The Inﬂuence of SBS, Viatop Premium and FRP on the Improvement of Stone Mastic Asphalt Performance

: The current study investigates the e ﬀ ects of Fiber Reinforce Polymer (FRP) additive on the performance of Stone Mastic Asphalt (SMA) mixtures with SBS and Viatop Premium additives. The asphalt mixture used in the current study included SBS (Styrene-Butadiene-Styrene) additive modiﬁed at the rate of 5% according to the necessary preliminary studies, and some SMA mixture modiﬁed by adding FRP (Fiber Reinforced Polymers) additive prepared in dimensions of 5 cm in di ﬀ erent proportions (0.3%, 0.5%, 0.7% and 0.9%). The mechanical properties of the mixtures were investigated, and the ﬁndings revealed that the SMA mixture; prepared by adding FRP additive, SBS modiﬁed bitumen, and Viatop Premium additive; increased the rutting, aging resistance and elasticity of SMAs. Moreover, load spread ability and fatigue life revealed an increase, whereas high temperature sensitivity and tendency to crack at low temperatures decreased throughout the study. The FRP contribution rate that improves the performance characteristics of the SMA mixture to the highest level was found to be 0.7%.


Introduction
The increase in traffic and heavy loads, and consequently the collapse of roads earlier than their term of service, leads researchers to consider improving the performance of asphalt mixtures as an important issue. They are working on new types of asphalt concrete, frequently hollow aggregate size and distribution, generally produced by low penetration and modified binder. SMA (Stone Mastic Asphalt), which is a widely used product worldwide, is one of these effective asphalt mixtures. SMA has a good resistance against rutting [1]. In order to provide stone contact gap, graded aggregates are applied for the purpose of mixing, which results in big free spaces on the mixture. The increase in the free space of the asphalt mixture decreases its resistance. Thus, to avoid the free space problem, it is recommended to fill the empty space with bitumen filler and additives to maintain an acceptable amount of air. Unlike conventional hot asphalt in which all asphalt mixture components are involved in load transfer operations, in SMA mixes the skeletal system has a major aggregate load. Furthermore, the second advantage SMA mixtures is the use of bitumen, which has a high rut resistance, high skid resistance, high durability, improved resistance to reflective cracking, better drainage condition, and reduced noise pollution [2]. With the widespread use of SMA mixtures, additives and amounts added have also been the subject of many researches. Although the initial construction costs of SMAs are high, the low cost of road maintenance as a result of lower accident rates caused in roads under construction make them highly cost effective [3]. Recent studies have shown that cracks in SMA are less than HMA [4]. Based on prior research, SBS content has been an effective additive which has The asphalt cement used in the current study was AC-60/70, provided from Pasargad Oil Company, Tehran, Iran. Physiochemical properties of this cement are provided in Table 2. SBS copolymer was provided from a company in Germany. The Physical properties of SBS are shown in Table 3. The Viatop Premium used in this study was provided from JRS Company, Germany. Physiochemical properties of Viatop premium are presented in Table 4.  Table 5.

SMA Design
Generally, there are three present methods for bituminous mix design: Marshall method, Hveem method, and Superpave method. In Marshall Method design, which was used throughout Turkey, load is applied to a cylindrical specimen of bituminous mix and the sample is monitored until its failure, as specified in the ASTM standard [33]. To determine the optimum bitumen content according to the Marshall method, three samples were prepared for each asphalt concrete containing  4.5, 5, 5.5, 6, 6.5, and 7% bitumen. To make SMAs, the aggregates were heated up at 160 • C for 24 h. Bitumen was heated up to 160 • C to determine the optimum bitumen percentage mixture. Furthermore, Marshall hammer was applied to both sides of compacted Specimens of 50 impacts to stimulate heavy traffic. The optimum asphalt cement content for the SMA was found to be 6.9%, with some amount of SBS additive. Based on the previous researches [7,8,34], 5% of SBS (including the weight of binder) was selected for adding to the preheated binder (170 • C). In this research the Viatop premium content was considered 0.3% of the total mixture (recommended by manufacturer) and the FRP content was 3%, 5%, 7% and 9% of the weight of OBC. Since the addition of FRP to the binder did not provide a homogenous mixture, it was decided to add FRP additives of 5 cm dimensions to the mixture in order to obtain a homogenous mixture.

