Engineering and leaching properties of asphalt binders modified with polyurethane and Cecabase additives for warm-mix asphalt application

Construction and Building Materials 238 (2020) 117699

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Engineering and leaching properties of asphalt binders modified with polyurethane and Cecabase additives for warm-mix asphalt application Nurul Aqilah Awazhar a, Faridah Hanim Khairuddin a,b, Suzielah Rahmad a, Syazwani Mohd Fadzil c, Hend Ali Omar d, Nur Izzi Md. Yusoff a,⇑, Khairiah Haji Badri e a

Smart and Sustainable Township Research Centre (SUTRA), Universiti Kebangsaan Malaysia, Selangor, Malaysia Dept. of Civil Engineering, Universiti Pertahanan Nasional Malaysia, Kuala Lumpur, Malaysia School of Applied Physics Studies, Universiti Kebangsaan Malaysia, Selangor, Malaysia d Dept. of Civil Engineering, University of Tripoli, Tripoli, Libya e School of Chemical Sciences, Universiti Kebangsaan Malaysia, Selangor, Malaysia b c

h i g h l i g h t s
The crystalline structure of the binders is unaffected by PU and Cecabase.
PU and Cecabase do not have a significant influence on thermal transition of the B-B.
The concentrations of all heavy metals leached out are within the standards.

a r t i c l e

i n f o

Article history: Received 12 September 2019 Received in revised form 26 October 2019 Accepted 24 November 2019

Keywords: Polyurethane Warm-mix asphalt Consistency Adhesion Thermal Leaching

a b s t r a c t Asphalt binders have been modified with various additives and modifiers as an effort to fulfil the demand for high-performance pavements. Therefore, this study aims to investigate the engineering and leaching properties of 60/70 penetration grade asphalt binder modified with polyurethane (PU) and Cecabase additives for warm-mix asphalt (WMA) application. Measurements of the physical properties of unmodified and modified asphalt binders were made via penetration, softening point, ductility and viscosity tests. The binder-aggregate adhesivity was established by performing the Vialit test while X-Ray Diffraction (XRD) analysis was conducted to determine crystallinity of the binder. Differential Scanning Calorimetry (DSC) was used to determine thermal behavior of the asphalt binders. Synthetic precipitation leaching procedure (SPLP) test was carried out to determine the mobility of organic and inorganic elements present in the binder. PU as modifier and Cecabase as the WMA additive-enhanced binder stiffness. In contrast to Cecabase, the addition of PU increased viscosity of the binder at varying temperatures. PU also enhanced the interfacial adhesion between the binder and the aggregates. The XRD patterns showed that the incorporation of PU and Cecabase has no influence in the crystalline structure of the asphalt binders. Both PU and Cecabase have the ability to improve the workability of the binder at low temperature. The incorporation PU and Cecabase to the asphalt binder showed insignificant shift of the Tg and Tm. SPLP test results indicated that the amount of heavy metals leached out from the asphalt binder samples have no adverse effect on the environment and also did not exceed the standard for drinking. Ó 2019 Elsevier Ltd. All rights reserved.

1. Introduction Warm-mix asphalt (WMA) technology is fast gaining popularity in the hot-mix paving application by virtue of its lower mixing and ⇑ Corresponding author. E-mail addresses: [email protected] (F.H. Khairuddin), [email protected]. my (S. Rahmad), [email protected] (S.M. Fadzil), [email protected] (H. A. Omar), [email protected] (N.I. Md. Yusoff), [email protected] (K.H. Badri).

https://doi.org/10.1016/j.conbuildmat.2019.117699 0950-0618/Ó 2019 Elsevier Ltd. All rights reserved.

compaction temperatures as well as reduced emission of incidental fumes and odours [1]. WMA is essentially similar to hot-mix asphalt (HMA) since the aggregates and asphalt binder of WMA have to be heated in order to achieve suitable mixing and workability [2]. The failure and performance of the pavements constructed utilizing WMA technologies were compared to those of HMA with regard to moisture damage, rutting, stripping, cracking, compaction level, modulus, etc. [3]. Capitao et al. [4], Rubio et al. [5], Kheradmand et al. [6], Abdullah et al. [7], Xu et al. [8], Mohd

