| Abstract: | Rolling Thin Film Oven Test (RTFOT) is the AASHTO T240 standard method to simulate asphalt plant mix aging. But it has proven inadequate in aging polymer-modified asphalts (PMA). NCHRP 9-10 offered a modified RTFOT (MRTFOT) by adding a steel rod in each bottle. Since construction temperature of PMA mixture is 10 ℃～20 ℃ higher than that of conventional asphalt mixtures in the field, elevating RTFOT temperature for PMA is necessary for adequate aging and proper simulation. Six PMAs with various PG grades and sources were aged with RTFO at elevated temperatures. Some were also treated with MRTFOT for comparison. SHRP performanc e grade and phase angle were used as indicators to analyze the effects of RTFOT under different conditions. The results show that elevating the temperature is more effective than using rods. And PMA proposed as critical viscosity for PMA, but still more work is necessary to validate this. Given the fact that equiviscous principle is seldom used in field practice, a simple approach was proposed: 173 ℃ is used for RTFOT of PG70 PMAs (grading herein from un-aged asphalts) , while 178 ℃ is for PMAs of PG76 or PG82 and 20 ℃higher than standard 163 ℃ is necessary for PG 88 or stiffer PMAs. |
