Laboratory Investigation of Moisture Damage in Rubberized Asphalt Mixtures Containing Reclaimed...

7/25/2019 Laboratory Investigation of Moisture Damage in Rubberized Asphalt Mixtures Containing Reclaimed Asphalt Pave

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Laboratory Investigation of Moisture Damage in Rubberized Asphalt

Mixtures Containing Reclaimed Asphalt PavementInternational Journal of Pavement Engineering

(Manuscript ID GPAV-2007-0053)

FEIPENG XIAO*

and SERJI N AMIRKHANIAN

Department of Civil Engineering, Clemson University, Clemson, South Carolina 29634-

0911, USA

Abstract

In many parts of the world highway officials are utilizing crumb rubber and reclaimed asphalt

pavement (RAP) in order to save money, protect the environment, and improve the life of

asphalt pavement. However, due to the use of these materials, the effects of moisture damage

should be investigated for rubberized asphalt concrete (RAC) mixtures containing RAP. The

objective of this research involved investigating the moisture susceptibility of RAC

containing RAP. The testing conducted included the determination of binder viscosity,

toughness and indirect tensile strength (ITS) analysis. Several mixtures containing different

crumb rubber types, two different RAP sources and various percentages of rubber and RAP

were evaluated. The results indicated that, in general, the additional of RAP was beneficial in

improving the ITS values and reducing the moisture susceptibility of the mixture although the

addition of crumb rubber had a slightly negative effect.

Keyword: Moisture susceptibility; Rubberized asphalt concrete; Reclaimed asphalt pavement;

viscosity; Indirect tensile strength; Toughness

*: Corresponding Author [email protected]


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1.Introduction

Moisture damage, caused by a loss of bond between the asphalt binder or the mastic and the

aggregate under traffic loading, can cause a decrease of strength and durability in asphalt

mixtures. Moisture damage is relatively prone to produce the separation and removal of

asphalt binder from the aggregate surface, thus, leading to stripping in the asphalt pavement

and ultimately causing premature failure. Some researchers identified six contributing

mechanisms that might produce moisture damage: detachment, displacement, spontaneous

emulsification, pore pressure-induced damage, hydraulic scour, and the effects of the

environment on the aggregate-asphalt system (Taylor and Khosla 1983, Kiggundu and

Roberts 1988, Terrel and Al-Swailmi 1994). However, it is apparent that moisture damage is

usually not limited to one mechanism but is the result of a combination of many processes.

From a chemical standpoint, the literature is clear that although neither asphalt nor aggregate

has a net charge, but components of both have nonuniform charge distributions, and both

behave as if they have charges that attract the opposite charge of the other material (Curtis et

al., 1992, Robertson, 2000, Little et al. 1999).

The viscosity of the asphalt binder does play a role in the propensity of the asphalt

mixture to strip. Previous research presented that high viscosity asphalt resists displacement

by moisture better than those that have a low viscosity. High viscosity asphalt provides a

better retention of asphalt on the aggregate surface (Khosla 1993; Xiao et al. 2007). However,

a low viscosity is advantageous during mixing because of increased coat ability, providing a

more uniform film of asphalt over the aggregate particles. Based on the theory of adhesion,

the properties of the binder and aggregate materials directly influence the adhesion developed

between the mix components (Khosla 1993).

In the United States, the Federal Highway Administration (FHWA) reported that 73

of the 91 million metric tons of asphalt pavement removed each year during resurfacing and

widening projects are reused as part of new roads, roadbeds, shoulders and embankments

(FHWA 2002). The recycling of existing asphalt pavement materials produces new

pavements with considerable savings in material, cost, and energy. Furthermore, mixtures

containing reclaimed asphalt pavement (RAP) have been found to perform as well as virgin


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mixtures. The National Cooperation Highway Research Program (NCHRP) report provided

basic concepts and recommendations concerning the components of mixtures, including new

aggregate and RAP materials (NCHRP 2001).

