Study of flow behavior for predicting mixing temperature of bitumen Nikhil Saboo ⇑ , Praveen Kumar Department of Civil Engineering, Indian Institute of Technology, Roorkee, India highlights  Modified binders behaves as a shear thinning fluid even at higher temperatures.  Carreau–Yasuda model can be used to model the viscosity master curves of bitumen.  Zero shear viscosity can be modeled using a simple exponential law.  A new method has been presented to predict the viscosity of bitumen.  The study suggests lower mixing temperatures for modified binders. article info Article history: Received 27 January 2015 Received in revised form 31 March 2015 Accepted 3 April 2015 Available online 13 April 2015 Keywords: Viscosity Rheology Shear rate Modifier Mixing temperature abstract Study of flow behavior is necessary for selection of proper grade and viscoelastic characterization of dif- ferent asphalt binders. Shear thinning behavior of modified binders demands a critical study of viscosity at a wide range of temperatures and shear rates. Such analysis also leads to practical calculation of more appropriate mixing temperatures for asphalt concrete. This study focusses on evaluating the flow proper- ties of different binders for a wide range of shear rates and temperatures using steady shear methods. Carreau–Yasuda (C–Y) and exponential model are combined with the concept of Rheogram to predict the viscosity of bitumen at any desired temperature and shear rate. It was found that C–Y model could be successfully applied to viscosity–shear rate master curves for all types of binders. Exponential model yielded good fit for zero shear viscosity and the model parameters were found to be binder specific. Lower mixing and compaction temperatures were obtained for modified binders, which decreased with increase in shear rate. A more practical method of obtaining mixing temperatures for bitumen is pre- sented and discussed. Ó 2015 Elsevier Ltd. All rights reserved. 1. Introduction Modification of bitumen is one of the several techniques to improve the structural performance of bituminous mix [1–4]. Polymer modified binders have been successfully used to amelio- rate the viscoelastic response of bitumen, especially at higher tem- peratures [1,5,6]. When it comes to applicability, contractors and practitioners remain skeptical, mostly due to the high mixing and compaction temperature requirements for these binders. Increase in cost is another main concern. Traditionally, rotational viscometer is used for evaluating the mixing and compaction tem- peratures of bitumen. The viscometer applies 6.8 s 1 (20 rpm) shear rate and the resulting torque is utilized to calculate the vis- cosity of the binder at different temperatures. The log–log plot of viscosity versus temperature is used to find the temperatures corresponding to 0.17 ± 0.02 Pa s and 0.28 ± 0.03 Pa s. These tem- peratures are used for mixing and compaction of bituminous mix. NCHRP report 648 [7] presented new methods for evaluating the mixing and compaction temperatures for modified binders, which resulted in reduction of temperature requirement by 20–30 °C, as compared to the conventional method. In the first method named as ‘‘Phase Angle Method’’, the mixing and compaction temperatures are established by construction of phase angle master curve at 80 °C. Phase angle is more sensitive to chemical changes, as found in modified binders [1]. So it is rather difficult to construct a smooth master curve for phase angle, which results in a ‘‘wavy nature’’ (attributable to the transition and plateau regions) [1,3–5,8,9]. Moreover the use of frequency corresponding to 86° seems to have no practical significance. In the second method named as ‘‘Steady Shear Viscosity Method’’, Dynamic Shear Rheometer (DSR) is employed for finding the viscosity at 500 Pa shear stress at different temperatures. Extrapolation of the viscosity data is made for pre- dicting the mixing and compaction temperature. The extrapolation http://dx.doi.org/10.1016/j.conbuildmat.2015.04.001 0950-0618/Ó 2015 Elsevier Ltd. All rights reserved. ⇑ Corresponding author. E-mail address: niks.iitkgp88@gmail.com (N. Saboo). Construction and Building Materials 87 (2015) 38–44 Contents lists available at ScienceDirect Construction and Building Materials journal homepage: www.elsevier.com/locate/conbuildmat