This article was downloaded by: [University of Ottawa]On: 01 October 2014, At: 01:20Publisher: Taylor & FrancisInforma Ltd Registered in England and Wales Registered Number: 1072954 Registeredoffice: Mortimer House, 37-41 Mortimer Street, London W1T 3JH, UK

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

Porous asphalt mixture with 100%recycled concrete aggregateMeng Jia Chena & Yiik Diew Wongb

a School of Civil and Environmental Engineering, NanyangTechnological University, N1-B1c-32, 50 Nanyang Avenue,Singapore 639798, Singaporeb School of Civil and Environmental Engineering, NanyangTechnological University, N1-B1b-09, 50 Nanyang Avenue,Singapore 639798, SingaporePublished online: 25 Sep 2013.

To cite this article: Meng Jia Chen & Yiik Diew Wong (2013) Porous asphalt mixture with100% recycled concrete aggregate, Road Materials and Pavement Design, 14:4, 921-932, DOI:10.1080/14680629.2013.837839

To link to this article: http://dx.doi.org/10.1080/14680629.2013.837839

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 tothe accuracy, completeness, or suitability for any purpose of the Content. Any opinionsand 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 Contentshould not be relied upon and should be independently verified with primary sourcesof information. Taylor and Francis shall not be liable for any losses, actions, claims,proceedings, demands, costs, expenses, damages, and other liabilities whatsoever orhowsoever caused arising directly or indirectly in connection with, in relation to or arisingout of the use of the Content.

This article may be used for research, teaching, and private study purposes. Anysubstantial 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

Road Materials and Pavement Design, 2013Vol. 14, No. 4, 921–932, http://dx.doi.org/10.1080/14680629.2013.837839

SCIENTIFIC NOTE

Porous asphalt mixture with 100% recycled concrete aggregate

Meng Jia Chena∗ and Yiik Diew Wongb

aSchool of Civil and Environmental Engineering, Nanyang Technological University, N1-B1c-32, 50Nanyang Avenue, Singapore 639798, Singapore; bSchool of Civil and Environmental Engineering, NanyangTechnological University, N1-B1b-09, 50 Nanyang Avenue, Singapore 639798, Singapore

Recycling of construction debris in Singapore is an important practice given the large amountgenerated annually. In order to maximise the rate of recycled concrete aggregate (RCA) gener-ated from construction debris, porous asphalt mixture (PAM) made of 100% RCA was studiedin both mechanical and functional aspects. Altogether, three designs of PAMs were evaluated,namely (a) PAM–RCA mixture comprising 100% RCA, (b) PAM–RCA–TAFPACK-Super(TPS) mixture comprising 100% RCA with enhanced asphalt binder, and (c) PAM–granitemixture comprising 100% granite, with PAM–granite mixture serving as the control. A seriesof laboratory tests were conducted, namely the draindown test, Cantabro test, Marshall test,permeability test, and ageing test. The results showed that PAM made of 100% RCA (PAM–RCA mixture) can offer the basic drainage function and possesses potential for low-strengthapplication, i.e. pedestrian/cyclist pathways. Meanwhile, PAM made of 100% RCA and mod-ified by specific additive TPS (PAM–RCA–TPS mixture) can adequately fulfil the Marshallcriteria of Singapore’s Land Transport Authority Standard stipulated for normal roads, indi-cating its potential usage in normal highway application. The results suggest the feasibleapplication of 100% RCA in PAM.

Keywords: porous asphalt mixture; recycled aggregate; low-strength pavement; draindowntest; Cantabro test

1. IntroductionThe amount of solid waste in Singapore is increasing continuously, and the fraction that cannot berecycled or incinerated is disposed at Pulau Semakau Landfill. However, the lifespan of the onlyavailable landfill in Singapore is expected to be around 40 years, but only if more waste couldbe reduced and recycled (Chia, 2007). Among the total waste generated in 2011, around 1.17million tonnes, which accounts for 17%, is construction debris (Tay, 2012). Recycled concreteaggregate (RCA), as a waste material arising from construction debris, is a valuable resourcethat is being recycled. Compared with virgin aggregate, RCA possesses lower density, higherporosity, and larger asphalt binder absorption, which could be attributed to the attached cementmortar (Bhusal, Li, & Wen, 2011; Limbachiya, Koulouris, Roberts, & Fried, 2004; Wong, Sun,& Lai, 2007; Zulkati, Wong, & Sun, 2012, 2013). The loads experienced during original usagefurther makes RCA weaker, which could be reflected by larger Los Angles Abrasion Value and/orAggregate Impact Value (Bhusal et al., 2011; Wong et al., 2007). However, existing research showsthat it is feasible to partially replace natural aggregate by RCA in conventional local dense asphaltmixture application (Wong et al., 2007). Meanwhile, reusing construction debris can reduce thedemand on quarrying as well as decrease the intensity of waste disposal.

