Asphalt materials are divided into two categories: ground asphalt and tar asphalt. Asphalt is divided into natural asphalt and petroleum asphalt.
Coal tar pitch: Tar pitch is the product of reprocessing the tar obtained from the distillation process of coal, wood and other organic matter, coal tar pitch is the product of coking, that is, the black substance left in the distillation kettle after tar distillation. It and refined tar is just physical properties have respectively, there is no obvious boundary, the general division method is to specify softening point in 26.7 ℃ (cube method) below for tar, 26.7 ℃ above for asphalt. Coal tar pitch mainly contains anthracene, phenanthrene, pyrene, etc. which are difficult to volatilize. These substances have toxicity, because of the different content of these components, coal tar pitch properties are also different. The change of temperature has great influence on coal tar pitch, which is easy to crack in winter and soften in summer. Special smell when heating; Heating to 260℃ in 5 hours later, the contents of anthracene, phenanthrene, pyrene, and other components will volatilize out.
Petroleum pitch: Petroleum pitch is the residue after distillation of crude oil, the product obtained after proper process treatment, according to the degree of refining, at room temperature into a liquid, semi-solid or solid. Petroleum asphalt is black and glossy, with high temperature sensitivity. Because it has been distilled to more than 400℃ in the production process, so contains very little volatile components, but there may still be high molecular hydrocarbons without volatilization, these substances are more or less harmful to human health, the vast majority of asphalt used in the project is petroleum asphalt, petroleum asphalt is a mixture of complex hydrocarbons and non-metallic derivatives. Usually the asphalt flash point is between 240℃ and 330℃, and the ignition point is about 3℃~6℃ higher than the flash point, so the construction temperature should be controlled below the flash point.
Natural asphalt: Natural asphalt is the residue of petroleum seepage from the surface after long-term exposure and evaporation. Natural asphalt is stored underground, and some form mineral layers or accumulate on the surface of the earth's crust. This asphalt mostly through natural evaporation, oxidation, generally does not contain any toxins.
1.1. Asphalt Concrete:
AC(Asphalt Concrete) called asphalt concrete, is continuous gradation, that is, the amount of each file material is continuous, step by step interlocking, the mixture belongs to suspension dense type skeleton. Marshall test compaction molding was used in laboratory grading design. Because of rich experience and mature technology, it is used a lot in our country, basically 70, 80% of the surface layer of 1, 2 highways will adopt this grade;
Marshall test is the test to determine the optimum oil stone ratio of asphalt mixture. The test process is to measure the stability and flow value of asphalt mixture under the standard compaction of the test piece under the specified temperature and humidity conditions. After a series of calculations, the relationship curves of the oil stone ratio and stability, flow value, density, porosity and saturation are drawn respectively, and finally the best oil stone ratio of asphalt mixture is determined.)
SMA is called asphalt mshoe grease gravel, is discontinuous gradation, that is, the amount of each file material is not continuous, its characteristics are more coarse material, less fine material, high oil content, ore powder, sometimes add fiber in the mixture to enhance the skeleton reinforcement effect, the mixture belongs to the skeleton dense structure, the surface structure depth is better, pavement anti-skid performance is better than AC, SUP. Marshall compaction molding was used in laboratory grading design. Such designs originated in Germany. With high cost, the mixture has better fatigue performance and high temperature performance.
1.2 SBS modified asphalt: (Most of the current pavement construction uses modified asphalt concrete)
SBS modified asphalt takes matrix asphalt as raw material, adding a certain proportion of SBS modifier, through shear, stirring and other methods to make SBS evenly dispersed in the asphalt, at the same time, adding a certain proportion of exclusive stabilizer to form SBS blend material, using SBS good physical properties for asphalt modification treatment.
