Highway Research Record

Evaluation of Polymer Modified Bituminous Mixes using Wheel Tracking Test

Date of Start:June 2004
(i) Indian Institute of Technology, Kharagpur (S, C)
(ii) TU Darmstadt, Germany (I)

Scope and Objective
The present research is concerned with evaluation of properties of Polymer Modified Bitumens (PMB) used in Germany that are being supplied by British Petroleum. Three types of gradation and five different types of binders are considered. The Laboratory work consisted of finding the Dynamic shear Rheometer test parameters of different Binders and also other Binder properties. Samples for Wheel tracking test are prepared in two layers to simulate multilayer bituminous construction in the field in place of conventional single layer and a steel wheel. A 2cm thick rubber sheet is placed below the sample in the mould and tested using rubber mounted steel wheel. The permanent deformation characteristics are analysed and correlated to Binder properties related aspects.
(i) To find the visco-elastic characteristics of different binders using Dynamic shear rheometer.
(ii) To find the rutting characteristics of different mixes using Wheel Tracking test.
(iii) To rate the mixes according to their resistance to permanent deformation.
(iv) To correlate the properties of Binder with the Rut depth characteristics of Mixes.
(v) To find the effect of Polymer modification on SMA.

In this study, the Wheel Tracking Test specimen consists of a three-layer system- wearing course, binder course and a rubber sheet. The bottom layer consists of 2 cm thick rubber sheet and middle one is Binder course with AB 0/16S gradation with PMB 45 binder and top one is the wearing course made of different mixes. Both rubber sheet and Binder course mix remain the same for all the tests and different specifications of wearing courses are used in the investigation. Samples are tested at 50oC.

Findings and Conclusions

The results of the laboratory investigation carried out the different aspects of the performance of the different binders and mixes are as follows.

1. The inferences drawn from the laboratory investigation carried out on Binder properties:
(i) Dynamic shear modulus, G*, of a PMB named ‘Olexobit 25’ is highest. Its stiffness is highest compared to other binders     hence it is better suited to resist deformation. Phase angle (ä) of Olexobit SMA is least and therefore it is more elastic than     other binders and hence has greater elastic recovery. On combining these two factors as can be seen G*/sinä value of     Olexobit 25 is much higher and hence it is better suited to resist rutting and perform better at higher temperatures and     followed by that Olexobit SMA is better.
(ii) The temperature susceptibility of Olexobit 25 is lower than other binders followed by Olexobit SMA.
(iii) Based on the Softening point values it can be said that Olexobit 25 should behave better at higher temperatures then      followed by Olexobit SMA because of their higher softening points.
(iv) Based over all binder properties Olexobit 25 is better in resisting deformations at higher temperatures, followed by Olexobit      SMA.

2. The inferences drawn from the Wheel Tracking test
(i) Based on the Rut depth values after 20000 passes AB 0/11S (German specification) mix with Olexobit 25 is better in re      sisting Permanent deformation but looking at rate of rutting mixes with Olexobit SMA and Olexobit 45 are better in long      term performance.
(ii) Olexobit SMA is best in the long run and rutting of mixes with other binders are higher, converging to a single value.
(iii) Based on both Binder properties and Mix rut depth results, it can be concluded that Olexobit SMA is better in resisting       permanent deformation than other used binders.
(iv) It is clear from the Wheel tracking test results of Stone mastic asphalt for 50/70 binder that SMA is much better in       resisting Rutting than Asphalt Concrete.
(v) It is observed that effect of polymer modification in resisting permanent deformation is more in case of Asphalt concrete      and is almost nil in case of Stone Mastic Asphalt.
(vi) It can be concluded that effect of polymer modification in improving mix rut resistance is very less in case of Stone Mastic      Asphalt.

3. Correlation of Binder properties with Mix Rut depth
(i) It is observed that the correlation between Mix Rut depth and softening point of binders is very high with a r2 value 0.81

(ii) The correlation between the Dynamic shear modulus G* of the 5 binders and rut depth of 5 mixes was poor. The r2 was      0.598. But the correlation with phase angle (δ) is relatively good with r2 value being 0.67.

(iii) The correlation between the High temperature stiffness (G*/sinδ) with Mix Rut depth is poor with r2 0.59. Therefore      G*/sinδ is not a correct parameter to judge the binders rutting resistance characteristics. But on other hand instead of      using G*/sinδ if we use G*/tanδ the r2 value increases to 0.63, which is relatively acceptable.