8
Laboratory comparison study for the use of stone matrix asphalt in hot weather climates Ibrahim M. Asi * Department of Civil Engineering, Hashemite University, Zarqa 13115, Jordan Received 17 November 2003; received in revised form 1 May 2005; accepted 30 June 2005 Available online 15 August 2005 Abstract Stone matrix asphalt (SMA) is a hot mixture asphalt consisting of a coarse aggregate skeleton and a high binder content mortar. It was developed in Germany during the mid-1960s and it has been used in Europe for more than 20 years to provide better rutting resistance and to resist studded tyre wear. The main objective of this research study was to compare the performance of the normally used dense graded asphalt mixtures, named in this research as control mixtures, and SMA mixtures. Samples from both mixtures were fabricated at their optimum asphalt contents that were 5.3% for control mixtures and 6.9% for SMA mixtures. Comparison performance tests that included Marshall stability, loss of Marshall stability, split tensile strength, loss of split tensile strength, resil- ient modulus, fatigue, and rutting testing were performed on both mixtures. Test results showed that although the control mixtures have higher compressive and tensile strengths, SMA mixtures have higher durability and resilience properties. In addition, although the research could not prove the superiority of SMA in rutting resistance because of the limited sample sizes, field performance of SMA mixtures proves its superiority. Therefore, especially in hot weather climates, these properties, (durability, resilience and rut- ting resistance) give SMA mixtures advantages over dense graded mixtures. Ó 2005 Elsevier Ltd. All rights reserved. Keywords: Stone matrix asphalt; Fatigue; Rutting; Indirect tensile strength; Stripping 1. Introduction Stone matrix asphalt (SMA) is a hot mixture asphalt consisting of a coarse aggregate skeleton and a high bin- der content mortar. SMA was developed in Germany during the mid-1960s and it has been used in Europe for more than 20 years to provide better rutting resis- tance and to resist studied tyre wear [1]. Because of its success in Europe, some States, through the cooperation of the Federal Highway Administration, constructed SMA pavements in the United States in 1991 [2]. Since that time the use of SMA in the US has increased signif- icantly. Japan has also started to use SMA paving mix- tures as well with good success [3]. Recently, the Ministry of Communications in Saudi Arabia has intro- duced SMA in its road specifications. In addition, one test road was constructed in the Eastern Province of Saudi Arabia. According to the SMA Technical Working Group [4], SMA is a gap graded aggregate–asphalt hot mixture that maximises the asphalt cement content and coarse aggregate fraction. This provides a stable stone-on-stone skeleton that is held together by a rich mixture of as- phalt cement, filler, and stabilising additive. The original purpose of SMA was to provide a mix- ture that offered maximum resistance to studded tyre wear. SMA has also shown high resistance to plastic deformation under heavy traffic loads with high tyre pressures, as well as good low temperature properties [2,5]. A study conducted in Ontario, Canada, by the Ministry of Transportation on SMA pavement slabs 0950-0618/$ - see front matter Ó 2005 Elsevier Ltd. All rights reserved. doi:10.1016/j.conbuildmat.2005.06.011 * Fax: +962 6 551 8867. E-mail address: [email protected]. Construction and Building Materials 20 (2006) 982–989 Construction and Building MATERIALS www.elsevier.com/locate/conbuildmat

Laboratory comparison study for the use of stone matrix asphalt in hot weather climates

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Page 1: Laboratory comparison study for the use of stone matrix asphalt in hot weather climates

Construction

Construction and Building Materials 20 (2006) 982–989

and Building

MATERIALSwww.elsevier.com/locate/conbuildmat

Laboratory comparison study for the use of stone matrixasphalt in hot weather climates

Ibrahim M. Asi *

Department of Civil Engineering, Hashemite University, Zarqa 13115, Jordan

Received 17 November 2003; received in revised form 1 May 2005; accepted 30 June 2005Available online 15 August 2005

