Special types of concrete
(1)- High strength concrete
(2)- Light weight concrete
(3)- Heavy weight concrete
(4)- pre- packed concrete
(5)- polymer concrete
(6)- Fibre reinforced concrete
(7)- Ready Mixed concrete (RMC)
(8)- pre -stressed concrete
(1) High strength concrete
High strength concrete (HSC) is considered to be the one having a compressive strength in excess of 40 MPa .To produce concrete above this strength more stringent quality control and more care in selection and proportioning of materials are needed. Most cement used to produce HSC,have fineness in the range of 300-400 m2 /kg with an exception of high early strength cement for which fineness should be at least 450 m2/kg
(2)- Light weight concrete
Light weight concrete are lighter in weight (1.6 kN/m3 to 22 kN/m3) as compared to normal concrete (24 kN/m3) . Light weight concrete is obtained by putting in light weight aggregate instead of normal heavy weight aggregate . In general light weight concrete have higher absorptions, lower strength ,lower elastic moduli, lower thermal conductivity and higher shrinkage than heavier concretes light weight concrete can be produced as expanded concrete .
(3)- Heavy weight concrete
The concrete having unit weight of 30 kN/m3 to 64 kN/m3 is called heavy weight concrete or high density concrete .Thus the unit weight of heavy weight concrete is more than about 25 % higher than that of conventional concrete which is in range of 24 kN/m3. Heavy weight concrete can be produced by using different types of heavy weight aggregate.
Heavy weight concrete is used for construction of nuclear shield walls , blast block ,counter weight ,sea walls and other applications where high density is important.
(4)- Pre packed concrete
Pre packed concrete consists of placing the aggregate only in the form and thoroughly compacting it to form a pre packed mass. This mass is then grouted with the cement mortar of the required proportions.The aggregate should be welted before being placed in position. The mortar that grouts the concrete displaces water and fills the voids.
(5)- Polymer concrete
Polymer concrete is also known as resin concrete. It is a composite material in which the binder consists of synthetic organic polymer. Polymer concrete consists of 5 to 10% polymer binder,of total weight of polymer concrete and mineral filler such as aggregate , gravel and crushed stone . polymer binder can be thermo plastic or more frequently thermo setting.
(6)- Fibre reinforced concrete
The fibre help to transfer loads at the internal micro cracks such a concrete is called fibre reinforced concrete .thus, the fibre reinforced concrete is a composite material essentially consisting of conventional concrete or mortar reinforced by fine fibres .The purpose underlying the introduction of fibre into the matix of a cement paste has been increase tensile and flexural strength, to improve impact resistance and to control cracks.
(7)- Ready Mix Concrete
A concrete whose constituents are weight batched at a central batching plant,mixed either at the plant itself or in truck mixer ,and then transported to the construction site and delivered in a condition ready to use , is termed as ready mixed concrete. The technique is useful in congested sites. Ready mixed concrete is produced under factory conditions and permits a close control of all operations of manufacture and transportation of fresh concrete . Due to its durability ,low cost and its ability to be customized for different applications.ready mixed concrete is one of the most versatile and popular building materials.
(8)- Pre stressed concrete
Pre- stressed concrete is basically concrete in which internal stresses of a suitable magnitude and distribution are introduced so that the stresses resulting from external loads are counter acted to a desired degree, pre stress is commonly introduced by tensioning the steel reinforcement either prior to concreting is called pre-stressing or after concrete has hardened by keeping steel bars in sheashing called post tensioning.
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