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Performance of 100% RAP

Performance of 100% RAP mixes

Performance of highly recycled mixtures should be determined using performance-based test methods. See an article and a video on how to design such mixtures. 

The results are described in two articles, the first focuses on test methods more common in the US while the second on those used in Europe: 


Publications

100% Recycled Hot Mix Asphalt: A Review and Analysis, (2014), Resour Conserv Recy 92: 230-245 http://goo.gl/rXFvbr  
Influence of Six Rejuvenators on the Performance Properties of Reclaimed Asphalt Pavement (RAP) binder and 100% recycled asphalt mixtures, (2014), Cons Build Mat 71: 538-550 https://sites.google.com/site/martinszaumanis/publications/publications-pdf-files/Zaumanis%20100%20recycled%20hot%20mix%20asphalt%20Res%20Cons%20Recycl.pdf?attredirects=0&d=1  
Determining optimum rejuvenator dose for Asphalt Recycling Based on Superpave Performance Grade Specifications, (2014), Cons Build Mat 69: 159-166 http://goo.gl/Vtlb3l  
Review of very high-content reclaimed asphalt use in plant-produced pavements: state of the art, (2015), Int J  Pavement Eng 16 (1): 39-55 https://www.researchgate.net/profile/Martins_Zaumanis/publication/261875706_Review_of_very_high-content_reclaimed_asphalt_use_in_plant-produced_pavements_state_of_the_art/links/54688c050cf2f5eb1804d9a9?ev=pub_int_doc_dl&origin=publication_detail&inViewer=true  
Evaluation of Different Recycling Agents for Restoring Aged asphalt Binder and Performance of 100% Recycled Asphalt, (2014), Mater Struct  https://sites.google.com/site/martinszaumanis/publications/publications-pdf-files/Zaumanis%20Recycling%20agents%20Materials%26Structures.pdf?attredirects=0&d=1  
Rheological, microscopic, and chemical characterization of the rejuvenating effect on asphalt binders, (2014), Fuel 135: 162-171 https://sites.google.com/site/martinszaumanis/publications/publications-pdf-files/Zaumanis%20Rejuvenation%20characterization%20Fuel.pdf?attredirects=0&d=1
Evaluation of Rejuvenator's Effectiveness with Conventional Mix Testing for 100% Reclaimed Asphalt Pavement Mixtures, (2013) Transp Res Rec 2370 (1): 17-25  https://sites.google.com/site/martinszaumanis/publications/publications-pdf-files/TRR%202013.pdf?attredirects=0&d=1  
Finite element modeling of rejuvenator diffusion in RAP binder film – simulation of plant mixing process, RILEM symposium 2013, Stockholm, Sweden, 06.12-14.2013    
Low temperature properties of 100% reclaimed asphalt pavement mixtures, 5th European Asphalt Technology Association, Braunschweig, Germany, 06.03-05.2013       
Use of Rejuvenators for Production of Sustainable High Content RAP Hot Mix Asphalt, 28th International Baltic Road Conference, Vilnius, Lithuania, 08.26-28.2013
Interactive presentation of Phase I results and research plans
 

Rejuvenators

Aromatic extract

An aromatic extract is a traditional rejuvenator contain approximately 75% polar aromatic oils, resin compounds with balance less polar aromatics. Recent findings show concern with unsaturated polar aromatic ring structure, which have been shown to be carcinogenic.

Waste Engine Oil (WEO)

WEO is produced from paraffinic oil with small dose of specialty compounds to improve viscosity characteristics, stability, cleaning and flammability for use in engines. WEO may contain short chain polar molecules that break apart during lubricating service.
Refined tall oil

Distilled Tall OilDistilled tall oil is a byproduct of paper manufacture being concentrated from kraft liquors. Tall oils have a long history of use in hot mix manufacture with many emulsifiers, antistrip agents and warm mix additives.

Waste Vegetable Oil

WV​ Oil is increasingly used for bio-diesel production and has very strict compositional specifications including low free fatty acid content (<15%)​, less than 2% MIU (Moisture, Impusrities, Unsaponifiables) and no hydrogenated oils​. The product used in this study consists predominately of peanut, sunflower, and canola oils, with large concentrations of Oleic and Linolic acids.

