A review of the rheology of bituminous materials

The colloidal structure of bitumen: Consequences on the rheology and on the mechanisms of bitumen modification

“…This applied reasonably well for the studied binders but proved difficult to extrapolate to all materials [182]. Therefore, other coefficients were later proposed and a good approximation was given for example by Duriez and Arrambide with b = 2 in all cases, and A =8 10 8 for soft bitumens (penetration grade 180/200) and A = 10 9 for harder ones (penetration grade 40/50) [188].…”

“…When monitoring the viscosity (or any mechanical property) of a bitumen versus time around room temperatures, a very slow heatreversible hardening is indeed observed and generally referred to as steric hardening [182]. The viscosity increase follows a power law versus time with a slope between 0.017 and 0.183 [183], corresponding to a viscosity increase between 10 and 200% in 2000 h at 25°C [27], depending on bitumen type.…”

“…It was early recognized that the penetration test was too complicated to interpret in rational terms and that only correlations could be found between penetration and intrinsic properties such as viscosity [182]. For example, penetration was shown to be a somewhat equiviscous temperature and Saal and Koens published equivalence between viscosity η (in Pa s) and penetration P (in 1/10 mm) using standard loading conditions (5 s and 100 g) at the same temperature in the form of the general relationship [187]:…”

“…As for penetration, it was early recognized that the Ring & Ball softening temperature was equally difficult to interpret in rational terms [182]. As a result, the viscosity of bitumen at the Ring & Ball softening temperature was initially thought to be an equiviscous temperature corresponding to a viscosity between 800 and 3000 Pa s [182], with an average value of 1200 Pa s [189].…”

“…The proposed interpretation generally relies on the sol-gel picture with the build-up of a stronger asphaltenes network with time [182], as suggested by the correlation between the rate of viscosity increase and the degree of complex flow, defined as the slope of the flow curve (stress versus rate of strain in a log-log scale) [183].…”