LIGHT WEIGHT CONCRETE

It is the type of special concrete whose density is very much lower than the conventional concrete.
The density of light weight concrete varies from 300 to 1850 kg/m3.

Methods adopted to obtain light weight concrete.

1) Replacing the natural aggregates with light weight aggregates : Here the concrete is made light weight by replacing conventional aggregates with light weight aggregates of less specific gravity.Aggregates used may be of natural or artificial in occurrence.

Natural aggregates:Pumice,Scoria ,Dolomite etc...

Artificial Aggregates:Expanded shale,Brick bats,Expanded perlite etc...

2) Aerated Concrete: Intrusion of gas bubbles in the concrete.

a) Method 1: By mixing preformed stable foam with concrete slurry

b) Method 2:i) Finely powdered Al or Zn is added to the slurry.

                    ii)This powder further reacts with calcium hydroxide,which is formed during hydration                             reaction of concrete.

                   iii) Further hydrogen is liberated by forming the cellular structure of concrete.

3) No fines Concrete: Fine aggregate fraction is totally eliminated in the concrete.Further the concrete in this state contains only cement and coarse aggregates along with certain amount of water.

Advantages of light weight concrete:

1) Due to low density self weight of the structure is reduced.

2) Easy to handle and reduces the cost of handling and transporting.

3) Possess high degree of fire resistance.

4) Possess high durability.

5) High resistance to freezing and thawing.

6) Reduced cost of transportation and placement.

7) Improves more workability.

8) Low tendency to shrinkage cracking.

Disadvantages of light weight concrete:

1) High degree of porosity.

2) Since porosity is high water requirement is more.

3) Mixing time is more than conventional concrete.

4) Difficult to place and finish.

Application of light weight concrete:

1) Bridge Decks.

2) Precast Elements.

3) Heat insulation on roofs.

4) Partition walls

5) Insulation of water pipes.

6) Fire and corrosion protection.

STANDARDIZATION IN PREFABRICATION

STANDARDIZATION

Standardization is to use of guidelines for the production of uniform interchangeable components especially for use in mass production.

It also refers to the establishment and adoption of guidelines for conduct to global marketing the term is used in describe the simplification of procurement & production to achieve economy.

ADVANTAGES OF STANDARDIZATION

1)      Easier in design.

2)      Easier in manufacture as there are limited number of variants.

3)      Makes repeated use of specialized equipment in erection and completion.

4)      Easier and quicker.

FACTORS INFLUENCING STANDARDIZATION

1)      To select the most rational type of member for each element from the point of production, assembly, serviceability and economy.

2)      To limit the number of types of elements and to use them in large quantities.

3)      To use the largest size of the extent possible, thus resulting in less number of joints.

4)     To limit the size and number of prefabricate by the weight in overall dimension that can be handled by the handling and erection equipment and by the limitation of transportation.

5)   To have all these prefabricates approximately of same weight very near to the lifting capacity of the equipment.

Prefabrication Standardization

Prefabrication Standardization:

It is the use of guidelines for production of uniform interchangeable components especially in mass production.

It refers to adoption and establishment of guidelines for global marketing

It is used for simplification of procurement and production to achieve economy

Advantages of standardization:

1.       Easier in design in accordance to guidelines so that complexity is reduced

2.       Easier to manufacture since the number of variants are limited

3.       It uses specialized and precise equipments for erection and completion

4.       Speed and easier construction

Factors affecting standardization:

1.       To select the member for each element from the point of productivity, assembly, serviceability and economy

2.       To limit number of types of elements and use them in large quantities

3.       To use large size of panels so that the number of joints is reduced

4.       To limit the size and weight of prefabricate so that it can be handled easily

5.       To use the prefabricate weight almost same as lifting capacity of the equipment

Principle of Prefabrication

Need for Prefabrication

Advantages of Prefabrication

Disadvantages of Prefabrication

Characteristics of Prefabrication Materials

Prefabrication Modular Co ordination

Prefabrication Modular Grid

Prefabrication Modular Grids

Modular Grid

A rectangular reference coordinate system in which distance between consecutive grid lines is a basic module or a multi module

Types of modular grid

1.       Continuous grid: it is the type of modular grid directed in either directions and spacing in between, each grid is constantly increment.