Approximately 299 million scrap tires were generated in the United States in 2005, 82

percentage of which were recycled or reused (RMA 2006). Rubberized asphalt, the largest

single civil engineering market using crumb rubber, is being used in increasingly large

amounts by many Departments of Transportation (DOTs) around the country. Most roads

comprised of experimental asphalt containing crumb rubber show improvements in durability,

crack reflection, fatigue resistance, skidding resistance, and resistance to rutting (Hicks et al.

1995; Choubane et al. 1999; Way 2003, Amirkhanian 2003).

Previous research (Xiao et al. 2007) results have indicated that the use of RAP

reduced the asphalt binder content and increased cohesive strength while the use of crumb

rubber was beneficial in improving low temperature, reflective, and fatigue crack resistance

of the mixtures. The results showed that it is possible to use crumb rubber and RAP together.

Furthermore, these specific mixtures containing crumb rubber and RAP, have not yet to be

fully investigated for moisture susceptibility. The mix properties such as viscosity of the

asphalt influence cohesive forces of the mixture that are inversely proportional to the

temperature of the mix. Therefore, it has become necessary to seek a more fundamental

understanding of the relationships between moisture damage process and viscosity by

carefully considering the rubberized asphalt concrete (RAC) and RAP that influence the

adhesive, the cohesive strength and durability of the mastics.

2. Experimental program and procedures

2. 1 Materi als

The experimental design detailed in this study included the use of two rubber types (ambient

and cryogenic), four rubber contents (0%, 5%, 10%, and 15% by weight of virgin binder),

one crumb rubber size (-40 mesh [-0.425 mm]), and four RAP contents (0%, 15%, 25%, and

30% by weight of the modified mixture). Two granite aggregate sources (designated as L and


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C) were used for preparing samples, and two binder grades from the same source, PG 64-22

and PG 52-28, were used for this project. The engineering properties of all binders (virgin

and extracted) are shown in Table 1. There were a total of 34 Superpave mix designs.

The RAPs were taken from the same geographical area as the virgin aggregates to

ensure that the aggregates in the RAP have similar properties to the virgin ones. Both RAP

sources (L and C) were mixed with an original binder equivalent to a PG 64-22 grade. Aged

binders extracted from two types of RAP according to ASTM D 5402 (Standard Practice for

Recovery of Asphalt from Solution Using the Rotary Evaporator) and AASHTO TP 2-01

procedures (Standard Test Method for the Quantitative Extraction and Recovery of Asphalt

Binder from Asphalt Mixtures) were only used for characterizing for the modified binders.

A mechanical mixer was used to blend the rubber, the aged and the virgin binder. The

crumb rubber and aged binder were added to the virgin binder using a reaction time of 30

minutes, a reaction temperature of 177 C (350 F), and a mixing speed of 700 rpm (Xiao

2006). The blended components were used for the rheological property tests. These

conditions are the same as field criteria used by South Carolina Department of Transportation

(SC DOT) for producing rubberized mixtures.

2.2 Mix Design

Though the original Superpave mix design system did not address the use of RAP, several

studies were later conducted on this subject. For example, research has resulted in the Black

Rock Study, the use of the Three-Tier Approach, the use of linear blending, and the

development of technician manuals for proper use of RAP (FHWA 1997; McDaniel et al.

2000; NCHRP 2001). For this paper, the Superpave system was used to determine the

optimum binder contents (OBC) for all mixtures.

A nominal maximum size of 9.5 mm Superpave mixture was used for all mix designs.

This particular mix design is used as a primary route surface course mix in many states in the

United States. The SCDOT 9.5 mm Superpave volumetric and compaction specifications,


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shown in Table 2, were used. The procedures described in AASHTO PP 19 and AASHTO T

312 regarding the preparation of hot mixture asphalt (HMA) specimens were followed.

The engineering properties of two aggregate sources L and C are shown in Table 3.

Some details of the mix design of two RAP sources are shown in Tables 4 and 5. The RAP

materials were first oven-dried and sieved to obtain particles with target sizes shown in Table

5. These materials were then blended with the virgin aggregate at the specified (target)

mixing temperatures (Xiao 2006). The mixture was heated for approximately one hour in

order to maintain the target mixing temperature. Finally, the modified binder (rubber and

virgin binder) was added to the mixtures and the final mixture was heated for about two hours

prior to compaction.

