RESEARCH OF THE PROPERTIES OF MECHANICALLY ACTIVATED ORGANIC-MINERAL INGREDIENTS AND ELASTIC-DEFORMATION-SHEAR-RESISTANT COMPOSITE ASPHALT CONCRETE MATERIALS ON THEIR BASIS FOR HIGHWAY COVERINGS

ABSTRACT

This article presents the results of studies of the microstructure and physical-mechanical properties of organic-mineral ingredients based on local and secondary raw materials, methods and devices for mechanic-chemical activation of mineral ingredients and their influence on the physical-mechanical and deformation-shear properties of the developed composite asphalt concrete materials for road pavements.

АННОТАЦИЯ

В данной статье приведены результаты исследований микроструктуры и физико-механических свойств органоминеральных ингредиентов на основе местного и вторичного сырья, способов и устройств механохимической активации минеральных ингредиентов и их влияния на физико-механические и деформационно-сдвигоустойчивые свойства разрабатываемых композиционных асфальтобетонных материалов для покрытий автомобильных дорог. 

Keywords: asphalt concrete materials, organic-mineral fillers, modification, shear strength, compressive strength, bitumen, rubber powder, natural sands, mechanical activation.

Ключевые слова: асфальтобетонные материалы, органоминеральные наполнители, модификация, прочность при сдвиге, прочность при сжатии, битум, резиновый порошок, природные пески, механоактивация.

Introduction. Today, an urgent task all over the world is to increase the durability of highways, bridges and airfields through complex physical and chemical modification of asphalt concrete compositions with high values ​​of elastic-deformation-shear resistance and deformation crack resistance. This gives rise to the need to conduct fundamental and applied research in the field of studying the physicochemical and strength properties of elastic-deformation-shear-resistant composite materials for the production of asphalt concrete materials for road surfaces. [1-5].

Based on the analysis of existing works, it should be noted that the issues of creating elastic-deformation-shear-resistant composite asphalt concrete materials for road surfaces using physical-chemically modified organic-mineral components have not been fully resolved [6-7]. This is mainly due to the insufficient research carried out to improve the adhesive strength, wear, water and heat resistance, elastic-deformation-shear resistance of existing asphalt concrete pavements, to reduce destruction and cracking of asphalt concrete pavements of roads, bridges and airfields, allowing for increased elastic-deformation resistance. shear-resistant properties, as well as the complexity of a comprehensive study of the physical-chemical, physical-mechanical and operational properties of the developed composite asphalt concrete materials and coatings based on them [8-17].

Object and methods of research. The objects of research are bitumens BN60/90, BN40/60 [18-19], finely ground rubber powder [20], finely ground physically activated natural sands, as well as 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.

It has been established that dune sands differ significantly from river sands in both chemical and mineralogical composition. From a practical, especially technological point of view, important properties of natural sands are their granulometric composition, bulk and true density, specific surface area, and grain roughness.

Natural sands of six deposits were studied, which differ in nature: Chirchik and Chinaz (river), Boz, Zhamashui, Yazyavan and Yangier (dune).

It should be noted that the use of natural sands in such a natural state in asphalt concrete pavements leads to a high consumption of binder material (bitumen) and an increase in the cost of asphalt concrete pavements, as well as a decrease in their quality indicators, such as deformation and shear resistance.

In addition, the indicators of compressive and shear strength are inferior to a certain extent and do not meet the necessary requirements that apply to asphalt concrete pavements used in our climatic conditions.

In this regard, for a comparative analysis of the influence of river and dune sands on the properties of the asphalt concrete composition and to establish the possibility of their use as mineral fillers for asphalt concrete pavements, we conducted studies of the physical and mechanical properties of the developed asphalt concrete composition using them.

The study found that to obtain asphalt concrete compositions with a shear strength of 0.7-0.9 MPa in accordance with State Standard, a bitumen content of at least 20-25% in the asphalt concrete composition is required, and this will lead to high bitumen consumption and is unprofitable for production.

Thus, analyzing modern achievements in the production of high-quality asphalt concrete compositions for covering asphalt concrete roads and based on the results we obtained, it was proposed to physically, mechanically and chemically process organic-mineral ingredients when producing asphalt concrete composite materials in order to increase their deformation and shear resistance.

The main role in physical and chemical mechanics in the field of activation of mineral raw materials used in the creation of various composite materials is played by the mechanic-chemical activation of organic-mineral ingredients. It is known that for the mechanical activation of mineral raw materials, grinders are currently used, in which the impact-splitting effect is realized.

However, the implementation of the impact-splitting effect for natural sands, including sand dunes, is impractical not only from the point of view of energy and labor costs, but also from the position of excessive consumption of binders for asphalt concrete pavements.

Our experiments on the mechanical activation of dune and river sands showed that such equipment is a dismembrator activator, developed by Ph.D. N.S. Negmatov and created at the SUE “Fan va Tarakkiyot”, which implements the impact-splitting-abrasion principle of grinding.

The study found that for the ultimate compressive and shear strength of the compositions and the optimal amount of dismembrator loading is 3 kg per minute, since with such loading the highest dispersion and specific surface area of ​​the sands are observed.

The mechanism of mechanical activation when processing minerals and natural sands in a dismembrator installation occurs as follows. During the shock-abrasive processing mode, activation occurs mainly due to the formation of new surfaces with a slight change in the granulometric composition, and when processing in the impact-splitting-abrasion mode, activation occurs both due to a change in the granulometric composition and due to the exposure of new surfaces.

Based on this, we investigated the effect of mechanical activation on the strength properties of asphalt concrete pavements. And the strength properties of the asphalt concrete composition, in turn, significantly depend on the particle size distribution and, accordingly, on the specific surface area of ​​mineral powder materials.

In this regard, the dependences of the ultimate shear and compressive strength on the specific surface area of ​​sand particles during their mechanical activation and the effect of mechanical activation on the shear strength of asphalt concrete pavements were studied (Figure 4 a, b).

1 - Chinaz; 2 - Zhamashuisky; 3 - Yazyavan; 4 - Bozsky; 5 -Yangiersky; 6 – Chirchik

Figure 4. Dependence of the compressive strength (a) and shear strength (b) of asphalt concrete composite materials on the specific surface area of ​​particles of mechanically activated natural sands

As can be seen from the course of the curves in Figure 4 (a, b), when mechanically activated sand is used in all compositions, due to an increase in the specific surface of their particles, an increase in the compressive and shear strength of asphalt concrete pavements is observed, and the maximum increase is observed at a specific surface area of ​​550 cm²/g.

Conclusion. Thus, the introduction of mechanically activated sands, both river and dune, into the compositions made it possible to increase the strength properties, especially shear and compressive strength, and deformation and shear resistance of the developed compositions for asphalt concrete pavements of highways.

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