**5. Asphalt concrete strength**

#### **5.1. Bitumen**

Bitumen of grade BND 100/130, produced by Pavlodar Petrochemical Plant (PPCP), was used for the preparation of fine-grained dense asphalt concrete in laboratory conditions in this work. Bitumen complies with the requirements of Kazakhstan standard ST RK 1373-2013 [29]. Standard indicators for bitumen are represented in **Table 1**. Content of bitumen in the asphalt concrete was 4.8% by the mass of the dry filler.

#### **5.2. Asphalt concrete**

Hot dense fine-grained asphalt concrete of Type B was adopted for test, which satisfies the requirements of the Kazakhstan standard ST RK 1225-2013 [30], and it was prepared with the use of aggregate of fractions 5–10 mm (20%), 10–15 mm (13%), 15–20 mm (10%) from Novo-Alekseevsk rock pit (Almaty oblast), sand fraction 0–5 mm (50%) from the plant "Asphaltconcrete-1" (Almaty city) and mineral powder (7%) from Kordai rock pit (Zhambyl oblast). The main standard indicators for asphalt concrete are represented in **Table 2**. The grading curve of mineral part of hot mix asphalt concrete is shown in **Figure 8**.

#### **5.3. Test methods**

In this study, asphalt sample tests have been performed according to the following methods:



**Table 1.** Main standard indicators for bitumen.

Stationary state is achieved at *<sup>R</sup>* <sup>=</sup> \_\_\_ <sup>3</sup>*<sup>B</sup>*

enon for the asphalt concrete pavement.

the asphalt concrete strength.

**5. Asphalt concrete strength**

concrete was 4.8% by the mass of the dry filler.

*Rcr* <sup>&</sup>gt; \_\_\_ <sup>3</sup>*<sup>B</sup>*

68 Modified Asphalt

of new cells is bigger.

**5.1. Bitumen**

**5.2. Asphalt concrete**

**5.3. Test methods**

sions of 5 × 5 × 16 cm.

*<sup>A</sup>* , that is, *ds* <sup>=</sup> 0. And at *<sup>R</sup>* <sup>&</sup>gt; \_\_\_ <sup>3</sup>*<sup>B</sup>*

*A* (*Rcr*: critical size of the cell) the cell should be separated, otherwise, it will die. The volumes of the mother cell and two daughter cells are similar, and the total area of the surfaces

The abovementioned examples for self-organization in thermodynamics systems—Benar's cells and cell separation can be used further for the explanation of the fatigue failure phenom-

Fatigue failure of the asphalt concrete pavement, of course, has been directly connected with

Bitumen of grade BND 100/130, produced by Pavlodar Petrochemical Plant (PPCP), was used for the preparation of fine-grained dense asphalt concrete in laboratory conditions in this work. Bitumen complies with the requirements of Kazakhstan standard ST RK 1373-2013 [29]. Standard indicators for bitumen are represented in **Table 1**. Content of bitumen in the asphalt

Hot dense fine-grained asphalt concrete of Type B was adopted for test, which satisfies the requirements of the Kazakhstan standard ST RK 1225-2013 [30], and it was prepared with the use of aggregate of fractions 5–10 mm (20%), 10–15 mm (13%), 15–20 mm (10%) from Novo-Alekseevsk rock pit (Almaty oblast), sand fraction 0–5 mm (50%) from the plant "Asphaltconcrete-1" (Almaty city) and mineral powder (7%) from Kordai rock pit (Zhambyl oblast). The main standard indicators for asphalt concrete are represented in **Table 2**. The

In this study, asphalt sample tests have been performed according to the following methods:

**1.** Determination of asphalt concrete strength at direct tension at various temperatures has been performed in thermal chamber of TRAVIS, manufactured by Infratest GmbH (Germany). Sample tests have been performed at deformation with constant rate 1 mm/ min in accordance with European standard pr EN 12697-46 [31]. Samples had dimen-

**2.** Cyclic (fatigue) asphalt concrete strength at various temperatures has been determined by sample testing with dimensions 5 × 5 × 38 cm in thermal chamber of four-point bending device under European standard EN 12697-24 [32]. Loading frequency was f = 10 Hz. The

stress, equal to σ = 1400 kPa, was kept as constant prior to the sample failure.

grading curve of mineral part of hot mix asphalt concrete is shown in **Figure 8**.

