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Tuesday 4 September 2018

September 04, 2018

GRADE OF CONCRETE

GRADE OF CONCRETE


               Concrete is generally graded according to its compressive strength. the various grades of concrete as stipulated i IS:1343-1980 are given in the table. In the designation of concrete mix, the letter M refers to the mix and the number to the specified characteristic strength of 150 mm work cubes at 28 days, expressed in MPa ( N/mm2). The concrete of grades M5 and M7..5 is suitable for lean concrete based, simple foundations, foundations for masonry walls and other simple or temporary reinforced concrete construction for masonry not be designed. The concrete grades lower than M15 is not suitable for reinforced concrete works and grades of concrete lower than M30 are not to be used in the prestressed concrete works.

GRADE OF CONCRETE is of three types.


  • Ordinary Concrete
  • Standard Concrete
  • High Strength Concrete


Ordinary Concrete

GROUP Ordinary
concrete
Standard concrete High Strength
Concrete
GRADE
DESIGNATION
M
10
M
15
M
20
M
25
M
30
M
35
M
40
M
45
M
50
M
55
M
60
M
65
M
70
M
75
M
80
Specified
characteristic
strength at
28 days, MPs

10 15 20 25 30 35 40 45 50 55 60 65 70 75 80

Sunday 2 September 2018

September 02, 2018

CONCRETE AS CONSTRUCTION MATERIAL

CONCRETE AS CONSTRUCTION MATERIAL


concrete is the most widely used man-made construction material in the world and is second only to water as the most utilized substance on the planet. It is obtained by mixing cementing materials, water, and aggregates, and sometime admixtures, are filled by the smaller particles (fine aggregates) the voids of fine aggregate are filled cement water paste which in addition to filling the voids of fine aggregate, coats the surface of fine and coarse aggregates and binds them together as it cures, thereby cementing the particles of the aggregates together in a compact mass.
                                                                     The strength, durability and other characteristics of concrete depend upon the properties, of its ingredients, on the proportions of the mix, the method of compaction and other controls during placing, compaction, and curing. the popularity of the concrete is due to the fact heat from the common ingredients, it is possible to tailor the properties of concrete to meet the demands of any particular situation. The advances in concrete technology have paved the way to make the best use of locally available materials by judicious mix proportioning and proper workmanship, so as to produce concrete satisfying performance requirements.

The key to producing a strong a durable and uniform concrete. CONCRETE AS CONSTRUCTION MATERIAL is the following.

CONCRETE AS CONSTRUCTION MATERIAL


  •  CEMENT
  • AGGREGATE
  • STEEL
  • WATER

CEMENT

       Portland cement, the most widely used cementing ingredient in present-day concrete comprises phases that consist of compounds of calcium, silicon, aluminum, iron, and oxygen.  Cement is used as the binding material and acts as a binder for coarse and fine aggregates. Generally, ordinary portland, cement is used to form concrete. Initial setting time of good cement should not be less than 30 minutes and the final setting time should not exceed 10 hours.

 AGGREGATE

               There are primarily naturally occurring, ind=ert granular materials such as sand, gravel, or crushed stone. However, technology is broadening t include the use of recycles materials and synthetic products.
              The granular material generally inert chemical such as natural sand, gravel, crushed stones and air-cooled iron blast furnace slag are called aggregates. If only CEMENT is used for the construction, the concrete will result in shrinkage and ultimately cracks develop. So as to avoid these cracks, aggregates are used. These aggregates are bound together by means of cement. The aggregates are classified into two categories such as final and coarse aggregates. The material which is passed through sieve no 480 is called fine aggregates and which retained on sieve no 480 is called coarse aggregates. These aggregates should be clean. sharp, angular, well graded, hard, durable and free from foreign matters.

STEEL

           The Steel reinforcement is generally in the form of round bars of mild steel. The diameters of bars vary from 5 mm to 40 mm. Sometimes the square bars or twisted bars or ribbed-bars or ribbed-tor steel are used as steel reinforcement.
        Following are the reason as to why mild steel has been adopted as reinforcing material
         These are a proper band between CEMENT concrete and mild steel. Hence, it enables concrete to transmit its stresses to steel.
        The coefficient of linear expansion of steel is almost the same as that of concrete. Hence o internal stresses are set up within reinforced concrete members due to rise or fall in temperature.
        Deformed or twisted bars which are made of mild steel have considerably high yield stress, tensile strength, and bond strength.

 WATER

           The water to be used in making concrete should conform to the drinking water standard. It is less expensive but the most important ingredient of concrete. The water, which is used for making concrete should be free from acids, alkalies, salts, oil, grease and decayed vegetable matters. The amount of water should be of that, which will produce concrete of required quality.




Friday 4 August 2017

August 04, 2017

PREPARATION OF R.C.C

PREPARATION OF R.C.C

 REINFORCED CONCRETE CEMENT

  •  CEMENT
  • AGGREGATE
  • STEEL
  • WATER

CEMENT

        Cement is used as the binding material and acts as a binder for coarse and fine aggregates. Generally ordinary partland, CEMENT is used to form concrete. Initial setting time of good cement should not be less than 30 minutes and final setting time should not exceed 10 hours.

