brusava tanmoy term paper cvl740

DIFFUSION OF

REJUVENATORS / VIRGIN BINDER DURING RECYCLING PROCESS

Brusava Kumar Swain1, Tanmoy Das2

1Indian Institute of Technology Delhi, Transportation Engineering Department of Civil Engineering, IIT Delhi, Hauz khas, New Delhi – 110 016, Entry Number: 2015CEP2090, PH (+91) 9910020793; email: [email protected] Institute of Technology Delhi, Transportation Engineering, Department of Civil Engineering, IIT Delhi, Hauz khas, New Delhi – 110 016, Entry Number: 2015CEP2101, PH (+91) 9599451268; email: [email protected]

ABSTRACT

Rejuvenators are products that have been used to remedy the deformation effects of aging to the exposed surface of Asphalt and to restore ductility and adhesion properties of aged binder. The evaluation for rate of diffusion into aged asphalt was done by determining the penetration test and chemical components of aged bitumen with rejuvenator coat before and after diffusion process. Investigation in regards to effects of temperature, time and viscosity of rejuvenator, the ability of diffusion into aged bitumen were carried out. On review of various results, it indicated that, diffusion of rejuvenator into aged bitumen could be increase with increasing of temperature and time of diffusion. Low viscosity Rejuvenator diffused into aged bitumen more easily.

Keywords: RAP, Rejuvenator, Virgin Binder

1.0 INTRODUCTION

Reclaimed Asphalt Pavement (RAP) is the process of reusing the existing bituminous materials that minimize the use of natural resources. The use of recycled materials in pavements has become an increasingly widespread practice in every corner of world.

Reclaimed asphalt is a useful alternative to virgin material because it reduces the need to use fresh aggregates which is treated as a scare in many places in today’s scenario. It also reduces the percentage of costly new asphalt binder required for paving mix.

Even if at end of the service life of the used aggregates and binder from old asphalt pavements are still valuable. Now, rejuvenator is one of the recycling agent which is suitable for highly oxidized and mixture containing a large amount of RAP. Rejuvenator of bitumen is replacement of the oil or volatile matter that lost during aging process and on the rebalancing of bitumen compositions so it becomes no longer brittle. The working mechanism (or diffusion process) of a rejuvenator consists of the following steps (Soohyok Im a, Fujie Zhou b, Robert Lee c, Tom Scullion b 2014):

The rejuvenator forms a very low viscosity layer that surrounds the asphalt coated aggregate which is highly aged binder layer.

The rejuvenator begins to penetrate into the aged binder layer, decreasing the amount of raw rejuvenator that coats the particles and softening the aged binder.

________________________________a Texas A&M Transportation Institute, Flexible Pavements – CE/TTI, Room 309G, 3135 TAMU, College Station, TX 77843-3135, United Statesb Texas A&M Transportation Institute, College Station, TX 77843-3135, United Statesc Texas Department of Transportation, Austin, TX 21915, United States of 10

No raw rejuvenator remains, and the penetration continues, decreasing the viscos-ity of the inner layer and gradually increasing the viscosity of the outer layer.

However, the addition rejuvenator percentage may be crucial to the properties of the blended aged asphalt. Rejuvenator should be mixed properly so that the properties under low temperature should improve while the properties under high temperature are not adversely affected. A successful use of rejuvenators should reverse the RAP binder aging process by restoring the properties of asphalt binder for another service period and make the RAP asphalt fully available to the mixture. The selection and content determination of the rejuvenator was usually based on performance tests of the recycled asphalt, which is composed of aged asphalt and the rejuvenator.As stated in the report Tao Ma, Xiaoming Huang, Yongli Zhao, and Yao Zhang (2015) aged asphalt was extracted and recovered from the RAP and then blended with the rejuvenator to obtain recycled asphalt. Performance tests were conducted on recycled asphalt to determine the proper type and content of rejuvenator. But during implementation at site the rejuvenators generally added to the RAP and then blend with fresh aggregate and virgin binder to make a recycled asphalt mix. The total blending procedure happens as low as 60-90 sec. Studies found that when 10–50% of the rejuvenator by the weight of the aged asphalt in the RAP was poured into the RAP directly, it can take 48–144 h for the rejuvenator to fully diffuse into the RAP. So it is very obvious that as the blending duration is very low at actual site as compared to the laboratory blending, mixing quality of rejuvenator with the RAP mix will be worse or below desired level. It can lead to improper mix design and may cause premature failure during implementation at site.It can be stated in other aspects like the mix design procedure has to be modified to determine the optimum dose and type of the additive based on the available RAP binder properties (Martins Zaumanis a, Rajib B. Mallick a, Robert Frank b 2013). So the findings of this paper can help to evaluate and explain the performance of rejuvenator in the recycled asphalt mixture.