Waste Vegetable Grease

WV ​Grease is also a food industry organic waste stream but semi solid at ambient temperatures due to predominance of saturated Lauric and Myristic triglcerides. The product used in study is also high in free fatty acids (>40%) but with its free glycerin and moisture removed industrially.

Organic Oil

Hydrogreen STM is an engineered product from PVS Meridian Technologies, Inc and is designed to be binder rejuvenator and a low temperature additive. It is composed of fast pyrolysis of pine tree biomass with other oils added to balance performance. The product is free flowing at room temperature, but slight heating may be necessary when used in cold weather.











In this phase the rejuvenator effect on restoring RAP binder and performance-related properties of rejuvenated 100 % RAP mixture were thoroughly evaluated. Six rejuvenators were used in the study: waste vegetable oil, waste vegetable grease, organic oil, distilled tall oil, aromatic extract, and waste engine oil. Test results showed that at 12 % dose most products can ensure the required binder performance grade of PG 64-22 with organic products being more effective than petroleum additives. All products provided rut resistant 100 % RAP mixture and several of them ensured cracking resistance equal to that of virgin reference mixture.



















Why use rejuvenators?

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 and does not allow to reach very high RAP doses. A successful use of rejuvenators should reverse the RAP binder aging process, restore the properties of asphalt binder for another service period and make the RAP asphalt effectively “available” to the mix, and hence allow a significant increase in the amount of RAP used in HMA mix design. However, it is necessary to carefully select the rejuvenator to provide the necessary short and long term properties, as follows. 

1. Short term. Rejuvenators should allow the production of high RAP content mixture by rapidly diffusing into the RAP binder and mobilizing the aged asphalt in order to produce uniformly coated mixtures. Rejuvenator should soften the binder in order to produce a workable mixture that can be easily paved and compacted to the required density without the hazard of producing harmful emissions. Major part of diffusion process should be completed before the traffic is allowed to avoid reduction of friction and increased susceptibility to rutting. 

2. Long term.
 Rejuvenators should reconstitute chemical and physical properties of the aged binder and maintain stability for another service period. The binder rheology has to be altered to reduce fatigue and low temperature cracking potential without over softening the binder to cause rutting problems. Sufficient adhesion and cohesion have to be provided in the mix to prevent moisture damage and raveling.

Test results (select)

Only some results are included here. See articles above for full test results.

Performance Grade

The extracted RAP binder was tested for penetration grade after addition of each of the rejuvenators and the results, along with the virgin binder PG 64-22, are illustrated in Figure and show that RAP binder has aged significantly and grades as PG 94-12. The addition of all products allowed to reduce both the high and low binder grade compared to the extracted binder showing that they work not only as softening agents, but also increase the binder elasticity and therefore can be defined as rejuvenators. None of the rejuvenators were quite able to reduce the high grade to the level of virgin binder indicating lower susceptibility to rutting. This shows that, despite the general concern, if adequate dose of rejuvenator is used and good diffusion occurs in asphalt binder film, there is most likely no danger of increased rutting susceptibility with the use of rejuvenators. Note that this assumes that there is 100% blending in the mix.

The required low penetration grade (-22°C) was reached in all cases except when using WEO. Most of the products are actually able to reduce the PG much lower than required, and at the dose of 12%,organic oil and yellow grease have provided the lowest cracking temperature. The intermediate temperature fatigue parameters (G*·sinδ) are indicated with diamonds; they demonstrate that all rejuvenators have decreased the dynamic shear from 12,600 kPa for extracted RAP binder to a level that passes the Superpave requirement of 5,000 kPa.


Rutting

The Hamburg WTT results are illustrated in Figure along with TxDOT requirement for maximum rut depth. It is clear that none of the rejuvenated samples exceeds the maximum rut depth and the only sample that fails this requirement is virgin mixture. This sample was prepared by burning off the RAP binder and replacing it with virgin PG 64-22 binder at a dose that is equal to the rejuvenated samples.  

Most of the rejuvenated mixtures did not reach stripping inflection point within the 20,000 wheel passes. According to Colorado DOT stripping inflection point before 10,000 passes indicates moisture susceptibility. Yellow grease and virgin mix did not pass this requirement, but organic oil, although reduced moisture resistance, didn’t fail this requirement.

