Construction and Building Materials 61 (2014) 1–9

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Construction and Building Materials

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Evaluation of warm mix asphalt containing recycled asphalt shingles

http://dx.doi.org/10.1016/j.conbuildmat.2014.02.0660950-0618/� 2014 Elsevier Ltd. All rights reserved.

⇑ Corresponding author. Tel.: +1 563 880 8098.E-mail addresses: abuss@iastate.edu (A. Buss), aacaxcio@iastate.edu

(A. Cascione), rwilliam@iastate.edu (R. Christopher Williams).1 Tel.: +1 520 481 4127.2 Tel.: +1 515 294 4419.

Ashley Buss a,⇑, Andrew Cascione a,1, R. Christopher Williams b,2

a Department of Civil, Construction and Environmental Engineering, Iowa State University, 394 Town Engineering Building, Ames, IA 50011, United Statesb Department of Civil, Construction and Environmental Engineering, Iowa State University, 490 Town Engineering Building, Ames, IA 50011, United States

h i g h l i g h t s

� Field production of recycled asphalt shingles (RAS) with warm mix asphalt (WMA).� Distress surveys on 18 pavement sections performed yearly after construction.� Moisture susceptibility comparison for WMA/RAS mixtures.� Beam fatigue testing to measure fatigue properties when RAS and WMA are used.� Low temperature tests imply similar thermal cracking between the mixtures studies.

a r t i c l e i n f o

Article history:Received 1 October 2013Received in revised form 21 February 2014Accepted 25 February 2014

Keywords:Recycled asphalt shinglesWarm mix asphaltPerformance testPavement surveys

a b s t r a c t

Advances in asphalt materials have led to the incorporation of higher amounts of recycled asphalt mate-rials in mixtures that can be produced at reduced temperatures. Two demonstration projects were con-structed to assess the performance of mixtures that use warm mix asphalt (WMA) and recycled asphaltshingles (RAS) at reduced temperatures. WMA mixes were produced at 120 �C. Eighteen pavement sec-tions were monitored each year after construction. Performance tests were conducted on all mixes tomeasure material properties at a range of temperatures. Additional tests were conducted for one ofthe field projects to show the influence of increasing RAS on moisture susceptibility. Results indicate thatWMA can successfully be used with a RAS mixture. Benefits of adding additional RAS include improve-ment in rutting, stripping inflection point (SIP), and higher or similar dynamic modulus values atincreased test temperatures.

� 2014 Elsevier Ltd. All rights reserved.

1. Introduction and background

The use of sustainable materials and practices in asphalt pavinghas garnered significant interest over the past decade. Modifyingasphalt mixes with recycled asphalt shingles (RAS) diverts materi-als from landfills and reduces liquid asphalt costs. The increaseduse of warm mix asphalt (WMA) technologies has reduced mixingand compaction temperatures of hot mix asphalt (HMA). The ben-efits of WMA include temperature reductions leading to reducedfuel costs, reduced compaction effort, and lower emissions [1].Combining the use of warm mix asphalt technology with RAS willprovide the contractor with benefits of using both technologieswhile creating a more sustainable product. Asphalt shingles typi-cally have 20–30% asphalt by weight of the shingles and utilization

of this waste product presents an economic opportunity, particu-larly when virgin asphalt binder prices are high. Using WMA tech-nologies or processes with RAS provides economic value due tovirgin binder cost reduction, utilization of materials that wouldotherwise be landfilled, reduction of HMA plant temperatures byapproximately 30 �C, saving fuel, and achieving improved fieldcompaction. Two mixes were studied, one from Indiana and onefrom Iowa, both use variable amounts of recycled asphalt pave-ment (RAP) and RAS as well as incorporate WMA technology. TheIndiana mixture compares HMA–RAP, HMA–RAS, and WMA–RASproduced from an asphalt plant foaming process. The Iowa mixtureuses a chemical additive WMA technology, RAP, and increasingamounts of RAS. The mixes were evaluated based on performancetesting and pavement surveys.

The use of RAS in HMA has been studied and used in asphaltpavements for the past twenty years. The vast majority of researchon RAS has been focused on post-manufacturer asphalt shinglesand its use in HMA historically. Over the last seven years, the focuson research has moved to post-consumer asphalt shingles due in

2 A. Buss et al. / Construction and Building Materials 61 (2014) 1–9

part to the limited availability of post-manufacturer asphalt shin-gles, the rise in asphalt prices and the success in the use of post-manufactured RAS in HMA pavements. It has been estimated thatmore than 10 million tons of asphalt shingles are landfilled everyyear and over sixty percent are post-consumer asphalt shingles[2]. The environmental incentive of diverting large quantities of as-phalt shingles from landfills combined with the economic value ofreplacing virgin asphalt, aggregate, and fibers, has brought this re-search to the forefront for state environmental and transportationengineers.

Research has shown that the composition of RAS provides botheconomic value and mix properties that can enhance the perfor-mance of asphalt pavements [3]. The continuing challenges in uti-lizing RAS are found to be the quality control and quality assuranceof the final product along with identifying mix designs that meetthe requirements of specifying agencies which includes the volu-metric properties of RAS for their inclusion in HMA volumetricproperties. Some of the earliest published literature on the use ofpost-manufacturers’ recycled shingles in HMA was done by Emeryand MacKay [4] and although it included other recycled materialsit accurately identifies the limiting factors to utilizing RAS in pave-ment construction today: material variability; collection, storageand processing costs; lack of technical guidance and specifications;environmental constraints; and agency conservatism. Researchcompleted on post-manufacturer recycled shingles has found thematerial to perform as well or better than HMA mixes not contain-ing post-manufacturers’ RAS [5–8].