2.0 LITERATURE REVIEW

2.1. Motivation

Application of RAP materials in new implemented pavements has gained a lot of interest due to the rise in crude oil prices during the last decade, limited aggregate resources and also for the sake of sustainability. Using recycled material in asphalt concrete is advantageous to preserve natural and energy resources and environment friendly.

Using RAP is preferred over the fresh material considering the increasing the cost of asphalt, shortage of aggregate sources and environmental considerations and lower cost comparing to fresh Hot Mix Asphalt (HMA) mixes. It may reduce the initial cost of mixture by 14 to 30 % after adding of 20 to 50% of RAP materials (Kandhal and Mallick 1997). Another benefit of using RAP is to reduce the waste produced and provide a good solution for disposal problems of highway construction materials (Al-Qadi, Elseifi and Carpenter, Reclaimed Asphalt Pavement - A literature review 2007). Due to oxidation and repetitive loading, the performances of asphalt pavements need to be replaced or rehabilitated. The unusable HMA layer is milled or excavated, crushed and screened to satisfy the gradation of the new designed HMA layer. The recycled material is added to aggregates during the HMA production. Higher

_______________________________________________a, b Worcester Polytechnic Institute (WPI), Worcester, MA, United Statesc Compliance Monitoring & RAP Technologies, Linwood, NJ, United States of 10

content of RAP used in the HMA will improve its rutting susceptibility while initiates some other issues such as low temperature and fatigue performance.

2.2. Review

Karlsson R. and Isacsson U. (2003) conducted a study on diffusion of rejuvenators into aged asphalt. The experiments were performed using two different procedures. A relationship was developed between penetration and aging time. The diffusion was monitored using commercial rejuvenator. The results showed that the increase in polarity and molecular size of the rejuvenators reduces the rate of diffusion. It was also indicated that, the diffusion rate is controlled by viscosity of maltene phase rather than whole binder. Therefore, as aging has small effect on viscosity of maltene and hence diffusion process is not affected significantly by aging. The second procedure to determine the diffusion rate by Dynamic Shear Rheometer (DSR) test. A mathematical solution of Fick's law and an assumption of a diffusion coefficient were used. Then, the obtained concentrations were fitted to experimental data using theoretical calculations of viscosity and complex modulus (G*). Using fitting curves and back calculation of the concentration, a single diffusion coefficient was determined for each mixing temperature. The results indicate that, diffusion determined by FTIR-ATR method happens with change in rheological properties. The results differ slightly but still are in the same order. It was assumed that the rate of diffusion in binder is enough to create a homogenous reclaimed binder during the recycling process.

J.W.H. Oliver (1975) conducted a study on diffusion using tritium labeling with aged asphalt. The objective of study was to investigate the possibility of replacing the aged binder at existing asphalt with oil spray. A 0.5 cm thick cylinder of asphalt binder was covered by a very thin layer (less than 1 μm) of tritium labeled diffusing material. After certain times, the samples collected by slicing. The radioactivity was inspected in different depths, and diffusion coefficient was calculated. It was found that although molecular weight is important for diffusion process, the molecular shape is also influences. Moreover, the result indicates that, the dodecyl benzene with a lower molecular weight diffused faster than the oils with heavier molecular weight.

