Causes of road wear. Ways to strengthen the top layer of asphalt

The service life of asphalt, depending on its composition, the nature of the laying, the place of laying and the technologies used, may vary. Each layer of asphalt has its own lifespan. For example, an earth cover can last up to 10 years without intervention. While the top layers of asphalt without repair should last about 3-5 years. However, a road is not a natural structure, but a very complex engineering structure, and therefore requires constant monitoring, diagnostics and periodic repairs. Road wear is a natural phenomenon. It is influenced by various factors, which are usually divided into internal and external. The internal ones are:

• Errors during road design. Often, errors in calculations, geodetic measurements lead to cracks, creases, pits and premature wear. Such errors are usually very difficult to correct, most often costly measures are required to eliminate them, in particular overhaul.
• Use of cheap and low quality materials. It is common to hear about unscrupulous contractors using materials that were not agreed upon in the agreement. Meanwhile, the use of each type of material in the construction of the road is determined by the purpose of the route, its throughput climatic conditions in which it will operate. Therefore, the use of low-quality materials leads to very rapid wear of the road. Sometimes, in 1-2 years of use, the road goes through all the stages of wear and tear and comes to a critical one, requiring a complete overhaul.

• Improper laying of the road and non-compliance with the rules of SNIP and GOST. Incorrect road laying is another situation that you often hear about. For example, which has already become anecdotal, laying hot asphalt in the rain. Or the delivery of hot asphalt to the laying site below the required temperature, which should be considered a marriage. Failure to comply with the technologies specified in GOST and SNIP when laying roadbed can subsequently cause early wear of the road - premature formation of cracks, holes, chips, deformation of the subgrade and upper layers roads. As a rule, such defects are corrected by “patching” cracks and patching. But they can not always correct the situation, and sometimes they can only aggravate it. Pothole repair is advisable to fix the problem on separate area roads. If the area is too large or the source of the defect is located in the deep layers, patching won't fix things.

The road is a complex engineering structure, where any mistake will certainly affect the future state of the track.

External factors leading to road wear include:

• Climatic conditions and weather. The more contrasting and changeable the climate, the worse the road will be. In almost the entire European part of Russia, there are three contrasting seasons in a year - spring and autumn that are similar to each other, abundant in rains and floods, frosty winters and hot summers. Such conditions for the road may be more difficult than, for example, in southern regions and countries where the main problem for the road is heat. The same for the northern regions - the main task is the frost resistance of the roadway. In areas with big amount precipitation, temperature fluctuations, the requirements for asphalt are higher. Asphalt mixtures must be able to operate over a wide temperature range. This is achieved by special compositions of polymer-bitumen binders.

• Excessive traffic flow. Traffic intensity is one of the main factors contributing to road wear. Impact calculations Vehicle taken on the basis the following indicators– brand of cars (light, medium, heavy) carrying capacity, total weight, capacity of people, traffic intensity in both directions (number of cars per day). The ratio of local and transit transport is also taken into account. Flow rate is a very dynamic category that needs constant monitoring. Since the intensity of transport can be affected by various factors that have nothing to do with the road sector. For example, holding sports competitions in a locality can dramatically increase the number of vehicles and the load on the track. Construction of warehouses, trading bases, shopping centers and other objects of urban infrastructure can affect in the same way. Road facilities themselves can also have an impact. The repair of one route or its critical wear can dramatically increase the intensity of the traffic flow on another route.

It is worth adding that the division into external and internal factors very conditional, since when designing a road external factors should be calculated with the greatest possible accuracy.

Stages of road wear

As mentioned above, road wear is a natural situation. If the road was built without errors in design, and its laying was carried out under proper conditions, then wear and tear will be quite predictable. It is possible to conditionally distinguish three stages of wear of the roadway.

The first stage is indicated by minor chips, cracks, dents on the asphalt. The coating becomes less rough. Such changes, depending on the type of road, its category and the intensity of the traffic flow, can occur both 1-2 years after the asphalt is laid, and 3-4 years later. It should be noted that the first stage of wear is normal condition roadbed. At this stage, the road can last a very long time without major changes.

When moving to the second stage of wear, the roadway is characterized by noticeable deformations - pits, cracks and potholes become more voluminous. There are noticeable dents and bumps. At this stage, a point reconstruction of the road is required - patching, sanitation of cracks, reinforcement.

The third stage is heavy wear. If the road comes to the third stage at all, this speaks first of all of its extremely neglected state. Movement on such asphalt becomes dangerous - strong potholes, cracks, deep holes, destruction of the roadside. The only possible way out of this situation is a major overhaul of the road.

