It is established that the best bedding course sands for flexible clay pavements are naturally occurring silica sands from the quaternary geological series and sea-dredged sands. Crushed rock sands should only be used in domestic applications.
Crushed stone with excessive fines, such as dolomitic ‘crusher dust’, are unsuitable because although they can be compacted, they fail to provide a capillary break.
Water entering this material carries with it fines providing a ‘lubricant’ for further breakdown of particles in heavily trafficked channelized areas which may result in eventual bedding course failure.
Pavements subjected to heavily channelized traffic, such as a bus lane, require a sand of high stability-a Category 1A or 1B sand.
1A Pavements receiving severely channelized traffic
1B Industrial pavements
II Adopted highways and other roads
Petrol station forecourts
Pedestrian areas with regular heavy traffic
Car parks receiving some heavy traffic
Footways regularly overridden by vehicles
III Pedestrianisation schemes receiving only occasional heavy traffic
Car parks receiving no heavy vehicles
IV Private drives
Areas receiving pedestrians only
Footways likely to be overridden by no more than occasional
Moisture content of bedding course
The moisture content of the bedding course should be uniform and moist without being saturated. Stockpiled material should be covered.
Bedding sand thickness
Following compaction, the bedding sand should be uniformly 35mm thick with a maximum specified of 50mm and a minimum of 25mm.
Bedding sand construction
This is best prepared by spreading the sand in a loose uncompacted layer and then compacting it with a vibrating plate compactor. The compacted sand is then screeded to level to receive the pavers and must not be disturbed as any disturbance to this sand layer may lead to final surface undulations.
Edge restraints must be provided around the perimeter of the area to be paved. The restraint construction, together with any haunching, should be mature before any vibration of the paving takes place. Gaps between edge restraints or at the intersection with other pavements should be sealed to avoid loss of bedding sand.