commonly adopted method  of propitiating  the aggregates in  a concrete  mix for small works  of  moderate  importance. This method is not  recommended for large works  or  important works in this  method, the volume  of  cement, sand  and coarse aggregates are  taken in  the proportion  of 1:n:2n respectively. The  quantity  of  water to  be used  a  varied suit the workability  descried. 

 Eg:   1:1:2  M250  rich  mix for columns, beams                                                               1:1:3 –  M200  Water retaining structures  etc 1:3:6  – M150 slab’s columns roads etc      1:3:6  – M100 – foundations,                       1:4:8  - For mass  concrete.

Qualities of a Good Building Stones

 The following are  the qualities or requirements of a good building stone. 

1. Crushing strength:  For a  good  building stone,  the crushing strength should be greater than l000kg per cm2. 

2. Appearance:  Good building stone should  be  a uniform colour,  and  free from  clay  holes, spots of other  colour bands etc  capable  of preserving the  colour  for longtime. 

3. Durability: A  good building stone  should  be  durable. The factors  like  heat and cold alternative  wet  and dry,  dissolved gases  in rain, high  wind  velocity  etc  affect  the durability. 

4. Fracture: For good  building  stone its fracture should  be sharp,  even and clear. 

5. Hardness:  The hardness  greater than  17, treated  as  hard used in  road works. It is between 14 to 17,  medium hardness, less 14 said be  poor hardness. 

6. Percentage wear:  For a  good building stone, the percentage wear should  be  equal to  or  less then  3 percent. 

7. Resistance to  fire: A  good  building  stone be  fire proof. Sandstone,  Argillaceous  stone resists fire quite  well 

8. Specific  gravity: For  a good building stone the  specific gravity  should be greater then  8.7 or  so. 

9. Texture:  A  good building stone  should  have  compact fine crystalline  structure should be  free  from  cavities, cracks  or patches of stuff or loose material. 

10. Water absorption:  For  a good building stone, the percentage absorption by  weight  after 24 hours should not  exceed 0.60. 

11. Seasoning:  Stones  should be well  seasoned before putting into  use. A period of  about  6 to  12  months is considered  to be sufficient for proper  seasoning. 

12. Toughness Index:  Impact  test, the  value  of toughness  less than  13 – Not tough,  between 13 and   19 –  Moderate,   greater than  19- high 

Uses of stones

 1. Structure: 

        Stones are  used for foundations, walls, columns, lintels,  arches, roofs,  floors, damp  proof course  etc. 

2.Face works: 

    Stones are adopted to give  massive appearance to  the structure. Wall  are of bricks  and facing is  done  in stones of desired shades. This is known as composite  masonry. 

3. Paving stones:  

       These are  used  to cover floor  of building of various types  such as residential, commercial,  industrial etc. They  are also adopted  to  form  paving of roads, foot paths etc. 

4. Basic material: 

         Stones  are disintegrated  and  converted  to form  a  basic  material  for cement concrete,  morum  of  roads, calcareous  cements, artificial stones,  hallow blocks  etc. 

5.Misalliances: 

      Stones are  also  used for 

(i)  ballast  for railways 

(ii) flux in  blast  furnace 

(iii)  Blocks  in  the construction of bridges, piers, abutments, retaining walls, light houses,  dams  etc.