Marshall Quotient
The Marshall quotient reflects the rigidity and resistance of asphalt against deformation. As the proportion of this ratio increased, the strength of the mixture against deformations also goes up. In order to determine this ratio, the specimens are placed inside Marshall Jacket and pressurized, which is used for estimating Marshall Stability and flow values [35].

Moisture Damage
For each SMA mixture, 6 Marshall asphalt samples were made which were listed according to the specifications given in ASTM D 4867. Three samples were dried and three samples were immersed under saturated conditions and after passing the freezing and melting cycles, they were examined with indirect tensile strength test (ITS). Then, the tensile strength ratio (TSR) was calculated as [35]: In this formula, ITS calculates tensile strength (kPa) and P: max applied load (N), t: thickness of specimen (mm), and D: diameter of specimen (mm).
Based on Report No. 425 [36] mentioned in NCHRP, the Minimum value for TSR SMA mixtures should not be less than 70%.

Drain Down
The Schellenberger bitumen drain down test was used in the experimental phase of the current study. The Schellenberger experiments were performed at the optimum bitumen ratios for each mixture. Firstly, an empty glass beaker with the capacity of 1000 mL was weighed and then 1000 g of SMA mixture was prepared at 135 • C and weighed with 1000 mL glass beaker by placing the weighing scale on 0.1 g sensitivity. The beaker was then covered and was kept in an oven at 170 • C for 1 h. Then, the mixture was removed from the oven and discharged from the beaker without any movement. Aggregates were removed from the glass beaker in case of any adherence before weighing. During the first mixing phase of the experiment, the bitumen drain down was determined by computing the amount of bitumen [37].

Nicholson Test
The Nicholson test was carried out to determine the resistance of asphalt binder against the separation of the aggregates through the water effect [38]. Diameter between 9.5-6.3 mm 200 g was taken from crushed aggregates and was dried in an oven at 110 • C after a thorough wash. An amount of 100 ± 0.5 g of sample from washed and dried aggregate was then taken and left to stand in an oven at 140 • C-150 • C for 1 h. An amount of 5.0 ± 0.1 g of asphalt cement was then added to the aggregates and mixed until the aggregates were covered with asphalt. Finally, the mixture was discharged into two Petri dishes in equal amounts which were left to stand for 10 min at laboratory temperature and were then placed in trays containing pure water. A minimum of 3 cm water film was formed. Finally, the trays containing the Petri dishes were kept for 24 h in the oven at 60 • C, which were removed after 24 h, and samples were visually inspected under a light from the side [39,40].

Resilient Modulus
Resilient modulus test is an experiment to determine the flexibility of asphalt mixtures under dynamic loads. The test methods consist of applying the loads applied periodically and observing sudden deformations [41]. Resilient modulus (MR) of asphalt mixtures is usually measured in indirect tensile mode (ASTM D4123 [42]) and used to evaluate the elastic properties of asphalt concrete mixtures [43]. Three Marshall samples produced at each additive rate were tested for deformation control at 5 • C, 25 • C and 40 • C. For each temperature, the test periods were 1000 ms, 2000 ms and 3000 ms and the speeds of the test were 40 m/s, 60 m/s and 80 m/s respectively. Based on the applied load, accepted or calculated Poisson's ratio and sample height the resilient modulus (MR) was calculated as in Equation (3).
where P stands for the maximum dynamic load applied (N), ϑ is Poisson's proportion, t is length of specimen (mm) and δh shows horizontal recoverable deformation (mm).

Fatigue Test
There are many experiments to determine the fatigue strength of asphalt concrete. Indirect tensile fatigue test is defined as the number of load replications acting on asphalt concrete until it breaks. In addition, each sample is subjected to fatigue test at different stress levels repeating the number of loads until it causes breakage at certain stress levels (N f ). The classical fatigue relationship between N f and stress (σ) is calculated from the logarithmic graph or Equation (4).
N f : Fatigue life K 1 , K 2 : Material characteristics σ: Stress Three marshall samples prepared at the rate of each additive for the indirect tensile fatigue test were performed at 25 • C according to ASTM D 6927 standard. Tests were carried out under controlled stress of 300 kPa. The loading period was 1500 ms, 124 ms of which was loading time while the remaining 1376 ms was the rest time. The experiment continued until the samples were completely broken and the number of repeats of the fracture were determined [44].