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Hassan et al. [9], Diab et al. [10] and Rondón-Quintana et al. [11] are among the researchers who have rigorously reviewed published papers focusing on WMA technologies with respect to their technical advantages and drawbacks, as well as economic and environmental issues. In addition, several studies have been undertaken to evaluate the ageing properties of WMA binders and mixtures [12–14]. Arefin et al. [12] discovered that the binder type plays a significant role in determining the ageing characteristics of foamed WMA and HMA mixtures. Generally, WMA additives can be classified into three categories based on the technology used: (i) organic additives, (ii) chemical additives, and (iii) foaming process [5,8]. Chemical and organic additives are blended with asphalt mixtures components, while the foaming process is carried out parallel to and during the mixing process by using water-based techniques or water-containing products, for instance, zeolite [13]. Yu et al. [15], for example, investigated the fatigue behavior of several warm-asphalt rubber (WAR) samples blended with crumb rubber and three types of WMA additives (organic, chemical, and foaming additives). The specimens modified with organic additive show improved fatigue resistance, whereas the fatigue resistance of WARs modified via foaming and the addition of WMA showed poor performance in comparison to asphalt rubber though its performance is still much superior to that of non-rubberized samples. Sahin and Ipek [16] used 0.2 and 0.5% PAWMA, which is a type of chemical WMA additive, to modify the 70/100 penetration grade binder. It is an amidoamine derivative. The addition of PAWMA at the same rotational speed resulted in reduced viscosity despite the increase in softening point and penetration values. Rani et al. [17] mixed varying amounts of an amine-based chemical WMA additive with PG 58–28 binder and examined the potential for moisture susceptibility by using surface free energy (SFE) method. The addition of WMA additive reduced the vulnerability of the mix to moisture-induced damage. The degree of improvement, however, is dependent primarily on aggregate type. Gong et al. [18] blended Sasobit with epoxidised asphalt rubber (EAR) that was fabricated using industrial asphalt rubber with 20 wt% crumb rubber as WMA additive. The incorporation of Sasobit reduced the viscosity of neat EAR and extends the operational lifetime of the asphalt mixture. Therefore, increasing the amount of Sasobit caused a reduction in the viscosity of Sasobit modified EARs. Tian et al. [19] blended a WMA agent known as EC-120 with two types of asphalt binder namely A-70 (matrix asphalt) and SBS I-D (SBS modified asphalt). Higher EC-120 content of up to a maximum of 4 wt% resulted in enhanced rutting resistance and reduced low-temperature thermal cracking. Arroyo-Martínez et al. [3] utilized a combination of 2.1% water and 2.1% green water-based additive containing 20% solids to achieve the benefit of foam technique in WMA technology. The additive increased the contact area of asphalt and this resulted in a complete coating of the aggregate and the formation of a large amount of small homogeneous bubbles. The enhanced workability and lubricity of the asphalt mixture via the formation of microbubbles resulted in better compaction in that the required densities can be achieved. As a result, it improved the stability of the binder [3]. Amongst those many methods, CecabaseÒ; a chemical WMA additive, which has an element of anti-stripping surfactant agents offers a good alternative. This material will not change the rheological properties of the asphalt binder since it works as a layer between binder and aggregate. Interfacial adhesion behavior and moisture condition of aggregate improved upon addition of Cecabase without eliminating the performance of pristine binder [4]. Vaitikus and Vorobjovas [20] conducted a study using Cecabase and revealed this material has decreased the compaction temperatures and stability of asphalt mixture. A research done by Ouni et al. [21] showed Cecabase mixture is comparable to hot mix

asphalt mixture and dense-type and generate resistance towards permanent deformation test under cyclic load. The utilization of Cecabase also had reduced the short term ageing parallel with the decrease in construction temperature [22]. Khairuddin et al. [23] employed Raman Spectroscopy to examine the morphology of 60/70 penetration grade binder (B) mixed with polyurethane (PU) and 0.5% Cecabase (C). The bee-structure observed in the Raman Spectroscopy indicates a reduced wax content of B-PU and B-C; resulted in a reduction in the catana phase relative to the content in B-B and B-PU-C. However, the ordered structures of all investigated binders did not exceed the boundary limits of both the D and G bands. Polyurethane (PU), on the other hand, is a block polymer involved the addition polymerization reaction between polyol (OH) and diisocyanate (NCO) to form urethane backbone (NHCOO-). Inclusion of PU in asphalt binder is still new in pavement industry. Khairuddin et al. [24] conducted a study using Response Surface Method (RSM) to determine the optimum percentage of PU to mix with the 60/70 penetration grade asphalt binder, discovered at 3% addition. The addition of PU exhibited an increase in viscosity which consequently showed improvement in resistance to fatigue and rutting. Carrera et al. [25] proved the inclusion of PU prepolymers to the base binder enhanced the engineering properties of the binder prior to type of asphalt binder and curing conditions. Another study using PU as binder replacement at 20%, 40% and 60% showed a decrease of 10% in mixing and compacting temperature [26]. Fourier Transform Infrared (FTIR) spectroscopy analysis indicated the presence of new functional group belonged to the C = C aromatic of the asphaltenes for the modified bitumen upon addition of PU. In other studies, thermoplastic polyurethane was used as the binder modifier. Lower penetration grade with higher softening point was observed upon addition of PU hence the performance of pristine binder improved under high-temperature condition [27]. A better performance in resistance towards deformation and rheology were observed using polyurethane modified emulsion [28]. An isocyanate pre-polymer was used to develop bituminous foam. Some changes in bitumen stiffness and the pre-polymer molecular weight were observed. [29,30]. Since the application of PU in pavement industry is still at an infant stage and the utilization of WMA is promising, this present study aims to examine the feasibility and effect of blending PU and WMA additives, namely Cecabase with asphalt binder on the physical including adhesion properties, chemical, thermal and leaching properties of the modified asphalt binder. Measurements of the physical properties of the unmodified and modified asphalt binders were made through penetration, softening point, ductility and viscosity tests. The adhesion capability of the asphalt binderaggregate was established through the Vialit Adhesion test while X-Ray Diffraction (XRD) analysis was carried out to examine the crystal structure of the binders. Differential Scanning Calorimetry (DSC) was used to characterize the thermal properties of the binders. Finally, the synthetic precipitation leaching procedure (SPLP) test was carried out to determine the mobility of the organic and inorganic elements present in the binders.