Implementation of WMA has become widespread over the pastdecade as more contractors utilize the technologies to take advan-tage of reduced mixing and compaction temperatures, reduced fuelconsumption and better compatibility. There are four main catego-ries of WMA technologies which include: chemical additives, waxadditives, foamed asphalt mix-additives and foamed asphalt-plantmodifications. For this study, a chemical additive derived from theforest products industry and a foamed asphalt-plant modificationwere studied. It is recommended that the forest products chemicaladditive be added at rate of 0.5% by weight of binder [9]. Foamingasphalt began in the 1950s but has more recently increased in pop-ularity. Foaming systems use nozzles to deliver small droplets ofwater to foam the asphalt.

Research in the area of warm mix asphalt has found overallfavorable results with its use. One area of concern for WMA ismoisture sensitivity. Multiple research studies have shown thatin cases where the WMA additive does not contain an anti-strip-ping agent, there is a reduction in tensile strength ratios in WMAcompared to HMA samples. A recent study investigated themechanical properties of plant-produced warm-mix asphalt mix-tures. This study found that the WMA dosage, production temper-ature and binder properties all significantly affected theperformance test results of the dynamic modulus and Hamburgwheel tracking tests (HWTT). Stripping inflection points (SIP) forfoamed asphalt and a Fischer–Tropsch wax were found to be lowerthan the HMA control mixtures [10]. This reinforces the findings ofearlier studies that WMA is susceptible to moisture conditioning[9,11]. In 2011, a survey sent out to the state agencies asking aboutthe current use of WMA. The published results showed thatapproximately 87% of the respondents indicated that WMA wasused in their state. The final question asked respondents if anymoisture damage related field distresses were observed in WMAmixes and no respondents answered ‘‘yes’’ [12]. WMA field sec-tions have also shown to perform well compared with HMA sec-tions in other published literature [13–15].

Low temperature semi-circular bending (SCB) tests will beimportant for developing a full profile of WMA–RAS materialbehavior. Disk-shaped compact tension (DCT) testing is also com-monly used for low temperatures. One published study showed

that fracture energy measured in the SCB and DCT at low temper-atures showed no significant differences by mix at the same testtemperatures [16]. Another study tested samples at intermediatetemperatures and correlations show that SCB is a viable way oftesting WMA samples and can be correlated to other tests [17].

Many studies have proven the successful use of RAS and WMAindependently of each other but only a limited number of studiesinvestigate the performance of RAS and WMA pavements whenboth technologies are used within the same mix. A state-of-the-art review of the Fischer–Tropsch wax technology [18] discussesseveral studies in which the use of RAS and WMA have shown toprovide satisfactory results in low volume roads [19,20] and instone matrix asphalt pavements [21]. The use of WMA and RAS to-gether can potentially decrease the amount of virgin liquid asphaltand reduce the carbon footprint by lowering production tempera-tures. This will lead to decreased costs while developing more sus-tainable highway materials. The objectives of this research are toevaluate the performance of plant produced WMA containing var-ious levels of RAS, investigate the influence of RAS and WMA tech-nologies on performance test results, and document pavementperformance over several years of service.

2. Material information and sample preparation

Two demonstration field projects from two different states are included in thisstudy to evaluate the use of RAS with WMA technologies at reduced temperatures.The first was an Indiana DOT demonstration project constructed on US Route 6 inAugust 2009. For the demonstration project, 1.5 inches of the HMA was milledand replaced with 1.5 inches of one of three experimental mix designs: an HMAcontrol section with 15% RAP (0% RAS), an HMA test section with 3% RAS (0%RAP), and a WMA test section with 3% RAS (0% RAP). The WMA was produced usingan asphalt plant modification that foamed the asphalt. Each mix design was adense-graded 9.5 mm Superpave mixture. Aggregate proportions in the 15% RAPmix design were slightly adjusted to create a 3% RAS mix design with the same gra-dation as the 15% RAP mixture. The 3% RAS–WMA mixture was the same design asthe 3% RAS–HMA mixture; the only difference between the two RAS mixtures wasthe plant temperature for the WMA mix, The average laydown temperature waslowered approximately 30�F (reduced from 300�F to 270�F) during plant foamingprocess. Post-consumer RAS with a 26.8% asphalt content and a high performancegrade (PG) of 134.2 was used for the mix designs. A polymer modified PG 70-22was used as the binder. A summary of the aggregate gradations and mix designproperties are presented in Tables 1 and 2, respectively.

The second project was a demonstration project constructed on US 61 betweenMuscatine and Blue Grass, Iowa in 2010. The project was construction of new as-phalt shoulders along existing Highway 61. This project used three mix designs: a20% recycled asphalt pavement (RAP) mixture (designated as IA-0) to achieve 21%virgin asphalt binder replacement, 13% RAP and 5% RAS (designated as IA-5) toachieve 32% virgin binder replacement, and 6% RAP with 7% RAS (designated asIA-7) to achieve 29% virgin asphalt binder replacement. Production of the mixes uti-lized a WMA technology derived from the forest products industry and all threemixtures were produced at the reduced temperature of 121 �C (250�F). The compac-tion temperature for reheating samples in the laboratory was 121 �C. The aggregategradations for each mixture are presented in Tables 1 and 2, respectively.

Laboratory performance testing was conducted on laboratory compacted sam-ples of loose mix collected in the field during the demonstration projects. For theIowa mixtures, the loose mix was reheated to compaction temperatures, 149 �C(300�F) for HMA samples and 121 �C (250�F) for WMA samples, split into properlysized samples and compacted using a Superpave gyratory compactor. The foamedasphalt in the Indiana mixture was reheated at HMA compaction temperatures be-cause it is assumed the benefit of the foam is diminished for reheated asphalt mix-tures. All samples were compacted to the exact dimensions needed for testing.Indirect tensile strength and HWTT analysis of the Iowa demonstration project alsoincluded core samples that were taken from the field after one year of service. Coresamples were saw cut to the correct dimensions for testing.

