A thickness of 150 mm is generally used. The chamber of the compactor that holds the loose mixture is deeper than the required thickness of the slab at the start of the compaction process. This is necessary in order to accommodate the larger volume of loose mixture. The bottom plate of the mold is free to move up and down. A hydraulic jack is used to push this plate upward during compaction to obtain the required slab thickness.
Thickness is monitored automatically.
At the end of the process, the slab should be at the required thickness with the top of the slab approximately level with the top of the steel mold. The density of the mixture at the required air-void level and the dimensions of the slab are used to calculate the mass of mixture needed. These parameters depend on the thickness of the slab and the required air-void level. Slabs in France are typically compacted to the low and high ends of the air-void range that is expected to be obtained in the field after compaction by the rollers. This air-void range can vary from mixture to mixture.