EVOLUTION OF THE RHEOLOGICAL PROPERTIES OF POLYMER-MODIFIED BITUMENS DURING AGEING

This work was included in a larger study on the ageing effect on the chemical and physical properties of polymer-modified bitumens (PmBs). The rheological properties of several PmBs were studied between -10 and 100 degrees C, using a dynamic shear rheometer (DSR). The PmBs were prepared out of two different bitumen bases: a conventional (commercial) and an oxydizable base (laboratory made). The effects of the chemical nature and the amount of polymer used as modifiers were analysed as well as the process utilized, i.e. physical blend or in-situ cross-linked. The rheological tests were carried out on unaged binders and on bitumens after conventional ageing (RTFOT+PAV). The study of the rheological properties of the neat bitumens shows that the matrix is oxidised after RTFOT and PAV: some associated species are formed leading to reinforcement at intermediate temperature, especially in the case of the oxydizable base. Polymer addition generally improves the rheological properties of the bitumen base, except in case of a poor compatibility with the base. At low temperature, the dispersed polymer-rich phase has little effect on the rheological behaviour because the nodules are trapped in a high modulus phase (bitumen-rich phase). As the temperature increases, the polymer nodules have a stronger effect because they are more elastic than the bitumen matrix. Hence, at high temperature, the polymer-rich phase improves the rheological behaviour of the binder. After ageing, the microstructure of the PmBs and the composition of the phases change. These changes lead to modifications in the rheological behaviour. In any case, the polymer still reinforces the bitumen matrix at high temperature after ageing, but this effect is more durable for in situ crosslinked PmBs. For the covering abstract see ITRD E121480.