Abstract

Stone matrix asphalt (SMA) is a hot mixture asphalt consisting of a coarse aggregate skeleton and a high binder content mortar.It was developed in Germany during the mid-1960s and it has been used in Europe for more than 20 years to provide better ruttingresistance and to resist studded tyre wear. The main objective of this research study was to compare the performance of the normallyused dense graded asphalt mixtures, named in this research as control mixtures, and SMA mixtures. Samples from both mixtureswere fabricated at their optimum asphalt contents that were 5.3% for control mixtures and 6.9% for SMA mixtures. Comparisonperformance tests that included Marshall stability, loss of Marshall stability, split tensile strength, loss of split tensile strength, resil-ient modulus, fatigue, and rutting testing were performed on both mixtures. Test results showed that although the control mixtureshave higher compressive and tensile strengths, SMA mixtures have higher durability and resilience properties. In addition, althoughthe research could not prove the superiority of SMA in rutting resistance because of the limited sample sizes, field performance ofSMA mixtures proves its superiority. Therefore, especially in hot weather climates, these properties, (durability, resilience and rut-ting resistance) give SMA mixtures advantages over dense graded mixtures.� 2005 Elsevier Ltd. All rights reserved.

Keywords: Stone matrix asphalt; Fatigue; Rutting; Indirect tensile strength; Stripping

1. Introduction

Stone matrix asphalt (SMA) is a hot mixture asphaltconsisting of a coarse aggregate skeleton and a high bin-der content mortar. SMA was developed in Germanyduring the mid-1960s and it has been used in Europefor more than 20 years to provide better rutting resis-tance and to resist studied tyre wear [1]. Because of itssuccess in Europe, some States, through the cooperationof the Federal Highway Administration, constructedSMA pavements in the United States in 1991 [2]. Sincethat time the use of SMA in the US has increased signif-icantly. Japan has also started to use SMA paving mix-tures as well with good success [3]. Recently, the

0950-0618/$ - see front matter � 2005 Elsevier Ltd. All rights reserved.

doi:10.1016/j.conbuildmat.2005.06.011

* Fax: +962 6 551 8867.E-mail address: [email protected].

Ministry of Communications in Saudi Arabia has intro-duced SMA in its road specifications. In addition, onetest road was constructed in the Eastern Province ofSaudi Arabia.

According to the SMA Technical Working Group [4],SMA is a gap graded aggregate–asphalt hot mixturethat maximises the asphalt cement content and coarseaggregate fraction. This provides a stable stone-on-stoneskeleton that is held together by a rich mixture of as-phalt cement, filler, and stabilising additive.

The original purpose of SMA was to provide a mix-ture that offered maximum resistance to studded tyrewear. SMA has also shown high resistance to plasticdeformation under heavy traffic loads with high tyrepressures, as well as good low temperature properties[2,5]. A study conducted in Ontario, Canada, by theMinistry of Transportation on SMA pavement slabs

Page 2: Laboratory comparison study for the use of stone matrix asphalt in hot weather climates

Table 1Suggested requirements for SMA mixtures developed by TWG [4]

Property Criteria

Coarse aggregate

L.A. Abrasion (AASHTO T 96) 30 MaxFlat and elongated particles (ASTM D 4791) 3:1, 20% Max

5:1, 5% MaxSodium sulfate soundness (AASHTO T 104) 15% MaxPercent fractured faces

One or more 100% MinTwo or more 90% Min

Absorption (AASHTO T 85) 2% MaxCoarse and fine durability index

(AASHTO T 210)40 Min

Fine aggregate 100% CrushedSodium sulfate soundness (AASHTO T 104) 15% MaxLiquid limit (AASHTO T 89) 25% Max

Total aggregate – gradation

19.0 mm 10012.5 mm 85–959.5 mm 75 Max4.75 mm 20–282.36 mm 16–24600 lm 12–16300 lm 12–1575 lm 8–1020 lm 3 Max

Asphalt cement AASHTO M 226

Mineral filler

Plasticity index 4 MaxPercent passing 20 mm 20%

I.M. Asi / Construction and Building Materials 20 (2006) 982–989 983

trafficked with a wheel-tracking machine gave less rutdepths in comparison to that occurring in a dense fric-tion coarse [3]. In the United States, the GeorgiaDepartment of Transportation has also performed a sig-nificant amount of wheel tracking tests on SMA mix-tures that gave positive results. In addition, SMA hasa rough surface texture, which provides good frictionproperties after the surface film of asphalt cement isremoved by traffic. Other essential factors that enhancethe feasibility of SMA in contrast to conventional hotmixture asphalt are increased durability, improved agingproperties and reduced traffic noise [4].

