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The investigation and comparison effects of SBS and SBS with new reactive terpolymer on the rheological properties of bitumen
Construction and Building Materials 38 (2013) 285–291
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The investigation and comparison effects of SBS and SBS with new reactive terpolymer on the rheological properties of bitumen Perviz Ahmedzade ⇑ Department of Civil Engineering, Ege University, Izmir, Turkey
h i g h l i g h t s Ò
" The effect of styrene–butadiene–styrene (SBS) and SBS + Entira Bond 8 additives on characteristics of bitumen was investigated. " The results showed that both polymers groups reduce temperature susceptibility of bitumen. Ò
" SBS + Entira Bond 8 modifications improved the properties of bitumen better than just SBS modifications.
a r t i c l e
i n f o
Article history: Received 8 April 2012 Received in revised form 16 July 2012 Accepted 23 July 2012 Available online 29 September 2012 Keywords: Bitumen Polymer–modified bitumen Reactive terpolymer Styrene–butadiene–styrene Rutting resistance
a b s t r a c t The effects of styrene–butadiene–styrene (SBS) and SBS with new reactive terpolymer (EntiraÒBond 8) modifications on the rheological properties of pure bitumen were investigated and compared to each other. Four polymer modified bitumens (PMBs) were produced by mixing bitumen with SBS at two polymer contents and with SBS + EntiraÒBond 8 at the same polymer contents. The rheologic characteristics of the PMBs were analyzed by means of conventional test methods like penetration, softening point and Fraas breaking point as well as rotational viscometer (RV), dynamic shear rheometer (DSR) and bending beam rheometer (BBR) test methods. Conventional binder properties of different PMB groups demonstrated that the polymers increase stiffness (hardness) and improve susceptibility of pure bitumen to temperature changes. Both polymers groups improve properties of bitumen, such as increased elastic responses (increased complex shear modulus and decreased phase angle) at low to high temperatures and reduced creep stiffness at low temperatures. Based on the results of this investigation it can be noted that SBS + EntiraÒBond 8 modifications improved the conventional and more fundamental properties of bitumen better than just SBS modifications. Ó 2012 Elsevier Ltd. All rights reserved.
1. Introduction An asphalt concrete road consists of a choice of different sizes of aggregate held together by bitumen. The bitumen only makes up 5–7% by weight or approximately 15% by volume of the asphalt concrete mix. Despite this small percentage, the performance of the bitumen has a significant influence on the long term performance of a road. The bitumen used in flexible pavements exhibits elastic behavior at low temperatures and under high speed vehicles where as viscous behavior at high temperatures and under low speed vehicles. Under normal conditions and intermediate temperatures, the bitumen shows viscoelastic behavior. In order to accommodate increasing traffic loadings as well as resist temperature changes, specific polymer based additives are utilized. Pavement with polymer modification exhibits greater ⇑ Tel.: +90 533 7212423; fax: +90 232 3425629. E-mail address: [email protected] 0950-0618/$ - see front matter Ó 2012 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.conbuildmat.2012.07.090
resistance to rutting and thermal cracking, and decreased fatigue damage, stripping and temperature susceptibility. Polymer modified binders have been used with success at locations of high stress, such as intersections of busy streets, airports, vehicle weigh stations, and race tracks [1–5]. Among these additives, the most commonly used polymer is elastomeric type styrene–butadiene–styrene (SBS) copolymer. SBS copolymers consist of block segments of styrene monomer units and butadiene rubber monomer units. Each block segment can consist of many monomer units. The most common form used in bitumen modification is a linear styrene–butadiene–styrene structure, but radial types are also available. The content, structure of SBS, structure of base bitumen as well as the mixing time and temperature are important factors that should be taken into account in the production of SBS polymer modified bitumen (PMB). Recent studies indicate that pavement with SBS polymer modification exhibits greater resistance to
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Table 1 Properties of the base bitumen. Test
Specification
Results
Specification limits
Penetration (25 °C; 0.1 mm) Softening point (°C) Fraas breaking point (°C) Penetration index (PI)
ASTM D5 ASTM D36 IP 80 –
130 45.7 20 0.33
100–150 39–47 max12 –
permanent deformation at hot climates, cracking at low temperatures and fatigue cracking due to the increased bitumen stiffness [6–9]. The temperature is an extremely important factor in the structure of the SBS polymer modified bitumen. After production, care must be taken in order to hold the polymer modified bitumen under constant temperature since the SBS can be easily decomposed from the base bitumen and is not appropriate for storage. Not holding the final product under required level of temperature can lead to adhesion, decomposition and frost problems. Besides the SBS is an expensive additive. In order to raise the efficiency of bitumen modification, to decrease the production cost as well as to increase the storage stability properties of SBS modified bitumens without additional heating procedures, DuPont Company produced a new reactive terpolymer (EntiraÒBond 8) to be used with SBS. The utilization of the EntiraÒBond 8 decreases the SBS polymer consumption by almost 50% which makes this additive a cost effective polymer [10]. This study aims to investigate and compare effects of SBS and SBS with EntiraÒBond 8 on the rheologic properties of bitumen. 2. Experimental 2.1. Materials The base bitumen with a 100/150 penetration grade has been procured from Turkish Petroleum Refineries Corporation (TUPRAS). Table 1 gives a summary of the results of some tests performed on the base bitumen. The SBS polymer used was Kraton D-1101 supplied by the Shell Chemicals Company. Kraton D-1101 is a linear SBS polymer in powder form that consists of different combinations made from blocks polystyrene (31%) and polybutadiene of a very precise molecular weight [11]. These blocks are either sequentially polymerized from styrene and butadiene and/or coupled to produce a mixture of these chained blocks. The reactive terpolymer EntiraÒBond 8 was provided by DuPont Company. 2.2. Preparation of samples The SBS Kraton D-1101 concentrations in the base bitumen were chosen as 3% and 4.5% by weight. In preparation, the base bitumen was heated to fluid condition (180–185 °C), and has been poured into a 2000 ml spherical flask. Then the SBS polymer was added slowly to the base bitumen. The SBS modified bitumen samples were prepared by means of laboratory type mixer rotating at 500 rpm. On reaching temperature of 190 °C, the temperature has been kept constant and the mixing process continued for 2 h. The SBS Kraton D-1101 concentrations in the base bitumen replaced half of the SBS polymer contents (1.5% and 2.25%) and then EntiraÒBond 8 was added to SBS modified bitumens to prepare SBS with EntiraÒBond 8 modified bitumen samples.
