8
Investigation on physical properties of waste cooking oil – Rejuvenated bitumen binder Hallizza Asli, Esmaeil Ahmadinia, Majid Zargar , Mohamed Rehan Karim Centre for Transportation Research, Faculty of Engineering, University of Malaya, 50603 Kuala Lumpur, Malaysia highlights " An environmental friendly use of waste cooking oil (WCO) is introduced. " Novelty is applied in the rejuvenating of aged bitumen by WCO. " Physical properties of aged and virgin bitumen are compared. " The statistical analysis of one-way ANOVA (single factor) was carried out. article info Article history: Received 15 October 2011 Received in revised form 14 June 2012 Accepted 22 July 2012 Available online 5 September 2012 Keywords: Rejuvenator Waste cooking oil Aged bitumen abstract Nowadays, the main problem pertaining to the use of the recycled asphalt pavement (RAP) material in hot mix asphalt (HMA) is the ageing of bitumen, which limits the percentage of applied RAP in the HMA. In this respect, rejuvenation of bitumen binder is the major but the most costly part of recycling. This paper investigates the novelty of using waste cooking oil (WCO), which is frequently found as a pol- luting waste material in landfills and rivers from the food industry, to rejuvenate the bituminous binder. The physical properties of the original bitumen, aged bitumen and rejuvenated bitumen were measured and compared by the conventional bitumen binder tests including softening point, penetration and Brookfield viscosity, and statistical analyses were used to assess the results. In general, the results showed that the aged bitumen was rejuvenated by the WCO due to a change in its physical properties, which resemble the physical properties of original bitumen (80/100). The optimum percentage of waste cooking oil for the rejuvenated aged bitumen group of 50/60, 40/50, and 30/40 was recognised by adding 1%, 3–4%, and 4–5% WCO, respectively. The statistical analyses also confirm that there was no significant difference between the original bitumen and rejuvenated bitumen. Ó 2012 Elsevier Ltd. All rights reserved. 1. Introduction Bitumen, as one of the base materials, plays an important role in the composition of bituminous pavements and their performance. There is a high annual demand of more than 110 million metric tons of bitumen in the world. A huge amount of money and energy is annually spent on construction, renovation and preservation of bituminous pavements [1]. Besides the high cost of virgin bitumen and insufficient resources of this material, other problems such as hardening or ageing of the bitumen during storage, mixing, trans- portation and laying down on the road, and its service life [2] are the other most important problems concerning the application of bitumen to pavements. Bitumen ageing is related to climate, bitumen composition, and aggregate, as well as pavement structure. The main ageing mecha- nism of bitumen is the loss of volatiles and oxidation. Aged bitu- men has higher viscosity and is stiffer than fresh bitumen and noticeable changes in its composition. These changes can lead to adhesion loss in the presence of moisture, and brittleness (Oxida- tion products have acidic characteristics and can be hydrolysed.). Surface ravelling and cracking, especially reflective cracking, may occur as bitumen becomes aged and more brittle [2,3]. As mentioned previously, the high demand of bituminous mate- rial, high expenses, low life cycling and ageing, lack of sufficient natural resources, increase in the concern about and emphasis on conservation of materials have encouraged highway agencies and governments to research to characterise, apply and optimise the properties of recycled asphalt materials such as bitumen in Re- claimed Asphalt Pavement (RAP) [4,5]. Generally, recycling hot mix asphalt (HMA) is the process in which Reclaimed Asphalt Pavement (RAP) materials are combined with the virgin bitumen 0950-0618/$ - see front matter Ó 2012 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.conbuildmat.2012.07.042 Corresponding author. Tel.: +60 379675339; fax: +60 379552182. E-mail addresses: [email protected], [email protected] (M. Zargar). Construction and Building Materials 37 (2012) 398–405 Contents lists available at SciVerse ScienceDirect Construction and Building Materials journal homepage: www.elsevier.com/locate/conbuildmat

Investigation on physical properties of waste cooking oil – Rejuvenated bitumen binder

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Construction and Building Materials 37 (2012) 398–405

Contents lists available at SciVerse ScienceDirect

Construction and Building Materials

journal homepage: www.elsevier .com/locate /conbui ldmat

Investigation on physical properties of waste cooking oil – Rejuvenatedbitumen binder

