AC Bitumen, or Asphalt Cement graded by viscosity, is classified mainly according to absolute viscosity at 60°C under the applicable specification. Grades such as AC-10, AC-20, AC-30 and AC-40 represent different viscosity levels and should be selected according to the project standard, climate, traffic, pavement design, asphalt-mixture requirements and construction conditions. This guide explains the AC grading system, compares the main grades, reviews the differences between AC, VG, penetration-grade and PG Bitumen, and outlines quality-control, storage, purchasing and pricing considerations.