 AGGREGATE

               The granular material generally inert chemical such as natural sand, gravels, cushed stones and air cooled iron blast furnace slag are called aggregates. If only CEMENT is used for the construction, the concrete will result in shrinkage and ultimately cracks are develop. So as to avoid these cracks, aggregates are used. These aggregates are bond together by means of cement. The aggregates are classified into two categories such as final and coarse aggregates. The material which is passed through sieve no 480 is called fine aggregates and which retained on sieve no 480 is called coarse aggregates. These aggregates should be clean. sharp, angular, well graded, hard, durable and free from foreign matters.

STEEL

           The Steel reinforcement is generally in the form of round bars of mild steel. The diameters of bars vary from 5 mm to 40 mm. Sometimes the square bars or twisted bars or ribbed-bars or ribbed-tor steel are used as steel reinforcement.
        Following are the reason as to why mild steel has been adopted as reinforcing material
         These is proper band between CEMENT concrete and mild steel. Hence, it enables concrete to transmit its stresses to steel.
        The coefficient of linear expansion of steel is almost the same as that of concrete. Hence o internal stressed are set up within reinforced concrete members due to to rise or fall in temperature.
        Deformed or twisted bars which are made of mild steel have considerably high yield stress, tensile strength and bond strength.

 Water 

           The water to be used in making concrete should confirm to the drinking water standard. It is leas expensive but most important ingredient of concrete. The water, which is used for making  concrete should be free from acids, alkalies, salts, oil, grease and decayed vegetable matters. The amount of water should be of that, which will produced concrete of required quality.


  • PROPERTIES OF R.C.C

  •  USES OF R.C.C


PROPERTIES OF R.C.C
 USES OF R.C.C

Thursday 20 July 2017

July 20, 2017

PRESTRESSED CONCRETE

PRESTRESSED CONCRETE

                       In this case of ordinary reinforced concrete which consists of concrete which consists of concrete and mild steel, compressive stresses are borne by concrete while tensile stresses are borne by steel. The concrete surrounding steel reinforcement does not take tension as concrete is weak in tension. Thus only that portion of concrete, which lies above the neutral axis is considered to be useful in resisting compressive stress. This results in heavy section.

                       Prestressed concrete is basically concrete in which internal stresses of a suitable magnitude and distribution are introduced so that the pre-compressive stress in concrete will balance the tensile stress produced in concrete (surrounded steel) due to an external force. due to this, the whole of the concrete can participate in consisting of the external forces. In reinforced concrete members, the prestress is commonly introduced by tensioning the steel reinforcement.
 Prestressed Material

    Principal Materials used in PSC


  •  High Tensile Steel
  •  High Strength Concrete

                         Ordinary mild steel wires are not useful because no prestress will be left in wires after losses. the initial tensile stain in steel is reduced after tensioning by as much as 15 to 20% due to various losses.
                    concrete used in PSC of good quality and high strength. A well compacted dense concrete has a less elastic strain and has less shrinkage plastic flow thus reducing the loss of prestressing considerably.

 Classification of prestressed concrete 

  1.   External and Internal prestressing system
  2.  Linear or Circular prestressing 
  3.  Predestining and Post Tensioning System
  4.  Full Prestressing or Partial prestressing

 External and Internal Prestressing system

  External prestressing is achieved by external reaction introduced through different support conditions.

Prestensioning and post-tensioning system

In Prestensioning system, the tendons are pre-stressed before the concrete is placed. In the post-tensioning system, the member is concreted and a duct is formed in member either with a tube or with a metal sheet. When the concrete is sufficiently hard, the tendons are tensioned and anchored to the concrete member of its each.

Linear or Circular Prestressing

 Linear prestressing is applied in straight members such as beams, slabs, piles etc. Circular prestressing is applied to the circular structure such as tanks, pipes, silos etc. where prestressing tendons are wound around the circumference.

Full Prestressing or Partials Prestressing 

If there are no tensile stresses in concrete under working load, concrete is said to be prestressed. If some tensile stresses are produced I concrete under working load conditions. It is said to be partially prestressed.

Monday 17 July 2017

July 17, 2017

CONCRETE TEST

CONCRETE TEST

There are following tests of concrete

  • Compaction Factor Test
  • Slump Cone Test

Compaction Factor Test

        Compaction of concrete is the process of removal of the air bubbles which are entrapped in the concrete, to give maximum density to the concrete. This test is developed to estimate the workability of the concrete.
       There are three vessels in this instrument. One is the cylindrical vessel, while others are hopper type. These are arranged one above the other like that, hopper B is placed below A, cylindrical vessel C is placed below the hopper B . The vessel A is filled with the sample of concrete. The hinged door which is provided at the bottom of vessel A is opened out so that, the concrete falls in to the cylinder. The concrete of cylinder are now weighed let it to be W1
  Now after removing the concrete the cylinder is again filled with the sample in 5cm layers which is compacted by ramming and vibrating and then weighed let it to be W
   The compaction factor= w1 /w2
 The following conclusions are made based on the value of the compacting factor

