Objectives of compaction

  • Reduction of voids
  • Improvement of load bearing properties
  • High longitudinal and transverse evenness
  • High initial grip
  • Maximum compaction result in the shortest possible time

Types of compaction

Static compaction

In the static compaction process, the applied load of the roller effects a shear stress in the layer to be compacted. However, compaction will take place only when the shear stress is approximate to the shear strength of the mixed material, i.e. whenever plastic deformation occurs. The individual mineral particles move and are rearranged in a more compact matrix. The proportion of voids is reduced and the stability increases.

Dynamic compaction

In the vibration and oscillation compaction process, the drum conducts vibratory energy into the asphalt layer in the form of a rapid succession of pulses. The individual particles of the asphalt layer are excited by these dynamic forces. This reduces the friction between the particles and enables them to be moved more easily into a favourable position for the creation of a more compact matrix.

  • Vibration compaction
    Conventional vibrating rollers have a circular vibrator inside the drum. Its fast rotation causes the drum to vibrate and conduct vertical forces into the ground. Vibration is suitable for almost every application in the fields of earthworks and asphalt construction. Today, it’s hard to imagine everyday work on the construction site without it and it yields the best compaction results.
  • Oscillation compaction
    Alongside vibration drums, HAMM also offers oscillation drums. In oscillation drums, the synchronous rotation of masses creates a moment centred on the drum axis. In the course of one revolution of the mass, the moment changes its effective direction (forward and backward), creating an oscillating motion of the drum that conducts shear forces into the ground.

Minimal vibration stresses for the surroundings

Oscillation generates significantly lower vibratory stresses. (see illustration, right). The stress levels it causes are only up to 10 per cent of those caused by vibration (see illustration, left). Oscillating drums do not use up their energy in the creation of undesired vibration in the surrounding area, but transmit it directly into the material to be compacted - precisely where the energy is needed. Minimised vibration guarantees a longer service life of the machine and provides optimal comfort for the operator.

The oscillation system developed by HAMM is not based on complicated mechanical control mechanisms, but relies entirely on the laws of physics. The amplitude value adapts automatically to the stiffness of the substrate. This means that the amplitude decreases continuously in inverse proportion to the increase of soil stiffness. The energy transferred into the soil therefore increases to the same extent as the amplitude decrease.

The following video illustrates the various different types of compaction:

The different drum types

Drum types – outer construction

  • Smooth drums
    With a smooth surface, smooth drums are primarily used for the construction of flat and even surfaces. Examples of this are asphalt surface layers or levelled surfaces in earthwork.
  • Padfoot drums
    Padfoot drums are used for earthwork and in cold recycling. This drum type kneads and roughens the ground. The padfeet enlarge the effective surface area of the ground to enable faster drying of moist ground. Padfoot drums are smooth drums with trapezoidal studs welded onto the surface of the drum.

Drum types - inner construction

  • Vibrating roller drums
    Rollers with smooth or padfoot drums for dynamic compaction featuring a centre shaft fitted with a vibrator system. This generates vibrations with the aid of imbalance masses attached to the shaft. In operation, the rotary vibrator generates and applies a vertical, sinusoidal force to the subsurface.
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  • Oscillation drums
    Up to four eccentric shafts (HD+ 120 and HD+ 140) with two imbalances each and phase shifted by 180°, rotate and create a forward-backward rotary motion of the drum. The drum maintains contact with the ground at all times. In many cases this type of dynamic compaction enables faster compaction of the road bed and the road surface and achieves higher degrees of compaction. Considerably less vibration stresses are created in the surroundings of the machine and the risks of particle crushing and over-compaction are minimised.
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  • VIO drums
    Depending on the positioning of the eccentric shafts relative to one another (in-phase or 180° phase-shifted), the compactor compacts the ground by means of vibration or oscillation. The frequency and amplitude of the front and rear drums can be individually adjusted to enable greater flexibility and increase compaction performance.
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