- Email: [email protected]
The effect of tyre rubber grinding method on the rubber-asphalt binder properties
Construction and Building Materials 154 (2017) 144–154
Contents lists available at ScienceDirect
Construction and Building Materials journal homepage: www.elsevier.com/locate/conbuildmat
The effect of tyre rubber grinding method on the rubber-asphalt binder properties M. Sienkiewicz a,⇑, K. Borze˛dowska-Labuda a, S. Zalewski b, H. Janik a a b
Polymer Technology Department, Chemical Faculty, Gdansk University of Technology, Gabriela Narutowicza Street 11/12, 80-233 Gdansk, Poland Department of Chemical and Process Engineering, Chemical Faculty, Gdansk University of Technology, Gabriela Narutowicza Street 11/12, 80-233 Gdansk, Poland
h i g h l i g h t s Specific surface area of GTR depends on its grinding method. Morphology of GTR grains influences the properties of rubber-asphalt binder. Storage stability of rubber-asphalt binder also depends on its modification method. Addition of GTR to asphalt binder changes percentage of asphalt fractions. Added GTR effects molecular weight distribution of rubberized asphalt binder.
a r t i c l e
i n f o
Article history: Received 31 August 2016 Received in revised form 3 July 2017 Accepted 23 July 2017
Keywords: Morphology Ground tyre rubber (GTR) Modification of asphalt Rubber-asphalt binder Knife granulation process Flat-die granulation process
a b s t r a c t Rubber products, especially those used in the automotive industry, are responsible for a significant amount of waste, mainly in the form of worn tyres. One way to recycle tyres is to use them as an asphalt binder modifier. The properties of rubber-asphalt binders vary greatly depending on the morphology of the ground tyre rubber (GTR) grains and the type of tyre to be recycled (car/truck). The paper presents the results of research in the field of rubber-asphalt binders modified with two types of GTR (which differ in grain morphology) used in various amount and processed at different mixing devices. One GTR is obtained with the use of a standard knives granulator (standard granulation process – SGP), and the other by a special flat die pelleting press (flat-die granulation process – FDGP). It has been proved that GTR grinding method affects its specific surface area, thus the properties of rubber-asphalt binders. Ó 2017 Elsevier Ltd. All rights reserved.
1. Introduction Worldwide, the amount of used rubber products is increasing year by year, most of which is produced by car tyres. Rubber products consist of long polymer chains, mostly crosslinked with sulfur bridges. Therefore, the difficulties associated with the recovery and recycling of used tyres are due to the very complex structure and composition of tyre materials. However, the progress made in recent years in waste management of polymers caused that postconsumer tyres came to be seen as a potential source of valuable raw materials. In this way, rubber wastes may be transformed into energy or new polymer products [1–3]. One of the methods of waste tyres recovery is using them as a modifier of asphalt. Rubber-asphalt binders obtained from the rubber wastes were described by many scientists [4–7]. The addition of recycled rubber ⇑ Corresponding author. E-mail address: [email protected] (M. Sienkiewicz). http://dx.doi.org/10.1016/j.conbuildmat.2017.07.170 0950-0618/Ó 2017 Elsevier Ltd. All rights reserved.
to asphalt improves tenacity, mechanical properties, fatigue life, flexibility, resistance to rutting, abrasion resistance, low temperature cracking, reduce noise during contact tyre with the ground [8–14]. Many studies have shown that properties of rubber-asphalt binders depend on many factors like: the content and particle size, type (car/truck) of ground tyre rubber (GTR), chemical and physical properties of asphalt matrix, as well as its source, and technology of asphalt modification [6,15–19]. Surface modification of ground tyre rubber is also known to affect the properties of rubberasphalt binders [20]. Scanning electron microscope (SEM) analysis showed that pure asphalt is characterized by a smooth surface. Addition of recycled rubber changes the surface homogeneity: the larger particle of recycled rubber the higher heterogenity. Airey and co-workers showed that the density of GTR is changing when it is added to asphalt binder. It was also proved that grains of rubber wastes swell when they are mixed with asphalt and then their mass
145
M. Sienkiewicz et al. / Construction and Building Materials 154 (2017) 144–154
increases up to 140% by weight. This is due to absorption of the aromatic hydrocarbons from asphalt binder by the rubber grains. Additionally, the interaction between the components of the rubber grains and asphalt depends on molecular weight of both components. The interaction is stronger when molecular weight of asphalt is lower. This is due to the possibility to spread the light fraction between the grains of the GTR. Absorption of light hydrocarbon fractions by GTR grains depends on asphalt content and the value of its penetration: the higher those parameters, the greater absorption. On the other hand, as it was noted before, rubber grains are easily swellen by asphalt, resulting in an increase in the viscosity of the rubber-asphalt binder, compared to the viscosity of the virgin asphalt [11,12]. Li and co-workers examined GTR modified asphalt prepared by preblending method. In this process GTR is firstly mixed with small amount of asphalt, then portion of fresh asphalt is added. SEM analysis indicated that interface of GTR without preblending was clear and scattered many slot holes, while interface of preblended GTR was indistinct and slot holes dissapeared. Furthermore, the scattering state of preblended GTR in rubber-asphalt binder is excellent and perfect polymer reticular structure is formed in the sample system. Thus the properties of asphalt with preblended GTR are improved significantly in comparison to asphalt with GTR without preblending [21]. An important role in the rubber-asphalt binder properties plays the specific surface area of the GTR [22,23]. Influence of GTR grinding method on the morphology of GTR surface and finally properties of rubber-asphalt binders were examinated by Thodesen et al. and Thives et al. [24,25]. Thodesen et al. showed that GTR grinded at ambient temperature is characterized by higher specific surface area (rougher surface) than GTR grinded at cryogenic temperature (smoother surface). In addition, viscosity of rubber-asphalt binder increases with increasing specific surface area. They also showed that viscosity increases when amount of GTR is increasing. Some work in turn refers to the impact of the type of mixing device on the properties of the rubber-asphalt product obtained. [26–28]. High shear mixing used for the modification of asphalt by GTR, transoctenamer rubber (Vestenamer) and polyphosphoric acid leads to more uniform texture of the composition in microscale in comparison to the process of mixing with conventional mixer [27]. Yao and co-workers showed that higher amount of carbon black and inorganic fillers are released from GTR to asphalt binder during high shear mixing at the high curing temperature in comparison to typical stirring procedure [28]. In turn, Glover et al. presented that the mixing speed of the rubber-asphalt binder can affect the degree of rubber digestion in bituminous phase, which may improve the stability of rubber-asphalt binder [29]. The paper presents results of research on the influence of GTR grinding method on morphology of granulates as well as properties of rubber-asphalt binders. The discussion concerns two types of GTR (asphalt binders modifiers): one obtained using a standard knives granulator (SGP) and the other with a flat die pelleting press (FDGP). Moreover, it was demonstrated that the type of mixing device (high shear mixer or anchor stirrer) and the amount of GTR used in the modification affect the properties of rubberasphalt binder.
Table 1 Properties of asphalt binder. Penetration at 25 °C, 1/10 mm Softening point, °C Fraas breaking point, °C, max Flash-point, °C, min Solubility, % m/m, min After aging RTFOT Mass change, % m/m, ma Other penetration at 25 °C,%, min Growth of a softening point after aging, °C, max
0.8 46 9
Table 2 Properties of ground tyre rubber (GTR). Properties
Modifier I
Modifier II
Purity or rubber content [wt%] Fiber content [wt%] Water content [wt%] Steel content [wt%] Mineral particles content [wt%]
98.57 0.30 0.45 0.15 0.53
98.85 0.32 0.54 0.03 0.26
Grain size analysis [mm] Grain size [mm]
Amount of fraction [wt%]
<0.20 0.20 0.30 0.50 0.63 0.71 >0.80
20.28 17.01 33.05 18.44 6.85 4.14 0.24
6.25 12.48 43.27 25.63 9.04 3.22 0.12
metal particles both granulates exceed the maximum level of 0.01 wt%. The same situation applies to the content of mineral impurities which in both modifiers exceeds maximum level 0.25% by weight. However, the amount of mineral and metal impurities is low enough, that there is no significant impact on the final properties of the modified asphalt binder. But, it may, according to industrial data, have a significant impact on the wear of moving parts of mixing equipment and pumps in industrial plants. The modifier I was obtained in a standard granulation process (SGP) by using typical knives granulator (mill). This granulator is normally used for grinding elastic and thermoplastics waste polymer materials. The main advantages of using SGP are high energy efficiency, low vibration and noise level. In this process whole tyres (car/truck – 50/50) are first shredded to get chips (particles size 10–50 mm), then cut through the knives until the assumed particles size of rubber are obtained (Fig. 1). In turn, the modifier II was obtained in flat-die granulation process (FDGP) via innovative KAHL flat die pelleting press. Flat die mill is normally
2. Experimental 2.1. Materials Asphalt binder 70/100 used in our studies was delivered by Lotos Asfalt Sp. z o. o. in Gdansk (Poland). Asphalt properties are presented in Table 1. Two types of grinded GTR (modifiers) in ambient condition were added to asphalt. Their sieve analysis is shown in Table 2. According to Standard Specification for AsphaltRubber Binder (ASTM D 6114-97) both rubber granulates used in the work contain less than 0.5 wt% of fibers and 0,75 wt% of water. In the case of amount of ferrous
70–100 43–51 10 230 99
Fig. 1. Scheme of knives granulator (SGP).
146
M. Sienkiewicz et al. / Construction and Building Materials 154 (2017) 144–154
used for grinding and compaction of many products (food and petfood, biomass, mineral materials, medicine, chemical compounds) but special construction of this machine, created by Amandus KAHL GmbH, with auxiliary equipment also allows the grinding of polymer waste, especially used tyres with separation of rubber, textile fibers and steel. In FDGP the whole car and truck tyres (50/50) are first shredded to obtain chips and then the pan grinder rollers in flat die pelleting press squeezed them through openings in a perforated flat die of the granulator (Fig. 2). In other words, no cutting process of wastes by knives was as used. 2.2. Preparation of rubber-asphalt binder First, pure asphalt was heated to a temperature of 180 °C in a metal container with a volume of approx. 1.2 dm3. Then the appropriate quantity of modifier I or II (5–15 wt%) was added, maintaining constant temperature using two different procedures of mixing. In the first procedure GTR with asphalt binder was blended via high shear mixer (laboratory homogenizer IKA T50 basic ULTRA-Turrax with rotor equipped mixing S 50 N – 45 G M), while in the second one mixing of GTR with asphalt binder via anchor stirrer powered by IKA RW 16 basic was realized. Homogenization of rubber/asphalt binder mixture was carried out for 1 h at 180 °C. After homogenization of asphalt/modifier mixture, three-hour ‘‘maturation” of the system took place at 180 °C in the oven. Table 3 shows the characterization of the rubber-asphalt binders obtained by two types of mixing procedures (from 70/100 asphalt) using two types of GTRs (modifies I and II). Samples A were obtained by addition of modifier I to asphalt binder (A1 – high shear mixer, A2 – anchor stirrer). In turn, samples B were obtained with the use of modifier II to asphalt binder (B1 – high shear mixer, B2 – anchor stirrer). 2.3. Gel-sol fraction, morphology and specific surface area of GTR The samples of GTR (modifier I and modifier II) and rubber-asphalt binders (A1 and B1 after homogenization containing 15 wt% of modifiers) were extracted with dichloromethane for 12 h at 45 °C in Soxlet. The gel fraction was calculated according to Eq. (1):
Gel fractionð%Þ ¼ W1 =W0 100%
ð1Þ
where W0 is the original weight of the GTR before extraction, and W1 is the weight of dried GTR after extraction. To determine W0 of GTR in rubber-asphalt binder, the weight of binder was multiplied by 0,15 (rubber-asphalt binder containing 15 wt% of GTR). To estimate specific surface area of GTR, the following samples were extracted and their morphology was analyzed: pure GTR, A1, B1 (samples were analyzed after homogenization and after storage stability test). Morphology of extracted rubber particles was estimated via scanning electron microscopy (SEM). Extracted samples were covered with gold in a QUORUM Q150T Sputter coater and viewed under SEM (Zeiss EVO-40). Additionally the specific surface area of GTR was determined via Bru nauer–Emmett–Teller (BET) method at a liquid nitrogen temperature (77 K) with the use of surface area analyzers (Micromeritics Gemini V series 2365).
