INFLUENCE OF THICKNESS AND GRANULOMETRIC COMPOSITION OF GRANULAR ASPHALT ON ITS STRENGTH CHARACTERISTICS WHEN PLACING INTO THE ROAD PAVEMENT

When performing roadway replacement and reconstruction works, the removal of the road surface by self-propelled road milling machine is provided. The material obtained during milling (granular asphalt) is used in the base layers and lower layers of the coating, provided that the strength requirements are met. The effectiveness of the applied technology in the construction of structural layers of road pavement depends on considering the properties of the used material and the parameters of the mechanic means during works. We have reviewed the infl uence of the granulometric composition and the granular asphalt layer thickness on its strength properties in the construction of road structures. On the basis of experimental studies, analytical dependences are obtained for calculating the deformation and compacting factor under the action of the compaction loading of used granular asphalt. We have obtained the results to calculate the deformation-stress relationship and the dependence of the compacting factor on deformation, taking into account the granulometric composition and layer thickness. That allows to justify the parameters of compacting machines to ensure the required quality of compacting of the granular asphalt layer.


INTRODUCTION
When constructing structural layers of road pavement, When constructing structural layers of road pavement, the effectiveness of the applied technology depends on the effectiveness of the applied technology depends on considering the properties of the used material and the considering the properties of the used material and the parameters of the mechanic means when performing parameters of the mechanic means when performing works. To ensure the required strength of the structural works. To ensure the required strength of the structural layer, compacting equipment is used. It is characterized layer, compacting equipment is used. It is characterized by a wide range of parameters. Achieving the required by a wide range of parameters. Achieving the required compacting quality of the material depends on the com-compacting quality of the material depends on the compliance of the equipment parameters with its strength pliance of the equipment parameters with its strength characteristics [1, 22,23]. characteristics [1, 22,23]. Currently, 97 % of the total length of roads is covered by Currently, 97 % of the total length of roads is covered by roads with non-rigid pavement. When performing road-roads with non-rigid pavement. When performing roadway replacement and reconstruction works it is planned way replacement and reconstruction works it is planned to remove the road surface. It is performed by self-pro-to remove the road surface. It is performed by self-propelled road milling machines. The material obtained pelled road milling machines. The material obtained during milling (granular asphalt) is used to prepare hot-during milling (granular asphalt) is used to prepare hotmixed asphalt, to strengthen road borders, to provide mixed asphalt, to strengthen road borders, to provide spur roads and for other purposes. It is found that when spur roads and for other purposes. It is found that when milling the road surface with a width of 7-7.5 m to a depth milling the road surface with a width of 7-7.5 m to a depth of 0.05 m, about 500-650 tons of waste are obtained of 0.05 m, about 500-650 tons of waste are obtained from one kilometer of the road. That signifi cantly allows from one kilometer of the road. That signifi cantly allows to reduce the cost of materials when performing works. to reduce the cost of materials when performing works. Normative documents SRC (sector road code) 218.3.039-Normative documents SRC (sector road code) 218.3.039-2003 and CS (code specifi cation) 78.13330.2012 defi ne 2003 and CS (code specifi cation) 78.13330.2012 defi ne the areas of granular asphalt application. With appropri-the areas of granular asphalt application. With appropriate processing, granular asphalt is used in the base and ate processing, granular asphalt is used in the base and lower layers of the coating, provided that the strength lower layers of the coating, provided that the strength requirements are met. The addition of a binding mate-requirements are met. The addition of a binding material (emulsifi ed bitumen or cement) into the granular as-rial (emulsifi ed bitumen or cement) into the granular asphalt helps to increase the tensile strength of the layer phalt helps to increase the tensile strength of the layer from 0.5 to 2.0 MPa. Granular asphalt without additives from 0.5 to 2.0 MPa. Granular asphalt without additives is used in the construction of motor roads of the 4 is used in the construction of motor roads of the 4 th th cat-category with a compressive strength of 0.7 MPa, as well egory with a compressive strength of 0.7 MPa, as well as when gutting the upper layer of crushed stone base. as when gutting the upper layer of crushed stone base. Depending on the application, it is deposited in layers Depending on the application, it is deposited in layers of different thickness and grain-size classifi cation, which of different thickness and grain-size classifi cation, which affects the strength characteristics of the layer and the affects the strength characteristics of the layer and the choice of parameters of compacting equipment in order choice of parameters of compacting equipment in order to achieve the required strength of the road structure. to achieve the required strength of the road structure. The normative document CS 78.13330.2012 defi nes The normative document CS 78.13330.2012 defi nes the parameters of the road rollers used for compaction the parameters of the road rollers used for compaction of granular asphalt: it should be