Sleeves are used to de-bond dowel bars from concrete to facilitate a sliding movement of the bars within the sleeves upon expansion, contraction of panels.
Sleeves must be robust in construction so as to not crack or tear from minor impacts caused by placement of the dowel bar filled sleeves into cradles or paver trolleys.
They must be smooth enough so as to pass the slip test stated below for conformance to MORTH code. And most importantly, they should be of thin wall thickness to minimize concrete cracks caused by compression sleeves under load.