SBS constituent structure
SBS belongs to styrene thermoplastic elastomers, is styrene - butadiene - styrene triblock copolymer, SBS polystyrene chain segment and polybutadiene chain segment obviously show two phase structure, polybutadiene for continuous phase, polystyrene for dispersed phase, so that it has two glass transition temperature, the first glass transition temperature (Tg1) -88~-83℃, The second glass transition temperature (Tg2) is 90℃, between Tg1~Tg2 end polystyrene gathered together to form a micro region dispersed in the continuous phase of polybutadiene, physical crosslinking, fixed chain segment, vulcanization enhancement and anti-cold flow effect, with vulcanized rubber high elasticity and fatigue resistance, when the temperature rises to Tg2, Polystyrene phase softening and flow make SBS have resin flow processing property. This two-phase separation structure can form a three-dimensional network structure with the asphalt matrix, so as to effectively improve the temperature property, tensile property, elasticity, cohesive adhesion property, stability of the mixture, aging resistance and so on. Among many asphalt modifiers, SBS can simultaneously improve the high and low temperature properties and temperature sensing properties of asphalt, making it the most researched and applied variety. SBS modified asphalt accounts for as much as 61% of the global demand for asphalt.
Main characteristics of SBS
1. The area with large temperature difference has good resistance to high temperature and low temperature
2. Good rutting resistance, good elasticity and toughness
3. It improves the fatigue resistance of the pavement, especially on the highway with large flow and serious overload, it has good strain capacity, which can reduce the permanent deformation of the pavement
4. The bonding ability is particularly strong, which can obviously improve the tensile ability of pavement after encountering water, and greatly improve the water stability of asphalt
5. Improve the anti-skid ability of the road surface
6. Enhanced the bearing capacity of the road surface
7. Reduce asphalt aging caused by ultraviolet radiation on pavement
8. Reduce damage caused by leakage of diesel, oil and gasoline from vehicles
SBS production technology
Generally speaking, SBS modification of asphalt needs to go through swelling, shear, development of three processes.
For SBS modified asphalt system, there is a close relationship between swelling and compatibility, swelling size directly affects the quality of compatibility, if SBS in the asphalt infinite swelling, the system becomes completely compatible. Swelling behavior is closely related to the production, processing technology and high-temperature storage stability of modified asphalt. With the increase of temperature, the swelling speed is obviously accelerated, and the swelling is obvious at the melting processing temperature of PS glass transition higher than SBS. In addition, the structure of SBS has obvious influence on swelling behavior: the swelling speed of star SBS is slower than that of linear SBS. The relative calculation showed that the density of SBS swelling component was concentrated between 0.97 and 1.01g/cm3, which was close to the density of aromatic phenol.
Shearing is a key step in the whole modification process, and often the shearing effect will affect the final result. Colloidal mill is the core of modified asphalt equipment, it is in high temperature, high-speed operation environment, the outer layer of colloidal mill for jacket structure, with a circulation insulation system, at the same time plays the role of shock absorption and noise reduction, the colloidal mill for a certain number of tooth slots ring moving disk and ring fixed disk sharpening, the gap can be adjusted, The uniformity of the material size and the gelatinization effect are determined by the depth and width of the tooth groove, the number of sharpening tools and the specific working area of the structure. With the high-speed rotation of the moving disc, the modifier is continuously dispersed by strong shear and collision, and the particles are ground fine to form a stable system of miscible with the asphalt, so as to achieve the purpose of uniform blending. After full swelling, SBS and asphalt mixed evenly, the smaller the grinding particles, the higher the dispersion degree of SBS in asphalt, the better the performance of the modified asphalt. Generally in order to achieve better results, can be carried out multiple grinding.
The production of modified asphalt finally goes through the development process. After grinding, the asphalt enters the finished product tank or the development tank. The temperature is controlled at 170-190℃, and the development process is carried out for a certain time under the action of agitator. In this process, some kind of modified asphalt stabilizer is often added to improve the storage stability of modified asphalt.
1.3 Asphalt concrete classification:
Asphalt concrete according to the used binder is different, can be divided into petroleum asphalt and coal asphalt two categories; Some countries or regions also use or mix with natural asphalt.
According to the different aggregate varieties used, can be divided into gravel, gravel, sand, slag several classes, to gravel is the most common.
According to the different maximum particle size of the mixture, it can be divided into coarse grain (35 ~ 40 mm below), medium grain (20 ~ 25 mm below), fine grain (10 ~ 15 mm below), sand grain (5 ~ 7 mm below) and so on.
