Manufacturing technology for asphalt filler production at asphalt concrete production
The dispersed component (mineral dust) plays an important factor while producing asphalt concrete for road building. It is a finished grinding product up to specific surface 2500 - 5000 cm2/g of limestone, dolomite, dolomitic limestone and other carbon rocks, metallurgic slag as well as industry powder waste.
Mineral dust in asphalt concrete fills the free space of sandy crushed stone frame and increases the density of mineral framework, and turns oil bitumen into solid asphalt binding substance.
For successful fulfillment of those functions the mineral dust shall have the following characteristics:
– It shall not be clumped or form packs when missing with bitumen;
– bonding of bitumen with mineral dust granules surface shall be as much strong so that water did not break bitumen throughout the whole normative service life of asphalt concrete in coating;
– physical and chemical interaction between the mineral dust granules surface and bitumen shall be strong enough for molecules orientation in a thin bitumen layer however at this the dust shall not speed up the process of bitumen aging;
– mineral dust content in mixture shall be minimum to the limit, required for asphalt concrete to reach normative density and hardness.
The main method of improving the mineral dusts characteristics is their physical and chemical activation whereby the material grinding process is accompanied by bitumen processing with surface acting agents (SAA) in the ratio 1:1–1:3.
As a result of mineral dust activation they accrue the whole set of useful characteristics:
– dust hydrophilic surface becomes moisture-repellent what simplifies its transporting and storage;
– activated dusts are not clumped enabling to reduce grinding fineness at their manufacturing;
– presence of hard bitumen film on dust surface significantly improves the conditions of subsequent interaction with bitumen when getting asphalt concrete;
– high quality of mineral dusts guarantees the opportunity to prepare asphalt concrete with enhanced density, hardness, water and frost resistance and in particular cases - with enhanced shear-resistance and crack resistance. Such asphalt concrete has the maximal number of closed supports what provides the lower water saturation at residual porosity planned and water permeability of cover;
– asphalt concrete mixtures on activated mineral dust are not slumped when storage; the coatings of such mixtures are formed faster experiencing pressure at road traffic;
– bitumen consumption for preparing asphalt concrete mixtures is 10 - 20% lesser than mixtures on nonactivated dust;
– preparation, laying and compacting of asphalt concrete mixtures on activated mineral dust are performed at lowered temperature by 20oС as compared with usual mineral dust;
– when laying and compacting of asphalt concrete, mixture processibillity improves.
In connection with the above-mentioned many road building organizations started using the activated mineral dust in a wide range.
Manufacturing technologies for activated mineral dusts
In USSR the production of activated mineral dusts was effected in ball tube mills by means of dozing the prefabricated activator on dried broken stone into the screw before the mill. Such equipment (for example, products of Samara plant “Strommashina”) with capacity 8–10 t/h has the installed power 450 kW, the mass up to 200 t and overall dimensions 36х16х11 m. There are also variants that provide combination of drying and grinding operation with activation in one unit – ventilating separator mill of a hammer or paddle type.