Empirical Pavement Design
Penetration Grade Bitumen
Although concepts for empirical pavement design procedure were described as early as the 1950's (referred to as “rational” design procedures), interest in these procedures became renewed in the 1980's. Since that time, significant advancements in computer capabilities have occurred, pavement technology, analysis, and testing have evolved, and a great number of countries worldwide have either initiated or implemented empirical pavement design procedures.
From early days, different grades of bitumen were involved in de mechanistic properties and were described in all kind of regulations. Until now penetration grades have lead in mix design models and, together with performance grade test results, are responsible for the choice of bitumen within required asphalt characterisation.
As long as bitumen came from vacuum refinery as a residue from fuels extraction, the characterisation was comparable and empirical pavement design was sufficient to get pavement performance within certain levels. With the growth of traffic and the introduction of recycling methods, the need for performance related bitumen tests arose. Also, over the last ten years changing refinery output, by use of cracking and cooking techniques in order to get more fuels out of the heavy crude oils, made it impossible to rely only on penetration grades. But, until now the penetration is leading in several regulations and also the controlling measurement system of bitumen producers.
Penetration Grade bitumens are specified by the penetration and softening point test. Designation is by penetration range only. The penetration grade bitumens have a thermoplastic property, which causes the material to soften at high temperatures and to harden at lower temperatures. This unique temperature/viscosity relationship is important when determining the performance parameters such as the adhesion, rheology, durability and application temperatures of bitumen.
Penetration Graded Bitumen are specified according to ASTM D946-09 and EN 12591-2009, including:
ASTM D946-09 Grades
Bitumen Penetration Grade 40-50
Bitumen Penetration Grade 60-70
Bitumen Penetration Grade 85-100
Bitumen Penetration Grade 120-150
Bitumen Penetration Grade 200-300
EN 12591-2009 Grades
Bitumen Penetration Grade 20/30
Bitumen Penetration Grade 30/45
Bitumen Penetration Grade 35/50
Bitumen Penetration Grade 40/60
Bitumen Penetration Grade 50/70
Bitumen Penetration Grade 70/100
Bitumen Penetration Grade 160/220