Hallizza Asli, Esmaeil Ahmadinia, Majid Zargar ⇑, Mohamed Rehan KarimCentre for Transportation Research, Faculty of Engineering, University of Malaya, 50603 Kuala Lumpur, Malaysia

h i g h l i g h t s

" An environmental friendly use of waste cooking oil (WCO) is introduced." Novelty is applied in the rejuvenating of aged bitumen by WCO." Physical properties of aged and virgin bitumen are compared." The statistical analysis of one-way ANOVA (single factor) was carried out.

a r t i c l e i n f o

Article history:Received 15 October 2011Received in revised form 14 June 2012Accepted 22 July 2012Available online 5 September 2012

Keywords:RejuvenatorWaste cooking oilAged bitumen

0950-0618/$ - see front matter � 2012 Elsevier Ltd. Ahttp://dx.doi.org/10.1016/j.conbuildmat.2012.07.042

⇑ Corresponding author. Tel.: +60 379675339; fax:E-mail addresses: [email protected]

(M. Zargar).

a b s t r a c t

Nowadays, the main problem pertaining to the use of the recycled asphalt pavement (RAP) material inhot mix asphalt (HMA) is the ageing of bitumen, which limits the percentage of applied RAP in theHMA. In this respect, rejuvenation of bitumen binder is the major but the most costly part of recycling.This paper investigates the novelty of using waste cooking oil (WCO), which is frequently found as a pol-luting waste material in landfills and rivers from the food industry, to rejuvenate the bituminous binder.The physical properties of the original bitumen, aged bitumen and rejuvenated bitumen were measuredand compared by the conventional bitumen binder tests including softening point, penetration andBrookfield viscosity, and statistical analyses were used to assess the results. In general, the resultsshowed that the aged bitumen was rejuvenated by the WCO due to a change in its physical properties,which resemble the physical properties of original bitumen (80/100). The optimum percentage of wastecooking oil for the rejuvenated aged bitumen group of 50/60, 40/50, and 30/40 was recognised by adding1%, 3–4%, and 4–5% WCO, respectively. The statistical analyses also confirm that there was no significantdifference between the original bitumen and rejuvenated bitumen.

� 2012 Elsevier Ltd. All rights reserved.

1. Introduction

Bitumen, as one of the base materials, plays an important role inthe composition of bituminous pavements and their performance.There is a high annual demand of more than 110 million metrictons of bitumen in the world. A huge amount of money and energyis annually spent on construction, renovation and preservation ofbituminous pavements [1]. Besides the high cost of virgin bitumenand insufficient resources of this material, other problems such ashardening or ageing of the bitumen during storage, mixing, trans-portation and laying down on the road, and its service life [2] arethe other most important problems concerning the application ofbitumen to pavements.

ll rights reserved.

+60 379552182.om, [email protected]

Bitumen ageing is related to climate, bitumen composition, andaggregate, as well as pavement structure. The main ageing mecha-nism of bitumen is the loss of volatiles and oxidation. Aged bitu-men has higher viscosity and is stiffer than fresh bitumen andnoticeable changes in its composition. These changes can lead toadhesion loss in the presence of moisture, and brittleness (Oxida-tion products have acidic characteristics and can be hydrolysed.).Surface ravelling and cracking, especially reflective cracking, mayoccur as bitumen becomes aged and more brittle [2,3].

As mentioned previously, the high demand of bituminous mate-rial, high expenses, low life cycling and ageing, lack of sufficientnatural resources, increase in the concern about and emphasis onconservation of materials have encouraged highway agencies andgovernments to research to characterise, apply and optimise theproperties of recycled asphalt materials such as bitumen in Re-claimed Asphalt Pavement (RAP) [4,5]. Generally, recycling hotmix asphalt (HMA) is the process in which Reclaimed AsphaltPavement (RAP) materials are combined with the virgin bitumen

Table 1Characteristics of bitumen pen-grade 80/100.

Test Standard test methods 80/100

Penetration (0.1 mm) at 25 �C ASTM D5 85Softening point (�C) ASTM D36 46Penetration Index (PI) – �0.968Ductility (mm) at 25 �C ASTM D113 >100Viscosity (mPa s) at 135 �C ASTM D4402 306.5

H. Asli et al. / Construction and Building Materials 37 (2012) 398–405 399

binder, aggregate, and a rejuvenator to form HMA mixtures. Simi-lar properties that lay somewhere between the designed recycledHMA mixtures and conventional HMA are expected [6,7]. Experi-ence has shown that the use of recycled asphalt pavements is abeneficial approach from the economical, environmental, and tech-nical perspectives [8,9].

