7. Results and discussion

#### 7.1. Experimental results

Field and laboratory test works were conducted on the super-structure of the road for a time period of 1 year under traffic and environmental conditions. Drilling core samples were taken from the super-structure of the road in certain periods. The experimental part of the study was carried out in two stages. In the first stage, the physical properties of the aggregates and the neat and SBS modified bitumen which are using the asphalt mixture were determined. In the second stage, various tests performed HMA samples. The mechanical properties of the samples collected from the different asphalt pavement were examined in the 1st, 4th, 8th and 12th months for a one-year period.

#### 7.1.1. Properties of bituminous binders and aggregates

• It ensures the opportunity of speed and optimization that can be analyzed via computer. • Any types of complex geometrical, material status and loading limit conditions may be

• It facilitates the solution of integrated problems in ways such as tension, shape-shifting

• The primary independent variables like place-shift, flow potential, which are selected, and the secondary unknown factors depending on these such as tension, shape-shifting, speed, and the amount of flow, etc., which are depending on these, are assessed together.

In this chapter, a finite elements model was developed by using the ANSYS Finite Elements Program for the super-structure of the road. The models, which consist of asphalt coating, the

Different models were prepared for various time periods, which were 1st, 4th, 8th and 12th Months, by considering the multi-layer structure of asphalt, the traffic and the environmental

Field and laboratory test works were conducted on the super-structure of the road for a time period of 1 year under traffic and environmental conditions. Drilling core samples were taken from the super-structure of the road in certain periods. The experimental part of the study was carried out in two stages. In the first stage, the physical properties of the aggregates and the neat and SBS modified bitumen which are using the asphalt mixture were determined. In the

• Results that are close to reality are obtained with adequate element definitions [36].

base and sub-base include 79,045 elements and 558,224 nodal point in average.

The Finite element model (FEM) of road is given in Figure 9.

defined.

30 Modified Asphalt

conditions [35].

7. Results and discussion

Figure 9. Finite element model (FEM) of road [34].

7.1. Experimental results

(statics) and consolidation (dynamics).

The binder was used in B50/70 class and constituted the building block of the HMA, which was used in the road platform. The characteristics of the pure (neat) and HMA-modified bitumen are given in Table 5 that the neat and SBS modified bitumen are a little susceptible to temperature in relation to the penetration index and they have a value above the limits of the specification as softening.

The gradation characteristics of the mixture are given in Table 6. The physical properties of the aggregate are shown in Table 7. It is understood that the aggregates used in the coating layer of HMA are within the limits of the related specifications in terms of their physical properties.


Table 5. The properties of the neat bitumen [34].


Table 6. Aggregate gradation.


Table 7. Aggregate characteristics [35].

#### 7.1.2. HMA design properties

In order to determine the HMA design properties, the pure and SBS-modified asphalt concrete coating sample road platform was prepared by taking the aggregate gradation as the basis. The pure HMA optimum bitumen rate was determined as 4.95%, and the SBS-added HMA optimum bitumen rate was determined as 5.24%. The properties of the design criteria are given in Table 8, and it is observed that they meet the Conditions List criteria.

From the pavement spread and compacted according to the predetermined design the core samples were taken at three different time periods on the vehicle wheel passing line and banquette of the road. The core samples were sized to those of Marshall samples and they were tested by Stiffness Modulus, Indirect Tensile, Fatigue and Marshall tests.

The average volumetric characteristics of the core samples are given in Table 9.

In Figure 10, It is indicated that the alteration in the stability of the samples over time. According to the result of the experiment, there have been remarkable increases in the stability with the hardening in the asphalt coating over time. SBS modified specimens were found to have 24% greater stability at 1st month and 72% greater at 12th months, respectively, when compared to neat specimens. The Stability increased 34% in neat mixtures and 76% more in SBS modified mixtures, respectively for 12th month compared to 1st month.

The change of the stiffness modules is illustrated in Figure 11.

water due to the transverse slope of the road [35].

Figure 11. The change of the stiffness modules in different period [35].

Figure 10. The change of stability in different period [35].

In Figure 11, the stiffness modulus values show significant increase over time. In addition, the stiffness module of the samples taken from the edges and the vehicle wheel pass line of neat and SBS modified asphalt pavement were similarly affected by the time factor. SBS modified sample values increased by 8–27% more than neat sample values. The edge asphalt samples which are taken from banquette value were higher than the vehicle wheel passing. This difference is seen 2.3% to 11.8% in neat specimens and 1.8–10% in modified specimens. The reason for this increase is due to the fact that the samples from the edge are exposed to more

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The graph in Figure 12 shows the average test results of the Indirect Tensile Strength Test.

In Figure 12, ITS values were found to be lowest at 1st month and highest at 12st months. In terms of monthly periods, ITS values of S and SK type core samples were more than N and NK


Gmb, bulk specific gravity; Vh, air voids; Vf, voids filled with asphalt; Vma, the void volume between the aggregates.


Table 8. Design properties of pure and SBS-modified HMA [34, 35].