pneumatic tired rollers of granular asphalt: it should be pneumatic tired rollers weighing at least 16 tons at a pressure in tires of 0.6-weighing at least 16 tons at a pressure in tires of 0.6-0.8 MPa; trailed vibrating rollers weighing at least 6 tons; 0.8 MPa; trailed vibrating rollers weighing at least 6 tons; grid rollers weighing not less than 15 tons; self-propelled grid rollers weighing not less than 15 tons; self-propelled rollers with smooth rollers weighing at least 10 tons and rollers with smooth rollers weighing at least 10 tons and combined rollers weighing more than 16 tons. An analy-combined rollers weighing more than 16 tons. An analysis of the recommended parameters of the rollers shows sis of the recommended parameters of the rollers shows that they belong to a heavy roller group used at the fi -that they belong to a heavy roller group used at the final stage of the material compacting. At the initial stage nal stage of the material compacting. At the initial stage of compacting, the use of such rollers leads to the de-of compacting, the use of such rollers leads to the development of plastic deformations, which characterizes velopment of plastic deformations, which characterizes the process of destruction of the placed material layer. the process of destruction of the placed material layer. Therefore, to improve the quality of the compacting and Therefore, to improve the quality of the compacting and achieve the required strength during the equipment work-achieve the required strength during the equipment working process, it is necessary to ensure that the stresses ing process, it is necessary to ensure that the stresses under the working object of the machine correspond to under the working object of the machine correspond to the properties of the material being compacted [1] - [3]. the properties of the material being compacted [1] - [3]. Determining the layer parameters (granulometric com-Determining the layer parameters (granulometric composition and thickness) of the used granular asphalt position and thickness) of the used granular asphalt which infl uence on its strength characteristics allows to which infl uence on its strength characteristics allows to select the link of machines to achieve the desired quality select the link of machines to achieve the desired quality   of compacting. Depending on the method of the material of compacting. Depending on the method of the material placement, the granulometric composition and thickness placement, the granulometric composition and thickness of the layer, its ability to resist external load will be differ-of the layer, its ability to resist external load will be different, that must be taken into account when choosing the ent, that must be taken into account when choosing the parameters of the compacting machine link. Therefore, parameters of the compacting machine link. Therefore, in order to ensure the required quality of compacting of in order to ensure the required quality of compacting of granular asphalt layers, it is necessary to specify the in-granular asphalt layers, it is necessary to specify the infl uence of the granulometric composition and layer thick-fl uence of the granulometric composition and layer thickness when placing on the choice of the roller parameters. ness when placing on the choice of the roller parameters.

MATERIALS AND METHODS MATERIALS AND METHODS
To determine the infl uence of the granulometric compo-To determine the infl uence of the granulometric composition and thickness of the granular asphalt layer on its sition and thickness of the granular asphalt layer on its strength and stress-related characteristics during com-strength and stress-related characteristics during compacting, a preliminary division of the total weight of the pacting, a preliminary division of the total weight of the material into fractions sizing 5-10, 10-20, 5-20 and 20-material into fractions sizing 5-10, 10-20, 5-20 and 20-40mm was carried out. Each fraction of a given thick-40mm was carried out. Each fraction of a given thickness was placed into the form of a testing bench with a ness was placed into the form of a testing bench with a preliminary compacting and its further post compaction. preliminary compacting and its further post compaction.
After completing the specifi ed number of passes with the After completing the specifi ed number of passes with the set load, the compaction coeffi cient was measured. It-set load, the compaction coeffi cient was measured. Itwas determined by a non-destructive method using the was determined by a non-destructive method using the ACD -1 (asphaltic concrete density) device. The study ACD -1 (asphaltic concrete density) device. The study was conducted at the CRT-RC-H2 testing bench (Fig. 1). was conducted at the CRT-RC-H2 testing bench (Fig. 1).
The principle of operation of the testing bench is based The principle of operation of the testing bench is based on the simulating the operation of the roller by rolling the on the simulating the operation of the roller by rolling the cylinder sector with a controlled force on the surface of cylinder sector with a controlled force on the surface of the sample placed into the form of the testing bench. the sample placed into the form of the testing bench. The dimensions of the form for placing the material are The dimensions of the form for placing the material are 305x400 mm. The completion of a task occurs when the 305x400 mm. The completion of a task occurs when the specifi ed number of cycles is performed. The research specifi ed number of cycles is performed. The research was carried out in accordance with the methodology set was carried out in accordance with the methodology set out in the regulatory document DNS 185-2016 ( draft out in the regulatory document DNS 185-2016 ( draft national standard) (EN 12697-33). national standard) (EN 12697-33).