The investigations illustrated that even though the life cycle ofHMA has reached to an end, the binder and aggregate from oldHMA are still valuable [10]. Investigations in 1997 suggested thatup to 15% RAP (without changing the grade of the added virgin bin-der) could be successfully used in superpave mixtures, while forthe application of 25% RAP in HMA, a rejuvenators and softer bin-der should be used for aged bituminous binder [9]. Investigationsshowed that using 19% rejuvenator (by weight of the bitumen) inthe RAP, if designed and properly used, made application of recy-cled mixtures containing 80% RAP possible [9]. In conclusion therejuvenator plays a key role and provides the possibility of usinga greater percentage of RAP material and hot in-place recycling,which is an important requirement of highway agencies.

Rejuvenating products are designed to restore the original char-acteristics to oxidised (aged) bitumen binders [11] in order to soft-en the aged binder and create a broad-spectrum rejuvenation thatreplenishes the volatiles and dispersing oils while promoting adhe-sion [3]. They restore the original ratio of asphaltenes to maltenes[11]. Generally, rejuvenating should be highly aromatic and able toimprove both temperature susceptibility and hardening suscepti-bility of aged bitumen. They should be composed in such a waythat they increase the peptizing power of the maltene phase [1].

Various researches have been conducted on the effect of therejuvenators on recycled mixtures and RAP binders. The resultsillustrate that rejuvenators with different ranges of viscosity influ-ence the penetration, properties of reconstituted RAP binder, andthe properties of the structural performance of recycled asphaltmixtures [9]. In Japan [12], a research was conducted on the prop-erties of recycled mixtures using rejuvenator with different com-ponents. The results indicate that the aged binders could berecovered to a target penetration by using different rejuvenator ifan adequate amount is added.

In recent years the application of rejuvenators in RAP materialhas considerably increased in HMA mixtures [9], chip seals, andrejuvenation seals [3] to rejuvenate the aged bitumen. Recently,following the high demand for rejuvenators, application of wasteproducts such as recycled motor oil (RO) as a rejuvenator have alsobeen investigated. Romera et al. [6], in Spain, applied recycled mo-tor oil (RO) and other rejuvenators in recycling HMA. The results ofthe investigation indicated that by employing RO as a rejuvenatorpermanent deformation can be postponed compared to a sample oforiginal bitumen. Furthermore, using RO considerably reduced themixing and compaction temperature. Finally, they reported that amixture of 80% aged bitumen with 20% recycled motor oil as a reju-venator, obtained exclusively from waste materials, forms a quali-fied bitumen that can compete with new 60/70 bitumen.

The successful application of recycled motor oil (RO) poweredthe theory of application of waste oil such as WCO as a rejuvenatorin bitumen. The novelty of this paper is using the waste cooking oil(WCO) as a rejuvenator in aged bitumen. Generally, waste cookingoil (WCO), also called used cooking oil (UCO), or non-edible oil orwaste (WEO), is collected from restaurants, food industries, house-hold disposables, and recycling centres by authorised companies[13]. The physical and chemical properties of WEO are almost sim-ilar to fresh edible oil [15]. WCOs are used as a fuel in bio diesel[14] yellow grease [15], animal foods [16], and soaps [17]. It hasbeen reported that although the amount of WCO available in theworld is approximately 15 million tons per year [17], only a smallamount of the used cooking oil is properly collected and recycled[16]. Major quantity of the used cooking oil is illegally dumped into

landfills and rivers causing environmental pollution. Supervision ofused cooking oil creates a significant challenge because of thedumping problems and possible pollution of the water and land re-sources [17].

This study investigates the possibility of WCO as a rejuvenatorfor aged bitumen. The potential uses of waste cooking oil as therejuvenator were examined using the conventional bitumen testmethods including penetration, softening point, Brookfield viscos-ity and chemical test. Thus, the optimum percentage of wastecooking oil for the rejuvenated bitumen was demonstrated usinga penetration blending chart. Consequently, the data were con-firmed using statistical analysis.

2. Materials and experimental procedure

2.1. Materials

The penetration grade 80/100 of bitumen was used in this study and suppliedfrom one source in order to ensure the consistency of the original bitumen proper-ties. Basically, this pen-grade bitumen has been used extensively for bituminouspavement in Malaysia. The Physical and rheological properties of the original bitu-men were ascertained by means of a penetration test, softening point test, viscositytest, and ductility test, etc. Details of the physical and rheological properties of bitu-men 80/100 are shown in Table 1.

