Features of the hot recycling method used to repair asphalt concrete pavements

The traditional method of repairing asphalt concrete pavements involves leveling them with asphalt concrete mixture and overlapping them with a new layer of asphalt concrete. As a result, the material of the old layers becomes a source of reflected cracks in the new road pavement. There are hundreds of millions of tons of asphalt concrete in the lower layers of road pavement, and these do not serve any useful purpose; the volume of stone materials exceeds these pavements by 2–3 times in the underlying layers and foundations [1]. Given the constant increase in the shortage and cost of road construction materials during the construction and reconstruction of highways, it is necessary to develop non-material-intensive or non-energy-intensive technologies using available reserves. The authors of this article developed a technical and technological solution to the problems of cost escalation and excessive energy consumption that commonly characterize the restoration of existing road networks. The solution allows reusing the material of the reconstructed roads.

A cost-effective, technological solution, which provides for quality road construction materials obtained from asphalt scraps, is to process them by their secondary products and industrial waste such as granulated slag, nepheline sludge, ash, ash-and-slag mixtures of thermal power plants (TPP), phosphogypsum, cement kiln dust (CKD), etc. [2]. A promising technological solution is to obtain organomineral material from a semi-finished product without heating it by processing the crushed scrap with a mineral binder. However, the use of this method is not always rational and possible, given the long-term formation of the organomineral material structure during the operation of the road under traffic.

The technology of processing asphalt scrap in an installation with heating and the addition of new constituent components is a modern technology that provides a durable asphalt concrete pavement in the upper layer without overlapping it with a layer of road surface treatment. Reheating asphaltic concrete leads to plasticizing the formed bitumen structure, which, in turn, reduces its viscosity and improves the processing properties of the mixture [3].

The viscosity of bitumen increases by 2–3 times in the “old” asphalt concrete due to a decrease in the number of light fractions. The addition of a plasticizer can bring the bitumen penetration to standard values. Such oils as petroleum, coal, or specifically developed oils are often used as plasticizers since they contain many aromatic compounds, and the use of fuel oil or liquid bitumen is rare. Hot technology methods for processing asphalt concrete involve high-temperature heating but do not provide for the restoration of the bitumen properties contained in long-term asphalt concrete; the addition of a new binder with enhanced properties will ensure the durability of the reclaimed asphalt concrete [4]. The method of regenerating “old” asphalt concrete using heating technology is promising since this technology is rapidly advancing in feasibility, and is thus being widely adopted. The hot recycling method can be carried out on the site of manufacture or by transporting the mixture to an asphalt recycling plant. The prolonged service life of pavement from the restored mixture fully pays off a slight increase in the cost of the transportation of milled scrap [5].

The study of performance features of the restored layer of the road pavement made of granular asphalt concrete with the fiber of fly ash under dynamic loading will make it possible to predict its performance properties throughout the entire service life. The assessment of the impact of technological processes of wear layers and the production of repair work on the environment confirms the idea of their relative environmental safety. It is necessary to do the following in order to obtain the results of the impact of the fiber of fly ash:

to substantiate the possibility of using fiber in granular asphalt concrete, given its composition and properties;

This article aims to develop the composition and determine the physical-mechanical and structural-rheological properties of asphalt concrete reclaimed by the hot recycling method and reinforced by fiber of fly ash from TPP. To achieve this aim, it is necessary to complete the following tasks:

to review and study the existing experience in using the fiber of fly ash from TPP as an additive to reclaimed asphalt concrete;

The primary indicators of performance reliability of the structural layers of the pavement are structure stability, which depends on the adhesion strength of the bitumen to mineral particles, the bending strength, structure stability to fluctuations in humidity and temperature conditions, the fatigue failure under dynamic loading, etc. The strength of granular asphalt concrete layers depends on the quality of the mixture preparation and the properties of milled asphalt concrete. Loading, climatic, periodic, and one-time impacts cause various processes in the road structure during its everyday performance. The pavement treatment by granular asphalt concrete is generally initiated for roads that are undergoing rapid deterioration, or in cases where the total area of pavement defects has reached 30% before the end of the performance period [6]. When the defects appear on pavements, it indicates low-quality materials and washing out of bitumen from the surface layer [7].

