NMR Study of Hydrated Lime and Limestone in Polyphosphoric Acid Modified Bitumen

摘要

Phosphorous-31 NMR spectroscopy has been used to study the effect of hydrated lime and limestone fines on polyphosphoric acid (PPA)-modified bitumens. NMR spectra were acquired on bitumen samples that were first modified with PPA and on bitumen samples when hydrated lime was added before the PPA. In both cases the NMR spectra showed that calcium phosphates, primarily dibasic calcium phosphate (monetite), and calcium dihydrogen phosphate were formed as a result of an acid-base reaction between the PPA and the hydrated lime. Fourier Transform Infrared (FTIR) Spectroscopy showed that hydrated lime was still present in the bitumen after the PPA was neutralized by the hydrated lime. In another set of experiments in which a calcitic or a dolomitic limestone was substituted for hydrated lime, no reactions were observed between the limestones and the PPA.