Concrete Technology (General Engineering) (SSC JE)

Workability of concrete–Workability is an important property of concrete in its stage. Workability in simple can be defined as the ease with which the concrete can be mixed, transported, placed and compacted.

• The workability of concrete has also been defined as the amount of work required to place concrete and to compact it thoroughly.

The workability is associated with the following four concepts–
1. Ease of flow (internal friction)
2. Prevention of segregation
3. Prevention of harshness
4. Prevention of bleeding.

• For hand placed pavement slump value should be between 1 – 3 inches (25 – 75 mm).

• For trench fill – 100 - 150 mm

• For heavily reinforced section in slab, beam, columns – 50- 100 mm

Bleeding– It is an autogenous flow of mixing water within or emergence to the surface from freshly placed concrete is usually due to excessive vibrations imparted to concrete to achieve full compaction.

Segregation–It is separation of coarse aggregate from fine aggregate.

Coarse aggregate–Aggregate retained on 4.75 mm IS sieve are identified as coarse aggregate. They are obtained by natural disintegration or by artificial crushing of rocks. The maximum size of coarse aggregate can be 80 mm.

• Compressive strength of concrete is maximum.
• Compressive strength of concrete is the most important property of concrete, because other properties like stress-strain relationship, tensile strength, shear strength, bond strength, modulus of elasticity density, impermeability, durability etc. depends on it.

Cement is a visco-elastic material because concrete has combination of elastic and viscous behaviour where the applied stress results in an instantaneous elastic strain followed by a viscous, timedependent strain.