The initialization of the mixture during its rolling is a critical operation in laying the pavement, and it is also the factor that determines the quality of these layers to the greatest extent. When a road roller passes along the pavement, pressure develops in the pavement layers, and numerous physicochemical processes occur under the influence of temperature, which results in the formation of spliced layers of the required strength. Exposure to temperature changes the balance within the materials used, resulting in a nonequilibrium thermodynamic state [8]. The interlayer compression pressure increases, and the internal moisture contained in the bituminous binders and mineral material influences their initiation. The correct choice of mixture compositions and technological conditions for laying ensure high strength and durability of pavements during construction usage, reconstruction, and repair. Temperature also affects the diffusion processes occurring during the formation of new pavement and its subsequent performance [9].

High temperature causes both unevenness of heating and premature aging of the bitumen binder, thus reducing the road strength characteristics. The heat from the compression surface of layers with the granular binder permeates into the lower layers. Excessive pressure appears, which causes the binder to penetrate the depth of the layer, leveling the temperature fields [2]. The curing process flows more evenly over the thickness of the layers, which improves the road strength characteristics. The conditions for the equality of heat fluxes and transfer of the liquid fraction of the binder during the formation of the layer can be expressed as follows: (1) −λ∂T(x,t)∂x|x=h=0,−αcρ∂U(x,t)∂x|x=h=0 \matrix{ \hfill { - \lambda {{\partial T(x,t)} \over {\partial x}}\left| {_{x = h}} \right. = 0,} \cr \hfill { - {\alpha _c}\rho {{\partial U(x,t)} \over {\partial x}}\left| {_{x = h}} \right. = 0\;} \cr }

Therefore, an adequate description of changes in the bitumen concentration in the asphalt layer can be an objective answer to the durability of the road pavement [10]. It is necessary to theoretically substantiate the functional dependence of the bitumen concentration on time and other natural parameters, such as access time for concentration to reach a certain threshold (minimum permissible) value. Such an estimate can be one of the predictive estimates of the pavement service life.

Zolotarev [11] proved that mixtures with optimum density have a high coefficient of relative thermal conductivity. Table 1 shows the temperature effect on the relative thermal conductivity of granular asphalt concrete mixtures with different densities.

According to Table 1, a mixture with a density ranging from 2.2 t/m³ to 2.4 t/m³ possesses a higher coefficient of thermal conductivity λ, even when heated to 90°C. The density of granular asphalt concrete with the studied fiber of fly ash should correspond to these optimum values. If the process of uniform bitumen distribution is regulated, it is possible to obtain a layer with high physical and mechanical characteristics. Figure 1 represents the dependence of the penetration rate of the binder in the formed layer.

Fig. 1

Figure 2 provides data, generated in the course of the present study, on the dependence of bitumen concentration on the thickness of the coating layer and the service life. The data are given for the amount of bitumen from 8% to 2% by weight of granular asphalt.

Fig. 2

The binder concentration constantly changes in the coating layers under atmospheric factors and traffic. There is a constant diffusion into the layer, and the concentration changes from higher (80% or 100%) to lower (20% or 60%). The binder does not fulfill its function when reaching a particular concentration limit, which accelerates pavement destruction. The minimum concentration will obviously be at a later date when the binder concentration is reducing in the upper layer and diffusing into the lower layers of asphalt pavement. It is possible to adjust the road service life based on this provision. The time during which the binder concentration decreases below 70% can be considered the beginning of intensive pavement destruction.

Literature sources claim that reinforcing additives reduce the diffusion of bitumen in the underlying layer due to the formation of a structural framework in the bitumen-fiber system [12]. The above is especially typical for fibers with a rough particle surface, such as the fiber of fly ash from TPP.

As the temperature rises, microparticles of the fiber of fly ash interpenetrate into the molecules of the most active part of bitumen, namely asphaltenes. The fixation of particles in the binder reduces the amount of free bitumen, structuring it and thereby preventing the binder from moving deeper into the layer, and increases the strength and durability of granular asphalt concrete in the pavement.

The author used the following materials to conduct experimental studies on the composition selection of granular asphalt concrete and determine its physical, mechanical, and performance properties when carpeting with an asphalt concrete pavement by the hot recycling method:

milled asphalt concrete;

Taking the conditions of Ukraine as a background, the authors justify the usage of the hot recycling method in carrying out restoration of asphalt concrete pavements as part of road repairing works (involving roads containing asphalt concrete pavements). Table 2 presents the variants for the restoration of asphalt concrete pavements.