*<sup>A</sup>* , that is, *ds* > 0, therefore, at


**Table 2.** Main standard indicators for asphalt concrete.

**Figure 8.** Asphalt mixture grading curve.

#### **5.4. Sample preparation**

Asphalt concrete samples of cylindrical shape, designed for direct compression, were prepared under Kazakhstan standard ST RK 1218-2003 [33] by compaction of the asphalt concrete mix in special mold. The samples of rectangular shape and in the shape of beam of various dimensions were prepared in the following way. First, the asphalt concrete samples in the shape of square slab with dimensions 5 × 30.5 × 30.5 cm were prepared by roller compactor (model CRT-RC2S, company Cooper, UK) in accordance with European standard EN 12697-33 [34]. Then, the samples with the shape of rectangular prism of various dimensions were obtained from square slabs.

which at any other equal conditions, the more is the ratio of elasticity modulus of the asphalt concrete layers to the elasticity modulus of the under layers of the pavement base and subgrade soil [10, 40]. It is considered that the abovementioned ratio of elasticity moduli in pavement structure is the biggest one in the spring season, when the upper part of subgrade has been defrosted and loosened, and the asphalt concrete pavement has a big stiffness due to the

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**Figure 9.** Strength of fine-grained asphalt concrete (BND 100/130, PPCP) at various types of stressed condition.

As it is seen from **Figure 10**, namely within the temperature interval 0 and +10°С, the difference in the asphalt concrete tensile strength and bending strength (compression) is the biggest one!

**Figure 10** shows the graphs of cyclic strength for fine-grained dense asphalt concretes at bending and tension at the temperature of 20°С. The upper graph has been constructed at testing of asphalt concrete samples under scheme of bending on the four-point bending device in Kazakhstan Highway Research Institute, and the bottom one has been constructed according to the experimental data, obtained in the University of North Carolina State (USA) at direct tension [44]. It is clearly seen that the cyclic strength of the asphalt concrete at bending is considerably higher than at tension. Similar regularity can be seen on the curves of the long-term

Thus, single loading, cyclic and long-term strength of the asphalt concretes at tension is con-

To answer the question: "Does the asphalt concrete strength depend on the tested sample dimensions at compression?", the test of samples for the fine-grained dense asphalt concrete of type B (BND 100/130) has been performed for direct compression. The thickness of all the samples was similar and equal to 5 cm, and the length and the width of the samples had the values

relatively low air temperature, which is within 0 and +10°С [2, 41–43].

strength of the asphalt concrete, as shown in **Figure 11** [45, 46].

siderably less, than at bending and compression.

#### **5.5. Single loading, cyclic and long-term strength of asphalt concrete**

**Figure 9** represents the graphs, showing the dependence of the asphalt concrete strength at various types of loading—tension, compression and bending. As it is seen, in the considered temperature interval (0–50°С), the asphalt concrete has the least tensile strength, and the largest—at compression. Bending strength occupies the intermediate location between tension and compression. Meanwhile, compression and bending strength of the asphalt concrete with the temperature increase decreases nearly with the similar rate within the whole temperature interval considered, and at tension, the rate of decrease is higher than two times compared with compression and bending strength. It is also seen that the difference between temperature curves of bending strength and compression strength is kept as constant in the whole temperature interval considered and it is equal to, at average, 1.0 MPa. The maximum difference between temperature curves of tensile strength and bending (compression) strength occurs at low temperatures (0–10°С), which is equal to 2.5 MPa (3.5 MPa) and decreases with the temperature increase; these differences at temperature 50°С are equal to 0.8 and 1.6 MPa, respectively.

It is generally accepted that the fatigue cracks occur due to the repeated impact of the tensile stress in the bottom surface of the asphalt concrete pavement [2, 35–39], the more the value of Fatigue Destruction of Asphalt Concrete Pavement: Self-Organization and Mechanical… http://dx.doi.org/10.5772/intechopen.75536 71

**Figure 9.** Strength of fine-grained asphalt concrete (BND 100/130, PPCP) at various types of stressed condition.

**5.4. Sample preparation**

70 Modified Asphalt

**Figure 8.** Asphalt mixture grading curve.

were obtained from square slabs.

Asphalt concrete samples of cylindrical shape, designed for direct compression, were prepared under Kazakhstan standard ST RK 1218-2003 [33] by compaction of the asphalt concrete mix in special mold. The samples of rectangular shape and in the shape of beam of various dimensions were prepared in the following way. First, the asphalt concrete samples in the shape of square slab with dimensions 5 × 30.5 × 30.5 cm were prepared by roller compactor (model CRT-RC2S, company Cooper, UK) in accordance with European standard EN 12697-33 [34]. Then, the samples with the shape of rectangular prism of various dimensions

