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.