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This article was downloaded by: [University of Connecticut] On: 08 October 2014, At: 03:49 Publisher: Taylor & Francis Informa Ltd Registered in England and Wales Registered Number: 1072954 Registered office: Mortimer House, 37-41 Mortimer Street, London W1T 3JH, UK Road Materials and Pavement Design Publication details, including instructions for authors and subscription information: http://www.tandfonline.com/loi/trmp20 Assessment of Fracture Properties of Emulsified Asphalt Mixtures Ormsby K. Monney a , Hussain A. Khalid a & Ignacio Artamendi a a The University of Liverpool, Department of Engineering , Civil Engineering Building Brownlow Street, Liverpool, L69 3GQ E-mail: Published online: 20 Sep 2011. To cite this article: Ormsby K. Monney , Hussain A. Khalid & Ignacio Artamendi (2007) Assessment of Fracture Properties of Emulsified Asphalt Mixtures, Road Materials and Pavement Design, 8:1, 87-102 To link to this article: http://dx.doi.org/10.1080/14680629.2007.9690068 PLEASE SCROLL DOWN FOR ARTICLE Taylor & Francis makes every effort to ensure the accuracy of all the information (the “Content”) contained in the publications on our platform. However, Taylor & Francis, our agents, and our licensors make no representations or warranties whatsoever as to the accuracy, completeness, or suitability for any purpose of the Content. Any opinions and views expressed in this publication are the opinions and views of the authors, and are not the views of or endorsed by Taylor & Francis. The accuracy of the Content should not be relied upon and should be independently verified with primary sources of information. Taylor and Francis shall not be liable for any losses, actions, claims, proceedings, demands, costs, expenses, damages, and other liabilities whatsoever or howsoever caused arising directly or indirectly in connection with, in relation to or arising out of the use of the Content. This article may be used for research, teaching, and private study purposes. Any substantial or systematic reproduction, redistribution, reselling, loan, sub-licensing, systematic supply, or distribution in any form to anyone is expressly forbidden. Terms & Conditions of access and use can be found at http:// www.tandfonline.com/page/terms-and-conditions

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This article was downloaded by: [University of Connecticut]On: 08 October 2014, At: 03:49Publisher: Taylor & FrancisInforma Ltd Registered in England and Wales Registered Number: 1072954 Registered office: MortimerHouse, 37-41 Mortimer Street, London W1T 3JH, UK

Road Materials and Pavement DesignPublication details, including instructions for authors and subscription information:http://www.tandfonline.com/loi/trmp20

Assessment of Fracture Properties of EmulsifiedAsphalt MixturesOrmsby K. Monney a , Hussain A. Khalid a & Ignacio Artamendi aa The University of Liverpool, Department of Engineering , Civil Engineering BuildingBrownlow Street, Liverpool, L69 3GQ E-mail:Published online: 20 Sep 2011.

To cite this article: Ormsby K. Monney , Hussain A. Khalid & Ignacio Artamendi (2007) Assessment of Fracture Propertiesof Emulsified Asphalt Mixtures, Road Materials and Pavement Design, 8:1, 87-102

To link to this article: http://dx.doi.org/10.1080/14680629.2007.9690068

PLEASE SCROLL DOWN FOR ARTICLE

Taylor & Francis makes every effort to ensure the accuracy of all the information (the “Content”) containedin the publications on our platform. However, Taylor & Francis, our agents, and our licensors make norepresentations or warranties whatsoever as to the accuracy, completeness, or suitability for any purpose ofthe Content. Any opinions and views expressed in this publication are the opinions and views of the authors,and are not the views of or endorsed by Taylor & Francis. The accuracy of the Content should not be reliedupon and should be independently verified with primary sources of information. Taylor and Francis shallnot be liable for any losses, actions, claims, proceedings, demands, costs, expenses, damages, and otherliabilities whatsoever or howsoever caused arising directly or indirectly in connection with, in relation to orarising out of the use of the Content.

