Study On Structure And Properties Of Asphalt Modified By Polyvinyl Copolymer

The asphalt is a residue of raw oil after distilled for many times, it is a ropy blend in a black brown color which is compounded by hydrocarbons with different molecular weight and non-metallic derivatives. Asphalt is widely used as cementing material in road pavement due to its perfect cohesiveness and waterproofness. However, asphalt is a viscoelasticity material and is easy to flow away in high temperature and freeze to crack in low temperature. It cannot meet the requirement of road pavement because of its sensitivity to temperature. Therefore, asphalt without modification is difficult to be applied into road pavement. Studying on asphalt modification is a hot field for road researchers all the time.In this paper, a new species of asphalt modifier was expected to be explored in order to conquer the defects of polyethylene modified asphalt on storage stability. The asphalt modified by new modifiers should not only have a perfect performance in high temperature, but also could enhance the storage stability at high temperature. A assumption had been put forward that asphalt can be modified by polyvinyl copolymer. Polyvinyl copolymer is a generic terms of copolymer which is polymerized by polyethylene and any other polymers. Ethylene links and links of other polymers are existed in the main chain of polyvinyl copolymer. In consequence, it exhibits a perfect elasticity on one hand and has a new property which is supplied by other polymers on the other hand. In this paper, two kinds of polyvinyl copolymers, polyolefin elastomer (POE) and ethylene-acrylic acid (EAA) were selected as modifiers to modify the basic asphalt. The optimal adding proportion was studied by control the content of modifiers. High temperature performance, viscosity and needle penetration were evaluated by measuring the general performance. The disperse state of modified asphalt after modification was observed by microscopic morphology analysis in order to confirm the suitable adding ratio. Rheological property of modified asphalt was measured by dynamic shear rheometer (DSR). Adhesive capacity between modified asphalt and alkalescent aggregates might be improved due to the existence of carboxyl in the acrylic acid links of EAA. Adhesive capacity between aggregates and asphalt modified by EAA was measured by adhesion experiments.Results showed that, polyvinyl copolymer could improve the performance in high temperature effectively. Meanwhile, the needle penetration and viscosity was enhanced accordingly. The microscopic morphology analysis indicated that the modified asphalt performed as "sea-island" structure and dispersed equally when modifying agent was in a small dosage (< 4 wt.%). When the content was higher enough (> 6 wt%), the particles of modifiers crashed and combined together and generated a complex net at last, a phase separation state of modified asphalt occurred obviously and which led to the separation when stored in high temperature. The rheology analysis indicated that the polyvinyl copolymer could enhanced the viscoelasticity of basic asphalt significantly. The reason is that basic asphalt exhibits a property of Newtonian fluid in high temperature and the polymer could replenish the lost viscoelasticity of basic asphalt by using its molecular chain which has a better viscoelasticity. Thus, the modified asphalt could still have a better performance in elasticity in high temperature. Adhesive experiments showed that with the increase of modified agents, the adhesive capacity between modified asphalt and aggregates improved according.Since the modified asphalt can not meet the requirments of construction. At the last part of this paper, a dissolving and cladding method was selected to prepare the EAA-bergmeal coated system. We expect that the cellular structure of bergmeal could synergy with EAA and play a better role in asphalt modifying. The cost of modifiers could decrease to some extent on the other hand. Ashes determination was conducted to analysis the actual coated ratio of the system. Scanning electron microscope (SEM) test was selected to scan the microstructure of the coated products. Meanwhile, the coated products were added into basic asphalt. The results showed that with the increase of bergmeal in the coated system, more and more bergmeals exposed to the surface of the matrix of EAA obtained from SEM. High temperature performance, viscosity and needle penetration of modified asphalt were all increased to some extent when the coated products were added into asphalt. The microscopic morphology analysis indicated that bergmeals desorbed from matrix EAA at a high content and dispersed into basic asphalt affected by shearing force which led to the break increment in performance of modified asphalt. The storage stability test illustrated that with the increase of bergmeal content, an obvious separation of modified asphalt would occur during a storage process in high temperature. EAA component would float upward while bergmeal component would submerge to the bottom and which led to the increment of difference between top and bottom in softening points.Although the polyvinyl copolymer modified asphalt cannot meet the standard requirements in performance at the present stage, it has an enormous potential in modifying asphalt. New blending methods, polymer grafting modification and compounded with other modifiers are still valuably to be studied.