2.4. Conventional properties and storage stability of rubber-asphalt binders After homogenization and 3 h of maturation the viscosity, softening point and penetration measurements were made for all types of rubber-asphalt binders. Viscosity test was performed at 180 °C with the use of a Haake Viscotester 2 Plus from TermoElectron. Softening point and penetration were measured according to EN 1427 and 1426 standards, respectively. The high-temperature storage stability was evaluated in the proper tubes (25.4 mm in diameter, 140 mm in height) filled with rubber-asphalt binders and vertically placed in an oven at 180 °C for 72 h. After that, samples of the rubber-asphalt binders were removed from the tubes and divided into three equal parts. Upper and lower parts of the samples were taken to measure penetration and softening point (the middle part of samples were rejected). According to the requirements of EN 13399:2010 standard, asphalt binder is considered as stable when the difference between the values of the parameters tested for the upper and lower portion of the sample is not more than 9–26 units (dependently on category of modified asphalt binder) in the case of penetration tests and no more than 5 units in the case of the test for softening point. The scheme of storage stability measurements are presented in Fig. 3.
2.5. Thin-layer chromatography with flame ionization detection TLC/FID Solutions of rubber-asphalt binder (10 mg of sample per 1 ml of solvent) used to TLC/FID analysis were prepared in dichloromethane, then GTR was separated from solution by filtration. After that 1 ll of solution was spotted on chromarods using a microsyringe. The separation of asphalt binder into five generic fractions (i. saturated hydrocarbons, ii. low polar, highly placed and naphthenic aliphatic, mononuclear aromatic hydrocarbons, iii. aromatic and polyaromatic, iv. resins, v. asphaltenes) was performed by a three-stage development using n-heptane, toluene and dichloromethane/methanol (95/5) by volume, respectively. Detection proceeded by transition of chromarods for 35 s through hydrogen flame detector FID with simultaneous digital recording electrometer signal. TLC/FID analysis was carried out for rubberasphalt binders containing the modifier I and modifier II (samples were analyzed after homogenization and after storage stability test) and unmodified asphalt binder.
2.6. Gel permeation chromatography (GPC) GPC was used to determine the molecular weight distribution of the asphalt binders modified by GTR. Polystyrene standards were used to calibrate the chromatography column. A sample of the asphalt binder in an amount of 50 mg was dissolved in 10 ml of tetrahydrofuran (THF). For the separation of components, two columns were used: LiChrogel PS MIX (50 lm, 250 7 mm, Merck, Germany) and Phenogel 5u Lineal (300 7.8 mm, Phenomenex, USA). Solution in amount of 50 ll was added at a flow rate of 0.7 ml/min. A spectrophotometric detector used with a diode array UV-DAD type 7450, refractive detector L-7490. GPC analysis was carried out for rubber-asphalt binders containing the modifier I and modifier II (samples were analyzed after homogenization and after storage stability test) and unmodified asphalt binder.
3. Results and discussion 3.1. Gel-sol fraction of GTR
Fig. 2. Scheme of flat-die pelleting press (FDGP) [30] with permission from Amandus Kahl GmbH & Co. KG.
Gel fractions of two types of modifiers (I and II) before and after addition to asphalt binder are shown in Table 4. According to the data given in Table 4 it can be concluded that gel fractions of modifier I and II (before adding to asphalt binder) are very similar and the differences should not influence the properties of rubber-asphalt binder. However, the differences in the content of gel fractions between modifier I and II are clearly increasing after the modification process of rubber-asphalt binder carried out with a homogenizer. The collected data show (Table 4) that rubber grains of modifier I have a greater degree of digestion in asphalt binder at 180 °C than modifier II. Based on the data described in the publications [31,32] this may be due to the fact that there are significantly more fine rubber grains (with size below 0.2 mm) in modifier I than in modifier II (Table 2), then swelling and digestion (depolymerization) of modifier I in asphalt binder are easier in comparison to larger grains, with size above 0.2 mm.
M. Sienkiewicz et al. / Construction and Building Materials 154 (2017) 144–154
147
Table 3 Composition of rubber-asphalt binders. Type of binder
Type of GTR (modifier)
Amount of GTR [wt%]
Amount of asphalt 70/100 [wt%]
Mixing device
A1
I
I
B1
II
B2
II
95 90 85 95 90 85 95 90 85 95 90 85
Homogenizer
A2
5 10 15 5 10 15 5 10 15 5 10 15
Anchor stirrer
Homogenizer
Anchor stirrer
Fig. 3. Scheme of high-temperature storage stability measurements.
Table 4 Gel fraction of GTR (modifier I and II) before and after modification process of the asphalt binder. Type of modifier
Gel fracions before modification [wt%]
Gel fracions after modification [wt%]
Modifier I Modifier II
89.2 84.6
47.2 75.6
Table 5 Specific surface area of modifier I and II used to asphalt binder modification measured via BET test. Rubber grains size
Specific surface area (BET test) [cm2/g] Modifier I
Modifier II
0–0.2 0.2–0.3 mm 0.7–0.8 mm 0–0.8 mm
2.28 1.16 0.54 4.12
2.20 3.44 0.69 2.57
3.2. Specific surface area and morphology of GTR The specific surface area of GTR measured by BET test is given in Table 5. From the results presented in Table 5 it can be concluded that both modifiers have similar specific surface area in the case of fine fraction of GTR (0–0.2 mm). Although, according to sieve analysis results given in Table 2, the amount of fraction 0–0.2 mm in modifier I (20.28 wt%) is much higher that in modifier II (6.25 wt%). Next to fine fraction of GTR there are present fractions of the order
of 0.2–0.8. Their specific surface area is different in modifier I and modifier II. Modifier II has higher specific surface area of fractions 0.2–0.3 mm and 0.7–0.8 mm. Taking altogether into account, the global specific surface area for fractions 0–0.8 mm of modifier I is higher than modifier II. This is due to the presence of much higher amount of fractions below 0.2 mm in modifier I (Table 2), which determine then the average global specific surface area. Figs. 4–7 present SEM micrographs of the modifier I (SGP) and the modifier II (FDGP) before and after homogenization with asphalt binders. As it can be seen in Fig. 4a and b, there are visible many small (0–0.2 mm) and some large (>0.5 mm) rough particles of the modifier I. The surface roughness of these particles may be explained by the multiple cutting of tyre pieces in the mill by knives of the granulator. Then, temperature of tyre pieces become higher and the rougher surface of GTR is obtained. In the modifier I there were also present a few large smooth particles of GTR having regular shape but their amount was small (Tables 2 and 4) and they did not have significant influence on the average global specific surface area of the modifier I. In the case of modifier II (Fig. 4c and d), rough (spongy) particles were mostly observed. This effect was achieved by using a granulator with a flat die and thickening rollers. As a result, the rubber material was squeezed through openings of a perforated plate granulator, which allow to obtain particles with rough surface. Summarizing, according to SEM micrographs, grain size analysis and BET results (Fig. 4, Table 2 and 5) it can be concluded that the modifier I was characterized by higher average global specific surface area than the modifier II due to the presence of much higher amount (20.28 wt%) of small rough particles (<0.2 mm).
148
M. Sienkiewicz et al. / Construction and Building Materials 154 (2017) 144–154
Fig. 4. Morphology of GTR grains obtained via SGP (a,b – modifier I) and FDGP (c,d – modifier II).
Fig. 5. Morphology of GTR after extraction with dichloromethane (a – modifier I; b – modifier II).
The morphology comparison of GTR before and after extraction with dichloromethane (Figs. 4 and 5) showed, that particles of rubber stucked together in both cases. It may be caused by migration of many components (e.g. not devulcanized polymer chains, oils and plasticizer) outside of the GTR. Taking into account all of the issues discussed above, homogenization of rubber-asphalt binder with GTR for 1 h at 180 °C changed the morphology of GTR (Fig. 6). Particles of GTR swelled due to the absorption of aromatic hydrocarbons present in asphalt binder, what is consistent with work of Airey et al. [11]. Further heating of rubber-asphalt binders after homogenization (storage stability test) caused deformation of GTR structure (it is clearly visible if one compares the images of GTR in Figs. 4, 6 and 7). The particles of GTR became thin and flat. It may be due to the devulcanization process, which occurs during heating of
rubber-asphalt binder at 180 °C for 72 h. Anyway, there was not distinct differences between GTR extracted from top and bottom of the tube. 3.3. Viscosity Table 6 presents the results of viscosity measurements of rubber-asphalt binders (containing 5, 10 and 15 wt% of GTR) modified by two types of GTR and using two homogenization methods. The value of viscosity is an important parameter for transportation process of asphalt binder. Too high viscosity is disadvantageous when transporting asphalt binder through pipelines. Consequently, over-viscous binders are unsuitable for use. As can be seen from the results presented in Table 6, asphalt binders modified by both types of GTR, have higher viscosity than
M. Sienkiewicz et al. / Construction and Building Materials 154 (2017) 144–154
149
Fig. 6. Morphology of GTR extracted with dichloromethane from rubber-asphalt binder after blended with homogenizer (a - modifier I; b – modifier II).
