As one of the three major indicators for asphalt evaluation, softening point has multiple effects on road performance. Starting from the analysis of asphalt components, the article discusses the influence of softening point on high temperature stability, low temperature crack resistance, fatigue resistance, aging resistance, adhesion performance, durability, water stability and skid resistance, and puts forward corresponding Measures to improve the level of road construction.

During the paving or repair of asphalt pavement, the determination of asphalt softening point is an essential routine item. In the special research report of our country in the eighth five-year national scientific and technological research, the research results of "petroleum asphalt technology for heavy traffic roads" show that the PI value of asphalt can well reflect the temperature sensitivity of asphalt, and the equivalent softening point T80 ( Excluding the influence of wax in asphalt on the softening point) as a key indicator of the high temperature stability of asphalt.

Asphalt is a temperature-sensitive material. Asphalt exhibits anisotropy in different temperature ranges. People usually use the softening point of asphalt to represent the temperature at which asphalt transitions from solid to liquid, that is, the temperature at which asphalt loses its ability to resist deformation under the action of motion. . There are many kinds of softening point test methods. In order to characterize the temperature-sensitive properties of asphalt, scholars from various countries have proposed different temperature-sensitive parameters. my country adopts the world's most extensive ring and ball method as a standard measurement method.

1 Influence of various components of asphalt on softening point

In order to study the influence of each component of asphalt on the softening point, the L.W. Corbet four-component analysis method in the United States is usually used: asphaltenes, resins, aromatic hydrocarbons and saturated hydrocarbons. Its different proportions form different colloidal structures, with asphaltene as the center, colloids are adsorbed on asphaltene to form micelles, and the whole is dispersed in the dispersion medium (aromatic component and saturated component) as a dispersed phase.

It is well known that waxes (n-paraffins) present in saturated hydrocarbons have a great influence on the road performance of asphalt, especially in the case of my country's rich production of paraffin-based crude oil, which is more concerned. Waxes will soften the asphalt at high temperatures, resulting in reduced high-temperature stability of the asphalt pavement and rutting. Similarly, the asphalt will become brittle and hard at low temperature, resulting in a decrease in the low-temperature crack resistance of the pavement and cracks appear. In addition, wax will reduce the adhesion between asphalt and stone materials. Under the action of moisture, pavement stones and asphalt will peel off and cause damage. Waxy asphalt will reduce the skid resistance of asphalt pavement and affect road safety.

The core substance of the asphalt colloidal system is asphaltene, which has a high content of asphaltene, a high softening point, low penetration and low ductility.

2-way performance impact

The road performance requirements of asphalt pavement mainly include: high temperature stability, low temperature crack resistance, fatigue resistance, aging resistance, adhesion performance, durability, water stability and skid resistance. .

2.1 Effect of softening point on rutting

There are two types of rutting caused by traffic loads, compaction deformation and plastic flow deformation.

Compaction deformation is mainly caused by the pressure of driving, and the asphalt concrete is crushed, usually accompanied by a vertical volume change. There is no volume change in plastic flow deformation, and it only manifests as lateral flow of asphalt concrete, which manifests as uplift on both sides of the subsidence of the wheel track.

In order to reduce the rutting of the asphalt pavement, the softening point of the selected asphalt should be controlled during engineering construction, and it must be higher than the maximum temperature that the road surface may reach, or appropriate measures should be taken to reduce the temperature of the road surface. Reasonable blending of asphalt with high softening point is an effective way to improve the rutting resistance of asphalt pavement.

2.2 Effect of softening point on pavement aging

When the asphalt is aged, the components are transformed, some aromatic hydrocarbons will be converted into resin, and part of the resin will be converted into asphaltene, resulting in an increase in asphaltene content, an increase in the overall average molecular weight and aromaticity of the asphalt, and an increase in softening point.

After asphalt aging, in terms of physical and mechanical properties, it shows that the penetration decreases, the ductility decreases, the softening point increases, the absolute viscosity increases, and the brittle point decreases. In terms of the content of chemical components, it shows that the saturated content changes little, and the aromatic components are obviously transformed into colloids, and the colloids are transformed into asphaltene. The transformation of aromatic components into colloids is not enough to compensate for the transformation of colloids into asphaltenes. So in the end, the colloid is significantly reduced, while the asphaltene is significantly increased, which is manifested as an increase in softening point.

2.3 Effect of softening point on high temperature stability

The high temperature sensitivity of asphalt materials is expressed by the softening point. When the asphalt material is in the temperature stage between the hardening point and the dripping point, it is a viscous flow state. In actual engineering, in order to ensure that the asphalt will not flow due to temperature rise, 87.21% of the temperature interval is taken is the softening point. According to the "Test Regulations for Asphalt and Asphalt Mixtures in Highway Engineering", the global softening point tester is used to measure the asphalt sample into the copper ring of the specified size, place a standard steel ball on the sample and immerse it in water or glycerin, at 5 ° C per minute Heating up to the temperature at which the asphalt softens and sags to a specified distance. The higher the softening point, the better the heat resistance of the asphalt, that is, the better the temperature stability.

Tests have shown that when the pavement temperature is higher than the softening point of the asphalt mixture, the cohesive force of the asphalt will decrease significantly, and the dynamic stability will decrease accordingly. It is worth noting that when the ambient temperature is near the softening point of the asphalt, the dynamic stability of the asphalt mixture will have a sudden change, that is, the stability value will suddenly drop and collapse. The road surface temperature is the main factor affecting the high temperature stability, and the softening point plays a decisive role. With the increase of the road surface temperature, the high temperature stability decreases obviously.

2.4 Effect of softening point on pavement viscoelasticity

The elastic deformation of asphalt pavement is mainly under the low temperature instantaneous load, and the viscous deformation is the main one under the high temperature long-term load. The stiffness modulus is an index that expresses the combined viscous and elastic effects of asphalt. According to the stiffness modulus nomogram of actual engineering, three parameters are required: load action time or frequency, penetration index, and temperature difference, that is, the temperature difference between the actual temperature of the road surface and the softening point of the ring and ball method. It can be seen that increasing the softening point within an appropriate range is conducive to maintaining the elasticity of the road surface.

3 Conclusion

There is a simple linear relationship between n-pentane asphaltene content and asphalt softening point, and its content is highly correlated with aging resistance. Properly increasing n-pentane content in asphaltene can improve road performance.

Among the four components of asphalt, asphaltene has the most significant effect on softening point because of its greater polarity, average molecular weight, heteroatom content and aromaticity.

When the temperature exceeds the critical temperature of high-temperature deformation resistance of asphalt mixture, the deformation resistance of the pavement drops sharply. Therefore, the asphalt mixture can be selected according to the maximum design temperature of the road surface of the project, that is to say, the critical temperature of the asphalt mixture used must be higher than the maximum design temperature of the road surface, and the softening point of the asphalt on the project site can be improved by blending.