Lec 3 - Testing of Concrete | Platen Effect | Concrete Technology 

Cubes with steel plates would be always better as they also dissipate the load evenly and avoid localised failures, also by applying lubrication platen effect is taken care of.

Yes

If incase we are testing compression test on opc 53 cement (which probably works on the same principle as that of concrete compression test ) and we found the value to be 53. This value here is being over stated again due to same reasons... Then can companies sell this cement in the name of grade 53 opc cement which doesn't represent the true strength but is over stated? How does IS code cope up this error of stating grades then .. What is the factor of safety code employs to counter this?

You'll get a strength probably more than 53 in that case. If its less than 53 its not permitted. In design however there are lot of safety factors that IS Code already recommends right from concrete mix design where TMS is greater than required strength to the partial material safety factor taken in LSM.

Cylinders give more appropriate results, they are slender than cube and also exhibit platen effect due to which the strength of cylinder is lesser than strength of cube. This also creates a safety margin and is almost near to true condition on site.

@@DCBAonline Thanks alot sir...

Ya its a mistake it should not be less than 3; you can see that at 0:47 i have told it should not be less than 3

In figure it is not shown as contracting, the figure shows that part of cube which remains intact.

@@DCBAonline sir at your video's 14:29 minute the contracting cube you have shown i am talking about that figure

That is not contracting that is the outer surface which has fallen and this shape is achieved.

@@DCBAonline thank you sir for clearing my doubt and sorry for your inconvenience sir Sir i am regularly watching your concrete technology videos that are very useful