of Transportation (DOT) budgets; DOTs would be able to pave sig-nificantly more miles than they can pave now with all virgin materials.Obviously the higher the percentage of RAP utilized in a job, thegreater the savings.

However, the maximum amount of RAP that is allowed to be usedin hot-mix asphalt (HMA) mixes is only about 30% in many states,largely because of concerns over RAP’s undesired intrinsic properties(such as aged binder) and the lack of a proper mix design procedurefor HMA mixes with very high RAP contents (2). Although a 100%RAP is virtually recycled in hot in-place recycling, for plant recycling,the use of 100% RAP is limited to some use with emulsion (plant mixRAP) to construct base courses only. A proper use of 100% RAP inhot-mix recycling for base course would be a significant improve-ment and provide a much needed cost-saving method for pavementrehabilitation.

A high-RAP content present in HMA mixes poses special chal-lenges in design and construction because of RAP’s aged and stiff-ened binders, which often cause problems with workability andcompactability, and in selection of a temperature during mixing andcompaction that is high enough to drive off moisture from aggregatesyet low enough to avoid further stiffening of the RAP’s alreadyaged binder.

With their capability of reducing asphalt viscosity at lower tem-peratures, warm-mix asphalt (WMA) technologies may provide afeasible solution to producing HMA containing 100% RAP. Somepromising results have been reported in the literature in the pastfew years. For instance, Mallick et al. (3) confirmed in a laboratorystudy that the use of Sasobit (one of the currently available WMAtechnologies) with RAP enabled the production of HMA at 125°C withproperties comparable to those of HMA produced at 150°C. Anotherstudy conducted by Mallick et al. (4) showed that it is possible toproduce HMA mixes with 75% RAP and 1.5% Sasobit H8 at 125°C.These mixes have air voids similar to those of virgin mixes (producedwith extracted aggregates, virgin stones and sand, and standardPG 64-28 at 150°C). In addition, with drum plants Maine DOT hasso far been able to utilize 70% RAP experimentally in an HMArecycling operation.

Successful use of WMA technologies was also reported in re-cycling RAP in field conditions. In 2005 the Maryland State HighwayAdministration launched two demonstration projects with SasobitWMA technology, in which 35% and 45% RAP were used in surfaceand base course layers, respectively, and 1.5% Sasobit (by weight ofthe total binder) was added to these recycled layers (5, 6). As shownby comparison with the HMA control sections with the same amountof RAP but without Sasobit, the use of Sasobit achieved better work-ability and compaction, improved the resistance to moisture damage

Effects of Warm-Mix Asphalt Additives on Workability and Mechanical Propertiesof Reclaimed Asphalt Pavement Material

Mingjiang Tao and Rajib B. Mallick

151

The soaring cost of liquid asphalt binder and anticipated stricter envi-ronmental regulations have driven highway agencies to maximize theamount of reclaimed asphalt pavement (RAP) used for pavement con-struction. However, because of already aged and stiffened asphalt binderin RAP, the use of high percentages of RAP in hot-mix asphalt (HMA)presents many challenges. Problems with workability and compactabil-ity during construction need to be resolved first. This study investigatedthe feasibility of using 100% RAP HMA as a base course with warm-mix asphalt (WMA) additives (Sasobit H8 or Advera zeolite) at a lowertemperature (125°C). Mix samples (control set with 100% RAP; a setwith 100% RAP plus Sasobit H8 at 1.5%, 2.0%, and 5.0%; and a setwith 100% RAP plus Advera zeolite at 0.3%, 0.5%, and 0.7%) werecompacted with 50 gyrations. Their workability, bulk specific grav-ity, indirect tensile strength at 0�C, and moduli at 0�C, 26.7�C, and 50�Cwere determined. The effects of different amounts of WMA additiveswere compared. The results showed that workability of the 100% RAPHMA improved with the addition of Sasobit H8 or Advera zeolite attemperatures as low as 110�C. At temperatures less than 80�C, theaddition of Sasobit H8 or Advera zeolite tended to stiffen the mix, asalso reflected in increased seismic moduli and indirect tensile strength.Seismic modulus of the mixes was also found to be dependent on bulkspecific gravity. The addition of Sasobit H8 proportionally increasedbulk specific gravity of the mixes. The effect of amounts of Adverazeolite on bulk specific gravity was less well defined. It seemed thatstiff asphalt binder in the RAP also affected compaction by prevent-ing asphalt foam from fully forming, as it would when Advera zeolitewas mixed with a virgin asphalt binder.