Ways to strengthen the top layer of asphalt

Strengthening the pavement, and in particular the upper layer of the road, as the most vulnerable, is an important measure that prolongs the life of the roadway and postpones the need for spot or major repairs.

The classic way to strengthen asphalt is to lay a new layer of asphalt concrete on top of the old pavement. There may not be one layer, but several. This method is quite costly, both financially and labor-wise. The fact is that, as practice shows, the thickness of the new reinforcing layer should be from 12 to 15 cm in order to effectively resist the deformations that the underlying layer provokes. If the reinforcing layer is smaller, then it will not be able to withstand the old coating and the work will lose all expediency.

Additional protective measure is the installation of so-called membranes, which serve as crack reflectors. These membranes are mixtures based on rubber and bitumen, as well as mineral additives. A popular way is to mix fine-grained crushed stone with a bituminous additive. The layer is laid between the new and old coating. The essence of this method is the strong adhesion of both layers.

Reinforcement of the upper layer with a geogrid has proven itself well. The material for geogrids is polyethylene, polyester, polyvinyl alcohol and similar synthetic fibers. The mesh protects the lower layers of the roadway from aging and prolongs their service life. It also reduces the possibility of ruts and dents, which is very important on roads with high traffic. In addition, geogrids in some way simplify the process of laying asphalt, reducing the possibility of technological errors.

Wear pavement and its reasons [add. in. 29]

Moving vehicles have the greatest influence on the wear of coatings. Under the load transferred to the wheel, the tire is deformed (fig.). At the same time, at the site of the tire entry into the contact zone with the coating, compression occurs in the tire, and expansion occurs at the exit from the contact. Way, passable point on the bus in the contact plane? 1, less than outside it?. Therefore, in the plane of contact, the point moves with an acceleration greater than how it moved before coming into 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 one rolling.

Under the action of these enhanced shear stresses in the plane of the track, abrasion of the coating and the tire of the car occurs. The greatest tangential forces and the greatest wear occur when the vehicle is braked. Wear while driving trucks about 2 times more than when driving cars. The greater the strength of the coating material, the smaller and more uniform the wear of the coating across the width. On coatings made of low-strength materials, the wear intensity is much higher, ruts and potholes are more often formed. 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 carriageway and the thickness of the coatings occurs unevenly and abrasion ruts are formed on the coating along the rolling strips, 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 properties of the coating and hydroplaning.

average value wear over the entire coverage area hav, is.

Moving vehicles have the greatest influence on the wear of coatings. Under the load transmitted to the wheel, the tire is deformed (Fig. 6.7). At the same time, at the area of ​​the tire entry into the contact zone with the coating, compression occurs in the tire, and expansion occurs at the exit from the contact. The path traveled by a point on the bus in the plane of contact ℓ 1 is less than outside it ℓ. Therefore, in the plane of contact, the point moves with an acceleration greater than how it moved before coming into 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 one rolling.

Under the action of these enhanced shear stresses in the plane of the track, abrasion of the coating and the tire of the car occurs. The greatest tangential forces and the greatest wear occur when the vehicle is braked. Wear during the movement of trucks is approximately 2 times greater than when driving cars. The greater the strength of the coating material, the smaller and more uniform the wear of the coating across the width. On coatings made of low-strength materials, the wear intensity is much higher, ruts and potholes are more often formed. 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%.

Table 6.5

The most common deformations and destructions of cement concrete pavements highways

Rice. 6.7. Deformations of the wheel tire, contributing to the wear of the coating:

A - compression zone, B - tension zone

The wear of the coating within the carriageway and the thickness of the coatings occurs unevenly and abrasion ruts are formed on the coating along the rolling strips, 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 properties of the coating and hydroplaning.

The average wear value over the entire coverage area h СР, mm, is:

h СР = k×h Н, mm, where (6.1)

k - coefficient of uneven wear, on average 0.6-0.7;

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

For advanced pavements, wear is measured in mm, and for transitional pavements also in terms of material loss in m 3 /km.

Features of wear of rough road surfaces. The wear of the rough surface of road surfaces is manifested in a decrease in height and in the grinding of irregularities of macroroughness. The decrease in the macroroughness of coatings under the action of car wheels occurs in two stages (see Fig. 7.3). At the first stage, immediately after the completion of construction, the roughness of the coating is reduced due to the immersion of the grains of the crushed stone of the wear layer into the underlying layer of the coating. 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 estimated 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 have absolute hardness.