**Figure 9** represents the graphs, showing the dependence of the asphalt concrete strength at various types of loading—tension, compression and bending. As it is seen, in the considered temperature interval (0–50°С), the asphalt concrete has the least tensile strength, and the largest—at compression. Bending strength occupies the intermediate location between tension and compression. Meanwhile, compression and bending strength of the asphalt concrete with the temperature increase decreases nearly with the similar rate within the whole temperature interval considered, and at tension, the rate of decrease is higher than two times compared with compression and bending strength. It is also seen that the difference between temperature curves of bending strength and compression strength is kept as constant in the whole temperature interval considered and it is equal to, at average, 1.0 MPa. The maximum difference between temperature curves of tensile strength and bending (compression) strength occurs at low temperatures (0–10°С), which is equal to 2.5 MPa (3.5 MPa) and decreases with the temperature increase; these differences at temperature 50°С are equal to 0.8 and 1.6 MPa, respectively. It is generally accepted that the fatigue cracks occur due to the repeated impact of the tensile stress in the bottom surface of the asphalt concrete pavement [2, 35–39], the more the value of

**5.5. Single loading, cyclic and long-term strength of asphalt concrete**

which at any other equal conditions, the more is the ratio of elasticity modulus of the asphalt concrete layers to the elasticity modulus of the under layers of the pavement base and subgrade soil [10, 40]. It is considered that the abovementioned ratio of elasticity moduli in pavement structure is the biggest one in the spring season, when the upper part of subgrade has been defrosted and loosened, and the asphalt concrete pavement has a big stiffness due to the relatively low air temperature, which is within 0 and +10°С [2, 41–43].

As it is seen from **Figure 10**, namely within the temperature interval 0 and +10°С, the difference in the asphalt concrete tensile strength and bending strength (compression) is the biggest one!

**Figure 10** shows the graphs of cyclic strength for fine-grained dense asphalt concretes at bending and tension at the temperature of 20°С. The upper graph has been constructed at testing of asphalt concrete samples under scheme of bending on the four-point bending device in Kazakhstan Highway Research Institute, and the bottom one has been constructed according to the experimental data, obtained in the University of North Carolina State (USA) at direct tension [44]. It is clearly seen that the cyclic strength of the asphalt concrete at bending is considerably higher than at tension. Similar regularity can be seen on the curves of the long-term strength of the asphalt concrete, as shown in **Figure 11** [45, 46].

Thus, single loading, cyclic and long-term strength of the asphalt concretes at tension is considerably less, than at bending and compression.

To answer the question: "Does the asphalt concrete strength depend on the tested sample dimensions at compression?", the test of samples for the fine-grained dense asphalt concrete of type B (BND 100/130) has been performed for direct compression. The thickness of all the samples was similar and equal to 5 cm, and the length and the width of the samples had the values

**Figure 10.** Cyclic strength of the asphalt concrete at bending and direct tension at the temperature of 20°С.

with the length of sample side equal to 7 cm, and the strength increases almost linearly at the

**Figure 12.** Compression strength of the fine-grained asphalt concrete samples of type B (BND 100/130, PPCP) of various

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These results serve as the reliable explanation for gradual decrease of the horizontal dimen-

The fatigue crack on the asphalt concrete pavement occurs when it almost completely lost its tensile strength (tension at bending). Let us raise the question: can such asphalt concrete have residual compression strength? To clarify the issue, we have carried out a special experiment. The same fine-grained dense asphalt concrete of type B (bitumen grade BND 100/130) has been adopted. First, the asphalt concrete samples with dimensions 5 × 5 × 38 cm have been tested on the four-point bending device for bending fatigue to failure (stiffness reduction to 10% of the initial one) at the temperatures of 10, 20 and 30°С. Then, the samples with dimensions

**Parallel 1 Parallel 2 Parallel 3 Average**

**Table 3.** Test results of the fine-grained dense asphalt concrete of type B (BND 100/130, PPCP, f = 10 Hz, σ = 1400 kPa) at

+10 5187 4965 10,180 6777 +20 568 512 534 538 +30 565 219 222 335

sions of the asphalt concrete pavement cells with progressing of its fatigue failure.

temperature of 0°С with the decrease of sample dimensions.

**5.6. Residual strength of asphalt concrete**

**Т, °С Number of cycles to failure Nf**

fatigue on the four-point bending device.

dimensions at different temperatures.

**Figure 11.** Long-term strength of the fine-grained asphalt concrete of type B (BND 60/90) at transverse bending and direct tension.

equal to 2, 5, 7, 10, 12 and 15 cm. The test has been performed at the temperatures of 0, 10 and 20°С. Three parallel tests have been performed at each temperature and dimensions of samples.

As it is seen from **Figure 12**, the asphalt concrete strength at compression depends considerably on sample dimensions. The biggest strength occurs at the temperatures of 10 and 20°С Fatigue Destruction of Asphalt Concrete Pavement: Self-Organization and Mechanical… http://dx.doi.org/10.5772/intechopen.75536 73

**Figure 12.** Compression strength of the fine-grained asphalt concrete samples of type B (BND 100/130, PPCP) of various dimensions at different temperatures.

with the length of sample side equal to 7 cm, and the strength increases almost linearly at the temperature of 0°С with the decrease of sample dimensions.