The use of reclaimed asphalt pavement (RAP) has become increas-ingly attractive to state highway agencies, given that liquid asphaltbinder costs have more than doubled in the last few years, from about$160 per ton in 2005 to $360 or even $400 in some areas in 2008 (1).RAP contains both aggregates and binder. Its use saves our naturalresources and money, and hence recycling of old asphalt pavementmaterials is environment-friendly. There are millions of tons of RAPstockpiled in the northeastern United States. Their increased use indifferent pavement courses can make a major impact on Department

Civil and Environmental Engineering Department, Worcester Polytechnic Insti-tute, 100 Institute Road, Worcester, MA 01609. Corresponding author: M. Tao,taomj@wpi.edu.

Transportation Research Record: Journal of the Transportation Research Board,No. 2126, Transportation Research Board of the National Academies, Washington,D.C., 2009, pp. 151–160.DOI: 10.3141/2126-18

of marginally moisture sensitive mixture, and resulted in a net savingsof $4.55/ton by switching from 25% RAP to 45% RAP with the WMAadditive.

All these promising results from previous studies warrant fur-ther investigation of the effects of WMA additives on workability,volumetric properties, and fundamental engineering properties ofRAP mixes.

OBJECTIVE

The objective of this study was to examine the effects of differentamounts of two types of WMA additives, Sasobit H8 and Adverazeolite, on workability, density, modulus, and strength of 100%recycled RAP.

RESEARCH PLAN, MATERIALS, AND TESTS

The scope of this study consists of obtaining RAP and WMA addi-tives, characterizing basic properties of RAP, preparing mixes withdifferent amounts of WMA additives, testing the samples, and ana-lyzing test results. The research approach employed is illustratedin Figure 1.

A typical RAP from a stockpile west of the Boston area was obtained,and two commonly used WMA additives, Sasobit H8 from Sasol WaxAmericas, Inc., and Advera zeolite from PQ Corporation, were usedin this study. Basic RAP properties of the RAP—such as moisturecontent, asphalt content, and gradation of extracted aggregates—were first determined. The gradation of the extracted aggregates isshown in Figure 2 with the control limits of 9.5 mm nominal maximumaggregate size (NMAS) also included. The RAP has 2.6% moisturecontent and 6.0% asphalt content.

152 Transportation Research Record 2126

No virgin asphalt binder was used for this study for two reasons:(1) asphalt content of the RAP is high (6.0%), and (2) the objective wasto more clearly investigate the effect of WMA additives on propertiesof the RAP mixes. The mixing temperature of 125°C was selectedto reduce standard mixing temperatures by at least 10°C and alsobecause good results have been obtained from RAP mixes with 1.5%Sasobit at 125°C in previous studies (3, 4). The control mix in thisstudy is prepared with 100% RAP only. One set of the mixes wasprepared at three Sasobit H8 concentrations (1.5%, 2.0%, and 5.0%by weight of the total asphalt binder), and another set of the mixeswas produced at three Advera zeolite concentrations (0.3%, 0.5%,and 0.7% by weight of the total mix). Before standard gyratory com-paction, RAP was heated in a 125°C oven for 4 h and then poured intoa gyration mold for compaction. The WMA additive (either Sasobit H8or zeolite) was added to the heated RAP and thoroughly mixed beforetransfer to a gyration mold for compaction.