A research paper by Imad L. Al-Qadi, Mostafa A. Elseifi, Samuel H. Carpenter (2007) shows the rejuvenation process in RAP material. Extracted binder was used to examine the rate of diffusion of rejuvenator with the RAP binder. It was observed that, the high-viscosity film thickness of RAP binder is surrounded by the low viscosity rejuvenator layer. Next, the rejuvenator begins penetrating in the aged binder and softens the old binder. After a while, no raw rejuvenating agent remains and the diffusion process still continues. The viscosity of inner layer of the film thickness is lowered due to rejuvenator and the viscosity of the outer layer is increased. The stiffness of outer layer increases while the inner layer softens.

Zaumanis and Mallick (2013) conducted study for use of optimum dose of rejuvenator. It was found that, the softening level of the aged binder depends on the parameters and types of rejuvenators used, but is not limited to viscosity. Refined tall oil as a rejuvenator was up to four times more effective than the virgin binder. The dosage of the rejuvenator changes the time to reach equilibrium condition. However,

of 10

the total diffusion time at 145oC according to simulation is sufficient. Simulation of staged diffusion, considering "black rock" effect may give more realistic results.

If the diffusion process has not been complete before opening to traffic because of insufficient time or low temperature, due to non-homogeneity of film will have lower viscosity which can lead to lower stiffness and instability under traffic.The simulation results only partly correlate with the bitumen and mix testing data, suggesting that diffusion is only one of the processes taking place. The others include mechanical mixing and homogeneous dispersion of the rejuvenator.The penetration test after addition of rejuvenators and the mechanical tests of asphalt mixture confirm that rejuvenators are much more effective in improving the performance of aged binder compared to addition of softer virgin binder.

3.0 MATERIALS

Because of the presence of stiffer (aged) binders, high RAP content mixes are perceived to be more susceptible to cracking failures and less workable than virgin mixtures. To overcome the above, different types of rejuvenator are used for RAP. Some of those material and their properties are described below in Table 1.

Table 1. Rejuvenator types and properties

Type of Rejuve-nator

Visco-sity at 135°C

Spe-cific

gravity

Engi-neered

/ Generi

c

Petrole-umum /Organic

Refin-ed /

Waste

Molecu-lar struc-ture

Polar-ity

Traditio-nal /Novel

Nustar PG 64-22

474 1.02 Generic

Petrole-um

Re-fined

Ring and Strand

Mixed Tradi-tional

Aro-mat-ic Extract

9.2 0.995 Generic

Petrole-um

Re-fined

Aroma-tic Ring

Very Tradi-tional

Waste Engine Oil

3.86 0.872 Generic

Petrole-um

Waste Alipha-tic

Slight Tradi-tional

Dis-tilled Tall Oil

5.6 0.95 Generic

Organic Re-fined

Ring and Strand

Mild Tradi-tional

WV Grease

4.28 0.924 Generic

Organic Waste Ring and Strand

Mild Novel

WV Oil 5.17 0.917 Generic

Organic Waste Ring and Strand

Non Novel

Or-ganic Oil

5.43 0.947 En-gine-ered

Organic Re-fined

Ring and Strand

Mild Tradi-tional

4.0 METHODOLOGY

of 10

Because of the presence of stiffer (aged) binders, high RAP content mixes are perceived to be more susceptible to cracking failures and less workable than virgin mixtures. The current practice of using softer binder grade to compensate for aged binder is costly.

DiffusionThe arbitrary motion of molecules (called Brownian motion) causes mass

transfer in the medium. To initiate this motion, the molecules should gain enough energy to move through the matter. This is known as diffusion and it can be affected by several factors, such as the shape and size of molecules, temperature, forces between molecules, bonding energy of diffusing molecules (Cussler 1997). According to Cussler, the diffusion rate has an inverse relationship with the viscosity of the fluid.

The diffusion of material is defined by diffusion coefficient indicating the mobility of material due to diffusion. Theoretically, the diffusion coefficient is calculated using first and second Fick’s laws.