SMA is a hot mixture with a relatively large propor-tion of stones and a substantial quantity of asphalt andfiller. The main concept of having a gap gradation of100% crushed aggregates is to increase a pavement�s sta-bility through interlock and stone-to-stone contact. Thismixture is designed to have 3–4% air voids, and a rela-tively high asphalt content due to the high amount ofvoids in the mineral aggregate. The mixture containshigh filler content (�10% passing the 0.075-mm sieve),and typically contains a polymer in the asphalt cement,or fibre (cellulose or mineral) in the mixture to preventdrainage of the asphalt cement. This mixture has a sur-face appearance similar to that of an open graded fric-tion course, however it has low in-place air voidssimilar to that of a dense graded HMA.

Brown et al. [2] carried out a study to evaluate the per-formance of SMA in the United States by evaluating 86SMA projects. Data was collected on material and mix-ture properties, and performance was evaluated on thebasis of rutting, cracking, ravelling, and fat spots. Themajor conclusions from their study were: (1) 85% of thesurveyed projects had an aggregate Los Angeles abrasionvalue more than 30%; (2) SMA mixtures were produced�90% of the time with 25–35% of the material passingthe 4.75-mm sieve and 80% of the time with 7–11% ofthe material passing the 0.075-mm sieve; (3) 30% of thesurveyed projects had average air voids during construc-tion less than 3%; (4) 60% of the projects exceeded 6.0%asphalt content; (5) over 90% of the SMA projects hadrutting measurements less than 4 mm; (6) SMA mixturesappeared to be more resistant to cracking than densemixtures; (7) there was no evidence of raveling on theSMA projects; (8) fat spots appeared to be the biggestperformance problem in SMA mixtures.

Stabiliser

Cellulose 0.3%Mineral fibre 0.4%Polymer –

Mix design

Stone on stone contact –Voids in total mix 3–4VMA 17Asphalt content 6.0% MinCompactive effort 50 BlowsDraindown 0.3% Max

2. Experimental program

The main objective of this research study was to com-pare the performance of densely graded hot mixture as-phalt mixtures and stone matrix asphalt mixtures. Inthis research, the densely graded mixtures are referredto as control mixtures, and the stone matrix mixturesare referred to as SMA mixtures. The Marshall mix

design procedure was used in this research to optimisethe asphalt content for both types of mixtures. WithSMA mixtures optimum asphalt contents are normallyselected as that which produces 3.0–4.0% air voids [6].Table 1 lists the suggested requirements for SMA mix-tures developed by the FHWA sponsored SMA Techni-cal Working Group (TWG) in publication IS 118 [4].These requirements were followed in this study for thedesign of SMA mixtures. The experimental researchprogramme followed in this study consisted of threetasks (Fig. 1). In the first task, a preliminary investiga-tion was conducted to characterise the used asphaltand aggregate. In the second task, optimisation of thetwo mixtures was performed and enough samples fromboth mixtures were fabricated at their obtainedoptimum asphalt contents. The third task was devoted

Page 3: Laboratory comparison study for the use of stone matrix asphalt in hot weather climates

Fig. 1. Research experimental program.

984 I.M. Asi / Construction and Building Materials 20 (2006) 982–989

to the comparison of the performance of both mixtures.The performance tests were Marshall stability, loss ofMarshall stability, split tensile strength, loss of split ten-sile strength, resilient modulus, fatigue and rutting.

3. Materials used

3.1. Aggregate

The used aggregate in this study was obtained fromAbu Hadriyah located in the Eastern Province of SaudiArabia. Fig. 2 shows the recommended gradation limitsfor the dense graded wearing coarse gradation and theselected gradation for the control mixture. The selectedgradation was in the middle of both limits. Fig. 2 alsoshows the recommended gradation limits by the TWGfor SMA mixtures and the selected gradation in this re-search which was in the middle of the limits.