From a series of WMA studies conducted at the National Centerof Asphalt Technology, Hurley and Prowell observed that the additionof WMA additives (Sasobit, Aspha-Min zeolite, or Evotherm) loweredthe measured air voids in comparison with their respective controlmixtures at the same PG binder (7). Since air void is an importantindicator of HMA construction quality in the field, the influence ofvarious amounts of WMA additives on bulk specific gravity (BSG) ofmixes was examined by compacting three samples of each mix with50 gyrations of the Superpave® gyratory compactor. Fifty gyrationswere determined on the basis of the design practice of Maine DOTfor a low-volume road base course under the state’s typical trafficand climatic conditions. Mixture temperature right before gyrationcompaction was about 105°C.

After the determination of bulk specific gravity, each sample wastested for its modulus and indirect tensile strength to assess the influ-ence of the WMA additives on mechanical properties. Moduli of thespecimens were determined at 0°C, 26.7°C (room temperature), and

Obtain SasobitH8 and Zeolite

Obtain RAP

Mix with 100% RAPat 125°C; Compact 3samples with 50gyrations;Compact 3 170-mmheight samples

Determine bulk specific gravity;Determine seismic modulus;Determine indirect tensile strength at 0°C

Mix with 100% RAPand Sasobit H8 (1.5,2.0, and 5.0%) at125°C; Compact 3samples with 50gyrations;Compact 3 170-mmheight samples with2.0% Sasobit H8

Mix with 100% RAPand zeolite (0.3, 0.5,and 0.7%) at 125°C;Compact 3 sampleswith 50 gyrations;Compact 3 170-mmheight samples with0.5% zeolite

Mix 12 kg of100% RAP;100% RAP plus2.0% Sasobit H8;and 100% RAPplus 0.5% zeoliteat 125°C forworkability

Prepare mixes with different amounts of WMA additives and conduct tests

Determine moisture content and asphaltcontent of RAP; Determine gradation andspecific gravity of extracted aggregates

FIGURE 1 Test plan employed in study.

50°C by seismic modulus testing for the suitability of testing a standardgyratory compacted sample, which is generally too thick to be fittedinside a resilient modulus jig. The procedure employs an electricpulse from a 54-kHz transmitting transducer, to determine the traveltime of a compression wave. The modulus (Eν) is calculated with thefollowing equation:

where

L = length,ρ = bulk density,ν = Poisson’s ratio, andtν = travel time of compression waves.

From a thorough study on precision and accuracy, Tandon et al. (8)concluded that the repeatability and reproducibility of the system withmulti-user and multi-devices are better than 2% and that the length-to-diameter ratio does not seem to affect the measured moduli ofspecimens. A value of 0.4 was used for Poisson’s ratio during thecalculation of seismic moduli, as suggested by Tandon et al. (8).

Another set of samples—100% RAP, 100% RAP plus 2.0%Sasobit H8, and 100% RAP plus 0.5% Advera zeolite—was alsoprepared with gyration height-control mode to achieve the sameBSG. These samples were also tested for seismic modulus to furtherinvestigate the influence of density on stiffness.

The lower and upper testing temperatures—0°C and 50°C—forseismic modulus were selected on the basis of in-place data obtained

EL

tνν

ρν ν

ν= ⎛

⎝⎜⎞⎠⎟

+( ) −( )−( )

21 1 2

1

Tao and Mallick 153

from a Maine DOT instrumented test section (9). Samples wereconditioned for 12 h in incubators to attain temperatures of 0°Cor 50°C.

After the seismic modulus test at 0°C, each sample was returnedto the incubator for another hour to restore the conditioned temper-ature. Then each sample was tested for its indirect tensile strengthat 0°C.