Value of compacting factor Standard of workablility
0.95
Good
0.92
Medium
0.85
Low

Slump Cone Test

         This test is used to fine out the consistency of concrete. Consistency of concrete means the fluidity of concrete. 
         Concrete is filled in the standard slump cone which consists of a vessel whose shape is like a frustum of a cone, in four layers. Each ;ayer is tamped by means of hammer 20 times
 Immediately after filling, the cone is lifted slowly and the unsupported concrete will slump. The decrease in the height of the highest part of the slumped concrete is called slump, 
July 17, 2017

REINFORCED CEMENT CONCRETE

REINFORCED CEMENT CONCRETE

      R.C.C is the combination of reinforcement, cement, aggregates and sand, in which reinforcement is provided for taking tensile stresses and combination of cement, aggregates and sand is provided for taking compressive stresses.
      Concrete is very weak in tension but it is strong in compression. Hence cement concrete is reinforced by embedding steel in tensile zone as well as in some cases in compression zone also. it is known as reinforced cement concrete. Reinforced concrete is thus a rational union of concrete and steel combined to act jointly. The joint action of steel and concrete in a reinforced concrete section is dependent on the following important factors-

  1.  Bond between concrete and steel
  2. Absence of corrosion of steel bars embedded in the concrete
  3. Practically equal thermal expansion of both concrete and steel

Advantages of R.C.C

 Advantages of R.C.C

  1.  Concrete can be moulded to any shape and hence any architectural shape may be given to the structure.
  2. R.C.C. ingredients are easily available.
  3.  Monolithic character of structure impart more rigidity to the structure.
  4. It is economical in initial construction.
  5. Its maintenance cost is partically nil.
  6. It  is sufficiently water tight and impermeable if proper controls are exercised during mixing, proportioning, placing , consolidation and curing etc.
  7. R.C.C. structures are completely fire resistant.
  8. They are durable and not easily affected by atmospheric agencies.

Properties of R.C.C.

      Properties of R.C.C

  1.  The co-efficient of linear expansion of concrete and steel are almost same. Therefore no internal stresses are developed in R.C.C due to change in temperature.
  2.  The coating of cement on reinforcement protects it from corrosion.
  3. Concrete transfers the stresses to steel, which it cannot resist itself.
  4. IT provides monolithic and rigid joints.
  5. It is not affected by termites and vermins etc.
  6. These member can be made to any desired shape.
  7. These member are economical than steel members.
  8. R.C.C is a watertight material.
  9. R.C.C is having less maintenance cost.

R.C.C USES

 Reinforcement cement concrete is commonly used to construct the following elements-
  1.  Slabs
  2. Lintels
  3. Beams
  4. Columns
  5. Footings
  6. piles 

Friday 14 July 2017

July 14, 2017

CURING

CURING

 Curing is process of keeping the concrete moist and warm enough, so that the hydration of cement can continue. In fact concrete derives strength by the hydration of cement
                                                                or
        Curing it the process of maintaining a satisfactory moisture content and a  favourable temperature in concrete, so that hydration of  cement may contiune until the concrete developes desired properties. 
        If curing is neglected in the early period of hydration, the quality of concrete will experience a sort of loss. If curing is not done well after placing of concrete, it will not give the desirable bond and strength characteristics.

METHOD OF CURING

  • Water curing
  • Membrane curing
  • Application of hear 
  • Application of curing compounds 

Water curing

     Water curing is the best method of curing. In this method, water is applied on the concrete surface for certain duration.
Way of Water Curing
  •  Ponding 
  • Spraying
  • Wet covering.
          Slabs, roofs, etc are covered under water by developing water pond on the concrete surfaces. Vertical walls, columns, plastered surfaces are cured by sprinkling of water on it. Vertical surface are also cured by using some wet coverings such as gunny bags, cloth, jute matting, straw etc. Horizontal surface are kept wet by covering concrete with wet saw dust etc.

Membrane curing

        In some places where there is acute shortage of water, membrane curing is adopted. Generally water. Mixed for making concrete is more than sufficient to  hydrate the cement. Membranes are applied all around the concrete which will effectively seal off the concrete. The membranes seal over the concrete by means of a firm impervious film to prevent moisture in concrete from escaping by evaporation. This prevention of moisture in concrete will worked as a curing of concrete

Application of Heat

       When concrete is subjected to higher temperature, it accelerates the hydration process and results in higher development of strength. Concrete cannot be subjected to dry heat because of moisture is also an essential requirement. Therefore for achieving this goal concrete is required to subjected, the steam curing. Steam curing will give not only economical advantage, but also technical advantages to the concrete. It is applied generally o perfabricated  concrete elements.

Application of curing compounds

         There are certain curing compounds those keeps the concrete wet. Calcium chloride is the one curing compound. It can be used as a surface coating or as admixture. calcium chloride is a salt, it shows affinity for moisture. The salt, not only absorb the moisture from atmosphere but also retain it at the surface. It keeps the concrete wet for a long time to promote hydration.