RESULTS RESULTS
Ensuring the required strength of the placed layer de-Ensuring the required strength of the placed layer depends on the strength characteristics of the granular as-pends on the strength characteristics of the granular asphalt, structural layers during placement and compact-phalt, structural layers during placement and compact-ing technology. Depending on the design solution when ing technology. Depending on the design solution when laying the material, the layer thickness can bedifferent. laying the material, the layer thickness can bedifferent. It was proved that the thickness of the layer affects the It was proved that the thickness of the layer affects the stress limit of the laid material, which must be taken into stress limit of the laid material, which must be taken into From the presented data it is seen that the strength limit From the presented data it is seen that the strength limit depends both on the granulometric composition of the depends both on the granulometric composition of the granular asphalt and the thickness of the placed layer. As granular asphalt and the thickness of the placed layer. As the fraction size increases, the strength limit increases, the fraction size increases, the strength limit increases, which is explained by the change in the structure of the which is explained by the change in the structure of the layer material during compacting. As an example, Fig. 2 layer material during compacting. As an example, Fig. 2 show shows the dependence of the strength limit on the granu-s the dependence of the strength limit on the granulometric composition for a layer with a thickness of 0.05. lometric composition for a layer with a thickness of 0.05.
(4) Figure 4: Dependence of the coeffi cient Kn on the layer thickness of granular asphalt The numerical value of the strength limit of the granular The numerical value of the strength limit of the granular asphalt layer for a fraction of 5-10 mm is determined by asphalt layer for a fraction of 5-10 mm is determined by the formula: the formula: where N is the fraction number. The correlation coeffi -where N is the fraction number. The correlation coefficient of the equation is 0.99. cient of the equation is 0.99.
To establish the common pattern of the infl uence of the To establish the common pattern of the infl uence of the granulometric composition of granular asphalt on the granulometric composition of granular asphalt on the strength limit, we present the data from Table.1 in a form strength limit, we present the data from Table.1 in a form of relative values, assuming the strength limit of each of relative values, assuming the strength limit of each layer at a thickness equal to 0.05 m per unit (Table 2). layer at a thickness equal to 0.05 m per unit ( Table 2).
The data of Table 2 demonstrate that the granulometric The data of Table 2 demonstrate that the granulometric composition of granular asphalt, independently of the composition of granular asphalt, independently of the layer thickness , affects the strength limit. Let us denote layer thickness , affects the strength limit. Let us denote the accepted value by the infl uence coeffi cient of gran-the accepted value by the infl uence coeffi cient of granulometric composition on the strength limit of granular ulometric composition on the strength limit of granular asphalt -Kf (Fig. 3). asphalt -Kf (Fig. 3).
The numerical value of the infl uence coeffi cient of the The numerical value of the infl uence coeffi cient of the granulometric composition on the strength limit is deter-granulometric composition on the strength limit is determined by the formula: mined by the formula: where N is fraction number. The correlation coeffi cient of where N is fraction number. The correlation coeffi cient of the equation is 0.99. the equation is 0.99. To clarify the infl uence of the thickness of the granular To clarify the infl uence of the thickness of the granular asphalt layer when placing, we present the data from asphalt layer when placing, we present the data from Table 1 in a form of the relative values, assuming the Table 1 in a form of the relative values, assuming the strength limit for fractions with a thickness of 0.05 m per strength limit for fractions with a thickness of 0.05 m per unit (Table 3). We denote the accepted value by the in-unit (Table 3). We denote the accepted value by the infl uence coeffi cient of the layer thickness on the strength fl uence coeffi cient of the layer thickness on the strength limit ( limit (Кn Кn). ).