Although WMA technologies offer benefits such as reducinggreenhouse gas emissions and reducing energy consumption, theirability to improve workability and better compaction through lower-ing viscosity is probably the real thrust for HMA producers to adoptWMA technologies (10). As such, workability of different mixesand the influence of different amounts of WMA additives on work-ability were investigated. Workability was evaluated with a torquetester fabricated at the Worcester Polytechnic Institute PavementResearch Laboratory. This torque tester was built and evaluated onthe basis of previously reported results (11). The validity of the torquetester has been verified by Gudimettla et al. (11). The method con-sists of determining the torque needed to move a paddle through amix inside a bucket at different times after mixing—the higher thetorque, the lower the workability of the mix, and vice versa. The torquetester consists of a metal bucket and a 3⁄4-in. torque wrench fixed bya socket extension to an axle stabilized by a double bearing system(shown in Figure 3). Attached to the axle are two metal paddles, thelower one placed at a 45° angle to the axle, and the higher bent 2 in.from the axle. During tests, a batch of 18-kg mix was heated in a 125°Coven for 4 h and then placed in the bucket (with the paddle alreadyinside it). When WMA additives were added, the heated RAP wasthoroughly mixed with the WMA additive and then transferred tothe bucket for measuring torque. The paddle was then rotated one full

Extracted aggregate

Control-low

Control-high

00.075 0.6 1.18 2.36 4.75 9.5 12.5 19

10

20

30

40

50

60

70

80

90

100

Sieve size (mm)

Per

cen

t p

assi

ng

FIGURE 2 Gradation of extracted aggregates from RAP.

circle by means of the torque wrench, and this action was repeatedthree more times. The first rotation always resulted in a higher torquereading, while the next three rotations showed similar readings. Thiswas repeated at different times after mixing, and the temperatureof the mix was noted at each reading. The torque values were alsoconverted to a workability number by multiplying the inverse of theaverage torque by 1,000.

154 Transportation Research Record 2126

TEST RESULTS, ANALYSIS, AND DISCUSSIONS

Bulk Specific Gravity

Average and standard deviation of BSG of the samples from thedifferent mixes are shown in Figure 4. Because of a problem withthe mixer, only one sample containing 0.7% Advera zeolite was

(a) (b)

FIGURE 3 Torque tester: (a) view from outside and (b) view of metal paddles.

FIGURE 4 Average bulk specific gravity of samples of different mixes (Stdev � standard deviation; SH8 � Sasobit H8).

compacted with the same mixing condition as the others. Therefore,no standard deviation value is available for this set. Compared withthe control mix, the mixes with Sasobit H8 additive achieved higherBSG. This is largely because of increased workability with theinclusion of Sasobit H8, which is also consistent with the observa-tions from previous studies (3, 4, 7). Another trend was that a higheramount of Sasobit H8 yielded a larger increase in BSG. For the mixeswith Advera zeolite, when 0.3% concentration was used, BSG wasincreased compared with that of the control mix. A similar observationwas reported in Hurley and Prowell’s study, in which 0.3% Aspha-Minzeolite was added (12). However, with the further increase in Adverazeolite concentration, BSG was decreased rather than increased. Theunexpected trend of decreased BSG may be explained by consider-ing the working mechanism of Advera zeolite: a very fine watervapor is formed when Advera zeolite is added to the heated binder;a volume expansion of the binder is created as a result of the releaseof water, which results in the formation of asphalt foam; and thusaggregates are coated, and workability is increased (12). However,at higher Advera zeolite concentrations (such as the 0.5% and 0.7%concentrations used in this study), water vapor and the resultedvolume expansion may become excessive and actually hinder thecompaction of the mixes for the regular gyration mold, especially inmixes with relatively high asphalt contents. To check this hypothesis,three 100% RAP mixes with 0.7% Advera zeolite were also com-pacted with a specially made gyratory mold with holes (as shown inFigure 5). This mold was originally designed to compact mixes withhigh fluid content. The holes allow the water to escape during thecompaction. The BSGs of the samples compacted with this mold areshown in Figure 4. All three samples had higher BSGs comparedwith those of the samples compacted with the regular gyratory moldwithout holes. However, the BSG values are still lower than that ofthe mix with 100% RAP only. It seems that the presence of stiff agedasphalt binder in the RAP prevents complete processing of the zeolite,

Tao and Mallick 155

such as formation of the foam as would occur in a mix with virginasphalt binder. This observation is true for a relatively high percentageof zeolite (compared with that used generally).

