Pen Grade Bitumen 60/70

Stability is an essential quality in the performance of a bitumen / aggregate mixture. it depends on friction and cohesion within the mixture. Too much bitumen actually acts as a lubricant for the aggregate particles, reducing friction and therefore the mixture's stability. The cohesion or internal binding force in the mixture increases as the proportion of bitumen in the mixture is increased, until it reaches the optimum. if the amount of bitumen is increased further, stability decreases. it is therefore essential to ensure that the optimum proportion of bitumen is used in any mixture.

The following are useful examples of what can be seen by simple observation. It can be treated as early warning signs that further checks should be made:

•  Smoke coming from the mix indicates overheating

•  Steam from the mixture indicates the presence of  moisture

•  If the distribution of bitumen on the aggregate is not uniform, the temperature in the mixing operation was too low

•  if the mixture looks stiff and dull rather than black and shiny there may be too little bitumen in the mixture

•  if the mix lies slumped on the floor of the truck there may be too much bitumen in it