Fick’s law for determining Diffusion coefficient

“Diffusion is the process by which matter is transported from one part of a system to another as a result of random molecular motion” (Crank 1975). Diffusion is process which an amount of a particular material transfers inside the other material due to Brownian motion of molecules. Diffusion coefficient is defined as amount of diffusing material across a unit area during 1 second,

Fick (1855) adjusted the same equations as used for heat conduction and put it in quantitative basis to calculate the diffusion. The basic assumption of the mathematical theory of diffusion is an isotropic substance; therefore, the rate of transfer of diffusing matter through the unit area is proportional to the perpendicular gradient of concentration measured in the section: As per Fick's first law, the diffusive flux from high concentration to low concentration, with a magnitude that is proportional to the concentration gradient.

∂ø J= - D ----------- - - - - - Eqn. 1

∂ xWhereJ= Diffusion in m2/SD= Diffusion coefficientø = Concentrationx= Distance

If the diffusion coefficient (D) is considered constant, the Fick’s second law for diffusion is should use as given below. The second law is time dependent. Fick's second law predicts how diffusion causes the concentration to change with time.

∂ø ∂2ø ------- = D --------- - - - - - Eqn. 2

∂ t ∂ x2

Whereø = Concentration of diffusing materialt= TimeD = Diffusion coefficient x= Distance

5.0 PROCEDURE OF TESTING

of 10

5.1 ProcessMartins Zaumanis and Rajib B. Mallick (2013) established the diffusion of rejuvenator

with aged asphalt (from RAP) in their paper study.The diffusion process was simulated by the help of finite element (FE) modeling, analysis and simulation using COMSOL "Multiphasic" software. The analysis was conducted with temperature transfer module. The research presents simulation of rejuvenator diffusion into aged binder film extracted from RAP. The process had been done assuming 100% RAP without any virgin asphalt. Different rejuvenators (Refined tall oil, Paraffin base oil, Brown grease and Yellow Grease) and aged RAP binder were tested to obtain the required input data for simulation - viscosity at different temperatures and molecular weight. Different temperatures were simulated for three rejuvenator dosages. The final viscosity for complete diffusion and the required time to reach this state was determined. The results show significant differences in the softening potential of different rejuvenators and temperature range to reach homogeneous concentration within the binder film before the production process is completed. Further, the results are compared with mechanical tests of binder penetration and mixture creep compliance to confirm the softening effect.Film thickness, volume and concentration of the rejuvenators are required for FE calculation.After obtaining the parameters of all Rejuvenators, extracted asphalt from RAP, the following process has to be done.

The diffusion processes is required to be observed at different time interval. The concentration of rejuvenator and viscosity of the resultant binder at each time

intervals of the RAP binder have to be determined. Total time of the simulation to reach homogeneous concentration and viscosity.

5.2 TestingMartins Zaumanis and Rajib B. Mallick (2013) carried out modeling and

simulation for diffusion test assuming that no virgin binder and aggregate is going to be used in the mix i.e. 100% RAP to be used with rejuvenator. The in plant mixing process very strongly depend on two main characteristics i.e. heating temperature and time of heating / duration.

In this research to simulate the mixing efficiency of the rejuvenator and the RAP, the Reclaimed Asphalt material has been heated at different temperature (145oC, 120oC and 95oC). The kinematic viscosity of four different types of rejuvenators has been worked out at different temperature. The aged binder from the RAP mix has been extracted and tested for penetration at 25oC and kinematic viscosity at 135oC. The penetration data has been converted in to viscosity by using the procedure by Davis (1981). The outcome values of viscosity of rejuvenator and aged binder has been given in the following Table 2.