The presented data show that the change in layer thick-The presented data show that the change in layer thickness when placing affects the strength limit of the placed ness when placing affects the strength limit of the placed layer regardless of the granulometric composition of the layer regardless of the granulometric composition of the material. The dependence of the layer thickness coeffi -material. The dependence of the layer thickness coefficient Kn is shown in Fig. 4. cient Kn is shown in Fig. 4. The numerical value of the infl uence coeffi cient of the The numerical value of the infl uence coeffi cient of the layer thickness on the strength limit is determined by the layer thickness on the strength limit is determined by the formula: formula: where where h h is the layer thickness, m. The correlation coeffi -is the layer thickness, m. The correlation coefficient of the equation is 0.99. cient of the equation is 0.99. Taking into account the dependencies obtained above, Taking into account the dependencies obtained above, the value of the strength limit of the granular asphalt the value of the strength limit of the granular asphalt layer, regardless of its granulometric composition and layer, regardless of its granulometric composition and thickness, can be determined with suffi cient accuracy for thickness, can be determined with suffi cient accuracy for practical calculations by the formula: practical calculations by the formula: It is proved that the nominal error when determining the It is proved that the nominal error when determining the strength limit of the granular asphalt layer is within 5%. strength limit of the granular asphalt layer is within 5%. As noted previously, when choosing the parameters of As noted previously, when choosing the parameters of machines for compacting the granular asphalt layer, it machines for compacting the granular asphalt layer, it is necessary to take into account its properties [7] - [9]. is necessary to take into account its properties   Depending on the method of placing granular asphalt, Depending on the method of placing granular asphalt, its volume weight is in the range from 1.15 to 0.6 t/m3, its volume weight is in the range from 1.15 to 0.6 t/m3, and when the maximum density is reached at the end and when the maximum density is reached at the end of compacting it is 2.3-2.35 t/m3.During the laying pro-of compacting it is 2.3-2.35 t/m3.During the laying process, the layer is pre-compacted, which is characterized cess, the layer is pre-compacted, which is characterized by a pre -compacting coeffi cient [10] - [12]. The value by a pre -compacting coeffi cient [10] - [12]. The value of pre-compaction depends on the method of laying the of pre-compaction depends on the method of laying the material and the mechanic means that are used fora lay-material and the mechanic means that are used fora layer installation. The use of earthmoving machinery when er installation. The use of earthmoving machinery when laying granular asphalt provides a pre-compaction coef-laying granular asphalt provides a pre-compaction coeffi cient in the range of 0.79-0.89, the use of crushed stone fi cient in the range of 0.79-0.89, the use of crushed stone pavers increases the pre-compaction coeffi cient to 0.9-pavers increases the pre-compaction coeffi cient to 0.9-0.92. The choice of material placement method affects 0.92. The choice of material placement method affects the parameters of the compacting machinery [13] - [15]. the parameters of the compacting machinery [13] - [15]. During the operation of compacting machinery deforma-During the operation of compacting machinery deformation is produced in the material layer due to the reloca-tion is produced in the material layer due to the relocation of material particles under load. And it promotesan tion of material particles under load. And it promotesan increase of its density and strength. The deformation increase of its density and strength. The deformation growth of the material layer depends on the thickness growth of the material layer depends on the thickness and granulometric composition of the applied material and granulometric composition of the applied material as well as the characteristics of the compacting equip-as well as the characteristics of the compacting equipment (line pressure of the roller and its radius) (Fig. 5). ment (line pressure of the roller and its radius) (Fig. 5). The data of Fig. 5 show that the value of deformation The data of Fig. 5 show that the value of deformation and the nature of its change depends on the stress, gran-and the nature of its change depends on the stress, granulometric composition and thickness of the layer. When ulometric composition and thickness of the layer. When placing a layer with a fraction of 5-10 mm and a thick-placing a layer with a fraction of 5-10 mm and a thickness of up to 0.05 m, the relationship between stress and ness of up to 0.05 m, the relationship between stress and deformation has linear character when stress is not more deformation has linear character when stress is not more than 1.0 MPa. With a further increase in stress, there is a than 1.0 MPa. With a further increase in stress, there is a decrease in the deformation growth, which is explained decrease in the deformation growth, which is explained by a strength improvement. When the thickness of the by a strength improvement. When the thickness of the fraction increases owing to a decrease in the ability of the fraction increases owing to a decrease in the ability of the material to resist an external load, the dependence has material to resist an external load, the dependence has a logarithmic character.The dependence between stress a logarithmic character.The dependence between stress and deformation is linear with stress up to 0.5 MPa. And and deformation is linear with stress up to 0.5 MPa. And with a further increase in stress, the deformation growth with a further increase in stress, the deformation growth rate slows down andthe decompression process starts rate slows down andthe decompression process starts at 2.0 MPa. at 2.0 MPa. Similar processes are proceeding when compacting Similar processes are proceeding when compacting granular asphalt with a fraction of 5-20 mm and a layer granular asphalt with a fraction of 5-20 mm and a layer thickness of 0.1 m. The use of granular asphalt with a thickness of 0.1 m. The use of granular asphalt with a fraction of 20-40 mm when placing a layer with a thick-fraction of 20-40 mm when placing a layer with a thickness of 0.1 m is characterized by the formation of con-ness of 0.1 m is characterized by the formation of contacts between the particles of the material. It makes tacts between the particles of the material. It makes possible to increase the greater resistance of the mate-possible to increase the greater resistance of the material to the load action. At the initial stage of compaction rial to the load action. At the initial stage of compaction under the action of the applied load there occur closer under the action of the applied load there occur closer contacts between the particles. And the desired density contacts between the particles. And the desired density is achieved when the load increases to a certain value. is achieved when the load increases to a certain value. Due to the formation of a frame structure, the scope of Due to the formation of a frame structure, the scope of deformation that occurs is far less than when compact-deformation that occurs is far less than when compacting other fractions. In Table 4 the dependence of defor-ing other fractions. In Table 4 the dependence of deformation on stress is presented, taking into account the mation on stress is presented, taking into account the granulometric composition of granular asphalt and the granulometric composition of granular asphalt and the layer thickness. layer thickness.