Workability

For different mixes—the control, RAP plus 2.0% Sasobit H8, and RAPplus 0.5% Advera zeolite—Figure 6 shows relative workability rightafter the mixing, and Figure 7 shows relatively workability 60 minafter the mixing. Appreciable increase in workability as a result ofthe addition of Sasobit H8 or Advera zeolite can be noticed fromFigure 6, with 2.0% Sasobit H8 outperforming 0.5% Advera zeolite

FIGURE 5 Slotted mold (with holes of approximately 1 mm in diameter).

45

Wo

rkab

ility

40

35

30

25

20

15

10

5

0

RAP RAP+2.0% SH8 RAP+0.5% zeolite

FIGURE 6 Relative workability of different mixes right after mixing [workability � 1,000/torque(in./lb)].

in workability improvement. The workability shown in Figure 6 wasthe average of three consecutive readings, with its standard deviationsuperimposed in the figure. When the workability values in Figure 6were measured, the temperature of the mixes was about 110°C becauseof some heat loss during mixing of the RAP with the WMA addi-tives. The temperature of the mixes dropped below 80°C when theworkability readings in Figure 7 were taken 60 min after the mix-ing. Workability readings were also taken in the period betweencompletion of the mixing and 60 min after the mixing, but for thepurpose of clarity, only the results taken at 60 min after the mixingare shown here to illustrate the temperature-dependency of the WMAadditives’ effectiveness in workability improvement. The stiffeningeffect caused by Sasobit H8 or Advera zeolite can also be inferredfrom the relative workability shown in Figure 7, which was alsoobserved during the cleaning of the mixes from the bucket after torquemeasurements. The stiffening effect is attributable to the formationof a lattice structure caused by the Sasobit H8, whereas the factorresponsible for the stiffening effect in the mixes with Advera zeo-lite is unknown. No workability of the RAP heated to 150°C wastested, given that such a scenario is less likely to be used in any fieldapplication.

Seismic Modulus

Figure 8 shows the average seismic moduli of different mixes atdifferent temperatures, with their volumetric data shown in Table 1.The same maximum specific gravity (Gmm) value is assumed fordifferent mixtures on the basis of previous research observationsthat the addition of the WMA additives had a negligible effect on

156 Transportation Research Record 2126

Gmm (12, 13). The Gmm value in Table 1 is the average of four Ricespecific gravity tests. (Gmb is the BSG that was the average of threereplicate test results.) The average seismic modulus values in Table 1are also based on three replicate tests. As expected, modulus val-ues decreased with the increase in temperature for all the mixes.Compared with the control mix, the mixes with Sasobit H8 hadhigher modulus values. In addition, higher amounts of Sasobit H8generally resulted in higher modulus values. These observations areexpected, because at temperatures lower than its melting point,Sasobit H8 forms a lattice structure in the asphalt binder that isthe basis for the reported increased stiffness of asphalt containingSasobit (13). For the mixes containing Advera zeolite, their mod-uli are higher than that of the control mix, but the modulus valuesseem largely independent of the Advera zeolite amount. DifferentBSGs (or air voids) were achieved among these mixtures, which havealso contributed to the difference in seismic moduli. The standarddeviation of seismic moduli is shown in Figure 9. Generally, standarddeviations for all the mixes were the lowest at room temperature,and the mixes with WMA additives had lower standard deviationat all three temperature levels compared with those of their con-trol counterparts. Such differences are more pronounced at 0°Cand 50°C. A relatively lower standard deviation associated with theWMA mixes may indicate good uniformity resulting from improvedworkability.