Considering the tropical climate of Singapore, namely being rainy and high temperature, porousasphalt mixture (PAM) is selected in this study as a possible alternative to conventional dense

∗Corresponding author. Email: c110021@e.ntu.edu.sg

© 2013 Taylor & Francis

Dow

nloa

ded

by [

Uni

vers

ity o

f O

ttaw

a] a

t 01:

20 0

1 O

ctob

er 2

014

922 M.J. Chen and Y.D. Wong

asphalt mixtures. Given the high content of air voids in PAM, usually in excess of 20%, watercan be transmitted through the structure rapidly. PAM improves skid resistance, enhances noiseabsorption, and engenders cooling effect (Fabb, 1998; Khalid & Jimenez, 1995). However, ravel-ling and clogging are the two significant issues encountered by PAM, and the large inside voidscould also jeopardise the mixture’s strength (Hamzah, Abdullah, Voskuilen, & van Bochove,2013; Huurman, Mo, & Woldekidan, 2010; Khalid & Jimenez, 1995).

In terms of asphalt mixture application, it can be divided into two categories, namely normalroad and pedestrian/cyclist pathways. Normal roads consist of expressways, arterial roads, col-lector roads, and local access roads; pedestrian/cyclist pathways include most of the pathwaysin communities and parks whose users are limited to pedestrians and cyclists rather than motorvehicles. In Singapore, the total road length of normal roads is 3411 km (Land Transport Authority[LTA], 2012), while great attention and interest are also placed on pedestrian/cyclist pathwayswhich can be inferred by the related projects such as Round Island Route (National Parks, 2013).

Given the drawbacks of PAM and the weaker nature of RCA materials, additives are usuallyused to enhance the mixture’s overall performance. In this study, TAFPACK-Super (TPS), aspecific additive that creates a highly viscous binder was applied on PAM (Qin, 2004). In addition,in the case of low-strength application, namely pedestrian/cyclist pathways, attention is mostlyfocused on functional performance, e.g. resistance to stripping, moisture susceptibility, ageingperformances, etc. while the requirement in strength can be lowered to some degree as comparedwith normal roads. However, for low-strength application, most countries including Singaporehave not proposed a limit in the usual design Marshall stability criterion. Herein, accordingto the Australia method, 4 kN is suggested as the limit of Marshall stability for low-strengthpathways (Australian Asphalt Pavement Association [AAPA], 2002). For normal roads, LTA(2010) prescribes the minimum requirement in Marshall stability to be 9 kN.

Some amount of research concerning the potential usage of RCA in pavements has been con-ducted. Bhusal et al. (2011) conducted a study on asphalt mixture with RCA at 20%, 40%, 60%,80%, and 100%. With the augmentation of the RCA content, bulk specific gravity of asphaltmixture decreased while optimum asphalt content (OAC) increased, and OAC even reached9.2% when RCA was at 100%. Considering low-quality RCA is still acceptable for low-volumeroads, it was recommended to be an alternative material to reduce the demand on virgin aggre-gates. Mills-Beale and You (2010) researched on mechanical properties of RCA and reportedthat resilient modulus increased while dynamic modulus decreased as RCA content increased.Meanwhile, based on the calculation of the Construction Energy Index, substituting virgin stonepartially by RCA could substantially save equipment compaction energy; consequently, a certainamount of RCA in asphalt mixture, not beyond 75%, was recommended for low-volume roads(Faheem & Bahia, 2004). In addition, research also showed that the asphalt mixture using partialRCA as aggregate was applicable in base layer and sub-base layer (Cho, Yun, Kim, & Choi,2011; Poon & Chan, 2005). Cho et al. (2011) conducted a series of tests on the RCA material,which included the Marshall test, indirect tensile strength test, and rutting resistance test, andthe comparable performance of mixtures with RCA suggested the potential usage of RCA inconstructing the base layer.

