CHEMICAL MODIFICATION OF BITUMEN THROUGH POLYPHOSPHORIC ACID: PROPERTIES-MICRO-STRUCTURE RELATIONSHIP

The high-temperature rheological characteristics as well as the low-temperature fracture properties of asphalt binders can be improved through the use of additives such as polymers. Chemical modification of bitumen is another way to improve asphalt binders properties: with polyphosphoric acid, an increase of one to two classification grades ('pene' grade) is obtained at a low addition content (< 2%). In combination with a polymer, a positive effect is also observed. The rheological and ageing properties of asphalt binder containing different amounts of polyphosphoric acid, alone or in combination with a polymer, were studied using dynamical mechanical analysis, creep test and conventional methods. The results indicated that the properties of the modified binders were largely dependent on the polyphosphoric content with an influence of the nature of the acid and the characteristics of the base bitumen. Field tests have been successfully made a few years ago in North America, reinforcing laboratory results on binders and leasing to a commercial use. Analysis of the modified bitumen microstructure shows that polyphosphoric acid acts as a de-agglomerant of asphaltenes; a fraction of added acid reacts with bitumen according to the basic site of asphalten itself. In fact, the results indicated a chemical modification of the base bitumen: increase the rate of the asphaltens + resins, a modification on hydroxyl groups with creation of phosphates esters function on asphaltene in the modified bitumen. For the covering abstract see ITRD E121480.