2. Experimental design 2.1. Materials and sample preparation The 60/70 penetration grade asphalt binder employed in the present study was supplied by Cenco Science Malaysia as the base binder; the physical properties of the asphalt binder are presented in Table 1. A chemical type of WMA additive; Cecabase RT 975 and PU were used as modifier and mixed with the base binder. Cecabase RT 975 is a light-yellow liquid produced by the CECA Arkema

N.A. Awazhar et al. / Construction and Building Materials 238 (2020) 117699 Table 1 Physical properties of 60/70 penetration grade asphalt binder. Physical Properties

ASTM Method

Value

Requirement

Penetration (0.1 mm) at 25 °C Softening point (°C) Ductility (cm) at 25 °C Viscosity (MPa.s) at 135 °C

D5 D36 D113 D4402

68.0 46.0 120 513

60–70 47 MIN 100 MIN –

3

friction of the presence molecules. The ductility test (ASTM D113) was used to measure the tensile properties of both asphaltic materials. For each test, three replicates sample were tested and the value is the average readings. 2.3. Storage stability test The storage stability test was performed to determine the stability of the modified asphalt binder when stored at high temperatures. A 140 mm long and 25 mm diameter aluminum tube was filled with the hot modified asphalt binder and then placed in a 163 °C oven for 48 h. The tube was allowed to cool and following this was then divided into three sections. The softening point test was carried out on the top and bottom sections of the tube. The difference between the softening points of the two sections should be less than or equal to 2.2 °C in order to pass this test. This test was conducted in accordance with ASTM-D5976 (2000). 2.4. Vialit adhesion test

Fig. 1. PKO-p and Cecabase RT975.

Group, France as shown in Fig. 1. The specific gravity is 1.00 and is insoluble in water. The PU was obtained via reaction between palm kernel oil-based monoester polyol (PKO-p) and 2,4diphenylmethane diisocyanate (MDI) as shown in Fig. 1 which was derived from palm kernel oil. The reaction involved condensation polymerization, also known as pre-polymerization method and added with MDI. Upon mixing MDI with PKO-p, polymerization occurred. PKO-p was obtained from UKM Technology Sdn Bhd through its pilot reactor in Bangi-Lama, Malaysia. This material is a golden yellow liquid with a cloud point of 13 °C. At 25C, the specific gravity is 0.992 g/cm3 with low viscosity of 374 cps and 0.992% moisture content [31]. Both modifiers were blended at a dosage rate of 0.5 wt% (Cecabase) and 3 wt% (PU) by weight of base binder, respectively [24]. In this study, the base binder was first heated at 145C until it turns fluid. The PKO-p and MDI were then added to the base binder at 110 °C and blended at 2000 rpm for 15 min using a shear mechanical mixer. Following the blending of BPU, Cecabase was added to the mixture and blended for another fifteen minutes to obtain BPUC. Similar blending parameters were adopted to prepare BC. The classification of the samples prepared for this study is presented in Table 2.

