Analysis of influencing factors of high temperature strength of hot mix asphalt mixture

Preface

Asphalt mixture is a kind of composite viscoelastic material, which is composed of asphalt, coarse aggregate, fine aggregate and filler and additives. In the summer high temperature asphalt pavement structure damage is mainly refers to the asphalt mixture at high temperature because of its shear strength or plastic deformation is too large and the pavement rutting, passage and so on. At present, the high temperature strength and stability theory of asphalt mixture is mainly required to have certain shear strength and resistance to deformation of asphalt mixture at high temperature.

The asphalt mixture shear strength of asphalt mixture mainly depends on the cohesion c and internal friction angle of two parameters. Through the application of three axis test method of Mohr Coulomb envelope equation: r = C + sigma Phi TG

R: asphalt mixture shear strength (MPa);

Sigma - normal stress (MPa);

C: asphalt mixture cohesion (MPa);

Phi - asphalt mixture internal friction angle (RAD).

Through the formula, we can see that the asphalt mixture cohesion c and internal friction angle determines the shear strength of the mixture and effect of hot mix asphalt mixture shear strength are mainly in the following aspects:

1 the influence of asphalt viscosity

Asphalt mixture is a multistage network structure of distributed system, a network structure from the micro point of view, it is a variety of mineral aggregates disperse in asphalt, so its anti shear strength and the concentration of the dispersed phase and dispersion medium viscosity are closely related. Under the condition of other conditions, the cohesive strength of the asphalt mixture increases with the increase of the viscosity of the C. Because the viscosity of asphalt indirectly reflects the mutual displacement of asphaltene micelle asphalt inside, is the dispersion medium resistance shear resistance, so the asphalt mixture is sheared, especially by the instantaneous load transient, with high viscosity asphalt to asphalt mixture viscosity resistance is large, so it has the strength of resistance high shear.

2 the influence of asphalt and aggregate on the chemical properties of ore

In the asphalt mixture, the interaction between asphalt and ore is a physical and chemical process. Interaction between asphalt and aggregate, asphalt re arrangement of chemical components in the slag surface, spread a layer formed on the surface of membrane powder agent. Asphalt, which is less than the thickness of the film, is called "structural asphalt" ". Asphalt outside the film is called "free asphalt" ".

If the contact between the asphalt particles is made up of the structure of the asphalt membrane, so that the asphalt has a higher viscosity and greater diffusion of the contact area of the melt film, and thus can get a greater cohesion. If the contact between the particles is free asphalt, it has only a small cohesive force.

Some properties of asphalt and aggregate interactions with the slag, adsorption on the melt film forming different structure and different thickness of surface properties of slag, adsorption of dissolved membrane more development in limestone surface formation, with high cohesion. Proved by a large number of related experiments on quartz powder surface adsorption film developing poor melt formation. So, powder must be by alkaline limestone aggregate processing, can also be used instead of cement or lime powder.

3 Influence of ore material ratio surface

The formation of structure asphalt is mainly due to the interaction of mineral aggregate and asphalt, and the re distribution of the asphalt chemical composition on the surface of the aggregate. As in the asphalt content under the same conditions, interact with asphalt aggregate surface area is larger, the asphalt film is formed thinner, ratio of structure in asphalt asphalt accounted for the larger, so the asphalt mixture cohesion is higher.

In the common asphalt mixture (e.g. AC-16I) powder consumption accounted for about 7% of its surface area accounted for more than the total surface area of mineral mixture is 80%, so the nature and amount of powder on asphalt mixture shear strength influence. Change the amount of slag, asphalt mixture Marshall test the technical indicators will also be with the change of asphalt mixture density increases with the amount of slag; stability and saturation increased with the amount of slag; void ratio increased with the amount of slag decreases; the softening point index of asphalt mixture increases the amount of fines. However, powder dosage should not be too much, the general powder dosage and asphalt dosage ratio of 1 ~ 1.6 is appropriate. If the excessive amount of powder, the opposite effect of asphalt mixture, the asphalt mixture in the rolling process is stable, and even goes to crack, asphalt paving and rolling difficult.

4 Influence of asphalt content

The ratio of asphalt and mineral aggregate is an important factor affecting the shear strength of asphalt mixture under the condition of fixed quantity of asphalt and aggregate. The asphalt content is very small, not enough to form a thin film of asphalt to adhesive structure of asphalt aggregate, with the increase of asphalt content, asphalt structure gradually formed, the surface asphalt wrapped in mine, the adhesion between asphalt and mineral aggregate increases with the amount of asphalt. When the amount of asphalt to form thin film and surface sufficient adhesion to slag particles, then the asphalt mixed material has the maximum cohesion. If the amount of asphalt will continue to increase, gradually aggregate away between the particles and the interaction of the formation of slag free asphalt, asphalt is the cohesion decreases with the increase of free asphalt. When the asphalt content reaches a certain amount, the shear strength of the asphalt mixture is almost unchanged, the free asphalt plays the role of lubricant, reducing the interaction between the coarse aggregate and the asphalt.