This article may be used for research, teaching, and private study purposes. Any substantial or systematicreproduction, redistribution, reselling, loan, sub-licensing, systematic supply, or distribution in anyform to anyone is expressly forbidden. Terms & Conditions of access and use can be found at http://www.tandfonline.com/page/terms-and-conditions

Road Materials and Pavement Design. Volume 8 – No. 1/2007, pages 87 to 102

Assessment of Fracture Propertiesof Emulsified Asphalt Mixtures

Ormsby K. Monney — Hussain A. Khalid — Ignacio Artamendi

The University of LiverpoolDepartment of EngineeringCivil Engineering BuildingBrownlow StreetLiverpool, L69 [email protected]

ABSTRACT. This paper presents an investigation into factors affecting the fracture properties ofa cold-laid material used as base or binder course on medium to lightly trafficked roads. TheSemi-Circular Bending beam test has been used to study the effect of temperature and rate ofloading on the fracture properties, expressed as fracture toughness and fracture energy, ofthe cold-laid material in mode I. A Hot Mix Equivalent mixture was used in the studycomprising the same aggregates and base binder. An immersion regime adopting vacuummoisture saturation was undertaken to assess the effect of ingested moisture on the measuredfracture properties. At -10 and -20oC, the fracture toughness of the cold material was almostindependent of temperature. At - 20oC, the fracture energy of the cold and hot materials werealmost equal irrespective of loading rate. The cold mixture attained reasonably high retainedfracture toughness upon vacuum moisture saturation.KEYWORDS: Fracture, Asphalt, Cold-lay, Semi-circular Bending, Moisture Damage.

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88 Road Materials and Pavement Design. Volume 8 – No. 1/2007

1. Introduction

The use of emulsions in asphalt for road construction and maintenance haswitnessed renewed vigour throughout Europe in recent years (Lesueur et al., 2004;Lesueur and Potti, 2004; Decker, 2004; Pasetto et al., 2004). This is a reflection ofthe promising performance potential of cold-laid asphalt mixtures and theirsignificant environmental advantages. However, there are still a few countries, e.g.UK, where the current level of use leaves considerable room for improvement.Research work is, thus, still necessary to characterise these materials’ properties toachieve a better understanding of their behaviour, which should, consequently,enhance confidence and usage level.

Optimum mixture performance is achieved by having a number of properties thatensure, among other things, adequate resistance to permanent deformation andcracking at high and low temperature conditions respectively. The design and natureof cold-laid asphalt mixtures, however, make it of particular interest to study theirlow temperature cracking properties at a fundamental level. Over the past decade, aconsiderable number of studies have used fracture mechanics to study the crackingresistance of hot asphalt mixtures. Within the fracture mechanics field, a number ofstudies have used the Semi-Circular Bending (SCB) test together with Linear ElasticFracture Mechanics (LEFM) concepts to evaluate fracture toughness and fractureenergy, among other properties (Marasteanu et al., 2004; Molenaar et al., 2000). TheSCB test is capable of testing laboratory prepared specimens and field cores, andobviates the self-weight problem encountered with prismatic beam specimens.

This paper aims at studying the fracture properties of an emulsion-based asphaltmixture used as base or binder course on medium to lightly trafficked roads. Onlymode I fracture, i.e. opening mode, has been considered in this work, in which theeffect of test temperature and loading rate on the fracture properties has beenstudied. Of particular relevance to cold-laid asphalt mixtures, the effect of moistureingress on fracture properties has also been considered in this study.

2. Materials and Specimen Production

2.1. Materials

Two mixtures were considered in this study, namely a Cold Emulsified AsphaltMixture (CEAM) and its hot mixture equivalent (HME). The CEAM comprised acationic emulsion manufactured with a 160/220 Pen binder and doleritic aggregatesfrom Duntilland in Scotland. The HME comprised the same crushed dolerite 14mmnominal size aggregates as in CEAM, and 160/220 Pen bitumen at 4% bindercontent. Both mixtures were continuously graded macadams suitable for bindercourse and base layers in road pavements in the UK (BSI, 2005).

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Fracture of Cold-laid Asphalt 89

The CEAM was prepared by mixing a prescribed aggregate blend with emulsionat a required residual binder content of 4% by total weight of mixture. The amountof water was around 7% by total weight of mixture.

2.2. Specimen preparation

The CEAM was prepared in 150mm diameter split cylindrical moulds using thedouble plunger static compaction method in a compression machine. A load of67.5kN was applied at the rate of 2kN/sec to compact the CEAM. The load was heldconstant for 5 minutes on each face to produce 65mm thick cylindrical samples.

The HME was produced in 300mm2 slabs at an average thickness of 65mm usinga roller compactor from which cylindrical specimens of 150mm diameter werecored.

Volumetric computations were then conducted on both mixtures aftercompaction and extrusion from the mould after 24 hours. Compacted densities ofCEAM on bulk and dry basis were 2171 and 2117kg/m3 respectively while thedensity obtained for the HME was 2319kg/m3. The voids content in the CEAM was18.6% while that obtained for the HME was 7.3%. The CEAM samples were thencured at 18 and 35°C in a fan assisted oven until no further changes in mass of thesamples were observed.