2.2. Physical tests Physical tests, including the penetration (ASTM D5) and softening point tests (ASTM D36), were carried out and the results of the test were compared to establish the fluidity of the binders. The rotational viscosity test (ASTM D4402) was carried out at two different temperatures in order to determine the resistance of the asphalt binder to deformation of flow on the basis of the internal Table 2 Sample classification. Binder Type

60/70 60/70 + 3% PU 60/70 + 3% PU + 0.5% Cecabase 60/70 + 0.5% Cecabase

Sample ID

BB BPU BPUC BC

Vialit plate shock test method was applied to determine the binder-aggregate adhesion capability, following standard specification EN 12272–3. A standard size tray was filled with 40 g asphalt binder and a hand-operated rubber roller was used to press a sample of 100 aggregate particles with size between 9.5 mm and 6.3 mm [32]. This test was conducted in two conditions; dry and wet conditions. As for wet condition, samples were immersed in a water bath at 60C for 6 h. Then, the samples were placed in a freezer for 30 min to complete the wet condition. The sample was left in the tray to cure, after which the tray was inverted, and a 500 g steel ball dropped on the tray three times from a height of 50 cm within 10 s. The force of the falling ball resulted in a detachment of the aggregate sample. The detached particles as a result of impact were counted and registered as a percentage of aggregate retention. A high percentage of aggregate retention indicates a strong adhesion between the binder and the aggregates. 2.5. X-Ray Diffraction test X-Ray Diffraction (XRD) analysis was conducted to identify the changes in the crystal structure of the binder. In this analysis, a diffractometer was connected to a computer. Samples were prepared by pouring asphalt binder which has been preheated at 110 °C for 8 min on a glass plate. The prepared sample was placed horizontally on the base plate of the diffractometer between the evacuated tube and the detector. In this study, the detector was set to rotate at an angle range of 5° to 80° at 0.5 steps of 2h during scanning in order to identify the bands of diffracted x-rays produced by the correctly aligned crystals within the sample. 2.6. Differential Scanning Calorimetry (DSC) test Differential Scanning Calorimetry (DCS) test was conducted to investigate the thermal conditions of unmodified and modified asphalt binders. The test was carried out in nitrogen gas atmosphere employing a Shimadzu DSC-50 calorimeter with a flow rate of 10 ml/min and the sample was heated from room temperature to 600 °C at a heating rate of 10 °C/min.

Sample composition (%)

2.7. Synthetic precipitation leaching procedure (SPLP) test

PU

Cecabase

0.0 3.0 3.0 0.0

0.0 0.0 0.5 0.5

Synthetic Precipitation Leaching Procedure (SPLP) test was conducted in accordance with SW-846 Test Method 1312: Synthetic Precipitation Leaching Procedure [33] with the aim of determining the mobility of the organic and inorganic elements present in the binder specimens. The samples were set by heating the sample

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in an oven at 110 °C for 5 min. At the same time, a conical flask was filled with water and heated to 95 °C. Following this, the heated asphalt binder was poured into the conical flask to obtain an asphalt binder to water ratio of 1:20. The flask containing the asphalt binder-water mixture was immediately covered using non-absorbent cotton and aluminum foil. The conical flask was then rotated manually 2 to 3 times; after which it was placed in an incubator shaker to be rotated at 30 rpm for 18 h at ambient temperature. The conical flask was then left to stand at room temperature for 14 days prior to performing the test to identify the organic and inorganic elements present in the asphalt binder samples.

with those of the penetration test, where addition of PU and Cecabase increased the binder stiffness. The crosslinking occurred during the hot melt processing increased with the addition of PU, again, contributed by both the existence of the hard segment by MDI combined with the presence of asphaltenes. As could be seen in Table 3, the standard deviation values were in the allowable average limit and reflect the repeatability of the results of the binders for each test, where the coefficient of variation confirms the limitation of the errors. Additionally, ANOVA analysis was performed to evaluate the reproducibility for each test, and the effect of the modification on the properties of the binders. The groups compared in this study are the control and modified binders and the variables evaluated are penetration, softening point, ductility and viscosity. The hypothesis was tested using level of significance (p) assumed as 0.05 where there is no statistically significant difference in the mean value between control and modified binders. Table 4 shows the null hypothesis for the assumption of homogeneity of variance was rejected as the (p) is less than 0.05 and indicated that there was statistically significant difference across the binders as determined by one-way ANOVA for all tests (F (3, 8) = 99, 116, 11 and 775 and the (p) = 0.00 for softening point, penetration, ductility and viscosity), which means that the modification of the binders significantly altered their physical properties and the binders produced different results.

2.8. Statistical analysis The One-way Analysis of Variance (ANOVA) method was selected for comparing the means of two or more groups of cases. Two different estimates for data variance were calculated. One of these, called between-groups variance, measures the effect of the variable combined with error. The other estimate, called withingroups variance, is the error variance. Another parameter, the Fratio, is the ratio of between groups variance to within-groups variance. The hypothesis was tested at a level of F-ratio significance (p) assumed to be 0.05. A significance value less than this means that the means are not equal and a significant difference is obtained. This method in which the modification of the binders can be statistically tested for every laboratory test method is very important and shows the effect of the modification on the properties of the binder.

