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Asphalt Pavement Technology
Bituminous Mixtures Laboratory (BML)
Equipment French (Laboratoire Central des Ponts et Chaussees) Plate Compactor
The French (Laboratoire Central des Ponts et Chaussees) Plate Compactor compacts asphalt mixtures using either one or two smooth, reciprocating, pneumatic rubber tires. Each tire has a diameter of 415 mm and a width of 109 mm. The Plate Compactor costs $110,000 and is shown in figure 1.
A wheel assembly containing one tire is used to compact slabs having a length of 500 mm, a width of 180 mm, and a thickness from 50 to 150 mm. The two standard thicknesses used by the French Pavement Rutting Tester are 50 and 100 mm.
A wheel assembly containing two tires is used to compact slabs having a length of 600 mm, a width of 400 mm, and a thickness from 50 to 150 mm. These slabs are fabricated in France when prismatic and core specimens are needed for fatigue, compression, and tensile tests. 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.
Various sequences of different downward vertical forces, tire pressures, and positions of the tire(s) relative to the width of a slab are used to compact a slab. 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. Standard high and low compaction procedures that supposedly offer these two levels are provided with the machine. Additional slabs are sometimes compacted to an intermediate air-void level to provide a third data point.
The vertical force and tire pressure used in the process are initially low to prevent the loose mixture from spilling out of the mold. Both are increased after several passes of the tire. A board or steel plate is placed on top of the slab after the mixture has been compacted. Several passes of the tire are then applied. This helps to level the surface; however, mixtures with maximum aggregate sizes larger than 20 mm may still have a rough surface after compaction. It takes 20 to 25 min to compact a slab. No heat is applied by the machine during compaction.