Given the pfa fineness effect noted, a means of achieving equivalent strength with BS EN 450 pfa was required. A number of methods exist for proportioning pfa concrete, including the k-factor and optimization methods. However, to minimize the changes required, it was decided to approach this by simple adjustment of the water/cement ratio. With the small strength changes observed with pfa fineness, modifying the w/c ratio was likely to be minor and the use of this method easy to apply in practice.