Question

Define initial set and final set. Briefly discuss one method used to determine them. The following laboratory tests are performed:
a. Setting time test of cement paste samples.
b. Compressive strength of mortar cubes.

What are the significance and use of each of these tests?

Answer 1

Answer:

Answer in explanation

Explanation:

Initial setting time is the time when the cement starts losing plasticity or begins hardening after addition of water to it.

Final setting time is the time when the cement has completly lost it's plasticity and has set and became hard after addition of water.

The test carried out is vicat's penetration test

The initial setting time can be defined as “time taken by paste to stiffen to such an extent that the Vicatt’s needle is not permitted to move down through the paste through 25 mm.”.

The final setting time can be defined as “ it is the time after which the paste becomes so hard that Vicatt’s 5mm needle doesn’t sinks visibly and leave no impression”.

The importance and use of setting time test of cement paste samples

The importance of setting time test is that it plays a very vital role in the fresh and used(hardened) state of concrete.

It plays a very important role in mixing, transportation, shrinkage, compacting, finishing and removal of formwork

The importance of compressive strength of mortar cubes is that it is the compressive strength that tells us about the performance characteristics of the binder of the concrete which is the cement in this case. The performance characteristics deals with the overall quality of the finished product. Hence, a cement or mortar with good compressive strength is good to ensure the delivery of quality work in the final concrete.

It is important to note that there are applicable standards in form of numbers for compressive strength of a cement or mortar