Fillers are finely divided substances which are insoluble in bitumen but cart be mixtures dispersed in it as a means of modifying its consistency and mechanical properties. They are usually mineral materials; organic fillers such as wood flour or cork dust, are rarely used. Typical mineral fillers are limestone dust, cement, hydrated lime, slate dust, pulverized fuel ash, talc, silica and asbestos. Non-fibrous fillers usually have a particle size of less than 75 micron (um). The general effect of adding filler to bitumen is to make it harder and stiffer in practical terms means that there is a reduction in the deformation or produced by a given load and is shown by an increase in softening poireduction in penetration and an increase in stiffness. The extent of this hardening or stiffening effect depends on the amount of filler added and on its particle shape, size and grading. Normal fillers such as limes or slate dust produce the least effect; fillers with plate-like particles, such as are intermediate, and fibrous fillers such as asbestos* show the greatest effect for a given concentration of filler. Hydrated lime is much more effective than limestone. The volume percentage must be calculated from the weight and density of the material and not estimated from the volume of filler added. For normal fillers, the effect of the filler on the penetration and softening point roughly proportional to the filler concentration for concentrations up to about 40% v of the mixture. For fibrous fillers, the upper limit for proportional behaviour is much lower.

model registered ©