Marshall Test
The relationship between Marshall Stability and type of mixtures are shown in Figure 1. As it can be seen, the highest stability value was found in samples with 5% SBS, 0.3% Viatop Premium Plus, and 0.7% FRP additives. The lowest stability value was found in the samples with 5% SBS. In samples with 5% SBS and 0.3% Viatop Premium, stability value increased by adding 0.3%, 0.5%, 0.7% and 0.9% FRP additive, to 6.4%, 11%, 18:46% and 14.78% respectively. As shown in Figure 2, the highest flow

Moisture Damage Test
Indirect tensile strength of asphalt samples is visible in Figure 4. The increase in elastic properties of polymer-containing samples leads to an increase in their tensile strength levels. When examined in Figure 4, the indirect tensile strength of unconditional and conditional samples has increased to 0.7% of the FRP additive. The highest indirect tensile strength value was found in 5% SBS plus 0.3% Viatop Premium and 0.7% FRP samples. The relationship between indirect tensile strength ratios (TSR) and type of mixtures are shown in Figure 5. As shown, the TSR of all mixtures are above 80% and they all pass the super pave limit. It can be said that the FRP additive increases the resistance of the mixtures against moisture damage.

Moisture Damage Test
Indirect tensile strength of asphalt samples is visible in Figure 4. The increase in elastic properties of polymer-containing samples leads to an increase in their tensile strength levels. When examined in Figure 4, the indirect tensile strength of unconditional and conditional samples has increased to 0.7% of the FRP additive. The highest indirect tensile strength value was found in 5% SBS plus 0.3% Viatop Premium and 0.7% FRP samples. The relationship between indirect tensile strength ratios (TSR) and type of mixtures are shown in Figure 5. As shown, the TSR of all mixtures are above 80% and they all pass the super pave limit. It can be said that the FRP additive increases the resistance of the mixtures against moisture damage.

Moisture Damage Test
Indirect tensile strength of asphalt samples is visible in Figure 4. The increase in elastic properties of polymer-containing samples leads to an increase in their tensile strength levels. When examined in Figure 4, the indirect tensile strength of unconditional and conditional samples has increased to 0.7% of the FRP additive. The highest indirect tensile strength value was found in 5% SBS plus 0.3% Viatop Premium and 0.7% FRP samples. The relationship between indirect tensile strength ratios (TSR) and type of mixtures are shown in Figure 5. As shown, the TSR of all mixtures are above 80% and they all pass the super pave limit. It can be said that the FRP additive increases the resistance of the mixtures against moisture damage.

Drain Down Test
The results obtained from Schellenberger bitumen drain down test are given in Figure 6. As the results show, the mixture with 0.3% Viatop Premium and 0.9% FRP yields the best results, whereas the most disappointing result belongs to the samples with 5% SBS in which the value is 3 times higher than the value of the samples with 5% SBS, 0.3% Viatop Premium and 0.9% FRP.

Nicholson Test
The results of Nicholson tests are given in Table 6. It is clear that the FRP additive has no considerable effect on the adhesion of aggregates to asphalt cement. Also, the Viatop Premium additive has an insignificant effect on the adhesion among the aggregate of asphalt cement. Based on the results, SMAs modified with Viatop premium and FRP are not effective in the performance of SMAs against stripping

Drain Down Test
The results obtained from Schellenberger bitumen drain down test are given in Figure 6. As the results show, the mixture with 0.3% Viatop Premium and 0.9% FRP yields the best results, whereas the most disappointing result belongs to the samples with 5% SBS in which the value is 3 times higher than the value of the samples with 5% SBS, 0.3% Viatop Premium and 0.9% FRP.

