However, since common initial strength does not exist among
the four categories of concrete, relative percentage strength gain
and loss were therefore considered as the main criterions for judging
the individual performance qualities. Fig. 6 presents strength
gain and loss percent in each of the categories. The strength gain
and loss (fg and fs) percents were expressed as ratios (f28 f0)/
f0 100 and (f28 f84)/f28 100 respectively, where f0, f28 and f84
are the compressive strength values at 0, 28 and 84 days of immersion
into the Na2SO4 respectively.