3.2. Storage stability The storage stability test is performed to make certain that the mixture has been effectively blended, thus ensuring the stability of the blend during storage. An asphalt binder sample is considered to be a storage stable blend if the difference of the softening point between the top and bottom sections is not more than 2.2 °C [35]. Fig. 2 shows the softening point difference between the top and bottom sections of the tube. It can be seen that the difference between top and bottom sections of all modified binders were 0.5 °C for B-PU, 0.90 °C for B-PU-C and 0.5 °C for B-C which does not exceed 2.2 °C. Therefore, all samples are considered to be storage stable blend and this result indicates that the modified mixes were homogeneously blended.

3. Results and discussion 3.1. Physical properties The physical properties of BPUC, BPU and BC are presented in Table 3. The table shows that the penetration values of BPU, BPUC and BC are within the standard limit of a 60/70 penetration grade asphalt binder with BPU having a decrease in penetration value than the control sample. This indicates that BPU is stiffer compared to the control sample. According to Bazmara et al. [27], adding PU to asphalt binder increased the viscosity and stiffness of the asphalt binder significantly. A study conducted by Khairuddin et al. [23] has also shown that adding PU to asphalt binder resulted in higher binder stiffness. PU has been proven to have the ability to increase binder stiffness, thereby improving binder resistance towards rutting. The stiffness and rigidity are contributed by the hard segment by the MDI. BPU has the highest softening point at 50.4 °C while BB has the lowest softening point at 46.0 °C. The addition of PU has also significantly increased the softening point of binders, resulting in higher melting point. Asphalt binder samples with high softening point are less temperature-sensitive. According to Cong et al. [34], the altered molecular structure of the binder caused an increase in softening point during ageing. The results for ductility obtained in this study are in agreement

3.3. Viscosity Table 5 shows viscosity of the samples at 110, 120, 135 and 165 °C. The addition of PU resulted in higher binder viscosity. The highest increase in viscosity was observed at 135 °C. Khairuddin et al. [36] obtained a similar result when incorporating PU to unmodified asphalt binder, where a 64% increase in viscosity was observed at 135 °C. On the contrary, BC has low viscosity when compared to the control binder. This is similar to the findings made by Yero and Hainin [37], where chemical additives were observed to reduce the viscosity of asphalt binder. Binders with lower viscosity ensure an efficient coating of the aggregates and improve workability during the mixing process.

Table 3 Physical properties of modified asphalt binder samples. Sample

BPU BPUC BC

Penetration (0.1 mm) at 25 °C

Softening point (°C)

Ave.

SD

CV

Ave.

SD

CV

Ave.

SD

CV

Ave.

SD

CV

62.5 64.0 67.0

0.5 0.6 0.2

0.8 0.9 0.3

50.1 49.2 48.9

0.6 0.5 0.5

1.2 1.1 1.2

113 115 101

3.5 5.7 2.0

3.1 5.0 2.0

842 353 213

16.2 18.2 12.5

1.9 5.2 5.9

Ave. = Average. SD = Standard Deviation. CV = Coefficient of Variation.

Ductility (cm) at 25 °C

Viscosity (MPas) at 135 °C

5

N.A. Awazhar et al. / Construction and Building Materials 238 (2020) 117699 Table 4 ANOVA analysis for the results of physical properties. Physical Properties Softening point

Between Groups Within Groups Total Between Groups Within Groups Total Between Groups Within Groups Total Between Groups Within Groups Total

Penetration

Ductility

Viscosity

Sum of Squares

df

Mean Square

F

Sig.

44 1 45 61 1 62 597 142 739 658,530 2266 660,796

3 8 11 3 8 11 3 8 11 3 8 11

15 0

99

0.00

20 0

116

0.00

199 18

11

0.00

219,510 283

775

0.00

properties of the samples against the binder by using Eqs. (1) and (2) [26,38–39].

g¼

v v0

rg ¼

Fig. 2. Difference between the top and bottom temperatures (oC).

The standard deviation values for the viscosity test results at different temperatures for all binders are shown in Table 5. It could be seen that the standard deviation values were in the allowable average limit and reflect the repeatability of the results of the binders for each temperature, where the coefficient of variation confirms the limitation of the errors. Also, ANOVA analysis was performed to evaluate the reproducibility for the temperature in viscosity test, and the effect of the modification on the viscosity of the binders. The groups compared in this study are the control and modified binders and the variables evaluated are their viscosity at 110, 120, 135 and 165 °C temperature. The hypothesis was tested using level of significance (p) assumed as 0.05 where there is no statistically significant difference in the mean value between control and modified binders. Table 6 shows the null hypothesis for the assumption of homogeneity of variance was rejected as the (p) is less than 0.05 and indicated that there was statistically significant difference across the binders as determined by one-way ANOVA for all tests (F (3, 8) = 79, 255, 775 and 275 and the (p) = 0.00 for the viscosity at 110, 120, 135 and 165 °C temperature), which means that the modification of the binders significantly altered their viscosity property at different temperature and the binders produced different results. The change in binder viscosity is due to the addition of PU and Cecabase. However, the increase in viscosity of each sample differs and can be established by comparing the altered rate of rheological