HME cores from the slabs and those produced for the CEAM were later cut intotwo halves in a direction perpendicular to the axis of the cored specimen to generatesemi-circular specimens for the three-point bending test. Before cutting, somecylindrical samples were chosen for stiffness testing and moisture conditionmonitoring to observe the effect of curing on strength build up. This will bediscussed in the next section.

3. Strength development

Curing was done to ensure that: a) the binder was not heated to a temperaturehigher than its softening point which was 35°C; b) ageing of the mixture wasavoided; and c) the curing process was accelerated (Carbonneau et al., 2003; Serfasset al., 2003). The nature of emulsified bitumen mixtures is more complex thanconventional hot-applied asphalt. The addition of water to ensure adequate coatingof the aggregates adds a third ingredient to the mixture (Fordyce, 1996). However, ithas been established (Carbonneau et al., 2003) that due to the difficulty inmeasuring the modulus of cold mixtures, it is necessary to determine the age of themixture and the curing method in addition to the mix formula. The age of themixture directly reflects the extent of evolution of the cold mixture’s performanceand functional characteristics with time. Hence, the change in the cold mixture’scharacteristics should be monitored. The monitoring helps in the definition of a

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90 Road Materials and Pavement Design. Volume 8 – No. 1/2007

process that allows one to obtain characteristic values in the laboratory that aresimilar to those obtained on cores taken insitu, thus, improving the predictive natureof the study.

3.1. Indirect tensile stiffness modulus

The indirect tensile stiffness modulus (ITSM) has been considered as beingappropriate for testing laboratory produced specimens as part of a mix designprocess (Brown et al., 1996). The ITSM is classified as a functional andperformance property of a pavement layer (Molenaar et al., 2000). The former isrelated to bearing capacity of the road pavement and the latter to its long-termbehaviour. Figures 1 and 2 show the moisture evolution and strength characteristicsof the CEAM cured using two temperatures, 18 and 35°C. Mass of the specimenscured at 35°C remained constant beyond 14 days. Those cured at 18°C, however,showed constant mass after 21 days. Monitoring of stiffness continued beyond 21days. At 14 days, a full cure state for CEAM is close to results obtained by Serfasset al. (2003), where full cure was attained after 12 days for Duriez-compactedmixtures. The minor difference could be due to various factors, such as thecompaction method and effort, and the geometry of the samples involved in thatstudy. From 14 to 21 days, the ITSM in this study continued to increase appreciablyeven after the specimen mass remained constant. This behaviour was in agreementwith the work by Serfass et al.

0

500

1000

1500

2000

2500

3000

0 3 6 9 12 15 18 21 24 27 30

Duration (Days)

ITSM

(MPa

)

0

1

2

3

4

5

6

Moi

stur

e C

ondi

tion

(%)

ITSM Moisture Condition

Figure 1. Stiffness evolution and moisture condition at 18°C curing

HME ITSM at 28 days

HME ITSM at 7 days

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Fracture of Cold-laid Asphalt 91

0

500

1000

1500

2000

2500

3000

0 3 6 9 12 15 18 21 24 27 30

Duration (Days)

ITSM

(MPa

)

0

1

2

3

4

5

6

Moi

stur

e C

ondi

tion

(%)

ITSM Moisture Condition

Figure 2. Stiffness evolution and moisture condition at 35°C curing

4. Semi-Circular Bending

4.1. Background and theory

The SCB beam test was initially developed by Chong et al. (1984) for mode Irock fracture testing. The technique was intended to be directly applicable to coredrock specimens. However, various studies have been conducted in the field ofasphalt technology using the technique with modified and unmodified asphalts asoutlined in Table 1.

Figure 3 shows a schematic of the SCB test. The specimen consists of a half discwith a crack machined from the centre of its bottom edge as shown in the figure. Astandard three point load is applied to fracture the specimen. A pure mode I stressfield is believed to exist at the crack tip if the crack were aligned parallel to andimmediately beneath the upper load point. A pure mode I condition is illustrated inFigure 4. Mode I is reported to occur when the displacements of the crack surfacesare perpendicular to the plane of the crack.

In Figure 3, F represents the applied load; 2S is the span length between supportsA and B; r is the radius of the half cylinder of diameter 2r and a is the notch depth.

