Abstract
ABSTRACT Phosphorous-31 NMR spectroscopy has been used to study the behavior of polyphosphoric acid (PPA) in bitumen. Phosphorous NMR spectra were acquired on a PPA-modified bitumen immediately after blending, and on samples that were stored at 135°C for different periods of time. The initial NMR spectra showed resonances characteristic of phosphorous atoms in orthophosphoric acid, and in middle and end groups of phosphate chains. However, over time the number of phosphorous atoms in the middle and end groups decreased, indicating a preference of polyphosphoric acid to revert back to the orthophosphoric acid in the presence of bitumen. The NMR data did not suggest the formation of organic phosphate esters as a result of PPA modification. Phosphorous NMR spectra were also acquired on bitumen samples modified with Elvaloy® in which polyphosphoric acid was used as a catalyst. The data showed that over time only one type of phosphorous atom remained in the bitumen. The NMR data suggest that the PPA did not react with Elvaloy® to form esters.
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