Surface Performance-Grading System to Grade Chip Seal Emulsion Residues

The performance-graded (PG) asphalt binder specification was developed to characterize asphalt binder properties that are directly related to the performance of hot-mix asphalt concrete in pavements. However, the PG specification cannot be applied directly to binders for use in chip seals. To address this need, the surface performance grading (SPG) specification was developed with the same equipment required for the PG system but with different limiting values for test parameters at high and low pavement surface design temperatures. NCHRP Project 14–17 used the PG and the SPG systems to grade base binders and recovered residues from five laboratory emulsions and from recovered residues for three emulsions for chip seal construction projects. Two residue recovery methods were used and compared: hot oven evaporation with nitrogen blanket and stirred can with nitrogen purge. Researchers compared the grades from the PG and the SPG systems and found that the grades were similar for the two residue recovery methods but slightly different from the base binder. On the basis of these results, a strawman specification for emulsion residues in chip seals is recommended for use with the stirred can recovery method. The current limiting values in the SPG system were developed for the Texas Department of Transportation. Limiting criteria should be developed for other regions and climatic conditions.