Determination of wear of coatings by calculation. The average value of the decrease in the thickness of pavements per year due to wear can be determined by the formula of prof. M.B. Korsunsky (it should be noted that these studies were carried out more than 50 years ago and quantitative values their results are of little relevance to modern roads and cars):

h = a + b×B (6.2)

h = a + , where (6.3)

h - annual wear of the coating, mm;

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

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

B - traffic intensity, million gross tons per year; N»0.001×B (N - traffic intensity, avt./day).

The wear of the pavement over T years, taking into account changes in the composition and intensity of traffic in the future, in a geometric progression, can be determined by the formula

h Т = a×T + × , where (6.4)

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

N 1 - traffic intensity in the initial year, avt./day;

K = 1.05-1.07 - coefficient taking into account the change in the composition of the movement;

q 1 - indicator of annual growth in traffic intensity, q 1 >1.0.

The values ​​of parameters a and b are given in Table. 6.6.

IN last years to increase the stability of the movement of cars, tires with spikes or chains began to be used. Experience shows that this dramatically increases the wear and tear of road surfaces.

Table 6.6

Notes. 1. The average values ​​of a and b are taken for roads located in the zone of moderate moisture (III road-climatic zone) and built of 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 (IV and V road-climatic zones), - lower limits values ​​a and b. 3. For roads with crushed stone and gravel, located in the zone of excessive moisture, the lower limits are accepted, and in areas with a dry climate - the upper limits a and b. 4. If the width of the carriageway exceeds 7.0 m, then the value of b is reduced by 15%, and if it is less than 6.0 m, then b is increased by 15%.

At the moment of contact with the coating, each spike strikes with high speed. The spike has a very small mass, but the repeated repetition of these blows in one place contributes to the weakening of the top layer of the coating. The stud coming out of the contact zone has a greater abrasive effect, where the tire, together with the stud, slides over the surface of the coating, abrading it.

The duration of wear of asphalt concrete pavements during the operation of tires with chains and spikes is reduced by 2-3 times. Even on high-strength cast asphalt concrete pavements on German highways, on which cars equipped with studded tires move, ruts up to 10 mm deep are formed along rolling strips after 1-2 years.

Therefore, in the conditions of operation of Russian roads, the use of tires with spikes and snow chains on the roads common use should be strictly limited.

As a criterion for the limit state of the pavement in terms of wear, the value of allowable wear H I can be taken: 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, when accepting roads after construction or repair with reinforcement, road maintenance organizations should require builders to have a coating thickness greater than that calculated from the strength condition by the amount of permissible wear, i.e.

h P \u003d h PR + H I, mm, where (6.5)

h PR - the calculated thickness of the pavement from the condition of the strength of the pavement, mm.

Wear measurement. The annual wear in fractions of mm of cement concrete, asphalt concrete and other monolithic pavements is measured using benchmarks embedded in the thickness of the pavement and a wear meter. With this method of wear measurement, brass reference cups are preliminarily laid in the coating. The bottom of the glass serves as the surface from which the reading is performed.

Wear is also determined using plates (grades) of trapezoidal shape 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 georadar devices used to measure the thickness of layers in layered half-spaces.

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

Coating wear and its causes. The wear of coatings is most affected by moving vehicles. Under load, the tire deforms, it contracts in the contact zone with the coating, and expands outside the contact (Fig. 5.8).

rice. 5.8. Tire abrasion pattern: BUT- compression zone; B - stretch zone

Path of a point on a bus in the plane of contact l 1 less than outside of it l, the point moves with an acceleration greater than the motion before it came into contact with the coating. At the same time, the angular velocity α in the sectors is practically the same. Therefore, the point passes along the pavement a path of a certain length with slipping instead of one rolling. Under the influence of these reinforced tangential stresses in the track plane abrade the coating and tires. The greatest tangential forces and the greatest wear occur when the vehicle is braked. Depreciation from trucks is about 2 times more than from cars. The greater the strength, the less and more uniform wear of the coating across the width.

On coatings made of low-strength materials, the wear intensity is much higher, ruts and potholes are more often formed.

Average wear over the entire coverage area (mm)

h cf = Kh n, (5.2)

where TO- coefficient of uneven wear (on average TO= 0.6 ÷ 0.7); h n - wear in the rolling strip, mm.

Wear of advanced coatings is measured in millimeters, and wear of transitional coatings is also measured in terms of material loss.

Peculiarities of wear of rough coatings. Their wear is manifested in a decrease in height and grinding of macroroughness irregularities.