In SMA recommended mixtures, 8–10% of the totalamount of aggregate in the mixture passes the

0.075-mm sieve. This large amount of filler plays animportant role in the properties of SMA mixture partic-ularly in terms of air voids, voids in the mineral aggre-gate, and optimum asphalt content [7]. Since theamount of material passing the 0.075-mm sieve is rela-tively large, the SMA mixtures perform very differentlyfrom other HMA mixtures.

3.2. Asphalt cement

The asphalt cement used in this investigation was ob-tained from Riyadh oil refinery. The asphalt was 60/70Penetration Grade with a softening point of 51 �C.

3.3. Fibre stabilisation

One of the major problems usually encountered inSMA mixtures is the draindown of the binder duringmixing, transporting and compaction. To overcome thisproblem, fibres are usually added to SMA mixtures.Loose organic fibres, such as cellulose, and mineral

Page 4: Laboratory comparison study for the use of stone matrix asphalt in hot weather climates

0.01 0.10 1.00 10.00 100.00

SIEVE OPENING, mm

0

20

40

60

80

100

PER

CE

NT

PA

SSIN

G, %

3/4

1/2

3/8#4#8#30

#50

#200

#500

SIEVE SIZE

Middle

Limit

Control

SMA

Fig. 2. Grain size distribution of both control and SMA mixtures.

I.M. Asi / Construction and Building Materials 20 (2006) 982–989 985

fibres are used as stabilising agents in SMA mixtures, atthe rate of 0.3% and 0.4% by weight of mixture, respec-tively [8,9].

In this study, 0.3% mineral fibres, by weight of mix-ture, were uniformly combined with the dry aggregatebefore the asphalt cement was added.

3.4. Polymer stabilisation

In addition to fibre stabilisation, polymer stabilisa-tion is also used in SMA mixtures. In SMA mixtures,polymer stabilisation is mainly used to minimise theasphalt cement draindown. In addition, it is used toincrease the stiffness of the AC at high in service temper-atures and/or to improve the low temperature propertiesof the binder material. Polymers are typically added tothe mixture at a rate of 3.0–8.0% by weight of the as-phalt cement [10].

In this research, no polymers were added to the SMAmixture, to exclude the effect of polymers when compar-ing the performance of the SMA and control mixtures.

3.5. Optimisation of the mixtures

Marshall mix design (ASTM D 1559) procedure isnormally used to optimise the HMA mixtures in SaudiArabia. The Marshall procedure was used in this re-search to optimise the control mixtures. Six percentagesof asphalt cement (3.5%, 4.0%, 4.5%, 5.0%, 5.5%, and6.0%) were used to optimise the asphalt content. Threesamples at each percentage were prepared using a stan-dard Marshall Compactor. Seventy-five blows on eachside of the specimens were applied, as per Ministry of

Communication (MOC) design requirement. StandardMarshall specimens (63.5-mm height · 101.6-mm diam-eter) were used in this optimisation process and the restof this study. According to the Ministry of Communica-tion (MOC) design procedure, the optimum asphalt con-tent was selected to have maximum stability, maximumunit weight, and median of allowable limits for percentair voids (AV limits for wearing coarse is 4.0–7.0%).The average asphalt cement (AC) content at these threevalues is selected and checked to satisfy the AV, VMA,stability and flow specification limits. The obtained opti-mum asphalt content for the control mixtures was 5.3%.

