Special Concrete – Definition, types and difference among plain concrete and special concrete
Special Concrete stands for the concrete that is used for certain purposes like light weigt, high density, fire protection, radiation shielding etc.
The concrete contains strong compressive strength but it has several shortcomings which range from low tensile strength, penetrability to liquids, erosion of reinforcement, vulnerability to chemical attack and low strength.
The enhancements are made in the following areas :-
a. Enhancement in mechanical properties like compressive strength, tensile strength, impact resistance.
b.Enhancement in stability with regard to improved chemical & freezing resistances.
c. Enhancement in imperviousness, thermal insulation, abrasion, skid resistance etc.
The following types of special concrete are mostly found :-
Light weight concrete, High density concrete, Plum concrete, No fines concrete, Aerated concrete, Fiber reinforced concrete (FRC), Polymer concrete, Ferro Cement, High strength concrete
Variations among ordinary and special concrete:
Ordinary concrete is utilized for normal applications like building, bridges, road etc.
Special concrete is utilized for special type of structure like nuclear reactor, buildings with acoustic treatment, air conditioned buildings etc.
The components of ordinary concrete range from cement, sand, aggregate and water.
For the light weight aggregate concrete, light weight aggregates are utilized. In polymer concrete, polymer binder is applied in place of water.
Construction is done by traditional system.
Concreting is performed by special methods.
Properties of concrete like density, strength etc. remain on normal range.
Properties of concrete like density, strength remain on higher range. As for instance density of light weight concrete remains approx 500 to 2000 kg/m3 and that of heavy weight concrete remains approx 3000 to 5000 kg.m3.
Ordinary concrete is inexpensive.
Special concrete is expensive.
The special concrete offers the following features.
1. Special concrete is suitable for extreme weather.
2. HPC has been applied in big structures.
3. Strong cohesiveness or sticky in mixes containing extreme binder content
4. Some loiter in setting times is based on the compatibility of cement, fly ash and chemical admixture
5. Marginally lower but adequate initial strength for most applications
6. Comparable flexural strength and elastic modulus
7. Superior drying shrinkage and considerably lower creep
8. Safeguard steel reinforcement in high chloride environment
9. Outstanding stability in aggressive sulphate environments
10. Lower heat characteristics
11. Low resistance to de-icing salt scaling
12. PC pipes offer good resistance to chemical attack from both acidic and caustic effluents inside the pipe, and from chemical attack on the exterior of the pipe.