Gmb, bulk specific gravity; Vh, air voids; Vf, voids filled with asphalt; Vma, the void volume between the aggregates.

Table 9. The volumetric characteristics of the core samples in the 1st month [35].

Figure 10. The change of stability in different period [35].

7.1.2. HMA design properties

32 Modified Asphalt

Practical specific gravity (Gmb, gr/cm3

In order to determine the HMA design properties, the pure and SBS-modified asphalt concrete coating sample road platform was prepared by taking the aggregate gradation as the basis. The pure HMA optimum bitumen rate was determined as 4.95%, and the SBS-added HMA optimum bitumen rate was determined as 5.24%. The properties of the design criteria are

From the pavement spread and compacted according to the predetermined design the core samples were taken at three different time periods on the vehicle wheel passing line and banquette of the road. The core samples were sized to those of Marshall samples and they

In Figure 10, It is indicated that the alteration in the stability of the samples over time. According to the result of the experiment, there have been remarkable increases in the stability with the hardening in the asphalt coating over time. SBS modified specimens were found to have 24% greater stability at 1st month and 72% greater at 12th months, respectively, when compared to neat specimens. The Stability increased 34% in neat mixtures and 76% more in

given in Table 8, and it is observed that they meet the Conditions List criteria.

were tested by Stiffness Modulus, Indirect Tensile, Fatigue and Marshall tests. The average volumetric characteristics of the core samples are given in Table 9.

SBS modified mixtures, respectively for 12th month compared to 1st month.

Optimum bitumen rate (%) 4.95 5.24

Marshall stability (kgf) 1222 1170 Flow (mm) 3.03 3.58 Aggregate void ratio (Vma, %) 15.10 13.9 Asphalt void ratio (Vf, %) 73.93 75.4 Air void ratio (Vh, %) 3.94 3.10

Table 8. Design properties of pure and SBS-modified HMA [34, 35].

Table 9. The volumetric characteristics of the core samples in the 1st month [35].

Property Pure HMA value SBS modified HMA value

) 2.415 2.411

Gmb, bulk specific gravity; Vh, air voids; Vf, voids filled with asphalt; Vma, the void volume between the aggregates.

Gmb, bulk specific gravity; Vh, air voids; Vf, voids filled with asphalt; Vma, the void volume between the aggregates.

Specimen Gmb Vh (%) Vma (%) Vf (%) N 2.267 8.929 19.362 53.899 NK 2.280 8.43 18.92 55.480 S 2.271 8.369 19.457 57.032 SK 2.280 8.004 19.136 58.188

The change of the stiffness modules is illustrated in Figure 11.

In Figure 11, the stiffness modulus values show significant increase over time. In addition, the stiffness module of the samples taken from the edges and the vehicle wheel pass line of neat and SBS modified asphalt pavement were similarly affected by the time factor. SBS modified sample values increased by 8–27% more than neat sample values. The edge asphalt samples which are taken from banquette value were higher than the vehicle wheel passing. This difference is seen 2.3% to 11.8% in neat specimens and 1.8–10% in modified specimens. The reason for this increase is due to the fact that the samples from the edge are exposed to more water due to the transverse slope of the road [35].

Figure 11. The change of the stiffness modules in different period [35].

The graph in Figure 12 shows the average test results of the Indirect Tensile Strength Test.

In Figure 12, ITS values were found to be lowest at 1st month and highest at 12st months. In terms of monthly periods, ITS values of S and SK type core samples were more than N and NK type of core samples. It was realized the lowest values in the N type and the highest values in the SK type. The increase of samples from 1st to the 12th month were seen 42.68% NK, 49.89% N, 20.4% SK and 26.93% S type of samples, respectively.

the flexibility of bituminous hot mixtures decreased after aging and for this reason a more

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FEM models have been solved to determine the Von Mises stresses besides vertical deforma-

The FEM models of the Von Mises stresses for one of sample material is given in Figure 14.

Numerical analysis was done by applying the finite element method on the super-structure of the road. Von Mises Stress properties of the road super-structure are evaluated in Figure 15.

brittle fracture may occupy [35].

tions in super structures of the road, as well.

7.2. Numeric analyses result

Figure 14. Von Mises FEM model [34].

Figure 15. Von Mises tension-time changes of the super-structure of the road [34].

Figure 12. The change of the indirect tensile strengths in different period [35].

The change of fatigue strength in different period is given in Figure 13.

In Figure 13, it was observed that the loading repetition required for the samples to reach a level of deformation of about 2 mm was significantly increased using the SBS additive material. It was seen that the maximum loading repetition number (Nmax) values were increased after time period. The fatigue resistance of the samples with neat was lower than the SBS ones. The lowest deformation was gained from SK type samples. In the same manner, the highest Nmax values were achieved from SK type samples. It was clearly understood that

Figure 13. The change of fatigue strength in different period [35].

the flexibility of bituminous hot mixtures decreased after aging and for this reason a more brittle fracture may occupy [35].