Fatigue


The Linear Amplitude Sweep (LAS) test has been proposed as a replacement to currently used PG grading intermediate temperature parameter G*·sinδ. The LAS procedure uses conventional DSR testing unit with 8mm plate and 2mm gap setting, but in contrast to the existing fatigue parameter, the test is performed by means of cyclic loading employing, increasing load amplitude to characterize the non-linear strain response of binder.

The test specimens were tested after short term (RTFOT) and long term (PAV) aging to simulate the pavement response at later stages of service. The test was performed in the Superpave intermediate temperature for PG64-22 (25°C). The results in Figure are expressed at 5% strain which corresponds to 1000 microstrain in the pavement layer and was found to correlate better with the mixture fatigue energy ratio test.

The results clearly demonstrate that the aged RAP binder has a reduced fatigue life compared to the virgin mixture. Addition of tall oil and organic oil has increased the number of cycles to fatigue failure compared to extracted binder. The use of WV grease and WV oil provides fatigue resistance that is similar to the virgin mix. However, surprisingly, WEO and aromatic extract have almost no influence on the fatigue of RAP binder. This is unexpected considering that these products have been extensively used for rejuvenation and provided good field results.

The current Superpave intermediate temperature fatigue parameter G*·sinδ (complex shear modulus viscous portion) results are indicated with diamonds in Figure 17. For easy visual comparison with LAS test results they are plotted on a reverse scale and fitted in relation to virgin binder result. Results demonstrate that all rejuvenators have decreased the G*·sinδ from 12,600 kPa for extracted RAP binder to a level that passes the maximum Superpave requirement of 5,000 kPa and the results are similar to virgin binder.

 Low temperature properties

Neither stiffness nor strength alone determines when a mixture will crack. A stiff mixture will not crack if its strength is high enough; and a weaker mixture will not crack if it is sufficiently flexible. The mixtures were tested for creep compliance and indirect tensile strength at -10°C for thermal cracking potential since these tests have been recognized as accurate ways of describing mixture properties at low temperatures and the test methodology is standardized by the AASHTO T322-07.

Tensile strength and fracture energy

Tensile strength and fracture energy were obtained from IDT strength test on 100mm samples.

The tensile strength is a function of adhesion and cohesion of binder and aggregates if all volumetric properties are kept constant. Based on the previous discussion of the effective binder content it can be presumed that the rejuvenators do not diffuse to the aggregate and RAP binder interface; therefore the adhesion likely has not been changed and the various tensile strength of samples can be attributed to changed binder cohesion. Since the interaction of binder and aggregates is likely similar to the rejuvenated mixes, the RAP+PG64-22 can be assumed as the baseline for evaluation of rejuvenator effect on cohesion. The comparison of mixes in Figure shows that most of the rejuvenators have cohesion that is similar to that of the reference, but WEO has slightly reduced it. The improved tensile strength of virgin mix may be a result of both better binder cohesion and better adhesion between the fresh binder and aggregates.
While tensile strength is often used as a parameter for evaluation of cracking resistance, since it depends on loading conditions it is not a fundamental parameter. It is believed that fracture energy is a more important property for characterizing the cracking potential. Fracture energy is defined as the energy required to initiate fracture of the mixture, and it is not dependent of loading rate. It was derived from the strength tests by calculating the area below the stress-strain curve to the point of maximum stress. The results in Figure show that as expected because of higher effective binder content and the lowest viscosity, virgin mix has the highest fracture energy. This is visible when the fracture energy is compared to those of aromatic extract and distilled tall oil. They both have very similar tensile strength compared to virgin mix, but the higher binder content of virgin mix has likely increased the failure strain resulting in higher fracture energy. The effect of lowering binder viscosity is visible when the rejuvenated mixtures are compared with the RAP+PG64-22 mixture. All of the rejuvenated mixtures have increased the fracture energy and are statistically similar to each other.

Creep compliance

 Creep compliance is measured by applying static indirect load to initiate asphalt deformation in the viscoelastic range. Both vertical and horizontal displacements are measured to determine the time dependency of strain resulting from stress. Therefore creep compliance can be characterized as the reverse property of asphalt stiffness and evaluation of this property at low temperature shows the pavements potential to creep in thermal load stress at low temperatures.

As expected the RAP+PG64-22 binder has the highest stiffness due to almost no softening of the binder. Compared to this, all rejuvenators have reduced the stiffness and WVO products have even reduced the stiffness to the level of virgin mixture. The virgin asphalt has higher creep compliance than other rejuvenated mixes, however, as shown by the rutting test, the effective binder content of virgin mix is likely higher compared to rejuvenated mixtures. Balanced mix design would probably require reduction of binder content and hence cause reduction of creep compliance.