ð1Þ



 h dgB Dg B g  go i ¼ ¼ B dB DB B

ð2Þ

where ƞ is the relative viscosity of the modified samples, v is the viscosity of the modified sample, v0 is the viscosity of the control binder, and 5ƞ is the non-dimensional viscosity of the samples and B indicates the modified binder. In this analysis, 5ƞ was used to determine the effect of adding 1% PU, 1% mixture of PU and Cecabase and 1% Cecabase on the viscosity of the asphalt binder at the selected test temperature. Fig. 3 and Table 7 show the connection between the nondimensional viscosity index of the asphalt binder samples (5ƞ) and relative density towards temperatures at 110, 120, 135 and 165 °C. BPU has the highest 5ƞ, followed by BC and BPUC at each tested temperatures. The non-dimensional viscosity indices of BPU, BPUC and BC at 135 °C were 1.48  103%, 4.2  106% and 9. 7  105%, respectively. This shows that the addition of 1% of PU, resulted in 1.48  103% increase in the viscosity of BPU. However, the addition of 1% of Cecabase additive reduced the viscosity of BC by 4.2  106% while the addition of 1% of PU and Cecabase reduce the viscosity of BPUC by 9.7  105%. 5ƞ value at 165 °C showed some increases in all samples of 1.7  103% for BPU, 1.3  106% for BPUC and 3.2  105% for BC. Fig. 3 clearly shows that the temperatures are randomly scattered and hence there is no discernible trend. It can be concluded that the change in performance referred to 5ƞ varies for the same test temperature by adding 1% PU, 1% mixture of PU and Cecabase and 1% Cecabase. Due to the changes in chemical interaction between the components of materials, the trend is unpredictable. Thus, the evaluation of the relative change in viscosity caused by adding 1% PU and 1% Cecabase could be complex [26]. 3.4. Activation energy A thermally activated rate process occurs when fluid flows; in this process fluid layers slide over one another to overcome energy

Table 5 Viscosity of asphalt binder samples. Temperature (°C)

Viscosity (MPas) BB

110 120 135 165

BPU

BPUC

BC

Ave.

SD

CV

Ave.

SD

CV

Ave.

SD

CV

Ave.

SD

CV

1040 764 513 150

33.4 14.1 19.6 10.0

3.2 1.3 3.8 6.7

1248 1057 842 325

24.0 30.0 16.2 17.9

1.9 2.8 1.9 5.5

1035 703 353 103

23.3 19.5 18.2 6.8

2.3 2.8 5.2 6.6

905 568 213 100

28.4 22.7 12.5 5.0

3.1 4.0 5.9 5.0

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N.A. Awazhar et al. / Construction and Building Materials 238 (2020) 117699

Table 6 ANOVA analysis for the viscosity at different temperatures. Temperature (°C) 110

Between Groups Within Groups Total Between Groups Within Groups Total Between Groups Within Groups Total Between Groups Within Groups Total

120

135

165

Sum of Squares

df

Mean Square

F

Sig.

180,692 6079 186,771 382,576 3995 386,571 658,530 2266 660,796 101,261 984 102,245

3 8 11 3 8 11 3 8 11 3 8 11

60,231 760

79

0.00

127,526 499

255

0.00

219,510 283

775

0.00

33,754 123

275

0.00

Fig. 3. Plot of non-dimensional viscosity (5ƞ) against temperature (°C).

Table 7 Relative viscosity of asphalt binder samples. Temperature (°C)

110 120 135 165

Relative Viscosity

Difference in relative viscosity (%)

BB

BPU

BPUC

BC

BPU

BPUC

BC

1.00 1.00 1.00 1.00

1.20 1.38 1.64 2.17

1.00 0.92 0.69 0.69

0.87 0.74 0.42 0.67

20.00 38.35 64.13 116.67

0.48 7.98 31.19 31.33

12.98 25.65 58.48 33.33

barrier due to intermolecular forces [38,40–41]. Therefore, an energy level that is higher than the intermolecular force is required for fluid to flow. The required energy to overcome intermolecular force is called activation energy (Ea) [39]. The higher the intermolecular force, the higher the energy required for the fluid to flow. In this study, high Ea is an indication that the asphalt binder requires a higher level of heat energy in order to flow during mixing. The requirement for a high level of heat energy renders the binder more vulnerable to aging. Additionally, high mixing and compaction temperature resulting in increasing fuel consumption and greenhouse gas (GHG) emissions [39]. The Arrhenius equation, which is given by Eq. (3), was employed to calculate the viscositytemperature dependency of the asphalt binder samples [38,40– 41]. Ea

