Study on Low-Temperature Performance of Packed Waste Polymer Modified Asphalt(4)

4 Low temperature performance analysis

4.1 Theoretical basis

Modified asphalt belongs to the blending modification of polymer materials. At present, there are mainly two theories for the blending modification of polymer materials.

4.1.1 Interface Theory

The theory is that the modification effect depends on the compatibility of the material and the nature of the material itself and the nature of the modifier-asphalt two-phase interface. The interface properties depend on the depth of the local diffusion on the two-phase interface and the two phases. The interaction energy. Only with proper compatibility and good interface properties can we obtain modified materials with good properties [15]. The use of interface theory to explain the mechanism of polymer composites is based on the assumption that effective stress transfer in the interface layer. Stress transmission mainly through the following ways:

(1) Chemical Bonds Glass Fibers - Coupling Agents - Studies of the chemical bonds at the interface of the resin matrix, suggesting that coupling agents containing chemical functional groups can react with both glass fibers and functional groups in the resin.

(2) The strained layer (relaxation interface) is considered to produce a strained layer between the dispersed phase and the dispersion medium to eliminate the generated stress under the action of the coupling agent, and the material constituting the internal interface is likely to be the dispersed phase and the dispersion medium. The third polymer outside.

(3) Deflection layer (rigid interface) Assuming that there is a moderate modulus of the internal interface layer, the transfer of stress between the high-modulus phase and the low-modulus phase can occur uniformly.

(4) Surface wettability In view of physical adsorption between the resin and the glass fiber, a greater cohesive force than the resin itself is generated.

(5) Combining the concept of "rigid interface" with the theory of the chemical layer and the inhibition layer, and the concept of "relaxation interface" with the deformation layer theory.

4.1.2 Solubility Theory

In reality, there are few cases in which the two materials can completely dissolve when blended. However, in the production practice, the reasonable selection of the two materials and the appropriate production process can be used to obtain the stability of microscopic heterogeneous and macroscopic uniform distribution. system. The two materials are blended, and due to mutual diffusion between macromolecules, the molecular chain segments are displaced to form a transition layer, thereby stabilizing the system. The thermodynamically compatible two materials can diffuse to complete dissolution of macromolecules, and eventually form a homogeneous thermodynamically stable system. Otherwise, local diffusion can only occur. The degree of diffusion depends on the difference in solubility parameters of the two phases. At the same time, when the two materials are blended under the action of mechanical forces, macromolecular chains are cut off, resulting in extremely active macromolecular radicals. Some of the long-chain radicals combine with oxygen to generate shorter-chain segments of the polymer, and the other Combined with each other to generate new copolymers, such as the formation of graft or block copolymers. The solubility parameters of this copolymer lie between the two blends, thus acting as a bridge between the two phases and improving the compatibility of the system.

Based on this theory, it is hopeful to select a polymer whose solubility parameter is close to that of matrix asphalt to modify it.

4.2 Analysis of Low Temperature Performance of Modified Asphalt

4.2.1 Analysis of test results

Based on the theoretical basis of the above-mentioned polymer modified asphalt, combined with the test and test data of packaging waste PE modified asphalt in this topic, the low temperature performance of packaging waste PE modified asphalt is analyzed.

From the experimental data in Chapter 3, Table 3-1 shows that as the amount of PE in the modified asphalt continues to change, the degree of extension of the modified asphalt constantly changes and decreases with the increase in the amount of PE, as shown in Figure 4-1.

4.2.2 Analysis of Low Temperature Performance Mechanism

From the experimental study, it can be seen that the PE modifier can obviously change the performance of the asphalt. With the increase of the amount of PE, the elongation of the modified asphalt decreases, and the frozen asphalt of the modified asphalt has a stress of 5 Mpa. Above, at the same time, the minimum freezing temperature is -34.2°C, satisfying the needs of colder regions.

The modifier used in this project is packaged waste PE. PE has good flexibility, elongation and impact resistance, has a very large molecular weight (up to 300,000), and belongs to the linear long-chain molecular structure. With more alkyl and methyl branches on the chain, it becomes a multi-branched dendritic structure. It is due to the presence of multi-branching branched chains and the presence of irregular molecular structures that can greatly increase the viscosity of the asphalt, improve the adhesion of the modified asphalt to the aggregate, and improve the overall performance of the asphalt. The mixing of PE and asphalt is a thermodynamically incompatible system. Thermodynamic compatibility refers to the ability of two or more substances to form a completely uniform dispersion system in proportion, and the entire system is a phase. PE and asphalt can not form molecular-level dispersion, there is a clear phase interface in the system. The mixing performance of PE and asphalt can only be described by physical compatibility in terms of whether there are good phase interfaces, uniformity, dispersibility, stability, and the like.

The degree of improvement of asphalt performance by packaging waste PE is mainly affected by the following factors:

(1) The smaller the particle size, the greater the degree of dispersion, that is, the larger the number of particles per unit volume, the closer the distance between the particles, the greater the interaction between particles.

(2) The finer the particle size of the PE dispersion, the greater the surface area in contact with the bitumen (specific surface area increase). This is beneficial to the PE swelling and dispersion process of the bitumen. The greater the degree of swelling of the microparticles, the greater the space occupied by the microparticles, and the smaller the space where the asphalt can flow, the greater the viscosity.

(3) The finer the particle size, the more asphalt components absorbed on the surfaces of the PE particles, and the amount of free bitumen is relatively reduced, which greatly increases the migration resistance and increases the viscosity.

(4) The finer the particle size is, the more finely packed the adsorption layer is, the closer to the asphalt are the many properties of the microparticle mass, which improves the stability of the modified asphalt:

(5) The composition and properties of the matrix asphalt itself.

The reason why the low-temperature performance of PE modified asphalt has been significantly improved, the modification mechanism can be interpreted as: the surface of the material or some of the defects in the internal stress caused by the concentration of small holes, these holes in the development of a very fine marks When the deformation progresses further and the molecular chain of orientation and orientation breaks, it turns into micro-cracks. Under low temperature conditions, the molecular flow of the matrix asphalt decreases, the intermolecular distance decreases, the intermolecular forces increase, and the brittleness increases. Also at low temperatures, due to the presence of fine particles of the PE modifier, the particles play a role in stress concentration. Modifier particles cause a large number of fine lines or shear bands under the stretching of external forces. The development of these fine lines or shear bands will terminate at another particle. When the fine lines and fine lines meet, the lines will turn to branching. The coordination of these processes has greatly delayed the destruction of materials. When the modified bitumen material is further stretched by external forces, modifier particles are present at the interface due to the transformation of the fine lines into cracks at low temperatures, which impedes its further development and absorption and consumption. The energy required to break the mixture, so the ductility increases at low temperatures, crack resistance increases. In addition, since the striated body is quite hard at the initial stage of stress, when the stress exceeds a certain value, the crass body begins to yield, and the deformation develops with the extension of time. After unloading, the strain gradually recovers, and the deformation disappears with the prolongation of time, so the PE modified asphalt has The good low-temperature performance, the low temperature freezing temperature of -34.2 °C, has also met the actual needs of cold regions.

Author: Jiang Shaohua Source: Chinese green ink network