The following structural and technological scheme was adopted as a compared variant:

hot recycling of 7 m wide asphalt concrete pavement to a layer depth of 8 cm using a WR-2500 recycler with the introduction of viscous bitumen;

Since hot recycling provides a higher modulus of elasticity and allows carrying out work over the entire thickness of the layer (8 cm), option No. 1 was adopted. The milled asphalt concrete was removed with a milling cutter to a layer with a thickness of 6 cm. Table 3 shows the grain size composition of the granular asphalt.

As can be seen from Table 3, with the exception of the 20 mm fraction, the grain size composition of the granular asphalt fails to meet the requirements of DSTU B V.2.7-119 for all fractions. Therefore, it is necessary to add a new mineral material such as crushed stone and screening in order to ensure the required density of granular asphalt concrete. The author of this article provides indicators of the properties of oil road bitumen BND 60/90 under the requirements of DSTU 4044 in Table 4 [13].

The bitumen used in the present research meets the DSTU 4044 requirements [13]. The author used the crushed granite of the Novopoltavsky quarry (Ukraine) in the research. Table 5 provides its physical and mechanical indicators.

As can be seen from Table 5, the crushed stone used fully meets the DSTU B V.2.3-39 requirements [14]. Stone screening dust is from the same quarry, and its physical and mechanical indicators are given in Table 6.

As can be seen from Table 6, the used stone screening dust fully complies with the DSTU B V.2.3-39 requirements [14]. The preparation of bitumen with the addition of fiber was as follows. The reinforcing additive, the fiber, was introduced into the bitumen, heated to 150°C, and stirred therein by hand until uniform. The distribution of fiber in the bitumen was quick and uniform within 10 min. The firm compression of the granules caused the poor distribution of Topcel, Antrocel, and Chrysotopes in the bitumen without preliminary destruction. Therefore, they were mechanically destroyed in a porcelain mortar that was operated by hand, and thus reduced to a fluffed state. After that, it was possible to achieve a uniform distribution of additives in the bitumen. The appearance of the bitumen with the fiber of fly ash added is a mobile, mushy mixture (without lumps) with a black gloss. At the same time, the viscosity of bitumen increased.

The author prepared the granular asphalt concrete with the fiber of fly ash in the following way. Dosed components of the mixture were heated to the required temperatures: crushed stone and screening dust to 175°C, and bitumen to 155°C. The heated temperature of the inner surface of the laboratory mixer was 140°C. The author added crushed stone and screenings to the mixer with the prepared mixture and mixed it for 30 s. Then, the fiber was loaded and mixed for 1.0 min; bitumen was added thereafter and mixed for 1.0 min until the bitumen completely covered the mineral material, and a homogeneous mixture was formed.

The total mixing time was 4.5 min. Before manufacturing the samples, the mixture was maintained for 20 min at a temperature of 150°C. Samples from the granular asphalt concrete mixture were made in accordance with GOST 12801-98 [15]. Samples were tested in accordance with GOST 12801-98, GOST 31015-2002, and VBN B.2.3-218-002-95 [15,16,17].

The author studied the microstructure of the fiber with an Axioskop 2 MAT microscope with a series of EC Epiplan-Neofluars lenses for improved color correction. The electron microscopic images were processed to obtain quantitative information about structural elements and their relative position in space. The geometric parameters of the additives were measured, and their appearance, the nature of their mutual arrangement, and the distribution of bitumen were studied. Color micrographs were obtained by photographing the pre-prepared fiber of fly ash of TPP. Figure 3 shows the appearance of the fiber used.

Fig. 3

The physical and mechanical properties of the used fiber of fly ash are as follows:

average diameter of the fiber is 160.0 μm;

The relative humidity of cellulose and mineral fibrous additives was determined according to GOST 16483.32-77 “Wood. Method for determining the limit of hygroscopicity” [18]. The hygroscopicity of fibrous stabilizers with natural humidity was determined by keeping the fiber for a day in a hermetically sealed desiccator at a relative humidity of 98% and a temperature of 20 ± 3°C. The author placed a weighed sample (in a pre-weighed weighing bottle) above water poured into a desiccator, where the room temperature was at 20 ± 3°C. The weight of samples of additives in the desiccator was measured in a day.

The degree of swelling and linear expansion of cellulose additives were determined according to GOST 7516-75 “Cellulose. Swelling method” [19]. The author determined the degree of swelling through the change in the weight of the additive samples after keeping them in water at 20 ± 3°C, by weighing the samples by weight method before and after their swelling. Prepared samples of cellulose additives were immersed in water for 1 day. Then, they were removed and kept on a mesh tray until free water flowed off the surface of the additives.

