Evaluation of a road section performance in North Kazakhstan

2.1. Short description

The length of the observed section is 47 km and is located on the “Yekaterinburg-Almaty” road (380-427 km). The section has the following main indicators: road category – III; number of traffic lanes – 2; carriageway width – 7.0 (2×3.5 m); shoulder width – 2×2.50 m. The section is located at a distance of 85 km from Kostanay city (Northern region of Kazakhstan) in the direction to Yekaterinburg (Russia). In 2005, a full depth repair of pavement was carried out on the section, and in 2014-2015 midterm repair was carried out-seal coat surface treatment was arranged.

2.2. Pavement structure

To determine the existing structure of the pavement, excavations of the pavement and subgrade were carried out at two places (Table 1): 1 – km 380+000; 2 – km 421+000. The excavation results are presented in Table 1.

3.1. Mobile diagnostic laboratory

A mobile diagnostic laboratory (Fig. 1(a)) which is equipped with laser and electronic systems for measuring and processing the roughness of a pavement, rutting and defects (cracks) on a pavement surface was used in the work [9]. This mobile laboratory also includes a falling weight deflectometer (FWD) to assess a pavement capacity (Fig. 1(b)).

Fig. 1a) A mobile diagnostic laboratory; b) a falling weight deflectometer. The photographs presented in this paper were taken by the co-author Azamat Zhaisanbayev during field studies carried out in July 2017 on a road section (length: 47 km) of the “Ekaterinburg-Almaty” highway located in the Kostanay region, Kazakhstan

a)

b)

The following indicators were determined by the laboratory: rut depth, roughness, cracking and bearing capacity of the road section. The roughness of the section pavement surface is characterized by the International Roughness Index (IRI, m/km) [10].The cracking is estimated by two indicators: the pavement surface which is occupied by block cracks and the total length of longitudinal and transverse cracks.

The bearing capacity of the pavement structures is characterized by the total elasticity modulus [11] $E_o$ (MPa) determined by the formula:

where $q$ is a specific load on a pavement surface, MPa; $D$ is a diameter of a loading plate, mm; $\nu$ is an average value of the Poisson’s ratio of the pavement structure, equal to 0.3; $l$ is a maximum deflection of the pavement surface, mm.

3.2. Intensity and composition of traffic

The MetroCount 5600 vehicle classifier system with two rubber pneumatic tubes (two pneumatic tubes) [12] was used to determine the intensity and classification of traffic on the road section. This system defines all vehicles passing on the selected section and divides them into 12 classes.

4.1. Intensity and composition of traffic

On the considered highway section the intensity and composition of traffic measured in 2017. Results of measured intensity are shown in Table 2: light vehicles (cars and minibuses) predominate (more than 50.1 %) in the traffic; single trucks with axle loads up to 2 tons – 31.7 %, single trucks with axle loads 5-10 tons – 3.5 %, trucks with trailers and tractors with semi-trailers – 14.7 %.

Thus, it can be considered that the pavement structure on the section is under average mechanical loading conditions.

4.2. Cracks and cracks network

The asphalt concrete pavement degradation in the form of cracks was characterized by the following two indicators: 1) the area of the asphalt concrete pavement on which there is a network of cracks and 2) the total length of longitudinal and transverse cracks.

Fig. 2Pavement area with a cracks network

The areas of the asphalt concrete pavement with a cracks network at different kilometers of the highway section are shown in Fig. 2 which shows that the values of cracks network areas vary over a very wide range: from 0.25 m² (388) to 106.7 m² (418 km). At the same time, half of all areas with a cracks network (82.9 %) have a value of up to 25 m² (Fig. 2).

The values of the total lengths of longitudinal and transverse cracks on the asphalt concrete pavement are shown in Fig. 3. This figure shows that the lengths of cracks at different kilometers of the highway section are not uniformly distributed, they have large spreads: from 125.6 m (a minimum value) to 2282 m (a maximum value). At the same time, 70.2 % of the cracks lengths are in the range from 100 m to 650 m (Fig. 3). In this interval, the average length of cracks is 375 m.

Fig. 3Total lengths of longitudinal and transverse cracks

4.3. Rut depth

It is clearly seen (Fig. 4) that both in the direct and reverse directions the rut depth on puts lines of the asphalt concrete pavement along the length of the section is distributed significantly not uniformly. The minimum and maximum rut depths in the direct direction are 1.8 mm and 12.8 mm, respectively, and in the reverse direction: 2.2 mm and 11.1 mm, respectively. It should be noted that nowhere in the section under consideration the rut depth no exceeds the permissible maximum value of 20 mm [13].

Fig. 4Rut depths on the asphalt concrete pavement

4.4. Roughness

From the histogram (Fig. 5) it can be seen that the IRI value in the direct and reverse directions has an approximately the same distribution over the highway section. Minimum and maximum IRI values in the direct direction equal to 1.7 m/km and 4.2 m/km, respectively, and in the reverse direction –1.7 m/km and 4.2 m/km, respectively. As can be seen from Fig. 5, in the direct direction, more than 50 % (in fact 53.2 %) of the IRI values are in the range from 2.2 to 2.8 m/km; in the reverse direction, more than 60 % (61.7 % in fact) of the IRI values are in the range from 2.2 to 2.8 m/km.

According to the standard on pavement surface roughness in Kazakhstan [10], at traffic intensity from 3000 to 4500 veh/day, highway sections with IRI value up to 3.1 m/km are rated as “excellent” and with IRI value from 3.1 to 3.6 m/km – as “good”. According to Fig. 5, we determine that 87 % and 94 % of the section in the direct and reverse directions, respectively, have an “excellent” rating in roughness, and 13 % and 6 %, respectively, have a “good” rating. Thus, it can be concluded that the highway section at the time of the survey had a good operational condition.

Fig. 5Roughness of the asphalt concrete pavement

4.5. Elasticity modulus

On the considered road section the total elasticity modulus of the pavement was measured only in direct (Kostanay-Yekaterinburg) direction. The values of the total elasticity modulus are shown in Fig. 6. Note that the modulus values have large spreads: minimum total elasticity modulus is 229 MPa (400 km), maximum total elasticity modulus is 869 MPa (395 km); the maximum value of the modulus is 3.8 times greater than its minimum value. At the same time, more than half (57.5 %) of the modulus values are in the range of 285-480 MPa.

Fig. 6Total elasticity modulus of the pavement