The rejuvenator used in this study was waste cooking oil obtained from resi-dences without cost. The waste cooking oil was prepared by means of a simple fil-tering process. In this process the filter paper, medium filter speed 12.5 cmdiameter (Same filter paper to separate the asphaltenes from maltenes for bitumenbinder according to ASTM D4124), was used to separate the suspended particlesfrom oil. The virgin WCO and filtered WCO are illustrated in Fig. 1.

The chemical properties in filtered waste cooking oil are the fundamental char-acteristics to control the behaviour of the rejuvenated bitumen. Therefore, thechemical compounds in waste cooking oil were measured using gas chromatogra-phy–mass spectrometry (GCMS) by the Combinatorial & Catalysis Research Centre(COMBICAT). From the chemical test results, the predominant chemical compoundsfound in this waste cooking oil were oleic acid, 43.67%, palmitic acid, 38.35% fol-lowed by linoleic acid, 11.39% (see Table 2).

2.2. Experimental procedure

A propeller mixer is defined as a device that comprises a rotating shaft with pro-peller blades attached that is used for mixing relatively low viscosity materials dis-persions and maintaining the contents in suspension. Consequently, a propellermixer (Fig. 2) was manipulated as a simulation of a non-standard method to hastenthe ageing process of the bitumen in the laboratory. This test was used for measur-ing the effects of heat and air on a moving semi-solid of bitumen film.

The original 80/100 bitumen was heated in the oven at a constant temperatureof 160 �C for about one and a half hours to 2 h until it was fluid enough to pour.Thereafter, approximately 900 g of the bitumen was poured into several 5 l cylindri-cal containers after it had melted completely. Then, the melted bitumen was placedon the hot plate and mixing of the bitumen commenced using the propeller mixer.The ageing process was continuous for 6 h at a speed of 350 rpm at 130 �C. After theageing process was completed, the aged bitumen was tested using the penetrationtest to determine the group of the aged bitumen. These procedures were repeatedusing various weights of bitumen (i.e., 900 g and 1200 g), speeds (i.e., 350 rpm and400 rpm) and duration times (i.e., 6–7 h), in order to attain several aged bitumengroups.

The aged bitumen groups based on the final ageing conditions are as statedbelow:

– Aged bitumen 50/60 penetration group: time = 6 h, speed = 350 rpm andmass = 1200 g.

– Aged bitumen 40/50 penetration group: time = 7 h, speed = 350 rpm andmass = 900 g.

Waste Cooking oil Filtered Waste Cooking Oil

Fig. 1. Preparing the waste cooking oil.

Table 2Chemical properties of used cooking oil in this study.

Fatty acid Waste cooking oil (%)

Lauric acid (C12:0) 0.34Myristic acid (C14:0) 1.03Palmitic acid (C16:0) 38.35Stearic acid (C18:0) 4.33Oleic acid (C18:2n9c) 43.67Linoleic acid (C18:2n6c) 11.39c-Linolenic acid (C18:3n6) 0.37Linolenic acid (C18:3n3) 0.29Cis-11-Eicosenoic acid (C20:1) 0.16Heneicosanoic acid (C21:0) 0.08

TOTAL 100

Fig. 2. The applied propeller mixer, heater and tines for preparing aged andrejuvenated bitumen.

400 H. Asli et al. / Construction and Building Materials 37 (2012) 398–405

– Aged bitumen 30/40 penetration group: time = 7 h, speed = 400 rpm andmass = 900 g.

Each different group of aged bitumen was then blended by 1%, 2%, 3%, 4% and 5%of waste cooking oil using the propeller mixer for 30 min at 130 �C with a constantspeed of 200 rpm. Subsequently, the outcome underwent the conventional bitumentests. The penetration, softening point and Brookfield rotational viscometer wereconducted for determining the physical properties of the original bitumen (as a con-trol specimen), aged bitumen and rejuvenated bitumen.

The penetration test was carried out according to ASTM D5 [18]. In this test, a1 mm diameter needle was loaded with a weight of 100 g and the distance it dropsin 5 s into a bitumen sample that maintained at a temperature of 25 �C. Accordingto Read and Whiteoak [19], the maximum difference between the highest and thelowest reading for the penetration group of 50–149 should be 4. This test was sig-nificant to classify the bitumen grade based on penetration ranges.

The softening point of various bitumen penetration groups were measuredbased on ASTM D36 [20]. The softening point was defined as the temperature re-corded at which the bitumen sample no longer sustained the weight of a 3.5 g steelball. The mean temperature of the two specimens should not differ by more than1 �C otherwise the test should be repeated.