Seismic moduli of the samples compacted by the height-controlmode are shown in Figure 10. The seismic moduli for their counter-parts—with the same WMA additive concentration but at higher bulkspecific gravity—were also included to examine the influence of BSG(or air void) on seismic modulus. Volumetric data for the mixturesshown in Figure 10 are listed in Table 2, again with the same Gmm

Wo

rkab

ility

3.0

2.5

2.0

1.5

1.0

0.5

0.0RAP RAP+2.0% SH8 RAP+0.5% zeolite

FIGURE 7 Relative workability of different mixes 60 min after mixing [workability � 1,000/torque (in./lb)].

assumed for each of the mixtures. By visual inspection of Figure 10,the following observations can be made:

• For each pair of mixes (RAP_H versus RAP_L; RAP plus 2.0%SH8_H versus RAP plus 2.0% SH8_L; and RAP plus 0.5% zeolite_Hversus RAP plus 0.5% zeolite_L), higher BSG yielded higher seismicmodulus.

• At the same BSG, the addition of WMA additives increasedseismic modulus (e.g., RAP_H versus RAP plus 0.5% zeolite_H, bothhaving a BSG of 2.357 but RAP plus 0.5% zeolite_H having a muchhigher modulus at all three temperatures).

Tao and Mallick 157

• The influence of BSG on seismic modulus can override thestiffening effect of WMA additives, if the difference in BSG is largeenough. For example, RAP_H with Gsb = 2.357 had higher seismicmodulus at all three temperatures than those of the mixes with 2.0%Sasobit H8 or 0.5% Advera zeolite but at lower Gsb values.

Indirect Tensile Strength

Indirect tensile strength was determined at 0°C for the specimensafter seismic modulus tests. Compared with the control mix, themixes with WMA additives achieved larger indirect tensile strength(see Figure 11). However, the increase in indirect tensile strength isnot proportional to the WMA additive concentrations. For instance,2.0% Sasobit H8 and 0.3% Advera zeolite yielded the largest indirecttensile strength among all the mixes.

DISCUSSION OF RESULTS

This study confirmed that it is possible to improve workability for100% RAP by adding Sasobit H8 or Advera zeolite. Because of highfine contents present in the RAP used in this study and a smallerNMAS (9.5 mm), the benefit of Sasobit or Advera zeolite in work-ability improvement may be limited, since it was found from a pre-vious study that the torque tester is sensitive to NMAS (3). In otherwords, more pronounced workability improvement can be expectedfor a RAP with less fine contents or a coarser gradation. This suggeststhe feasibility of using 100% RAP for pavement base courses at leastfrom construction point of view.

Seismic M @ 0 C20,000

18,000

Sei

smic

Mo

du

lus

(MP

a)16,000

14,000

12,000

10,000

8,000

6,000

4,000

2,000

0RAP RAP+2.0%

SH8RAP+5.0%

SH8RAP+0.3%

zeoliteRAP+0.5%

zeoliteRAP+0.7%

zeoliteRAP+1.5%

SH8

Seismic M @ 26.7 C

Seismic M @ 50 C

FIGURE 8 Average seismic moduli of different mixes at different temperatures (M � moduli).

TABLE 1 Volumetric Mix Design Data for Different Mixtures

Sample ID Gmma Gmb

b Air Void (%)

RAP 2.449 2.357 3.7

RAP + 1.5% SH8 2.449 2.388 2.5

RAP + 2.0% SH8 2.449 2.401 2.0

RAP + 5.0% SH8 2.449 2.418 1.3

RAP + 0.3% zeolite 2.449 2.409 1.6

RAP + 0.5% zeolite 2.449 2.357 3.7

RAP + 0.7% zeolite 2.449 2.361 3.6

aGmm = maximum specific gravity that was the average of fourRice specific gravity test results.bGmb = bulk specific gravity that was the average of three replicatetest results.

158 Transportation Research Record 2126

Seismic M @ 0 C

Sei

smic

Mo

du

lus

Sta

nd

ard

Dev

iati

on

(M

Pa)

1,400

1,200

1,000

800

600

400

200

0RAP RAP+2.0%

SH8RAP+5.0%

SH8RAP+0.3%

zeoliteRAP+0.5%

zeoliteRAP+1.5%

SH8

Seismic M @ 26.7 C

Seismic M @ 50 C

FIGURE 9 Standard deviation of seismic moduli of different mixes.