The decrease in the macroroughness of coatings under the action of car wheels occurs in two stages. At the first stage, immediately after the completion of construction, the roughness of the coating is reduced by immersing the crushed stone into the underlying layer of the coating. The size of this immersion depends on the intensity and composition of the movement, the size of the crushed stone and the hardness of the coating, which is estimated by the depth of immersion of the hardness tester needle; asphalt concrete pavements can be 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 have absolute hardness.

According to Cand. tech. Sci. M. V. Nemchinov, the overall decrease in macroroughness can be described by the equation

R cf = ae-b m+ c, (5.3)

where m is the number of passing cars; but,b, c- coefficients depending, respectively, on the size of the crushed stone, the hardness of the coating and the composition of the traffic flow.

Determination of wear of coatings by calculation. The average value of the decrease in the thickness of coatings per year due to wear can be determined by the formula of prof. M. B. Korsunsky

h = a + bB(5.4)

h = a + bN/1000, (5.5)

where but - 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 intensity, million gross tons per year; N- traffic intensity, vehicles/day ( N ≈ 0,001 IN).

Coating wear for T years, taking into account changes in the composition and intensity of the flow in the future in a geometric progression

(5.6)

where N 1- traffic intensity in the initial year, avt./day; TO= 1.05 ÷ 1.07 - coefficient taking into account changes in the flow composition; q 1- an indicator of the annual increase in traffic intensity

In recent years, tires with spikes and chains have been used to increase the stability of the movement of cars. When used with chains and spikes, asphalt concrete pavements wear out 2-3 times faster. Even on high-strength cast asphalt concrete pavements on highways in Germany, where studded tires are used, after one or two winters, ruts are formed along the rolling strips up to 10 mm deep. Therefore, in the conditions of the USSR, the use of tires with spikes and snow chains on public roads should be strictly limited.

As a criterion for the limit state of the pavement in terms of wear, one can take the size of the allowable wear R and for pavements: asphalt concrete - 10-20 mm; crushed stone (gravel), treated with an organic binder, -30-40 mm; crushed stone from durable crushed stone - 40-50 mm; gravel - 50-60 mm.

Wear measurement. The annual wear of cement, asphalt concrete and other monolithic coatings is measured using benchmarks laid in the thickness of the coating and a wear meter. With this method of wear measurement, brass reference cups are preliminarily laid in the coating. The bottom of the glass serves as the surface from which the reading is performed. Wear is also determined using plates (grades) of trapezoidal shape made of limestone or soft metal, embedded in the coating and abraded together with it.

To determine the wear of coatings, various types can be used. electrical devices for measuring the thickness of layers in layered half-spaces. For example, in Germany they use electromagnetic device reflection based strat test electromagnetic waves. A similar device was also developed in the Leningrad branch of Soyuzdornia.

Similar information.

Coating wear- reduction of the thickness of the road surface due to the loss of material in the process of abrasive action of the wheels of vehicles in combination with negative influence weather and climate factors.

All types of road surfaces are subject to wear without exception (both asphalt and cement concrete), however, the rate and amount of wear depend on many factors.

The main causes of road surface wear

Moving vehicles have the greatest influence on the wear of the coating. The wear process from vehicles looks like in the following way. Under the load transferred to the wheel, the tire is deformed in such a way that compression occurs in the area of ​​the tire entry into the contact area with the coating, and expansion occurs at the exit. The path traveled by a point on the tire in the contact plane is less than outside it by 5 ... 10%. Thus, in the plane of contact, the point of the tire moves with an acceleration greater than how it moved before coming into contact with the coating. At the same time, the angular velocity in the sectors is practically the same. Therefore, the point passes along the pavement a path of a certain length with slipping instead of one rolling. Under the action of these enhanced shear stresses in the plane of the track, abrasion of the road surface occurs. The greatest shear stresses and the greatest wear occur when the car is braking. When driving a truck, the wear of the coating turns out to be approximately 2 times greater than when driving a car.

The process of pavement wear is greatly influenced by the heterogeneity of the pavement material itself, from which, during wear, mineral filler grains (sand and gravel) are abraded and knocked out, the fine-grained fraction (smaller than 0.05 mm) is separated and removed along with bitumen (if the pavement is asphalted). ) or without it, washing out of the bituminous binder in the presence of water or aggressive solutions.

How stronger material coating, the less and more uniform its wear. On coatings made of low-strength materials, the wear intensity is much higher, which is why rutting and potholes appear more often. The use of crushed stone from igneous rocks in the composition of the asphalt concrete mixture instead of sedimentary ones reduces the wear of the coating by 60%. Increasing the bitumen content from 5 to 7% reduces wear by 50...80%.