The rotational viscometer (RV) was introduced by the Superpave system to testthe viscosity of bitumen at elevated temperatures. The standard rotational (orBrookfield) viscometer test was performed based on ASTM D4402 [21]. In this test,a spindle of 27 with a constant shear rate, 6.8 s�1 was submerged into the samplechamber containing 8–10 ml of bitumen at three main temperatures (i.e., 110 �C,135 �C and 150 �C),and at a fixed speed of 20 rpm. Consequently, the rotated spindlegenerated results of the viscosity of the bitumen after 20 min for each temperature.Furthermore, to assess the basic chemical changes, the ratio of asphaltenes to malt-enes (ASTM D 4124) was measured for virgin, aged and rejuvenated bitumen fol-lowing the n-heptan insolubility method (ASTM D 4124).

2.3. Statistical analysis method

For further verification, the statistical analysis of variance, ANOVA on Excel wascarried out with 95% confidence interval. This test was important to determinewhether there is a significant difference between two sample means of two popu-lations. Due to the test conditions, the hypothesis test of two populations should beidentified in advance. Therefore, the hypotheses for the two-tailed test are asfollows:

� The proposed hypothesis, H1: the rejuvenated bitumen is different from the ori-ginal bitumen.� The null hypothesis, H0: the rejuvenated bitumen is similar to the original

bitumen.

From the results of ANOVA analysis, the two populations were found to be sta-tistically significantly different as the F statistic is greater than the F critical with thep-value smaller than the significance level, a, hence, the proposed hypothesis is ac-cepted. From these statistical tests it can be concluded that there is sufficient evi-dence to reject the null hypothesis in this case. The primary variables wereincluded the penetration value, softening value, viscosity, temperatures and thepercentages of waste cooking oil.

0

20

40

60

80

100

120

140

160

180

Aged Bitumen 30/40 Aged Bitumen 40/50 Aged Bitumen 50/60

0%WCO 1%WCO 2%WCO 3%WCO 4%WCO 5%WCO

Pen

etra

tion

Val

ue (

0.1

mm

)

Fig. 3. Relationship of penetration value and different aged bitumen groups.

30

35

40

45

50

55

60

Aged Bitumen 30/40 Aged Bitumen 40/50 Aged Bitumen 50/60

0%WCO 1%WCO 2%WCO 3%WCO 4%WCO 5%WCO

80/100

Soft

enin

g P

oint

val

ue (

C)

Fig. 4. Relationship of softening point value and different aged bitumen groups.

H. Asli et al. / Construction and Building Materials 37 (2012) 398–405 401

3. Results and discussion

3.1. Penetration value

Through simulation of the unconventional ageing method usingthe propeller mixer, various degrees of aged bitumen penetrationvalue were generated, as shown in the red clustered1 column inFig. 1. The aged bitumen were classified into several categories,namely, 50/60, 40/50 and 30/40, which have penetration valuesranging from 50 to 60, 40 to 50 and 30 to 40, respectively.

Subsequently, a series of three aged bitumen binders were reju-venated with waste cooking oil (WCO) at 1%, 2%, 3%, 4% and 5% byweight of bitumen. The effects of mixing waste cooking oil intoaged bitumen on the penetration value are clearly illustrated inFig. 3. It was observed that the penetration value increases linearlyas the amount of added waste cooking oil into aged bitumen in-creases. Increasing the penetration value for various degrees ofageing is caused by changes to the bitumen by the chemical groups(asphaltenes and maltenes) [11], due to the addition of waste cook-ing oil, that lead to having a softer binder. However, when itreached an optimum percentage of waste cooking oil, the lowerpenetration value resembled that of the original bitumen. Tradi-tional methods to determine the percentage of the rejuvenatorare predominantly based on blending charts of either penetrationor viscosity [23].

1 For interpretation of color in Fig. 1, the reader is referred to the web version ofthis article.

The penetration value of the original bitumen (specific value) is85 (l0 = 85). As displayed in Fig. 3, adding approximately 1% ofwaste cooking oil does rejuvenate the aged bitumen of 50/60penetration group to a similar level as the original bitumen. Simi-larly, with the addition of approximately 3% waste cooking oil tothe aged bitumen penetration group of 40/50, the penetration va-lue of original bitumen is attained. Furthermore, the penetrationvalue of the original bitumen is achieved when almost 4% wastecooking oil is added to the aged bitumen penetration group of30/40.

