It depends on the type and melting point of the PCM; given the low thermal conductivity of concrete, specimens subjected to temperatures below 200 degrees centigrade are expected to exhibit practically no change during the compression test (since the temperature reached to PCMs is very low). For temperatures beyond this value and assuming the use of polymeric materials, they mainly contribute to reduced workability and may also contributed to degradation of mechanical properties since voids replace them as they melt. In general you have to be more specific about the heating regime, duration and type of PCMs to get a specific answer. For start, check the following link:

Article Phase change materials in concrete: An overview of properties

thanks Hamed for your reply. i am using two PCMs having Melting temperatures 32 and 44 C. Compressive strength of PCM 44 is substantially lesser than PCM 32 C. what can be possible reason for this substantial difference in compressive strength.???@

Yes I agree with Hamed Sadaghian

Good information here thank you all