8. Characterization of Apparent Viscosity of Bitumen Processed in India
Date of Start

August 2005
Indian Institute of Technology, Madras (R, C)


Scope and Objectives

The measurements were carried out from 80oC to 180oC. Though the viscometer can measure the viscosity up to 300oC, measurements up to 180oC will be made considering the flash and fire point limitations. Due to the fact that at temperature below 60oC, the repeatability is very poor for rotational viscometers, the investigation is restricted to measuring temperature up to 80oC only. Only the short term aging of bitumen and its influence on the viscous characteristics will be investigated.

To characterize the apparent viscosity of unmodified and modified bitumen under un-aged and short-term aged conditions.

Findings and Conclusions
(i) The flow properties of bitumen are affected by temperature and stress-strain conditions. Bitumen behaves as a non-Newtonian at low temperatures and approaches to Newtonian as the temperature increases. This phenomenon can be observed from the apparent viscosity-shear rate graphs at various temperatures. The transition is gradual and the rate of change is a function of composition and the type of bitumen. It is observed that the parent bitumen i.e. 60/70 grade changes faster to Newtonian state than that of polymer modified (PMB 70) and changes to Newtonian state at about 100 oC whereas the polymer modified one changes at about 135 oC.

(ii) The flow characteristics of bitumen are also affected by the rate of shear or stress levels. As the rate of shear increases from 3.4 s-1 (10 rpm) to 34 s-1 (100 rpm), the structural changes occurring in bitumen are evident from the dependency of apparent viscosity on the rate of shear and from the thixotropic behaviour of bitumen.

(iii) The variation in the behaviour of bitumen due to the effect of temperature and the rate of shear can be shown by the flow index which is also known as non-Newtonian constant derived from an empirical power law equation. Test results shows that as the temperature increases, the flow index increases and approaches unity which is an indication of the behaviour of Newtonian fluids and 60/70 grade bitumen changes from non-Newtonian state to Newtonian state at about 100 oC whereas PMB 70 changes at about 135 oC.

(iv) The above investigations reported here are some of the preliminary results related to the characterizing the non-Newtonian behaviour of bitumen processed in India. Such kind of investigation will help us in understanding the constitutive behaviour of bitumen, role of modifiers and the influence of short term ageing of bitumen on its mechanical properties. Detailed investigations are necessary at this stage on the temperature ranges of 40 to 80oC. Due to the limitation of the equipment available, it was not possible to study the flow characteristics at this critical temperature range.