In SMA mix design, usually the Marshall method ofmix design is used to verify satisfactory voids in SMAmixtures. Laboratory specimens were prepared usingfifty blows of the Marshall hammer per side. Seventy-five compaction blows were not used since they wouldtend to break down the aggregate more and would notresult in a significant increase in density over that pro-vided by 50 blows. SMA mixtures have been more easilycompacted on the roadway to the desired density thanthe effort required for conventional HMA mixtures[11]. The optimum AC content for SMA mixtures is usu-ally selected to produce 3.0–4.0% air voids. Marshallstability and flow values are generally measured forinformation but not used for acceptance [4]. In thisresearch, compaction of all the SMA samples wasperformed using fifty blows of the Marshall hammerper side. Fig. 3 shows the effect of varying the asphaltcontent on the values of Marshall stability, flow, specificgravity, voids in mineral aggregate (VMA), and airvoids (AV) for the SMA mixtures. Four asphalt percent-ages (5.0%, 6.0%, 7.0% and 8.0%) were used in the

Page 5: Laboratory comparison study for the use of stone matrix asphalt in hot weather climates

Determination of Optimum

Asphalt Content

Asphalt Content at 3.5 %

Air Voids = 6.90 %

4.5 5.0 5.5 6.0 6.5 7.0 7.5 8.0 8.5

Asphalt Content, %

2.30

2.32

2.34

2.36

2.38

2.40

Gm

b

4.5 5.0 5.5 6.0 6.5 7.0 7.5 8.0

Asphalt Content, %8.5

4.5 5.0 5.5 6.0 6.5 7.0 7.5 8.0

Asphalt Content, %8.5

18.0

18.5

19.0

19.5

20.0

Voi

ds in

Min

eral

Agg

rega

te,%

6.2

6.4

6.6

6.8

7.0

Mar

shal

l Sta

bili

ty, k

N

4.5 5.0 5.5 6.0 6.5 7.0 7.5 8.0 8.5

Asphalt Content, %

2.0

2.5

3.0

3.5

4.0

4.5

5.0

Air

Voi

ds,

%

4.5 5.0 5.5 6.0 6.5 7.0 7.5 8.0 8.5

Asphalt Content, %

3.0

3.5

4.0

4.5

5.0

5.5

6.0

6.5

7.0

7.5

8.0

Mar

shal

l Fl

ow, m

m

Fig. 3. Mix design of SMA mixtures.

986 I.M. Asi / Construction and Building Materials 20 (2006) 982–989

design of the SMA mixtures. It was found that at 3.5%air voids, the required asphalt cement was 6.9%.

4. Comparison of the performance of control and SMA

mixtures

In order to compare both the control and SMAmixtures, 30 samples of the control mixture using theMarshall mixing procedure and the selected gradationat an asphalt content of 5.3% were fabricated. Anadditional 30 samples of the SMA mixtures were

compacted using the 50 Marshall compaction blowseach side at an asphalt content of 6.9%. The preparedsamples were subjected to the following tests: Mar-shall stability, loss of Marshall stability, split tensilestrength, loss of split tensile strength, resilient modulus,and fatigue and rutting evaluation. Following is a dis-cussion of these tests and their results.

4.1. Marshall stability and loss of Marshall stability

In order to find the difference in the Marshallstability and loss of Marshall stability between the

Page 6: Laboratory comparison study for the use of stone matrix asphalt in hot weather climates

Table 2Marshall test results

Mix type Marshall stability at60 �C, 35 min waterimmersion (kN)

Marshall stability at60 �C, 24 h waterimmersion (kN)

% Loss

Control 10.8 8.4 29SMA 7.1 6.3 20

1000 10000 100000Number of Load Repetitions to Failure

10

100

1000

Initi

al T

ensi

le S

trai

n, m

icro

ns

SMA@ 25 CControl@ 50 C

Control@ 25 CSMA@ 50 C

Fig. 4. Fatigue curves for control and SMA mixtures at different testtemperatures.

I.M. Asi / Construction and Building Materials 20 (2006) 982–989 987

control and SMA mixtures, six samples from eachmixture were immersed in the water bath at 60 �C.The Marshall stability values for three samples fromeach mixture were obtained after 35 min of waterimmersion. In addition, the Marshall stability valuesafter 24 h water immersion were also obtained. Table2 shows the test results and the percent loss in Mar-shall stability of both mixtures. It can be observedthat although the stability of control samples is higherthan SMA samples, but the loss in Marshall stabilityis higher in the control mixtures. The reasons behindthese properties are that control mixtures have a densegraded aggregate gradation giving them higher stabil-ity, but the SMA mixtures have a higher asphalt con-tent resulting in a thicker asphalt film thickness on theaggregate leading to a higher protection against waterdamage.