HME ITSM at 28 days

HME ITSM at 7 days

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92 Road Materials and Pavement Design. Volume 8 – No. 1/2007

Table 1. Use of SCB technique in asphalt research

No. Authors Year Study Test mode Material

1Mohammad

et al.2004

Characterisation offracture and fatigue

resistance

Monotonicand Cyclic

Recycled polymermodified AC

2 Marasteanuet al.

2004 Low temperaturefracture

MonotonicFracture

Superpavemixtures

3 Mullet al.

2002 Characterisation offracture resistance

MonotonicFracture

Crumb rubbermodified asphalt

4Molenaar

et al.2000

Fracture toughnessMonotonic

FractureDAC, SMA PA

neat and polymermodified

Notes: DAC: Dense Asphalt Concrete; AC: Asphalt Concrete; SMA: Stone Mastic Asphalt;PA: Porous Asphalt.

Figure 3. A schematic of the SCB test set-up

The variation of mode I stress intensity factor as a function of crack length wasstudied by Chong et al. (1984) and a good reproducibility of the measured fracturetoughness was observed. More recently, Lim et al. (1993 and 1994) performed alarge number of tests with this technique on synthetic mudstone. The technique wasfound capable of measuring the fracture envelope of mode I opening with goodrepeatability results. According to Lim et al. (1993), the most appropriate

2S

2r

B

F

A

a

r

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Fracture of Cold-laid Asphalt 93

relationship relating the normalized stress intensity factor and the critical fracturetoughness is given in Equation [1].

X

Mode I

Y

Z

Figure 4. Schematic of the opening mode of a crack

BroS

)r/oS(IYao

IK ∆

πσ+= [1]

where

IK = Mode I stress intensity factor

rt2

Po =σ [2]

P = applied loadr = specimen radiust = specimen thickness

++= )r

a(4Cexp3C)

r

a(2C1C)r/oS(IY [3]

represents the normalized stress intensity factor, where,

iC are constants,a is the notch length.

roS

raS

roS

−=∆

[4]

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94 Road Materials and Pavement Design. Volume 8 – No. 1/2007

raS

is the actual span ratio

roS

is the nearest span ratio (typical values from Lim et al were 0.8, 0.67, 0.61, 0.5)

16)r

a(0839.2155.6)

r

a(97042.275.2)

r

a(64035.1655676.6B +++= [5]

4.2. Fracture parameters

The SCB test parameters evaluated in this study were fracture toughness orcritical stress intensity factor, KIC, and fracture energy, Gf. KIC was calculated usingthe equations given in section 4.1 assuming LEFM conditions apply and Gfrepresented the area under the load/load-line displacement curve. KIC and Gf are bestreferred to as “apparent” fracture properties since linear elastic condition may notstrictly apply to all the test conditions adopted in the study. Nonetheless, Molenaaret al. (2000) have shown that, at temperatures ≤ 0oC and low loading rates, the SCByielded fracture toughness values for dense asphalt mixtures that were considered asvalid material properties. As regards the Gf values evaluated in this study, theyincluded energy consumed in deformations at the supports and, to a lesser extent, atthe point of load application, together with any viscous deformations, albeit verysmall, in the bulk material. For this reason, the fracture energy values may beconsidered as over-estimates.

4.3. Repeatability of mode I fracture toughness test

The repeatability value, r1, is defined as the value below which the absolutedifference between two single test results obtained under identical conditions maybe expected to lie at a probability of 95% (Richardson, 1994). It is calculated fromthe following equation:

rSr ×= 8.21 [6]

where Sr is an estimate of repeatability standard deviation, 2.8 is a factor derivedfrom the basic statistical model used.

The repeatability tests were carried out on 12 SCB samples of CEAM having acommon nominal notch depth of 10mm sawn perpendicular to the base of thesectional plane normal to the sample thickness. The samples were of averagethickness of 65mm. Tests were carried out at a loading rate of 10mm/min at a testtemperature of -10°C. These tests were carried out repeatedly by one person in thesame laboratory.

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Fracture of Cold-laid Asphalt 95

Normal distribution is usually used in evaluating r1, which requires that N ≥ 30.For any sample size < 30, such as 12 used in this study, use of the student’s tdistribution is recommended.

From the test results, the mean fracture toughness was 12.74 MPa.mm0.5 and therepeatability standard deviation was 1.59 MPa.mm0.5. The calculated r1 value was4.45 which is 35% of the mean. The repeatability standard deviation, as coefficientof variation, was 12.5%. The 95% confidence interval of the mean fracturetoughness of the CEAM is between 11.73 and 13.75 MPa.mm0.5 for 12determinations. For three determinations at a confidence level of 90%, the meanfracture toughness of the CEAM would lie within ± 11.8% of the true mean.