3. Test methodology

3.1. Mix testing

Five performance tests were conducted to analyze and evaluatethe performance of using RAS with WMA. High-temperature teststo evaluate the mix for rutting include flow number and HWTT.Dynamic modulus evaluates the stiffness of the mixture over a

Table 1Aggregate gradation for Indiana and Iowa mixtures.

Sieve size (mm) Indiana project Iowa WMA project

HMA 3% RAS WMA 3% RAS HMA 5% RAP IA-0 IA-5 IA-7

12.5 100 100 100 87 87 869.5 95 96 97 75 74 744.75 74 75 77 54 55 562.36 53 54 56 41 42 441.18 37 38 39 30 29 300.6 26 26 26 20 18 190.3 16 16 15 8.9 9.5 9.40.15 10 10 9 4.2 5.5 5.00.075 6.2 6.3 5.5 2.8 4.1 3.6

Table 2Volumetric properties for Indiana and Iowa mixtures.

Mix property Indiana project Iowa WMA project

HMA–RAP HMA-RAS WMA-RAS IA-0 IA-5 IA-7

% RAS 0 3 3 0 5 7% RAP 15 0 0 20 13 6% Total AC 5.7 6.2 6.2 4.6 5.0 5.5% Virgin AC 4.6 5.4 5.4 3.6 3.4 3.9% Binder replacement 19.3 12.9 12.9 21.7 32.0 29.1% Effective asphalt 5.1 5.2 5.2 4.35 4.8 5.23% VMA 15.3 15.1 15.1 13.2 14 14.9% VFA 73.9 73.5 73.5 77.2 78.5 79.9Continuous PG in field sample 75.6–20.1 77.6–14.2 78.8–15.1 72.3–25.9 79.3–23.4 >82–16.9

A. Buss et al. / Construction and Building Materials 61 (2014) 1–9 3

range of temperatures and frequencies. The four point bendingbeam (beam fatigue) evaluates the mixtures for fatigue crackingand the SCB test measures the fracture energy, fracture toughness,and stiffness at low temperatures.

Fig. 1. Example of permanent strain vs. loading cycles and types of deformation.

3.1.1. Dynamic modulusThe dynamic modulus test is conducted to determine the

stress–strain relationship of the asphalt mixtures under continu-ous sinusoidal loading over a range of temperatures and frequen-cies. Dynamic modulus testing measures the stiffness of theasphalt and can be used to determine which mixes may be moresusceptible to performance issues including rutting, fatigue crack-ing and thermal cracking. A high dynamic modulus indicates high-er stiffness, or lower strains, under repeated traffic loading. Thetest method followed was American Association of State Highwayand Transportation Officials (AASHTO) TP62-07. Five replicate testspecimens of each asphalt mixture were compacted to 100 mm(3.94 in.) in diameter and 150 mm (5.91 in.) in height at 7 ± 0.5percent air voids. The specimens were directly compacted to theirgeometry using a gyratory compactor with a compaction moldmodified to a 100 mm (3.94 in.) inner diameter. A study publishedin 2006 compared the dynamic modulus results between coredsamples and samples compacted to the exact sample dimension.The comparison showed that the dynamic modulus test results be-tween the two methods of sample preparation showed no statisti-cal differences [22]. Specimens were tested by applying acontinuous sinusoidal load at 9 frequencies (0.1, 0.3, 0.5, 1, 3, 5,10, 20, 25 Hz) and three different temperatures [4 �C (39�F), 21 �C(70�F), 37 �C (99�F)].

The equipment used for dynamic modulus testing is a universaltesting machine (UTM) with a 25 kN load capacity housed in anenvironmental chamber capable of maintaining a constant testtemperature. Three linear variable differential transformers (LVDT)are used to measure the strain. The dynamic modulus values (E�)are used to construct master curves that display the E⁄ values overthe wide range of temperatures and frequencies tested.

3.1.2. Flow numberThe dynamic modulus test is non-destructive and allows for

further destructive, flow number testing on the same samples.Fig. 1 shows the three types of deformation that occur during theflow number test. The flow number measures the point where anasphalt material reaches tertiary flow. The flow number test wasconducted at 37 �C using a haversine load with a frequency of1 Hz with a loading time of 0.1 s and a rest period of 0.9 s.

3.1.3. Four-point bending beamThe four-point beam fatigue testing was conducted according to

AASHTO T321, ‘‘Determining the Fatigue Life of Compacted Hot-Mix Asphalt (HMA) Subjected to Repeated Flexural Bending’’. Sam-ples of field produced asphalt were compacted to 7 ± 0.5 air voidsin a linear kneading compactor to obtain a compacted slab. Eachslab was saw-cut into three beams with dimensions 380 mm(15 in.) in length, 63 mm (2.5 in.) in width and 50 mm (2 in.) in

Fig. 2. Typical SCB testing results.

4 A. Buss et al. / Construction and Building Materials 61 (2014) 1–9

height. The slabs for the Iowa mixture were compacted to 60 mm(2.36 in.) in height. Two slabs were compacted for each asphaltmixture to produce six beams for testing for the Iowa mix. Dueto a limited amount of material, only 3 beams were tested forthe Indiana mixtures containing 3% RAS. The test equipment is adigitally controlled, servo-pneumatic closed loop beam fatigueapparatus. A control data and acquisition system (CDAS) is con-nected to the beam fatigue and computer which controls the load-ing during the test. The beam fatigue apparatus is housed in anenvironmental chamber maintained at the testing temperature of20 ± 0.5 �C (68 ± 1�F). Beams were conditioned for at least twohours prior to testing. The mode of loading used for the test wasstrain controlled. Haversine wave pulses were applied to the spec-imen during the test at 10 Hz. Testing was conducted at variousstrain levels to generate a fatigue curve for each asphalt mixture.For each of the six beams prepared from each asphalt mixture,strain levels of 350, 450, 525, 650, 800, and 1000 micro-strainswere applied. The Indiana RAS mixes only tested three beams atthe strain rates of 400, 700 and 1000 micro-strain levels due to alimited amount of material.

