(a) Technical Field
The present invention relates to a modified asphalt composition containing a styrenic block copolymer and a vegetable wax as modifier.
(b) Background Art
In general, unmodified asphalt behaves very sensitively to temperature during road paving or water-proof sheet manufacturing. At high temperatures, it is vulnerable to plastic deformation by heat or load. Meanwhile, at low temperatures, it may experience cracking due to fatigue crack from the bottom portion caused by repeated load and repeated expansion and contraction from the top portion caused by abrupt temperature change. After the pavement, the resistance of asphalt to plastic deformation, temperature sensitivity, fatigue crack, low-temperature cracking, etc., decreases rapidly with time as the traffic volume and mid-to-large vehicles increase.
To solve this problem, polymers are used to modify asphalt recently. For example, low-density polyethylene, ethylene vinyl acetate, styrene-butadiene rubber, butyl rubber, etc., are used as asphalt modifier. By adding these polymers to asphalt, resistance to plastic deformation caused by softening at high temperature is improved and cracking caused by repeated low and repeated expansion and contraction at low temperature is prevented. The use of asphalt modified with polymers in road pavement is gradually increasing.
Asphalt modified with polymers has been intensively studied. For example, U.S. Pat. Nos. 3,985,694 and 4,130,516 disclose asphalt/polymer compositions in which thermoplastic elastomers such as linear polyethylene, ethylene vinyl acetate or styrene-butadiene rubber are added as asphalt modifier to improve physical properties. Further, U.S. Pat. No. 3,345,316 discloses an asphalt composition comprising a chlorinated polyphenyl resin in which a thermoplastic elastomer such as a linear styrene-butadiene-styrene triblock copolymer or a styrene-ethylene-butylene-styrene block copolymer prepared by anionic polymerization is included. US Statutory Invention Registration No. H1580 discloses an asphalt composition comprising a radial styrene-butadiene-styrene block copolymer. U.S. Pat. No. 4,130,516 discloses an asphalt composition comprising asphalt, sulfur and a polymer. U.S. Pat. No. 5,130,354 discloses an asphalt composition comprising a butadiene rubber or a styrene-butadiene-styrene triblock copolymer in which a conjugated diene is grafted using a silane compound or maleic anhydride as a modifier. U.S. Pat. No. 4,412,019 discloses an asphalt composition comprising asphalt, sulfur and a styrene-ethylene-butylene-styrene block copolymer. In addition, Korean Patent Registration No. 10-0,712,579 discloses an asphalt composition using a mixture of a linear styrene-butadiene-styrene triblock copolymer and a radial styrene-butadiene-styrene triblock copolymer as an asphalt modifier.
The above-described methods are aimed at improving the physical properties of asphalt such as high-temperature properties, low-temperature properties, aging resistance, resistance to plastic deformation, etc., by adding polymer modifiers. However, the addition of the polymer modifier results in increased viscosity at high temperature as compared to that of pure asphalt. Accordingly, high temperature is required for the preparation of asphalt and road pavement, which results in increased emission of carbon dioxide and toxic gas as well as increased consumption of fuels for providing the required high temperature. In addition, considerable time is needed for the asphalt to cool to ambient temperature.
Thus, researches have been made about use of wax instead of the polymer modifier as modifier in order to solve the high viscosity problem of asphalt at high temperatures.
Korean Patent Registration No. 10-0,770,785 presents addition of a polyethylene-based wax to asphalt to decrease viscosity of asphalt at high temperature and thus to solve the problem of increased temperature and time. However, the use of the polyethylene-based wax causes the problem of low-temperature cracking.
Korean Patent Registration No. 10-0,949,380 discloses an asphalt composition comprising a polyethylene-based wax as well as a vegetable wax as modifier instead of the polymer modifier. While decreasing viscosity at high temperature through the addition of the polyethylene-based wax, the patent also solves the problem of rapid decrease of ductility at low temperature by adding the vegetable wax.
In general, waxes are solid at ambient temperatures and become liquid at elevated temperatures. They have a molecular weight of several hundreds. The wax that has been used as asphalt modifier is the polyethylene-based wax. By rapidly decreasing the viscosity of asphalt at temperatures above the melting temperature of the wax and becoming solid at temperatures below the melting temperature, it is expected to solve the high viscosity problem of the asphalt containing the polymer modifier at high temperatures. But, although the polyethylene-based wax can decrease the viscosity of asphalt, it causes low-temperature cracking of the asphalt mixture. The low-temperature cracking occurs mainly in winter. It is characterized by cracks formed in the transverse direction of the pavement because of imbalance in the temperature distribution and propagated from the top portion to the bottom portion. The ductility at low temperature has a decisive effect on the physical properties of asphalt. A low ductility results in rapid breakage because of fatigue caused by loads or cracking caused by thermal expansion and contraction. Accordingly, the problem of decreased ductility of asphalt including the polyethylene-based wax as modifier at low temperature needs to be solved.
As described above, although the addition of the polymer modifier significantly improves the physical properties of asphalt, the asphalt modified with polymers requires high temperature for manufacturing because of high viscosity at high temperature. Although there have been efforts to improve the high viscosity problem at high temperature by using a wax instead of the polymer modifier and thus lowering the manufacturing temperature, physical properties at low temperature are becoming another problem. Accordingly, development of a modifier capable of solving the problems of the physical properties asphalt and their preparation is still required.