Polyphosphoric acid (PPA) has been used in 3.5% to 14% of the asphalt placed in the United States over the past 5 years. This represents up to 400 million tons of hot mix. As with all other components of the mix, testing is required to demonstrate the performance of PPA with each formulation of asphalt and aggregate, together with polymer, antistrip agents, and other additives that may be used. Results of the following tests are presented: dynamic shear rheometer, Hamburg, Lottman, and multiple stress creep and recovery tests on a matrix of a common asphalt with aggregate, three antistrip agents, two types of polymers, and PPA. Laboratory data for the materials tested show that the performance of PPA-modified asphalt can be improved with the addition of antistrip agents such as a phosphate ester, a particular polyamine compound, and hydrated lime. These findings hold true for cases where modification includes the use of polymers: styrene–butadiene–styrene and Elvaloy.
Polyphosphoric acid (PPA) is widely used asphalt modifier to improve the properties of neat asphalt binders when added at low concentrations. Since PPA acts to stiffen the binder, there has been a concern that PPA also accelerates oxidative aging of asphalt. The purpose of this study was to evaluate the effect of PPA on the aging kinetics of asphalt binder. We used extended PAV aging at various times followed by determination of carbonyl contents and PG grade after each aging period. PAV material containing the binder modified with 1% PPA was investigated by DSR and BBR and showed that such binder has wider Effective Temperature Range, compared to control without PPA. The binder with 1% PPA exhibits improved high temperature stiffness. After 60 hours of PAV aging, the low temperature properties of the PPA modified binder are comparable to those of the original, unaged binder. The control binder without PPA exhibited expected changes due to oxidative aging, proportionate to PAV exposure time. The rate of carbonyl formation was approximately 12% slower for PPA-containing binder than the control without PPA. These improvements strongly suggest that the use of PPA improves a binder's resistance to oxidative aging. Bitumen recovered from compacted mixes containing 35% of recycled asphalt pavement (RAP) and PPA-modified binder also show lower stiffness for PPA-containing binders. This suggests that PPA-modified binders may provide anti-aging benefit and reduce the need for rejuvenating agent in the RAP mixes.
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