From the beam fatigue tests conducted at the multiple strainlevels, a log–log regression is performed between strain and thenumber of cycles to failure (Nf). The relationship between strainand Nf can be modeled using the power law relationship as pre-sented in the following equation:

Nf ¼ K1ð1=e0ÞK2

where Nf is the cycles to failure; e0 is flexural strain; K1 is regressionconstant; and K2 is the regression constant.

When the tensile strains are such that a pavement exhibits nocumulative damage over an infinite number of load cycles, thislower strain boundary is referred to as the fatigue endurance limit(FEL). The FEL can only be estimated because it is impossible to testa sample to an infinite number of cycles. NCHRP Report 646 hasdeveloped a practical procedure for estimating the FEL based onthe definition that the FEL is the strain level at which a samplecan withstand 50 million load cycles. The FEL is the lower 95% pre-diction limit at 50 million load cycles from a regression analysis offatigue data corresponding reasonable close to the FEL. This tech-nique uses the following equation to estimate the fatigue life:

Lower Prediction Limit ¼ yo � tasffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi1þ 1=nþ ðx0 � �xÞ2=Sxx

q

where yo = the one-sided lower 95% prediction interval at the mi-cro-strain level corresponding to 50,000,000 cycles;ta = value of tdistribution for n-2 degrees of freedom for a significance level of0.05; s = standard error of the regression analysis; n = number ofsamples; Sxx = sum of squares of the x values; xo = log 50,000,000;and�x = average of the fatigue life results [23].

3.1.4. Semi-circular bendingRAS increases binder stiffness making mixtures more suscepti-

ble to thermal cracking. The temperature reduction in WMA mayhelp ease the effects of the binder stiffening or may impede binderblending. The semi-circular bending test will be used to calculatethe low temperature-fracture properties of the RAS-modified mix-tures. Fracture energy calculations will be calculated to determinethe susceptibility to thermal cracking. The SCB tests were con-ducted by following the procedure in ‘‘Investigation of LowTemperature Cracking in Asphalt’’ [24]. Testing was conducted atvarious low temperatures depending on the initial PG grade ofthe asphalt. All tests were performed inside an environmentalchamber that uses liquid nitrogen to obtain the required low test-ing temperatures. A crack mouth opening displacement (CMOD)was used to keep the CMOD rate at a constant 0.0005 mm/s duringthe test and the load line displacement curve was plotted to

calculate the fracture toughness and fracture energy (Gf). The test-ing was stopped when the load dropped to 0.5 kN in the post peakregion. Fig. 2 shows the force and average load line displacement ofa typical SCB test.

3.1.5. Hamburg wheel tracking testHWTT was performed for the Iowa mixtures. The HWTT was

performed according to AASHTO T-324. The samples used in thisstudy are 6 in. (152.4 mm) diameter and 23/8 in. (60.33 mm) tall.Both pavement cores and plant produced/gyratory compactedsamples were tested for this study. The test measures the amountof rutting occurring in samples as a heavy metal wheel passes overthe samples. Rutting depth is measured using a LVDT. The pressurefrom the wheel is 71.7 kg (158 pounds) at the center. The samplesare cut with a saw along a secant line so there is no space or gapwhen two samples are joined together for testing. All samples weretested in 50 �C (122�F) water and conditioned for 30 min. The re-sults were calculated using the spreadsheet provided by the IowaDOT which follows standard AASHTO T-324 guidelines. Fig. 3shows an example of how the SIP is determined. The smoothcurved line is the best fit curve and the inflection slopes are shownas straight lines that meet at a point. The horizontally decreasinglinear line is determined by the first steady-state portion of theexperimental curve and the vertically decreasing line shows thesecond steady-state portion of the curve. The SIP is the numberof wheel passes that have elapsed where the two inflections slopescross on the graph. A minimum stripping inflection point must bemet in order to determine if samples meet moisture susceptibilityrequirements. The SIP requirements will change based on the typeof mix.

3.2. Pavement condition surveys

Pavement condition surveys were performed after one, two andthree winters. Three 152.4 m (500 feet) sections were randomly se-lected and surveyed for each pavement. The Iowa pavement hasonly been surveyed for two years because it was paved a year laterthan the Indiana pavement. The surveys were conducted in accor-dance with the Distress Identification Manual for Long-Term PavementPerformance Program [25]. The pavement surveys for the Indianaproject were conducted within the lanes of traffic where thecorresponding mix was located. The Iowa RAS study was performedon a shoulder mix and the pavement sees little traffic loading.

4. Results

4.1. Dynamic modulus

The master curves were constructed at a reference temperatureof 21 �C (70�F) and plotted on a log-log scale for general compari-son in Figs. 4 and 5. The Indiana mixture, Fig. 4, shows the RAP and

-12.0

-10.0

-8.0

-6.0

-4.0

-2.0

0.00 5,000 10,000 15,000 20,000

Rut

Dep

th, m

m.

Pass Number

Measured Rutting Inflection Slopes Fit

Fig. 3. Hamburg wheel tracking test results.

1.0.E+04

1.0.E+05

1.0.E+06

1.0.E+07

1.0.E+08

1.E-05 1.E-02 1.E+01 1.E+04 1.E+07

|E*|

, kPa

Log Reduced Frequency, Hz

IA-0

IA-5

IA-7

Fig. 5. Iowa dynamic modulus master curves WMA mixes with 0%, 5%, 7% shingles.