Seismic M @ 0 C

RAP_H RAP+2.0%SH8_H

RAP+2.0%SH8_L

RAP+5.0%zeolite_H

RAP+0.5%zeolite_L

RAP_L

Seismic M @ 26.7 C

Seismic M @ 50 C

18,000

Sei

smic

Mo

du

lus

(MP

a)

16,000

14,000

12,000

10,000

8,000

6,000

4,000

2,000

0

FIGURE 10 Average seismic moduli of different mixes with different BSGs at differenttemperatures (H � high BSG; L � low BSG).

The addition of the WMA additives has an appreciable impact ondensity of the mix. While the influence of different Sasobit concen-trations on BSG is consistent and definite, the influence of differentAdvera zeolite concentrations on BSG of the mixes needs furtherstudy. Compaction in a slotted mold definitely improves the densityof mixes with zeolites, but the interaction of the aged and stiff asphaltbinder with zeolite could be a significant factor in compaction of RAPmixes containing relatively high amounts of zeolite.

CONCLUSIONS

Some specific conclusions drawn from this study include the following:

1. It is feasible to build a 100% RAP HMA base course with the aidof Sasobit H8 or Advera zeolite from the construction point of viewwith the improved workability measured from the torque tester.

Tao and Mallick 159

2. The addition of Sasobit H8 or Advera zeolite helps in lower-ing the viscosity of the 100% RAP, thus improving workability attemperatures as low as 110°C. Nevertheless, it is most likely thatboth Sasobit H8 and Advera zeolite have a stiffening effect at lowtemperatures.

3. Such a stiffening effect resulted in higher values of seismicmodulus and indirect tensile strength, while its impact on other engi-neering properties, such as moisture susceptibility and resistanceagainst low temperature cracking, remains to be investigated.

4. Besides the stiffening effect of the WMA additives, BSG alsohas an important impact on seismic modulus. This impact can evenoverride the effect of WMA additive, if the difference in BSG issignificant.

5. The inclusion of Sasobit H8 or Advera zeolite has an apprecia-ble influence on density of HMA containing 100% RAP. Althoughadding Sasobit H8 caused the BSG to increase proportionally to theSasobit H8 concentration, the relationship between BSG and Adverazeolite concentration remains to be further studied. A slotted moldis suggested when a high RAP content mix is used with relativelyhigh zeolite content.

6. The long-term performance of 100% RAP HMA modified withSasobit H8 or Advera zeolite needs more research. Proper laboratorymixing and compaction methods need to be investigated for accurateevaluation of mixes containing zeolites.

ACKNOWLEDGMENTS

The authors thank Karen O’Sullivan and Don Pellegrino for their gen-erous help during this study, and John Shaw of Sasol Wax Americas,Inc., Annette Smith of PQ Corporation; and Ron Tardiff of AggregateIndustries for providing the materials.

TABLE 2 Volumetric Mix Design Data for Different Mixtures

Sample ID Gmm Gmb Air Void (%)

RAP_H 2.449 2.357 3.8

RAP_L 2.449 2.224 9.2

RAP + 2.0% SH8_H 2.449 2.401 2.0

RAP + 2.0% SH8_L 2.449 2.247 8.2

RAP + 0.5% zeolite_H 2.449 2.357 3.8

RAP + 0.5% zeolite_L 2.449 2.239 8.6

RAP RAP+2.0%SH8

RAP+5.0%SH8

RAP+0.3%zeolite

RAP+0.5%zeolite

RAP+0.7%zeolite

RAP+1.5%SH8

Ind

irec

t te

nsi

le s

tren

gth

(M

Pa)

3.0

2.5

4.0

3.5

5.0

4.5

2.0

1.5

1.0

0.5

0.0

FIGURE 11 Indirect tensile strength of different mixes at 0�C.

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The Characteristics of Nonbituminous Components of Bituminous Paving MixturesCommittee sponsored publication of this paper.