Concentration of EntiraÒBond 8 was chosen as 1% according to the manufacturers (DuPont Company). Conditions of preparing process of SBS with EntiraÒBond 8 modified bitumen specimens such as temperature, speed and time of mixing used were the same as in preparation of SBS modified bitumen samples. After complete blending for 2 h, the blended samples were cured for 2 h at 190 °C to achieve chemical reaction which allowed to create permanently modified binders. The uniformity of dispersion of polymers in the base bitumen was confirmed by passing the mixture through an ASTM 100# sieve. After completion, the samples were removed from the flask and divided into small containers, covered with aluminum foil and stored for testing. The different binders were coded as follows:
base base base base base
2.3. Testing program 2.3.1. Conventional bitumen tests The unmodified and modified bitumens were subjected to the following conventional bitumen tests: penetration, softening point and Fraass breaking point. In addition, the temperature susceptibility of the modified bitumen samples has been calculated in terms of penetration index (PI) using the results obtained from penetration and softening point tests. Temperature susceptibility is defined as the change in the consistency parameter as a function of temperature. A classical approach related to PI calculation has been given in the Shell Bitumen Handbook [12] as shown with the following equation:
PI ¼
1952 500 logðPen25 Þ 20 SP 50 logðPen25 Þ SP 120
Oscillating Plate
ð1Þ
where, Pen25 is the penetration at 25 °C and SP is the softening point temperature of bitumen. 2.3.2. Rotational viscosity test The rotational viscometer determines the bitumen viscosity by measuring the torque necessary to maintain a constant rotational speed of a cylindrical spindle submerged in a bitumen specimen held at a constant temperature, as per the AASHTO TP48 standard test method. Unlike the capillary viscometers used with the viscosity-graded method, the rotational viscometer can evaluate modified bitumen binders [13]. The viscosity of bitumen binders can be measured within the range of 0.01 Pa s (0.1 poise) to 200 Pa s (2000 poise) [14]. The Asphalt Institute recommends taking the first viscosity measurement at 135 °C, and the second at 165 °C. A Brookfield viscometer (DV-III) was used for the viscosity tests on the base and modified bitumens. 2.3.3. Dynamic shear rheometer test The dynamic shear rheometer (DSR) was adopted to characterize the viscoelastic behavior of bitumen binders at low and at intermediate to high service temperatures. The DSR provides an indication of the rutting resistance of bitumen immediately following construction. Resistance to rutting at high service temperatures in the early stages of pavement life is also evaluated [15,16]. The DSR evaluates the behavior of a bitumen specimen by subjecting it to oscillatory (sinusoidal) stresses. The AASHTO TP5 standard test method requires that a thin bitumen specimen be sandwiched between two parallel metal plates held in a constant temperature medium. One plate remains fixed while the other oscillates, at an angular frequency (x) of 10 radians per second for 10 cycles, with respect to the other. A complete DSR loading cycle is shown in Fig. 1 [15]. When torque from the DSR motor is applied, the oscillating plate moves from point A to point B. The plate then passes back through point A to point C. The cycle of oscillation is completed as the plate passes back through point A again. The spin-
Position of Oscillating Plate
Applied Stress
bitumen – ‘‘B’’; bitumen + 3%SBS – ‘‘B-3S’’; bitumen + 1.5%SBS + 1% EntiraÒBond 8 – ‘‘B-1.5S-1E’’ bitumen + 4.5%SBS – ‘‘B-4.5S’’; bitumen + 2.25%SBS + 1% EntiraÒBond 8 – ‘‘B-2.25S-1E’’.
B
Fixed Plate
A
Asphalt B
A
A A
Time
C
C 1 cycle Fig. 1. Configuration and load cycle of dynamic shear rheometer [15].
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P. Ahmedzade / Construction and Building Materials 38 (2013) 285–291 dle is oscillated back and forth using either a constant stress or constant strain. Constant stress means that the spindle is rotated through a certain distance until a fixed stress is achieved. Constant strain means that the spindle is rotated every time through a fixed distance, regardless of the stress achieved. While this rotation occurs, the resulting strain or stress is monitored. The relationship between the applied stress and the resulting strain provides information necessary to compute complex shear modulus (G⁄) and phase angle (d). A higher G⁄ and a lower d are desired for rutting resistance. The bitumen with a high G⁄ is stiffer and provides increased resistance to deformation. The bitumen exhibiting a lower d has a greater elastic component, thus allowing more of the total deformation to be recovered. The relationship G⁄/sin d was chosen as the parameter for SHRP specifications with respect to rutting resistance of bitumen binders [16]. For specification purposes, the frequency is 10 radians per second which has been related to a traffic speed of 100 km/h. For slower moving traffic, a lower frequency could be used for evaluation of a proposed product. For example, with city street traffic a frequency of 5 radians per second could be used (corresponding to 50 km/h); for standing traffic, a very low frequency, such as 1 radian per second might be appropriate [17]. 2.3.4. Bending beam rheometer test The bending beam rheometer (BBR) was used to measure the low-temperature creep stiffness and logarithmic creep rate of the bitumen binder. In this test, a beam of bitumen binder 125 mm long, 12.5 mm wide, and 6.25 mm thick is formed by pouring binder into a mold and allowing it to cool. This beam is placed in a lowtemperature bath to equilibrate its temperature to the desired test temperature. During testing, which must be accomplished within 60 min of placing the beam in the bath, the beam is placed on two simple supports having a span of 100 mm. A constant load of 980mN, maintained for 240 s, was applied to the center of the simply supported beam. The creep stiffness, S, and the creep rate (slope, m) of the relationship between log (stiffness) and log (time) were measured at 60 s (loading time). The loading geometry of the BBR is shown in Fig. 2. The BBR test measures creep stiffness value at the lowest in-service temperature, S(t) as designated by SHRP, which is indicative of the susceptibility to lowtemperature cracking. The rate of change of binder stiffness with time is represented by the m-value, which is the slope of the log stiffness versus log time curve from the BBR test results. A high m-value is desired because as the temperature decreases and pavement contraction begins to occur, the binder will respond as a material that is less stiff. This decrease in stiffness leads to smaller tensile stresses in the binder and less chance for low-temperature cracking. For an adequate low temperature cracking resistance the creep stiffness must be less than 300 MPa and the m-value must be greater than 0.3 [18,19].
3. Results and discussion 3.1. Conventional bitumen tests The results obtained using conventional test methods are summarized in Table 2. This table shows that polymer modified speci-
Table 2 Changes in conventional binder properties following polymers modifications. Properties
Penetration (25°C; 0.1 mm) Softening point (°C) Penetration index (PI) Fraas breaking point (°C)
Binder types B
B-3S
B-1.5S-1E
B-4.5S
B-2.25S-1E
130
71
69
54
51
45.7
53.6
55
58
60
0.32
0.56
0.81
0.81
1.08
20
22.1
23
24
25.6
mens have decreased penetration and increased softening point in comparison with unmodified specimens. In addition, it can be noted that SBS + EntiraÒBond 8 polymers modifications further decrease penetration and further increase softening point of base bitumen compared to only SBS polymer modifications. The increase in softening point (which is an indicator of the stiffening effect of PMBs) is favorable since bitumen with higher softening point may be less susceptible to permanent deformation (rutting). Polymer modification reduces the temperature susceptibility of the bitumen. Lower values of PI indicate higher temperature susceptibility. Asphalt mixtures containing bitumen with higher PI are more resistant to low temperature cracking as well as permanent deformation [20]. Table 2 also shows the effects of the SBS and SBS + EntiraÒBond 8 polymers on the penetration index of bitumen. It is clearly seen that polymer modified bitumens have increased PI values compared to pure bitumen. Increased PI indicates a significant reduction in temperature susceptibility of binders. The Fraass breaking point results show that polymers have the considerable influence on the low temperature physical properties of base bitumen. The reduction in Fraass breaking point indicates an increased low temperature flexibility of the PMBs. The increase in softening point and the decrease in Fraass breaking point values of polymer modified bitumens, means that polymer additives on the one side make bitumen stiffer and on the other side make it more elastic.SBS and SBS + EntiraÒBond 8 modified binders were compared to each other and it is clearly seen that B-1.5S-1E and B-2.25S-1E have better results than B-3S and B-4.5S, respectively. Among the all tested binders, B-2.25S-1E binder exhibits the best results.