Therefore, despite the fact that RCA is weaker than virgin aggregate, it could still be usedin low-volume roads and/or base layer of normal roads. However, most relevant research wasimplemented on dense asphalt mixtures with aggregate partially substituted by RCA. In the caseof PAM, little research has been done with RCA substitution, due to the high voids content furthermaking the hybrid asphalt mixtures weaker, especially when RCA is used at a high proportion. Inthis study, a series of performance tests, namely the draindown test, permeability test, Cantabrotest, and ageing test, were carried out on the PAM material. Three designs of PAMs were testedand assessed, which were (a) PAM–RCA: PAM made of 100% RCA; (b) PAM–RCA–TPS: PAM

Dow

nloa

ded

by [

Uni

vers

ity o

f O

ttaw

a] a

t 01:

20 0

1 O

ctob

er 2

014

Road Materials and Pavement Design 923

made of 100% RCA and asphalt binder modified by TPS; and (c) PAM–granite: PAM made of100% granite, of which PAM–granite was used as a control group.

2. Materials and methods2.1. MaterialsAsphalt graded as Pen 60/70 was used in this study. In the case of the PAM–RCA–TPS mixture,asphalt binder was produced by mixing straight bitumen with TPS, a specific granular additivedesigned for PAM. TPS was initially developed in Japan and the addition of TPS could producehighly viscous binder and consequently improve PAM’s performance in several aspects, e.g.anti-cracking, resistance to abrasion, and anti-clogging (Qin, 2004; Subagio, Kosasih, Busnial, &Tenrilangi, 2005).

For PAM–RCA and PAM–RCA–TPS mixtures, RCA material was used as aggregate at 100%.For control group, i.e. PAM–granite mixture, Indonesian granite was used, which is the commonaggregate used in Singapore roads. Physical properties and mechanical properties of both kinds ofaggregates were tested with the results given in Tables 1 and 2, respectively (Ang, 2008; Cheong,2007; Chua, 2008; Lai, 1997; Toh, 1997). RCA’s bulk specific gravity is slightly lower than granitein the coarse part but notably lower in the fines component. Water absorption of RCA is 10.4times and 6.3 times of granite in coarse and fine parts, respectively, which is mainly attributedto the large amounts of minute pores in the attached cement mortar on the RCA surface. Thecrushing value of RCA was about twice as that of granite, while Los Angeles (LA) abrasion and10% fines value of the two types of aggregates was comparable.

2.2. Preparation of PAM specimensCompared with the conventional Marshall compaction hammer, gyratory compaction is moreable to orient the aggregate particles as in-field condition (Asphalt Institute [AI], 1996; Cerni &

Table 1. Bulk specific gravity and water absorption of granite and RCA (Ang, 2008;Cheong, 2007; Chua, 2008).

Bulk specific gravity Water absorption (%)

Size (mm) Granite RCA Granite RCA

19.0–13.5 2.592 2.323 0.47 4.8813.2–9.5 2.596 2.3289.5–4.75 2.596 2.3314.75–2.36 2.599 2.331 1.36 8.522.36–0.075 2.525 2.058< 0.075 2.560 1.838

Table 2. Mechanical properties of granite and RCA (Ang, 2008; Lai, 1997; Toh, 1997).

LA abrasion Aggregate crushing 10% finesProperty value (%) value (%) value (kN)

Granite 36.0 9.9 145.1RCA 32.3 21.6 146.0Requirementa <40 <35 >130

aThe requirement is to LTA (2010) specification.

Dow

nloa

ded

by [

Uni

vers

ity o

f O

ttaw

a] a

t 01:

20 0

1 O

ctob

er 2

014

924 M.J. Chen and Y.D. Wong

Table 3. Compaction parameters.

Compaction type Gyratory compaction

Ram pressure (kPa) 300Gyratory number (cycle) 50Compaction angle (degree) 1.25

Table 4. LTA–PA aggregate gradation.

Percentage byweight passing, in Percentage used

Sieve size (mm) specification in experiment

19 100 10013.2 79–89 849.5 67–77 724.75 17–26 222.36 13–23 180.6 8–18 130.3 6–12 90.15 4–10 70.075 4–8 6

Note: PA, porous asphalt.

Camilli, 2011). Thus, asphalt mixture specimens around 101.6 mm in diameter were fabricatedby a gyratory compactor in this study, and triplicate tests were carried out for each laboratorymeasure of each mixture design. Compaction parameters are given in Table 3. Considering theweak nature of the RCA material, the ram pressure generated by the compactor is reduced to300 kPa, which is half of the 600 kPa value recommended by the Superpave method (AI, 1996).

