RESEARCH OF PHYSICAL-CHEMICAL AND MECHANICAL PROPERTIES AND DEVELOPMENT OF EFFECTIVE COMPOSITE MATERIALS COMPOSITIONS FOR THE PRODUCTION OF ASPHALT CONCRETE HIGHWAY COVERINGS

ABSTRACT

This article presents the results of studies of the compositions and physical-chemical properties of selected bitumens, rubber powders and other organic-mineral ingredients based on local raw materials, the possibility of improving the physical-chemical properties of bitumens by modifying fine rubber powders and other organic-mineral ingredients, the influence of fine rubber powders on the physical- mechanical properties of bitumen-polymer composite materials, as well as the development of effective compositions of composite asphalt concrete polymer-bitumen materials using fine rubber powders and other organic-mineral fillers for use in asphalt concrete pavements in the production of highways, bridges and airfields.

АННОТАЦИЯ

В данной статье приведены результаты исследований составов и физико-химических свойств выбранных битумов, резиновых порошков и других органоминеральных ингредиентов на основе местного сырья, возможности улучшения физико-химических свойств битумов путём модификации тонкодисперсными резиновыми порошками и другими органоминеральными ингредиентами, влияние тонкодисперсных резиновых порошков на физико-механические свойства битумно-полимерных композиционных материалов, также разработка эффективных составов композиционных асфальтобетонных полимер-битумных материалов с использованием тонкодисперсных резиновых порошков и других органоминеральных наполнителей для применения в асфальтобетонных покрытиях в производстве автомобильных дорог, мостов и аэродромов.

Keywords:  composite materials, coatings, asphalt concrete materials, elastic-deformation-shear-resistant.

Ключевые слова: композиционные материалы, покрытия, асфальтобетонные материалы, упруго-деформационно-сдвигоустойчивые.

Currently, on a global scale, the dominant position is given to roads, along which 90% of national economic goods and more than 95% of passengers from the total volume of traffic carried out by all types of transport are transported. Therefore, special attention is paid to the creation of elastic-, deformation-, shear- and crack-resistant composite materials that improve the quality of highways and improve the technical condition of the transport network and the development of transport communications [1-5].

All over the world, based on organic-mineral ingredients of polymer binders and local raw and secondary resources, research is being conducted to create effective components, composite polymer and asphalt concrete materials and to develop technologies for their production. For this purpose, research is being conducted to study the structure of composite polymer materials and coatings made from them and their physical and chemical properties, to substantiate the influence of the composition, type and quantity of organic-mineral fillers on the physical, mechanical and operational properties of composite and asphalt concrete materials, to develop and organize technologies for their production for construction highways, bridges and airfields that meet modern requirements and ensure durability during their operation [6-15]. 

It should be noted that, despite the sufficiency of raw materials, the resulting elastic-deformation-shear-resistant asphalt concrete materials do not sufficiently meet the relevant requirements for highways today [16-17].

In this aspect, the development of elastic-deformation-shear-resistant composite asphalt concrete materials for road surfaces by physical and chemical modification of organic-mineral components from local and recycled raw materials is an urgent problem today.

Object and methods of research. The objects of research are bitumens BN60/90, BN40/60 [18-19], finely ground rubber powder [20], finely dispersed physically activated natural sands, lime, recycled polyethylene, lignin [20-24].

The work used standard physical and mechanical research methods, in particular, determination of compressive and shear strength, needle penetration depth - penetration, adhesion strength to concrete, water absorption and other physical and mechanical indicators of composite asphalt concrete materials in accordance with the requirements adopted in the CIS State Standard (State Standard -26589, State Standard -11506, State Standard -11501, 11507 and TU RUZ 14.04.2004).

The results were studied and analyzed. To develop effective compositions of composite asphalt concrete materials using fine rubber powders, their properties were studied.

Table 1 shows the properties of rubber powder by extrusion grinding.

Table 1

Properties of Extrusion Grinded Rubber Powder

As can be seen from the data presented, rubber powder produced by extrusion grinding is qualitatively different in particle structure from powders produced by traditional methods (cutting, roller grinding). The main difference between extrusion-ground rubber powders is a highly developed surface with many irregularities: depressions and protrusions, as well as a high specific surface area. The particles of the dispersed phase have a pronounced asymmetric shape and have a highly developed surface, which determines their tendency to agglomerate.

Analysis of the given data on the geometric parameters of extrusion-ground rubber powder particles in combination with the results of microscopic studies of the particle structure indicates that the shape of TIRP particles is close to ellipsoidal with a semi-axial ratio of 2 – 2.5.

Next, we will consider the influence of organic-mineral ingredients and rubber powders on the physical and mechanical properties of bitumen compositions used to develop elastic-deformation asphalt concrete compositions for producing road surfaces.

Figure 1 shows the dependence of the softening temperature of bitumen on the content of hydrolytic lignin from cotton husks, recycled polyethylene and fine rubber powder.