Fig. 7. Morphology of GTR extracted with dichloromethane from rubber-asphalt binder mixed with homogenizer, after high-temperature storage stability test (a – modifier I extracted from top part of tube; b – modifier II extracted from top part of tube; c – modifier I extracted from bottom part of tube; d – modifier II extracted from bottom part of tube).
the unmodified asphalt binders, what is consistent with the literature data [4,33]. The viscosity of the rubber-asphalt binder increased with increasing GTR content, especially when 15 wt% of it was added. It is worth to note that viscosity of samples obtained by using GTR grinded via FDGP (modifier II) was lower than viscosity of samples obtained by using GTR grinded via SGP (modifier I). The higher viscosity of asphalt binder modified by modifier I, as compared to asphalt modified with modifier II, can be explained by its higher average global surface area, as evidenced by BET studies (Table 5) and sieve analysis (Table 2). This is consistent with the data presented in the literature [25,31,34], indicating that the finer grains of GTR with a high surface area more effectively swell in
asphalt as compared to larger grains, what causes greater increase of the rubber-asphalt binder viscosity. Maturation of rubber-asphalt binders for 3 h resulted in an increase in viscosity in the case of sample A1 containing 10 wt% of the modifier I. On the other hand, viscosity decreased after 3 h of A2 and B1 samples maturation, which contained 15% by weight of the modifier. In other cases, the viscosity of rubber-asphalt binders did not change significantly after maturation. The type of mixing device had no significant effect on the viscosity of the rubberasphalt binder for samples A1, and a slight decrease in the viscosity of rubber-asphalt binder modified by a homogenizer can be explained by the process of devulcanization and digestion of the fine rubber grains, which are prominent in modifier I.
150
M. Sienkiewicz et al. / Construction and Building Materials 154 (2017) 144–154
Table 6 Viscosity of rubber-asphalt binders. Type of binder
Amount of modifier [wt %]
Asphalt A1
0 5 10 15 5 10 15 5 10 15 5 10 15
A2
B1
B2
Viscosity at 180 °C [Pas] After homogenization
After maturation
0.007 0.090 0.210 1.800 0.080 0.210 2.100 0.090 0.190 0.900 0.040 0.130 0.560
0.007 0.080 0.230 1.600 0.080 0.330 2.000 0.090 0.210 0.870 0.060 0.180 0.480
ing point value depending on the type of GTR (modifier I and II) used as asphalt modifiers. However, few samples modified by GTR obtained with SGP achieved softening point above 60 °C. Furthermore, modification method (homogenizer or stirrer) did not change significantly the softening point of rubberasphalt binders. Rubber-asphalt binders containing 5% by weight of the modifiers I or II mixed with a stirrer were characterized by lower softening point after maturation in comparison to samples after homogenization. In other cases it was noticed an increase in the softening point after maturation process. However, this growth was not higher than 3 °C, except sample containing 15 wt% of the modifier I mixed with homogenizer, when the difference between homogenization and maturation was around 6 °C. The increase in the softening point after maturation indicated that the rubberasphalt binders were cured, which improved their temperature under operating conditions. 3.5. Penetration
This conclusion is reflected in the results of the content of dissolved fractions in modifier I (Table 4), which amount increases after the interaction of rubber grains with asphalt binder. However, in case of rubber-asphalt binder prepared with 5–15% by weight of modifier II, the influence of modification conditions on its viscosity is evident and is higher when the modification process is carried out using a homogenizer. It may be explained by high mixing speed of homogenizer (high shear rate) causing turbulent mixing of the rubber in the bitumen binder, which reduces the size of the coarse rubber grains. This process can enhance the interaction of smaller rubber grains with asphalt binder, increasing their swelling capability and thereby reducing the viscosity of rubber-asphalt binder [34–38].
Fig. 8 presents results of softening point measurements of rubber-asphalt binders modified by two kinds of GTR (having 5, 10 and 15t% of GTR) using two different homogenization methods. It can be concluded that with an increasing amount of the modifier content the softening point became higher. It should be noted that the increase in the softening temperature was relatively proportional to the increase of GTR content. As can be seen in Fig. 8, there were rather slight differences in soften-
Fig. 9 presents values of penetration of rubber-asphalt binders modified by two kinds of GTR (having 5, 10 and 15 wt% of GTR) using two different homogenization method. As can be seen in Fig. 9, as opposed to the softening point measurement, the more modifier was added the lower penetration value was achieved. However, the penetration value of samples after maturation for 3 h did not change more than 4 units. Generally, rubber-asphalt binders obtained with the homogenizer had a lower value of penetration compared to those binders obtained using a stirrer. This is due to the better dispersion of the rubber granules with the homogenizer than the stirrer and is consistent with Yadollahi et al. observations [27]. Exceptions were samples containing 5–10 wt% of modifier I, in which the modification method did not affect the penetration value. Adding modifier I to the asphalt binders improved the penetration value compared to the modifier II. This was particularly evident in samples containing 5–10% by weight of GTR. In addition, several samples containing modifier I had a penetration value of less than 45 [0.1 mm], which was not observed in the rubber-asphalt binders containing the modifier II. This may be due to the different chemical composition of modifiers I and II. It may also indicate that GRT grains obtained with standard granulator had higher specific surface area what was described in Section 3.2.
Fig. 8. Softening point of rubber-asphalt binder modified by GTR shredded via flat die or standard granulation process, obtained by mixing with homogenizer or stirrer.
Fig. 9. Penetration of rubber-asphalt binders modified by GTR shredded via flat die granulation process or standard granulation process (modification with the use of homogenizer or stirrer).
3.4. Softening point
151
M. Sienkiewicz et al. / Construction and Building Materials 154 (2017) 144–154 Table 7 Stability of rubber-asphalt binders modified by GTR. Type of binder
Amount of modifier [wt%]
A1
5 10 15 5 10 15 5 10 15 5 10 15
A2
B1
B2
Fig. 10. Differences in penetration of rubber-asphalt binders after high-temperature storage stability test.
Penetration [0.1 mm]
Softening point [°C]
Top
Bottom
Top
Bottom
64.7 64.0 60.0 64.0 60.0 57.0 64.7 62.0 57.0 50.0 49.0 59.0
84.7 89.7 80.3 83.0 68.0 68.0 75.0 73.7 70.0 59.0 58.0 74.0
48.3 48.6 50.4 54.3 48.3 57.9 48.5 50.1 53.5 55.8 58.4 56.7
48.9 58.9 63.5 52.1 57.0 59.4 51.2 57.9 63.1 51.7 50.3 59.5
modifier, rubber-asphalt binders containing the modifier II (except samples containing 10–15 wt% prepared with the stirrer) were characterized by lower differences in penetration value after high-temperature storage stability test. It is also worth to mention that penetration of the lower parts of the samples increases with the respect to the upper part of samples and samples after homogenization (Table 7). This is caused by settlement of GTR particles, which are thermally devulcanized due to the storage at 180 °C for 72 h and then they play the role of a plasticizer of rubberized bitumen [6]. According to Fig. 11 and EN 13399:2010 standard, rubberasphalt binders containing 5 wt% of modifiers (I or II) are stable with respect to the softening point. However, it was reported that stability mainly depends on rheological properties of rubberasphalt binder and the difference in the softening point should not be considered as the unequivocal and decisive criterion [6,33,39–40]. Moreover, it was found that increase in the viscosity of the binder improves the storage stability due to the inhibition of rubber particle settling. It is in accordance with the results presented in the paper for rubber-asphalt binders mixed with stirrer having 15 wt% of GTR (independently on the type of used modifier). When using the homogenizer high shear rate is changing the particle shape of rubber grains, what increases their sedimentation velocities, thus the viscosity is then of less decisive factor. In the case of GTR type (Table 7, Fig. 11), rubber-asphalt binders containing 10–15 wt% of the modifier II were characterized by lower differences in the softening point in comparison to samples containing the modifier I.
3.7. Thin-layer chromatography with flame ionization detection TLC/ FID
Fig. 11. Differences in softening point of rubber-asphalt binders after hightemperature storage stability test.
3.6. Stability Table 7 and Figs. 10 and 11 show the results of stability tests of rubber-asphalt binders aged for 72 h at asphalt processing temperatures (180 °C). Based on results presented in Table 7 and Fig. 10, it can be concluded that rubber-asphalt binders mixed with the use of the stirrer (except sample containing 15 wt% of modifier II) had lower differences in the penetration value compared to samples obtained with the homogenizer. In addition, the rubber-asphalt binder blended with the stirrer, containing 10 wt% of the GTR had the best stability considering penetration. According to the type of used
Figs. 12 and 13 present results of TLC/FID measurements for asphalt binders modified by two kinds of GTR (15 wt%) mixed with homogenizer. Samples were analyzed after homogenization and after high-temperature storage stability test. Those analysis showed the presence of the following five fractions: i) saturated hydrocarbons ii) low polar, highly placed and naphthenic aliphatic, mononuclear aromatic hydrocarbons iii) aromatics and polyaromatics iv) resins v) asphaltenes Thin-layer chromatography with flame ionization detection TLC/FID indicated that addition of GTR (both modifiers) to asphalt binder affects on the percentage of fractions, except of percentage of asphaltenes, which were similar in all cases. Modification of the
152
M. Sienkiewicz et al. / Construction and Building Materials 154 (2017) 144–154
Fig. 12. The influence of addition modifier I on asphalt binder groups in the final product.
Fig. 13. The influence of addition modifier II on asphalt binder groups in the final product.
asphalt binder by modifier I resulted in a percentage increase of the following fractions: ii) low polar, highly placed and naphthenic aliphatic, mononuclear aromatic hydrocarbons, iii) aromatics and iv) resins and percentage decreasement of i) saturated hydrocarbons. In turn, modification of asphalt binder by the modifier II resulted in increase of fraction‘‘iv” and decrease of fraction ‘‘i and iii‘‘. The differences in percentages of individual fractions observed between unmodified and modified asphalt binders can be explained by the migration of asphalt molecules from fraction to fraction, induced by GTR addition. However, percentage differences between asphalt binders A1 and B1 might be explained by various absorption of asphalt binder fractions by GTR due to its specific surface area or type of tyres (content of natural and synthetic rubber) used to produce GTR. 3.8. Gel permeation chromatography (GPC) Figs. 14 and 15 present results of GPC analysis for asphalt binders modified by 15 wt% of GTR with homogenizer.
Number average molar mass (Mn) did not change significantly after homogenization of asphalt binder by GTR and after hightemperature storage stability test. Type of the modifier also did not affect Mn. In turn, weight average molar mass (Mw) increased when GTR was added to asphalt binder. In the case of asphalt binders modified by GTR, the lowest values of Mw had samples after homogenization and the highest values were obtained for samples taken from bottom part of the tube after high-temperature storage stability test. Additionally, Mw of rubber-asphalt binders containing the modifier I was higher than those containing the modifier II. It is worth to note that the modification of asphalt binder by GTR affected percentage increasement of fractions having molecular weight bigger than 1000. The highest results in molecular weight were obtained for rubber-asphalt binder B2 (bottom). However, differences in molecular weight between asphalt binders A1 and B1 might be explained by different absorption degree of asphalt binder light fractions by the modifier I and II due to various chemical composition of modifiers or their specific surface area.
M. Sienkiewicz et al. / Construction and Building Materials 154 (2017) 144–154
153
Fig. 14. Change in molar mass of asphalt binders modified by GTR.
Fig. 15. Change in molecular weight distribution of asphalt binders modified by GTR.