3.2. Softening point value

The relationship between the softening point value and severalaged bitumen penetration groups: aged bitumen penetrationgroup of 50/60, aged bitumen penetration group of 40/50 and agedbitumen penetration group of 30/40 developed by propeller mixer(MIXER) are presented in Fig. 4. As illustrated in the graph below,with the increasing ageing times, the penetration value decreaseswhile the softening point temperature increases due to the oxida-tion reaction and more asphaltene micelles appear [24]. However,the softening point value decreases with the addition of wastecooking oil content into aged bitumen. In the aged bitumen,increasing the asphaltene content with high molecular weightcan produce harder bitumen [25], while the chemical groupschanges during the mixture of waste cooking oil can rejuvenatethe diverse groups of aged bitumen.

As can be seen in Fig. 4, when approximately 1% of waste cook-ing oil is added into the aged bitumen penetration groups of 50/60,

700

950

1200

1450

1700

1950

2200

2450

2700

2950

Aged Bitumen 30/40 Aged Bitumen 40/50 Aged Bitumen 50/60

0%WCO 1%WCO 2%WCO 3%WCO 4%WCO 5%WCO

Vis

cosi

ty (m

Pa.

s)

Fig. 5. Viscosity versus different aged bitumen groups at 110 �C.

0

100

200

300

400

500

600

700

800

Aged Bitumen 30/40 Aged Bitumen 40/50 Aged Bitumen 50/60

0%WCO 1%WCO 2%WCO 3%WCO 4%WCO 5%WCO

Vis

cosi

ty (

mP

a.s)

Fig. 6. Viscosity versus different aged bitumen groups at 135 �C.

0

100

200

300

400

500

600

Aged Bitumen 30/40 Aged Bitumen 40/50 Aged Bitumen 50/60

0%WCO 1%WCO 2%WCO 3%WCO 4%WCO 5%WCO

Vis

cosi

ty (

mP

a.s)

80/100

Fig. 7. Viscosity versus different aged bitumen groups at 150 �C.

402 H. Asli et al. / Construction and Building Materials 37 (2012) 398–405

they resemble the original bitumen value. Moreover, the originalsoftening point value of 46 �C is achieved when 2% of waste cook-ing oil is added into the aged bitumen penetration group of 40/50.At the same time, adding around 4% of waste cooking oil changedthe aged bitumen to resemble the original bitumen.

3.3. Viscosity

By using the rotational viscometer, the viscosity of a binder canbe determined over a relatively wide range of temperatures and

shear rates. As stated by Apeagyei [22], the usefulness of asphaltbinders as paving materials is dependent on the resistance tochange their physical properties across the range of temperaturesencountered in a typical pavement. The viscosity for high temper-ature at 135 �C is usually conducted according to the Superpavespecification. Accordingly, Al-Khateeb and Al-Akhras [26] have re-ported that the temperature of 135 �C represents the average mix-ing and laydown temperature for hot mix asphalt (HMA). Theelevated temperatures of 110 �C, 135 �C and 150 �C are conductedand tested for this research.

9.00

10.00

11.00

12.00

13.00

14.00

15.00

16.00

17.00

50/60 40/50 30/40

Aged bitumen Rejuvenated bitumen

Rat

io o

f as

phal

tene

s to

mal

tene

s (%

)

80-100

Fig. 8. Ratio of asphaltenes to maltenes for virgin, aged, and rejuvenated bitumen.

Table 3ANOVA: single factor between the original bitumen and aged bitumen group of 50/60 + 1%WCO on penetration value.

Source of variation SS df MS F p-Value Fcrit

Between groups 90.25 1 90.25 27.76923 0.034176 18.51282Within groups 6.5 2 3.25Total 96.75 3

Table 4ANOVA: Single factor between the original bitumen and aged bitumen group of 40/50 + 3%WCO on penetration value.

Source of variation SS df MS F p-Value Fcrit

Between groups 1 1 1 0.1 0.781782 18.51282Within groups 20 2 10Total 21 3

Table 5ANOVA: single factor between the original bitumen and aged bitumen group of 30/40 + 4%WCO on penetration value.

Source of variation SS df MS F p-Value Fcrit

Between groups 16 1 16 3.2 0.215535 18.51282Within groups 10 2 5Total 26 3

Table 6ANOVA: single factor between the original bitumen and aged bitumen group of 50/60 + 1%WCO on softening point value.

Source of variation SS df MS F p-Value Fcrit

Between groups 0.0625 1 0.0625 1 0.42265 18.51282Within groups 0.125 2 0.0625Total 0.1875 3

Table 7ANOVA: single factor between the original bitumen and aged bitumen group of 40/50 + 2% WCO on softening point value.