4.2. Water sensitivity test (Lottman test AASHTO

T-283)

This test was carried out in order to find the watersusceptibility (stripping resistance) of control andSMA mixtures utilising indirect tensile strength (ITS).Table 3 shows the percentage loss in the indirect tensilestrength after Lottman conditioning of the samples. Theobtained results indicate that the average percentage lossin strength due to water damage is effectively reduced inSMA mixtures. This is attributed to the higher asphaltfilm thickness around the aggregate.

4.3. Resilient modulus test, MR (ASTM D 4123)

Resilient modulus (MR) is the most important variableto mechanistic design approaches for pavement struc-tures. It is the measure of pavement response in termsof dynamic stresses and corresponding strains. At 25 �Ctest temperature, SMA mixtures showed higher MR val-ues (1894.7 MPa) than the control mixtures (936.3 MPa).Therefore, SMA has improved the diametral resilient

Table 3I.T.S test results

Mix type Initial ITS (kN) Final ITS (kN) % Loss

Control 10.8 8.4 22SMA 7.1 6.3 11

modulus of asphalt mixtures compared to the controlmixtures. This might be attributed to the higher asphaltcontent and mineral filler in the SMA mixtures than thecontrol mixtures giving the SMA mixtures better resil-ience properties.

4.4. Fatigue performance

Diametral fatigue test results for control and SMAmixtures at testing temperatures of 25 and 50 �C areshown in Fig. 4. These results show a normal linear rela-tionship between the logarithm of applied initial tensilestrain and the logarithm of fatigue life (number of ap-plied load repetitions until failure). The fatigue datawere analysed by running a regression analysis to deter-mine the fatigue relationship parameters in the followingform:

et ¼ I � ðN fÞS ; ð1Þwhere et is the initial tensile strain, Nf is the number ofload repetitions to failure, I is the anti-log of the inter-cept of the logarithmic relationship, and S is the slopeof the logarithmic relationship. Regression parametersfor Eq. (1) are shown in Table 4. The results shown inFig. 4 and Table 4 show that the SMA mixtures havelower fatigue life than the control mixtures. This isattributed to the lack of the mechanical locking of theaggregate.

Table 4Regression factors for fatigue test

Mix type Regression factors at25 �C

Regression factors at50 �C

I S I S

Control 175842 �0.7295 2788459 �1.212SMA 42524 �0.6282 4935231 �1.295

Page 7: Laboratory comparison study for the use of stone matrix asphalt in hot weather climates

10 100 1000 10000 100000

Number of Load Repetitions

0.01

0.1

1

10

Per

man

ent

Def

orm

atio

n, m

icro

ns

Control @ 50 msSMA @ 50 msControl @ 75 msSMA @ 75 msControl @ 100 msSMA @ 100 ms

Fig. 5. Rutting curves for control and SMA mixtures at 25 �C.

10 100 1000 10000

Number of Load Repetitions

0.01

0.10

1.00

10.00

Perm

anen

t Def

orm

atio

n, m

icro

ns

Control @ 50 msSMA @ 50 msControl @ 75 msSMA @ 75 msControl @ 100 msSMA @ 100 m

Fig. 6. Rutting curves for control and SMA mixtures at 50 �C.

988 I.M. Asi / Construction and Building Materials 20 (2006) 982–989

4.5. Permanent deformation

The permanent deformation was simultaneously re-corded while running the fatigue test at both testing tem-peratures of 25 and 50 �C. Results are presented in Figs.5 and 6. These results indicate that a straight-line rela-tionship exists between the logarithm of number of loadrepetitions and the logarithm of permanent strain. Thepermanent deformation properties were determinedusing the following equation form:

ep ¼ I � ðNÞS ; ð2Þ

where ep is the accumulated permanent strain, N is thenumber of load repetitions, I is the anti-log of the inter-cept of the logarithmic relationship, and S is the slope of

straight line. Parameters I and S in the above equationwere obtained by using permanent deformation experi-mental data in a regression analysis.