The author determined the linear expansion of cellulose by the increment in the height of the cellulose additive samples in water and expressed it as a percentage. Linear expansion was measured simultaneously with the degree of swelling of the cellulose by weight. The above presupposed the height of the cylinder with the additive to be measured. The discrepancy between the results of three parallel determinations should not be more than 0.5% (in absolute value). The result was the arithmetic mean of three parallel determinations, rounded to the first decimal place.

The flowability of all studied additives was determined according to GOST 25139-93 “Plastics. Methods for determining flowability” [20]. The outflow rate of stabilizing additives characterized their flowability. The outflow rate was determined on the developed model of the receiving hopper for stabilizing additives (Figure 4). A plastic hopper had an outlet through which the additives passed. The fixation of the hopper was in an upright position on a tripod. The outlet was closed with a pawning device.

Fig. 4

To check compliance with GOST 31015-2002 and GOST 9128-2009, the authors studied the characteristics obtained as a result of the addition of the fiber of fly ash to bitumen, asphalt binder, bitumen fiber, granular asphalt, and granular asphalt concrete [16, 21]. The author used Vibra AJ 2200 CE laboratory electronic balance to weigh the dosing of crushed stone, screenings, bitumen, and fiber when preparing a mixture of asphalt binder and the asphalt concrete mixture. A drying oven was used to heat the mixture components; mixing was carried out in a laboratory mixer SL - AB. The temperatures of the heated materials were monitored with an OPTRIS SIGHT MS pyrometer having a temperature measurement range from −32°C to 420°C. A vacuum setup with a filter moisture separator and a Wigem vacuum pump was used to determine the water saturation and strength of the samples in a water-saturated state.

The author determined the strength of asphalt binder and asphalt concrete by hydraulic presses P-50 and IP-100, providing an error in measurement of no more than 1%. The possibility of adjusting the rate of application to the sample was within 0.2–0.6 MPa/s. The choice of hydraulic presses is motivated by the expectation that the breaking load should be 0.2%–0.8% of the maximum force. When investigating the properties of bitumen with the added fiber of fly ash from Chinese TPP, the author used the following equipment: a ductilometer DMF-1480 No. 06, which is a viscometer for determining the relative viscosity of the bitumen. Table 7 provides the indicators of the properties of bitumen with the added fiber, and Figures 5–7 show the dependence of these indicators on the content of additives in the bitumen.

Fig. 5

Fig. 6

Fig. 7

Analysis of the data in Figure 5 shows that an increased amount of fiber decreases the viscosity of the bitumen, i.e., the stiffness increases.

According to Figure 6, the fiber structures the bitumen since the indicators of the needle penetration depth are high even at 5% of its introduction.

According to Figure 7, the elongation of the bitumen with the fiber added decreases at 25°C, i.e., binder stiffness increases. The calculation of the amount of new crushed stone in the granular asphalt concrete mixture depends on the amount of the bitumen in the granular asphalt. Based on the ratio, the authors determined the amount of binder in the granular asphalt by burning the mixture to the amount of new binder. We can calculate the amount of crushed stone added to the granular asphalt concrete according to the following formula: (2) M=ZX0⋅100% M = {Z \over {{X_0}}} \cdot 100\% where Z is the amount of binder in the granular asphalt; (3) Xb=7−Z {X_b} = 7 - Z where 7% is the bitumen content in the granular asphalt concrete according to DSTU B V.2.7-119. Then, (4) Xb=7−4=3% {X_b} = 7 - 4 = 3\% The ratio obtained is: (5) M=34⋅100%=0.75⋅100=75% M = {3 \over 4} \cdot 100\% = 0.75 \cdot 100 = 75\%

The calculation of the amount of addition of new crushed stone (G) is as follows: (6) G=100%−M G = 100\% - M where 100% represents the composition of the granular asphalt concrete; (7) G=100%−75=25% G = 100\% - 75 = 25\%

However, it is necessary to remember that the granular asphalt concrete mixture (P) consists of crushed stone (G), bitumen (X), and fiber (F). The addition of fiber is in an amount of 4% above the weight of the mineral part: (8) P=G+X+F P = G + X + F

To accurately calculate the amount of new crushed stone, we subtract the bituminous fiber from the total composition of the granular asphalt concrete mixture. (9) P1=G−X−F {P_1} = G - X - F (10) P1=100−3−4=93% {P_1} = 100 - 3 - 4 = 93\%

Then, the amount of the granular asphalt in the mixture will be as follows: (11) Ka=75⋅93=69.75=70% {K_a} = 75 \cdot 93 = 69.75 = 70\%

The amount of new crushed stone added will be as follows: (12) Kcr=100−69.75=30.22=30% {K_{cr}} = 100 - 69.75 = 30.22 = 30\%

Thus, the following granular asphalt concrete mixture (shown in Table 8) was adopted for further research.