5. Fracture behaviour

CEAM and HME samples were monotonically tested for mode I fractureproperties at different temperatures and rates of loading. Figures 5-8 illustrate thebehaviour exhibited by both materials in the SCB test.

0

5

10

15

20

25

30

-20°C -10°C 0°C

Test Temperature

Frac

ture

Tou

ghne

ss

KIC

(MPa

. mm0.

5 )

1mm/min 10mm/min 100mm/min

Figure 5. Fracture toughness results for the HME

5.1. Fracture behaviour of HME

At temperatures of -10 and -20°C in Figure 5, the fracture toughness of the hotmixture seemed to be independent of temperature since the difference in toughnessvalues at these temperatures was insignificant. At these two temperatures, thefracture toughness decreased with increase in loading rate, probably due to increasedbrittle behaviour. At 0°C however, the fracture toughness of the hot mixture

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96 Road Materials and Pavement Design. Volume 8 – No. 1/2007

increased with increasing loading rate, as expected. The fracture toughness of thehot mixture increased with temperature at the highest loading rate. However, at-20°C the fracture toughness of the hot mixture exhibited more sensitivity to theloading rate. A general trend observed with the fracture energy, in Figure 6, was thatit increased with temperature for all the hot mixture samples tested at all loadingrates used.

0

1

2

3

4

5

-20 -10 0

Test Temperature T(°C)

Frac

ture

Ene

rgy

G f (

kJ/m

2 )

1mm/min 10mm/min 100mm/min

Figure 6. Fracture energy for the HME

0

5

10

15

20

25

30

-20 -10 0

Test Temperature T(°C)

Frac

ture

Tou

ghne

ss K

IC (M

Pa m

m0.5 )

1mm/min 10mm/min 100mm/min

Figure 7. Fracture toughness for the CEAM

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Fracture of Cold-laid Asphalt 97

0

1

2

3

4

5

-20 -10 0

Test Temperature T(°C)

Frac

ture

Ene

rgy

G f

(kJ/

m2 )

1mm/min 10mm/min 100mm/min

Figure 8. Fracture energy for the CEAM

5.2. Fracture behaviour of CEAM

For the CEAM, the fracture toughness increased with loading rate consistentlyfor tests conducted at -20 and 0°C, as seen in Figure 7. This trend is similar to theobserved behaviour of the HME and the reasons given earlier could be applied forthe cold mixture. There was no significant difference between the fracture toughnessvalues for the three test temperatures at the highest loading rate of 100mm/min. Thisis because at this rate the toughness is insensitive to temperature. Except for thelowest loading rate of 1mm/min, the fracture energy of the CEAM in Figure 8marginally increased with temperature, as expected. It is of interest to note that, at-20oC, the difference in fracture energy between hot and cold asphalt was negligible.

It should be noted, however, that the obtained fracture test results are specimensize and thickness dependent. Thus, care should be taken when comparing withresults obtained on specimens of different size and geometry.

6. Effect of moisture ingress

Vacuum moisture saturation was conducted using the Asphalt Institute method(Asphalt Institute, 1989). The test is used to simulate, in the laboratory, the effects ofmoisture on the stiffness of in-situ asphalt mixtures which form part of a roadpavement made of either hot or cold-laid mixtures. The procedure entails moisturesaturation for one hour under 100mm Hg vacuum pressure with immersion in water

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98 Road Materials and Pavement Design. Volume 8 – No. 1/2007

at 20°C continued for another hour. Selected cores of the HME and CEAM wereused in the study. The set-up is shown in Figure 9.

Pressure Dial GaugeTransformer

Vacuum Pressure Pump Test Tank

Figure 9. Vacuum moisture saturation set up

The material ingests moisture as a result of the vacuum saturation procedure. Thepresence of moisture at certain levels has been identified to cause material damagein the form of loss in mechanical property. The amount of ingested moisture wasevaluated as in Equation [7]. AW and AB are the mass of the specimen after andbefore moisture saturation respectively, and AD is the mass of oven dried specimento constant mass after cooling to room temperature.

100DA

BAWAIM,MoistureIngested ×

−= [7]

IM values for the CEAM and HME materials were 1.2 and 0.7% respectively.