Table 2: Viscosity of rejuvenators and bitumen

Product Viscosity, Pa-s

60oC 95oC 120oC 135oC 145oC

Extracted RAP binder

344.71* 14.92 4. 12 2.31* 1.65

Virgin AC-20 binder**

198.44* 3.5

0.78 0.40* 0.28

Refined Tall Oil 0.0277 0.0055* 0.0033 0.0027 0.0025 *Paraffinic base oil 0.0529 0.0054* 0.0029 0.0023 0.0

021*

of 10

Brown Grease 0.0438 0.0085* 0.0049 0.0040 0.0035 *Yellow Grease 0.4326 0.0092 * 0.0058 0.0048 0.00

43**Test temperature**Viscosity obtained from source (Houston 2006)

Ref: Martins Zaumanis and Rajib B. Mallick (2013) “Finite Element Modeling of Rejuvenator Diffusion in RAP Binder Film - Simulation of Plant Mixing Process”. For finite element modeling the parameters of rejuvenator (Film thickness, volume and concentration) has been worked out and given in Table 3 below. Table 3: Rejuvenator parameters

Product Descrip-

tion

Spe-cific

gravity

Dosage

%

Film thickn-ess, μm

Mass in 2500 g

Sample, g

Mo-lecular weight, g/mole

Volume, m3

Num-ber of moles, mole

Con-cen-tra-

tion, mol/m3

Refined Tall oil

0.90* 1 1.14 25 283* 2.80E-05

8.90E-02

31 86

Paraffinic base oil

0.88* 1 1.16 25 395 * 2.80E-05

6.30E-02

2228

Brown Grease

0.92* 1 1.11 25 77 1 2.70E-05

3.20E-02

1193

Yellow Grease

0.92* 1 1.1 1 25 2442 2.70E-05

1.00E-02

377

AC-20 1.02* 1 1.00 25 730 2.50E-05

3.20E-02

1320

*Provided by the producer material data sheetsRef: Martins Zaumanis and Rajib B . Mallick (2013) “Finite Element Modeling of Rejuvenator Diffusion in RAP Binder Film - Simulation of Plant Mixing Process”. The aged binder parameter as shown in this literature given below Table 4.Table 4: Parameters of the aged binder

Parameter Value

Specific gravity 1.02Film thickness, μm 9.00Molecular weight, g/mole 877.2Thermal conductivity, W/m-K 1.0Specific heat capacity, J/kg-K 1006Molecular radius, m 3.00E-10

Ref: Martins Zaumanis and Rajib B. Mallick (2013) “Finite Element Modeling of Rejuvenator Diffusion in RAP Binder Film - Simulation of Plant Mixing Process”.

The simulation process output (Time vs. viscosity and film thickness vs. viscosity) from this research has been shown on the following two figures (Fig. 1 and Fig. 2)

of 10

Fig. 1 The viscosity at different times for 1% Brown Grease

Fig. 2 Viscosity at 145oC through film thickness at 20 sec for yellow grease rejuvenator

From the Fig. 1 above it is clear that for the initial phase with the increase in time the viscosity gets reduced and after that remains constant. This is due to that till that time rejuvenator does not reached in to the contact point of aged binder and aggregate interface. In the next phase due to the diffusion process the rejuvenator softens the bitumen and kept constant for few seconds (205 to 215). It means that maximum softening point has been reached. Fig. 2 states that due to the diffusion process at constant temperature the rejuvenator penetrates in the aged binder resulting increased film thickness. This process continues until a homogeneity level reaches. The kinematic viscosity (at 145oC) performance of the aged binder with varying dosage of rejuvenator has been evaluated in this paper and shown in the following Fig. 3.

Fig. 3 Viscosity at different dosages Fig. 4 Required time to reach equilibrium at different rejuvenator dosages

Ref: Martins Zaumanis and Rajib B . Mallick 2013 “Finite Element Modeling of Rejuvenator Diffusion in RAP Binder Film - Simulation of Plant Mixing Process”.