In order to compare the research results, the author also tested the granular asphalt concrete mixture without the fiber of fly ash.

According to the data presented in the figures, the fiber of fly ash has a positive influence on the water resistance and compressive strength at 20°C and 50°C. Indicators of water saturation increase with the addition of the fiber to 2.5%, and thus the mixture is not dense. An increase in the amount of fiber up to the calculated 4.0% and even up to 5% leads to a decrease in water saturation. Thus, a mixture with a dense structure has been obtained, in which the bitumen completely covers the grains of the mineral material.

The hot granular asphalt concrete with the fiber added has higher strength at 20°C and 50°C than the traditional composition. The ultimate strength and density of the mixture are achieved by introducing the fiber in the amount of 5% of the weight of the mineral part. However, it increases the amount of bitumen, which is undesirable. Therefore, our calculated threshold of a 5% fiber content is judged prescient in ensuring that optimal strength and density parameters are obtained for the mixture, while keeping the amount of bitumen within an acceptable limit. Figure 8 shows how water resistance k_w and water resistance at long-term water saturation k_ws of the hot asphalt concrete depend on the content of the fiber of fly ash at the optimum bitumen content. Figures 9 and 10 present the compressive strength at the optimum bitumen content.

Fig. 8

Fig. 9

Fig. 10

The selection and observance of the optimum temperature conditions for preparation are critical for obtaining high-quality asphalt concrete mixtures [22]. When unloading from the mixer and laying, the temperature of the hot granular asphalt concrete, depending on the bitumen binder used, must correspond to the values specified in Table 9.

The author determined the effect of temperature of mixing (T_mix) granular asphalt concrete mixture on the physical and mechanical properties by assessing the strength indicator (R₂₀ and R₅₀) and water resistance (k_w and k_ws) of the fiber-reinforced granular asphalt concrete samples, prepared at various mixing temperatures. The temperature of mixing was varied in increments of 5°C, and the temperature variation interval was 140–155°C. Table 10 presents the obtained physical and mechanical properties of hot granular asphalt concrete.

According to the test results, the hot granular asphalt concrete mixture with the fiber prepared at a temperature T_mix 145°C possessed the highest strength and water resistance indicators. An increase in the mixing temperature decreased the strength and water resistance indicators and increased water saturation. If T_mix decreases below 165°C, the strength and water resistance decrease significantly, and the water saturation indicators practically do not change.

The traditional hot asphalt concrete mixtures are prepared according to the technological scheme, which involves the simultaneous supply and mixing of crushed stone, sand, mineral powder, and bitumen [23]. The better part of bitumen combines with mineral powder due to the high surface activity of its grains, and as a result, the surface of crushed stone and sand with bitumen gets wet to a worse extent.

According to research, the introduction of mineral powder into the mixer simultaneously with crushed stone and sand worsens the wetting of crushed stone and sand grains with bitumen due to the adhesion of mineral powder particles to their surface. Crolley [24] believes it is possible to improve the wetting of stone material with bitumen by introducing a mineral powder after mixing crushed stone and sand with bitumen. The result is a perfect distribution of the asphalt binder, which increases the system density, strength, and water resistance.

In order to improve the technology for preparing hot granular asphalt concrete mixture, the author examined how the sequence in introducing the components of granular asphalt concrete influenced its properties. The preparation of hot granular asphalt concrete was carried out in two ways:

Option 1: Mineral aggregate, fiber of fly ash, and bitumen would be heated to the required temperature and dosed, followed by feeding into the mixer and mixing all components.

Option 2: The mineral aggregate and bitumen, heated to the required temperature and dosed, would be fed into the mixer and mixed; and then, the dosed amount of fiber would be added to the mixer.

Samples were made from hot granular asphalt concrete mixtures prepared according to the proposed options. Then, the samples were tested for compressive strength at 20°C and 50°C (R₂₀ and R₅₀), water resistance (k_w and k_ws), and water saturation (W). The test results are presented in Table 11.