Results indicate that the control mixtures have betterpermanent deformation resistance as compared to theSMA mixtures. In spite of the fact that the researchcould not prove the superiority of SMA in rutting resis-tance, but field performance of SMA mixtures provedthis superiority [1,2,7,11,12]. The lack of the resem-blance of the laboratory samples to field performancein rutting resistance can be attributed to the tested sam-ple size (100 · 65 mm) which might not have facilitatedthe stone to stone contact which is the main advantageof the SMA mixtures that gives it the superiority in rut-ting resistance.

5. Conclusion

This research focused on a laboratory evaluation ofthe performance of stone matrix asphalt by comparingits performance with dense graded mixtures. The follow-ing points can be concluded from the research:

1. Stone matrix asphalt (SMA) is hot mixture asphaltconsisting of a coarse aggregate skeleton and a highbinder content mortar.

2. Although the Marshall stability of control mixtures ishigher than SMA mixtures, but the loss in Marshallstability is higher in the control mixtures.

3. SMA mixtures have better durability (resistance towater damage) than control mixtures. This is attrib-uted to the higher asphalt film thickness around theaggregate.

4. SMA has improved the diametral resilience proper-ties of the asphalt mixtures as compared to the con-trol mixtures.

5. SMA mixtures have a lower fatigue life than controlmixtures.

6. Although the research could not prove the superiorityof SMA in rutting resistance due to the limited sam-ple sizes, the field performance of SMA mixturesproved this superiority.

7. For hot weather climates, durability, resilience andrutting resistance give SMA mixtures advantage overdense graded mixtures.

References

[1] Scherocman JA. SMA reduces rutting. Better Roads 1991;61(11).[2] Brown ER, Mallick RB, Haddock JE, Bukowski J. Performance

of stone matrix asphalt (SMA) mixtures in the United States.National Center for Asphalt Technology, NCAT Report No.97-1, Auburn University, Alabama; 1997.

Page 8: Laboratory comparison study for the use of stone matrix asphalt in hot weather climates

I.M. Asi / Construction and Building Materials 20 (2006) 982–989 989

[3] Brown ER, Haddock JE, Mallick RB, Lynn TA. Development ofa mixture design procedure for stone matrix asphalt (SMA).National Center for Asphalt Technology, NCAT Report No. 97-3, Auburn University, Alabama; 1997.

[4] National Asphalt Pavement Association. Guidelines for mate-rials, production, and placement of stone matrix asphalt(SMA). Technical Working Group (TWG), Publication No. IS118; 1994.

[5] Cooley LA, Brown ER, Potential of using stone matrix asphalt(SMA) for thin overlays. National Center for Asphalt Technol-ogy, NCAT Report No. 03-01, Auburn University, Alabama;2003.

[6] Brown ER, Mallick RB. Stone matrix asphalt – propertiesrelated to mixture design. National Center for Asphalt Tech-nology, NCAT Report No. 94-2, Auburn University, Alabama;1997.

[7] Davidson JK, Kennepohl GJ. Introduction of stone masticasphalt in Ontario. Report for AAPT meeting in Charleston,South Carolina, February 24–26; 1992.

[8] Brown ER, Manglorkar H. Evaluation of laboratory properties ofSMA mixtures. National Center for Asphalt Technology NCATReport No. 93-5, Auburn University, Alabama; 1993.

[9] Cooley LA, Brown ER, Watson DE. Evaluation of OGFCmixtures containing cellulose fibers. National Center for AsphaltTechnology, NCAT Report No. 2000-05, Auburn University,Alabama; 2000.

[10] An introduction to stone mastic asphalt (SMA), introductoryhandout. Scanroad, Sweden, Nobel Industry; 1991.

[11] Scherocman JA. Construction of SMA test sites in the US. AAPTmeeting; February 24–26, 1992.

[12] Brown ER. Experience with stone mastic asphalt in the UnitedStates. Alabama: NCAT Publication, Auburn University; 1992.