These results serve as the reliable explanation for gradual decrease of the horizontal dimensions of the asphalt concrete pavement cells with progressing of its fatigue failure.

#### **5.6. Residual strength of asphalt concrete**

equal to 2, 5, 7, 10, 12 and 15 cm. The test has been performed at the temperatures of 0, 10 and 20°С. Three parallel tests have been performed at each temperature and dimensions of samples. As it is seen from **Figure 12**, the asphalt concrete strength at compression depends considerably on sample dimensions. The biggest strength occurs at the temperatures of 10 and 20°С

**Figure 11.** Long-term strength of the fine-grained asphalt concrete of type B (BND 60/90) at transverse bending and

**Figure 10.** Cyclic strength of the asphalt concrete at bending and direct tension at the temperature of 20°С.

direct tension.

72 Modified Asphalt

The fatigue crack on the asphalt concrete pavement occurs when it almost completely lost its tensile strength (tension at bending). Let us raise the question: can such asphalt concrete have residual compression strength? To clarify the issue, we have carried out a special experiment. The same fine-grained dense asphalt concrete of type B (bitumen grade BND 100/130) has been adopted. First, the asphalt concrete samples with dimensions 5 × 5 × 38 cm have been tested on the four-point bending device for bending fatigue to failure (stiffness reduction to 10% of the initial one) at the temperatures of 10, 20 and 30°С. Then, the samples with dimensions


**Table 3.** Test results of the fine-grained dense asphalt concrete of type B (BND 100/130, PPCP, f = 10 Hz, σ = 1400 kPa) at fatigue on the four-point bending device.

**7. Bifurcation**

into two saves it from "death."

is bigger than at bending.

(**Figure 14**).

follow further.

tion under the scheme of bending (tension).

time ("life cycle") of separate parts of the asphalt concrete pavement.

The principle of consequential change of deformation types at fatigue failure for an asphalt concrete pavement formulated earlier can be explained on the basis of provisions for thermo-

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In short description of the examples for dissipative structure occurrence—Benar's cells and cell separation, it has been mentioned earlier that the action of systems in critical conditions in both cases is a benefit for them: liquid flow along the hexagonal cells allows including additional convective mechanism of heat exchange with environment; separation of the cell

We also consider that the realization of the fatigue failure according to the consequent stages, changing deformation type from "tension" into "bending" and from "bending" into "compression" at the continuous mechanical impact is a benefit to the asphalt concrete pavement, as:

**1.** The asphalt concrete strength at bending is bigger than at tension, and at compression, it

**2.** Residual strength of asphalt concrete at compression is relevant after its failure at deforma-

Such staged failure with consequential change of deformation type prolongs the existence

The formulated principle can be visually demonstrated by the bifurcation scheme proposed

In thermodynamics and synergetics, it is accepted to consider that the system away from the equilibrium condition acquires new properties. The system in the strong nonequilibrium condition becomes more active and all substructural elements of the system work jointly, consistently, fluctuations are synergized and new structures occur at the critical moment [18–26, 48]. In addition, the system has a choice in critical conditions—what scenario of evolution to

In accordance with the proposed bifurcation scheme, the asphalt concrete pavement works as continuous medium under scheme of volumetric stressed-deformed condition since the moment of starting of operation to the moment of losing of the tension resistance (0–1). At the time moment of the complete losing of the tension resistance (point 1), the thermodynamics system (substructural elements of the asphalt concrete pavement) has a choice—which thermodynamics branch (branch А and branch B)—to function further. If the system in point of bifurcation chooses the thermodynamics branch A, the parallel cracks occur on the patch lines in point 1, and the asphalt concrete strips work as a long beam between points 1 and 2, and they are deformed under the scheme of bending. The transverse cracks occur in point 2, long asphalt concrete strips are divided into more short parts, each of the obtained parts for the period of

dynamics of irreversible processes and nonlinear dynamics (synergetics).

**Figure 13.** Residual strength of the asphalt concrete at compression after cyclic bending at various temperatures.

5 × 5 × 5 cm have been prepared from these samples, and they have been tested for direct compression at the same temperatures. Three asphalt concrete samples have been tested at each temperature. The results of the initial tests of the asphalt concrete samples at cyclic bending have been represented in **Table 3**, and their further test at direct compression—in **Figure 13**. As it is seen, the asphalt concrete has a high residual compression strength after the cyclic bending to failure, comparable with the strength of a new asphalt concrete (**Figures 9** and **12**).