Gradation design in this study was according to LTA–PA aggregate gradation (Table 4) asprescribed by Singapore’s LTA (2010). In terms of asphalt binder content, 5.0% asphalt bindercontent was initially selected for PAM–RCA–TPS and PAM–granite mixtures, given that asphaltbinder content usually falls in the range 4.0%–6.0% (Zhu, 2005). For the PAM–RCA mixture,considering the high absorption of RCA and non-modified effect, 5.5% asphalt binder content wasused. Rationality of the selected asphalt binder content was subsequently evaluated by the drain-down test and Cantabro test. Meanwhile, TPS dosage was used at 12% by weight of total asphaltbinder in the case of the PAM–RCA–TPS mixture, which was recommended by the supplier.

3. Experimental results and discussion3.1. Volumetric propertiesFor PAM, high content of air voids is the most significant feature which ensures the essentialfunction of drainage. By measurement and calculation, density and air voids content of the PAMsamples were obtained (Table 5). Both PAM–RCA and PAM–RCA–TPS mixtures possessedlower densities than PAM–granite mixture, being mainly due to the lower density of the attachedcement mortar on the surface of RCA aggregate. Air voids content of PAM–RCA and PAM–RCA–TPS mixtures were slightly smaller than that of PAM–granite and the lower limit in LTAspecification (i.e. 20%) as well, which may be contributed by the partial breakage of weak piecesin RCA or abrasion of cement mortar during mixing and compaction (Zulkati et al. 2013).

Dow

nloa

ded

by [

Uni

vers

ity o

f O

ttaw

a] a

t 01:

20 0

1 O

ctob

er 2

014

Road Materials and Pavement Design 925

Table 5. PAM density and air voids contenta .

Mixture type Density (g/cm3) Air voids content (%)

PAM–granite 2.14 (±0.02) 20.9 (±0.02)PAM–RCA 1.90 (±0.02) 19.4 (±0.01)PAM–RCA–TPS 1.92 (±0.04) 18.9 (±0.02)Requirement – 20 to 26

aValue in parenthesis refers to standard deviation.

3.2. Draindown test and Cantabro testWhen assessing the asphalt binder content for PAM materials, the draindown test and Cantabrotest are generally used to obtain the upper limit and lower limit, respectively (Qin, 2004; Zhu,2005).

Draindown describes the phenomenon that asphalt binder flows down during mixing and usuallyhappens in asphalt mixtures with high coarse aggregate content, being heavily due to the lack offine aggregates and fillers to hold asphalt binder and form an asphalt mastic. Generally, draindowntends to occur in the case of high asphalt binder content and/or asphalt binder with large penetrationvalue. Draindown should be carefully controlled since it may lead to rutting and ravelling. In thisstudy, the draindown test prescribed by ASTM D6390-11 was carried out (American Societyfor Testing and Materials, 2011), and the general procedure was: (a) to prepare the loose asphaltmixture sample at the designed asphalt binder content and determine the initial mass; (b) to put theloose asphalt mixture into a wire basket and place the basket into an oven at mixing temperaturewith a plate below; and (c) to remove the basket from oven after 1 h heating and record the lossweight of sample, namely the asphalt mastic flowed to the plate. The loss percentage of the asphaltmixture by mass is regarded as the draindown value.

The results of the draindown test for three groups are given in Table 6. It was found thatdraindown results from all three groups can overly satisfy the upper limit of 0.3%, which wassuggested by Rajib, Prithvi, Cooley, and Donald (2000). Especially in the case of the PAM–RCA–TPS mixture, there were no fines and/or fillers drained through the basket after being placed inan oven at 185 C for 1 h (Figure 1), which further substantiates the superior function of TPS inenhancing viscosity at elevated temperate.

The Cantabro test, which was originally developed in Spain, is currently widely used to evaluatethe resistance to wear or particle losses for PAM materials, and it is used to determine the lowerlimit of the asphalt binder content for PAM as well. Usually abrasion loss value decreases with theincrease in the asphalt binder content due to the stronger adhesiveness offered by higher asphaltbinder content which directly enhances the resistance to abrasion.

The procedure of the Cantabro test is similar to that of LA abrasion test except that no steel ballis added in the drum. Namely, the LA abrasion machine is involved in this test and the asphaltmixture sample should undergo 300 drum revolutions at 25 C without steel balls inside at a

Table 6. Results of draindown test.

Mixture type Testing temperature (C) Draindown (%)

PA–granite 130 0.02 (±0.01)PA–RCA 130 0.03 (±0.00)PA–RCA–TPS 185 0.00 (±0.00)Requirement Mixing temperature <0.30

Dow

nloa

ded

by [

Uni

vers

ity o

f O

ttaw

a] a

t 01:

20 0

1 O

ctob

er 2

014

926 M.J. Chen and Y.D. Wong

Figure 1. Draindown test of the PAM–RCA–TPS mixture (after 1 hour heating at 185 C).

