The results from test on concrete containing pfa of the same fineness (27.0%), but varying LOI (3.5 and 8.0%) for binder contents of 250 – 450 kg/m3 indicated differences generally less than 2.0 N/mm2 between these. Hence, an increase in LOI to 7.0% allowed nationally in BS EN 450 and that in the recently revised edition of BS 3892, Part 1, is of little practical significance, provided the LOI is relatively constant.