Question

There is many types of compactors and rollers used in the construction of flexible pavement. mention all the types of those rollers and compactor and what are the differences between them and why each type is used for. Take in consideration the effect of changing in the bitumen viscosity with the decrease in the mix temperature during construction.

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Answer 1

Different Types of earthwork equipments used for compacting soils are as fallows:

1. Grid rollers:- Grid rollers are used for compaction of weathered rocks, well graded coarse soils. These rollers are not suitable for clayey soils, silty clays and uniform soils. The main use of these rollers are in subgrade and sub-base in road constructions. As the name suggests, these rollers have a cylindrical heavy steel surface consisting of a network of steel bars forming a grid with squire holes. The weight of this roller can be increased by ballasting with concrete blocks.

Typical weights vary between 5.5 tonnes net and 15 tonnes ballasted. Grid rollers provide high contact pressure but little kneading action and are suitable for compacting most coarse grained soils.

2. Sheep's Foot Rollers:-
Sheep's foot rollers are suitable for compacting fine grained materials such as clays and mixtures of sand and clay.
These cannot compact granular soils such as sand and gravel.
Depth of a layer of soil to be compacted is limited to approximalely the length of the feet.
They are used for manipulation and compaction of plastic clays where stratification must be eliminated, such as clay cores in dams.

3. Smooth-wheel Rollers:-
Smooth-wheel Rollers can be self-propelled or of the towed type with smooth steel roll surfaces. These rollers may be classified by type or by weight.
These rollers are effective in compacting granular soils, such as sand, gravel, and crushed stone and they are also effective in smoothening surfaces of soils that have been compacted by tamping rollers.
When compacting cohesive soils, these rollers tend to form a crust over the surface, which may prevent adequate compaction in the lower portion of a lift.

4. Pneumatic-tyred Rollers:-
Pneumatic-tyred Rollers are surface rollers, which apply the principle of kneading action to effect compaction below the surface.
These rollers are used for rolling subgrades, airfield and bases of earthfill dams.
They can be self-propelled or towed, small-or large-tyred units.
These rollers rely on dead weight acting or upon pneumatic tyred wheels to produce the compacting effort.

5. Impact Rollers:-
The impact roller is a recent development.
It consists of a square concrete block with steel covering rounded corners.
It relies for its compaction effect on the impacts when this specially profiled roller is towed at fairly high speed.
Impact roller can compact up till a considerable depth with certain soils and to be applicable to a wide range of soil types.

6. Vibrating Compactors:- Vibratory compactors enhance the performance of static weight rollers by adding dynamic forces, usually achieved by a rotating eccentrically weighed shaft mounted inside the roller. Vibrating compactors have shown their abilities to produce excellent densification of soils such as sand, gravel and relatively large stones.
As these materials are vibrated, the particles shift their position and nestle more closely with adjacent particles to increase the density of the mass.

7. Cylindrical roller:- One type of walk-behind roller is a cylindrical roller. These ones are traditional in that they are relatively lightweight and are pushed by a person. All of the other types of rollers on this list have walk-behind and ride-on counterparts and are sometimes still powered by an engine.

Cylindrical rollers are used mainly for small and private projects, like yard work. Cylindrical rollers are typically 1 meter in diameter and are generally made of iron, stone or concrete.

8. Pad foot/Tamping roller:- The static pad foot rollers also called tamping rollers have static weights in the range of 15 to 40 tonnes and their static linear drum loads are between 30 and 80 kg/cm. These rollers are more preferable than sheepsfoot roller due to their high production capacity, and they are replacing sheepsfoot rollers.

The degree of compaction achieved is more than sheepsfoot rollers. The density of soil achieved after compaction with this roller is more uniform.

These rollers operate at high speeds, and are capable to breaking large lumps. These rollers also consists of leveling blades to spread the material.