Figure 2. Specimens in the Cantabro test (left: after test and right: before test).

speed of 30–33 rpm (Figure 2). The result is described as the weight loss after testing as shownin Equation (1)

P = P1 − P2

P1 × 100, (1)

where P is the abrasion loss value (%), P1 is the initial weight of the sample, and P2 is the finalweight of the sample.

Dow

nloa

ded

by [

Uni

vers

ity o

f O

ttaw

a] a

t 01:

20 0

1 O

ctob

er 2

014

Road Materials and Pavement Design 927

Table 7. Results of the Cantabro test.

Asphalt binder Abrasion lossMixture type content (%) value (%)

PAM–granite 5.0 3.7 (±0.2)PAM–RCA 5.5 6.8 (±0.5)PAM–RCA–TPS 5.0 15.2 (±3.4)Requirement – <20.0

The abrasion loss values of the three groups from the Cantabro test are given in Table 7, andall three groups satisfied the recommended upper limit of 20%, which was specifically suggestedfor PAM (Rajib et al., 2000). It can be seen that PAM–granite mixture had the largest resistanceto abrasion, and PAM–RCA–TPS mixture was most prone to abrasion effect.

For PAM–RCA, the abrasion loss value was 83.8% higher than that of PAM–granite, whichwas mainly attributed to the complete usage of RCA as aggregate. In effect, much more asphaltbinder was absorbed into the minute pores on the surface of the cement mortar (which waswidely attached on RCA), and hence lesser asphalt binder being available to exert the functionof adhesiveness among aggregates. The effect of an additional 0.5% more asphalt binder wasinsufficient to compensate for the asphalt binder absorption.

As regards to the PAM–RCA–TPS mixture, the abrasion loss value was substantially higher thanthat of PAM–granite and PAM–RCA mixtures by 310.8% and 123.5%, respectively, indicatingthat TPS would not improve asphalt mixture’s resistance to abrasion. The much larger abrasionloss value of PAM–RCA–TPS could again be attributed to the result of using RCA at 100%.

3.3. Marshall stability and moisture susceptibilityThe Marshall stability test is generally used to estimate an asphalt mixture’s ability in resistingload and deformation. For the dense asphalt mixture, the minimum required Marshall stabilityis set as 9 kN in LTA’s specification for normal highway application. In terms of low-strengthapplication, requirement in Marshall stability has been rarely stipulated by researchers or roadauthorities.

In this study, Marshall tests were carried out in two situations, namely unconditioned andconditioned states (Figure 3 and Table 8). Unconditioned specimens were soaked in a water bath

Figure 3. Profile of the Marshall test.

Dow

nloa

ded

by [

Uni

vers

ity o

f O

ttaw

a] a

t 01:

20 0

1 O

ctob

er 2

014

928 M.J. Chen and Y.D. Wong

Table 8. Results of the Marshall test.

Mixture type Unconditioned (kN) Conditioned (kN) Retained stability (%)

PAM–granite 8.1(±1.0) 7.6 (±0.4) 94.4PAM–RCA 5.3 (±1.1) 4.9 (±0.1) 92.1PAM–RCA–TPS 14.5 (±0.1) 13.7 (±0.1) 94.3

of 60 C for 30 min, while conditioned specimens were soaked in the same bath for 24 h beforetesting.

In the case of unconditioned state, the PAM–RCA–TPS mixture possessed the highest Marshallstability, being followed by PAM–granite and PAM–RCA mixtures. For the PAM–granite mixture,the strength value nevertheless qualified for low-strength application, namely larger than theminimum requirement (i.e. 4 kN) suggested by AAPA (2002), and it can even be used on normalroads with some modifications given that the Marshall stability was close to the lower limitstipulated for normal application (i.e. 9 kN).

Considering the PAM–RCA mixture, the value of Marshall stability was lower by 34.6% thanthat of the PAM–granite mixture and this could be attributed to the weaker nature of RCA and theminute pores dispersed on the surface of RCA. Meanwhile, although the asphalt binder contentof the PAM–RCA mixture was 0.5% higher than that of the PAM–granite mixture, more asphaltbinder would be absorbed into the minute pores on the aggregate surface for PAM–RCA due tothe attached cement mortar. Thus, for the PAM–RCA mixture, the combined effects of the weaknature of RCA and minute surface pores on aggregate surface resulted in a much lower Marshallstability despite the 0.5% more asphalt binder content. However, the PAM–RCA mixture couldstill be useful for paving on pedestrian/cyclist pathways, given that the Marshall stability of 5.3 kNmet the requirement in AAPA (2002).