From Fig. 3 it is evident that as the aged binder quantity and binder parameters are constant the paraffin base oil and refined tallow has highest softening performance as compared to yellow grease and Virgin AC 20 binder. As analysed, Martins Zaumanis and Rajib B. Mallick (2013), time that required at balanced viscosity that also depends on the type of rejuvenator used. More broadly when the concentration and viscosity remains constant for a particular rejuvenator, the weight and volume gets increased. So as shown in Fig. 4 as the concentration of yellow grease is little low from other rejuvenator so it takes more time to reach the equilibrium condition.

of 10

In Martins Zaumanis and Rajib B. Mallick 2013, literature penetration values of aged binder, virgin AC 20 binder and aged binder with combination of rejuvenator and AC 20 binder has been evaluated as shown in Table 5 below.

Table 5 Parameters of the aged binder

Binder type Rejuvenator dosage, % from binder mass

Penetration @ 25oC, 1/10mm

RAP extracted binder - 16

Virgin AC-20 binder - 76

RAP binder + Refined tallow 9 84

RAP binder + Paraffinic base oil 18 91

RAP binder + Yellow grease 12 90

RAP binder + Brown grease 9 89

RAP binder + Virgin AC-20 binder 18 21

Ref: Martins Zaumanis and Rajib B. Mallick 2013 “Finite Element Modeling of Rejuvenator Diffusion in RAP Binder Film - Simulation of Plant Mixing Process”.

From above Table 5, it is clear that the rejuvenators act more effectively as compared to virgin binder. It is also to be noted that brown grease is considered as the most effective and optimal softening performer as compared to other options of rejuvenators. This may be due to as the FE analysis has been done at a temperature as high as 145oC as compared to 25oC.

6.0 CONCLUSION

In Low temperature, the Performance Grade (PG) can be reduced to level of virgin binder by addition of rejuvenators. But in high temperature, it is difficult.

The rejuvenators are more efficient than normal binder to reduce the viscosity of aged asphalt. But it depends upon the process time of diffusion.

The % increases of dosages of rejuvenator will decrease the time of processing for diffusion.

Considering "black rock" effect, staged diffusion process should be allowed to in-crease the penetration depth and will give more realistic results.

The dilution process must be completed before opening to traffic. Due to insufficient time, the outer layer will have lower viscosity which will tend to failure of the sur-face.

The mechanical test for penetration after addition of rejuvenators indicates that, the rejuvenators are much more effective to improve the performance of aged binder as compared to addition of softer binder.

The rejuvenator with lower viscosity has better ability to diffuse but bad stability against temperature variability.

Some study also indicates that, the skid resistance of rejuvenator used pavement sur-face is lower than virgin binder.

of 10

The rejuvenator should not use on the pavement surface having excess binder con-tent. When excess binder is present on the surface and will soften by reducing the viscosity and the surface to become tacky and slippery.

REFERENCES

[1] Im, S., Zhou, F., Lee, R., Scullion, T. (2014). Impacts of rejuvenators on perfor-mance and engineering properties of asphalt mixtures containing recycled materi-als.

[2] Ma, T., Huang, H., Zhao, Y., Zhang, Y. (2015). Evaluation of the diffusion and distribution of the rejuvenator for hot asphalt recycling.

[3] Karlsson, R. and Isacsson, U. (2003). Application of FTIR-ATR to Characteriza-tion of Bitumen Rejuvenator Diffusion. J. Mater. Civ. Eng., 15(2), 157–165.

[4] Zaumanis, M., Mallick, R.B., Frank, R. (2013). Use of rejuvenators for production of sustainable high content rap hot mix asphalt.

[5] Kandhal, P. S., and Mallick, R.B. (1997). Pavement Recycling Guidelines for State and Local Governments – Participant’s Reference Book, Report No. FHWA-SA-98-042, National Center for Asphalt Technology, Auburn, AL, 1997.

[6] Al-Qadi, I. L., Elseifi, M. A., Carpenter, S. H. (2007). Reclaimed Asphalt Pave-ment – A Literature Review.

[7] Oliver, J.W. (1975). Diffusion of Oils in Asphalt. Australian Road Research Board.

[8] Zaumanis, M., Mallick, R.B. (2013). Finite Element Modeling of Rejuvenator Diffusion in RAP Binder Film – Simulation of Plant Mixing Process.

of 10

brusava tanmoy term paper cvl740

Documents