Figures 10 and 11 illustrate the extent of moisture damage of the HME andCEAM materials in relation to ITSM and fracture toughness properties. The fracturetoughness after vacuum moisture saturation was measured at -10°C and 10mm/minloading rate. CEAM appears to show consistency in achieving retained ITSM andtoughness of 75 and 73% respectively, when subjected to moisture ingresstreatment, in contrast to the HME material’s disparity with corresponding values of52 and 97%.

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Fracture of Cold-laid Asphalt 99

485

1695

932

2260

0

500

1000

1500

2000

2500

3000

HME CEAM

Type of Mixture

ITSM

(MPa

)

Retained Stiffness Original stiffness

Figure 10. Effect of vacuum moisture saturation on mix stiffness measured at 20˚C

22.1

11.9

22.8

16.6

0

5

10

15

20

25

30

HME CEAM

Type of Mixture

Frac

ture

Tou

ghne

ss K

IC (M

Pa.m

m0.5 )

Retained Toughness Original Toughness

Figure 11. Effect of vacuum moisture saturation on fracture toughness measured at-10˚C

As can be seen from Figures 10, the CEAM and HME behave as twoindependent materials, each undergoing a change due to moisture conditioningcommensurate with its stiffness value. It can be recalled from Figures 1 and 2 that

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100 Road Materials and Pavement Design. Volume 8 – No. 1/2007

The CEAM’s ITSM continued to increase appreciably even after the specimen massremained constant. The behaviour observed in this study was similar to thatobserved by Serfass et al. (2003). It appears that significant hardening of theCEAM’s emulsion binder occurs as the moisture escapes during accelerated curingcompared to the HME material, giving rise to the higher stiffness levels observed.This hardening could be aided by the higher voids content of the CEAM.

The obtained fracture toughness values for both materials after vacuum moisturesaturation seem to suggest that the samples have undergone very little damage. Iffracture toughness were considered a measure of the material’s resistance to crackgrowth, then the reasonably good toughness retention level exhibited by the CEAMsuggests that moisture ingress is not detrimental to their service performance.Further research and field validation are required to substantiate this observation.

7. Conclusions

From the work presented in this paper, the following comments can be made:– Curing temperature is influential in the development of the cold mixture’s

mechanical properties during curing and at full-cure condition. The ITSM of thecold-laid material cured at 35oC was higher than that cured at 18oC, both measuredat 20oC.

– The SCB is a useful test to evaluate the fracture properties of asphalt mixturesin mode I with adequate repeatability.

– The fracture toughness and fracture energy of both the cold and hot appliedmaterials showed varying sensitivities to temperature and loading rate in the SCBtest. At -10 and -20oC, the fracture toughness of both materials was almostindependent of temperature. Both materials were too brittle to clearly exhibitexpected trends with respect to loading rate. At -20oC, the fracture energy of bothmaterials was almost equal.

– The cold material showed high retained toughness values after vacuummoisture saturation, consistent with its retained ITSM results. The hot mixture,however, showed disparity between retained fracture toughness and stiffness.Although the high toughness retention values obtained in this study are supportive ofgood service performance by the cold-laid material on medium to lightly traffickedroads, additional research and field validation would be desirable to furthersubstantiate this observation.

Acknowledgement

The authors wish to thank Colas Ltd. for their financial and technical support of thework reported in this paper.

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Fracture of Cold-laid Asphalt 101

8. Bibliography

The Asphalt Institute, “Asphalt Cold Mix Manual, Manual Series No. 14 (MS-14)”,Lexington, Kentucky, 1989.

Brown S.F., Gibb J.M., Read J.M. and Scholz T.V., “Laboratory protocols for the design andevaluation of bituminous mixtures”, Euroasphalt & Eurobitume Congress, Strasbourg,May 1996, E&E.4.088.

British Standard Institution, “Coated Macadam (asphalt concrete for roads and other pavedareas), BS 4987: Part 1, BSI, London, 2005.

Carbonneau X., Le Gal Y. and Bense P., “Evaluation of the indirect tensile stiffness modulustest”, 5th Int. RILEM Symposium PTEBM’03, Zurich, April 2003, p. 308-315.

Chong K.P. and Kuruppu M.D., “New method to determine the fracture toughness of rockswith oil shale specimens”, SEM/AIME Fall Meeting, Colorado, Vol. 278, 1984, p. 1853-1857.

Chong K.P. and Kuruppu M.D., “New specimen for fracture toughness determination for rockand other materials”, International Journal of Fracture, Vol. 26, 1984, p. 59-62.

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Eurasphalt and Eurobitume Congress, Vienna, May 2004, p. 435-446.

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Received: 1 November 2005Accepted: 20 September 2006

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