Drain Down Test
The results obtained from Schellenberger bitumen drain down test are given in Figure 6. As the results show, the mixture with 0.3% Viatop Premium and 0.9% FRP yields the best results, whereas the most disappointing result belongs to the samples with 5% SBS in which the value is 3 times higher than the value of the samples with 5% SBS, 0.3% Viatop Premium and 0.9% FRP.

Nicholson Test
The results of Nicholson tests are given in Table 6. It is clear that the FRP additive has no considerable effect on the adhesion of aggregates to asphalt cement. Also, the Viatop Premium additive has an insignificant effect on the adhesion among the aggregate of asphalt cement. Based on the results, SMAs modified with Viatop premium and FRP are not effective in the performance of SMAs against stripping  Figure 6. Results of Drain down test. Figure 6 shows that adding 0.3% of Viatop Premium to the mixture and increasing the amount of FRP increases the resistance of SMAs against bitumen drain down. Hence, it is clear that SMAs modified with Viatop Premium and FRP are very efficient in performing against asphalt binder drain down.

Nicholson Test
The results of Nicholson tests are given in Table 6. It is clear that the FRP additive has no considerable effect on the adhesion of aggregates to asphalt cement. Also, the Viatop Premium additive has an insignificant effect on the adhesion among the aggregate of asphalt cement. Based on the results, SMAs modified with Viatop premium and FRP are not effective in the performance of SMAs against stripping

Resilient Modulus Test
Figures 7-9 present the results obtained from the current experiments. As seen in the figures, the highest elastic modulus was found in samples with 5% SBS, 0.3% Viatop Premium plus 0.7% FRP. Variation in the amount and period of loads, keeping 5% SBS and 0.3% Viatop premium constant, resulted in an increase in FRP additives which consequently increased Elastic modulus of the samples. It can be seen that increasing FRP level to more than 7% decreases the elastic modulus of the samples. Thus, it is suggested that adding additives to pure asphalt increases its resistance against permanent deformations caused by tensile and compressive stresses caused by traffic. Also, by increasing the modulus of elasticity, the load distribution capability of asphalt coating is improved. However, as expected, in short loading times a higher elastic modulus value was obtained for each loading period. The elastic modulus values for differing temperatures, various loading periods, and different speeds were investigated according to the diagram prepared by the Asphalt Aggregate Mixture Analyzing System (AAMAS) and the flexibility modules of the mixtures were evaluated. According to the diagram, the flexibility modulus range for the temperature of 5 • C remains between about 8411 MPa and 23,212 MPa, while the values above this range demonstrated higher elastic modulus, and the values below revealed a lower elastic modulus. Similarly, in temperatures around 25 • C and 40 • C, the appropriate elastic modulus was between 1946 MPa-6205 MPa and 781 MPa-2355 MPa respectively [45]. According to the test results, the elastic modulus values of all samples remained within the above-mentioned limit values specified in all temperatures. 5% SBS + 0.3% Viatop Premium + 0.5% FRP 9 5% SBS + 0.3% Viatop Premium +0.7% FRP 9 5%SBS + 0.3% Viatop Premium +0.9% FRP 9

Resilient Modulus Test
Figures 7-9 present the results obtained from the current experiments. As seen in the figures, the highest elastic modulus was found in samples with 5% SBS, 0.3% Viatop Premium plus 0.7% FRP. Variation in the amount and period of loads, keeping 5% SBS and 0.3% Viatop premium constant, resulted in an increase in FRP additives which consequently increased Elastic modulus of the samples. It can be seen that increasing FRP level to more than 7% decreases the elastic modulus of the samples. Thus, it is suggested that adding additives to pure asphalt increases its resistance against permanent deformations caused by tensile and compressive stresses caused by traffic. Also, by increasing the modulus of elasticity, the load distribution capability of asphalt coating is improved. However, as expected, in short loading times a higher elastic modulus value was obtained for each loading period. The elastic modulus values for differing temperatures, various loading periods, and different speeds were investigated according to the diagram prepared by the Asphalt Aggregate Mixture Analyzing System (AAMAS) and the flexibility modules of the mixtures were evaluated. According to the diagram, the flexibility modulus range for the temperature of 5 °C remains between about 8411 MPa and 23,212 MPa, while the values above this range demonstrated higher elastic modulus, and the values below revealed a lower elastic modulus. Similarly, in temperatures around 25 °C and 40 °C, the appropriate elastic modulus was between 1946 MPa-6205 MPa and 781 MPa-2355 MPa respectively [45]. According to the test results, the elastic modulus values of all samples remained within the above-mentioned limit values specified in all temperatures.

