I think that the unit weight of regular sand is more than unit weight of foundry sand. Did you check this ?

I think that the unit weight of regular sand is more than unit weight of foundry sand. Did you check this ?

Thanks Mohannad Husain, The bulk density of foundry sand (70-90lbs/ft3) is less than natural sand (95-105lbs/ft3).

Thanks a lot for your valuable insite B.B. Jindal Sir, but particle size distribution was done on the mixed aggregates and the same material is used for preparing 2-mixes, then how can particle size distribution effect the weight.

Check specific gravity.

Thanks @Parveen Jangra and @Bharat Bhushan Sir, Specific gravity may be the main reason but here specific gravity of both the material is around same i.e. 2.6. Now bulk density may be the reason as mentioned by Mohannad Sir.

Physical properties for foundry sand such as specific gravity, bulk density, grains shape and size, and size grading are all affecting the weight of sand in a given volume, and consequently affecting the weight of the concrete.

Thanks @Muhammad A. Husain for your valuable reply.

Because it has one size (poor gradient sand)

Thanks @Fatimah hameed Naser for your kind information.