Ballast
Also called Counterweight
Additional weight, such as concrete or steel blocks, added to a crane or piece of plant to increase stability and counteract the overturning effect of a load. Ballast increases the loads transmitted to the ground through tracks, wheels or outriggers, so it must be accounted for in ground-bearing calculations, not just the load being lifted.
In practice
Ballast is the reason the heaviest thing on the mat is usually not the load. Adding counterweight to reach a radius adds directly to what the ground carries, and it does so whether or not anything is being lifted — a rigged crane standing idle is imposing most of its worst-case reactions all the time it is on site.
Where this comes from: Standard lift planning practice; the ground-bearing consequence of ballast is what makes it a temporary works issue as well as a stability one.
Where it matters on site
Watch for ballast changing after the lift was planned. A crane rigged with more counterweight than the plan assumed — to gain radius, or because that is what came on the wagon — invalidates the reactions the matting was sized from. Where ballast is added or removed on site, the ground bearing check is part of what has to be revisited, not only the load chart.