2.       Superimposed grid: the type of modular grid in which a basic fundamental unit of 100mm is super imposed on the multi modular grid

3.       Displacement grid: it is the type of modular grid which arrives by a repetitive relation between at least two multi modular increments.

Example: 1m + 3m or 1/2m + 3/4m

4.       Interrupted grid or neutral grid zones: when there are non modular interruption of grid neutral zones are created in order to achieve economy

Principle of Prefabrication

Need for Prefabrication

Advantages of Prefabrication

Disadvantages of Prefabrication

Characteristics of Prefabrication Materials

Prefabrication Modular Co ordination

Prefabrication Modular Co-ordination

It is concept of co ordination of dimension and space in which building components are dimensioned and positioned in terms of basic units.

Types of Modules

1.       Basic Module: it is fundamental unit size in modular co ordination and used for general application to building component. It is denoted by m. 1m = 100mm

2.       Multi Module: it is the whole multiple of basic module and I s express with numerical prefix of m. that is 1m, 2m, 3m….,

3.       Sub Module: it is a simple fractional multiple of the basic module system and it is always samller than the value of the basic unit. Example 1/2m, 3/4m, 2/3m ….,

Principle of Prefabrication

Need for Prefabrication

Advantages of Prefabrication

Disadvantages of Prefabrication

Characteristics of Prefabrication Materials

Characteristics of Prefabrication Materials

Materials chosen for prefabrication construction should be,

1. Easily available
2. Light weight
3. Sound Insulation
4. Thermal insulation
5. Economic
6. Durable and Workable

Principle of Prefabrication

Need for Prefabrication

Advantages of Prefabrication

Disadvantages of Prefabrication

Need for Prefabrication

1.       Prefabricated construction is obtained in places where it is not suitable for normal construction practices such as Hills

2.       Prefabrication construction is adopted in places where the materials are not locally available

3.       In order to achieve speed in construction

4.       In order to obtain high quality of work with higher degree of precision

5.       If there is lack of space in the construction site

6.       If there is bad weather conditions in the construction site

7.       Non-availability of local workers near to the construction site

8.       If there are mass construction practices

Principle of Prefabrication

Advantages of Prefabrication

Disadvantages of Prefabrication

Prefabrication

Prefabrication Structures

Definition:

Prefabrication is the practice of assembling the components of a structure in a factory or manufacturing site and transporting complete assembly to the construction site where the structure is to be located. It is the new technique and is desirable for large scale housing practices.

Principle of Prefabrication:

1.       To improve quality of work, as it is manufactured under improved and controlled conditions

2.       To speed up the construction, since no curing is necessary

3.       To achieve a good quality of construction with minimal cost

4.       To use materials which possess innate characteristics such as light weight, sound insulation, thermal conductivity etc…,

5.       To use locally available materials with required characteristics

6.       Use of reusable materials in construction

7.       Design for flexibility and adaptability

8.       Simplify and standardize building systems

9.       To provide safety working platform during deconstruction

10.   To minimize complexities in building design

Advantages ofprefabrication construction

Disadvantages ofprefabrication construction

Disadvantages of prefabrication construction

1.       Careful handling of prefabricated panels are required

2.       If the joints are not properly sealed there may be problem of leakages

3.       Cost of transportation may be high

4.       Transport of high voluminous materials requires larger road width

5.       Traffic congestion is the big issue during mass transportation

6.       Large prefabricated structure requires heavy duty crane, high precision measurement and proper placing of components

7.       Attention has to be paid towards strength and corrosion resistance of sections while joining in order to avoid failures

8.       Local jobs may be lost

Principle of prefabrication

Advantages of prefabrication

Advantages of prefabrication construction

1.       Self supporting readymade components are used, hence use of scaffolding and shuttering is greatly reduced

2.       Speeder construction than normal one

3.       Quality control can be easier in factory than in construction site

4.       Quality obtained in prefabrication process is higher than normal one

5.       Prefabricated construction is independent of bad weather conditions in the construction site

6.       Onsite construction and congestion is eliminated

7.       Provides safer working platform for labourers

8.       There is minimization of noise and dust in the construction site

9.       Prefabrication mode is economical than conventional methods

10.   Lesser expansion joints are required

Principle of prefabrication

Disadvantages of prefabrication