For PAM–RCA–TPS mixture, whereby the asphalt binder was modified by TPS and the asphaltbinder content was kept at 5.0%, the Marshall stability was the highest among the three groups,which was highly sufficient and amply exceeded the requirement of 9 kN for normal roads byaround 60%. It suggested the excellent enhancement effect of TPS in the aspect of asphalt mixturestrength, which makes this type of PAM a potential asphalt mixture to be used on heavy-dutyroads.

After conditioning, the values of retained Marshall stability of the three groups showed quitegood resistance in moisture susceptibility (Figure 3 and Table 8). The good performance inmoisture susceptibility is desirable since PAM is required to maintain its integrity even whenlarge amount of water runs through and/or be contained within the pavement structure for longerperiods during the usual rainy seasons in Singapore.

3.4. PermeabilityAlthough air voids content can indicate the percentage of air voids in an asphalt mixture, per-meability is a more direct parameter to represent the drainage performance, which is the basicfunction of PAM materials (Pratico & Moro, 2007). In this study, a simple set-up was used tomeasure permeability of PAM as shown in Figure 4 (Yeung, 2009). The specimen was fixed inthe hose-like rubber tube and the time needed for water to flow from point A to point B (30 cm)was recorded, so as to calculate the flow rate of water through the specimen.

All the three PAM groups can meet the minimum requirement in permeability (Table 9),i.e. 0.01 cm/s, which was proposed by Darin Tech (2001). Given that the air voids contents ofthe three groups were similar (Table 5), the difference in permeability may be attributed to the

Dow

nloa

ded

by [

Uni

vers

ity o

f O

ttaw

a] a

t 01:

20 0

1 O

ctob

er 2

014

Road Materials and Pavement Design 929

Figure 4. Permeability test set-up (Yeung, 2009).

Table 9. Results of the permeability test.

Mixture type Permeability (cm/s)

PAM–granite 0.29 (±0.05)PAM–RCA 0.59 (±0.07)PAM–RCA–TPS 0.54 (±0.05)Requirement 0.01

different voids structure generated in the three PAM types, and it can be inferred that more inter-connected voids were created in PAM–RCA and PAM–RCA–TPS mixtures as compared withPAM–granite mixture.

3.5. Ageing testDue to the high air voids existing in PAM, it is likely that PAM may get hardened faster thanthe conventional dense asphalt mixture. Therefore, an accelerated test should be conducted toevaluate the performance of PAM in the aspect of ageing. The procedure of ageing test is similarto the Cantabro test except that the samples have been conditioned in the oven at 60 C for sevendays before testing, and the upper limit of aged abrasion loss is 30% (Rajib et al., 2000).

The results showed that all the three PAM groups can meet the requirement, and the agedabrasion loss of PAM–granite mixture was much lower than that of the PAM–RCA and PAM–RCA–TPS mixtures (Table 10). It suggested that adhesion between granite and asphalt binder wasmuch stronger than that between RCA and asphalt binder. Meanwhile, although TPS can produceasphalt binder of high viscosity, the adhesion between asphalt and RCA was hardly enhanced, andit also may be attributed to the minute pore on RCA surface, which absorbed the asphalt binderinstead of increasing the thickness of functional asphalt binder.

Dow

nloa

ded

by [

Uni

vers

ity o

f O

ttaw

a] a

t 01:

20 0

1 O

ctob

er 2

014

930 M.J. Chen and Y.D. Wong

Table 10. Results of the ageing test.

Mixture type Aged abrasion loss (%)

PAM–granite 1.9 (±0.2)PAM–RCA 14.2 (±0.8)PAM–RCA–TPS 13.8 (±0.9)Requirement <30.0

4. ConclusionsExperimental results showed that both the PAM with 100% RCA, i.e. PAM–RCA and PAM–RCA–TPS mixtures, can meet the functional requirements, which were evaluated by thedraindown test, Cantabro test, ageing test, and permeability test. Nevertheless, PAM–granitemixture possessed much higher resistance to abrasion loss in both unaged and aged states. Mean-while, the addition of TPS in PAM with 100% RCA, namely the case of PAM–RCA–TPS, couldsignificantly enhance the asphalt mixture’s strength, which was reflected by the high Marshall sta-bility. In addition, the draindown value of PAM–RCA–TPS was zero, indicating that the asphaltmixture modified by TPS could keep its integrity without ravelling at high temperature, which isvital for PAM applied in a tropical environment. Nonetheless, for PAM made with 100% RCA,TPS could hardly improve the performance in the Cantabro test and ageing test, probably sinceTPS is not able to enhance the adhesion between asphalt binder and aggregate, while noting thatthe substantial minute pores dispersed on the RCA surface resulted in increased absorption of theasphalt binder and reduced thickness in the functional asphalt film.

