Aaron Nolan

Rheological Properties of the Polymer Modified Bitumen with Emphasis on SBS Polymer and Its Microstructure

The rheological properties of bitumen are improved by addition of small quantities of polymers. A review of different polymers such as styrene-butadiene-styrene (SBS), styrene-butadiene-rubber (SBR), ethylene vinyl acetate (EVA) and poly phosphoric acid (PPA) with emphasis on SBS and its microstructure is presented in this paper. The polymers are divided into two groups: elastomers and plastomers. SBS, an elastomer, has shown greater potential compared to other modifiers when blended with bitumen and improves the mechanical properties and rheological behavior of conventional bitumen. SBS is made up of styrene and butadiene monomer units. It was found that maltene interacts preferentially with the polybutadiene unit of SBS, whereas asphaltene interacts predominantly with the polystyrene unit. SBR is another elastomer which also has polystyrene and polybutadiene units with a different structural make up. EVA is a plastomer which when blended with bitumen has improved the rheological properties and stability, provided the asphalt has asphaltene content below a critical level. PPA is a liquid mineral polymer. Addition of PPA to asphalt contributes to more interactions within the asphaltenes network, thus increasing the elastic behavior. A study was also conducted to determine the influence of asphaltenes and maltenes on the rheological properties of polymer modified binders.

Development of Blending Chart for Different Degrees of Blending for Reclaimed Asphalt Pavements in HMA

The demand to utilize higher percentages of reclaimed asphalt pavement (RAP) in the construction of hot mix asphalt (HMA) pavements continues to rise. Utilization of RAP in HMA is an environmentally friendly and cost effective method of recycling. At high percentage of RAP properties of RAP binder and its interaction with virgin binder plays critical role. Researchers have consistently shown that when RAP is mixed with virgin binder and aggregates, partial blending occurs, that is, something between 100% blending and the “black rock” effect occurs. Impact of partial blending on new virgin binder content is apparent which may cause under-asphalted mixture, resulting in poor pavement performance. Also influence of partial blending on final grade of RAP mix and allowable percentage of RAP has not been evaluated. The purpose of this paper is to develop the blending chart for different degree of blending to study the impact of partial blending on final grade of blended binder. To achieve the objective, blending chart for 100%, 70% and 50% RAP has been developed for PG 70-28 and PG 58-28 binder by carrying out binder study.

A Study to Evaluate the Effects of SBS Polymer Modification on the True Grade of an Asphalt Binder

Polymers are currently added to asphalt to increase characteristics that essentially improve the life of the asphalt. One polymer commonly added to asphalt is styrene-butadiene-styrene (SBS). This polymer is common due to its elastic properties that increase viscosity, elastic response, and complex modulus. Although this is known, the current PG grading system may not adequately show the attributes of polymer modified asphalt. Historically, additional tests, known as PG Plus tests, have been performed on polymer modified asphalt to ensure the asphalt has been modified to the end user specification. The new multiple stress creep and recovery (MSCR) test has been proposed to eliminate the proliferation of plus specifications throughout the states. The current performance grading specification, AASHTO M320, and the elastic recovery test were compared to the new MSCR grading specification, AASHTO MP-19, to ascertain a more appropriate grading system. This will be studied by taking in-house polymer modified binders (PMB) that were developed and verified to have achieved full interlocking by use of fluorescence microscopy and measuring the mechanical properties of the in-house PMB to obtain the continuous grade of the binders. The addition of polymers increased the rheological properties and high grades of the base binder, as well as increasing the traffic grades of the proposed MP 19 specification. Although, the low PG grade was not changed, the continuous grading system showed that addition of polymer did, in fact, change the low-temperature properties of the binder.

Fatigue Behavior of Neat and Polymer-Modified Binders and Mastics

The purpose of the study is to determine the influence of strain amplitude and filler on long term-aged neat and polymer modified binders using two different methods of analysis. The strain amplitudes tested were 0.5% and 1.5%. The filler content for the mastic binder was 3% dust to binder by mass. The paper will compare the fatigue life of the neat and modified PAV-aged binders and mastics, and determine the influence of strain amplitude, and filler on fatigue life. The lesser the strain amplitude, the longer is the fatigue life. Adding 3% filler to neat binder shortens the fatigue life. However, adding 3% filler to a modified binder will lengthen the fatigue life. The impact of addition of dust to the binders on fatigue life is dependent on whether the binder is modified or not.

Correlation between PG Plus, Superpave PG Specifications and Molecular Weight from GPC for Different Polymer Modified Binders

The purpose of this paper is to present a correlation of Multiple Stress Creep and Recovery (MSCR) parameters with elastic recovery and molecular weight of different polymer modified binders (PMB). The MSCR test which was recently developed by Federal Highway Administration (FHWA) enables one to correctly grade the field performance of polymer modified asphalts. The polymer modification of asphalts is one of the solutions to overcome the asphalt pavement defects such as rutting, thermal cracking, fatigue and stripping. However, the different polymer modified asphalts can behave differently even though they have the same performance grade. The MSCR test measures the high temperature binder specification parameter called non-recoverable creep compliance or J nr , and percent recovery. In this study eight different polymer modified binders are measured. The molecular weights were determined using Gel Permeation Chromatography (GPC). The correlation of the MSCR results with the molecular weight will provide an insight into how modification effects mechanical response and the rutting potential as measured from MSCR.