Hydrated lime, used as an anti-strip additive, was added at a rate of 1% by dry mass

of virgin aggregate. Gradations of the 9.5mm mixtures are illustrated in Figure 1. All mixes

satisfied the requirements as specified in Table 2 and Figure 1. When the rubber contents

were varied for other mix designs, the same gradation of the aggregate, as shown in Figure 1,

was used.

2.3 Property Testing of Modifi ed Binder and Mixtu re

Three aging states of the virgin and extracted asphalt binders were tested for several

engineering properties (i.e., viscosity, dynamic shear rheometer, bending beam rheometer,

and Gel Permeation Chromatographic). High pressure-gel permeation chromatography

separates an asphalt binder into fractions of various molecular sizes, thus establishing a

profile of molecular size distribution plotted with detector responses on the vertical axis and

elution time on the horizontal. Some researchers (Jennings et al. 1985; Noureldin and Wood

1989; Kim et al. 1993; Wahhab et al. 1999; Shen et al. 2006) reported that the variations in

the molecular size distribution of virgin and recycled asphalt binders are associated with

rheological properties of the binder and engineering properties of the mixture. As shown in

Table 1, the aging process increases the percentage of large molecular size (LMS), as

reported before by many researchers, and reduces the percentage of small molecular size


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(SMS). As expected, the aged binders extracted from RAP have the larger amount of LMS

than other virginal binders.

The viscosity of all binders was obtained using the procedures described in AASHTO

T 316 (Viscosity Determination of Asphalt Binder Using Rotational Viscometer). Bulk

specific gravity (BSG) was determined using the ASTM D 2726. Moisture susceptibility was

conducted by comparing the ITS values of various mixture types (ASTM D 4867). Three wet

and three dry samples were tested at room temperature (25 1oC), and the specimens were

compacted to 6-8% air voids with a Marshall hammer. Furthermore, toughness value was

measured and computed to test the moisture sensitivity of these mixtures.

3. Analysis of test results

3.1 Statistical considerations

Results of the viscosity, ITS and toughness values were statistically analyzed with 5% level

of significance. For these comparisons, it should be noted that all specimens were produced at

OBC. Regression analysis was used to develop the correlations of the binder viscosity and the

mixture ITS values in this study.

3.2 Viscosity analysis of modif ied binders

Viscosity values of various modified binders are shown in Figure 2. The results show that the

viscosity of the modified binder composed of two types of crumb rubber (ambient and

cryogenic), increases as the percentage of RAP increases due to the increasing amount of

LMS in the components. In most cases, binders containing the same percentage crumb rubber

(ambient and cryogenic) exhibited similar viscosity values at the percent of 0%, 5%, and 10%

rubber, while the modified binders containing 15% ambient rubber had a higher viscosity

value than those made with 15% cryogenic rubber regardless of the RAP percentage and

types. Furthermore, the viscosity of the binder blended with a binder graded as PG 64-22

shows a greater value than the binder blended with the soft binder (PG 52-28) when using the


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same percentage of RAP (30%RAP). Figure 2(b) presents the ITS values of the modified

mixtures containing RAP C, where the viscosity property of the modified binders is similar to

Figure 2(a).

3.3 Optimum binder content analysis

For this study, the optimum asphalt binder content was defined as the amount required to

achieve 4.0% air voids at a given number of design gyrations (Ndesign= 75). Table 6 shows

OBC for mix designs with various percentages of RAP, rubber, and rubber type. Table 6 also

shows, as expected, that the OBCs of the mixtures decrease slightly as the percentage of RAP

increases for both rubber types (cryogenic and ambient). In most cases, the OBCs of the

cryogenic modified binders are found to be slightly higher than those of the ambient binder.