3.2. RV test results
Fig. 2. Loading geometry of the bending beam rheometer.
Rotational viscosities (g) and modification indices (g for PMB divided by g for the base bitumen) at 135 °C and 165 °C for the all binders used in this study are shown in Table 3. The viscosity of bitumen blends increases with increasing the content of polymer additives at both temperature conditions. From comparing of four PMBs blends to each other it can be seen that both blends have relatively similar viscosity values at 135 °C, but with increasing temperature to 165 °C, viscosities of SBS PMBs are more de-
Table 3 Rotational viscosities following polymers modifications. Binder types
Rotational viscosity at 135 °C (cP)
Rotational viscosity at 165 °C (cP)
gPMB/ gBitumen at 135 °C
gPMB/ gBitumen at 165 °C
B B-3S B-1.5S-1E B-4.5S B-2.25S-1E
375 1110 1115 1775 1790
125 325 370 575 630.5
1.00 2.93 2.97 4.73 4.77
1.00 2.6 2.96 4.6 5.04
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Table 4 Traffic speeds equivalent frequencies.
Table 5 DSR test parameters.
Traffic speed, km/h
Traffic speeds equivalent frequencies, Hz (rad/s)
Test parameters
Low, 6 km/h Medium, 45 km/h High, 120 km/h
0.1 Hz (0.628 rad/s) 0.72115 Hz (4.53 rad/s) 1.9355 Hz (12.15494 rad/s)
Mode of loading
Controlled-strain
Frequencies, Hz (rad/sn)
0.1 Hz (0.628 rad/s), 0.72115 Hz (4.53 rad/s), 1.9355 Hz (12.15494 rad/s) 10, 15, 20, 30, 35, 40, 45, 50, 55, 60, 65, 70, 25 75 8 25 2 1
Temperatures, °C
creased than ones of SBS + EntiraÒBond 8 PMBs. As with the penetration and softening point tests, the viscosities give a clear indication of the stiffening effect of both polymers modification, especially of SBS + EntiraÒBond 8 modification. 3.3. DSR test results The rheologic properties of the binders at low and at intermediate to high temperatures are obtained from the Dynamic Shear
Diameter spindle, mm Testing gap, mm
Rheometer (DSR). In this study, two different spindle diameters and testing gaps were selected depending on test temperature ranges. Table 4 shows frequencies used in the test procedure which were accepted as equivalent to different frequencies of traffic. In order to determine the effect of SBS and SBS + EntiraÒBond 8 poly-
Complex modulus (Pa)
1.E+07 B B-3S B-1.5S-1E B-4.5S B-2.25S-1E
1.E+06 1.E+05 1.E+04 1.E+03 1.E+02 1.E+01 0
10
20
30
40
50
60
70
80
Temperature ( oC) Fig. 3. Curve of complex shear modulus (G⁄) versus temperature for base and PMBs at 0.1 Hz.
Complex modulus (Pa)
1.E+07
B B-3S B-1.5S-1E B-4.5S B-2.25S-1E
1.E+06 1.E+05 1.E+04 1.E+03 1.E+02 1.E+01 0
10
20
30
40
50
60
70
80
Temperature ( oC) Fig. 4. Curve of complex shear modulus (G⁄) versus temperature for base and PMBs at 0.72115 Hz.
Complex modulus (Pa)
1.E+08
B B-3S B-1.5S-1E B-4.5S B-2.25S-1E
1.E+07 1.E+06 1.E+05 1.E+04 1.E+03 1.E+02 0
10
20
30
40
50
60
70
80
Temperature ( oC) Fig. 5. Curve of complex shear modulus (G⁄) versus temperature for base and PMBs at 1.9355 Hz.
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Phase angle (degrees)
90 85 80 75 70 65 60 B B-3S B-1.5S-1E B-4.5S B-2.25S-1E
55 50 45 40 0
10
20
30
40
50
60
70
80
Temperature ( oC) Fig. 6. Curve of phase angle (d) versus temperature for base and PMBs at 0.1 Hz.
Phase angle (degrees)
85 80 75 70 65 60 B B-3S B-1.5S-1E B-4.5S B-2.25S-1E
55 50 45 40 0
10
20
30
40
50
60
70
80
Temperature ( oC) Fig. 7. Curve of phase angle (d) versus temperature for base and PMBs at 0.72115 Hz.
Phase angle (degrees)
80 75 70 65 60 B B-3S B-1.5S-1E B-4.5S B-2.25S-1E
55 50 45 40 0
10
20
30
40
50
60
70
80
Temperature ( oC) Fig. 8. Curve of phase angle (d) versus temperature for base and PMBs at 1.9355 Hz.
1.E+07 B B-3S B-1.5S-1E B-4.5S B-2.25S-1E
G*/sin (Pa)
1.E+06 1.E+05 1.E+04 1.E+03 1.E+02 1.E+01 0
10
20
30
40
50
60
70
Temperature ( oC) Fig. 9. Curve of G⁄/sin d versus temperature for base and PMBs at 0.1 Hz.
80
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P. Ahmedzade / Construction and Building Materials 38 (2013) 285–291
1.E+07 B B-3S B-1.5S-1E B-4.5S B-2.25S-1E
G*/sin (Pa)
1.E+06 1.E+05 1.E+04 1.E+03 1.E+02 1.E+01 0
10
20
30
40
50
60
70
80
Temperature ( oC) Fig. 10. Curve of G⁄/sin d versus temperature for base and PMBs at 0.72115 Hz.
1.E+08 B B-3S B-1.5S-1E B-4.5S B-2.25S-1E
G*/sin (Pa)
1.E+07 1.E+06 1.E+05 1.E+04 1.E+03 1.E+02 0
10
20
30
40
50
60
70
80
Temperature ( oC) Fig. 11. Curve of G⁄/sin d versus temperature for base and PMBs at 1.9355 Hz.