A. Buss et al. / Construction and Building Materials 61 (2014) 1–9 5

RAS mixtures have similar dynamic modulus values across a widefrequency range even though one mix contains 15% RAP andthe other two mixes contain 3% RAS. This is likely the result ofthe mixes containing blended binders with similar properties. Thebinder from the RAS has a higher stiffness modulus than the binderfrom the RAP, but the 15% RAP mix design contains a 19.3% binderreplacement while the 3% RAS mix designs contain a 12.9%binder replacement. This created mixtures with similar binderperformance grades (Table 2), resulting in mixtures with similarmodulus values. The results also show that the WMA technologydid not change the dynamic modulus of the mixture.

The master curves for the Iowa mixture are shown in Fig. 5. Eachcurve represents an average of five samples tested for each mixture.The stiffest mixture at low temperatures is IA-0 but is also the soft-est at high temperatures. Statistical multiple comparison tests, Tu-key honestly significant difference (HSD), were performed on theaverage dynamic modulus measured at each test temperature, (4,21, 37 �C). The multiple comparisons test help distinguish statisti-cal differences between the test results, in this case, the mixes con-taining 0%, 5% and 7% RAS. Tukey HSD tests, Table 3, show mixtureIA-0 having a statistically higher dynamic modulus than IA-5 andIA-7 at temperatures 4 and 21 �C (39 and 70�F), where a = 0.05.The levels in Table 3 that are not connected by the same letter arestatistically different, where a = 0.05. At 37 �C (99�F), the effect ofthe shingles causes IA-7 to have a statistically higher average dy-namic modulus followed by IA-5 and IA-0. The high temperaturestiffness is also reflected in the flow number results shown inFig. 6. The increased high temperature grade from the RAS is evi-dent at 37 �C but the lower temperatures mask the difference be-tween the high temperature grades. The analysis shows theimportance of observing the entire master curve when makingcomparisons for the RAS. Averaging E� over a range of temperaturescan mask the true effect of the shingles at high temperatures.

4.2. Flow number

The flow number test results are shown in Fig. 6. The columnsshow each mix with increasing RAS content. The Iowa mixture,

1

10

100

1000

10000

1E-5 1E-3 1E-1 1E+1 1E+3 1E+5 1E+7

|E*|

, ks

i

Log Reduced Frequency, Hz

HMA 15% RAP

HMA 3% RAS

WMA 3% RAS

Fig. 4. Indiana demonstration project dynamic modulus results.

which used the a chemical additive derived from the forest prod-ucts industry at WMA production temperatures, showed poor per-formance in flow number with IA-0 (20% RAP and 0% RAS). Theflow number improved slightly with IA-5 (5% RAS) but there wasa large improvement in the IA-7 mixture (7% RAS), indicating notertiary flow due to the increased stiffness. The Indiana mixtureshowed similar improvements with the addition of RAS. TheHMA mixture with 15% RAP showed a significant increase in flownumber when RAS was added at 3%. The flow number for theWMA-3% RAS mixture showed slightly higher but similar perfor-mance to the HMA-3% RAS mixture. This study also indicates thatif a mixture has poor performance without RAS, it may take a high-er percentage of RAS to overcome the low initial mixture stiffness.The Indiana mix showed flow number improvement with the addi-tion of 3% RAS and the Iowa mix showed only little improvementwith 5% RAS but saw significant improvement for 7% RAS. It ap-pears that the reduced mixing temperature does not negatively im-pact the flow number when shingles are added.

4.3. Four-point bending beam

Pavements that have a higher resistance to tensile strains thatdevelop at the bottom of an asphalt layer due to repeated trafficwill have a greater resistance to fatigue cracking. The materialsthat are stiffer may not perform as well under the constant straintesting of the beam fatigue testing due to increased micro-crack-ing. The power law relationship between the applied strain andthe fatigue life gives Nf, the intercept (K1) and the slope (K2); Theseparameters are used to estimate the fatigue endurance limit. Thelarger endurance limit is an indicator of better fatigue endurance.The K1 and K2 coefficients, R2 value and predicted fatigue endur-ance limit (FEL) are presented in Table 4. The beam fatigue resultsof this study were compared with a comprehensive beam fatiguestudy that evaluated performance data from an Illinois study[26]. The Illinois study found that nearly ninety percent of mix-tures tested showed K2 values above 4. The tested mixtures inthe cited study did not have RAS or WMA additives. All of the Indi-ana mixes, with or without RAS, performed well with respect to fa-tigue cracking since all the K2 coefficients are above 4. The additionof 3% RAS did not have a significant effect on the fatigue endurancelimit. IA-0 did not perform well due low Nf values and variability inthe data set. Higher variability increases the width of the confi-dence interval used to calculate the endurance limit and this isthe reason for the low FEL. The relatively high variability may bedue to the higher amount of RAP in IA-0 compared with IA-5 andIA-7. The fatigue testing seemed to improve with the addition ofRAS, with IA-7 having a higher FEL and higher K2 value than IA-5. This shows that the RAS does not always negatively influencethe fatigue cracking susceptibility of a mixture. The improvementin fatigue may be due to the addition of the fibers in the shinglescreating better fatigue resistance.

Table 3Multiple comparison tests for the Iowa RAS–WMA mixtures.

4 �C test temperature 21 �C test temperature 37 �C test temperature

Level Least Sq mean Level Least Sq mean Level Least Sq mean

FM7-0 A 11397 FM7-0 A 4239 FM7-7 A 1270FM7-5 B 9501 FM7-7 B 3774 FM7-5 B 1078FM7-7 B 8919 FM7-5 B 3726 FM7-0 B 1052

Fig. 6. Flow number test results.

