Rubber asphalt has the advantages of environmental protection, anti-rutting, noise reduction, and improved durability. The research on the microscopic interaction mechanism between rubber powder and asphalt has not yet reached an exact conclusion. The more representative ones are physical blending theory, network filling theory and chemical blending theory. In ordinary rubber asphalt, rubber particles can effectively absorb oil wax in asphalt, reduce the content of free wax, reduce the temperature sensitivity of asphalt, and improve the cohesiveness of asphalt. However, due to the high viscosity characteristics of ordinary rubberized asphalt and the interference between large particle rubber and fine aggregates, it often adopts intermittent grading for mixture design and the oil stone is relatively large. Reactive rubber modified asphalt reduces the viscosity of rubber asphalt and reduces the interference with fine aggregates through rubber powder crushing and infrared desulfurization, catalytic reaction and conditional curing, which provides the possibility for rubber asphalt to be used in intensive mixing design and reduce the oil-to-stone ratio.
Micro modification mechanism
Modification Mechanism of Rubber Modified Asphalt
The research shows that: after the rubber powder is added to the asphalt, the rubber powder molecules are separated under the action of oil and aromatic components in the asphalt, and in the process of high temperature and high speed shearing reaction, the rubber powder has obvious swelling effect, and then the swollen micelles are formed. Disperse each other so that the rubber powder is randomly distributed in the asphalt matrix in the form of particles or filaments. On the other hand, a small part of the rubber powder undergoes desulfurization and degradation in the asphalt, dissolves in the asphalt, and can generate a vulcanized macromolecular network structure, and the two exist in a material transfer and exchange process. Therefore, the modification mechanism of rubber asphalt is a combination of physical and chemical effects.
Infrared spectroscopy test
In order to study the chemical modification characteristics of reactive rubber-modified asphalt, the paper uses infrared spectroscopy to study reactive rubber-modified asphalt and rubber asphalt produced by wet process. Wet rubber asphalt was prepared with Donghai AH-70# base asphalt, the sample rubber powder content was 20%, and sheared by Shanghai AE300L-P laboratory shear emulsifying machine, the time was 30min, and the speed was 5000r/min. Generally, the swelling effect and the degree of chemical reaction between rubber powder and asphalt have a great relationship with curing time and temperature. The rubber asphalt sample is HW reaction type rubber powder modified asphalt produced in Jiangsu.
Comparing the differences between the test results of the two asphalts, the infrared spectrum of the reactive rubber-modified asphalt has a small absorption peak in the range of 1180~980Cm-1, while the infrared spectrum of the wet rubber asphalt does not have this feature. absorption peak. The research shows that the absorption peaks of S=O bond are in the range of 1200~1040Cm-1, the absorption bands of SO2-4 are in the bands of 1150~1025Cm-1 and 650~600Cm-1, and the absorption bands of SO2-3 are in the bands of 1000~900Cm-1 and 700~ Therefore, the absorption peak in the range of 1180~980Cm-1 in the infrared spectrum of reactive rubber-modified asphalt can be determined to be thiol groups. When the sulfate radical concentration in wet rubber asphalt is not large, the absorption peak of functional groups is not obvious. The absorption peak in the reactive rubber asphalt is obvious, mainly because a large number of sulfur-sulfur single bonds are broken during the pretreatment of the rubber powder, and the broken sulfur bonds combine with oxygen to form sulfur-oxygen bonds, which make the original broken sulfur bonds. Linear structure, re-form network structure in rubberized asphalt.
The same strong absorption peaks around 3000~2800Cm-1 represent the vibration of CH in alkanes and cycloalkanes; the two absorption peaks at 1457Cm-1 and 1376Cm-1 represent -CH- in C-CH and -CH2- In-plane stretching vibration; the absorption peak in the region of 910~650 cm-1 represents the out-of-plane rocking vibration of CH on the benzene ring. These three components are the main components of the base asphalt.
Scanning Electron Microscope Test
In order to study the physical modification characteristics of reactive rubber-modified asphalt and the morphology and distribution of rubber powder in base asphalt, the reactive rubber-modified asphalt and rubber asphalt prepared by wet method were studied by scanning electron microscope.
Comparing the electron microscope images of wet rubber asphalt and reactive rubber modified asphalt, it can be seen that the particles of reactive rubber modified asphalt rubber powder are relatively uniformly dispersed, the surface is radiating like snowflakes, and the rubber powder particles have shown a planar network structure. The rubber asphalt produced by the wet method has an uneven surface, and the particle structure of the rubber powder can be clearly seen. The rubber powder is agglomerated together and does not show good dispersibility. In the production process of reactive rubber-modified asphalt, the reaction time of the rubber powder in the asphalt is long, and the rubber powder is pre-treated with infrared light to break the original sulfur bond of the rubber powder, and the network structure is broken into a linear structure. The linear structure of rubber powder particles splits and the asphalt swells sufficiently, and the rubber powder can undergo more sufficient degradation and desulfurization reactions.
According to the modification principle of reactive rubber-modified asphalt, the vast majority of reactive-rubber-modified asphalt can be dissolved in the asphalt to form amorphous fine substances, and there is no swollen particle core, that is, a relatively small amount of time has occurred during the reaction process. strong chemical action.