Table 6 Creep stiffness and m-value of the binders at a loading time of 60 s and different temperatures. Binder types
B B-3S B-1.5S-1E B-4.5S B-2.25S-1E
Creep stiffness (MPa)
m-value
15 °C
25 °C
35 °C
15 °C
25 °C
35 °C
67.6087 51.8939 50.5037 39.1204 37.3053
265.6285 218.6787 212.1806 172.2082 164.9458
555.5819 479.7824 464.0381 444.0802 416.8523
0.356604 0.393607 0.412190 0.430611 0.454496
0.303768 0.322522 0.343140 0.345559 0.353863
0.292394 0.309587 0.320034 0.323589 0.335751
mers on rutting resistance of bitumen binders, all binders were subjected to DSR test according to parameters given in Table 5. Complex shear modulus (G⁄) is determined as a result of the DSR experiments by applying stress at different frequencies on pure and PMBs samples. The relationship between the complex shear modulus and the temperature is shown in Figs. 3–5. These figures show that complex shear modulus data of the PMBs are higher than of pure bitumen. These high values indicate that additives make binders stiffer, consequently, increase their resistance to deformation. Comparing modified binders to each other, G⁄ values of B-1.5S-1E and B-2.25S-1E are higher than of B-3S and B-4.5S, respectively. Changes in values of phase angles to different test temperatures are illustrated in Figs. 6–8. The phase angles data of PMBs have lower values than of pure bitumen. The decrease in phase angle values obtained by polymer modification is an indicator of increasing in binder elastic properties and of reduction in binder permanent deformation occurred as a result of applied stress. Changes in rutting parameters (G⁄/sin d) to temperature increases is shown in Figs. 9–11. From Fig. 9 it is clear seen that rutting parameters of SBS and SBS + EntiraÒBond 8 PMBs are higher than of unmodified binders at low frequency. Increases tend to
be similar at medium and high frequencies. G⁄/sin d results values of B-1.5S-1E and B-2.25S-1E are higher than of B-3S and B-4.5S, respectively. These results show that SBS and EntiraÒBond 8 polymers together have more considerable effects on rutting resistance of base bitumen than only SBS. Considering the results obtained by all DSR tests it is seen that B-2.25S-1E binder exhibits increases in complex shear modulus (G⁄) values and rutting parameters (G⁄/sin d), and has more decreased phase angle values compared to all binders used in this study, consequently, using SBS and EntiraÒBond 8 polymers together in these ratios considerably improve elastic properties and rutting resistance of bitumen. 3.4. BBR test results To study influence of polymer additives on the low-temperature creep responses of bitumen, the bending beam rheometer test was employed at different loading times (8, 15, 30, 60, 120 and 240 s) and temperatures (35, 25 and 15 °C). Table 6 compares creep stiffness and m-value obtained at three temperatures and at a loading time of 60 s. This table shows that the polymer modified binders display lower creep stiffness than base bitumen, especially at
P. Ahmedzade / Construction and Building Materials 38 (2013) 285–291
temperatures lower than 15 °C. Comparing modified binders to each other it can be noted that B-1.5S-1E and B-2.25S-1E have better values of creep stiffness and m-value than B-3S and B-4.5S, respectively. Low stiffness values, shown by SBS + EntiraÒBond 8 PMBs, indicate that the asphalt mix produced using these binders may be less susceptible to low-temperature cracking. 4. Conclusions The following conclusions can be drawn based on the results obtained in the study: Conventional binder properties such as penetration, softening point and Fraas temperature of different PMB groups demonstrated that SBS and SBS + EntiraÒBond 8 polymers increase stiffness (hardness) and improve susceptibility of pure bitumen to temperature changes. In addition to conventional tests methods, which are generally unable to quantitate the unique rhelogical characteristics of PMB groups, RV, DSR, and BBR tests were performed to determine more fundamental rheologic parameters. RV test results showed the stiffening effect of polymer modifications on the pure bitumen, especially of SBS + EntiraÒBond 8 polymers modification. The results obtained from all DSR tests exhibit that B-2.25S-1E binder has increased complex shear modulus (G⁄) values and rutting parameters (G⁄/sin d), and has decreased phase angle (d) values compared to all binders used in this study. And hence it can be noted that SBS and EntiraÒBond 8 polymers together in these ratios considerably improve elastic properties and rutting resistance of bitumen. Creep stiffness (the creep stress resistance of the binders) and creep ratio (the change in the stiffness of the binders during loading) values obtained by BBR tests were evaluated to check the effect of polymer modifications on pure bitumen. According to these values it can be concluded that polymer modified binders display lower creep stiffness than base bitumen and if compared to each other modified binders B-1.5S-1E and B-2.25S-1E have better values of creep stiffness and m-value than B-3S and B-4.5S, respectively. Based on the results of investigation of rheologic properties PMBs it can be noted that SBS + EntiraÒBond 8 polymers reduce temperature susceptibility of bitumen what in its turn allows to increase the stiffness of the binder at high pavement service temperatures in order to reduce rutting and, at the same time, to decrease the creep stiffness of the binder at low pavement temperatures in order to reduce brittleness and cracking.
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References [1] King G et al. Additives in asphalt. J Assoc Asphalt Paving Technol A 1999;68:32–69. [2] Yousefi A. Rubber-polyethylene modified mitumens. Iran Polym J 2004;12:101–12. [3] Ahmedzade P, Yilmaz M. Effect of polyester resin additive on the properties of asphalt binders and mixtures. Constr Build Mater 2008;22:481–6. [4] Gorkem C, Sengoz B. Predicting stripping and moisture induced damage of asphalt concrete prepared with polymer modified bitumen and hydrated lime. Constr Build Mater 2009;23(6):2227–36. [5] Airey GD. Rheological evaluation of ethylene vinyl acetate polymer modified bitumens. Constr Build Mater 2002;16:473–87. [6] Lu X, Isacsson U, Ekblad J. Low-temperature properties of styrene–butadiene– styrene polymer modified bitumens. Constr Build Mater 1998;12:4405–14. [7] Iskender E, Aksoy A, Ozen H. Indirect performance comparison for styrene– butadiene–styrene polymer and fatty amine anti-strip modified asphalt mixtures. Constr Build Mater 2012;30:117–24. [8] Airey GD. Rheological properties of styrene butadiene styrene polymer modified road bitumens. Fuel 2003;14:1709–19. [9] Lu X, Isacsson U. Rheological characterization of styrene–butadiene–styrene copolymer modified bitumens. Constr Build Mater 1997;11:23–32. [10] Babcock G. New Jersey APA annual conference. [available 11.03.09]. [11] Preparing blends of Kraton D polymers and bitumen. Shell Tech Bull 1995. [12] Whiteoak D, Read JM. The Shell bitumen handbook. London: Thomas Telford Services Ltd.; 2003. [13] Anderson DA, Christensen DW, Bahia HU, Dongre R, Sharma MG, Antle CE, et al. Binder characterization and evaluation. Physical characterization, vol. 3. Strategic highway research program report no. SHRP-A-369. Washington (DC): National Research Council; 1994. [14] Petersen, JC, Robertson RE, Branthaver JF, Harnsberger PM, Duvall JJ, Kim SS, et al. Binder characterization and evaluation. Test methods, vol. 4. Strategic highway research program report no. SHRP-A-370. Washington (DC): National Research Council; 1994. [15] Roberts FL, Kandhal PS, Brown ER, Lee D, Kennedy TW. Hot mix asphalt materials, mixture design and construction. Lanham (MD): NAPA Research and Education Foundation; 1996. [16] Bahia HU, Anderson DA. Strategic highway research program binder rheological parameters: background and comparison with conventional properties. Transportation research record 1488 TRB. Washington (DC): National Research Council; 1995. p. 32–9. [17] Kennedy TW, Huber GA, Harrigan ET, Cominsky RJ, Hughes CS, Quintus HV, et al. Superior performing asphalt pavements (Superpave): the product of the SHRP asphalt research program SHRP-A-410. Washington (DC 170): National Research Council; 1994. [18] Bahia HU, Anderson DA. The development of the bending beam rheometer; basics and critical evaluation of the rheometer. ASTM Spec Publ 1995;STP 1241:28–50. [19] Bahia HU, Anderson DA, Christensen DW. The bending beam rheometer; a simple device for measuring low-temperature rheology of asphalt binders. Proc J Assoc Asphalt Paving Technol 1992;61:117–53. [20] Lu X, Isacsson U. Characterization of SBS polymer modified bitumen – comparison of conventional methods and DMA. J Testing Evaluat 1997:383–90.