Source of variation SS df MS F p-Value Fcrit

Between groups 0.25 1 0.25 2 0.292893 18.51282Within groups 0.25 2 0.125Total 0.5 3

Table 8ANOVA: single factor between the original bitumen and aged bitumen group of 30/40 + 4%WCO on softening point value.

Source of variation SS df MS F p-Value Fcrit

Between groups 0.0625 1 0.0625 1 0.42265 18.51282Within groups 0.125 2 0.0625Total 0.1875 3

H. Asli et al. / Construction and Building Materials 37 (2012) 398–405 403

The fluidness in mixtures of bitumen and aggregate duringplacement and compaction in a hot asphalt plant are greatly influ-enced by the viscosity. The results of viscosity for several agedbitumen groups at elevated temperatures are graphically reportedin Figs. 5–7. These viscosity figures display several aged bitumenpenetration groups: 50/60, 40/50 and 30/40 with various percent-ages of waste cooking oil at medium to high temperatures and

compare them to the original bitumen pen-grade 80/100. As thetemperatures increase (i.e. 110 �C, 135 �C and 150 �C), respectively,the viscosity figures clearly show the decrease in viscosity due tothe addition of waste cooking oil contents into different aged bitu-men groups.

At 110 �C, 135 �C and 150 �C, the graphs show that the additionof 1% waste cooking oil into aged bitumen penetration groups of50/60, could achieve almost the same viscosity of the original bitu-men. With the same temperatures as well, it was found that 4% ofwaste cooking oil could rejuvenate aged bitumen penetrationgroup of 40/50. Similarly, when 5% of waste cooking oil wasblended into it, the rejuvenated bitumen managed to achieve theaged bitumen penetration group of 30/40. The resembling of vis-cosity of aged bitumen by adding the WCO, is in relation to thereduction of the ratio of asphaltenes to maltenes, which will beelaborated upon in the next section.

3.4. Ratio of asphaltenes to maltenes

In general, Bitumen can be divided into two broad chemicalgroups: asphaltenes and maltenes. High molecular weight asphal-tene micelles disperse or dissolve in a lower molecular weight oilymedium (maltenes) [24]. Oxidation (ageing) depends on the tem-perature and time changes the fractional chemical compositionof bitumen, which leads to an increase in the asphaltenes content(due to oxidation of polar resins) [24] and a decrease in the per-centage of maltenes. Consequently, ageing leads to an increase inthe ratio of asphaltenes to maltenes, which is directly in relationto the increase in viscosity [25,27]. In this study, to measure thechemical changes, the ratio of asphaltenes to maltenes (ASTM D4124) was measured for virgin, aged and rejuvenated bitumen, fol-lowing the n-heptan insolubility method (ASTM D 4124). As Fig. 8illustrates, the ratio of asphaltenes to maltenes are higher for allaged groups of bitumen (30/40, 40/50, 50/60) compared to the vir-gin bitumen. However, adding WCO leads to a decrease in the ratioof asphaltenes to maltenes, which is due to the increase in the ratioof lower molecular weight oily medium (maltenes) in the rejuve-nated bitumen.

4. Analysis of variance (ANOVA)

The statistical analysis of one-way ANOVA (single factor) wascarried out in this research with 95% confidence interval to deter-mine whether there is a significant difference between the originalbitumen and rejuvenated bitumen in respect of the physical prop-erties. Tables 3–9 present the variance analyses of penetration,softening point, viscosity.

Table 9ANOVA: single factor between the original bitumen and different aged bitumen groups on viscosity.

Temperature (�C) Aged bitumen group Optimum (%WCO) Fstat value p-Value Fcrit value Significance

110 50/60 1 4.84131 0.158776 18.51282 NS40/50 4 0 1 18.51282 NS30/40 5 5.484989 0.143963 18.51282 NS

135 50/60 1 0.123448 0.758887 18.51282 NS40/50 4 0.222183 0.683798 18.51282 NS30/40 5 2.644698 0.245413 18.51282 NS

150 50/60 1 0.099723 0.78207 18.51282 NS40/50 4 0.661672 0.501409 18.51282 NS30/40 5 2.699639 0.242085 18.51282 NS

Note: NS = Not significant.