4. Conclusions The properties of asphalt binders modified by ground tyre rubber (GTR) in the amount of 5–15 wt% were analyzed. GTR was obtained by two different grinding method: standard granulation process (SGP, modifier I) and flat-die granulation process (FDGP, modifier II). It was shown that GTR grinding method had the influence on the morphology characteristic and specific surface area of rubber grains, thus properties of rubber-asphalt binder. The properties of rubber-asphalt binders depended on the amount of the modifier and the type of mixing devices (homogenizer or stirrer) used to carry out the modification process. The following conclusions can be drawn from the research: 1. Microscopic analysis showed that grains of modifier II had ‘‘spongy” form due to obtaining this GTR by flat die pelleting press (FDGP). In turn the GTR grinded by knives granulator (modifier I) had grains with the complex morphology: some
large grains of this GTR had smooth surface and small grains (<0.2 mm) had a very rough surface. Therefore the BET analysis proved that the GTR grains obtained by FDGP with size between 0.2 and 0.3 mm and 0.7 and 0.8 have higher specific surface area. However GTR obtained by SGP (modifier I) was characterized by higher average global specific surface area. This is due to presence of high amount (20.28 wt%) of smaller rough particles (0–0.2 mm) in GTR in comparison to GTR obtained by FDGP (modifier II). 2. From the economic and material properties point of view, the optimum amount of GTR added to asphalt binder should be 15 wt%. 3. The modifier I added to asphalt binder improved its softening point and penetration value. In turn, addition of the modifier II to asphalt binder contributed to lower viscosity after homogenization. Moreover, it was observed the improvement of hightemperature storage stability in the case of penetration for all samples having the modifier II. In the case of softening point,
154
M. Sienkiewicz et al. / Construction and Building Materials 154 (2017) 144–154
stability was improved for the samples containing 10–15 wt% of modifier (rubber-asphalt binders prepared with the homogenizer contained). Thus, in the case of penetration and softening point of rubber-asphalt binder, GTR obtained by SGP is more favorable modifier. Although in the case of rubber-asphalt binder viscosity and stability, more favorable is GTR obtained via FDGP. 4. Modification of rubber-asphalt binder by the stirrer improved high-temperature storage stability of samples in comparison to rubber-asphalt binder modified by homogenizer. However, modification with the use of the homogenizer improved penetration value after homogenization of samples containing GTR in the amount of 10–15 wt% due to better dispersion of modifier in the asphalt binder. 5. Percentage of fraction and its molecular weight distribution in asphalt binders changed when GTR was added and depended on chemical components and the specific surface area of GTR.
References [1] J. Karger-Kocsis, L. Meszaros, T. Barany, Ground tyre rubber (GTR) in thermoplastics, thermosets and rubbers, J. Mater. Sci. 48 (2013) 1–38. [2] M. Sienkiewicz, J. Kucin´ska-Lipka, H. Janik, A. Balas, Progress in used tyres management in the European Union: a review, Waste Manage. 32 (2012) 1742–1751. [3] G. Ivan, Some aspects of tyre impact on environment: production, service and recycling, Elastomery 4–5 (6) (2002) 24–38. [4] F. Xiao, S.N. Amirkhanian, Laboratory investigation of utilizing high percentage of RAP in rubberized asphalt mixture, Mater. Struct. 43 (2010) 223–233. [5] W. Cao, Study on properties of recycled tire rubber modified asphalt mixtures using dry process, Constr. Build. Mater. 21 (2007) 1011–1015. [6] F.J. Navarro, P. Partal, F. Martínez-Boza, C. Gallegos, Thermo-rheological behaviour and storage stability of ground tire rubber-modified bitumens, Fuel 83 (2004) 2041–2049. [7] Y. Huang, R.N. Bird, O. Heidrich, A review of the use of recycled solid waste materials in asphalt pavements, Resour. Conserv. Recycl. 52 (2007) 58–73. [8] I. Gaweł, M. Kalabin´ska, J. Piłat, Asfalty Drogowe (Bitumen used for Pavements) , WKŁ, Warszawa, 2001. [9] P. Radziszewski, M. Kalabin´ska, J. Piłat, Wykorzystanie miału gumowego ze _ zuzytych opon samochodowych w modyfikacji asfaltów drogowych (The use of rubber granulate from scrap tires for asphalt modification), Elastomery 4 (2001) 8–16. [10] F.J. Navarro, P. Partal, F. Martínez-Boza, C. Gallegos, Novel recycled polyethylene/ground tire rubber/bitumen blends for use in roofing applications: thermo-mechanical properties, Polym. Test. 29 (2010) 588–595. [11] G. Airey, M. Rahman, A. Collop, The influence of crude source and penetration grade on the interaction of crumb rubber and bitumen, in: International Asphalt and Rubber Conference, Brasilia, Brazil, 2003. [12] G. Ying, C. Rongji, Interation theory of asphalt and rubber, J. Wuhan Univ. Technol. Mater. 25 (2010) 853–855. [13] I. Gaweł, R. Stepkowski, F. Czechowski, Molecular interactions between rubber and asphalt, Ind. Eng. Chem. Res. 45 (2006) 3044–3049. [14] P. Radziszewski, J. Piłat, M. Sarnowski, K. Kowalski, J. Król, I. Ruttmar, S. Witczak, P. Heinrich, D. Skowron´ski, Z. Krupa, M. Nawracaj, K. Gil, _ Opracowanie i wdrozenie innowacyjnej, przyjaznej s´rodowisku technologii modyfikacji asfaltów drogowych guma˛ (Development and implementation of innovative, environmentally friendly technologies to modify road bitumen by rubber), Nawierzchnie Asf. 3 (2011) 10–15. [15] S.J. Lee, C.K. Akisetty, S.N. Amirkhanian, The effect of crumb rubber modifier (CRM) on the performance properties of rubberized binders in HMA pavements, Constr. Build. Mater. 22 (2008) 1368–1376. [16] S. Liu, W. Cao, J. Fang, S. Shang, Variance analysis and performance evaluation of different crumb rubber modified (CRM) asphalt, Constr. Build. Mater. 23 (2009) 2701–2708.
[17] H. Shi, M. Zou, K. Liao, Research progress of ground tire rubber modified pavement asphalts, J. Chem. Ind. Eng. 26 (2005) 27–30. [18] Y. Yildirim, Polymer modified asphalt binders, Constr. Build. Mater. 21 (2007) 66–72. [19] M. Liang, X. Xin, W. Fan, H. Sun, Y. Yao, B. Xing, Viscous properties, storage stability and their relationships with microstructure of tire scrap rubber modified asphalt, Constr. Build. Mater. 74 (2015) 124–131. [20] S. Kocevski, S. Yagneswaran, F. Xiao, V.S. Punith Jr., D.W. Smith, S.N. Amirkhanian, Surface modified ground rubber tire by grafting acrylic acid for paving applications, Constr. Build. Mater. 34 (2012) 83–90. [21] X. Li, J. Cheng, G. Que, Microstructure and performance of crumb rubber modified asphalt, Constr. Build. Mater. 23 (2009) 3586–3590. [22] S.J. Lee, S.N. Amirkhanian, K. Shatanawi, K.W. Kim, Short-term aging characterization of asphalt binders using gel permeation chromatography and selected superpave binder tests, Constr. Build. Mater. 22 (2008) 2220– 2227. [23] J. Shen, S. Amirkhanian, F. Xiao, B. Tang, Influence of surface area and size of crumb rubber on high temperature properties of crumb rubber modified binders, Constr. Build. Mater. 23 (2009) 304–310. [24] L.P. Thives, J.C. Pais, P.A.A. Pereira, G. Trichês, S.R. Amorim, Assessment of the digestion time of asphalt rubber binder based on microscopy analysis, Constr. Build. Mater. 47 (2013) 431–440. [25] C. Thodesen, K. Shatanawi, S. Amirkhanian, Effect of crumb rubber characteristics on crumb rubber modified (CRM) binder viscosity, Constr. Build. Mater. 23 (2009) 295–303. [26] L. Zanzotto, G. Kennepohl, Development of rubber and asphalt binders by depolymerization and devulcanization of scrap tires in asphalt, Transp. Res. Rec. 1530 (1996) 51–58. [27] G. Yadollahi, H.S. Mollahosseini, Improving the performance of crumb rubber bitumen by means of Poly Phosphoric Acid (PPA) and vestenamer additives, Constr. Build. Mater. 25 (2011) 3108–3116. [28] H. Yao, S. Zhou, S. Wang, Structural evolution of recycled tire rubber in asphalt, J. Appl. Polym. Sci. 133 (2016) 1–7. [29] C. Glover, R.R. Davison, J. Bullin, C.K. Estakhri, S.A. Williamson, T.C. Billiter, J. F. Chipps, J.S. Chun, P. Juristyarini, S.E. Leicht, P. Wattanachai, A comprehensive laboratory and field study of high-cure crumb-rubber modified asphalt materials, Report 1460-1, Texas Transportation Institute, USA, 2000. [30] Amandus Kahl GmbH & Co. KG, Recycling Plants for Waste Tyres. https://www. akahl.de/en/service/downloads/, (accessed 27.06.17). [31] D. Lo Presti, Recycled tyre rubber modified bitumens for road asphalt mixtures: a literature review, Constr. Build. Mater. 49 (2013) 863–881. [32] M. Heitzman, Design and construction of asphalt paving materials with crumb rubber modifier, Transp. Res. Rec. 1339 (1992) 1–8. [33] F.J. Navarro, P. Partal, F. Martínez-Boza, C. Gallegos, Influence of crumb rubber concentration on the rheological behavior of a crumb rubber modified bitumen, Energy Fuel 19 (2005) 1984–1990. [34] T. McNally, Polymer Modified Bitumen, Woodhead Publishing Ltd, 2011. [35] F. Xiao, B.J. Putman, S.N. Amirkhanian, Laboratory investigation of dimensional changes of crumb rubber reacting with asphalt binder, Road Mater. Pavement Des. 10 (2006) 1–21. Relationship between Crumb Rubber Morphology and Asphalt Rubber Viscosity. [36] Relationship between Crumb Rubber Morphology and Asphalt Rubber Viscosity. https://www.researchgate.net/profile/Michele_Lanotte/publication/ 266208406_Relationship_between_Crumb_Rubber_Morphology_and_Asphalt_ Rubber_Viscosity/links/542a7dc40cf29bbc1267a120/Relationship-betweenCrumb-Rubber-Morphology-and-Asphalt-Rubber-Viscosity.pdf/, 2012 (accessed 27.06.17). [37] J. Shen, S.N. Amikrhanian, The influence of crumb rubber modifier (CRM) microstructures on the high temperature properties of CRM binders, Int. J. Pavement Eng. 6 (2005) 265–271. [38] D. Lo, G. Presti, Airey P. Partal, Manufacturing terminal and field bitumen-tyre rubber blends: the importance of processing conditions, Proc. Soc Behav. Sci 53 (2012) 485–494. [39] O. Gonzalez, M.E. Munoz, A. Santamaria, M. Garcia-Morales, F.J. Navarro, P. Partal, Rheology and stability of bitumen/EVA blends, Eur. Polym. J. 40 (2004) 2365–2372. [40] F.M. Nejad, P. Aghajani, A. Modarres, H. Firoozifar, Investigating the properties of crumb rubber modified bitumen using classic and SHRP testing methods, Contr. Build. Mater. 26 (2012) 481–489.
