Formed free-movement joints open during the drying shrinkage phase, potentially in excess of 20mm. At this level of opening, the arris becomes vulnerable to damage when trafficked by MHE. This is especially true for MHE with small, hard wheels such as pallet trucks. To prevent this damage the joint can be armoured.
The most common form of joint armour is strips of steel around 40x10mm. The armour is fixed into the slab with shear studs, which are welded to the steel strips. Below the armoured strips is a sheet of steel that acts as a permanent formwork. It is within this formwork that plates dowels are typically pre-installed to act as load-transfer mechanisms at the joint.
For the armour to be effective, it must be sufficiently stiff and well bonded to the concrete to resist and distribute the impact forces from the MHE. The steel should also be strong enough and thick enough to resist deformation.
Long term performance of an armoured joint can be improved by monitoring the joints over the first year or two of life and filling with a suitable joint to support the arrises, as required.