6 A. Buss et al. / Construction and Building Materials 61 (2014) 1–9

4.4. Semi-circular bending

The low temperature cracking susceptibility was measured inthe SCB test. The fracture energy (Gf) and fracture toughness (Kic)results for both the Iowa and Indiana mixtures are shown inFig. 7 with 95% confidence intervals. On average, there is a decreasein Gf as the temperature decreases with the exception of �22 �C(�7.6�F) in the Indiana mixture. The low temperature of �22 �Cin the Indiana mixes (�7.6�F) increases the peak strength whichcorrelates to toughness and may also lead to the general increase

Table 4Beam fatigue results.

State agency Mix ID % RAS % RAP K1

Indiana HMA–RAP 0 15 7.04HMA–RAS 3 0 1.41WMA–RAS 3 0 1.17

Iowa IA-0 0 20 2.67IA-5 5 13 2.80IA-7 7 6 1.13

0

500

1000

1500

2000

2500

3000

3500

4000

4500

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

IA-0 IA-5 IA-7

Gf(J

/m2 )

Kic

, MP

a*m

0.5

-6 Kic -18 Kic -30 Kic-6 -18 -30

Kic

(M

Pa*

0.5)

Fig. 7. Fracture toughness (Kic) and fracture energy (

in Gf at �22 �C. The WMA mixes with shingles appear to showhigher variability in the Gf measurements, but overall there arefew statistically significant differences suggesting that the additionof shingles do not negatively impact the mixture’s low tempera-ture cracking properties. The Iowa mixture trends show a decreasein fracture energy with decreasing temperature, with variabletrends in the fracture toughness (Kic). The high variability is likelydue to the differences in each sample’s individual heterogeneity atthe place where the sample notch was cut; the heterogeneitycauses crack propagation to be different in each sample. Thereare differences between the measured Gf values for the Iowa mixand Indiana mix, shown in the solid bars, is likely due to the differ-ent loading frames used at the two testing locations. It is not rec-ommended to compare between the two mixes but comparisonscan be made between the variables within each of the mixes.

4.5. Pavement condition survey

Table 5 presents the results of the annual pavement conditionsurveys. Surveys were conducted yearly after the first winter thepavements were constructed. Three 152 m (500 feet) sections wererandomly selected for each pavement. In general, RAS mixturesare more susceptible to transverse cracking and so the transversecracking is the primary distress of interest for the surveys. Trans-verse cracking was measured using a measuring wheel. The Indiana

K2 R2 Endurance limit (micro-strain)

E-12 4.87 0.993 114E-11 4.77 0.970 118E-11 4.81 0.985 110

E-05 2.72 0.982 16E-10 4.35 0.975 75E-13 5.43 0.971 114

0

200

400

600

800

1000

1200

1400

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

Control Mix HMA + RAS WMA + RAS

Gf

(J/m

2)

-6 Kic -12 Kic -18 Kic -22 Kic-6 -12 -18 -22

Gf) data for Iowa and Indiana RAS–WMA mixes.

Table 5Pavement distress survey results.

State agency Mix ID Transverse cracking, meters (feet) per 152.4 m (500 feet) of 1 traffic lane

1 winter after construction, 2 winters after construction 3 winters after construction

Indiana HMA–RAP 1.22 (4) 48.16 (158) 58.23 (191)HMA–RAS 10.67 (35) 49.38 (162) 52.43 (172)WMA–RAS 14.33 (47) 80.47 (264) 84.43 (277)

Iowa IA-0 0 0 –IA-5 0 0 –IA-7 0 0 –

0

200

400

600

800

1000

1200

1400

Stre

ngth

(kP

a)

IA-5IA-0 IA-7

4" Lab 4" Field 4" Lab 6" Lab6" Lab 4" Lab 6" Lab6" Cores

IA-0

IA-5

IA-7

Fig. 8. Indirect tensile strength results for Iowa mixtures.

0.00

0.20

0.40

0.60

0.80

1.00

1.20

Ten

sile

Str

engt

h R

atio

IA-0 WMA Lab IA-0 WMA Field IA-0 WMA Lab 6" IA-5 WMA Lab

IA-5 WMA Lab 6" IA-7 WMA Lab IA-7 WMA Lab 6"

Fig. 9. Iowa mixes TSR values for 4 in. and 600 samples.

A. Buss et al. / Construction and Building Materials 61 (2014) 1–9 7

mixture showed the highest cracking in the WMA-RAS after thefirst winter but had only 3.66 m (12 feet) of additional crackingcompared with the HMA-RAS mix. There was a considerable in-crease in cracking for all Indiana pavement sections after the secondwinter with the WMA-section showing substantially higher dis-tresses when compared with the HMA-sections after two and threewinters. The Indiana WMA mixture was an overlay so underlyingcracking may be causing some of the performance differences.The HMA-RAP and HMA-RAS sections show similar performancetwo and three winters after construction. The survey after the thirdwinter showed only a small increase in cracking. The Iowa WMA-RAS project replaced gravel shoulders with new asphalt shouldersso the Iowa pavement sections do not see traffic loads. The pave-ment surveys found no pavement distresses or transverse cracking.Rumble strips are milled into this shoulder and there are no pave-ment distresses from the rumble strips as well. The performancetest that would most likely correlate to the transverse low temper-ature cracking is the SCB and the SCB results showed that all theIowa mixtures performed in a similar manner. The SCB results forthe Indiana mixture did not show the differences that were seenin the pavement survey data but this may be due to underlyingpavement conditions which can greatly influence transverse crack-ing in the field.