#### 7.2. Numeric analyses result

type of core samples. It was realized the lowest values in the N type and the highest values in the SK type. The increase of samples from 1st to the 12th month were seen 42.68% NK, 49.89% N,

20.4% SK and 26.93% S type of samples, respectively.

34 Modified Asphalt

The change of fatigue strength in different period is given in Figure 13.

Figure 12. The change of the indirect tensile strengths in different period [35].

Figure 13. The change of fatigue strength in different period [35].

In Figure 13, it was observed that the loading repetition required for the samples to reach a level of deformation of about 2 mm was significantly increased using the SBS additive material. It was seen that the maximum loading repetition number (Nmax) values were increased after time period. The fatigue resistance of the samples with neat was lower than the SBS ones. The lowest deformation was gained from SK type samples. In the same manner, the highest Nmax values were achieved from SK type samples. It was clearly understood that

FEM models have been solved to determine the Von Mises stresses besides vertical deformations in super structures of the road, as well.

The FEM models of the Von Mises stresses for one of sample material is given in Figure 14.

Numerical analysis was done by applying the finite element method on the super-structure of the road. Von Mises Stress properties of the road super-structure are evaluated in Figure 15.

Figure 14. Von Mises FEM model [34].

Figure 15. Von Mises tension-time changes of the super-structure of the road [34].

According to Figure 15; the highest Von Mises tensions were occurred the coating layer and the lowest values were observed in the base layer. It is fixed that The Von Mises tensions increased in the coating layer within 1 year period. It has been determined that the highest Von Mises tension were in SK type road coating whereas, the lowest Von Mises tensions were in N type coating. The Von Mises tensions of base layer indicated similarity properties and no significant changes were observed [34].

Vertical deformation (y)-time changes of the super-structure of the road is given in Figure 16.

When Table 10 is examined, It is understood that R<sup>2</sup> values are close to 1 for all road layers. It has been inferred that numerical analyzes have supported empirical studies because of the

Table 10. Function and regression analyses of the relation between the super-structures of the road vertical deformation

Von Mises stress function R2 Vertical deformation function R2

Aging Effects on Mechanical Characteristics of Multi-Layer Asphalt Structure

5E-05x + 0,0147 0,9645

37

http://dx.doi.org/10.5772/intechopen.75698

4E-05x + 0,0147 0,923

5E-05x + 0,0147 0,8528

–0,0002x + 0,0147 0,9271

–0,0001x + 0,0111 0,9683 y = 2E-06x<sup>2</sup>

–0,0001x + 0,0111 0,946 y = 1E-06x2

9E-05x + 0,0111 0,8926 y = 2E-05x<sup>2</sup>

–0,0001x + 0,0111 0,8963 y = 7E-07x<sup>2</sup>

It came out that the performance characteristics of the SBS-added the HMA are improved due to the use of the SBS polymer material as compared to the unmodified ones. This is because when the SBS polymer is used, the adhesion between the aggregates increases. It has been seen that the flexible structure of asphalt is stiffened due to environmental conditions due to oxidation, which is caused by temperature changes and precipitation during transportation, storage, mixing and production processes. In addition to, as the air void ratio increases, the hardening time decreases due to air contact. The hardening of the asphalt road coating was found to be higher in the coating without additive material and it was appeared that the polymer increased the deformation resistance at high temperatures and increased

Analytical calculations from different material types and different strata in the flexible road coating are complex. The traffic loads and the distribution of pressure on the superstructures of the roads are varied, and different materials are used on each layer, and therefore the mechanical properties and the load distribution ability vary. Climate and various environmental conditions affect the road. Because of these reasons, empirical studies must be promoted with numerical analyzes to establish performance characteris-

The author would like to thank Transportation Laboratory, Department of Civil Engineering, Firat University; Geotechnical &Transportation Laboratory, Department of Civil Engineering,

Dicle University, Istanbul University and Bimtas Research Laboratories, Istanbul.

strong relationship [34].

Layer types Regression models Function type

sub base SK y = 5E-06x<sup>2</sup>

S y = 5E-06x<sup>2</sup>

NK y = 3E-06x<sup>2</sup>

<sup>N</sup> y = 2E-07x2

the tendency to fracture at low temperatures.

8. Conclusion

time [34].

tics of the road.

Acknowledgements

Figure 16. Vertical deformation (y)-time changes of the super-structure of the road [34].

When Figure 16 is evaluated, it is seen that the highest vertical deformations are found at the base and lower base layers and the lowest deformations are found at the coating layer. Within a year, there have been small deviations in the amount of deformation. The amounts of deformation were confirmed as 0.014492 mm in SK-type, and 0.0145 mm in NK-type in the 12th month [34].

Von Misses stress and vertical deformation function and R2 values are submitted in Table 10.



Table 10. Function and regression analyses of the relation between the super-structures of the road vertical deformation time [34].

When Table 10 is examined, It is understood that R<sup>2</sup> values are close to 1 for all road layers. It has been inferred that numerical analyzes have supported empirical studies because of the strong relationship [34].