According to the data in Table 11, the hot granular asphalt concrete prepared according to the first option has the highest strength and water resistance indicators. Thus, the sequence involved in introducing the components of hot granular asphalt concrete into the mixer according to the first option, which involves mixing the mineral material with fiber and bitumen, is the most rational.

Thus, the conducted studies of the technological properties of hot granular asphalt concrete showed that the addition of fiber does not complicate the process of preparing asphalt granulometric concrete and is carried out by combining the constituent components with bitumen. The resulting mixture is characterized by homogeneity, that is, uniform distribution of fiber and bitumen on the grains of the mineral material. There are no lumps and uncoated surface of grains of mineral material. Analyzing the data, the author of this article posit the following arguments:

the use of the fiber of fly ash provides sufficient water and crack resistance to hot granular asphalt concrete;

All these confirm the rationality of using fiber as a reinforcing additive when restoring asphalt concrete pavements using the hot recycling method.

The conducted review of the available literature data indicates that the restoration of asphalt concrete pavements by the hot recycling method must be performed on roads that can be categorized into a high level of damage owing to the presence of a significant number of defects and substantial destruction. Processing of granular asphalt in a plant with the addition of a new binder and mineral material will ensure its higher technical, physical, and mechanical characteristics than when using other methods of restoring the transport and operational properties of non-rigid pavements. The theoretical studies carried out prove the possibility and feasibility of using fiber of fly ash to improve the quality and durability of granular asphalt concrete prepared from milled asphalt by hot recycling.

The introduction of fiber of fly ash into the granular asphalt mixture contributes to the uniform distribution of new bitumen on the grains of the mineral material throughout the entire layer thickness due to the combination of fiber microparticles with bitumen and structuring of the binder. Experimental laboratory studies have shown that the use of fiber of fly ash in hot granular asphalt concrete makes it possible to obtain a material with higher strength characteristics and lower water saturation and swelling.

The mechanism of interaction of fiber with bitumen in asphalt binder has been developed. A feature of the interaction is that interactions occur in bituminous layers between grains of mineral material, and microfibers of the fiber are in the zone of action of the forces of active groups of bitumen. The process of distribution of microparticles of fiber in hot granular asphalt concrete with stirring has been studied, as well as the mechanism of interaction between the components of granular asphalt concrete at all stages of its preparation (heating, mixing). The conducted studies of the mixture of fiber and bitumen fully confirm the theoretical premises on the chemical interaction of these substances by combining fiber microparticles of fly ash and the most active part of bitumen – asphaltenes and asphaltenic acids.

The design of the composition of hot granular asphalt concrete in terms of adding new crushed stone was carried out in relation to the ratio of bitumen in the milled granular asphalt and the amount of added binder, and showed that the optimal amount of mineral material that can be introduced is up to 30%. Based on the study of the structure and chemical composition of bitumen, it can be argued that the interaction of the binder with microparticles of fiber occurs according to the type of chemical compound present as the active components of these substances.

There is a diffuse penetration of a viscous liquid – bitumen – into the structure of fiber particles, which is facilitated by the presence of pores and a rough surface of the particles. The use of fiber of fly ash is an extension of the range of additives that are used in granular asphalt concrete and shows the possibility of its use in traditional asphalt concrete compositions. Technological solutions have been tested that increase the performance of the pavement structure, which is ensured by the introduction of fiber of fly ash into the composition. As a result, dispersed-reinforced structures with increased crack resistance at low temperatures and resistance to the formation of plastic deformations in the summer are obtained.

The use of fiber of fly ash, either when carrying out restoration of asphalt concrete pavements using the hot recycling method or when implementing the same technology using the cold method, makes it possible to reduce the cost and ensure that the completed work results in a high-quality and durable structural layer of pavement. The resulting composition indicates the structural integrity of the formed pavement. Hot recycling allows cohesive layers of great thickness to be obtained, which are characterized by homogeneous material. This eliminates the need for liquid binders between thin layers of pavement, which is required in traditional garments.

The addition of fiber of fly ash to the asphalt concrete mixture shows a direct reduction in the cost of materials and construction work involved in the hot recycling method, since the use of fiber as a reinforcing additive increases the structural and mechanical properties of the milled asphalt concrete mixture and provides an increase in the operational properties and durability of the asphalt concrete pavement, which can be restored using suitable recycling methods.