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Construction and Building Materials journal homepage: www.elsevier.com/locate/conbuildmat
The investigation and comparison effects of SBS and SBS with new reactive terpolymer on the rheological properties of bitumen Perviz Ahmedzade ⇑ Department of Civil Engineering, Ege University, Izmir, Turkey
h i g h l i g h t s Ò
" The effect of styrene–butadiene–styrene (SBS) and SBS + Entira Bond 8 additives on characteristics of bitumen was investigated. " The results showed that both polymers groups reduce temperature susceptibility of bitumen. Ò
" SBS + Entira Bond 8 modifications improved the properties of bitumen better than just SBS modifications.
a r t i c l e
i n f o
Article history: Received 8 April 2012 Received in revised form 16 July 2012 Accepted 23 July 2012 Available online 29 September 2012 Keywords: Bitumen Polymer–modified bitumen Reactive terpolymer Styrene–butadiene–styrene Rutting resistance
a b s t r a c t The effects of styrene–butadiene–styrene (SBS) and SBS with new reactive terpolymer (EntiraÒBond 8) modifications on the rheological properties of pure bitumen were investigated and compared to each other. Four polymer modified bitumens (PMBs) were produced by mixing bitumen with SBS at two polymer contents and with SBS + EntiraÒBond 8 at the same polymer contents. The rheologic characteristics of the PMBs were analyzed by means of conventional test methods like penetration, softening point and Fraas breaking point as well as rotational viscometer (RV), dynamic shear rheometer (DSR) and bending beam rheometer (BBR) test methods. Conventional binder properties of different PMB groups demonstrated that the polymers increase stiffness (hardness) and improve susceptibility of pure bitumen to temperature changes. Both polymers groups improve properties of bitumen, such as increased elastic responses (increased complex shear modulus and decreased phase angle) at low to high temperatures and reduced creep stiffness at low temperatures. Based on the results of this investigation it can be noted that SBS + EntiraÒBond 8 modifications improved the conventional and more fundamental properties of bitumen better than just SBS modifications. Ó 2012 Elsevier Ltd. All rights reserved.
1. Introduction An asphalt concrete road consists of a choice of different sizes of aggregate held together by bitumen. The bitumen only makes up 5–7% by weight or approximately 15% by volume of the asphalt concrete mix. Despite this small percentage, the performance of the bitumen has a significant influence on the long term performance of a road. The bitumen used in flexible pavements exhibits elastic behavior at low temperatures and under high speed vehicles where as viscous behavior at high temperatures and under low speed vehicles. Under normal conditions and intermediate temperatures, the bitumen shows viscoelastic behavior. In order to accommodate increasing traffic loadings as well as resist temperature changes, specific polymer based additives are utilized. Pavement with polymer modification exhibits greater ⇑ Tel.: +90 533 7212423; fax: +90 232 3425629. E-mail address: [email protected] 0950-0618/$ - see front matter Ó 2012 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.conbuildmat.2012.07.090
resistance to rutting and thermal cracking, and decreased fatigue damage, stripping and temperature susceptibility. Polymer modified binders have been used with success at locations of high stress, such as intersections of busy streets, airports, vehicle weigh stations, and race tracks [1–5]. Among these additives, the most commonly used polymer is elastomeric type styrene–butadiene–styrene (SBS) copolymer. SBS copolymers consist of block segments of styrene monomer units and butadiene rubber monomer units. Each block segment can consist of many monomer units. The most common form used in bitumen modification is a linear styrene–butadiene–styrene structure, but radial types are also available. The content, structure of SBS, structure of base bitumen as well as the mixing time and temperature are important factors that should be taken into account in the production of SBS polymer modified bitumen (PMB). Recent studies indicate that pavement with SBS polymer modification exhibits greater resistance to
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Table 1 Properties of the base bitumen. Test
Specification
Results
Specification limits
Penetration (25 °C; 0.1 mm) Softening point (°C) Fraas breaking point (°C) Penetration index (PI)
ASTM D5 ASTM D36 IP 80 –
130 45.7 20 0.33
100–150 39–47 max12 –
permanent deformation at hot climates, cracking at low temperatures and fatigue cracking due to the increased bitumen stiffness [6–9]. The temperature is an extremely important factor in the structure of the SBS polymer modified bitumen. After production, care must be taken in order to hold the polymer modified bitumen under constant temperature since the SBS can be easily decomposed from the base bitumen and is not appropriate for storage. Not holding the final product under required level of temperature can lead to adhesion, decomposition and frost problems. Besides the SBS is an expensive additive. In order to raise the efficiency of bitumen modification, to decrease the production cost as well as to increase the storage stability properties of SBS modified bitumens without additional heating procedures, DuPont Company produced a new reactive terpolymer (EntiraÒBond 8) to be used with SBS. The utilization of the EntiraÒBond 8 decreases the SBS polymer consumption by almost 50% which makes this additive a cost effective polymer [10]. This study aims to investigate and compare effects of SBS and SBS with EntiraÒBond 8 on the rheologic properties of bitumen. 2. Experimental 2.1. Materials The base bitumen with a 100/150 penetration grade has been procured from Turkish Petroleum Refineries Corporation (TUPRAS). Table 1 gives a summary of the results of some tests performed on the base bitumen. The SBS polymer used was Kraton D-1101 supplied by the Shell Chemicals Company. Kraton D-1101 is a linear SBS polymer in powder form that consists of different combinations made from blocks polystyrene (31%) and polybutadiene of a very precise molecular weight [11]. These blocks are either sequentially polymerized from styrene and butadiene and/or coupled to produce a mixture of these chained blocks. The reactive terpolymer EntiraÒBond 8 was provided by DuPont Company. 2.2. Preparation of samples The SBS Kraton D-1101 concentrations in the base bitumen were chosen as 3% and 4.5% by weight. In preparation, the base bitumen was heated to fluid condition (180–185 °C), and has been poured into a 2000 ml spherical flask. Then the SBS polymer was added slowly to the base bitumen. The SBS modified bitumen samples were prepared by means of laboratory type mixer rotating at 500 rpm. On reaching temperature of 190 °C, the temperature has been kept constant and the mixing process continued for 2 h. The SBS Kraton D-1101 concentrations in the base bitumen replaced half of the SBS polymer contents (1.5% and 2.25%) and then EntiraÒBond 8 was added to SBS modified bitumens to prepare SBS with EntiraÒBond 8 modified bitumen samples.