Static Creep Test
For optimum asphalt content obtained from Marshall Stability test, each mixture was subjected to uniaxial static creep test at 25 °C. As shown in Figure 10, the highest amount of deformation occurred only in samples with 5% SBS addition. The lowest amount of deformation was also found in 0.3% Viatop Premium and 0.7% FRP added samples. Compared to the mixture with 5% SBS modified bitumen, the deformation of samples with 0.3% Viatop Preium and 0.3%, 0.5%, 0.7% and 0.9% FRP were decreased by 3.1%, 8.68%, 15.62% and 11.47% after 3600 s. Therefore, it was observed that the risk of rutting decreased at 0.7% FRP additive ratio. The values of creep modulus are given in Figure 11. A thorough analysis of the graph reveals that there is a sudden decrease in creep modulus values up to 200 s and a gentler slope in creep modulus values until the end of the experiment. The highest creep modulus was found in samples with 0.3% Viatop Premium plus 0.7% FRP and the lowest belonged to the samples with 5% SBS. Thus, it can be clearly stated that FRP additive increases the resistance of SMA mixtures against permanent deformations.

Static Creep Test
For optimum asphalt content obtained from Marshall Stability test, each mixture was subjected to uniaxial static creep test at 25 • C. As shown in Figure 10, the highest amount of deformation occurred only in samples with 5% SBS addition. The lowest amount of deformation was also found in 0.3% Viatop Premium and 0.7% FRP added samples. Compared to the mixture with 5% SBS modified bitumen, the deformation of samples with 0.3% Viatop Preium and 0.3%, 0.5%, 0.7% and 0.9% FRP were decreased by 3.1%, 8.68%, 15.62% and 11.47% after 3600 s. Therefore, it was observed that the risk of rutting decreased at 0.7% FRP additive ratio. The values of creep modulus are given in Figure 11. A thorough analysis of the graph reveals that there is a sudden decrease in creep modulus values up to 200 s and a gentler slope in creep modulus values until the end of the experiment. The highest creep modulus was found in samples with 0.3% Viatop Premium plus 0.7% FRP and the lowest belonged to the samples with 5% SBS. Thus, it can be clearly stated that FRP additive increases the resistance of SMA mixtures against permanent deformations. that the risk of rutting decreased at 0.7% FRP additive ratio. The values of creep modulus are given in Figure 11. A thorough analysis of the graph reveals that there is a sudden decrease in creep modulus values up to 200 s and a gentler slope in creep modulus values until the end of the experiment. The highest creep modulus was found in samples with 0.3% Viatop Premium plus 0.7% FRP and the lowest belonged to the samples with 5% SBS. Thus, it can be clearly stated that FRP additive increases the resistance of SMA mixtures against permanent deformations.

Dynamic Creep Test
Each mixture was subjected to uniaxial repetitive creep test at 25 °C. The relationship between deformation and load repetition was shown in Figure 12. As expected, 5% modified SMA mixture with SBS has the least resistance against rutting. The residual deformations in the mixtures decreased by increasing the amount of FRP. The variation in accumulated dynamic creep modules versus the number of cycles for all specimens were presented in Figure 13. Examining the graph reveals that there is a sudden decrease in creep modulus values up to 2000 load repetitions, and a slighter decrease in creep modulus values after load repetitions.