Contents lists available at ScienceDirect
Construction and Building Materials journal homepage: www.elsevier.com/locate/conbuildmat
The effect of tyre rubber grinding method on the rubber-asphalt binder properties M. Sienkiewicz a,⇑, K. Borze˛dowska-Labuda a, S. Zalewski b, H. Janik a a b
Polymer Technology Department, Chemical Faculty, Gdansk University of Technology, Gabriela Narutowicza Street 11/12, 80-233 Gdansk, Poland Department of Chemical and Process Engineering, Chemical Faculty, Gdansk University of Technology, Gabriela Narutowicza Street 11/12, 80-233 Gdansk, Poland
h i g h l i g h t s Specific surface area of GTR depends on its grinding method. Morphology of GTR grains influences the properties of rubber-asphalt binder. Storage stability of rubber-asphalt binder also depends on its modification method. Addition of GTR to asphalt binder changes percentage of asphalt fractions. Added GTR effects molecular weight distribution of rubberized asphalt binder.
a r t i c l e
i n f o
Article history: Received 31 August 2016 Received in revised form 3 July 2017 Accepted 23 July 2017
Keywords: Morphology Ground tyre rubber (GTR) Modification of asphalt Rubber-asphalt binder Knife granulation process Flat-die granulation process
a b s t r a c t Rubber products, especially those used in the automotive industry, are responsible for a significant amount of waste, mainly in the form of worn tyres. One way to recycle tyres is to use them as an asphalt binder modifier. The properties of rubber-asphalt binders vary greatly depending on the morphology of the ground tyre rubber (GTR) grains and the type of tyre to be recycled (car/truck). The paper presents the results of research in the field of rubber-asphalt binders modified with two types of GTR (which differ in grain morphology) used in various amount and processed at different mixing devices. One GTR is obtained with the use of a standard knives granulator (standard granulation process – SGP), and the other by a special flat die pelleting press (flat-die granulation process – FDGP). It has been proved that GTR grinding method affects its specific surface area, thus the properties of rubber-asphalt binders. Ó 2017 Elsevier Ltd. All rights reserved.
1. Introduction Worldwide, the amount of used rubber products is increasing year by year, most of which is produced by car tyres. Rubber products consist of long polymer chains, mostly crosslinked with sulfur bridges. Therefore, the difficulties associated with the recovery and recycling of used tyres are due to the very complex structure and composition of tyre materials. However, the progress made in recent years in waste management of polymers caused that postconsumer tyres came to be seen as a potential source of valuable raw materials. In this way, rubber wastes may be transformed into energy or new polymer products [1–3]. One of the methods of waste tyres recovery is using them as a modifier of asphalt. Rubber-asphalt binders obtained from the rubber wastes were described by many scientists [4–7]. The addition of recycled rubber ⇑ Corresponding author. E-mail address: [email protected] (M. Sienkiewicz). http://dx.doi.org/10.1016/j.conbuildmat.2017.07.170 0950-0618/Ó 2017 Elsevier Ltd. All rights reserved.
to asphalt improves tenacity, mechanical properties, fatigue life, flexibility, resistance to rutting, abrasion resistance, low temperature cracking, reduce noise during contact tyre with the ground [8–14]. Many studies have shown that properties of rubber-asphalt binders depend on many factors like: the content and particle size, type (car/truck) of ground tyre rubber (GTR), chemical and physical properties of asphalt matrix, as well as its source, and technology of asphalt modification [6,15–19]. Surface modification of ground tyre rubber is also known to affect the properties of rubberasphalt binders [20]. Scanning electron microscope (SEM) analysis showed that pure asphalt is characterized by a smooth surface. Addition of recycled rubber changes the surface homogeneity: the larger particle of recycled rubber the higher heterogenity. Airey and co-workers showed that the density of GTR is changing when it is added to asphalt binder. It was also proved that grains of rubber wastes swell when they are mixed with asphalt and then their mass
145
M. Sienkiewicz et al. / Construction and Building Materials 154 (2017) 144–154
increases up to 140% by weight. This is due to absorption of the aromatic hydrocarbons from asphalt binder by the rubber grains. Additionally, the interaction between the components of the rubber grains and asphalt depends on molecular weight of both components. The interaction is stronger when molecular weight of asphalt is lower. This is due to the possibility to spread the light fraction between the grains of the GTR. Absorption of light hydrocarbon fractions by GTR grains depends on asphalt content and the value of its penetration: the higher those parameters, the greater absorption. On the other hand, as it was noted before, rubber grains are easily swellen by asphalt, resulting in an increase in the viscosity of the rubber-asphalt binder, compared to the viscosity of the virgin asphalt [11,12]. Li and co-workers examined GTR modified asphalt prepared by preblending method. In this process GTR is firstly mixed with small amount of asphalt, then portion of fresh asphalt is added. SEM analysis indicated that interface of GTR without preblending was clear and scattered many slot holes, while interface of preblended GTR was indistinct and slot holes dissapeared. Furthermore, the scattering state of preblended GTR in rubber-asphalt binder is excellent and perfect polymer reticular structure is formed in the sample system. Thus the properties of asphalt with preblended GTR are improved significantly in comparison to asphalt with GTR without preblending [21]. An important role in the rubber-asphalt binder properties plays the specific surface area of the GTR [22,23]. Influence of GTR grinding method on the morphology of GTR surface and finally properties of rubber-asphalt binders were examinated by Thodesen et al. and Thives et al. [24,25]. Thodesen et al. showed that GTR grinded at ambient temperature is characterized by higher specific surface area (rougher surface) than GTR grinded at cryogenic temperature (smoother surface). In addition, viscosity of rubber-asphalt binder increases with increasing specific surface area. They also showed that viscosity increases when amount of GTR is increasing. Some work in turn refers to the impact of the type of mixing device on the properties of the rubber-asphalt product obtained. [26–28]. High shear mixing used for the modification of asphalt by GTR, transoctenamer rubber (Vestenamer) and polyphosphoric acid leads to more uniform texture of the composition in microscale in comparison to the process of mixing with conventional mixer [27]. Yao and co-workers showed that higher amount of carbon black and inorganic fillers are released from GTR to asphalt binder during high shear mixing at the high curing temperature in comparison to typical stirring procedure [28]. In turn, Glover et al. presented that the mixing speed of the rubber-asphalt binder can affect the degree of rubber digestion in bituminous phase, which may improve the stability of rubber-asphalt binder [29]. The paper presents results of research on the influence of GTR grinding method on morphology of granulates as well as properties of rubber-asphalt binders. The discussion concerns two types of GTR (asphalt binders modifiers): one obtained using a standard knives granulator (SGP) and the other with a flat die pelleting press (FDGP). Moreover, it was demonstrated that the type of mixing device (high shear mixer or anchor stirrer) and the amount of GTR used in the modification affect the properties of rubberasphalt binder.
Table 1 Properties of asphalt binder. Penetration at 25 °C, 1/10 mm Softening point, °C Fraas breaking point, °C, max Flash-point, °C, min Solubility, % m/m, min After aging RTFOT Mass change, % m/m, ma Other penetration at 25 °C,%, min Growth of a softening point after aging, °C, max
0.8 46 9
Table 2 Properties of ground tyre rubber (GTR). Properties
Modifier I
Modifier II
Purity or rubber content [wt%] Fiber content [wt%] Water content [wt%] Steel content [wt%] Mineral particles content [wt%]
98.57 0.30 0.45 0.15 0.53
98.85 0.32 0.54 0.03 0.26
Grain size analysis [mm] Grain size [mm]
Amount of fraction [wt%]
<0.20 0.20 0.30 0.50 0.63 0.71 >0.80
20.28 17.01 33.05 18.44 6.85 4.14 0.24
6.25 12.48 43.27 25.63 9.04 3.22 0.12
metal particles both granulates exceed the maximum level of 0.01 wt%. The same situation applies to the content of mineral impurities which in both modifiers exceeds maximum level 0.25% by weight. However, the amount of mineral and metal impurities is low enough, that there is no significant impact on the final properties of the modified asphalt binder. But, it may, according to industrial data, have a significant impact on the wear of moving parts of mixing equipment and pumps in industrial plants. The modifier I was obtained in a standard granulation process (SGP) by using typical knives granulator (mill). This granulator is normally used for grinding elastic and thermoplastics waste polymer materials. The main advantages of using SGP are high energy efficiency, low vibration and noise level. In this process whole tyres (car/truck – 50/50) are first shredded to get chips (particles size 10–50 mm), then cut through the knives until the assumed particles size of rubber are obtained (Fig. 1). In turn, the modifier II was obtained in flat-die granulation process (FDGP) via innovative KAHL flat die pelleting press. Flat die mill is normally
2. Experimental 2.1. Materials Asphalt binder 70/100 used in our studies was delivered by Lotos Asfalt Sp. z o. o. in Gdansk (Poland). Asphalt properties are presented in Table 1. Two types of grinded GTR (modifiers) in ambient condition were added to asphalt. Their sieve analysis is shown in Table 2. According to Standard Specification for AsphaltRubber Binder (ASTM D 6114-97) both rubber granulates used in the work contain less than 0.5 wt% of fibers and 0,75 wt% of water. In the case of amount of ferrous
70–100 43–51 10 230 99
Fig. 1. Scheme of knives granulator (SGP).
146
M. Sienkiewicz et al. / Construction and Building Materials 154 (2017) 144–154
used for grinding and compaction of many products (food and petfood, biomass, mineral materials, medicine, chemical compounds) but special construction of this machine, created by Amandus KAHL GmbH, with auxiliary equipment also allows the grinding of polymer waste, especially used tyres with separation of rubber, textile fibers and steel. In FDGP the whole car and truck tyres (50/50) are first shredded to obtain chips and then the pan grinder rollers in flat die pelleting press squeezed them through openings in a perforated flat die of the granulator (Fig. 2). In other words, no cutting process of wastes by knives was as used. 2.2. Preparation of rubber-asphalt binder First, pure asphalt was heated to a temperature of 180 °C in a metal container with a volume of approx. 1.2 dm3. Then the appropriate quantity of modifier I or II (5–15 wt%) was added, maintaining constant temperature using two different procedures of mixing. In the first procedure GTR with asphalt binder was blended via high shear mixer (laboratory homogenizer IKA T50 basic ULTRA-Turrax with rotor equipped mixing S 50 N – 45 G M), while in the second one mixing of GTR with asphalt binder via anchor stirrer powered by IKA RW 16 basic was realized. Homogenization of rubber/asphalt binder mixture was carried out for 1 h at 180 °C. After homogenization of asphalt/modifier mixture, three-hour ‘‘maturation” of the system took place at 180 °C in the oven. Table 3 shows the characterization of the rubber-asphalt binders obtained by two types of mixing procedures (from 70/100 asphalt) using two types of GTRs (modifies I and II). Samples A were obtained by addition of modifier I to asphalt binder (A1 – high shear mixer, A2 – anchor stirrer). In turn, samples B were obtained with the use of modifier II to asphalt binder (B1 – high shear mixer, B2 – anchor stirrer). 2.3. Gel-sol fraction, morphology and specific surface area of GTR The samples of GTR (modifier I and modifier II) and rubber-asphalt binders (A1 and B1 after homogenization containing 15 wt% of modifiers) were extracted with dichloromethane for 12 h at 45 °C in Soxlet. The gel fraction was calculated according to Eq. (1):
Gel fractionð%Þ ¼ W1 =W0 100%
ð1Þ
where W0 is the original weight of the GTR before extraction, and W1 is the weight of dried GTR after extraction. To determine W0 of GTR in rubber-asphalt binder, the weight of binder was multiplied by 0,15 (rubber-asphalt binder containing 15 wt% of GTR). To estimate specific surface area of GTR, the following samples were extracted and their morphology was analyzed: pure GTR, A1, B1 (samples were analyzed after homogenization and after storage stability test). Morphology of extracted rubber particles was estimated via scanning electron microscopy (SEM). Extracted samples were covered with gold in a QUORUM Q150T Sputter coater and viewed under SEM (Zeiss EVO-40). Additionally the specific surface area of GTR was determined via Bru nauer–Emmett–Teller (BET) method at a liquid nitrogen temperature (77 K) with the use of surface area analyzers (Micromeritics Gemini V series 2365).