Table 6 further illustrates that an increase in the percentage of RAP leads to an increase of

aged binder and a decrease of virgin binder in the mixtures. Thus, the higher mixing and

compacting temperatures were needed to lower the viscosity of the age binder in order to coat

the aggregate surface. As the percentage of crumb rubber increased, the OBCs in the mixtures

also slightly increased. Previous research indicated that the rubber particles in modified

binders swell in the presence of the asphalt due to the absorption of some of the lighter

fractions (aromatic oils) of the binder (Airey et al. 2003; Green and Tonlonen 1997;

Heitzman 1992; Bahia and Davis 1994; Zanzotto and Kennepohl 1996; Kim et al. 2001).

These crumb rubber particles form a viscous gel causing an increase in the overall viscosity

of the modified binder. Due to the increased viscosity, more modified binder is needed to

achieve the target air void of the mixture at the specified mixing and compacting

temperatures.

3.4 Bulk specif ic gravity analysis

In this study, the BSG value of the compacted paving mixtures was measured according to

the AASHTO T166. Previous research indicated that compared to the virgin binders, the high

temperature viscosity, complex modulus and elastic response of rubberized mixtures show


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considerable increases (Khedaywi et al. 1993; Airey et al. 2003, Xiao et al. 2008). To achieve

a target air void of the rubberized mixtures during the mixing and compaction process at

design gyrations, the higher temperature, greater compaction pressure or extensively

modified binders will be needed than conventional mixtures. At the same time, the

incorporation of the RAP in the mixtures also affects the BSG values. Table 6 shows that

increasing the percentage of crumb rubber causes a reduction in the BSG values regardless of

the rubber types and aggregate sources.

The increase of crumb rubber also results in a decrease in weight of specimens

possessing identical volumes and air voids with the conventional HMA specimens. This

decrease is due to the fact that the bulk specific gravity of the crumb rubber is significantly

smaller than the fine aggregate in the mixture. However, Table 6 shows that as the percentage

of RAP increases, the BSG value of the mixtures also increase. Therefore, the aged binder in

the mixture plays a key role in achieving the target air voids, mixing and compacting

temperatures. A similar trend is attainable when using the PG 52-28 virgin binder in place of

PG 64-22, mixed with 30%RAP.

3.5 Toughness analysis

Toughness was defined as the area under the tensile stress-deformation curve up to a

deformation of twice that incurred at maximum tensile stress (Freeman et al., 1989, Putman

and Amirkhanian, 2004). As shown in Table 7, statistical analysis of the average toughness

results of the specimens with the same percentage of rubber or RAP shows no significant

differences with the mixtures made with PG64-22 binder. However, in most cases, the

toughness values of specimens containing 15% rubber are significantly lower than those

specimens containing rubber in respective amounts of 0%, 5% and 10% regardless of the

RAP percentage and the rubber type. This shows that the greater percentages of rubber in

specimens results in a greater loss of bond strength between the asphalt binder and the

aggregate. In Table 7, in general, statistical analysis further illustrates that dry specimens, as

expected, show higher toughness values than wet specimens made with the same percentages


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of rubber and RAP regardless of the rubber type. However, an analysis of the toughness

results of both wet and dry specimens indicate that the mixture made with PG 52-28 asphalt

binder has a significantly lower toughness values compared to that made with PG 64-22.

3.5 ITS and TSR Analysis

The ITS test is often used to evaluate the moisture susceptibility of an asphalt mixture. A

higher ITS and TSR values typically indicate that the mixture will perform well with a good

resistance to moisture damage. At the same time, mixtures that are able to tolerate higher

strain prior to failure are more likely to resist cracking than those unable to tolerate high

strains. The viscosity is an important factor in determining the mixing and compacting

temperatures of the mixture. Temperature plays a key role in determining asphalt film

thickness, thus, affecting the cohesion and air voids of the mixtures. As such, it is necessary

to analyze the relationship between viscosity and ITS values.