404 H. Asli et al. / Construction and Building Materials 37 (2012) 398–405

It was found that there is no significant difference in the pene-tration value between the original bitumen and rejuvenated bitu-men (i.e. aged bitumen groups + optimum percentage of wastecooking oil) for the 50/60, 40/50 and 30/40 aged bitumen groupsas shown in Tables 3–5. Since the p-value > a (0.05) and Fstat < Fcrit

for each condition below, thus the proposed hypothesis is rejectedand decides that the penetration value for rejuvenated bitumencould be 85. However, as shown in Table 3, there is a significantdifference between the rejuvenated bitumen and original bitumenwhen 1% waste cooking oil was added into the aged bitumen pen-etration group of 50/60 since the p-value < a (0.05) and Fstat > Fcrit.This indicates that rejuvenated bitumen might be achieved whenless than 1% of waste cooking oil is blended into it. The evidenceshows that waste cooking oil can be used as a rejuvenator in recy-cled bituminous pavement.

The analysis of one-way ANOVA with single factor shows thatthere is no statistically significant difference in the softening pointvalue between the original bitumen and the rejuvenated bitumen(Tables 6–8). The results of the analysis indicate that F > Fcrit andp-values are less than the significance level, a = 0.05, therefore, itcan be concluded that there is not enough evidence to suggest adifference between the original bitumen and rejuvenated bitumenfor each aged bitumen group. This shows that the addition andblending of waste cooking oil has positive impact on the aged bitu-men binder.

Further verification of the viscosity was derived using one-wayANOVA analysis, as indicated in Table 9. From the table, it showsthat there is no significant difference between the rejuvenatedbitumen and original bitumen, since the Fstat < Fcrit and p-valueare more than the significance level (a = 0.05) for each case at ele-vated temperatures. It can be concluded that there is insufficientsolid evidence to claim a difference between the rejuvenated bitu-men and original bitumen concerning the viscosity for each condi-tion. According to these analyses and the visual examination fromthe graph shown, it suggests that waste cooking oil is suitable foruse as a rejuvenator in recycled bituminous pavement. Therefore,from the viscosity, softening point and penetration results obvi-ously can understand that waste cooking oil can be used as therejuvenator in recycling asphalt pavement.

5. Conclusion

As mentioned earlier, the main purpose was to investigate thepossibility and effects of waste cooking oil as the rejuvenator foraged bituminous pavement. In this study, waste cooking oil be-haves as an antioxidant or rejuvenator on age-hardened bitumen.The physical properties of bitumen binders were measured beforeand after the selected degree of ageing. The effectiveness of wastecooking oil in reducing age-hardening was evaluated using thepenetration test, softening point test and the Brookfield viscositytest. From these preliminary results, the conclusions of the findingscan be drawn as follows:

(1) The ANOVA evaluation confirms that there is no significantdifference between the rejuvenated bitumen and the origi-nal bitumen. The penetration value shows that there is a sig-nificant difference between the rejuvenated bitumen (theaged bitumen pen-grade 50/60 with 1% waste cooking oilcontent) and the original bitumen. This means that less than1% added waste cooking oil into the aged bitumen mayresemble the original bitumen. However, the softening pointtest and the Brookfield viscosity test indicate that there areno statistically significant differences between the rejuve-nated bitumen and the original bitumen.

(2) Meanwhile, the physical tests show that when 3–4% ofwaste cooking oil content was blended into the aged bitu-men group of 40/50 it successfully rejuvenated the bitumen.The results of ANOVA analysis verified that the rejuvenatedbitumen properties were similar to the original bitumenproperties.

(3) Moreover, compared to the original bitumen behaviour, theoptimum percentage of rejuvenator (waste cooking oil) thatgenerates the rejuvenated bitumen was 4–5% for the agedbitumen group of 30/40. The results of ANOVA clarified thatthere is insufficient evidence to determine any differencebetween the rejuvenated bitumen and the original bitumen.

(4) Comparing the ratio of asphaltenes to maltenes of virgin(80–100), aged (50/60, 40/50, 30/40) and rejuvenated bitu-men illustrates that adding WCO as a rejuvenator in variousgrades of aged bitumen can rejuvenate the aged bitumen’sby reducing the ratio of asphltanes to maltenes but cannotresemble the virgin bitumen (80–100).

(5) The results show the ability and potential of a rejuvenator,such as waste cooking oil, for recycling bituminous pave-ment in order to decrease the maintenance cost of the exist-ing asphalt pavement.

Acknowledgments

This study is part of a research project that is sponsored by theInstitute of Research Management and Consultancy, University ofMalaya, which provided the financial assistance through the GrantPS138/2009B to accomplish the present and ongoing work. And itis an honour to have Kajang Rock Sdn. Bdn. as the cooperative sup-plier of bitumen 80/100.

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