Even within the roadway, the wear of the coating can occur unevenly, due to which abrasion ruts are formed along the runways, the depth of which can vary from a few millimeters to 5 cm or more. In such ruts, during rain, a significant layer of water is created, which leads to a decrease in the adhesion properties of the coating and the occurrence of aquaplaning effect.

Effect of studded tires on road surface wear

The use of studded tires on vehicles dramatically increases the wear of the road surface. When driving on icy or snow covered roads, studded tires are really effective. However, on a clean road surface, studded tires do nothing but harm. Taking into account the fact that winter slipperiness on roads is observed only 3-4 weeks a year, while slippery sections of the road alternate with those free from snow and ice, most winter period the studs come into contact with the open road surface, causing increased wear.

At the moment of contact of the wheel with the coating, each spike strikes it at high speed. And although the spike itself has a small mass, repeated repetition of such blows in one place leads to a weakening of the coating material. In addition to the shock load, the spikes have a large abrasive effect. This happens at the moment the spike leaves the contact zone with the coating and the wheel slips along the surface.

When using tires with spikes, the wear time of asphalt pavements is reduced by 2-3 times. On straight sections of the road, with uniform (without sharp accelerations and braking) traffic of vehicles with studded tires, the service life of the coating is reduced by about 20%. Even on asphalt pavements made of high-strength cast asphalt concrete, when driving cars with studded tires, after 1–2 years, ruts up to 10 mm deep are formed along the rolling lanes. In addition to road surface wear, studded tires cause increased wear of road markings, the service life of which is reduced by 3-4 times.

Factors that determine the intensity of wear of the coating

The overall wear of the pavement depends on the speed of movement, traffic density (predominance of cars or trucks), traffic intensity (number of passing vehicles), as well as the quality (mainly strength) of the pavement material, the hardness of the pavement and the size of the coarse-grained filler (crushed stone) in the composition of the asphalt concrete mixture. .

The harder the coating, the less it is subject to wear. The hardness of the coating is estimated by the depth of immersion of the hardness tester needle. Cement-concrete pavements have absolute hardness, and asphalt pavements are divided into:

• very hard - 0 ... 2 mm immersion of the needle;
• solid - 2 ... 5 mm;
• normal - 5 ... 8 mm;
• soft - 8 ... 12 mm;
• very soft - 12 ... 18 mm.

Weather and climatic conditions - humidity and temperature - have a great influence on the wear of the coating.

Ways to measure the degree of wear of the road surface

The general degree of wear of monolithic coatings (asphalt concrete and cement concrete) is measured using benchmarks (from French repère - mark, sign, starting point), as well as electromagnetic and laser wear meters.

When measuring the degree of wear with the help of benchmarks, a glass-bench made of brass is laid into the coating, even at the stage of asphalting. The bottom of the glass serves as the surface from which the reading is taken. Wear is defined as the difference between the values ​​of the current and previous measurements.

Also, wear can be determined using special trapezoid-shaped limestone or soft metal plates that are laid during asphalting and abraded along with it. The half-difference between the length of the plate rib on the pavement surface, measured after abrasion, and the original length characterizes the wear.

Electromagnetic and laser wear meters are used to measure the wear of monolithic road surfaces. Stratotest - a device for measuring the thickness of the coating, which is based on the principle of reflection of electromagnetic waves. To work with this device, it is necessary in advance, even during asphalting, to lay a metal film (foil) in certain places between the layers of the pavement, which will later work as a reflector of electromagnetic waves.

For improved (asphalted and cement-concrete) pavements, wear is measured in millimeters, and for transitional pavements (black-crushed stone, crushed stone, gravel, etc.) also by the volume of material loss in cubic meters per kilometer.

Permissible wear rate for various types of road surface

As a criterion for the limit state of the pavement in terms of wear, allowable wear can be taken:

• for asphalt concrete pavements - 10 ... 20 mm;
• for crushed stone and gravel coatings treated with organic binders - 30 ... 40 mm;
• for crushed stone coatings made of durable crushed stone - 40 ... 50 mm;
• for gravel coatings - 50 ... 60 mm.

Based on the value of permissible wear, during the construction of a new or repair of an old road, during the installation of the upper asphalt layer of the road surface, a corresponding increase in its thickness is provided, or the creation of a separate wear layer (2–3 cm thick), as well as the installation of a thin protective layer (1– 2 cm) using cast emulsion-mineral mixtures.

Asphalting, repair, prevention and maintenance of roads

Unidorstroy LLC carries out asphalt repair, as well as the prevention of road damage (filling cracks, installing a protective membrane, thin-layer processing of asphalt pavement, creating a wear layer).