Figure 3 shows that the ITS values of the wet specimens generally decrease as the

rubber percentage of modified mixture increase regardless of the RAP percentage. The

addition of crumb rubber can increase the viscosity of an asphalt rubber binder, which results

from the effects of increase in volume of rubber particles due to the light oil absorption of

rubber. Therefore, this decrease in oil likely inhibits the ability of the modified binder to

adequately coat the surface of the aggregate, thereby lead to the potential loss of bonds

between the rubber, binder and the aggregate. In addition, as the RAP percentages increase in

a mixture, the ITS values of the wet specimens increase. The addition of RAP in a HMA

mixture might require the need for a higher compaction temperature to achieve target air

voids. The specimens made with the aggregate source C, as shown in Figure 3(c), indicated

the same trend ITS values as for aggregate source L.

As shown in Figure 4, the tensile strength ratio (TSR) values of the specimens with

15% rubber (ambient and cryogenic) containing 0% and 15% RAP are less than 85%, a

minimum TSR value set forth by SCDOT. These values illustrate that the specimens

containing 15% rubber have more significant moisture susceptibility. In this case, it might be


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necessary to include a higher percentage of RAP to achieve the satisfied TSR values or the

need for additional anti-striping additive to improve the mixtures moisture damage

resistance.

When comparing the specimens made with PG 64-22 binder and the softer binder (PG

52-28), as shown in Figure 3, the ITS values of the specimens made with PG 52-28 is lower.

Figure 3 also shows that the specimens containing ambient rubber produced results very

similar to cryogenic specimens even though there are some differences in manufacturing

process for these two types of crumb rubber.

3.6 Correlati on Analysis between Viscosity and I TS

The viscosity of an asphalt binder is often used to determine the mixing and compaction

temperatures of HMA. The mixture blended with higher viscosity binder is produced at a

higher temperature according to ASTM D 2493. This approach is simple and provides

reasonable temperature for the virgin binders. However, some specific modified binders

containing RAP and rubber have exhibited relatively high mixing and compaction

temperatures. This is due to the fact that the modified binders containing rubber particles and

RAP have different properties to shear rate compared to the virgin binder. The previous

research (Xiao 2006) was performed to determine reasonable mixing and compaction

temperatures for these specific mixtures. In this study, the measured viscosity of the modified

binder was not used as the viscosity value of the binder in determining the mixing and

compaction temperatures in accordance with ASTM D 2493. The temperature is an important

factor that directly affect the bulk specific gravity and optimum asphalt content of the mixture

which are associated with the ITS value and moisture susceptibility.

Figure 5(a) illustrates the relationships between the wet ITS value of the mixtures and

viscosity value of the modified binders with respect to RAP percentage. Regression analysis

was performed to develop the predictive models between the ITS and viscosity values at the

same percentages of rubber. It can be seen that, for each individual curve, the increase of

viscosity value results in an increase of the ITS value regardless of the rubber percentage and


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RAP type. Obviously, this increased viscosity value caused by the additional RAP percentage.

In Figure 5, the ITS value of the mixtures without the RAP and crumb rubber is defined as

the control mixture and it is shown as a straight line. Although Figure 5(a) only presents the

relationship between the wet ITS and viscosity values, the dry ITS specimens exhibited

similar trend. In addition, the specimens made with either ambient or cryogenic crumb

rubbers showed similar ITS and viscosity properties, therefore, the effect of asphalt

composition on the rubber types appears to much less pronounced.

With respect to the effect of rubber percentage, as shown in Figure 5(b), the additional

rubber significantly, as expected, increases the viscosity values; however, this increase does

not result in an increase of ITS values. A decrease of ITS value is found for each curve that

was obtained based on the regression logarithmic analysis. Especially, when using 0% or

15% RAP, the ITS values decrease although the viscosity values increase significantly as the

rubber percentage increased. In most cases, these values were less than the control ITS

values. However, when using 25% and 30% RAP, the ITS values are significantly higher

than the control mixtures. Both RAP sources, C and L, showed similar results. In the

previous study, it can be seen that the additional RAP is beneficial in mitigating the loss of

bond in the mixture caused by the additional rubber. On the other hand, the crumb rubber is

effective in improving the long term performance (fatigue resistance) and diminishing low

temperature and reflective cracking due to the additional RAP (Xiao 2006).