2.4. Conventional properties and storage stability of rubber-asphalt binders After homogenization and 3 h of maturation the viscosity, softening point and penetration measurements were made for all types of rubber-asphalt binders. Viscosity test was performed at 180 °C with the use of a Haake Viscotester 2 Plus from TermoElectron. Softening point and penetration were measured according to EN 1427 and 1426 standards, respectively. The high-temperature storage stability was evaluated in the proper tubes (25.4 mm in diameter, 140 mm in height) filled with rubber-asphalt binders and vertically placed in an oven at 180 °C for 72 h. After that, samples of the rubber-asphalt binders were removed from the tubes and divided into three equal parts. Upper and lower parts of the samples were taken to measure penetration and softening point (the middle part of samples were rejected). According to the requirements of EN 13399:2010 standard, asphalt binder is considered as stable when the difference between the values of the parameters tested for the upper and lower portion of the sample is not more than 9–26 units (dependently on category of modified asphalt binder) in the case of penetration tests and no more than 5 units in the case of the test for softening point. The scheme of storage stability measurements are presented in Fig. 3.
2.5. Thin-layer chromatography with flame ionization detection TLC/FID Solutions of rubber-asphalt binder (10 mg of sample per 1 ml of solvent) used to TLC/FID analysis were prepared in dichloromethane, then GTR was separated from solution by filtration. After that 1 ll of solution was spotted on chromarods using a microsyringe. The separation of asphalt binder into five generic fractions (i. saturated hydrocarbons, ii. low polar, highly placed and naphthenic aliphatic, mononuclear aromatic hydrocarbons, iii. aromatic and polyaromatic, iv. resins, v. asphaltenes) was performed by a three-stage development using n-heptane, toluene and dichloromethane/methanol (95/5) by volume, respectively. Detection proceeded by transition of chromarods for 35 s through hydrogen flame detector FID with simultaneous digital recording electrometer signal. TLC/FID analysis was carried out for rubberasphalt binders containing the modifier I and modifier II (samples were analyzed after homogenization and after storage stability test) and unmodified asphalt binder.
2.6. Gel permeation chromatography (GPC) GPC was used to determine the molecular weight distribution of the asphalt binders modified by GTR. Polystyrene standards were used to calibrate the chromatography column. A sample of the asphalt binder in an amount of 50 mg was dissolved in 10 ml of tetrahydrofuran (THF). For the separation of components, two columns were used: LiChrogel PS MIX (50 lm, 250 7 mm, Merck, Germany) and Phenogel 5u Lineal (300 7.8 mm, Phenomenex, USA). Solution in amount of 50 ll was added at a flow rate of 0.7 ml/min. A spectrophotometric detector used with a diode array UV-DAD type 7450, refractive detector L-7490. GPC analysis was carried out for rubber-asphalt binders containing the modifier I and modifier II (samples were analyzed after homogenization and after storage stability test) and unmodified asphalt binder.
3. Results and discussion 3.1. Gel-sol fraction of GTR
Fig. 2. Scheme of flat-die pelleting press (FDGP) [30] with permission from Amandus Kahl GmbH & Co. KG.
Gel fractions of two types of modifiers (I and II) before and after addition to asphalt binder are shown in Table 4. According to the data given in Table 4 it can be concluded that gel fractions of modifier I and II (before adding to asphalt binder) are very similar and the differences should not influence the properties of rubber-asphalt binder. However, the differences in the content of gel fractions between modifier I and II are clearly increasing after the modification process of rubber-asphalt binder carried out with a homogenizer. The collected data show (Table 4) that rubber grains of modifier I have a greater degree of digestion in asphalt binder at 180 °C than modifier II. Based on the data described in the publications [31,32] this may be due to the fact that there are significantly more fine rubber grains (with size below 0.2 mm) in modifier I than in modifier II (Table 2), then swelling and digestion (depolymerization) of modifier I in asphalt binder are easier in comparison to larger grains, with size above 0.2 mm.
M. Sienkiewicz et al. / Construction and Building Materials 154 (2017) 144–154
147
Table 3 Composition of rubber-asphalt binders. Type of binder
Type of GTR (modifier)
Amount of GTR [wt%]
Amount of asphalt 70/100 [wt%]
Mixing device
A1
I
I
B1
II
B2
II
95 90 85 95 90 85 95 90 85 95 90 85
Homogenizer
A2
5 10 15 5 10 15 5 10 15 5 10 15
Anchor stirrer
Homogenizer
Anchor stirrer
Fig. 3. Scheme of high-temperature storage stability measurements.
Table 4 Gel fraction of GTR (modifier I and II) before and after modification process of the asphalt binder. Type of modifier
Gel fracions before modification [wt%]
Gel fracions after modification [wt%]
Modifier I Modifier II
89.2 84.6
47.2 75.6
Table 5 Specific surface area of modifier I and II used to asphalt binder modification measured via BET test. Rubber grains size
Specific surface area (BET test) [cm2/g] Modifier I
Modifier II
0–0.2 0.2–0.3 mm 0.7–0.8 mm 0–0.8 mm
2.28 1.16 0.54 4.12
2.20 3.44 0.69 2.57
3.2. Specific surface area and morphology of GTR The specific surface area of GTR measured by BET test is given in Table 5. From the results presented in Table 5 it can be concluded that both modifiers have similar specific surface area in the case of fine fraction of GTR (0–0.2 mm). Although, according to sieve analysis results given in Table 2, the amount of fraction 0–0.2 mm in modifier I (20.28 wt%) is much higher that in modifier II (6.25 wt%). Next to fine fraction of GTR there are present fractions of the order
of 0.2–0.8. Their specific surface area is different in modifier I and modifier II. Modifier II has higher specific surface area of fractions 0.2–0.3 mm and 0.7–0.8 mm. Taking altogether into account, the global specific surface area for fractions 0–0.8 mm of modifier I is higher than modifier II. This is due to the presence of much higher amount of fractions below 0.2 mm in modifier I (Table 2), which determine then the average global specific surface area. Figs. 4–7 present SEM micrographs of the modifier I (SGP) and the modifier II (FDGP) before and after homogenization with asphalt binders. As it can be seen in Fig. 4a and b, there are visible many small (0–0.2 mm) and some large (>0.5 mm) rough particles of the modifier I. The surface roughness of these particles may be explained by the multiple cutting of tyre pieces in the mill by knives of the granulator. Then, temperature of tyre pieces become higher and the rougher surface of GTR is obtained. In the modifier I there were also present a few large smooth particles of GTR having regular shape but their amount was small (Tables 2 and 4) and they did not have significant influence on the average global specific surface area of the modifier I. In the case of modifier II (Fig. 4c and d), rough (spongy) particles were mostly observed. This effect was achieved by using a granulator with a flat die and thickening rollers. As a result, the rubber material was squeezed through openings of a perforated plate granulator, which allow to obtain particles with rough surface. Summarizing, according to SEM micrographs, grain size analysis and BET results (Fig. 4, Table 2 and 5) it can be concluded that the modifier I was characterized by higher average global specific surface area than the modifier II due to the presence of much higher amount (20.28 wt%) of small rough particles (<0.2 mm).
148
M. Sienkiewicz et al. / Construction and Building Materials 154 (2017) 144–154
Fig. 4. Morphology of GTR grains obtained via SGP (a,b – modifier I) and FDGP (c,d – modifier II).
Fig. 5. Morphology of GTR after extraction with dichloromethane (a – modifier I; b – modifier II).
The morphology comparison of GTR before and after extraction with dichloromethane (Figs. 4 and 5) showed, that particles of rubber stucked together in both cases. It may be caused by migration of many components (e.g. not devulcanized polymer chains, oils and plasticizer) outside of the GTR. Taking into account all of the issues discussed above, homogenization of rubber-asphalt binder with GTR for 1 h at 180 °C changed the morphology of GTR (Fig. 6). Particles of GTR swelled due to the absorption of aromatic hydrocarbons present in asphalt binder, what is consistent with work of Airey et al. [11]. Further heating of rubber-asphalt binders after homogenization (storage stability test) caused deformation of GTR structure (it is clearly visible if one compares the images of GTR in Figs. 4, 6 and 7). The particles of GTR became thin and flat. It may be due to the devulcanization process, which occurs during heating of
rubber-asphalt binder at 180 °C for 72 h. Anyway, there was not distinct differences between GTR extracted from top and bottom of the tube. 3.3. Viscosity Table 6 presents the results of viscosity measurements of rubber-asphalt binders (containing 5, 10 and 15 wt% of GTR) modified by two types of GTR and using two homogenization methods. The value of viscosity is an important parameter for transportation process of asphalt binder. Too high viscosity is disadvantageous when transporting asphalt binder through pipelines. Consequently, over-viscous binders are unsuitable for use. As can be seen from the results presented in Table 6, asphalt binders modified by both types of GTR, have higher viscosity than
M. Sienkiewicz et al. / Construction and Building Materials 154 (2017) 144–154
149
Fig. 6. Morphology of GTR extracted with dichloromethane from rubber-asphalt binder after blended with homogenizer (a - modifier I; b – modifier II).