Given that the PAM–RCA mixture can meet the strength requirement for low-strength pathwayand satisfied all the functional requests, it can be concluded that it is feasible to apply the PAM–RCA mixture in pedestrian/cyclist pathways in Singapore. In the case of the PAM–RCA–TPSmixture, despite the usage of RCA at a ratio of 100%, mixture with 12% TPS can fulfil Marshallstability criteria stipulated for normal roads and also meet almost all the requirements of otherperformance tests. Thus, the experimental results indicated the potential in using the PAM–RCA–TPS mixture on normal roads in Singapore.

Future research should be carried out on other aspects, e.g. resilient modulus, dynamic creeptest, rutting test, etc. to further evaluate feasibility in applying in high-traffic highways. On thewhole, the two types of PAM made with 100% RCA, namely PAM–RCA and PAM–RCA–TPSmixtures, are potential alternatives as paving materials in low-strength pathways and normalroads, respectively, meanwhile being a resource conservation strategy in road construction andsustainable measurement in waste disposal.

AcknowledgementsThe authors would like to thank Shell Bitumen Singapore, Taiyu Kensetsu Co. LTD, and Samwoh Co.LTD for supplying bitumen (PEN 60/70), TAFPACK-Super (TPS), and recycled concrete aggregate (RCA),respectively. The authors also thank BE degree students in characterising some of the material properties.Lastly, gratitude goes out to Nanyang Technological University for providing financial support for theresearch.

ReferencesAmerican Society for Testing and Materials. (2011). Standard test method for determination of draindown

characteristics in uncompacted asphalt mixtures (vol. D6390-11). Philadelphia, PA: Author.Ang, C. H. (2008). Performance characteristics of hot-mix asphaltic concrete with recycled PCC aggregate

(BE Final Year Project Report). Singapore: Nanyang Technological University.

Dow

nloa

ded

by [

Uni

vers

ity o

f O

ttaw

a] a

t 01:

20 0

1 O

ctob

er 2

014

Road Materials and Pavement Design 931

Asphalt Institute. (1996). Superpave mix design (No.2 (SP-2)). Lexington, KY: Author.Australian Asphalt Pavement Association. (2002). Light duty asphalt pavement (No. IG-5). Kew: Author.Bhusal, S., Li, X. J., & Wen, H. (2011). Evaluation of effects of recycled concrete aggregate on volu-

metrics of hot-mix asphalt. Journal of the Transportation Research Board (Low-Volume Roads), 3,36–39.

Cerni, G., & Camilli, S. (2011). Comparative analysis of gyratory and proctor compaction processes ofunbound granular materials. Road Materials and Pavement Design, 12(2), 397–421.

Cheong, C. M. (2007). Performance evaluation of recycled concrete aggregate in hot-mix asphalt (BE FinalYear Project Report). Singapore: Nanyang Technological University.

Chia, J. Y. J. (2007). Pulau Semakau. Singapore Infopedia. Retrieved from http://infopedia.nl.sg/articles/SIP_1008_2010-03-22.html

Cho, Y. H., Yun, T., Kim, I. T., & Choi, N. R. (2011). The application of recycled concrete aggregate(RCA) for hot mix asphalt (HMA) base layer aggregate. Korean Society of Civil Engineers, 15(3),473–478.

Chua, S. S. (2008). Performance characteristics of hot-mix asphaltic concrete with recycled PCC aggregate(BE Final Year Project Report). Singapore: Nanyang Technological University.

Darin Tech. (2001). Ecophalt quality assurance specification. Paper presented on Echophalt PavementTechnology, Malaysian Highway Authority, Malaysia.

Fabb, T. R. J. (1998). Porous asphalt surface courses. In J. C. Nicholls (Ed.), Asphalt surfacings (pp. 185–218).London: Spon Press.

Faheem, A., & Bahia, H. U. (2004). Using the gyratory compactor to measure the mechanical stabilityof asphalt mixtures (Wisconsin Highway Research Program Report [WHRP] 05-02 (0092-01-02)).Wisconsin: Wisconsin Highway Research Program.

