| According to the expressway preventive maintenance requirements in the Southern muggy areas of China,where represented by Guangxi; and base on Nanning to Youyiguan Expressway Project (NYEP), an overall and comprehensive research on the ultra-thin wear layer has been carried out by means of the old road technology research, the anti-sliding mechanism analysis, the material laboratory test and actual cases verification.. Finally, a feasible, economical, reasonable proposal which is suitable for the application of the Guangxi freeway construction and maintenance's project, especially the application on the asphalt pavement preventive maintenance has been recommended.Through a systematic study, the results obtained in this research lead to the following conclusions:(1) Researching on the usage conditions of representative expressway asphalt pavement in Guangxi,we found that the damage of expressway asphalt pavement in Guangxi can be primarily divided into two categories:one is the functional damage of the asphalt layer, the other is the structural damage of the pavement. For the functional damage, using ultra-thin wear layer mask repair is a preferable proposal with better technical and economic benifits which can also be applicable to the all high-way projects in all traffic levels and climate conditions.(2)By reseaching and analyzing the road aggregates used in Guangxi expressways, we found a shortage of high quality coarse aggregate used on the surface layer. Due to the expansion of asphalt pavement construction along with the lack of control and supervision on the storage yard it leads to a drop of the production of high quality of road aggregates, the greater coarse fluctuation and fine aggregate gradation, the lower qualified rate, a common rise in the dust content of the fine aggregate, and a severe misuse of material processing sieve..For this purpose, this paper discussed the measures on the technical indexes of the coarse aggregate used to the ultra-thin wearing layer by the quality of aggregate production can be guaranteed and did further research.(3)The paper studied the anti-slip performance factors under the muggy environment and vehicle driving load, and then recommended several construction measures, such as adjusting oil/water ratio, refining asphalt, adopting disconnected graded mixed aggregate which would improve the durability of anti-sliding performance on the ultra-thin wear layer in muggy environment..(4)Through the research on the gradation composition of ultra thin asphalt concrete, we found that,in order to reduce the thickness of ultra-thin wear layer, it is necessary to add a 7.2mm sieve which can make the pavement thickness effectively reduce to 2cm. In the research, two mixed aggregates for the ultra-thin wear layer are designed based on the philosophy of coarse aggregate disconnect gradation. It recommend the gradation composition and fluctuation range of dense graded AC-8 and open graded OGFC-8 used for the ultra-thin wear layer.(5)For the study on design system of the ultra-thin wear layer asphalt concrete, the core ideas are as follows:by grading optimization to ensure the thickness of wear lay as thin as possible; through the material design and gradation design to guarantee the durability of anti-sliding performance; For material selection,high quality coarse aggregates and asphalt binder should be used; and as for the requirements of road performance, the duraiblity of anti-sliding performance should be maily considered and followed by the water stability and high temperature stability and anti-oxygen aging property.(6)An experimental road of dense graded AC-8 and open graded OGFC-8 was put into effect in the Nanyou Expressway as a preventive conservation measures,which were proved effective and having a expected operating life of 5-6 years.Acoording to the research of the Surface durability,the dense graded AC-8 was more suitable for the Nanyou Expressway and other similar high-grade expressways under wet-hot hygrothermal environment in Guangxi on account of its cost-effective.As a comparison for open graded OGFC-8,the rate of decay was faster and the Surface durability was worse.It is suggestd to be applied in the situation thar surface drainage and noise reduction needed.In this paper, the ultra-thin wear layer which differs to both domestic and foreign technologies which is more targetable and applicable..We paved approximately 72km preventive maintenance entity project in NYEP, in which the design method of ultra-thin asphalt concrete mix proportion is based on anti-sliding performance and concrete structure style, the determination of concrete structure as well as the application of new technology, such as a complete design system and evaluation index have ensured the quality of actual projects to extend the service life of the pavement, meanwhile, reduced a large number of projects investment directly or indirectly, which has remarkable economic benefits and social benefits... |
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