Dynamic Creep Test
Each mixture was subjected to uniaxial repetitive creep test at 25 • C. The relationship between deformation and load repetition was shown in Figure 12. As expected, 5% modified SMA mixture with SBS has the least resistance against rutting. The residual deformations in the mixtures decreased by increasing the amount of FRP. The variation in accumulated dynamic creep modules versus the number of cycles for all specimens were presented in Figure 13. Examining the graph reveals that there is a sudden decrease in creep modulus values up to 2000 load repetitions, and a slighter decrease in creep modulus values after load repetitions. deformation and load repetition was shown in Figure 12. As expected, 5% modified SMA mixture with SBS has the least resistance against rutting. The residual deformations in the mixtures decreased by increasing the amount of FRP. The variation in accumulated dynamic creep modules versus the number of cycles for all specimens were presented in Figure 13. Examining the graph reveals that there is a sudden decrease in creep modulus values up to 2000 load repetitions, and a slighter decrease in creep modulus values after load repetitions. According to the results, there was a decrease in SMAs with SBS, Viatop premium and FRP compared to the mixtures with SBS. Mixtures containing SBS, Viatop premium and FRP exhibit lower creep modulus in the same cycle compared to the mixture with SBS, indicating greater plastic deformation in the mixture with SBS. It is suggested that the addition of nano-clay with Arbesol strengthen WMAs against deformation compared to conventional WMAs. The results also suggest that the hardness in the mixtures containing Viatop premium and FRP increased. In addition, these mixtures showed higher resistance against rutting compared to SMAs with SBS. Hence, the modified mixture is claimed to have more service life than the non-modified mixture.

Fatigue Test
The results of fatigue test are given in Figure 14. Following an increase in the amount of FRP additives, an increase was also witnessed in the number of load repetitions required to break the samples. The number of load repeats including 4 mm deformation of the mixtures and the repetition rate of samples with 5% SBS, 0.3% Viatop Premium and 0.3%,0.5%, 0.7% and 0.9% FRP considerably increased compared to the samples with only %5 SBS additive. According to the results, there was a decrease in SMAs with SBS, Viatop premium and FRP compared to the mixtures with SBS. Mixtures containing SBS, Viatop premium and FRP exhibit lower creep modulus in the same cycle compared to the mixture with SBS, indicating greater plastic deformation in the mixture with SBS. It is suggested that the addition of nano-clay with Arbesol strengthen WMAs against deformation compared to conventional WMAs. The results also suggest that the hardness in the mixtures containing Viatop premium and FRP increased. In addition, these mixtures showed higher resistance against rutting compared to SMAs with SBS. Hence, the modified mixture is claimed to have more service life than the non-modified mixture.

Fatigue Test
The results of fatigue test are given in Figure 14. Following an increase in the amount of FRP additives, an increase was also witnessed in the number of load repetitions required to break the samples. The number of load repeats including 4 mm deformation of the mixtures and the repetition rate of samples with 5% SBS, 0.3% Viatop Premium and 0.3%,0.5%, 0.7% and 0.9% FRP considerably increased compared to the samples with only %5 SBS additive.

Fatigue Test
The results of fatigue test are given in Figure 14. Following an increase in the amount of FRP additives, an increase was also witnessed in the number of load repetitions required to break the samples. The number of load repeats including 4 mm deformation of the mixtures and the repetition rate of samples with 5% SBS, 0.3% Viatop Premium and 0.3%,0.5%, 0.7% and 0.9% FRP considerably increased compared to the samples with only %5 SBS additive. Increasing the amount of stress on the mixture causes a break in the bond between bitumen and rock material, resulting in a rapid decrease in the hardness of the mixtures and their failure to reach fracture conditions. The results of the experiments show that adding Viatop premium and FRP was efficient in increasing the hardness of the mixtures and improving the fatigue behavior of the SMAs. The models obtained for fatigue showed that by increasing FRP content, the hardness of SMA mixtures also increased. This effect on the mixture could be due to the fiber and polymer behavior of the FPR in the mixture. So, it is suggested that adding FRP to asphalt mixture significantly increase fatigue life.

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According According to the results from the indirect tensile fatigue test, the load repeats of the mixtures with 0.3%, 0.5%, 0.7% and 0.9% and 0.3% Viatop Premium increased by 21%, 38.3%, 48.93% and 0.3%, respectively, compared to the mixtures with 5% SBS. In conclusion, FRP additives were found to increase the fatigue resistance of the mixture, which consequently helped SMA coatings to live longer without any necessary maintenance.