Question

a – List down the common testing of cement, fresh concrete, and hardened concrete.

b – How many types of curing for concrete specimen? What are they? Which curing method is practically required for laboratory testing?

c – Explain why the strength of concrete is increase as increasing of curing age?

Answer 1

a)

1) Tests on Cement -

Field Testing:

(a) Open the bag and take a good look at the cement. There should not be any visible lumps. The colour of the cement should normally be greenish grey.

(b) Thrust your hand into the cement bag. It must give you a cool feeling. There should not be any lump inside.

(c) Take a pinch of cement and feel-between the fingers. It should give a smooth and not a gritty feeling.

(d) Take a handful of cement and throw it on a bucket full of water, the particles should float for some time before they sink.

Lab Testing:

(a) Fineness test.

(b) Setting time test.(Initial Setting time and Final Setting time)

(c) Strength test.

(d) Soundness test.

(e) Heat of hydration test.

(f ) Chemical composition test.

(g) Consistency test

2) Tests on Fresh Concrete -

(a) Slump Cone test

(b) Compaction factor test

(c) Vebe test

(d) Flow test

(e) Air Content of Fresh Concrete

3) Tests on Hardened Concrete -

(a) Compression test

(b) Flexural Strength of Concrete

(c) Split Cylinder Test

(d) Rebound Hammer test

(e) Pulse Velocity test

  

b) Curing methods may be divided broadly into four categories:

(a) Water curing

(b) Membrane curing

(c) Application of heat

(d) Miscellaneous

Water curing can be done in the following ways: (a) Immersion (b) Ponding (c) Spraying or Fogging (d) Wet covering

The concrete test specimens are normally immersed in curing tanks for testing in Laboratory.

(c)

The concrete develops strength with continued hydration. The rate of gain of strength is faster to start with and the rate gets reduced with age. It is customary to assume the 28 days strength as the full strength of concrete. Actually concrete develops strength beyond 28 days also. Earlier codes have not been permitting to consider this increase of strength beyond 28 days for design purposes.