V ¼ AeRT

ð3Þ

where V is viscosity (Pas); A is the regression constant; Ea is activation energy for flow (kJ/mol); T is temperature (K), and R is universal gas constant (8.34 J/mol. K). In addition to Eq. (3), the linear form y = mx + c was utilized to determine the Ea of binder flow. In this study, a graph of ln (V) against 1/T for each sample is plotted where Ea/R is the slope of the graph [26,38,41]. The Ea is calculated by multiplying a constant R with the slope (c) of the graph. Fig. 4 shows the graph of ln (V) against 1/T while Fig. 5 shows the Ea value for each unmodified and modified binders. The Ea for the base binder with temperature range between 110, 120, 135 and 165C was 49 kJ/mol. According to Mohab et al. [26], the Ea of bio-binders ranges between 85 kJ/mol and 90 kJ/mol. Previously, the result obtained by Salomon and Zhai [40] shows that the Ea for the flow of various types of modified asphalt binder ranges between 40 kJ/mol and 90 kJ/mol. It can be seen that the

N.A. Awazhar et al. / Construction and Building Materials 238 (2020) 117699

7

Fig. 4. Plot of ln (V) against 1/T.

Fig. 5. Activation energy of binder samples.

Ea value of BPU decreases by 28.6% in contrast to that of BB; this is in agreement with the results obtained by Salomon and Zhai [38] which demonstrate that the addition of polymer was able to reduce the Ea of asphalt binders. Asphalt binders with low Ea are temperature sensitive [42–43]. The 20.4% increase in the Ea value of BPUC and 16.3% increase in Ea value of BC indicates that both modified samples have a higher resistance to flow compared to BB. With higher Ea value, more energy needed for binder to coat

with the aggregate that indicates the mixture is susceptible to aging. 3.5. Adhesion of binder Fig. 6 revealed the result for vialit adhesion test. BPU has the highest retention percentage under dry and wet conditions, followed by BPUC, BB and BC. High percentage of aggregate retention

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Fig. 6. Retention No (%) for all dry and wet binder samples.

indicates a strong adhesion bond between the binder and the aggregates. Results of this study show that BPU has the strongest binder-aggregate adhesion bond. Omar et al. [44] pointed out that the adhesion strength of asphalt binder increased when the percentage of nano-clay additive incorporated was increased from 2 to 4%, whereas the addition of hydrated lime resulted in reduced adhesion strength. In the present study, the addition of Cecabase additive resulted in lowering the adhesion strength. This indicates that different types of additives have different effect on interfacial bond strength. Fig. 6 shows that the adhesion strength of all binder samples decreased under wet condition. Previous studies have also demonstrated that exposing binder samples to water frequently resulted in reduced adhesion strength [44]. 3.6. Chemical properties Fig. 7 shows the XRD patterns for the binder samples. The graph shows that the XRD pattern of BB has only one wide peak, indicating that BB has an amorphous (non-crystalline) structure. The XRD patterns for BPU, BPUC and BC are also similar, indicating that both PU and Cecabase are non-crystalline in nature. The XRD pattern obtained by Ali et al. [45] indicated that PMB has an amorphous structure. However, the intensity of the modified binder was lower compared to the control binder. The observed lower intensity in the XRD patterns indicated that PU and Cecabase particles were uniformly distributed [46].

97, 100, and 90 °C, respectively. The temperature whereupon the wax thoroughly melts is substantially higher compared to the temperature for initial crystallization. The shape of the DSC curve is strongly determined by the thermal history before the recording of the scans. BC is more resistant to low temperature cracking due to its lowest Tg value; BPUC shows the highest Tm value relative to those of BB and BPU. Segregation was detected at 447, 457, 461, and 451 °C for BB, BPU, BPUC and BC, respectively. The endothermic peaks for BB, BPU, BPUC, and BC occurred at 505, 513, 519, and 520 °C, respectively. Fig. 8 shows that Tg is unaffected by the incorporation of PU or Cecabase. B-B encompassing of natural wax has lower Tg and this may be ascribed to the stiffening effect of natural wax when the penetration value was measured at 25 °C. Natural wax is partially crystalline at 25 °C and this has an effect of stiffening the binder. Therefore, asphalt binders with a lower penetration grade would probably have a higher Tg [48–49]. As a consequent, the Tg and

3.7. Thermal properties The DSC analysis was performed in order to establish the thermal transitions, in term of crystallization and melting temperatures of the asphalt binders. Fig. 8 is a DSC curve which shows the transition glass temperature (Tg), melting temperature (Tm), and segregation temperatures of all specimens. BB has lower Tg, Tm, and segregation temperature in comparison to the modified samples. Glass transition temperature (Tg) is a good indicator of how binder properties are affected by low temperatures. The exothermic peak of Tg for BB, BPU, BPUC and BC occurred at 33, 31, 32, and 29 °C, respectively. These peaks are established to be the wax crystallization or reaction of oxidation [47]. The temperature for the melting transition, Tm, of BB, BPU, BPUC, and BC are 88,

Fig. 7. XRD diffractogram of BC, BPU, BPUC and BB.

