Objectives 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.
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: