Experience of the Scandinavian countries

Wear of asphalt concrete pavements with studded tires

This article aims to facilitate and accelerate the adaptation to Russian conditions of foreign, primarily Scandinavian, experience in the design, construction, maintenance and operation of highways - taking into account the wear of road surfaces with studded tires.

The problem of rutting is one of the most pressing, along with other road “diseases” that are more advanced in age. It is especially relevant for designers, builders, operators and owners of those highways that are characterized by high traffic intensity and/or located in road-climatic zones I and II and in high mountain areas.

A generalization of the results of studies carried out in foreign countries with cold climates, as well as a survey of the operational and technical condition of road surfaces in St. Petersburg, showed that a significant reason for the formation of rutting on non-rigid road pavements is wear by studded tires. Studded tires, used in the cold (and not only) seasons, are similar in their effect to a road mill, only with less effect.

The annual wear of the top layer of asphalt concrete pavement on roads with different levels of traffic intensity varies within a fairly wide range - from 5 to 10 mm or more.

Unfortunately, the current regulatory documents in the Russian Federation practically do not take into account the wear of road surfaces with studded tires; there are no methods for predicting this wear, as well as requirements for the wear resistance of road surfaces of different technical categories.

At the same time, in the Scandinavian countries (especially Finland and Sweden), the northern states of the USA, Canada and other countries, a huge amount of scientific research has been carried out on this problem, methods for assessing the amount of wear have been developed, and methods for reducing rutting have been proposed.

Relevance and statistics

According to research by Unhola (1997), in Finland, a passenger car with four studded tires at a speed of 100 km/h, over 100 km in the 1960s, wore out 11 kg of coating material, in the 1990s - only 2.5 kg. Research by Lampinen (1993) showed that rutting was reduced by introducing effective system management of the condition of the road pavement (Pavement Management System), as well as by regulating the requirements for studded tires, reducing driving speeds in winter period and the use of high quality stone aggregates for asphalt concrete.

Coating wear in Sweden was 100 g/vehicle-km in 1975, but only 20 g/vehicle-km in 1995 (Jacobson, 1997). Research by Gustafson (1997) showed that during the winter period of 1988-1989. Road surfaces in Sweden “lost” 450,000 tons of material. This cost the Swedes about $35 million. Öberg (1997) reports the same figures, noting that the additional costs of eliminating road marking wear and cleaning road signs from contamination dropped from $4-8 million to $2-4 million.

Jacobson and Hornwall in 1999 concluded that 60-90% of rutting on busy roads is caused by studded tires.

Tests on a DD simulator carried out by the Swedish Road Transport Institute (VTI) showed that tires with light studs (1.0 g) create half the wear of tires with heavier steel studs (1.8 g), ( Jacobson and Wågberg, 1998). Even with the increased use of studded tires, tire wear has been significantly reduced (Jacobson and Hornwall, 1999). The Swedish government has now decided to make the use of studded tires mandatory in winter slippery conditions (Öberg, 2002).

According to research by Løberg (1997), studded tires wear out 300,000 tons of material annually on Norway's 63,000 km of paved roads.

In recent years, all Scandinavian countries have seen a steady trend towards reducing the wear of studded tires. Factors contributing to this are discussed in more detail below.

Regulatory regulation of the use of studded tires in Scandinavian countries

Studded tires are allowed to be used in winter (with some seasonal restrictions) in Denmark, Finland, Norway and Sweden. In Denmark and Sweden, the periods of permitted use of studded tires are the same (from 1 October to the end of April). In Finland and Norway - from November 1 to the first Monday after Easter (with the exception of Northern Norway where this period is slightly extended). In Finland and Sweden, the number of studs installed on one tire, the protrusion of the stud and its weight are regulated. In Norway these requirements are somewhat relaxed. Table 1 provides a summary of the regulations in force in the Scandinavian countries (“Ordic Regulations”, 2003)

Tab. 1.Summary of Scandinavian studded tire regulations

A country	Permitted season for using studded tires	Number of studs on one tire, pcs.	Spike protrusion	Spike force/weight
Denmark	From October 1 to April 30	Not limited	Not limited	Not limited
Finland	From November 1 to the first Monday after Easter	The quantity depends on the tire size: 13” tire – max. 90 pcs. tire 14 – 15“-max. 110 pcs.	PC – 3.2 mmCV – 3.5 mm
Norway	From November 1 to the first Monday after Easter. (In northern Norway from 16 October to 30 April)	tire 14 – 15“-max. 110 pcs. tire 16” or more – max. 150 pcs.	PC – 3.2 mmCV – 3.7 mm	PC 120N/3.1g. C/LT 180N/2.3g.
Sweden	From October 1 to April 30	The quantity depends on the tire size: 13” tire – max. 90 pcs. tire 14 – 15“-max. 110 pcs. tire 16” or more – max. 130 pcs.	PC – 3.2 mmCV – 3.5 mm	PC 120N/3.1g. C/LT 180N/2.3g.
Iceland	From November 1 to April 15

In Finland, studded tires have been used since the 1960s, and in winter they are installed on approximately 95% of passenger cars. Anti-icing treatment of road surfaces in Finland is carried out with road salt. The combined use of salt and studded tires causes a number of negative consequences for the environment. In the early 1990s, the Finnish government carried out a series of experiments to determine the feasibility of reducing the number of cars with studded tires and reducing salt consumption (or both in different combinations). Research has shown that, taking into account the socio-economic costs associated with the increased risk of road accidents, the use of studded tires and salt consumption at current levels is optimal.

If in Finland studded tires are used en masse, in Norway in recent years they have tried to limit this use, especially in urban settlements, where the roads are clear of snow almost throughout the winter. It has been established that studded tires create up to 17% of dust pollution in cities (Krokeborg, 1998). In Oslo, in 1999, in order to reduce the use of studded tires by 20%, a decree was issued to levy a tax on them in the amount of $160. Norwegian authorities actively promote the use of non-studded winter tires and snow chains (Fridstrom, “Winter Tires and Chains”, 1998).

Some researchers report an unsuccessful attempt to reduce the use of studded tires in Sweden (“Studded Tires”, 2001). The proposed restrictions did not produce results, and in recent years the use of studded tires has increased slightly.

Alternatives to studded tires

The main alternatives to spikes are traditional methods of winter road maintenance. These include scattering sand on an icy surface (friction method), preventative treatment coatings until an ice layer forms or melting the ice or snow-ice layer, if it has already formed, with road salt ( chemical methods). All this negatively affects environment and people's health.

Foreign and domestic experience in operating roads in winter shows that the introduction of a ban on studded tires, even when using traditional methods of winter maintenance, leads to an increase in the number of accidents.

Friction method is the main alternative to studded tires. However, increased sand consumption leads to increased dust on the roads. A study of respiratory diseases caused by road dust showed that increasing the consumption of sand does not provide an advantage compared to the use of studded tires. In addition, the costs of sand distribution and removal must be considered.

Finnish authorities have made some progress in reducing the overall amount of dust generated from friction sand. For this purpose, requirements have been set for the quality of sand materials and wet sand distribution technology has been applied (Valtonen, 2002). It has been established that the harm of dust can be reduced by using sand made from dark stone material with a reduced content of quartz, which crumbles less on the road.

A further study by Tervahuttu (2004) showed that friction sand applied to a roadway removes a significant amount of material from the asphalt concrete pavement, causing wear on the road surface (sandpaper effect), and this wear can be very large. This problem currently being studied in Finland.

Regarding application road salt or its combination with sand(sand-salt mixture), then in Finland sodium chloride (NaCl) is usually used as a de-icing material. Finnish authorities have found that on high-traffic roads, reducing salt consumption increases the number of accidents by 5-20%. On roads with low traffic volumes, sand is used instead of salt.

The use of salt creates a number of environmental problems: contamination of drinking water sources, toxic effects on flora and fauna, etc. In addition, salt causes corrosion of cars, steel and concrete structures. One study found that the damage from the use of salt is 15 times higher than the cost of its acquisition and distribution

Pavement wear studies

Finland

In 1982 - 1988 Lampinen studied temperature and precipitation data and measured rut depths on 8,000 to 10,000 km of Finnish roads. By examining the factors influencing rutting, he determined their relative importance. It was also found that the main volume of the rut (70-80%) is formed due to wear by studded tires. Plastic deformations of road pavement materials during the movement of heavy vehicles create 10-20% of the track volume. Typically, one heavy vehicle forms the same track as 3 to 5 passenger cars with studded tires. In Finland, from December to February, 85-90% of passenger cars and less than 50% of heavy vehicles are equipped with studded tires. Based on these data, Lampinen came to the conclusion that it is possible to partially reduce rutting by regulating the requirements for studded tires and limiting the season of their permitted use.

In the period from 1982 to 1988 Rutting on Finnish roads has been steadily decreasing. Thus, in 1982 the average rut depth was 9.5 mm, and in 1988 only 5.9 mm. The decrease is due to an increase in the volume of relaying the top layer of pavements, as well as the introduction of an effective pavement management system (PMS). According to PMS requirements, sections of roads with the deepest ruts must be covered in a timely manner with a new top layer of pavement. The measurement results showed that the average annual increase in rutting (increase in cross-sectional area) was about 487 mm 2 per 1000 SSID vehicles. The average annual increase in rut depth was about 0.36 mm per 1000 SSID vehicles. One passenger car wears out about 24 g of coating material per 1 km, and the wear of one stud is 100 micrograms. Annual costs are estimated at $35 million.

It has been found that rutting is strongly influenced by the type of stud (Lampinen, 1993). Wear is caused by the impact of the tenon and the scraping of material as the tenon leaves contact with the coating (reminiscent of the operation of a road mill). The impact energy depends on the mass of the spike and the vertical speed. The vertical speed is 10–15% of the vehicle speed and depends on the type of tire and the size of the stud protrusion above the tread surface. The force of the impact depends on the size of the protrusion of the spike and its design. The abrasive effect is also influenced by the speed and driving style of the car, i.e. movement in a straight line or curve, acceleration and braking.

Further research by Lampinen is aimed at refining the size of the protrusion and determining the force of the spike. From Figure 1.1. It can be seen that the lighter the stud, the less wear. It was found that wear is strongly influenced by the type of stone aggregate (crushed stone). The effect of travel speed on wear is shown in Fig. 1.2. The size of the tenon projection and the force of its impact have less influence on wear than the type of stone aggregate, the mass of the tenon and the vehicle speed (Sistonen and Alkio, 1986).

Unhola continued the research carried out by Sistonen and Alkio, using a similar test methodology (the “run-over” method). He confirmed that the wear of the coating is mainly determined by the weight of the tenon and the type of stone aggregate. It was also confirmed that the size of the protrusion and the force of the stud do not have a noticeable effect on wear. The studies were carried out at a car speed of 100 km/h.

Lampinen noted that the wear resistance of the coating increases significantly with increasing size of the coarse crushed stone fraction and the percentage of fraction larger than 8 mm. Specific area Mineral filler should be as small as possible.

Rice. 1.1.The influence of the stud mass on the wear of the coating at a vehicle speed of 100 km/h,SistonenAndAlkio, 1986

Rice. 1.2.Effect of travel speed and weight on coating wearthorn2.3 years

SistonenAndAlkio, 1986

Having summarized the data from these observations made during a survey of Finnish roads in 1982-1988, Lampinen investigated the influence of weather conditions on the formation of ruts. The process of rutting accelerates (compared to a dry surface) when the humidity of the coating increases and the temperature decreases below 0 C 0. Surface moisture has a greater effect on rutting than low temperature.

Lampinen believes that rutting on pavements can be reduced by reducing the number of stud impacts (i.e. fewer vehicles with studded tires and fewer studs embedded in the tread); reduction of initial rutting due to improved coating technology; improving the design of studs to reduce their abrasive properties (while maintaining traction characteristics) and by developing types of coatings that are less sensitive to rutting.

The final report, Design of Asphalt Concrete Pavements, carried out by a group of researchers in collaboration with the Finnish National Oil Company (Saarela, 1993), states that the most important pavement characteristic affecting studded tire wear is the wear resistance of the asphalt concrete. The most important factors affecting wear also include the intensity of vehicle traffic and the humidity of the coating surface. In some cases, vehicle speeds and cold climates must be taken into account in the design.

To determine the wear resistance of the coating to studded tires, laboratory tests using the SRK (“SRK” method) are used. When tested by the SRK method, three miniature studded tires are rotated at a temperature of 5 C for two hours on the surface of a wet sample of asphalt concrete with a diameter of 100 mm, used in the design of an asphalt concrete mixture according to Marshall. The abrasive wear index using the SRK method (SRK-value) is estimated by the loss of sample volume in cm 3 (European standard, 2000).

Using the SRK indicator, the service life of a pavement can be determined at a known traffic intensity. The most important factor influencing the wear of the coating is the quality of the stone aggregate used (Fig. 1.3). For example, the use of high-quality crushed stone (with all other factors being the same) can ensure a service life of the coating layer of 5 years, of poor quality - 2 years.

It is not recommended to select crushed stone based on its mineralogical composition, since in this case, depending on the percentage of different minerals, the suitability of crushed stone for use in coating varies widely. Crushed stone should be selected based on the results of laboratory tests. There are several testing methods for crushed stone, but the main laboratory test method currently used in Finland is the Ball Mill Test, called the Nordic Abrasion Test in the USA (Alkio, 2001). G.).

A sample of stone aggregate (crushed stone) weighing 1000 g is rotated at a speed of 90 rpm for one hour. in a standard mill together with 7 kg of steel balls with a diameter of 15 mm in the presence of approximately 2 liters of water. Crushed stone of fraction 11.2 – 16 mm is tested. The test result (Ball Mill Value) is assessed by the percentage of particles smaller than 2 mm remaining at the end of the test. Figure 1.4 shows the relationship between the ball mill test results and the SRK test results.

The standards for the application of ball mill test results (Ball Mill Value = Nordic Abrasion Value) established by the Finnish Road Administration are given in Tables 2.1. and 2.2 (Alkio, 2001). Stone aggregate (crushed stone) is divided into four classes depending on its strength. The most durable crushed stone is recommended for use on roads with traffic intensity SSID > 5000 vehicles/day. at a speed of more than 60 km/h and SSID > 10,000 vehicles/day. – at a speed of less than 60 km/h.

Another method for testing stone aggregate is commonly used in Finland (Saarela, 1993). A rock core placed between two pyramidal (angle 60 0 , radius 5 mm) heads is brought to destruction. The heads are made of steel with a Vickers hardness greater than 1200. The point load strength index is calculated from Equation 1.1.

Field tests have shown that the magnitude of rutting is correlated with the value of this index. This test is part of the Finnish Asphalt Pavement Specifications.

PLI = (D/50) 0.45 F/D Equation 1.1

where: PLI = point load strength index, MPa;

B = core diameter;

F = breaking force, N.

Rice. 1.3.The relative importance of factors affecting the wear of studded tiresSaarela, 1993

Rice. 1.4.Relationship between ball mill test results and test resultsS.R.K.method,Saarela, 1993

Table 2.1.Classification of stone aggregate quality(crushed stone),Alkio, 2001

Table 2.2.Selecting the quality of mineral filler (crushed stone),Alkio, 2001

Class	I	II	III	IV
Intensity (SSID, vehicles/day) on roads with speed > 60 km/h	> 5000	2500-5000	1500-2500	500-1500
Intensity (SSID, vehicles/day) on roads at driving speed< 60 км/ч	> 10000	5000-10000	2500-5000	500-2500

The next most important factor after the quality of the mineral aggregate affecting the wear of the pavement is the composition of the asphalt concrete mixture. The results of field tests showed that a pavement made of dense fine-grained asphalt concrete with a maximum crushed stone size of 20 mm (AB20) wears out 10% faster than a pavement made of SMA with a crushed stone size of 16 mm (SMA16). For this reason, on roads with high traffic volumes, the Finnish Ministry of Roads (FINRA) recommends the use of SMA. The characteristics of the composition of mixtures AB16 and SMA16 according to the Finnish Standards for Asphalt Concrete 2000 (Finnish Asphalt Specifications, 2000) are given in table. 3 and in Fig. 1.5. In Fig. Figure 1.6 shows the relationship between the percentage of particles larger than 8 mm in crushed stone and the abrasive wear index (SRK-value), determined by the SRK method. The larger the crushed stone used in the asphalt concrete mixture, the less wear.

Table 3.Characteristics of the composition of mixtures AB16 andSMA16 (Finnish Standardson Asphalt concrete, 2000)

Rice. 1.5.Grain compositionAB20 andSMA16 (Finnish Standards onAsphalt concrete, 1995)

Bitumen binder does not have a significant effect on wear. The use of more viscous bitumen slightly increases wear resistance. The amount of wear is not directly affected by the introduction of additives into the bitumen binder. Additives are usually used to improve other characteristics. However, in some cases (when crushed stone of a larger fraction is used than in a typical dense asphalt concrete mixture), the introduction of additives can increase wear resistance. Fiber, natural bitumen and polymers can be used as additives. The introduction of polymer additives improves wear resistance in extremely cold winters (Saarela, 1993).

Rice. 1.6.Influence of fraction percentage > 8 mm on wear determined by the methodS.R.K. (Saarela, 1993).

The results of field surveys of 14 experimental roads were analyzed by Kurki (1998). These test roads included pavement sections with different characteristics: type of crushed stone, grain composition, bitumen binder, adhesive additive, mineral powder, fiber, gilsonite and natural bitumen. A control section was set up at the beginning and end of each experimental road. The pavements in the control areas were made of dense asphalt concrete (AB20/IV) with a maximum nominal particle size of 20 mm. Crushed stone from granodiarite was used. Residual bitumen with a penetration of 120, obtained from the distillation of heavy Arab oil, was used as a bitumen binder. The transverse profile of the pavement and the rut depth were measured with a profilometer. The amount of wear was assessed by area (cm2) or wear coefficient.

The test results showed that, compared with the average wear for three winters of 1990-91, 91-92 and 92-93. wear of coatings during the winter of 1996-1997 decreased by 20%. This is entirely due to the transition to light spikes. In 1997, tires with light studs were installed on 43% of passenger cars, while in 1990 light studs were not used at all. In cold winters, wear was approximately 10% less than in warm winters. In the interior of Finland, where the climate is colder and drier, wear was less than in the coastal areas.

The relationship between wear area and rut depth depends on the width of the road. The rut depth, depending on the wear area and the width of the road, can be determined from equations 1.2 - 1.5.

Rice. 1.6. Effect of fraction percentage > 8 mm on wear determined by the SRK method (Saarela, 1993).
The results of field surveys of 14 experimental roads were analyzed by Kurki (1998). These test roads included pavement sections with different characteristics: type of crushed stone, grain composition, bitumen binder, adhesive additive, mineral powder, fiber, gilsonite and natural bitumen. A control section was set up at the beginning and end of each experimental road. The pavements in the control areas were made of dense asphalt concrete (AB20/IV) with a maximum nominal particle size of 20 mm. Crushed stone from granodiarite was used. Residual bitumen with a penetration of 120, obtained from the distillation of heavy Arab oil, was used as a bitumen binder. The transverse profile of the pavement and the rut depth were measured with a profilometer. The amount of wear was assessed by area (cm2) or wear coefficient.
The test results showed that, compared with the average wear for three winters of 1990-91, 91-92 and 92-93. wear of coatings during the winter of 1996-1997 decreased by 20%. This is entirely due to the transition to light spikes. In 1997, tires with light studs were installed on 43% of passenger cars, while in 1990 light studs were not used at all. In cold winters, wear was approximately 10% less than in warm winters. In the interior of Finland, where the climate is colder and drier, wear was less than in the coastal areas.
The relationship between wear area and rut depth depends on the width of the road. The rut depth, depending on the wear area and the width of the road, can be determined from equations 1.2 - 1.5.

Tread depth (mm) = 0.071 * wear area (cm2) – 3 width<8 м – 1.2
Track depth (mm) = 0.089* wear area (cm2) – 9 10 m >width > 6.5 m – 1.3
Track depth (mm) = 0.077* wear area (cm2) – 8 width > 12 m – 1.4
Tread depth (mm) = 0.071* wear area (cm2) – 3rd right lane
multi-lane road – 1.5

The rut depth correlates well with the wear index determined by the SRK method. It follows that the formation of rutting is strongly influenced by the quality of the stone aggregate (Kurki, 1998). The relationship between rut depth and SRK is shown in Equation 4.1.6

Track depth (mm) = 3.31 SRK + 8.14 (R = 0.80) – 1.6

On test roads, Equation 1.6 was used to convert rut depth to SRK. The mineral aggregate test results were then compared to the converted SRK. The comparison results confirmed that on test roads, the Ball Mill value and Point Load Index were well correlated with wear, while the Los Angeles abrasive wear test result was less correlated (Kurki , 1998).

Bituminous binder has a much smaller effect on the wear of the coating than crushed stone. This makes it difficult to assess the effect of the binder on wear. However, it has been found that the use of polymer-bitumen binder increases wear resistance by approximately 10%. Mineral powder does not affect wear resistance. Adhesive additives increase wear resistance when using certain types of crushed stone. It is recommended to consider the issue of using adhesive additives as an integral part of the design (selection) of the mixture composition (Kurki, 1998).

Kurki has developed a model for predicting SRK based on material properties. The model (described by equation 1.7) correlates well with the results of measurements on experimental roads.

SRK = G * B* (1.15 BM – 1.25 * PLI + 33.01) – 1.7,

where: BM is the ball mill test index, PLI is the point load index, G is the correction factor taking into account the grain composition (equation 1.8) and B is the correction factor taking into account the bitumen binder (B = 0.9 for polymer-modified binders and 1 ,0 – for all others).

G = 0.0069 * A + 0.004 * B + 0.496 – 1.8,

where: A = percentage of passage through the 8 mm sieve, B = percentage of passage through the 16 mm sieve.

The influence of traffic intensity, speed and climatic conditions on test roads on wear has not been studied.
The effect of winter road maintenance methods on wear was studied by Leppänen (1995). Thus, treatment with salt accelerates the wear of the studded tire coating, because The surface of a salt-treated coating remains wet longer than an untreated surface. Therefore, a wet coating wears out more than a dry one. Additionally, preventing winter slipperiness by treating with salt creates corrosion problems and negatively impacts groundwater quality. The expenditure of $3.5 million on a research program on the combined effect of studded tires and salt during winter road maintenance can be considered justified, because losses from road accidents significantly exceed this amount.

Sweden

According to a report (Jacobson, 1997), pavement wear in Sweden was 100 g/vehicle-km in 1975, but only 20 g/vehicle-km in 1995. Research has shown that the use of coatings with higher wear resistance reduces wear by 20 g/vehicle-km, the use of SMA - by 20 g/vehicle-km, the introduction of the ball mill test method for testing crushed stone (Ball Mill Test) - by 10 g/vehicle-km. km and the introduction of restrictions on the maximum permissible weight of studs - by 30 g/vehicle-km. Using more suitable crushed stone reduced overall wear by 38%. In relation to crushed stone, factors affecting wear include the percentage of coarse crushed stone and maximum size crushed stone Other factors that influence the wear of pavements include: the degree of compaction of asphalt concrete, the intensity of traffic and the number of studs on the tire, the speed of vehicles, the width of the road, the moisture content of the pavement surface, the type of stud, the size of the protrusion and the force of the stud. The wear of a wet coating significantly exceeds the wear of a dry one (depending on the type of crushed stone). Lightweight studs weighing 0.7 - 1.0 g wear half as much as steel studs weighing 1.8 g (Jacobson, 1997 and Hornwall, 1999).

Gustafson (1997) confirmed that in perfect coverage asphalt concrete should include wear-resistant crushed stone firmly bonded with binder with the highest (possible) content of coarse fraction. However, such a fraction should be limited to a size of 16 mm, because the use of a larger fraction increases rolling resistance and increases noise. Currently, the Swedish National Road Administration (SNRA) has adopted the concept of using crushed stone-mastic mixtures made from high-quality crushed stone for the installation of a top layer of coating on highways with high traffic volumes at speeds of 90 - 110 km/h.

In his article, Gustafson, citing the work of Jacobson, states that the annual wear of SMA coatings prepared on high-quality crushed stone currently ranges from 0.2 to 2 mm, while when using slightly lower-quality crushed stone, the annual wear increases up to 3 – 4 mm. With high traffic intensity, the wear of the studded tire coating is about 50 - 70% of the total wear. Gustafson also refers to studies carried out by Carlsson, according to which the wear of coatings made of high-quality SMA is about 6 g/vehicle-km, and the wear of coatings made of ordinary dense asphalt concrete on local crushed stone is 37 g/vehicle-km. Gustafson states that in the late 1980s, deep ruts were the rule rather than the exception, and in the early 1990s they became largely the exception as a result of the use of wear-resistant coatings, the use of less traumatic studs and the introduction of studded tire regulations.

The wear resistance of pavements is included in the functional requirements for road pavements in Sweden (Safwat and Sterjnberg, 2003).

In laboratory testing of asphalt concrete mixtures, the Prall test is used. The required value of the Prall index depends on the specified traffic intensity (SSID) - tab. 4. The SSID is clarified by introducing correction factors, taking into account the relative number of cars with studded tires, driving speed, lateral distribution of passenger cars (by lane) and winter maintenance methods.

Tab. 4.Swedish requirements for the Prall index value independing on traffic intensity (Safwat and Sterjnberg, 2003)

When tested by the Prall method, a cylindrical sample (Fig. 1.7.) with a diameter of 100 ± 1 mm, a thickness of 30 ± 1 mm is kept at a temperature of 5 ± 2 C 0 and then treated for 15 minutes with steel balls (40 pcs.) bouncing off the sample at rotation speed 950 rpm. The sample is continuously washed with water to remove particles of worn material from the test chamber. The Prall index (an indicator of abrasive wear) is the decrease in sample volume in cm 3. It is determined from the ratio of the difference in dry weight of a sample before and after testing to the bulk density of the sample (European Standard 2000).

Rice. 1.7.Cylindrical sample of asphalt concrete after testingPrall's method

Jacobson and Hornwall (1999) examined the effect of studded tires on rutting on five test roads with either SMA or porous asphalt wear layers and six control roads with dense asphalt or SMA wear courses. Cross section ruts were measured with a laser profilometer. For a comprehensive examination of surface defects, RST (Road Surface Tester) equipment mounted on a vehicle was used. Eight years of monitoring (1990 – 1998) showed that the wear of studded tire surfaces has decreased significantly over these years. Jacobson and Hornwall attribute this reduction to the construction of more wear-resistant coatings, the use of high-quality stone aggregates and the use of less traumatic studded rubber. The quality of the stone aggregate has the greatest influence on the wear resistance of coatings. The content of coarse crushed stone and the use of light spikes are somewhat less influential. The type of bitumen binder (regular or PBB) does not have a noticeable effect on wear resistance.

Jacobson and Wågberg (2004) developed models to predict rutting caused by studded tires. The models are based on 10 years of work carried out in the 1990s by the Swedish National Road Research Institute (VTI). They consist of three parts:

• a model for calculating the amount of wear depending on the number of cars with studded tires;
• model for calculating the wear distribution across the lane (wear profile);
• model for calculating annual costs based on material costs and service life.

It has been established that the amount of wear depends on the value of the ball mill test, the size of the maximum crushed stone fraction, grain composition and relative porosity. Several models have been developed, two of which are represented by Equations 1.9. and 2.1.

S d = 2.179 + KV * 0.167 – HALT4 * 0.047 + HM * 0.287 (R 2 = 0.84) – 1.9

S s = 1.547 + KV * 0.143 – MS * 0.087 (R 2 = 0.71) – 2. 1

Sd and Ss = relative wear of dense asphalt concrete mixture and SMA, respectively;
KV = ball mill test value;
HALT4 = crushed stone content larger than 4 mm;
HM = Marshall relative porosity;
MS = maximum crushed stone size.

When using the model to calculate the service life of a pavement, information about the distribution of wear across the lane (wear profile) is important because start date for work current repairs pavement is determined by the rut depth (Jacobson and Wågberg, 2004). The developed models of wear distribution across the traffic lane are based on the distribution of the flow of passenger cars along the traffic lanes close to normal. Standard deviation of the distribution of traffic flow in the transverse direction on roads with wide stripes traffic and on roads with shoulders is approximately 0.45 m, on roads with narrow lanes and multi-lane expressways and highways - 0.25 m. On roads with very high traffic volumes, the standard deviation approaches 0.20 m.

The combination of these two models is applied in a computerized version used to predict rut depth, service life and annual costs. The program contains the following data:

• Properties of crushed stone: fraction content > 4 mm (%), nominal size of coarse fraction (mm), ball mill test value for coarse fraction.
• Road and traffic parameters.
• Cost data: crushed stone, bitumen binder, additives, production of the mixture, mobilization of equipment, transportation, laying of the mixture, other possible costs (unit cost / m2).

Calculation using these models allows us to obtain the output abrasive wear profile, service life and annual costs. The model was confirmed by field data obtained on 16 experimental roads in the winter of 1996-1997. Experimental roads of different technical categories with different speeds with a service life of 1-6 years had wear layers of different types and qualities. The validity of the model was confirmed by its testing by Jacobson and Wågberg (2004).

The initial data for constructing the models is based on a large program of laboratory research carried out on the VTI road simulator. The research report includes the factors listed in Table. 5., and their influence on the wear of coatings. The models do not take into account the durability of coating materials.

Table 5.Factors studied in the road simulator and their influence (except traffic volume, use of studs, distribution of traffic flow along the width of the roadway and surface conditions (dry / wet or snow covered)

Materials	Small	Sometimes big	Big	Verybig
Crushed stone
Quality				X
Contents of large fraction				X
Nominal size of coarse fraction		X
Mixture design (dense or SMA)				X
Type of bitumen binder	X
Production
Fragility (flakiness)		X
Compaction degree		X
External factors
Travel speed			X
Climatic conditions	X
Type of studs, force of impact of the stud			X

Norway

According to a report by Løberg (1997), on Norwegian roads, the depth of ruts formed in runways depends on the mix design, quality of pavement construction, type of vehicles, driving speed, climatic conditions and pavement parameters, with the quality of the crushed stone being the most important. The Norwegian Road Administration measures 63,000 km of roads twice a year. Based on the results of these measurements, the wear resistance index of each road section is determined. As an indicator of wear resistance, the weight of the coating material (in grams) worn out per 1 km of a passenger car with four studded tires is taken. This value depends on the quality of the crushed stone used.

The Norwegians consider the mechanical strength of the crushed stone aggregate of the asphalt concrete mixture to be the most important characteristic. They use three methods to measure mechanical strength, measuring impact strength, abrasion and the EN studded tire wear rate (SRK test). They consider the abrasive wear indicator to be the most important characteristic. It is determined by the number of cubic centimeters of stone material (crushed stone) that wears out under the conditions established by the test methodology. The results of laboratory tests are consistent with the results of measurements of actual rutting on roads. The Løberg report (1997) states that even if high-quality crushed stone is used, the coating will not last long if the work is not carried out correctly.

Norwegian road maintenance regulations provide for the laying of a new layer of pavement on road sections with a rut depth of more than 25 mm and a rutting level exceeding 10%. On city roads with a permitted speed of less than 60 km/h, tracks with a depth of no more than 35 mm are allowed.

Methods to reduce coating wear

Research has shown that the intensity of pavement wear is determined by a number of factors depending on traffic parameters, road geometry, pavement characteristics, external influence and quality of pavement construction. Some of these factors affect wear more than others. Degree of influence various factors depends on local conditions. The following summarizes these factors and their impact on wear rates, and provides recommendations for reducing coating wear.

Traffic

The formation of rutting is directly influenced by traffic intensity, driving speed, and the percentage of cars with studded tires. As these parameters increase, the rutting process intensifies.

To reduce the wear of coatings without compromising traffic safety, the following measures are proposed:

• Reducing traffic intensity on highways (reorientation of traffic flows, transit, etc.)
• Regulating the period of permitted use of studded tires and limiting the number of studs on a tire.
• Speed ​​limit in winter.

Coating materials

Research has shown that the main factors influencing the wear rate of studded tire pavements include the properties of the pavement materials and the type of asphalt concrete mixture. It has been established that the most important factors are the properties of crushed stone. The main characteristics of crushed stone include resistance to abrasive wear and the content of a coarse fraction. It is recommended to use crushed stone that has passed laboratory tests in a ball mill (Ball Mill test) and asphalt concrete tested according to Prall (Prall test). The higher the content of coarse crushed stone, the less wear. When designing an asphalt concrete mixture, the adhesion of crushed stone to the bitumen binder and the need to introduce adhesive additives should be determined.

The next most important factor after crushed stone is the composition of the asphalt concrete mixture. Studies have shown that SMA has greater wear resistance than dense asphalt concrete mixtures. Bitumen binder has less effect on wear than crushed stone and mixture composition. The extent of this influence cannot be quantified. It has been established that in some cases the use of polymer-bitumen binder slightly reduces wear.

External factors

As the outside air temperature drops below 0 0 C and the humidity of the coating increases, the intensity of rutting increases. The intensity of rutting is influenced more strongly by the moisture content of the coating than cold temperature. The coating treated with de-icing reagents remains wet longer than the untreated one. The socio-economic impact of winter road maintenance should be taken into account.

The most important external factor to reduce wear is to limit the use of studded tires to those winter months when the surfaces are covered with ice or a snow-ice layer.

Road geometry

The intensity of wear increases in areas of acceleration and braking of vehicles. These sections include curves, ups and downs, and intersections. The rut depth is affected by the width of the lane. The narrower the lane, the deeper the rut.

The intensity of rutting with studded tires can be reduced by positioning curves, reducing the steepness of ascents and descents, reducing the length of transitional express lanes, and widening traffic lanes.

An important factor is the transverse profile of the coating, which accelerates water flow, because wet asphalt concrete wears out with studded tires more intensively. The construction of the pavement base from non-cohesive materials accelerates the flow of water from the surface.

Construction

It has been established that very an important condition Reducing rutting on roads is the quality of construction. The following factors influence the reduction of rutting of studded tires:

• Specification and compliance with the required density of asphalt concrete.
• Use of suitable equipment for the production and installation of appropriate mixtures, for example, SMA.
• Laying asphalt concrete on a dry surface (without water and ice crust) and with sufficient high temperature outside air.
• Intensive implementation of quality control and quality assurance activities.

The experience of Scandinavian and other countries indicates the possibility of significantly reducing the wear of studded tires.

The wear rate of the top layer of the stud coating is most influenced by the quality of the asphalt concrete stone aggregate. It is assumed that of the stone materials available in the North-West region, crushed porphyrite stone is the most resistant to the effects of studded rubber. This assumption should be confirmed by testing.

Depending on the predicted intensity of vehicle traffic, the stone aggregate used on the road being designed / repaired must meet the requirements of tables 2.1, 2.2 - (Finnish experience).

On sections of roads with high traffic intensity, it is not recommended to use dense, fine-grained asphalt concrete in the top layer of the pavement; it is recommended to use ShMA-20 (SMA 16 according to Finnish asphalt standards 2011). When selecting the composition of the mixture, you should, if possible, strive for the highest percentage of particles larger than 8 mm.

According to Finnish experience, the wear resistance of crushed stone should be periodically monitored by laboratory methods: Ball Mill Test, Point Load Test, and the Los Angeles method (optional).

It is recommended to use the functional method for designing asphalt concrete mixtures, adopted in the EU, in particular in Finland (Finnish Asphalt Standards 2011). In particular, for the top layer of coating, the functional properties of the mixture (SMA) of the top layer of coating include: wear resistance, shear resistance, water resistance, frost resistance, aging of asphalt concrete.

The wear resistance of asphalt concrete should be periodically monitored by laboratory methods: SRK test (Finnish experience) or Prall test (Swedish experience) or EN 16697-16 (European standards).

The design documentation should also include functional requirements for the wear resistance of the top layer, taking into account the data in Table. 4 or according to the Finnish Asphalt Standard 2011

– regulate the season of permitted use of studded tires. Install appropriate road signs;

– consider the possibility of reducing the permitted speed in winter (on highways to 90 – 100 km/h);

– consider the feasibility of using technologies for sealing ruts without surface milling existing coverage. For example, the Microsurfacing technology (filling the tracks with an emulsion-mineral mixture modified by polymers) or the technology used on bridges in St. Petersburg by JSC Lemminkäinen Dor Stroy (filling the tracks with cast asphalt concrete with embedded porphyrite crushed stone);

– Consider using a computer program developed in Sweden to predict studded tire wear and rutting costs (Jacobson and Wågberg, 2004).

©A.G. Spector, chief specialist of Dorservice LLC

When using this analytical material in full or in part, a link to the site
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ODM 218.3.082-2016

INDUSTRY ROAD METHODOLOGICAL DOCUMENT

Preface

1 DEVELOPED by a federal state budgetary educational institution higher education"Moscow Automobile and Highway State Technical University(MADI)".

Team of authors: Dr. Tech. Sciences V.V.Ushakov, Ph.D. tech. Sciences M.G. Goryachev, Ph.D. tech. Sciences S.V. Lugov, engineer A. Kudryavtsev.

2 INTRODUCED by the Department of Scientific and Technical Research and Information Support of Rosavtodor

3 ADOPTED by order of the Federal Road Agency dated 02/03/2017 N 142-r

5 INTRODUCED FOR THE FIRST TIME

1 area of ​​use

1 area of ​​use

These recommendations are intended to carry out work on the design, construction, reconstruction, overhaul, repair and maintenance of sections of federal highways.

The methodological recommendations are aimed at establishing the frequency of work on the installation of wear layers and protective layers installed during construction, reconstruction, overhaul, repair and maintenance of highways.

2. Normative references

1. GOST 33220-2015. Public roads. Requirements for operational condition.

2. GOST 9128-2009. Mixtures of asphalt concrete road, airfield and asphalt concrete. Technical conditions.

3. GOST 31015-2002. Mixtures of asphalt concrete and asphalt concrete crushed stone-mastic. Technical conditions.

4. GOST 33133-2014. Public roads. Viscous petroleum road bitumens. Technical requirements.

5. GOST R 52128-2003. Bitumen road emulsions. Technical conditions.

6. GOST 33078-2014. Public roads. Methods for measuring the adhesion of a car wheel to a surface.

3. Abbreviations

The following abbreviations are used in these recommendations:

BMO: Bitumen-mineral open mixtures.

LEMS: Cast emulsion-mineral mixtures.

SHPO: Rough surface treatment.

SMA: Crushed stone-mastic asphalt concrete.

SMAS: Crushed stone-mastic asphalt concrete mixture.

4. Terms and definitions

4.1. Highway- a transport infrastructure object intended for movement Vehicle and includes land plots within the boundaries of the highway right of way and structural elements located on or under them (roadbed, road surface and similar elements) and road structures that are its technological part - protective road structures, artificial road structures, industrial objects, elements of road construction.

4.2. Asphalt concrete- compacted asphalt concrete mixture.

4.3. Asphalt concrete mixture- a rationally selected mixture of mineral materials [crushed stone (gravel) and sand with or without mineral powder] with bitumen, taken in certain proportions and mixed in a heated state.

4.4. Bitumen-mineral open mixtures (BMO)- mixtures with a high content of crushed stone (55-85%), providing a frame structure of the layer and a surface with high roughness parameters.

4.5. Top coating layer- a structural element of the upper part of the road pavement, directly receiving forces from the wheels of vehicles and being directly exposed to atmospheric factors. Protective layers can be installed on the surface of the coating to extend its service life and restore transport and operational qualities.

4.6. Leveling layer- a layer placed on the base or existing coating, including after milling, in order to bring them into compliance with the requirements for evenness, to ensure the technological and operational parameters of the newly installed overlying layers.

4.7. Travel clothing- a structural element of a highway that absorbs the load from vehicles and transfers it to the roadbed.

4.8. Protective layer- a layer no more than 4 cm thick, designed to protect the underlying layer of asphalt concrete pavement from the direct impact of wheels road transport and a complex of weather and climatic factors. The protective layer is not taken into account when calculating the structural layers of road pavements and is subject to periodic restoration during operation.

4.9. Protective layer using the technology of constructing thin wear-resistant layers of hot bitumen-mineral mixtures- a layer 1.5-3.0 cm thick with increased frictional and waterproofing properties from a hot bitumen-mineral mixture laid over a pre-applied membrane of bitumen-latex cationic emulsion.

4.11. Cast emulsion-mineral mixture (LEMS)- a mixture of cast consistency, consisting of bitumen emulsion, stone material, mineral filler, water and special additives, selected in certain proportions, mixed using specialized equipment.

4.12. Wear layer- the top closing layer of road pavement, which directly absorbs the impact of vehicle wheels and weather and climatic factors. Subject to periodic restoration during operation.

In the absence of a protective layer, the top layer of the coating acts as a wear layer. In this case, the wear layer is taken into account when calculating the structural layers of road pavements and its thickness must be reduced by the amount of the maximum permissible transverse unevenness as required by the current regulations. regulatory documents technical regulation.

4.13. Rough surface treatment (RST)- technology for constructing a protective layer by pouring organic binding materials over the surface of the coating and distributing durable stone materials with compaction.

4.14. Crushed stone mastic asphalt concrete (SMA)- compacted crushed stone-mastic asphalt concrete mixture.

4.15. Crushed stone-mastic asphalt concrete mixture (SCMAS)- a rationally selected mixture of mineral materials (crushed stone, sand from crushing screenings and mineral powder), road bitumen (with or without polymer or other additives) and a stabilizing additive, taken in certain proportions and mixed in a heated state.

5. General provisions

5.2. Thin wear-resistant coatings made from hot bitumen-mineral mixtures, cast emulsion-mineral mixtures, bitumen-mineral open mixtures (BMO) and rough surface treatments (RST) can be used as a protective layer.

5.3 Rough surface treatments (RST) include:

- single surface treatment performed by separate or simultaneous application of organic binder and mineral material;

- double surface treatment.

5.4 The decision to install a protective layer should be made on the basis of a feasibility study, regardless of the stage of the life cycle of the road.

5.5 The wear layer should be restored during the operation of the highway by replacing it with a new layer of the same thickness made of materials that are not inferior in their physical and mechanical characteristics to the material of the restored layer.

5.6. The assignment of work on the installation of wear layers and protective layers on exploited sections of highways must be preceded by an examination of the condition of the existing road surface.

5.7. Based on the results of the survey, preparatory (preliminary) road work is prescribed. Preparatory road work may include:

Elimination of small defects with a low frequency of repetition (potholes, cracks, waves, sagging, dents, etc.). According to ODN 218.0.006-2002 “Rules for diagnostics and assessment of the condition of highways,” the weighted average score of such coverage is at least 3.5. In this case, the permissible sizes of defects should not exceed the sizes established by GOST 33220-2015.

Installation of a leveling layer of asphalt concrete mixture. It is prescribed in case of reduction of the longitudinal evenness of the coating to the maximum permissible values, in accordance with the requirements of GOST 33220-2015 and.

Eliminating ruts. Assigned in accordance with the "Recommendations for identifying and eliminating ruts on non-rigid road surfaces". The criterion for assigning such work is to reduce the transverse evenness of the coating to the maximum permissible values.

Milling the surface followed by laying asphalt concrete layers. Milling to the thickness of the coating layer can be performed when installing a wear layer of asphalt concrete. This measure should be used in the event of a reduction in the longitudinal and/or transverse evenness of the pavement to the maximum permissible values, but with the requirement to maintain design elevations or the unsatisfactory condition of the pavement itself (weighted average score less than 3.5) - see Table 1.

5.8. The frequency of work on the installation of wear layers and protective layers is assigned based on the actual average annual daily traffic intensity in physical units, established according to data automated points taking into account traffic intensity. In case of their absence, traffic recording should be carried out monthly, once on weekdays and weekends (holidays), for 2 hours of continuous observation in the interval from 10.00 to 18.00. The result of a 2-hour measurement is converted into daily intensity using the formula:

Where is the daily traffic intensity, vehicles;

- traffic intensity of 2-hour measurement, auto.

The average monthly daily traffic intensity is determined using the formula:

Where is the average monthly daily traffic intensity, vehicles;

and - daily traffic intensity on weekdays and weekends (holidays), respectively, author;

and - the number of weekdays and weekends (holidays) in a given accounting month, respectively.

The average annual daily traffic intensity is determined using the formula:

Where is the average annual daily traffic intensity, vehicles;

- the sum of average monthly daily traffic intensity for the reporting year, auto.

It is allowed to establish the average annual daily traffic intensity for an incomplete reporting year, but not less than based on the results of accounting for nine months.

5.9. Determination of the intensity of traffic flow in the busiest lane is carried out on the basis of data from systematic recording of vehicle traffic either in individual lanes, or using a formula taking into account the number of lanes:

Where is the average annual daily traffic intensity along the busiest lane, vehicles;

- band coefficient (Table 1).


Table 1 - Bandwidth coefficient values

Number of lanes
Bandwidth factor

5.10. Based on data on the actual average annual daily traffic intensity on the busiest lane, monitoring is carried out to ensure compliance of the actual service life of the wear layer or protective layer with regulatory requirements. In case of non-compliance, the reasons for the non-compliance are identified in order to take measures to comply with regulatory requirements for overhaul periods.

6. Frequency of work on the installation of wear layers and protective layers of the road surface

6.1. Asphalt concrete mixtures must meet the requirements of GOST 9128-2009.

6.4. The frequency of work on the installation of wear layers and protective layers is indicated in Tables 2...12.

6.5. It is recommended to carry out work on the installation of rough surface treatment on roads of categories III-V when the traffic flow intensity on the busiest lane is no more than 5000 vehicles/day.

The frequency of work is shown in Table 2.


Table 2 - Frequency of work on the installation of rough surface treatment

Actual intensity of traffic flow in the busiest lane, vehicles/day	Frequency of work for road climatic zones, years
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Moving cars have the greatest impact on the wear of coatings. Under the load transmitted to the wheel, the tire deforms (Fig. 6.7). In this case, at the entrance of the tire to the contact zone with the coating in the tire, compression occurs, and at the exit from the contact, expansion occurs. Path traveled by a point on the tire in the plane of contact l 1, less than outside it l. Therefore, in the plane of contact, the point moves with an acceleration greater than how it moved before entering contact with the coating. At the same time, the angular velocity a in sectors is practically the same. Therefore, the point passes along the coating a path of a certain length with slipping instead of just rolling.

Rice. 6.7. Wheel tire deformations that contribute to coating wear:
A - compression zone, B - tension zone

Under the influence of these increased tangential stresses in the plane of the track, abrasion of the vehicle's coating and tire occurs. The greatest tangential forces and the greatest wear occur when the vehicle is braking. Wear and tear when driving trucks is approximately 2 times greater than when driving cars. The greater the strength of the coating material, the less and more uniform the wear of the coating across the width. On coatings made of low-strength materials, the wear rate is much higher, and ruts and potholes form more often. The use of igneous rocks for crushed stone instead of sedimentary rocks reduces wear by 60%. Increasing the bitumen content from 5 to 7% reduces wear by 50-80%.

The wear of the coating within the roadway and the thickness of the coating occurs unevenly and abrasion ruts form on the coating along the rolling stripes, the depth of which can vary from a few millimeters to 40-50 mm. In such ruts, during rain, a significant layer of water is created, which leads to a decrease in the adhesion qualities of the surface and aquaplaning.

Average wear over the entire coverage area h avg, mm, is:

h avg = k× h n, mm, where (6.1)

k- wear unevenness coefficient is on average 0.6-0.7;

h n- amount of wear in the rolling strip, mm.

For advanced coatings, wear is measured in mm, and for transitional coatings also by the volume of material loss in m 3 /km.

Features of wear of rough road surfaces. Wear of the rough surface of road surfaces manifests itself in a decrease in height and in the grinding of uneven macro-roughness. The reduction in macro-roughness of coatings under the influence of car wheels occurs in two stages (see Fig. 7.3). At the first stage, immediately after completion of construction, the roughness of the coating is reduced due to the immersion of the crushed stone grains of the wear layer into the underlying coating layer. The magnitude of this immersion depends on the intensity and composition of the movement, the size of the crushed stone and the hardness of the coating. The hardness of the coating is assessed by the depth of immersion of the hardness tester needle and for asphalt concrete pavements it is divided into: very hard - 0-2 mm; hard - 2-5 mm; normal - 5-8 mm; soft - 8-12 mm; very soft - 12-18 mm. Cement concrete coatings are absolutely hard.

Determination of coating wear by calculation. The average reduction in the thickness of road surfaces per year due to wear can be determined using the formula of Prof. M.B. Korsunsky (it should be noted that these studies were carried out more than 50 years ago and the quantitative values ​​of their results are not very applicable to modern roads and cars):

h = a + b× B (6.2)

h- annual wear of the coating, mm;

A- a parameter that depends mainly on the weather resistance of the coating and climatic conditions;

b- an indicator depending on the quality (mainly strength) of the coating material, the degree of its moisture, composition and speed of movement;

IN- traffic volume, million gross tons per year; N» 0.001× IN (N- traffic intensity, vehicles/day).

Coating wear for T years, taking into account changes in the composition and intensity of traffic in the future in geometric progression can be determined by the formula

where (6.3)

h T- wear of the coating for T years, mm;

N 1 - traffic intensity in the reference year, vehicles/day;

TO= 1.05-1.07 - coefficient taking into account changes in the composition of the movement;

q 1 - indicator of annual growth in traffic intensity, q 1 > 1,0.

Parameter values A And b are given in table. 6.6.

Table 6.6

Coatings	A, mm	b, mm/million gross tons	[h], mm, taking into account uneven abrasion
Asphalt concrete	0,4-0,6	0,25-0,55
Crushed stone and gravel, treated with viscous organic binders, restored:
double surface treatment	1,3-2,7	3,5-5,5
single surface treatment	1,4-2,8	4,0-6,0
Crushed stone:
made of durable stone	4,5-5,5	15,0-20,0
from low-strength stone materials	5,5-6,5	19,0-25,0
Gravel:
made of durable gravel	3,0-4,0	16,0-22,0
from low-strength gravel	4,0-6,0	20,0-30,0

Notes 1. Average values A And b accepted for roads located in a zone of moderate moisture (III road-climatic zone) and built from stone materials that meet the requirements of the standards. 2. For roads with improved pavements located in the zone of excessive moisture (road climatic zone II), the upper limits are accepted, and for roads located in areas with a dry climate (road climatic zones IV and V), the lower limits of values ​​are accepted. A And b. 3. For roads with crushed stone and gravel surfaces located in an area of ​​excessive moisture, lower limits are accepted, and in areas with a dry climate - upper limits A And b. 4. If the width of the carriageway exceeds 7.0 m, then the value b reduced by 15%, and if it is less than 6.0 m, then b increase by 15%.

In recent years, tires with studs or chains have been used to improve vehicle stability. Experience shows that this dramatically increases the wear of road surfaces.

At the moment of contact with the coating, each spike strikes at high speed. The spike has a very small mass, but repeated repetition of these blows in one place helps to weaken the top layer of the coating. A greater abrasive effect is exerted by a spike emerging from the contact zone, where the tire together with the spike slides along the surface of the coating, abrading it.

The duration of wear of asphalt concrete pavements when operating tires with chains and studs is reduced by 2-3 times. Even on surfaces made of high-strength cast asphalt concrete on German highways, on which vehicles equipped with studded tires move, after 1-2 years ruts form along rolling strips up to 10 mm deep.

Therefore, under the operating conditions of Russian roads, the use of tires with studs and snow chains on public roads should be strictly limited.

The value of permissible wear can be taken as a criterion for the limiting state of the road surface for wear N and: for asphalt concrete pavements 10-20 mm; for crushed stone and gravel treated with organic binders - 30-40 mm; crushed stone from durable crushed stone - 40-50 mm, gravel - 50-60 mm.

Based on this, road maintenance organizations, when accepting roads after construction or repair with reinforcement, must require from builders that the coating have a thickness greater than that calculated from the strength condition by the amount of permissible wear, i.e.

h n = h np + N and, mm, where (6.5)

h np- calculated thickness of the pavement based on the strength of the road pavement, mm.

Wear measurement. Annual wear in fractions of mm of cement concrete, asphalt concrete and others monolithic coatings measured using benchmarks embedded in the thickness of the coating and a wear gauge. With this method of measuring wear, reference cups made of brass are first placed in the coating. The bottom of the cup serves as the surface from which the count is made.

Wear is also determined using trapezoidal-shaped plates (marks) made of limestone or soft metal, embedded in the coating and abraded together with it. To determine the wear of coatings can be used various kinds electrical or ground penetrating radar instruments used to measure the thickness of layers in layered half-spaces.

Having data on the actual wear of the coating and the maximum permissible wear, the wear coefficient of the coating is determined.

CHAPTER 7. Patterns of changes in the main transport and operational characteristics of highways

Wear (abrasion)- the main type of destruction of the road surface, determines the conditions and terms of its service. Wear is a reduction in the thickness of the coating due to the loss of material during operation under the influence of car wheels and natural factors.

Wear of the coating occurs under the influence of tangential forces acting in the plane of the track of automobile wheels and caused by the work of tires to overcome friction forces. Tangential stresses in the plane of the track cause abrasion of the road surface and car tires along the entire route. Such stresses increase from a complex of influences that cause the wheel tire to slip in the plane of the track under normal rolling conditions. In addition, natural factors contribute to increased wear, since the coating material weakens when saturated with water, and in winter due to its freezing.

Wear of the coating occurs across the entire width of the roadway, but most of all on the rolling strips, where car wheels often pass in one track. In studies, the amount of wear is conventionally assumed to be uniformly distributed over the entire coating area. In this case, the average wear value h av mm is h av =kh n. where k is the coefficient of uneven wear, averaging 0.6-0.7; h„ is a certain amount of wear in the rolling strip, mm.

For advanced coatings, wear is measured in millimeters, and for transitional and simplest type coatings also by the volume of material loss, m 3 /km.

In addition to wear, road surfaces are subject to deformation and destruction, described below and shown in Fig. 25 and 26.

Peeling- exposure of the coating surface, separation of thin surface films and flakes of the coating material, deformed under the influence of water and frost, as well as car wheels. This process is especially intense in the spring when the upper layers of the coating are often heated by sunlight during the day and frozen at night. Peeling occurs the more intensely, the higher the porosity and the lower the strength of the coating material. The peeling process also develops from the action of chlorides used in the fight against ice. They are especially harmful for cement concrete pavements with a high content of surface pores. Chlorides indirectly increase peeling of coatings, reducing the frost resistance of concrete. These influences release the latent heat of melting of the ice on the coating, causing it to thaw and then freeze again. To stop peeling, it is necessary to reduce the porosity of the upper part of the coating by treating it in the summer with bitumen with a scattering of fine mineral material.

Chipping- the process of destruction of the coating that follows after peeling, during which larger grains of mineral material are separated from the coating. Not only transitional type coatings chip, but also all advanced ones due to the loss of connection between the grains of the materials. The material from porous cement concrete coatings crumbles as a result of increased peeling processes. Crushed stone grains that are poorly bonded to bitumen (silicon grains) fall out of asphalt concrete pavements. The reasons for coating chipping are also the low quality of mixtures due to their transportation in dump trucks (sand residues get into the coating), under-rolling of the coating in cold and rainy weather, etc. This process can be stopped by laying a protective layer.

Edge breaking- destruction of coatings in places where they interface with roadsides, which occurs most often in cases of heavy trucks driving over the edges of coatings. On cement concrete pavements, in addition, the edges break off along expansion joints when the quality of the concrete is low or when there is no connection between the slabs. When a car moves through a seam, the slab bends and, if there is no good connection between the slabs, the wheel hits the edge of the next slab. When constructing a road, the edges of the pavement must be protected from breaking off, for which purpose reinforcing (edge) strips are installed on the roadsides. On those roads where there are no such stripes, they must be made during repair work.

Waves- These are deformations that form on coatings with excessive plasticity. The top layer of asphalt concrete pavements, under the influence of tangential forces, especially during braking, shifts on slopes and in places where public transport stops. Waves, or folds, form mainly in hot sunny weather, when the coating heats up to 60° or more. On overly flexible soil and gravel surfaces treated with organic binders, waves can reach such sizes that driving on the road becomes impossible, causing vehicles to move to the side of the road. The formation of waves can be stopped by scattering fine, acute-angled mineral material and then rolling it with heavy rollers on metal rollers. A type of wave is sagging, in which the material moves in the transverse direction. For example, in places where public transport stops, the material is displaced onto the curbs.

Comb- type of destruction of transitional type coatings, mainly gravel, and sometimes lightweight advanced type coatings. The comb has the appearance of regular, more or less clearly defined transverse protrusions, alternating with depressions. To eliminate this drawback, it is necessary to carry out pickling of the coating, followed by correction of the road profile using motor graders and rolling.

Shifts- deformations of the coating that occur under the action of tangential forces from car wheels, especially in places where they are braking. Shifts are formed mainly in the absence of proper connection of the coating with the base or the upper layer of the coating with the lower one. Shifts are accompanied by cracks. In places of shear, especially in cracks, the coating begins to collapse.

Dents- depressions in plastic coatings in the form of imprints of the pattern of car tires or tracks of tracked vehicles, formed in hot weather.

Cracks, formed on cement concrete pavements, usually serve as a sign of insufficient strength and the beginning of destruction. Transverse temperature cracks form at large distances between seams and in cases where adhesion has occurred concrete slabs with the base and they lost the ability to move with temperature changes.

Longitudinal cracks occur when the subgrade is not uniformly compacted - when its edges, compacted less than the middle, begin to produce precipitation. Oblique cracks appear above local voids - sediments of the subgrade and with insufficiently strong coatings.

Transverse temperature cracks form on coatings, the surface of which is treated with organic binders, with a sharp decrease in air temperature in autumn and with large temperature changes in winter. They are regularly distributed at certain distances from each other (6-10 m). They are formed due to insufficient resistance of the coating material to temperature stresses.

Axial cracks on asphalt concrete pavements appear due to poor coupling of the asphalt concrete mixture of two adjacent strips, when the hot mixture is adjacent to a previously laid cold strip. Oblique cracks are the development of transverse and longitudinal cracks with insufficient coating strength.

Network of cracks occurs on the road surface, usually when the base strength is insufficient. Especially often, a network of cracks forms in the spring, when waterlogged soil causes large deflections of the base under load. A more rigid coating material cannot withstand such deflections, as a result of which cracks appear. All types of cracks listed above are shown below.

Wear of road surfaces and its causes [add. V. 29]

Moving cars have the greatest impact on the wear of coatings. Under the load transmitted to the wheel, the tire is deformed (Fig.). In this case, at the entrance of the tire to the contact zone with the coating in the tire, compression occurs, and at the exit from the contact, expansion occurs. The path traveled by a point on the bus in the plane of contact?1 is less than outside it?. Therefore, in the plane of contact, the point moves with an acceleration greater than how it moved before entering contact with the coating. At the same time, the angular velocity a in the sectors is practically the same. Therefore, the point passes along the coating a path of a certain length with slipping instead of just rolling.

Under the influence of these increased tangential stresses in the plane of the track, abrasion of the vehicle's coating and tire occurs. The greatest tangential forces and the greatest wear occur when the vehicle is braking. Wear and tear when driving trucks is approximately 2 times greater than when driving cars. The greater the strength of the coating material, the less and more uniform the wear of the coating across the width. On coatings made of low-strength materials, the wear rate is much higher, and ruts and potholes form more often. The use of igneous rocks for crushed stone instead of sedimentary rocks reduces wear by 60%. Increasing the bitumen content from 5 to 7% reduces wear by 50-80%.

The wear of the coating within the roadway and the thickness of the coating occurs unevenly and abrasion ruts are formed on the coating along the rolling stripes, the depth of which can vary from several millimeters to 40-50 mm. In such ruts, during rain, a significant layer of water is created, which leads to a decrease in the adhesion qualities of the surface and aquaplaning.

The average amount of wear over the entire coverage area hav is.