Evaluation of an Improved Rotavapor Aging Apparatus Using a Morton Flask for Simulation of Hot-Mixing on Modified Asphalts

A modified Rotavapor apparatus and method had been previously developed at the University of Florida for simulation of short-term aging of modified asphalts. Due to the great potential of this aging procedure, further refining of this procedure had been undertaken. This paper presents the evaluation of an improved Rotavapor aging apparatus using a Morton flask. It was observed that greater temperature uniformity was obtained in the oil bath when the Morton flask was used. The equivalent aging severity between the modified rotavapor aging process and the standard short-term aging methods (TFOT and RTFOT) was established. INTRODUCTION Only two methods which simulated hot-mix plant aging of asphalt have been adopted as standard methods by ASTM and AASHTO. These are the Thin Film Oven Test [(TFOT), ASTM D1754, AASHTO T179 ] and the Rolling Thin Film Oven Test [(RTFOT), ASTM D 2872, AASHTO T240 ]. Both TFOT and the RTFOT processes are intended to simulate aging which occurs during hot mixing in a hot-mix plant operated at 150 °C. These two standard processes have been successfully used to age conventional asphalts for years. However, problems have been reported [1, 2, 3] with these two standard processes when modified asphalts are used. Due to the increasing use of GTR-modified asphalts and potential use of other modified asphalts in Florida, it is necessary that a laboratory process be developed to replace TFOT or the RTFOT, so that the aging characteristics of these modified asphalts could be properly determined. To solve the problems with TFOT and RTFOT processes when modified asphalts are used, an alternative short-term aging method using a Rotavapor apparatus was developed to simulate hot-mix plant aging of modified asphalts at the University of Florida [4]. Further refining of the developed aging method was undertaken. This paper presents the evaluation of the aging characteristics of an improved Rotavapor aging apparatus using a Morton flask. BACKGROUND Due to the shortcomings of the TFOT and the RTFOT processes with modified asphalts, studies were conducted by the researchers to develop alternative short-term aging procedures for modified asphalts. Bahia et al. [5] modified the RTFOT process to solve the problem of highly viscous asphalts. In this method, RTFOT was modified by using some steel rods International Balkans Conference on Challenges of Civil Engineering, BCCCE, 19-21 May 2011, EPOKA University, Tirana, ALBANIA inside the RTFOT bottles to spread the thin films uniformly. In a previous study at the University of Florida [4], rotavapor apparatus, which is commonly used for the recovery of asphalts from solutions and as an aging device in a German standard test (DIN 52016) for determining changes in mass and changes in the properties of asphalt due to heating, was modified to be used for simulating hot-mix plant aging of modified asphalts. The schematic representation of the modified rotavapor aging apparatus is shown in Figure 1. In the previous study, asphalt binder was aged in a standard distillation flask. However, it was observed that there were some advantages of using a Morton flask in place of the standard distillation flask in the modified rotavapor aging process. The Morton flask has two advantages over the standard distillation flask, as follows: 1. It provides better agitation of thin films inside the flask. 2. It reduces the temperature variation by stirring the oil in the oil bath.