4. Conclusions

The following conclusions were determined based upon the experimental results obtained

from a laboratory investigation of various HMA mixtures which contain both RAP and RAC:

1.

Statistical analysis of viscosity showed no significant differences in the viscosity values

of modified binders between two types of rubber (ambient and cryogenic) under identical

conditions (0%, 5%, and 10% rubber). The binders blended with ambient rubber had


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higher viscosity values than those blended with cryogenic rubber when using 15% rubber

regardless of RAP percentages and types.

2. In comparison with 15% rubber, in general, specimens containing 0%, 5% and 10%

crumb rubber had significantly higher toughness values regardless of the percentage of

RAP and the rubber type (ambient and cryogenic). The toughness values of mixtures

made with the softer binder showed a lower value compared to specimens made with PG

64-22 binder.

3. When using 15% rubber, the specimens exhibited moisture damage, however, the

increased RAP content significantly improves the moisture resistance and increase the

bonds between the aggregate, rubber particle, and modified binder.

4. The viscosity values of modified binder increased, caused by an increase of rubber

content, and the ITS values of both the dry and wet specimens decreased. However, the

increase of the percentage of RAP resulted in an increase in viscosity and ITS values. The

additional RAP plays a key role in mitigating the loss of bond in the mixture due to the

influence of the additional rubber.

5. Two aggregate and RAP sources showed similar effects on the viscosity of the binder and

the ITS values of the mixture although there are some differences in engineering

properties of the aggregates and RAP materials.

Acknowledgements

Financial support was possible through a grant from South Carolinas Department of Health

and Environment Control (DHEC) and the Asphalt Rubber Technology Service (ARTS) of

Clemson University.


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Table 1 Engineering properties of asphalt binders

PG64-22 PG52-28 Source L Source C

Viscosity @135oC (Pa-s) 0.430 0.213 5.982 2.55

G*/sin() @64oC (kPa) 1.279 0.398 58.542 45.625

RTFO G*/sin() @64oC (kPa) 2.810 0.825 109.780 95.298

G*sin() @25oC (kPa) 4074 821 8000 11000

Stiffness @-12o

C (MPa) 217 60.4 294 277

m-value @-12oC 0.307 0.476 0.241 0.243

LMS (%) 21.42 11.94 38.45 34.74

MMS (%) 59.99 51.89 34.42 33.53

SMS (%) 18.59 36.17 27.15 31.72

LMS (%) 22.26 12.74 - -MMS (%) 59.07 52.62 - -

SMS (%) 18.67 35.62 - -

LMS (%) 30.25 13.65 - -

MMS (%) 51.05 52.34 - -

SMS (%) 18.70 34.01 - -

No aging

PAV

Aging states Test propertiesVirgin Binder Extracted Binder

No aging

RTFO

PAV

Note:

LMS, MMS, and SMS: Large, Medium, and Small Molecular Size


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Table 2 SCDOT 9.5 mm Superpave volumetric specifications

% Max. Density at Ndes 96

% VMA >15.5

%Voids Filled 70 - 80

% Max. Density at Ni < 89

% Max. Density at Nm < 98

Dust to Asphalt Ratio 0.6-1.2

Superpave 9.5 mm Mix Specifications


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18

Table 3 Aggregate engineering properties

Aggregate

Source

LA Abrasion

Loss (%)

Absorption

(%)

Sand

Equivalen

Hardness

Dry (BLK) SSD (BLK) Apparent 11/2 to3/4 3/4 to3/8 3/8 to #4

L 51 0.70 2.650 2.660 2.690 0.3 0.2 0.3 76 5

C 23 0.50 2.610 2.620 2.640 0.2 2.4 1.0 60 6

Specific Gravity Soundness % Loss at 5 Cycles


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19

Table 4 Blends of two aggregate sources

L C L C L C L C

Stone 789 59 50 52 49 56 - 53 47R. S. 22 18 12 15 8 - 8 7

M. S. 18 31 19 20 10 - 8 14

Lime 1 1 1 1 1 - 1 1

-4RAP 0 0 9 9 15 - 18 18

+4RAP 0 0 6 6 10 - 12 12

Specification

%

byweighto

f

aggregate

Types of Superpave Mixture

0%RAP 15%RAP 25%RAP 30%RAP

Note:

