influence of aging on evolution of structure, morphology and rheology of base and sbs modified...

Influence of aging on evolution of structure, morphology and

rheology of base and SBS modified bitumen

Surya Pavan PyndaCE12B049

1.INTRODUCTION

What is SBS ?

▸ Family of synthetic rubber derived from styrene and butadiene

▸ It is added to base bitumen to make polymer modified bitumen which has better properties

Objective

▸ Various tests have been carried out on base and modified bitumen like▹ Fourier Transform Infrared (FTIR)▹ Atomic Force Microscopy (AFM)▹ Dynamic Shear Rheometer (DSR)▹ Rolling Thin Film Oven (RTFO)▹ Pressure Aging Vessel (PAV)

▸ The objective is to see how structure, morphology and rheology of base and modified bitumen changes due to aging.

▸ FTIR - Structure▸ AFM - Morphology▸ DSR - Rheology▸ RTFO - Short Term Aging▸ PAV - Long Term Aging

2.Materials and Experiments

Materials

▸ Base Bitumen - AH70▸ Modified Bitumen - PG 70, PG 76

Fourier Transform Infrared

▸ A technique used to find infrared spectrum of absorption of solid, liquid or gas

▸ Shines beam of different frequencies at once. Measures how much is absorbed.

▸ Next beam has different combination of frequencies. Repeat this process to get different data points.

▸ All the data is processed to infer absorption at each wavelength.

▸ Change in chemical structure of a material can be found by measuring indices at different points.

Atomic Force Microscopy

▸ Technique to measure roughness of a sample surface at high resolution

▸ Probe is moved along X-Y axes ▸ Movement along Z axis takes place due to the

sample and is traced by laser on a photodiode

Dynamic Shear Rheometer

▸ Used to characterise viscous and elastic behaviour of asphalt binders

▸ Uses thin asphalt binder sample between two circular plates

▸ Lower plate is fixed while upper plates oscillates back and forth to create shear action

Rolling Film Thin Oven

▸ Provides simulated short term aged asphalt binder for physical property testing

▸ Gives a quantitative measure of volatiles lost during testing

▸ Procedure is outlined in ASTM D 2872 and AASHTO T 240

▸ Has a problem with high viscous binders as they do not flow properly when rotated

Pressure Aging Vessel

▸ Provides simulated long term aged asphalt for physical property testing

▸ Exposed to heat and pressure to simulate 7 to 10 years of in service aging

▸ Procedure is outlined in AASHTO R 28▸ Process is carried out after RTFO

Base Bitumen - AH 70 - Specifications

Modified Bitumen - PG 70 and PG 76 - Specifications

Characteristics of sample bitumen

Aging and DSR Procedure

▸ RTFO test is carried out using standardised procedure

▸ PAV test is carried out at 60℃ instead of 90℃ - 110℃ and aging time is varied from 600, 1200 to 2000 hours

▸ DSR temperature sweep done at 10 rad/s from 5℃ to 80℃ with a temperature increment of 2℃/min

▸ For tests at 35℃ or higher, 1 mm gap and 25 mm diameter plate were used while for tests below 35℃, 2 mm gap and 8 mm plates were used

3.Results

Evolution of chemical structure

▸ FTIR is used to monitor evolution of chemical structure of bitumen

▸ Absorption peaks at▹ 1700 cm-1 - Carbonyl▹ 1030 cm-1 - Sulphoxide▹ 968 cm-1 - Butadiene


▸ Peaks at 1700 cm-1 and 1030 cm-1 are present only in unmodified binders but modified binder has an extra peak at 968 cm-1

▸ Peaks at 1700 cm-1 and 1030 cm-1 increases while peak at 968 cm-1 decreases in unaged, RTFO and PAV samples

▸ More carbonyl and sulfoxides are formed as aging increases while amount of butadiene decreases as aging progresses


▸ During aging oxidation, dehydrogenation and crosslinking occur at the same time

▸ More severe oxidation causes more carboxide and sulfoxides to be formed

▸ In SBS, unsaturated midblock gives free radicals which cause degradation

▸ Comparing all kinds of binders, we can say that modified binders have less carboxyls and sulfoxides, indicating that modifiers reduce the aging effects

Evolution of morphology

▸ AFM used to find surface image of binders at different stages of loading


▸ Unmodified binders have few tubers before aging and number of tubers increased after aging

▸ Modified had relatively rough surface without obvious tubers but after aging had more but smaller tubers

▸ Rough surface is due to the network structure of SBS


▸ The bee like structure is the asphaltene micelle dispersed in the bitumen matrix

▸ In unmodified binder, these micelle exist both before and after aging but individual size increases due to aging


▸ In modified binders, micelle exists only after aging. It is absent before aging, due to the network structure of SBS

▸ During aging, SBS degrades and leads to the formation of micelle. More in number but smaller size in modified binder

Softening Point

▸ Before aging, modified binders have higher softening point due to network structure

▸ During aging, this network is destroyed while as well as asphaltenes with high molecular weight are formed

▸ Destruction of network decreases softening point whereas asphaltene formation increases it

Softening Point

▸ In the initial stages, network destruction is more compared to asphaltene increase. Hence the softening point decreases on a whole for modified bitumen

▸ After some time, as more and more asphaltene is formed, softening point increases for all bitumen

Dynamic Rheological Properties


▸ |G*| of modified binder is greater than unmodified binder at high temperature whereas |G*| of modified binder is lesser than unmodified binder at low temperature

▸ This means SBS improves the temperature susceptibility of bitumen

▸ After aging |G*| of all bitumen come closer to the same value. Hence they exhibit similar performance after aging


▸ SBS decreases the phase angle at high temperature and aging further reduces the phase angle

▸ Plateau regions are formed in modified binders▸ With increase in aging time, this plateau region is

extended to higher temperature and finally disappears

▸ This acts as an indicator of damage in polymeric structure of bitumen. During aging, as the network gets destroyed, the plateau region shifts to a higher temperature and finally disappears

▸ Consistent with results of FTIR and AFM

4.Conclusions

Conclusions

▸ From FTIR, it is found that more carbonyl and sulphoxide but less butadiene were available after aging, indicating oxidation and degradation in bitumen

▸ From AFM, we can observe how micelle and network structures are created and destroyed respectively during aging

▸ From SP and DSR, a correlation was found relating structural and morphological evolution with mechanical and rheological properties

▸ The effect of SBS is more pronounced before aging. As aging destroys the network, performance of modified binder became similar to unmodified binder.

Drawbacks

▸ In choosing samples, modified bitumen were PG 70 and PG 76 whose values are close. Instead modified bitumen with larger difference could be used to see the change across spectrum

▸ PAV aging was carried out at a temperature of 60 ℃ instead of the normal temperatures of 90 - 110 ℃. It could have been carried out in the normal range to allow for standardisation

▸ AFM was carried out for unaged and PAV aged samples. It could have been done for RTFO aged samples also to differentiate between destruction of network in short term aged and in long term aged conditions.

Thank You

Reference : Shao-peng Wu, Ling Pang, Lian-tong Mo, Yong-chun Chen, Guo-jun Zhu, Influence of aging on the evolution of structure, morphology and rheology of base and SBS modified bitumen, Construction and Building Materials, Volume 23, Issue 2, February 2009, Pages 1005-1010, ISSN 0950-0618, http://dx.doi.org/10.1016/j.conbuildmat.2008.05.004

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