can't we check the strength of cement mortar which was designed for concrete mix to save some material, pl clarify my doubt

What do you mean for "cement mortar"? Is it cement paste (without sand)? If it is the case, then testing on the cement paste which has the same w/c ratio is the typical way for studying the properties of the paste of corresponding concrete. However, only some properties can be investigated by this way, not the strength! For the admixtures, you can keep the same admixture/cement ratio. 

Are you referring to a Standard procedure for cement testing?

With regards to mortars with additives, I would use the same mix ratio to ensure that any evident variation in properties can confidently be attributed to the presence of the additive, rather than being influenced by inconsistencies in mix proportions.

Dear all thank you for the answers.

my clarification for cement mortar: It is a mixture of cement and sand and I am not testing the strength of cement as this is done by standard procedure of 1:3 proportion of cement and standard sand with w/c ratio equal to (p/4+3) where p= water for consistency test.

I am giving an example: if concrete is designed for M20 grade with 1:1.5:3 with w/c ratio of 0.5 then in my cement mortar mix I use 1:1.5 proportion with same w/c ratio by avoiding the coarse aggregate, can I proceed with some admixtures also by using volume batching. Does the test of compressive strength and flexural strength of mortar can be  related  with concrete?  

thank you

Dear Sastri Vss,

Unforunatly, no. Complessive and flexural strength will depend also on the coarse aggregate. Even more on the interface between the aggregate and the mortar.

Most researchers just remove the fraction of coarse aggregates and keep al other proportions constant.. Some researchers use the Concrete Equivalent Mortar (CEM) approach, in which the fracion of sand is slightly increased (an amount of sand with the same surface area of the removed coarse aggregates surface area is added to the mortar).