4.6. Moisture sensitivity testing on Iowa mixes

Moisture sensitivity has been an ongoing concern with WMAmixes. In order to see how shingles impact the moisture sensitivityof WMA, tensile strength ratio and HWTT were performed on theIowa mixtures. The indirect tensile strength was conducted for4 in. (102 mm) and 6 in. (152 mm) plant-produced lab-compactedsamples. Cores from the roadway were collected and tested forboth HWTT and IDT. Generally, a passing TSR is 80% or greaterwhen taking the ratio of the wet and dry strengths. TSR valueswere calculated for both 6 in. (152 mm) and 4 in. (152 mm) diam-eter samples. Iowa, prior to the implementation of the Hamburg,had used 4 in. (102 mm) IDT samples to calculate TSR values. TheHWTT uses the stripping inflection point to measure moisturesusceptibility.

The IDT strength values for the Iowa mixtures are shown inFig. 8. The strength values show that different amounts/types ofrecycled material have similar strength values when the samplehas not been moisture conditioned. Six inch (152 mm) sampleshave a reduced strength compared with the 4 in. (102 mm) sam-ples. The TSR values are shown in Fig. 9 and indicate that this mix-ture is prone to moisture susceptibility because not all of thesamples reach a TSR value of 80%. There is a decreasing trend inTSR values as more shingles are added to the mixture with IA-7having the lowest TSR. All of the cores tested appear to have sim-ilar strength values and strength values correlate well with the6 in. (152 mm) strength values for the gyratory compactedsamples.

The HWTT, shown in Fig. 10, suggest an improvement with rut-ting and moisture susceptibility as RAS content increases. Theopposite trend is observed in the TSR averages. IA-7 has the lowestTSR and has the lowest rutting average due to the increased RAS.IA-0 shows the highest rutting values IA-0 passed the TSR mini-mum criteria. The IA-0 HWTT mixes show differences in the ruttingpattern but past 5000 cycles, the rutting values are similar,

-18.0

-16.0

-14.0

-12.0

-10.0

-8.0

-6.0

-4.0

-2.0

0.0

Rut

Dep

th, m

m.

Pass Number

IA-0 Lab IA-0 Core IA-5 Core

IA-5 Lab IA-7 Core IA-7 Lab

Fig. 10. Hamburg wheel tracking tests results for Iowa mixes showing improve-ment with increased RAS.

8 A. Buss et al. / Construction and Building Materials 61 (2014) 1–9

suggesting that passing the HWTT may be correlated with binderstiffness.

5. Conclusions and recommendations

RAS and WMA technologies were used successfully at reducedtemperatures in two demonstration projects with a chemical addi-tive and asphalt foaming. The laboratory performance tests andfield performance surveys show encouraging results for the incor-poration of RAS with WMA technology at reduced temperatures.Two demonstration projects were constructed to assess the perfor-mance of mixtures that use WMA and RAS at reduced tempera-tures. The first demonstration project was an overlay in Indianaconstructed in 2009. The mixes tested were HMA–RAP, HMA–RAS, and WMA–RAS. The second demonstration project includedconstruction of asphalt shoulders in 2010 using three mixes thatincluded the following: WMA and 20% RAP, WMA and 13% RAP-5% RAS and WMA with 6% RAP-7% RAS. The dynamic modulus re-sults for the Indiana demo project indicate similar values betweenall three mixes. The Indiana HMA–RAP mixture had higher totalbinder replacement compared with the RAS mixes, creating similardynamic modulus values at all temperatures tested. The dynamicmodulus results for the Iowa mixtures show the importance ofevaluating all temperatures and frequencies within the mastercurve. The shingles appeared to play an important role in the stiff-ness at various temperatures. The IA-7 mixture showed the lowestdynamic modulus values at low temperatures but at the highesttemperatures, the increased stiffness in the binder from the addi-tion of shingles increased the stiffness at high temperatures. Whenstudying the influence of shingles on mixtures, it is important toensure that all temperatures and frequencies are considered.

Flow number for both projects increase with the addition ofshingles. The Iowa mixtures did not see a significant increase until7% RAS was added. The flow number results suggest that for mixeswith a lower initial flow number, a higher percentage of shinglesmay be necessary to noticeably improve the flow number. Thebeam fatigue results for the Indiana mixture showed that therewere no differences between the RAP and RAS mixtures and therewere no differences between the HMA and WMA mixture. TheIowa mixture showed an improvement in fatigue life with theaddition of shingles. The IA-0 mixture did not perform well dueto the low cycles to failure and variability in the test results. SCBresults showed similar results between all mixes. Fracture energytrends appeared to be more sensitive to temperature than to frac-ture toughness.

The moisture sensitivity tests for the Iowa mixes showed de-creased TSR values as the RAS amount was increasing. The HWTTshowed improvement in the rutting depth and the SIP as the RASpercentage increased. Depending on the moisture sensitivity spec-ification used, RAS may help or hurt a mixture. If TSR is used as aspecification, the TSR values as RAS is increased should be closely

monitored when used at WMA temperatures. If HWTT is used forthe moisture conditioning specification, improvement in the SIPcan be achieved with the addition of RAS.

Owner agencies should be encouraged to perform additionaldemonstration projects that combine these sustainable technolo-gies. Based on the results of this study, lowering the plant produc-tion temperature by 30�F when foaming the asphalt or using aWMA additive, did not negatively impact the laboratory perfor-mance of the mixes that contained RAS. However, more researchon how lowering plant temperatures affect the activation of theRAS binder is still needed to concisely determine mixture perfor-mance. Yet, the results of this study, along with future research,will help state highway agencies develop construction specifica-tions that allow both RAS and WMA technologies in asphalt mixdesigns. Since the Indiana mixture was an overlay on previouslydistress pavements, it was challenging to discern if the distressesin the field were from the materials used in the mix design or fromreflective cracking. The Iowa WMA was constructed as new asphaltshoulders and all RAS/RAP combinations showed excellent fieldperformance. It would be helpful for future field demonstrationprojects that study the combination of WMA and RAS technologiesto be constructed as new pavements to evaluate field performancemore clearly.