Hamzah, M. O., Abdullah, N. H., Voskuilen, J. L. M., & van Bochove, G. (2013). Laboratory simulationof the clogging behaviour of single-layer and two-layer porous asphalt. Road Materials and PavementDesign, 14(1), 107–125.

Huurman, R. M., Mo, L., & Woldekidan, M. F. (2010). Unravelling porous asphalt concrete towards amechanistic material design tool. Road Materials and Pavement Design, 11(3), 583–612.

Khalid, H., & Jimenez, P. F. K. (1995). Performance assessment of Spanish and British porous asphaltsperformance and durability of bituminous materials. London: Spon Press.

Lai, Y. L. (1997). Assessment of the mechanical properties of non-conventional bituminous mixes (BE FinalYear Project Report). Singapore: Nanyang Technological University.

Land Transport Authority. (2010). Engineering group materials & workmanship specification forcivil & structural works. Retrieved from http://www.lta.gov.sg/content/dam/ltaweb/corp/Industry/files/EGD09104A1-Overall.pdf

Land Transport Authority. (2012). Singapore land transport statistics in brief. Retrieved fromhttp://ltaacademy.gov.sg/doc/J12%20May-p58Singapores%20Land%20Transport%20Statistics%20as%20at%20end%202011r2.pdf

Limbachiya, M. C., Koulouris, A., Roberts, J. J., & Fried, A. N. (2004). Performance of recycled aggregateconcrete. Paper presented at the RILEM International Symposium on Environment-Conscious Materialsand Systems for Sustainable Development, Kiroyama, Japan.

Mills-Beale, J., & You, Z. (2010). The mechanical properties of asphalt mixtures with recycled concreteaggregates. Construction and Building Materials, 24(3), 230–235.

National Parks. (2013). City in a garden. Retrieved from http://www.nparks.gov.sg/cms/index.php?option=com_news&task=view&id=289&Itemid=50

Poon, C. S., & Chan, D. (2005). Feasible use of recycled concrete aggregates and crushed clay brick asunbound road sub-base. Construction and Building Materials, 20, 578–585.

Pratico, F. G., & Moro, A. (2007). Permeability and volumetric of porous asphalt concrete. Road Materialsand Pavement Design, 8(4), 799–817.

Qin, M. (2004). Study on application of modifiers to performance of porous asphalt mixture (Unpublishedmaster’s thesis). Southeast University, Nanjing, China.

Rajib, B. M., Prithvi, S. K., Cooley, L. A., & Donald, E. W. (2000). Design, construction, and performance ofnew-generation open-graded friction courses (National Center for Asphalt Technology [NCAT] ReportNo. 2000-01). Saratoga Spring, NY: National Center for Asphalt Technology (NCAT).

Subagio, B. S., Kosasih, D., Busnial, & Tenrilangi, D. (2005). Development of stiffness modulus and plasticdeformation characteristics of porous asphalt mixture using TAFPACK Super. The Eastern Asia Societyfor Transportation Studies, 5, 803–812.

Tay, E. (2012). Singapore 2011 waste statistics. Zerowastesg. Retrieved from http://www.zerowastesg.com/category/recycle/

Dow

nloa

ded

by [

Uni

vers

ity o

f O

ttaw

a] a

t 01:

20 0

1 O

ctob

er 2

014

932 M.J. Chen and Y.D. Wong

Toh, C. L. (1997). Flexural stiffness characteristics of stone mastic asphalt (BE Final Year Project Report).Singapore: Nanyang Technological University.

Wong, Y. D., Sun, D. D., & Lai, D. (2007). Value-added utilisation of recycled concrete in hot-mix asphalt.Waste Management, 27, 294–301.

Yeung, J. S. (2009). Exploration of high porosity asphaltic concrete (URECA Report). Singapore: NanyangTechnological University.

Zhu, Z. H. (2005). The application of ’Bailey method’ in porous asphalt (Unpublished master’s thesis).Taiwan National Cheng Kung University, Tainan, Taiwan.

Zulkati, A., Wong, Y. D., & Sun, D. D. (2012). Effects of fillers on properties of asphalt concrete mixture.Journal of Transportation Engineering, 138(7), 902–910.

Zulkati, A., Wong, Y. D., & Sun, D. D. (2013). Mechanistic performance of asphalt concrete mixtureincorporating coarse recycled concrete aggregate (RCA). Journal of Materials in Civil Engineering(Proceeding). 25(9), 1299–1305.

Dow

nloa

ded

by [

Uni

vers

ity o

f O

ttaw

a] a

t 01:

20 0

1 O

ctob

er 2

014