Concentration of EntiraÒBond 8 was chosen as 1% according to the manufacturers (DuPont Company). Conditions of preparing process of SBS with EntiraÒBond 8 modified bitumen specimens such as temperature, speed and time of mixing used were the same as in preparation of SBS modified bitumen samples. After complete blending for 2 h, the blended samples were cured for 2 h at 190 °C to achieve chemical reaction which allowed to create permanently modified binders. The uniformity of dispersion of polymers in the base bitumen was confirmed by passing the mixture through an ASTM 100# sieve. After completion, the samples were removed from the flask and divided into small containers, covered with aluminum foil and stored for testing. The different binders were coded as follows:
base base base base base
2.3. Testing program 2.3.1. Conventional bitumen tests The unmodified and modified bitumens were subjected to the following conventional bitumen tests: penetration, softening point and Fraass breaking point. In addition, the temperature susceptibility of the modified bitumen samples has been calculated in terms of penetration index (PI) using the results obtained from penetration and softening point tests. Temperature susceptibility is defined as the change in the consistency parameter as a function of temperature. A classical approach related to PI calculation has been given in the Shell Bitumen Handbook [12] as shown with the following equation:
PI ¼
1952 500 logðPen25 Þ 20 SP 50 logðPen25 Þ SP 120
Oscillating Plate
ð1Þ
where, Pen25 is the penetration at 25 °C and SP is the softening point temperature of bitumen. 2.3.2. Rotational viscosity test The rotational viscometer determines the bitumen viscosity by measuring the torque necessary to maintain a constant rotational speed of a cylindrical spindle submerged in a bitumen specimen held at a constant temperature, as per the AASHTO TP48 standard test method. Unlike the capillary viscometers used with the viscosity-graded method, the rotational viscometer can evaluate modified bitumen binders [13]. The viscosity of bitumen binders can be measured within the range of 0.01 Pa s (0.1 poise) to 200 Pa s (2000 poise) [14]. The Asphalt Institute recommends taking the first viscosity measurement at 135 °C, and the second at 165 °C. A Brookfield viscometer (DV-III) was used for the viscosity tests on the base and modified bitumens. 2.3.3. Dynamic shear rheometer test The dynamic shear rheometer (DSR) was adopted to characterize the viscoelastic behavior of bitumen binders at low and at intermediate to high service temperatures. The DSR provides an indication of the rutting resistance of bitumen immediately following construction. Resistance to rutting at high service temperatures in the early stages of pavement life is also evaluated [15,16]. The DSR evaluates the behavior of a bitumen specimen by subjecting it to oscillatory (sinusoidal) stresses. The AASHTO TP5 standard test method requires that a thin bitumen specimen be sandwiched between two parallel metal plates held in a constant temperature medium. One plate remains fixed while the other oscillates, at an angular frequency (x) of 10 radians per second for 10 cycles, with respect to the other. A complete DSR loading cycle is shown in Fig. 1 [15]. When torque from the DSR motor is applied, the oscillating plate moves from point A to point B. The plate then passes back through point A to point C. The cycle of oscillation is completed as the plate passes back through point A again. The spin-
Position of Oscillating Plate
Applied Stress
bitumen – ‘‘B’’; bitumen + 3%SBS – ‘‘B-3S’’; bitumen + 1.5%SBS + 1% EntiraÒBond 8 – ‘‘B-1.5S-1E’’ bitumen + 4.5%SBS – ‘‘B-4.5S’’; bitumen + 2.25%SBS + 1% EntiraÒBond 8 – ‘‘B-2.25S-1E’’.
B
Fixed Plate
A
Asphalt B
A
A A
Time
C
C 1 cycle Fig. 1. Configuration and load cycle of dynamic shear rheometer [15].
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P. Ahmedzade / Construction and Building Materials 38 (2013) 285–291 dle is oscillated back and forth using either a constant stress or constant strain. Constant stress means that the spindle is rotated through a certain distance until a fixed stress is achieved. Constant strain means that the spindle is rotated every time through a fixed distance, regardless of the stress achieved. While this rotation occurs, the resulting strain or stress is monitored. The relationship between the applied stress and the resulting strain provides information necessary to compute complex shear modulus (G⁄) and phase angle (d). A higher G⁄ and a lower d are desired for rutting resistance. The bitumen with a high G⁄ is stiffer and provides increased resistance to deformation. The bitumen exhibiting a lower d has a greater elastic component, thus allowing more of the total deformation to be recovered. The relationship G⁄/sin d was chosen as the parameter for SHRP specifications with respect to rutting resistance of bitumen binders [16]. For specification purposes, the frequency is 10 radians per second which has been related to a traffic speed of 100 km/h. For slower moving traffic, a lower frequency could be used for evaluation of a proposed product. For example, with city street traffic a frequency of 5 radians per second could be used (corresponding to 50 km/h); for standing traffic, a very low frequency, such as 1 radian per second might be appropriate [17]. 2.3.4. Bending beam rheometer test The bending beam rheometer (BBR) was used to measure the low-temperature creep stiffness and logarithmic creep rate of the bitumen binder. In this test, a beam of bitumen binder 125 mm long, 12.5 mm wide, and 6.25 mm thick is formed by pouring binder into a mold and allowing it to cool. This beam is placed in a lowtemperature bath to equilibrate its temperature to the desired test temperature. During testing, which must be accomplished within 60 min of placing the beam in the bath, the beam is placed on two simple supports having a span of 100 mm. A constant load of 980mN, maintained for 240 s, was applied to the center of the simply supported beam. The creep stiffness, S, and the creep rate (slope, m) of the relationship between log (stiffness) and log (time) were measured at 60 s (loading time). The loading geometry of the BBR is shown in Fig. 2. The BBR test measures creep stiffness value at the lowest in-service temperature, S(t) as designated by SHRP, which is indicative of the susceptibility to lowtemperature cracking. The rate of change of binder stiffness with time is represented by the m-value, which is the slope of the log stiffness versus log time curve from the BBR test results. A high m-value is desired because as the temperature decreases and pavement contraction begins to occur, the binder will respond as a material that is less stiff. This decrease in stiffness leads to smaller tensile stresses in the binder and less chance for low-temperature cracking. For an adequate low temperature cracking resistance the creep stiffness must be less than 300 MPa and the m-value must be greater than 0.3 [18,19].
