[@Alfhedil]Um, acccording to [url=http://www.45thdivision.org/Pictures/General_Knowlege/combatload.htm]this source[/url], WW2 soldiers were already carrying some 40 kilos of equipment and gear. As incredulous as it initially sounds.
Tripling it won't be possible, neither it makes sense.
An armor which doesn't cover mot of the limbs or such but 5mm thick would weigh around 25 kilos.
So at best you're raising their load to 65 kilos (which is of course pretty ridiculously lot),