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Fig. 8. DSC thermograms for unmodified and modified asphalt binders.

Table 8 Heavy metal concentration leached from asphalt binder samples. Element

Concentration (mg/L) BB

Arsenic Cadmium Chromium Copper Iron Manganese Plumbum/Lead Zinc

0.002 0.001 0.001 0.008 0.121 0.009 0.005 0.168

BPU

0.002 0.000 0.001 0.006 0.121 0.008 0.003 0.064

Tm of the binders show an almost similar peak trend, including both unmodified and modified asphalt binders. From Fig. 8, the energy consumed for transition peak from room temperature to 600 °C were 0.45 mW/mg for BB, 0.41 mW/mg for BPU, 0.60 mW/mg for BPUC and highest for BC, 1.08 mW/mg. The heat required to increase the energy to the endothermic peak was highest for BC that is 708 J/g, followed by BPU 367 J/g, BPUC 295 J/g and BB 182 J/g.

3.8. Leaching properties Leaching is defined as the transfer of chemicals through liquid such as water as well as other solutions [50]. The SPLP test for the present study was conducted to evaluate the leaching of heavy metals from the asphalt binder samples. Table 8 shows the chemical elements leached from each sample and their concentrations. The concentrations of these chemicals were compared with the drinking water standard for Malaysia [51] and the United States [52]. Table 8 shows that the concentrations of all chemicals detected are within the standards for both countries. Lwin and Utomo [53] reported that Cu (II), Pb (II), Zn(II) and Cd(II) were leached from crumb rubber modified asphalt binder and that the concentration of these heavy metal is within the allowable limit. Shedivy et al. [54] reported that the concentrations of all chemicals

BPUC

0.002 0.001 0.001 0.007 0.118 0.009 0.004 0.149

BC

0.002 0.000 0.003 0.004 0.146 0.010 0.005 0.180

Drinking water standard Malaysia

US

0.010 0.003 0.050 1.000 0.300 0.100 0.010 3.000

0.010 0.005 0.100 1.000 0.300 0.050 0.015 5.000

leached from a RAP are within the standard for drinking water, with the exception of manganese and arsenic. The concentrations of the two metals exceed the permissible limit for drinking water. Arsenic is carcinogenic to humans and exposure to it could result in anemia, gangrene and cancer [55]. Table 8 indicated that the concentration of arsenic leached from the samples was not affected upon addition of PU and Cecabase although there is a reduction in the amount of copper leached from the samples. The reduced copper concentration may be due to the enhanced bonding strength between the modifier and the additive, thereby causing the asphalt binder to leach a smaller amount of copper in comparison to the control sample. The concentrations of iron and zinc leached from BC are higher than those leached by BB. This can be attributed to the weak intermolecular bonding that allows higher amounts of iron and zinc to leach out from BC. However, the concentration of both iron and zinc are still within the allowable limit.

4. Conclusions The penetration test indicated that incorporation of PU as modifier and Cecabase as WMA additive in the binder system may result in enhanced binder stiffness. The softening point and ductility of the asphalt binders increase significantly when PU is blended with the unmodified asphalt binder. The addition of PU resulted in

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higher binder viscosity at varying temperatures. However, the addition of Cecabase resulted in reduced binder viscosity. The low viscosity of BC improved workability at low temperature in comparison to HMA. Analysis of activation energy showed that PU has the ability to reduce activation energy whereas the addition of Cecabase could lead to a higher activation energy. The interfacial adhesion between the binder and the aggregates was enhanced by the addition of PU. The XRD patterns show that the crystalline structure of the binders is unaffected by the incorporation of PU and Cecabase. In general, this study has shown that the greatest improvement in binder properties was achieved when using PU as a modifier. PU and Cecabase have the ability to improve the workability of the binders at low temperature. The results of the DSC test show similar trends for the tested binders, with B-B having the lowest Tg and Tm values. This shows that the incorporation of PU and Cecabase does not have a significant influence on the thermal transition of the B-B. Finally, the results of SPLP test indicated that the concentration of all heavy metals leached out from the asphalt binder samples is within the standards for drinking water of both Malaysia and the United States.

Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgements The authors would like to express their gratitude to Universiti Kebangsaan Malaysia for the financial support for this work (GUP-2018-094 and DIP-2017-004).

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