Conclusions

The conclusions include evaluation of test results for each rejuvenator from the complete research for 12% rejuvenator dose. Not all of the test results are included in this website. See upcoming publications for all details. 

Virgin mixture

Virgin mixture was prepared by burning off the RAP binder and mixing the aggregates with a dose of PG 64-22 binder that is equal to the rejuvenated mixtures. This mixture was the only one to fail the Hamburg WTT test requirement, showing that this binder dose is probably higher than optimum. Consecutively the mixture has the best workability, good low temperature and the best fatigue performance. 

RAP+PG 64-22

The penetration tests showed that only minimal softening of binder occurs by addition of virgin PG64-22 binder. Therefore this mixture was used as a representation of blend that is close to original reclaimed asphalt. This is demonstrated by the worst workability and as expected such mixture will have low temperature cracking problems as confirmed by the creep compliance and fracture energy results. The FWD and LAS results show significantly reduced fatigue performance compared to virgin mix.

Organic oil

At the tested dose of 12% organic oil (Hydrogreen S) significantly improved workability and along with VW Oil provided the most reduction of low temperature PG grade of aged binder. The Hamburg WTT results, although indicated slightly increased susceptibility to stripping, suggest very high resistance to rutting and therefore increase in dose can be considered to further improve the fatigue performance and low temperature mixture cracking resistance. 
 

Aromatic extract

The use of aromatic extract is not encouraged due to possible carcinogenic effect. The 12% dose that was used in this study is likely too small for the rejuvenator, since it did not allow reaching the viscosity or PG grade of virgin binder and therefore low temperature mixture stiffness is high and the rutting results - excellent. Surprisingly the addition of this rejuvenator actually reduced the binder fatigue resistance, but at the same time the mixture fatigue performance was satisfactory.

Waste engine oil

The 12% dose of WEO that was used in the study did not allow to sufficiently reduce viscosity of the RAP binder and therefore the mixture has the lowest workability. The stiffness and fracture energy at low temperature have been improved; however the binder low temperature grade was not reduced to the required level. The good correlation with other rejuvenator results shows that this performance can likely be improved by increased rejuvenator dose. The Superpave fatigue parameter G*sinδ was reduced to the required level, but the newly introduced LAS and FWD test results showed slightly reduced fatigue performance. WEO exhibits slightly increased loss of volatile fractions in mass loss test and therefore may have increased aging susceptibility, but at the same time it exhibits the least bleeding (flushing) suggesting stable diffusion into the binder film.

Distilled tall oil

Distilled tall oil performed averagely in most of the tests, with exception of creep compliance where the mixture that was rejuvenated with this additive showed the least reduction in stiffness and high tensile strength. This suggests that the pavement may have increased thermal stress at low temperature. At the same time, low temperature PG was reduced even more than required suggesting that if complete diffusion occurs, problems with low temperature cracking should not occur. The binder fatigue resistance was not improved compared to extracted binder. However, all of the results suggest that higher dose of tall oil can be used, which would likely improve fracture resistance.

Waste Vegetable Oil

WV Oil showed the most rejuvenation potential on the aged binder. From all of rejuvenators it provided the highest increase in binder fatigue life and largest reduction in penetration grade. Along with the largest reduction of low temperature stiffness and high fracture energy this promises exceptionally good cracking resistance. However, the Hamburg WTT results suggest that this rejuvenator has significantly increased the susceptibility to moisture damage and therefore reduction from the dose of 12% may be necessary, if no other measures of promoting adhesion are used.
Waste Vegetable Grease
WV Grease along with WV Oil demonstrated the highest increase in fatigue resistance of binder and good mixture fatigue resistance. At the same time it significantly reduced the PG and demonstrated the best binder as well as mixture workability. As evident from Hamburg WTT and penetration results, this performance is a result of most softening of the binder compared to other rejuvenators. The selected dose of 12% is likely close to the maximum that should be used for this rejuvenator for the tested RAP in order to not cause plastic deformations. However, at this dose the bleeding test suggested high migration of lighter fractions and therefore skid resistance should be tested before applying this product to surface courses.
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