L and C: Aggregate Sources L and C

R. S. and M. S.: Regular Screenings and Manufactured Screenings


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20

Table 5 Components of two RAP sources

9.5 mm 4.75 mm 2.36 mm 0.60 mm 0.150 0.075

3/8" #4 #8 #30 #100 #200

+4 RAP 97 59 45 30 14 8 4.66-4 RAP 100 100 88 57 24 14 6.96

+4 RAP 84 43 33 21 9 5.4 4.46

-4 RAP 100 100 90 56 16 8 5.66

Aggregate

Source

Type of

RAP

Asphalt

Binder (%)

L

C


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21

Table 6 Optimum binder content and bulk specific gravity of the mixtures

0% 5% 10% 15% 5% 10% 15% 0% 10%

0% 5.40 5.60 5.85 6.35 5.25 6.08 6.11 5.00 5.7515% 5.25 5.45 5.75 5.90 5.25 5.85 5.30 5.10 5.53

25% 4.70 5.02 5.08 5.65 5.02 5.18 5.10 - -

30% 4.82 4.59 5.12 5.25 4.80 5.30 5.08 - 5.10

30%* 4.65 4.95 4.90 5.05 - - - 4.85 5.00

0% 2.345 2.336 2.322 2.299 2.340 2.297 2.305 2.323 2.303

15% 2.361 2.345 2.330 2.327 2.344 2.318 2.304 2.347 2.317

25% 2.364 2.350 2.325 2.322 2.367 2.332 2.352 - -

30% 2.373 2.376 2.363 2.354 2.372 2.348 2.367 - 2.338

30%* 2.388 2.373 2.372 2.370 - - - 2.346 2.339

OBC

BSG

RAP%

Cryogenic Ambient

Aggregate L Aggregate C

Ambient

Note:

OBC: Optimum binder content (%)BSG: Bulk specific gravity

*: PG52-28 asphalt binder

: Percentage of rubber by weight of virgin binder


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22

Table 7 Toughness values of mixtures

0% 5% 10% 15% 5% 10% 15% 0% 10%

0% 3.25 3.17 3.07 3.03 3.04 2.80 2.88 2.99 3.02

15% 3.22 3.04 3.16 2.90 2.80 2.72 2.19 3.51 3.1225% 3.09 3.05 3.05 2.88 2.92 2.88 2.41 - -

30% 3.09 3.00 3.05 2.89 2.96 2.76 2.13 - 3.24

30%* 2.04 2.00 1.81 1.52 - - - 2.35 2.35

0% 2.79 2.94 2.99 3.22 2.57 2.75 2.66 3.20 3.88

15% 2.83 3.08 3.08 2.86 2.22 2.64 1.94 3.66 3.69

25% 2.81 2.96 2.99 2.78 2.80 2.79 2.36 - -

30% 2.55 2.93 2.87 2.70 2.66 2.53 2.45 - 3.31

30%* 1.83 2.00 2.08 1.63 - - - 2.17 2.19

Dry

Wet

Aggregate L Aggregate C

Ambient Cryogenic Ambient

RAP%

Note:

Toughness unit: N/mm

*: PG52-28 asphalt binder: Percentage of rubber by weight of virgin binder


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23

0

10

20

30

40

50

60

70

80

90

100

Sieve Size (mm)

PercentPassing(%)

Source L: 0% RAP

Source L: 15% RAP

Source L: 25% RAP

Source L: 30% RAP

Source C: 0%RAP

Source C: 15%RAP

Source C: 30%RAP

Lower Range of GradationUpper Range of Gradation

0.075 0.60 2.360 4.750.15 9.5 12.5

Fig. 1. 9.5-mm mixture gradations


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24

0

500

1000

1500

2000

2500

3000

3500

4000

0 15 25 30 30*Percentage of RAP (%)

Viscosity(cP)

0%(A) 5%(A) 10%(A) 15%(A)

0%(C) 5%(C) 10%(C) 15%(C)

A: Ambient Rubber; C: Cryogenic Rubber

*: PG52-28

|: STD.

