ASPHALT LAYING AND INFLUENCE FACTORS:

In laboratory simulation as well as during the laying of asphalt the compaction process is influenced by a number of factors, which interact integrally in a very complicated manner and can only be examined separately in the analysis. Both the mixture components as well as the compaction temperatures belong to the factors with highest influence and leaflet on compaction of asphalt.

COMPACTION OF MIXTURE:

By experience, mixture  components and mineral aggregates in particular have the most significant influence on the compaction resistance. The mechanical properties of the mineral aggregates influence the compatibility in such a way, that ,due to their lower inherent friction and interlocking resistance, round particle mixture are easier to compact than mixtures consisting of crushed particle. Sand particle and chipping fractions thereby have the strongest effect, whereby the compaction resistance mainly rises with the increasing proportion of crushed sand or a  high content of chippings.

               With a decreasing coarse particle fraction bigger than 2mm the so-called mortar components(binder, sand, filler) gain a higher influence with mixture types composed according to the asphalt concrete principle, whereas the compaction resistance does not increase to such an extent when increasing the coarse particle content. Mixtures with a very high proportion of chippings( stone mastic asphalt and drainage asphalt) are also mainly influenced by the mortar content.

               The influence of the filler with its stabilising effect on the compatibility of the mixture is only of minor significance, but is effective in the entirety of the mortar components, whereby the compaction resistance of the mixture decreases with increasing mortar content. The  compaction resistance is highly influenced by the binder content, however, the grade of binder is only of minor significance. The sliding resistance on the binder film on the particle surfaces, which enhances the compaction of the mixture.

INFLUENCE OF THE TEMPERATURE TO ASPHALT:

The highly temperature dependent properties of the bituminous binder in turn result in a significant influence of the temperature on the compaction characteristics of the mixture. The temperature of the mixture is very sensitive influential factor, which has an effect in combination with the mixture composition and temperature dependent variable viscosity of the binder. With increasing compaction resistance the mixture specific critical compaction temperature rises to a  level, where an  effective compaction temperature must therefore not drop below a critical limiting value. The required minimum temperature is considerably higher than for easily compactible material. The critical temperature limits must be carefully evaluated by suitability tests and monitored during the laying and compaction of the asphalt by measurements

Under aspects of compaction practice the temperature shall be as permissible at beginning of compaction work, since this is of advantage for compaction effect. The top temperature limit is specified because the fact that the mixture must remain stable under the influence of the roller and that an effective particle redistribution and reduction of air voids occurs during compaction must be accomplished without any shoving or lateral displacement of mixure. Depending on the grade of binder the normal temperature when tipping the mixture into paver is 150-180c, the compaction temperature range approx..130-170c. In temperature range between 90-100c compaction must be finished, because a futher drop in temperature will result in an excessive increase of the binder viscosity, making compaction work almost effective.