According to scanning electron microscope test and infrared spectrum analysis test, it is concluded that:
(1) The particle size of the reactive rubber powder is small and the specific surface area is large. The particle core makes the reactive rubber modified asphalt stronger, while the wet rubber asphalt has a weaker interaction between asphalt and rubber powder.
(2) At high temperature, the active components in the rubber powder enter the asphalt colloid system, and accompanied by strong desulfurization and degradation, it becomes a large number of small-sized network structures and a small amount of chains. Eventually, the rubber particles disintegrate to form a more uniform and stable sol-gel structure system.
Relevant studies have shown that there is a degradation process of rubber powder in the process of rubber asphalt modification, and the rubber after desulfurization will undergo a decomposition reaction to produce substances with smaller molecular weights, thereby increasing the aromatic content and gum in the recycled asphalt. Saturated content plays a lubricating and soft role in asphalt. The less saturated content, the higher the softening point of the asphalt, the smaller the penetration, and the higher the consistency. The increase of colloid can greatly improve the ductility and cohesion of asphalt.
Asphalt performance analysis
Routine index test of reactive rubber-modified asphalt
In order to study the basic technical indicators of reactive rubber-modified asphalt, the penetration and softening point tests of the 20% reactive rubber-modified asphalt and the rubberized asphalt prepared by wet method with 20% content studied in Section 1.2 were carried out. .
Experiment on SHRP Index of Reactive Rubber Modified Asphalt
For wet-process rubberized asphalt and reactive rubberized asphalt, the indicators of viscosity and elastic recovery ability were measured. In order to reflect the viscosity-temperature characteristics of reactive rubberized asphalt, Donghai I-C type SBS modified asphalt was used for comparison in the test.
It can be seen that the viscosity of reactive rubber-modified asphalt at 135 °C has reached the requirement of less than 3 Pa s. At the same time, its viscosity is basically the same as that of SBS-modified asphalt, while the viscosity of ordinary rubber-modified asphalt is significantly higher than that of reactive rubber-modified asphalt and SBS. Modified Asphalt. The viscosity at 135°C is generally considered to affect the mixture’s whetstone ratio, the higher the asphalt viscosity, the greater the whetstone ratio. The viscosity of reactive rubber-modified asphalt is lower at 135℃, indicating that the oilstone ratio of this rubber-asphalt mixture is much lower than that of ordinary rubberized asphalt.
From the analysis of the basic index data and SHRP test data of wet rubber asphalt and reactive rubber modified asphalt with the same dosage and curing conditions, it can be found that:
(1) The viscosity of reactive rubber-modified asphalt is 1/3 of that of wet rubber asphalt, wax modified asphalt mixtures which reflects the low viscosity characteristics of reactive rubber-modified asphalt, so that good workability can be obtained in actual construction.
(2) The improvement degree of penetration and softening point of the reactive rubber modified asphalt is not obvious compared with the wet rubber asphalt, which shows that the performance of the reactive rubber modified asphalt decreases while reducing the viscosity.
(3) The ductility of reactive rubber-modified asphalt at 15°C is significantly smaller than that of base asphalt, and the ductility at 5 and 10°C is significantly lower than that of SBS-modified asphalt. The addition of rubber powder does not significantly improve the low-temperature performance of asphalt. However, analyzing ductility as a function of temperature shows that this rubberized asphalt is less sensitive to temperature.
(4) The elastic recovery rate of reactive rubber modified asphalt is lower than that of wet rubber asphalt, but it still has good elastic recovery performance.
At present, rubber asphalt is mainly used in broken grading and open grading. The main reason is that the ratio of rubber asphalt to oil is generally too large. The viscosity of asphalt is usually related to the construction and workability of the mixture. The viscosity of ordinary rubberized asphalt is relatively high, and it is not easy to mix evenly. Big. The viscosity of reactive rubber asphalt at 135°C is much lower than that of ordinary rubber asphalt, and it is closer to the viscosity of SBS modified asphalt, which also provides the control of mixing, transportation, paving and rolling of this asphalt mixture. in accordance with. Through the above demonstration, it can be preliminarily considered to introduce reactive rubber-modified asphalt into dense-graded asphalt mixture.
The modification mechanism of rubberized asphalt is a combination of physical and chemical effects. In terms of microscopic morphology, it was found by scanning electron microscopy that the reactive rubber-modified asphalt powder was uniformly dispersed in the asphalt and swelled relatively deeply; Rubber-modified asphalt contains obvious sulfur groups, and the appearance of sulfur groups indicates that the original linear sulfur bond is opened, and the broken linear structure re-forms a network structure in the rubber asphalt. Therefore, the rubber powder of the reactive rubber-modified asphalt is cross-linked with the asphalt, and it is mostly two-dimensional surface without an obvious particle core, and the rubber particles are mostly dispersed into small amorphous substances.
In terms of macroscopic performance, reactive rubber asphalt has lower viscosity and good toughness. However, compared with wet rubber asphalt, this kind of performance characteristic has some losses in elastic performance and high temperature performance. In addition, through SHRP test analysis, the reactive rubber modified asphalt has good fatigue performance and low temperature performance.
At present, rubberized asphalt is mainly used in broken grading and open grading, and the prominent feature is that the ratio of oil to stone of rubberized asphalt is generally too large. The reactive rubber-modified asphalt has the characteristics of low viscosity, which provides a basis for the application of reactive rubber-modified asphalt in dense grading.
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