(a)

0

500

1000

1500

2000

2500

3000

3500

4000

0 15 25 30 30*

Percentage of RAP (%)

Viscosity

(cP)

0%(A) 5%(A) 10%(A) 15%(A)

0%(C) 5%(C) 10%(C) 15%(C)

A: Ambient Rubber; C: Cryogenic Rubber

*: PG52-28

|: STD.

(b)

Fig. 2. Viscosity comparisons of all binders containing PG 64-22 or PG 52-28 and

ambient or cryogenic crumb rubber for RAP sources, (a) L and (b) C


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25

0

400

800

1200

1600

0 15 25 30 30*


WetITSValues(kPa)

0%Rub 5%Rub

10%Rub 15%Rub

*: PG52-28

|: STD.

(a)

0

400

800

1200

1600

0 15 25 30 30*


WetITSValues(kPa)

0%Rub 5%Rub10%Rub 15%Rub *: PG52-28|: STD.

(b)


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0

400

800

1200

1600

0 15 25 30*


WetITSValues(kPa)

0%Rub 10%Rub *: PG52-28

|: STD.

(c)

Fig. 3. Wet ITS comparisons of all mixtures made with PG 64-22 or PG 52-28 for

specimen containing, (a) ambient crumb rubber, RAP L; (b) cryogenic crumb rubber,

RAP L; and (c) ambient crumb rubber, RAP C


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27

0

20

40

60

80

100

120

0 15 25 30 30*


TSRValues(

%)

0%Rub 5%Rub 10%Rub 15%Rub

*: PG52-28; |: STD.

(a)

0

20

40

60

80

100

120

0 15 25 30 30*


TSRValues(%)

0%Rub 5%Rub 10%Rub 15%Rub

*: PG52-28; |: STD.

(b)


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28

0

20

40

60

80

100

120

0 15 25 30*


TSRValues(%)

0%Rub 10%Rub

*: PG52-28; |: STD.

(c)

Fig. 4. TSR comparison of all mixtures made with PG 64-22 or PG 52-28 for specimen

containing (a) ambient crumb rubber, RAP L; (b) cryogenic crumb rubber, RAP L; and (c)

ambient crumb rubber, RAP C


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600

800

1000

1200

1400

1600

0 500 1000 1500 2000 2500 3000 3500

Viscosity (cP)

WetITSValues(kPa)

Control

(2)

(1)

a: RAP L; b: RAP C; A: Ambient; C: Cryogenic

(1): 0% Ruba

(2): 0% Rubb

(3): 5% Rub (C)a

(4): 5% Rub (A)a

(5): 10% Rub (A)b

(6): 10% Rub (A)a

(7): 10% Rub (C)a

(8): 15% Rub (C)a

(9): 15% Rub (A)a

(7)

(5)

(8)

(9)(6)

(4)

(3)

(a)

600

800

1000

1200

1400

1600

0 500 1000 1500 2000 2500 3000 3500

Viscosity (cP)

WetITSValues(kPa)

(1): 0% RAP (A)a

(2): 0% RAP (C)a

(3): 15% RAP (A)a

(4): 15% RAP (C)a

(5): 25% RAP (A)a

(6): 25% RAP (C)a

(7): 30% RAP (A)

a

(8): 30% RAP (C)a

(9): 0% RAPb

(10): 15% RAPb

a: RAP L; b: RAP C; A: Ambient; C: Cryogenic

Control

(3) (5)

(7)(10)

(1)(4)

(9)

(2)

(6) (8)

(b)

Fig. 5. Relationship of the wet ITS and viscosity values, (a) RAP effect; (b) rubber effect

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