Acknowledgments

The authors would like to thank the Iowa Highway ResearchBoard for sponsoring the research for the Iowa project. Specialthanks are due to Scott Schram at the Iowa Department of Trans-portation for assistance with conducting Hamburg Testing andcoordinating the collection of field cores. The authors would alsolike to thank Bill Rosener and the members of the Asphalt PavingAssociation of Iowa. For the Indiana project, the authors would liketo thank Mike Prather from the Indiana DOT. The Indiana projectwas part of Transportation Pooled Fund 5-(213). Thank you to Dr.Mihai Marasteanu of University of Minnesota for SCB testing ofthe Indiana mixtures.

References

[1] Middleton B, Forfylow RW. Evaluation of warm-mix asphalt produced with thedouble barrel green process. Transport Res Board 2009;2126:19–26.

[2] Booz Allen Hamilton. Analysis of recycling of asphalt shingles in pavementmixes from a life cycle perspective. Denver, CO: Environmental ProtectionAgency; 2013.

[3] Sengoz B, Topal A. Use of asphalt roofing shingle waste in HMA. Constr BuildMater 2005;19(5):337–46.

[4] Emery J, MacKay M. Use of wastes and byproducts as pavement constructionmaterials. In: Proceedings of the Transportation Association of Canada AnnualConference. Winnipeg, Manitoba, Canada, 1991.

[5] Watson DE, Johnson A, Sharma HR. Georgia’s experience with recycled roofingshingles in asphaltic concrete. Transport Res Board 1998;1638:129–33.

[6] Foo KY, Hanson DI, Lynn TA. Evaluation of roofing shingles in hot mix asphalt. JMater Civil Eng 1999;11(1):15–20.

[7] Amirkhanian SN, Vaughan KM. Field evaluation of use of waste shingles inasphalt mixtures Columbia, S.C.; [Springfield, VA]: South Carolina Dept ofTransportation; [Available through the National Technical InformationService], 2001.

[8] Reed AB. Reclaimed manufacturer asphalt roofing shingles in asphaltmixtures. Harrisburg, PA: Pennsylvania Department of Transportation; 1999.

[9] Hurley G. Evaluation of new technologies for use in WMA. Auburn, AL: AuburnUniversity; 2006.

[10] Zelelew HP. Laboratory evaluation of the mechanical properties of plant-produced warm-mix asphalt mixtures. Road Mater Pavement; 2012.

[11] Kvasnak AW, West R, Moore J, Nelson J, Turner P, Tran N. Case study of warmmix asphalt moisture susceptibility in birmingham. Transportation researchboard annual meeting. Washington, DC: Transportation Research Board; 2009.

[12] Mogawer WS, Austerman AJ, Kassem E, Masad E. Moisture damagecharacteristics of warm mix asphalt mixtures. J Assoc Asphalt PavingTechnol 2011;80.

[13] Diefenderfer SD, McGhee KK, Donaldson BM. Installation of warm mix asphaltprojects in Virginia. Charlottesville, VA: Virginia Department ofTransportation; 2007.

A. Buss et al. / Construction and Building Materials 61 (2014) 1–9 9

[14] D’Angelo J, Harm E, Bartoszek J, Baumgardner B, Corrigan M, Cowsert J, et al.Warm mix asphalt. Washington, DC.: European Practice Publication, U.S.Department of Transportation; 2008.

[15] Kasozi AH, Hajj EY, Sebaaly PE, Elkins JC. Evaluation of foamed warm-mixasphalt incorporating recycled asphalt pavement for volumetric andmechanical properties. Int J Pavement Res Technol 2012;5(2):75–83.

[16] Bernier A, Zofka A, Josen R, Mahoney J. Warm-mix asphalt pilot project inconnecticut. Transport Res Board 2012;2294:106–14.

[17] Kim M, Mohammad L, Elseifi M. Characterization of fracture properties ofasphalt mixtures as measured by semicircular bend test and indirect tensiontest. Transport Res Rec: J Transport Res Board 2012:115–24.

[18] Jamshidi A, Hamzah MO, You ZP. Performance of warm mix asphalt containingsasobit (R): state-of-the-art. Constr Build Mater 2013;38:530–53.

[19] Shivaprasad PV, Xiao FP, Amirkhanian SN. Performance of warm-mix asphaltmixtures containing recycled coal ash and roofing shingles with moistaggregates for low-volume roads. Transport Res Board 2011;2205:48–57.

[20] Xiao FP, Shivaprasad PV, Amirkhanian SN. Low-volume road wma mixtures:moisture susceptibility of mixtures containing coal ash and roofing shinglewith moist aggregate. J Mater Civil Eng 2012;24(1):48–56.

[21] Al-Qadi IL, Wang H, Baek J, Leng Z, Doyen M, Gillen S. Effects of curing time andreheating on performance of warm stone-matrix asphalt. J Mater Civil Eng2012;24(11):1422–8.

[22] Robinette CRCW. The effect of the testing history and preparation method onthe superpave simple performance test. Assoc Asphalt Paving Technol2006;75.

[23] Prowell BD, Brown ER, Anderson RM, Daniel JS, Swamy AK, Von Quintus H,et al. Validating the fatigue endurance limit for hot mix asphalt. Washington,DC: National Highway Research Council; 2010.

[24] Marasteanu M, Zofka A, Turos M, Li X, Valasquez R, Li X, et al. Investigation ofLow Temperature Cracking in Asphalt Pavements: National Pooled Fund Study776. St. Paul, MN: Minnesota Department of Transportation; 2007.

[25] Miller JB, Bellinger WY. Distress identification manual for the long-termpavement performance program. McLean, VA: Federal HighwayAdministration; 2003.

[26] Carpenter SH. Fatigue performance of IDOT mixtures. In: Engineering DoCaE,editor. Urbana, IL: Illinois Center for Transportation; 2006.