3. Results and discussion 3.1. Conventional bitumen tests The results obtained using conventional test methods are summarized in Table 2. This table shows that polymer modified speci-
Table 2 Changes in conventional binder properties following polymers modifications. Properties
Penetration (25°C; 0.1 mm) Softening point (°C) Penetration index (PI) Fraas breaking point (°C)
Binder types B
B-3S
B-1.5S-1E
B-4.5S
B-2.25S-1E
130
71
69
54
51
45.7
53.6
55
58
60
0.32
0.56
0.81
0.81
1.08
20
22.1
23
24
25.6
mens have decreased penetration and increased softening point in comparison with unmodified specimens. In addition, it can be noted that SBS + EntiraÒBond 8 polymers modifications further decrease penetration and further increase softening point of base bitumen compared to only SBS polymer modifications. The increase in softening point (which is an indicator of the stiffening effect of PMBs) is favorable since bitumen with higher softening point may be less susceptible to permanent deformation (rutting). Polymer modification reduces the temperature susceptibility of the bitumen. Lower values of PI indicate higher temperature susceptibility. Asphalt mixtures containing bitumen with higher PI are more resistant to low temperature cracking as well as permanent deformation [20]. Table 2 also shows the effects of the SBS and SBS + EntiraÒBond 8 polymers on the penetration index of bitumen. It is clearly seen that polymer modified bitumens have increased PI values compared to pure bitumen. Increased PI indicates a significant reduction in temperature susceptibility of binders. The Fraass breaking point results show that polymers have the considerable influence on the low temperature physical properties of base bitumen. The reduction in Fraass breaking point indicates an increased low temperature flexibility of the PMBs. The increase in softening point and the decrease in Fraass breaking point values of polymer modified bitumens, means that polymer additives on the one side make bitumen stiffer and on the other side make it more elastic.SBS and SBS + EntiraÒBond 8 modified binders were compared to each other and it is clearly seen that B-1.5S-1E and B-2.25S-1E have better results than B-3S and B-4.5S, respectively. Among the all tested binders, B-2.25S-1E binder exhibits the best results.
3.2. RV test results
Fig. 2. Loading geometry of the bending beam rheometer.
Rotational viscosities (g) and modification indices (g for PMB divided by g for the base bitumen) at 135 °C and 165 °C for the all binders used in this study are shown in Table 3. The viscosity of bitumen blends increases with increasing the content of polymer additives at both temperature conditions. From comparing of four PMBs blends to each other it can be seen that both blends have relatively similar viscosity values at 135 °C, but with increasing temperature to 165 °C, viscosities of SBS PMBs are more de-
Table 3 Rotational viscosities following polymers modifications. Binder types
Rotational viscosity at 135 °C (cP)
Rotational viscosity at 165 °C (cP)
gPMB/ gBitumen at 135 °C
gPMB/ gBitumen at 165 °C
B B-3S B-1.5S-1E B-4.5S B-2.25S-1E
375 1110 1115 1775 1790
125 325 370 575 630.5
1.00 2.93 2.97 4.73 4.77
1.00 2.6 2.96 4.6 5.04
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Table 4 Traffic speeds equivalent frequencies.
Table 5 DSR test parameters.
Traffic speed, km/h
Traffic speeds equivalent frequencies, Hz (rad/s)
Test parameters
Low, 6 km/h Medium, 45 km/h High, 120 km/h
0.1 Hz (0.628 rad/s) 0.72115 Hz (4.53 rad/s) 1.9355 Hz (12.15494 rad/s)
Mode of loading
Controlled-strain
Frequencies, Hz (rad/sn)
0.1 Hz (0.628 rad/s), 0.72115 Hz (4.53 rad/s), 1.9355 Hz (12.15494 rad/s) 10, 15, 20, 30, 35, 40, 45, 50, 55, 60, 65, 70, 25 75 8 25 2 1
Temperatures, °C
creased than ones of SBS + EntiraÒBond 8 PMBs. As with the penetration and softening point tests, the viscosities give a clear indication of the stiffening effect of both polymers modification, especially of SBS + EntiraÒBond 8 modification. 3.3. DSR test results The rheologic properties of the binders at low and at intermediate to high temperatures are obtained from the Dynamic Shear
Diameter spindle, mm Testing gap, mm
Rheometer (DSR). In this study, two different spindle diameters and testing gaps were selected depending on test temperature ranges. Table 4 shows frequencies used in the test procedure which were accepted as equivalent to different frequencies of traffic. In order to determine the effect of SBS and SBS + EntiraÒBond 8 poly-
Complex modulus (Pa)
1.E+07 B B-3S B-1.5S-1E B-4.5S B-2.25S-1E
1.E+06 1.E+05 1.E+04 1.E+03 1.E+02 1.E+01 0
10
20
30
40
50
60
70
80
Temperature ( oC) Fig. 3. Curve of complex shear modulus (G⁄) versus temperature for base and PMBs at 0.1 Hz.
Complex modulus (Pa)
1.E+07
B B-3S B-1.5S-1E B-4.5S B-2.25S-1E
1.E+06 1.E+05 1.E+04 1.E+03 1.E+02 1.E+01 0
10
20
30
40
50
60
70
80
Temperature ( oC) Fig. 4. Curve of complex shear modulus (G⁄) versus temperature for base and PMBs at 0.72115 Hz.
Complex modulus (Pa)
1.E+08
B B-3S B-1.5S-1E B-4.5S B-2.25S-1E
1.E+07 1.E+06 1.E+05 1.E+04 1.E+03 1.E+02 0
10
20
30
40
50
60
70
80
Temperature ( oC) Fig. 5. Curve of complex shear modulus (G⁄) versus temperature for base and PMBs at 1.9355 Hz.
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Phase angle (degrees)
90 85 80 75 70 65 60 B B-3S B-1.5S-1E B-4.5S B-2.25S-1E
55 50 45 40 0
10
20
30
40
50
60
70
80
Temperature ( oC) Fig. 6. Curve of phase angle (d) versus temperature for base and PMBs at 0.1 Hz.
Phase angle (degrees)
85 80 75 70 65 60 B B-3S B-1.5S-1E B-4.5S B-2.25S-1E
55 50 45 40 0
10
20
30
40
50
60
70
80
Temperature ( oC) Fig. 7. Curve of phase angle (d) versus temperature for base and PMBs at 0.72115 Hz.
Phase angle (degrees)
80 75 70 65 60 B B-3S B-1.5S-1E B-4.5S B-2.25S-1E
55 50 45 40 0
10
20
30
40
50
60
70
80
Temperature ( oC) Fig. 8. Curve of phase angle (d) versus temperature for base and PMBs at 1.9355 Hz.
1.E+07 B B-3S B-1.5S-1E B-4.5S B-2.25S-1E
G*/sin (Pa)
1.E+06 1.E+05 1.E+04 1.E+03 1.E+02 1.E+01 0
10
20
30
40
50
60
70
Temperature ( oC) Fig. 9. Curve of G⁄/sin d versus temperature for base and PMBs at 0.1 Hz.
80
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1.E+07 B B-3S B-1.5S-1E B-4.5S B-2.25S-1E
G*/sin (Pa)
1.E+06 1.E+05 1.E+04 1.E+03 1.E+02 1.E+01 0
10
20
30
40
50
60
70
80
Temperature ( oC) Fig. 10. Curve of G⁄/sin d versus temperature for base and PMBs at 0.72115 Hz.
