The plinth beam will not hold the volume of the blocks, due to the large size, it will shrink & cracks in entire wall can be visible, there is no meaning for interlock. without joint packing & plastering you can't build a house with blocks. Initially it may look well, but after a year fungus unavoidable. Mixer of bottom fly ash ( wet ash) is only a filling agent. Exact cement adding gives the strenth 11NT, if less it is unfit.