Figure 1. Dependence of the softening temperature of bitumen grades BND - 60/90 and BND-40/60 not modified with 6% slaked lime (a) and modified with 6% slaked lime (b) on the content of fillers: 1 and 1¹-secondary polyethylene; 2-2¹-hydrolytic lignin from cotton husks; 3-3¹ fine rubber powder obtained by finely grinding waste rubber

As can be seen from the curves in Figure 1, the softening temperature of bitumen tends to increase as the content of hydrolyzed lignin, recycled polyethylene and fine rubber powder increases. Thus, if the softening temperature of bitumen without hydrolytic lignin, recycled polyethylene and fine rubber powder is in the range from 47 to 54⁰C, and with a content of 45-50% hydrolytic lignin, recycled polyethylene and fine rubber powder this figure increases to 65-70, 69-75 and 88-100⁰С, respectively (Fig. 1a). It can be seen, that the introduction of rubber powder doubles the softening temperature of the composition. 

Figure 1.b shows the results of studies depending on the softening temperature of bitumen-rubber compositions based on BND-60/90 and BND-40/60 modified with 6% slaked lime on the content of fillers: 1 and 1¹-recycled polyethylene; 2-2¹-hydrolytic lignin from cotton husks; 3-3¹ fine rubber powder obtained by fine grinding of waste rubber.

As can be seen from the curves in Fig. 1.b it is observed that the softening temperature of bitumen-rubber compositions based on bitumen grades BND-60/90 and BND-40/60 modified with 6% slaked lime increases by 10 and 12⁰C. And with the addition of fine rubber powders to the modified bitumen with slaked lime, it also significantly increases their softening temperature. So, with an increase in the content of fine rubber powder to 50% of the mass of modified bitumen with slaked lime, temperature, the softening of modified bitumen-rubber compositions based on BND-60/90 bitumen increases from 60⁰C to 110⁰C, and for compositions based on BND-40/60 bitumen increases from 65⁰C to 120⁰C.

Figures 2 (a, b) show the dependence of the influence of the content of fine rubber powders on the physical and mechanical properties of bitumen-polymer compositions based on BND-60/90 and BND-40/60 bitumens, respectively.

As can be seen from the curves in Figure 2a, the softening temperature of bitumen-polymer compositions based on BND-60/90 bitumens with an increase in the content of fine rubber powders to 50% in the composition increases from 47⁰C to 85⁰C, elongation at 25⁰C increases from 55 cm to 77 cm, strength, adhesion increases from 48 MPa, and penetration decreases from 80 mm^-1 to 10 mm^-1

Similar results are observed for the bitumen-polymer composition based on bitumen BND-40/60 (Fig. 2b).

Figure 2. Dependence of the softening temperature (1), elongation at 25⁰C (2), penetration (3) and adhesion strength to concrete (4) of a bitumen-polymer composition based on bitumen grade (a) BN-60/90 and BN-40/60 (b) from the content of fine rubber powders

The results of studies to determine compressive and shear strength are shown in Figure 3.

As can be seen from the course of the curves in Figure 3.a, with an increase in the content of finely ground rubber powders, the compressive strength of asphalt concrete compositions has an extreme character, passing through a maximum, and lies within the range for river sands 4-4.2 MPa, for dune sands 3-3.3 MPa. The maximum compressive strength is observed in a ratio of bitumen and rubber powder of 3/3. Moreover, with an increase in the content of finely ground rubber powders of bitumen-polymer compositions containing the above-mentioned river and velvet sands, the shear strength monotonically increases (Fig. 3 b).

 a)                                                                           b)

Figure 3. Dependence of the compressive strength (a) and shear strength (b) of composite asphalt concrete materials for road surfaces on the ratio of bitumen and fine rubber powders at a constant content of 1.5% slaked lime, crushed stone 45%, sand 41% and mechanically activated sand 7.5 %

Next Table 2 shows the physical and mechanical properties of the developed elastic-strain composite asphalt concrete materials for producing road surfaces.

Table 2

Comparative comprehensive characteristics of the physical and mechanical properties of the developed elastic-deformation asphalt concrete pavements

As can be seen from Tables 2, the developed bitumen-polymer asphalt concrete composition for road pavements fully meets all indicators of physical and mechanical characteristics and even exceeds the requirements of technical specifications TU (Technical conditions) 20-28: 2021 or State Standard 9128-2013.

Conclusion. It has been established that the introduction of fine rubber powders into bitumen-polymer compositions makes it possible to purposefully regulate the structure and increase the elastic-strain characteristics of composite asphalt concrete materials and, accordingly, the resulting road surfaces. A scientifically based approach to the creation of elastic-deformation composite asphalt concrete materials based on local and secondary raw materials using fine rubber powders, gossypol resin and natural sands for the production of asphalt concrete pavements for highways with increased strength and performance properties for use in hot climates and high mountains is proposed. Uzbekistan.

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