Fig. 7. Morphology of GTR extracted with dichloromethane from rubber-asphalt binder mixed with homogenizer, after high-temperature storage stability test (a – modifier I extracted from top part of tube; b – modifier II extracted from top part of tube; c – modifier I extracted from bottom part of tube; d – modifier II extracted from bottom part of tube).
the unmodified asphalt binders, what is consistent with the literature data [4,33]. The viscosity of the rubber-asphalt binder increased with increasing GTR content, especially when 15 wt% of it was added. It is worth to note that viscosity of samples obtained by using GTR grinded via FDGP (modifier II) was lower than viscosity of samples obtained by using GTR grinded via SGP (modifier I). The higher viscosity of asphalt binder modified by modifier I, as compared to asphalt modified with modifier II, can be explained by its higher average global surface area, as evidenced by BET studies (Table 5) and sieve analysis (Table 2). This is consistent with the data presented in the literature [25,31,34], indicating that the finer grains of GTR with a high surface area more effectively swell in
asphalt as compared to larger grains, what causes greater increase of the rubber-asphalt binder viscosity. Maturation of rubber-asphalt binders for 3 h resulted in an increase in viscosity in the case of sample A1 containing 10 wt% of the modifier I. On the other hand, viscosity decreased after 3 h of A2 and B1 samples maturation, which contained 15% by weight of the modifier. In other cases, the viscosity of rubber-asphalt binders did not change significantly after maturation. The type of mixing device had no significant effect on the viscosity of the rubberasphalt binder for samples A1, and a slight decrease in the viscosity of rubber-asphalt binder modified by a homogenizer can be explained by the process of devulcanization and digestion of the fine rubber grains, which are prominent in modifier I.
150
M. Sienkiewicz et al. / Construction and Building Materials 154 (2017) 144–154
Table 6 Viscosity of rubber-asphalt binders. Type of binder
Amount of modifier [wt %]
Asphalt A1
0 5 10 15 5 10 15 5 10 15 5 10 15
A2
B1
B2
Viscosity at 180 °C [Pas] After homogenization
After maturation
0.007 0.090 0.210 1.800 0.080 0.210 2.100 0.090 0.190 0.900 0.040 0.130 0.560
0.007 0.080 0.230 1.600 0.080 0.330 2.000 0.090 0.210 0.870 0.060 0.180 0.480
ing point value depending on the type of GTR (modifier I and II) used as asphalt modifiers. However, few samples modified by GTR obtained with SGP achieved softening point above 60 °C. Furthermore, modification method (homogenizer or stirrer) did not change significantly the softening point of rubberasphalt binders. Rubber-asphalt binders containing 5% by weight of the modifiers I or II mixed with a stirrer were characterized by lower softening point after maturation in comparison to samples after homogenization. In other cases it was noticed an increase in the softening point after maturation process. However, this growth was not higher than 3 °C, except sample containing 15 wt% of the modifier I mixed with homogenizer, when the difference between homogenization and maturation was around 6 °C. The increase in the softening point after maturation indicated that the rubberasphalt binders were cured, which improved their temperature under operating conditions. 3.5. Penetration
This conclusion is reflected in the results of the content of dissolved fractions in modifier I (Table 4), which amount increases after the interaction of rubber grains with asphalt binder. However, in case of rubber-asphalt binder prepared with 5–15% by weight of modifier II, the influence of modification conditions on its viscosity is evident and is higher when the modification process is carried out using a homogenizer. It may be explained by high mixing speed of homogenizer (high shear rate) causing turbulent mixing of the rubber in the bitumen binder, which reduces the size of the coarse rubber grains. This process can enhance the interaction of smaller rubber grains with asphalt binder, increasing their swelling capability and thereby reducing the viscosity of rubber-asphalt binder [34–38].
Fig. 8 presents results of softening point measurements of rubber-asphalt binders modified by two kinds of GTR (having 5, 10 and 15t% of GTR) using two different homogenization methods. It can be concluded that with an increasing amount of the modifier content the softening point became higher. It should be noted that the increase in the softening temperature was relatively proportional to the increase of GTR content. As can be seen in Fig. 8, there were rather slight differences in soften-
Fig. 9 presents values of penetration of rubber-asphalt binders modified by two kinds of GTR (having 5, 10 and 15 wt% of GTR) using two different homogenization method. As can be seen in Fig. 9, as opposed to the softening point measurement, the more modifier was added the lower penetration value was achieved. However, the penetration value of samples after maturation for 3 h did not change more than 4 units. Generally, rubber-asphalt binders obtained with the homogenizer had a lower value of penetration compared to those binders obtained using a stirrer. This is due to the better dispersion of the rubber granules with the homogenizer than the stirrer and is consistent with Yadollahi et al. observations [27]. Exceptions were samples containing 5–10 wt% of modifier I, in which the modification method did not affect the penetration value. Adding modifier I to the asphalt binders improved the penetration value compared to the modifier II. This was particularly evident in samples containing 5–10% by weight of GTR. In addition, several samples containing modifier I had a penetration value of less than 45 [0.1 mm], which was not observed in the rubber-asphalt binders containing the modifier II. This may be due to the different chemical composition of modifiers I and II. It may also indicate that GRT grains obtained with standard granulator had higher specific surface area what was described in Section 3.2.
Fig. 8. Softening point of rubber-asphalt binder modified by GTR shredded via flat die or standard granulation process, obtained by mixing with homogenizer or stirrer.
Fig. 9. Penetration of rubber-asphalt binders modified by GTR shredded via flat die granulation process or standard granulation process (modification with the use of homogenizer or stirrer).
3.4. Softening point
151
M. Sienkiewicz et al. / Construction and Building Materials 154 (2017) 144–154 Table 7 Stability of rubber-asphalt binders modified by GTR. Type of binder
Amount of modifier [wt%]
A1
5 10 15 5 10 15 5 10 15 5 10 15
A2
B1
B2
Fig. 10. Differences in penetration of rubber-asphalt binders after high-temperature storage stability test.
Penetration [0.1 mm]
Softening point [°C]
Top
Bottom
Top
Bottom
64.7 64.0 60.0 64.0 60.0 57.0 64.7 62.0 57.0 50.0 49.0 59.0
84.7 89.7 80.3 83.0 68.0 68.0 75.0 73.7 70.0 59.0 58.0 74.0
48.3 48.6 50.4 54.3 48.3 57.9 48.5 50.1 53.5 55.8 58.4 56.7
48.9 58.9 63.5 52.1 57.0 59.4 51.2 57.9 63.1 51.7 50.3 59.5
modifier, rubber-asphalt binders containing the modifier II (except samples containing 10–15 wt% prepared with the stirrer) were characterized by lower differences in penetration value after high-temperature storage stability test. It is also worth to mention that penetration of the lower parts of the samples increases with the respect to the upper part of samples and samples after homogenization (Table 7). This is caused by settlement of GTR particles, which are thermally devulcanized due to the storage at 180 °C for 72 h and then they play the role of a plasticizer of rubberized bitumen [6]. According to Fig. 11 and EN 13399:2010 standard, rubberasphalt binders containing 5 wt% of modifiers (I or II) are stable with respect to the softening point. However, it was reported that stability mainly depends on rheological properties of rubberasphalt binder and the difference in the softening point should not be considered as the unequivocal and decisive criterion [6,33,39–40]. Moreover, it was found that increase in the viscosity of the binder improves the storage stability due to the inhibition of rubber particle settling. It is in accordance with the results presented in the paper for rubber-asphalt binders mixed with stirrer having 15 wt% of GTR (independently on the type of used modifier). When using the homogenizer high shear rate is changing the particle shape of rubber grains, what increases their sedimentation velocities, thus the viscosity is then of less decisive factor. In the case of GTR type (Table 7, Fig. 11), rubber-asphalt binders containing 10–15 wt% of the modifier II were characterized by lower differences in the softening point in comparison to samples containing the modifier I.
3.7. Thin-layer chromatography with flame ionization detection TLC/ FID
Fig. 11. Differences in softening point of rubber-asphalt binders after hightemperature storage stability test.
3.6. Stability Table 7 and Figs. 10 and 11 show the results of stability tests of rubber-asphalt binders aged for 72 h at asphalt processing temperatures (180 °C). Based on results presented in Table 7 and Fig. 10, it can be concluded that rubber-asphalt binders mixed with the use of the stirrer (except sample containing 15 wt% of modifier II) had lower differences in the penetration value compared to samples obtained with the homogenizer. In addition, the rubber-asphalt binder blended with the stirrer, containing 10 wt% of the GTR had the best stability considering penetration. According to the type of used
Figs. 12 and 13 present results of TLC/FID measurements for asphalt binders modified by two kinds of GTR (15 wt%) mixed with homogenizer. Samples were analyzed after homogenization and after high-temperature storage stability test. Those analysis showed the presence of the following five fractions: i) saturated hydrocarbons ii) low polar, highly placed and naphthenic aliphatic, mononuclear aromatic hydrocarbons iii) aromatics and polyaromatics iv) resins v) asphaltenes Thin-layer chromatography with flame ionization detection TLC/FID indicated that addition of GTR (both modifiers) to asphalt binder affects on the percentage of fractions, except of percentage of asphaltenes, which were similar in all cases. Modification of the
152
M. Sienkiewicz et al. / Construction and Building Materials 154 (2017) 144–154
Fig. 12. The influence of addition modifier I on asphalt binder groups in the final product.
Fig. 13. The influence of addition modifier II on asphalt binder groups in the final product.
asphalt binder by modifier I resulted in a percentage increase of the following fractions: ii) low polar, highly placed and naphthenic aliphatic, mononuclear aromatic hydrocarbons, iii) aromatics and iv) resins and percentage decreasement of i) saturated hydrocarbons. In turn, modification of asphalt binder by the modifier II resulted in increase of fraction‘‘iv” and decrease of fraction ‘‘i and iii‘‘. The differences in percentages of individual fractions observed between unmodified and modified asphalt binders can be explained by the migration of asphalt molecules from fraction to fraction, induced by GTR addition. However, percentage differences between asphalt binders A1 and B1 might be explained by various absorption of asphalt binder fractions by GTR due to its specific surface area or type of tyres (content of natural and synthetic rubber) used to produce GTR. 3.8. Gel permeation chromatography (GPC) Figs. 14 and 15 present results of GPC analysis for asphalt binders modified by 15 wt% of GTR with homogenizer.
Number average molar mass (Mn) did not change significantly after homogenization of asphalt binder by GTR and after hightemperature storage stability test. Type of the modifier also did not affect Mn. In turn, weight average molar mass (Mw) increased when GTR was added to asphalt binder. In the case of asphalt binders modified by GTR, the lowest values of Mw had samples after homogenization and the highest values were obtained for samples taken from bottom part of the tube after high-temperature storage stability test. Additionally, Mw of rubber-asphalt binders containing the modifier I was higher than those containing the modifier II. It is worth to note that the modification of asphalt binder by GTR affected percentage increasement of fractions having molecular weight bigger than 1000. The highest results in molecular weight were obtained for rubber-asphalt binder B2 (bottom). However, differences in molecular weight between asphalt binders A1 and B1 might be explained by different absorption degree of asphalt binder light fractions by the modifier I and II due to various chemical composition of modifiers or their specific surface area.
M. Sienkiewicz et al. / Construction and Building Materials 154 (2017) 144–154
153
Fig. 14. Change in molar mass of asphalt binders modified by GTR.
Fig. 15. Change in molecular weight distribution of asphalt binders modified by GTR.