1.E+08 B B-3S B-1.5S-1E B-4.5S B-2.25S-1E
G*/sin (Pa)
1.E+07 1.E+06 1.E+05 1.E+04 1.E+03 1.E+02 0
10
20
30
40
50
60
70
80
Temperature ( oC) Fig. 11. Curve of G⁄/sin d versus temperature for base and PMBs at 1.9355 Hz.
Table 6 Creep stiffness and m-value of the binders at a loading time of 60 s and different temperatures. Binder types
B B-3S B-1.5S-1E B-4.5S B-2.25S-1E
Creep stiffness (MPa)
m-value
15 °C
25 °C
35 °C
15 °C
25 °C
35 °C
67.6087 51.8939 50.5037 39.1204 37.3053
265.6285 218.6787 212.1806 172.2082 164.9458
555.5819 479.7824 464.0381 444.0802 416.8523
0.356604 0.393607 0.412190 0.430611 0.454496
0.303768 0.322522 0.343140 0.345559 0.353863
0.292394 0.309587 0.320034 0.323589 0.335751
mers on rutting resistance of bitumen binders, all binders were subjected to DSR test according to parameters given in Table 5. Complex shear modulus (G⁄) is determined as a result of the DSR experiments by applying stress at different frequencies on pure and PMBs samples. The relationship between the complex shear modulus and the temperature is shown in Figs. 3–5. These figures show that complex shear modulus data of the PMBs are higher than of pure bitumen. These high values indicate that additives make binders stiffer, consequently, increase their resistance to deformation. Comparing modified binders to each other, G⁄ values of B-1.5S-1E and B-2.25S-1E are higher than of B-3S and B-4.5S, respectively. Changes in values of phase angles to different test temperatures are illustrated in Figs. 6–8. The phase angles data of PMBs have lower values than of pure bitumen. The decrease in phase angle values obtained by polymer modification is an indicator of increasing in binder elastic properties and of reduction in binder permanent deformation occurred as a result of applied stress. Changes in rutting parameters (G⁄/sin d) to temperature increases is shown in Figs. 9–11. From Fig. 9 it is clear seen that rutting parameters of SBS and SBS + EntiraÒBond 8 PMBs are higher than of unmodified binders at low frequency. Increases tend to
be similar at medium and high frequencies. G⁄/sin d results values of B-1.5S-1E and B-2.25S-1E are higher than of B-3S and B-4.5S, respectively. These results show that SBS and EntiraÒBond 8 polymers together have more considerable effects on rutting resistance of base bitumen than only SBS. Considering the results obtained by all DSR tests it is seen that B-2.25S-1E binder exhibits increases in complex shear modulus (G⁄) values and rutting parameters (G⁄/sin d), and has more decreased phase angle values compared to all binders used in this study, consequently, using SBS and EntiraÒBond 8 polymers together in these ratios considerably improve elastic properties and rutting resistance of bitumen. 3.4. BBR test results To study influence of polymer additives on the low-temperature creep responses of bitumen, the bending beam rheometer test was employed at different loading times (8, 15, 30, 60, 120 and 240 s) and temperatures (35, 25 and 15 °C). Table 6 compares creep stiffness and m-value obtained at three temperatures and at a loading time of 60 s. This table shows that the polymer modified binders display lower creep stiffness than base bitumen, especially at
P. Ahmedzade / Construction and Building Materials 38 (2013) 285–291
temperatures lower than 15 °C. Comparing modified binders to each other it can be noted that B-1.5S-1E and B-2.25S-1E have better values of creep stiffness and m-value than B-3S and B-4.5S, respectively. Low stiffness values, shown by SBS + EntiraÒBond 8 PMBs, indicate that the asphalt mix produced using these binders may be less susceptible to low-temperature cracking. 4. Conclusions The following conclusions can be drawn based on the results obtained in the study: Conventional binder properties such as penetration, softening point and Fraas temperature of different PMB groups demonstrated that SBS and SBS + EntiraÒBond 8 polymers increase stiffness (hardness) and improve susceptibility of pure bitumen to temperature changes. In addition to conventional tests methods, which are generally unable to quantitate the unique rhelogical characteristics of PMB groups, RV, DSR, and BBR tests were performed to determine more fundamental rheologic parameters. RV test results showed the stiffening effect of polymer modifications on the pure bitumen, especially of SBS + EntiraÒBond 8 polymers modification. The results obtained from all DSR tests exhibit that B-2.25S-1E binder has increased complex shear modulus (G⁄) values and rutting parameters (G⁄/sin d), and has decreased phase angle (d) values compared to all binders used in this study. And hence it can be noted that SBS and EntiraÒBond 8 polymers together in these ratios considerably improve elastic properties and rutting resistance of bitumen. Creep stiffness (the creep stress resistance of the binders) and creep ratio (the change in the stiffness of the binders during loading) values obtained by BBR tests were evaluated to check the effect of polymer modifications on pure bitumen. According to these values it can be concluded that polymer modified binders display lower creep stiffness than base bitumen and if compared to each other modified binders B-1.5S-1E and B-2.25S-1E have better values of creep stiffness and m-value than B-3S and B-4.5S, respectively. Based on the results of investigation of rheologic properties PMBs it can be noted that SBS + EntiraÒBond 8 polymers reduce temperature susceptibility of bitumen what in its turn allows to increase the stiffness of the binder at high pavement service temperatures in order to reduce rutting and, at the same time, to decrease the creep stiffness of the binder at low pavement temperatures in order to reduce brittleness and cracking.
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References [1] King G et al. Additives in asphalt. J Assoc Asphalt Paving Technol A 1999;68:32–69. [2] Yousefi A. Rubber-polyethylene modified mitumens. Iran Polym J 2004;12:101–12. [3] Ahmedzade P, Yilmaz M. Effect of polyester resin additive on the properties of asphalt binders and mixtures. Constr Build Mater 2008;22:481–6. [4] Gorkem C, Sengoz B. Predicting stripping and moisture induced damage of asphalt concrete prepared with polymer modified bitumen and hydrated lime. Constr Build Mater 2009;23(6):2227–36. [5] Airey GD. Rheological evaluation of ethylene vinyl acetate polymer modified bitumens. Constr Build Mater 2002;16:473–87. [6] Lu X, Isacsson U, Ekblad J. Low-temperature properties of styrene–butadiene– styrene polymer modified bitumens. Constr Build Mater 1998;12:4405–14. [7] Iskender E, Aksoy A, Ozen H. Indirect performance comparison for styrene– butadiene–styrene polymer and fatty amine anti-strip modified asphalt mixtures. Constr Build Mater 2012;30:117–24. [8] Airey GD. Rheological properties of styrene butadiene styrene polymer modified road bitumens. Fuel 2003;14:1709–19. [9] Lu X, Isacsson U. Rheological characterization of styrene–butadiene–styrene copolymer modified bitumens. Constr Build Mater 1997;11:23–32. [10] Babcock G. New Jersey APA annual conference.