It is known that the scope of material deformation during It is known that the scope of material deformation during compaction is characterized by the dependence [5]: compaction is characterized by the dependence [5]: where σ is the contact stress, MPa; where σ is the contact stress, MPa; t t is the load action is the load action time; dσ/dt is the rate of change of stresses under the time; dσ/dt is the rate of change of stresses under the movable object of the equipment. movable object of the equipment. The studies have proven that at the existing operating The studies have proven that at the existing operating speeds of the rollers during compaction, the rate of speeds of the rollers during compaction, the rate of change of stress under the movable object of the equip-change of stress under the movable object of the equipment does not practically affect the development of ma-ment does not practically affect the development of material deformation. The load action time is determined terial deformation. The load action time is determined by the speed of machinery movement during compac-by the speed of machinery movement during compaction and the number of passes per one track. With an tion and the number of passes per one track. With an increase in the number of load application to the surface increase in the number of load application to the surface of the compacting layer, the total deformation of the layer of the compacting layer, the total deformation of the layer increases. And that contributes to an increase in the den-increases. And that contributes to an increase in the density of the material and, consequently, to an increase in sity of the material and, consequently, to an increase in the compacting factor. Figure 6 shows the dependences the compacting factor. Figure 6 shows the dependences of the deformation of granular asphalt layer taking into of the deformation of granular asphalt layer taking into account its thickness and granulometric composition at account its thickness and granulometric composition at a constant contact stress of the roller drum (0.5 MPa). a constant contact stress of the roller drum (0.5 MPa). The submitted data show that the intensive development The submitted data show that the intensive development of deformation occurs at a certain number of passes of of deformation occurs at a certain number of passes of the roller, depending on the thickness of the layer and the roller, depending on the thickness of the layer and the granulometric composition of the material. When cre-the granulometric composition of the material. When creating a layer using a fraction of 5-20 mm, the maximum ating a layer using a fraction of 5-20 mm, the maximum compacting effect is achieved when the roller passes compacting effect is achieved when the roller passes three times per one track at a given load, regardless of three times per one track at a given load, regardless of the thickness of the layer. Further increase in passes at the thickness of the layer. Further increase in passes at   a given load is ineffi cient and to increase the strength of a given load is ineffi cient and to increase the strength of the layer, it is necessary to use rollers with a larger mass. the layer, it is necessary to use rollers with a larger mass. The value that characterizes the material compaction The value that characterizes the material compaction process is the compacting factor [16] - [18]. It was found process is the compacting factor [16] - [18]. It was found that the dependence of the compacting factor on defor-that the dependence of the compacting factor on deformation is characterized by a linear dependence at the mation is characterized by a linear dependence at the layer thickness of 0.05 m and it does not depend on the layer thickness of 0.05 m and it does not depend on the fractional composition of the material. With increasing fractional composition of the material. With increasing layer thickness, the dependence is exponential [19], [20], layer thickness, the dependence is exponential [19], [20], [21]. The dependences for calculating the compacting [21]. The dependences for calculating the compacting factor on deformation are presented in Table 5. factor on deformation are presented in Table 5.

CONCLUSIONS CONCLUSIONS
1. 1. The strength limit of the granular asphalt layer de-The strength limit of the granular asphalt layer depends on the granulometric composition and thick-pends on the granulometric composition and thickness of the layer to be placed, which must be taken ness of the layer to be placed, which must be taken into account when choosing the parameters of com-into account when choosing the parameters of compacting equipment. pacting equipment. 2. 2. The obtained dependences to calculate the deforma- The obtained dependences to calculate the deformation-stress relationship and the compacting factor on tion-stress relationship and the compacting factor on deformation that takes into account the particle size deformation that takes into account the particle size and the layer thickness, allow to justify the parame-and the layer thickness, allow to justify the parameters of compacting equipment to ensure the required ters of compacting equipment to ensure the required quality of the compacting of granular asphalt layer. quality of the compacting of granular asphalt layer.