4. Conclusions The properties of asphalt binders modified by ground tyre rubber (GTR) in the amount of 5–15 wt% were analyzed. GTR was obtained by two different grinding method: standard granulation process (SGP, modifier I) and flat-die granulation process (FDGP, modifier II). It was shown that GTR grinding method had the influence on the morphology characteristic and specific surface area of rubber grains, thus properties of rubber-asphalt binder. The properties of rubber-asphalt binders depended on the amount of the modifier and the type of mixing devices (homogenizer or stirrer) used to carry out the modification process. The following conclusions can be drawn from the research: 1. Microscopic analysis showed that grains of modifier II had ‘‘spongy” form due to obtaining this GTR by flat die pelleting press (FDGP). In turn the GTR grinded by knives granulator (modifier I) had grains with the complex morphology: some
large grains of this GTR had smooth surface and small grains (<0.2 mm) had a very rough surface. Therefore the BET analysis proved that the GTR grains obtained by FDGP with size between 0.2 and 0.3 mm and 0.7 and 0.8 have higher specific surface area. However GTR obtained by SGP (modifier I) was characterized by higher average global specific surface area. This is due to presence of high amount (20.28 wt%) of smaller rough particles (0–0.2 mm) in GTR in comparison to GTR obtained by FDGP (modifier II). 2. From the economic and material properties point of view, the optimum amount of GTR added to asphalt binder should be 15 wt%. 3. The modifier I added to asphalt binder improved its softening point and penetration value. In turn, addition of the modifier II to asphalt binder contributed to lower viscosity after homogenization. Moreover, it was observed the improvement of hightemperature storage stability in the case of penetration for all samples having the modifier II. In the case of softening point,
154
M. Sienkiewicz et al. / Construction and Building Materials 154 (2017) 144–154
stability was improved for the samples containing 10–15 wt% of modifier (rubber-asphalt binders prepared with the homogenizer contained). Thus, in the case of penetration and softening point of rubber-asphalt binder, GTR obtained by SGP is more favorable modifier. Although in the case of rubber-asphalt binder viscosity and stability, more favorable is GTR obtained via FDGP. 4. Modification of rubber-asphalt binder by the stirrer improved high-temperature storage stability of samples in comparison to rubber-asphalt binder modified by homogenizer. However, modification with the use of the homogenizer improved penetration value after homogenization of samples containing GTR in the amount of 10–15 wt% due to better dispersion of modifier in the asphalt binder. 5. Percentage of fraction and its molecular weight distribution in asphalt binders changed when GTR was added and depended on chemical components and the specific surface area of GTR.
References [1] J. Karger-Kocsis, L. Meszaros, T. Barany, Ground tyre rubber (GTR) in thermoplastics, thermosets and rubbers, J. Mater. Sci. 48 (2013) 1–38. [2] M. Sienkiewicz, J. Kucin´ska-Lipka, H. Janik, A. Balas, Progress in used tyres management in the European Union: a review, Waste Manage. 32 (2012) 1742–1751. [3] G. Ivan, Some aspects of tyre impact on environment: production, service and recycling, Elastomery 4–5 (6) (2002) 24–38. [4] F. Xiao, S.N. Amirkhanian, Laboratory investigation of utilizing high percentage of RAP in rubberized asphalt mixture, Mater. Struct. 43 (2010) 223–233. [5] W. Cao, Study on properties of recycled tire rubber modified asphalt mixtures using dry process, Constr. Build. Mater. 21 (2007) 1011–1015. [6] F.J. Navarro, P. Partal, F. Martínez-Boza, C. Gallegos, Thermo-rheological behaviour and storage stability of ground tire rubber-modified bitumens, Fuel 83 (2004) 2041–2049. [7] Y. Huang, R.N. Bird, O. Heidrich, A review of the use of recycled solid waste materials in asphalt pavements, Resour. Conserv. Recycl. 52 (2007) 58–73. [8] I. Gaweł, M. Kalabin´ska, J. Piłat, Asfalty Drogowe (Bitumen used for Pavements) , WKŁ, Warszawa, 2001. [9] P. Radziszewski, M. Kalabin´ska, J. Piłat, Wykorzystanie miału gumowego ze _ zuzytych opon samochodowych w modyfikacji asfaltów drogowych (The use of rubber granulate from scrap tires for asphalt modification), Elastomery 4 (2001) 8–16. [10] F.J. Navarro, P. Partal, F. Martínez-Boza, C. Gallegos, Novel recycled polyethylene/ground tire rubber/bitumen blends for use in roofing applications: thermo-mechanical properties, Polym. Test. 29 (2010) 588–595. [11] G. Airey, M. Rahman, A. Collop, The influence of crude source and penetration grade on the interaction of crumb rubber and bitumen, in: International Asphalt and Rubber Conference, Brasilia, Brazil, 2003. [12] G. Ying, C. Rongji, Interation theory of asphalt and rubber, J. Wuhan Univ. Technol. Mater. 25 (2010) 853–855. [13] I. Gaweł, R. Stepkowski, F. Czechowski, Molecular interactions between rubber and asphalt, Ind. Eng. Chem. Res. 45 (2006) 3044–3049. [14] P. Radziszewski, J. Piłat, M. Sarnowski, K. Kowalski, J. Król, I. Ruttmar, S. Witczak, P. Heinrich, D. Skowron´ski, Z. Krupa, M. Nawracaj, K. Gil, _ Opracowanie i wdrozenie innowacyjnej, przyjaznej s´rodowisku technologii modyfikacji asfaltów drogowych guma˛ (Development and implementation of innovative, environmentally friendly technologies to modify road bitumen by rubber), Nawierzchnie Asf. 3 (2011) 10–15. [15] S.J. Lee, C.K. Akisetty, S.N. Amirkhanian, The effect of crumb rubber modifier (CRM) on the performance properties of rubberized binders in HMA pavements, Constr. Build. Mater. 22 (2008) 1368–1376. [16] S. Liu, W. Cao, J. Fang, S. Shang, Variance analysis and performance evaluation of different crumb rubber modified (CRM) asphalt, Constr. Build. Mater. 23 (2009) 2701–2708.
[17] H. Shi, M. Zou, K. Liao, Research progress of ground tire rubber modified pavement asphalts, J. Chem. Ind. Eng. 26 (2005) 27–30. [18] Y. Yildirim, Polymer modified asphalt binders, Constr. Build. Mater. 21 (2007) 66–72. [19] M. Liang, X. Xin, W. Fan, H. Sun, Y. Yao, B. Xing, Viscous properties, storage stability and their relationships with microstructure of tire scrap rubber modified asphalt, Constr. Build. Mater. 74 (2015) 124–131. [20] S. Kocevski, S. Yagneswaran, F. Xiao, V.S. Punith Jr., D.W. Smith, S.N. Amirkhanian, Surface modified ground rubber tire by grafting acrylic acid for paving applications, Constr. Build. Mater. 34 (2012) 83–90. [21] X. Li, J. Cheng, G. Que, Microstructure and performance of crumb rubber modified asphalt, Constr. Build. Mater. 23 (2009) 3586–3590. [22] S.J. Lee, S.N. Amirkhanian, K. Shatanawi, K.W. Kim, Short-term aging characterization of asphalt binders using gel permeation chromatography and selected superpave binder tests, Constr. Build. Mater. 22 (2008) 2220– 2227. [23] J. Shen, S. Amirkhanian, F. Xiao, B. Tang, Influence of surface area and size of crumb rubber on high temperature properties of crumb rubber modified binders, Constr. Build. Mater. 23 (2009) 304–310. [24] L.P. Thives, J.C. Pais, P.A.A. Pereira, G. Trichês, S.R. Amorim, Assessment of the digestion time of asphalt rubber binder based on microscopy analysis, Constr. Build. Mater. 47 (2013) 431–440. [25] C. Thodesen, K. Shatanawi, S. Amirkhanian, Effect of crumb rubber characteristics on crumb rubber modified (CRM) binder viscosity, Constr. Build. Mater. 23 (2009) 295–303. [26] L. Zanzotto, G. Kennepohl, Development of rubber and asphalt binders by depolymerization and devulcanization of scrap tires in asphalt, Transp. Res. Rec. 1530 (1996) 51–58. [27] G. Yadollahi, H.S. Mollahosseini, Improving the performance of crumb rubber bitumen by means of Poly Phosphoric Acid (PPA) and vestenamer additives, Constr. Build. Mater. 25 (2011) 3108–3116. [28] H. Yao, S. Zhou, S. Wang, Structural evolution of recycled tire rubber in asphalt, J. Appl. Polym. Sci. 133 (2016) 1–7. [29] C. Glover, R.R. Davison, J. Bullin, C.K. Estakhri, S.A. Williamson, T.C. Billiter, J. F. Chipps, J.S. Chun, P. Juristyarini, S.E. Leicht, P. Wattanachai, A comprehensive laboratory and field study of high-cure crumb-rubber modified asphalt materials, Report 1460-1, Texas Transportation Institute, USA, 2000. [30] Amandus Kahl GmbH & Co. KG, Recycling Plants for Waste Tyres. https://www. akahl.de/en/service/downloads/, (accessed 27.06.17). [31] D. Lo Presti, Recycled tyre rubber modified bitumens for road asphalt mixtures: a literature review, Constr. Build. Mater. 49 (2013) 863–881. [32] M. Heitzman, Design and construction of asphalt paving materials with crumb rubber modifier, Transp. Res. Rec. 1339 (1992) 1–8. [33] F.J. Navarro, P. Partal, F. Martínez-Boza, C. Gallegos, Influence of crumb rubber concentration on the rheological behavior of a crumb rubber modified bitumen, Energy Fuel 19 (2005) 1984–1990. [34] T. McNally, Polymer Modified Bitumen, Woodhead Publishing Ltd, 2011. [35] F. Xiao, B.J. Putman, S.N. Amirkhanian, Laboratory investigation of dimensional changes of crumb rubber reacting with asphalt binder, Road Mater. Pavement Des. 10 (2006) 1–21. Relationship between Crumb Rubber Morphology and Asphalt Rubber Viscosity. [36] Relationship between Crumb Rubber Morphology and Asphalt Rubber Viscosity. https://www.researchgate.net/profile/Michele_Lanotte/publication/ 266208406_Relationship_between_Crumb_Rubber_Morphology_and_Asphalt_ Rubber_Viscosity/links/542a7dc40cf29bbc1267a120/Relationship-betweenCrumb-Rubber-Morphology-and-Asphalt-Rubber-Viscosity.pdf/, 2012 (accessed 27.06.17). [37] J. Shen, S.N. Amikrhanian, The influence of crumb rubber modifier (CRM) microstructures on the high temperature properties of CRM binders, Int. J. Pavement Eng. 6 (2005) 265–271. [38] D. Lo, G. Presti, Airey P. Partal, Manufacturing terminal and field bitumen-tyre rubber blends: the importance of processing conditions, Proc. Soc Behav. Sci 53 (2012) 485–494. [39] O. Gonzalez, M.E. Munoz, A. Santamaria, M. Garcia-Morales, F.J. Navarro, P. Partal, Rheology and stability of bitumen/EVA blends, Eur. Polym. J. 40 (2004) 2365–2372. [40] F.M. Nejad, P. Aghajani, A. Modarres, H. Firoozifar, Investigating the properties of crumb rubber modified bitumen using classic and SHRP testing methods, Contr. Build. Mater. 26 (2012) 481–489.