EFFECT OF AGGREGATE TYPE AND GRADATION ON SURFACE FRICTION OF ASPHALT PAVEMENT UNDER DIFFERENT ENVIRONMENTAL CONDITIONS

Public Works Department, Faculty of Engineering, Cairo University, Giza, Egypt

The main objective of this research is to investigate the effect of mix components on

pavement friction. Mix components include asphalt content, aggregate type, and mix

gradation (dense versus open). Three locally-produced aggregates (dolomite, basalt, and

gravel) having different physical and engineering properties were selected to represent a wide

range of properties of available aggregates in Egypt. The British Pendulum was used to

measure the pavement coefficient of friction. Test slabs were prepared using two different

methods of compactions (static and dynamic). The coefficient of friction was measured under

two different surface conditions (wet versus dry) and two temperatures (25 C, 50 C).

Results showed that the coefficient of friction varies among the three aggregate types included

in the study. The average measured BPN for dry dense mix gradation at 25 C were 81, 76,

and 79 for dolomite, basalt, and gravel, respectively. Open-graded mix has a higher

coefficient of friction than dense-graded mix. Results showed significant deterioration in

coefficient of friction due to the change of surface condition (wet versus dry). The average

measured BPN of dry surface was reduced by about 30% due to the surface wet condition.

Coefficient of friction also varied between samples made of natural and crushed particles.

The measured BPN for dry-dense mix gradation at 25 Cْ were 77 and 87 for the natural and

crushed particles, respectively.