AGGREGATE QUALITY DEMANDS IN ROAD CONSTRUCTION

In view of the fact that the aggregate constitutes 93-94% by weight of a bituminous road mixture, the quality of aggregate is of vital importance. The essential material properties are 1. Accuracy of grading (least possible variation), 2. Particle shape (elongated or flaky particles reduce fatigue life and make attainment of a uniform surface structure difficult), 3. Surface structure (smooth or rough), 4. Porosity (excessive porosity causes lean patches while too little porosity is bad for adhesion), 5. Density (variations must be avoided), 6. Colour (light colour is better for traffic safety), 7. Strength (critical with regard to wear resistance of the surfacing), 8. Thermal resistance (aggregate must withstand heat during mixing), 9. Moisture content (if this is high, costs of drying are excessive), 10. Adhesion to bitumen and asphalt (this can be enhanced by additives, but this increases the cost). /TRRL/