According to the different degree of density of the mixture, it can be divided into dense gradation, semi-open gradation and open gradation. Open gradation mixture is also called asphalt gravel. Among them, the dense graded gravel mixture of hot mix and hot spread is durable, high strength and good integrity. It is the representative material of building advanced asphalt pavement and is the most widely used. Different countries have different specifications for asphalt concrete. In the technical specifications for hot mix asphalt mixture formulated in China, those with a porosity of 10% or less are called asphalt concrete, which is subdivided into type Ⅰ and type Ⅱ. The porosity of type Ⅰ is 3(or 2) ~ 6%, belonging to the dense matching type. Type Ⅱ is 6-10%, which belongs to half-open type. The porosity of 10% or more is called asphalt gravel, which belongs to open type; The physical and mechanical indexes of the mixture include stability, flow value and porosity.
According to the maximum aggregate particle size:
Coarse grain type (ATB-25, LASM-25, AC-25,Superpave-25, etc.),
Medium grain (AC-20,Superpave-20, AC-16, etc.),
Fine grain type (AC-13,Superpave-13, OGFC-13, OGFC-9.5, etc.);
Classification by gradation type: continuous gradation (dense gradation such as AC, Superpave),
Open (such as OGFC), semi-open (such as SMA);
Divided by thickness: type C (coarse), type F (fine)
According to the composition of the mixture structure: suspension dense type, skeleton dense type, skeleton pore type;
According to mixing and spreading temperature: hot mix asphalt concrete, warm mix asphalt concrete, cold mix asphalt concrete.
Such as: SBS AC-13F SBS: SBS modified, AC: asphalt concrete, -13: particle size less than 13mm, F: fine type.
1.4. Pervious asphalt concrete
It refers to the new asphalt concrete surface layer with a void ratio of about 20% after compaction, which can form a drainage channel inside the mixture. Its essence is the open-graded asphalt mixture with a skeleton - void structure formed by single particle size gravel according to the extrusion mechanism. On the other hand, with the graded friction course (OGFC, open-graded friction course) and the graded friction course (PAWC, porous asphalt wearing course), etc. The composition characteristics of these materials are basically the same, but they are given different names because of the differences in the function, description Angle and emphasis. Sometimes there are differences in technical characteristics.
Pervious asphalt concrete is porous concrete made of asphalt as cementing material, natural stone as coarse aggregate, and adding a small amount of fine aggregate and asphalt to form the base material of cohesiveness and stability, and the discontinuous gradation of coarse aggregate bonded together, which is mainly used for road pavement. The permeable asphalt concrete mainly relies on coarse aggregate to form the skeleton, and at the same time, a small amount of fine aggregate is mixed to adjust the viscosity of the mixture. The asphalt is wrapped on the surface of the aggregate to form a bonding layer and bond the aggregate particles together.
The permeable asphalt pavement uses the large void asphalt mixture as the surface layer, penetrates the rain into the drainage function layer, and drains the rain horizontally through the layer, thus eliminating the road surface water film which brings many adverse effects of driving, and significantly improves the safety and comfort of driving in rainy days. At the same time, it is also known as low-noise asphalt pavement because it can greatly reduce traffic noise due to its porous characteristics.
With the rapid development of economy and society, people's demand for travel quality is constantly upgraded, and the concept of "environment-friendly" is increasingly highlighted in transportation construction. In the field of road engineering, how to improve the use of pavement function, how to provide high safety, more comfortable, more environmentally friendly road surface characteristics to the society, has become the new goal pursued by the Chinese traffic department in the new period.
Taking a comprehensive look at the technological frontier at home and abroad, the drainage asphalt pavement with large voids features has outstanding advantages such as high skid resistance, low noise, water mist inhibition, water drift prevention and glare reduction. It can be said that the "top pavement performance" in the existing asphalt pavement technology has become the best pavement form to realize the leap of road surface characteristics and quality.
At present, pervious asphalt concrete pavement faces the most. The big problem is that roads soften in the heat of summer, and when they soften under heavy pressure they squeeze, clogging up the pores in the road and rendering it impervious to water. Another problem is that the asphalt pavement is subjected to the action of sunlight and air oxidation, the surface gradually becomes brittle, and then it is crushed and rubbed off by tires. This kind of pavement material has high strength, high cost, sensitive to temperature and humidity changes, poor weather resistance and easy aging.
