**2. Field observation**

**Figure 1** represents the photos showing fatigue failure of the asphalt concrete pavement of Karagandy-Shakhtinsk highway. These photos show clearly that the fatigue failure occurs by stage: first, parallel quasi-straight line longitudinal cracks occur on the patch line, between which quasi-straight line asphalt concrete strips have been formed, and then these quasistraight line asphalt concrete strips are divided into cells of small sizes due to the occurrence of quasi-transversal cracks. Thus, in the considered case, the formation of a grid of alligator

**Figure 1.** Fatigue failure of asphalt concrete pavement (860 km) of Karagandy-Shakhtinsk highway (Kazakhstan, Karagandy oblast, July, 2016).

cracks on the asphalt concrete pavement represents by itself a two-staged process, each of which has been realized during less or more prolonged period.

should be calculated for strength under the criterion of tensile bending strength of the cast-in-

It is considered that the fatigue cracking on the asphalt concrete pavement of highways occurs

Hveem F.N. of the far abroad country has been one of the first researchers, who mentioned the phenomenon of fatigue in the asphalt concrete pavement of a highway [3]. The first investigations of the fatigue properties for the asphalt concretes in laboratory conditions were performed by Sall R.N.J., Pell P.S., Taylor I.F. in the UK [4, 5] and Monismith C.L. in the USA [6]. The study of the fatigue of the asphalt concretes in the former Soviet Union was started by the works of Sall A.O. (Leningrad), Radovskiy B.S. (Kiev), Zolotaryov V.A. (Kharkov), Rudenskiy

It was found out that the phenomenon of fatigue failure for the asphalt concrete pavement of a highway was a complex one. In spite of the fact that the specialists of many countries of the world have been studying the phenomenon to the present day, the issue of the fatigue life for

**Figure 1** represents the photos showing fatigue failure of the asphalt concrete pavement of Karagandy-Shakhtinsk highway. These photos show clearly that the fatigue failure occurs by stage: first, parallel quasi-straight line longitudinal cracks occur on the patch line, between which quasi-straight line asphalt concrete strips have been formed, and then these quasistraight line asphalt concrete strips are divided into cells of small sizes due to the occurrence of quasi-transversal cracks. Thus, in the considered case, the formation of a grid of alligator

**Figure 1.** Fatigue failure of asphalt concrete pavement (860 km) of Karagandy-Shakhtinsk highway (Kazakhstan,

at frequently repeated load impact of the vehicles' wheels [2].

the asphalt concretes and asphalt concrete pavement remains actual.

A.V. and Kalashnikova T.N. (Moscow) [7–11].

situ (asphalt concrete) layers.

62 Modified Asphalt

**2. Field observation**

Karagandy oblast, July, 2016).

The fragments of another sequence for crack occurrence in the staged process of fatigue failure of alligator type on the asphalt concrete pavement are shown in **Figures 2** and **3**. As it is seen from **Figure 2**, there are only specific (separated from each other) quasi-parallel transverse cracks on the asphalt concrete pavement within the patch line. At first sight, they are similar to the low-temperature cracks. But that is not the case. The considered highway is located in Sharjah city (United Arab Emirates), where there is actually no winter. But, **Figure 3** shows the patterns of fatigue cracks of alligator type, which are formed at the further occurring of longitudinal cracks, connecting the existing transverse ones. During the period of observation, it has been determined that a large number of multiaxle heavy vehicles run along the highway, and it suggests that this type of staged fatigue failure has been connected with dense traffic of multiaxle heavy vehicles. Based on the abovementioned types of the staged failure for asphalt concrete pavements of the highways, we can formulate the following principle: "The process of fatigue failure for the asphalt concrete pavements of the highways occurs stage by stage and according to various types of stages. Type 1: stage I—quasi-linear parallel longitudinal cracks occur on the patch lines, between which quasi-straight line asphalt concrete strips are formed; stage II—formation of patterns of fatigue cracks of the alligator type by division of quasi-straight line strips of the asphalt concrete into the cells with small sizes by quasi-transverse cracks. Type 2: stage I—occurrence of insulated quasi-parallel transverse cracks; stage II—formation of alligator type cracks with relatively large dimensions of cells due to the occurrence of longitudinal cracks, connecting the existing transverse ones; stage III—decrease of dimensions for the cells of crack patterns due to the sequential occurrence of transverse and longitudinal cracks within each cell".

We suppose that the staged progressing of the fatigue failure is mechanically and thermodynamically "of benefit" to the system—to the asphalt concrete pavement, and which type of the stage is progressed—"the system will choose itself" depending on specific conditions: volume and type of traffic, regime and speed of traffic, weather and climatic conditions, design features, properties of the materials, including asphalt concretes, and so on.

**Figure 2.** Fatigue failure of asphalt concrete pavement: transverse fatigue cracks (Sharjah city, United Arab Emirates, August, 2010).

**Figure 3.** Fatigue failure of asphalt concrete pavement: alligator cracks (Sharjah city, United Arab Emirates, August, 2010).
