Study On Asphalt Concrete Waterproof Layer On High-Speed Railway Subgrade In Cold Regions

Based on the behaviors of existing railways in Northeast China, the existing waterproof layers on high-speed railway subgrade haven’t met the needs of waterproofing and drainage in cold regions. That is one of important factors which cause frost heave and thaw of subgrade. For the above-mentioned reasons, some researches were conducted based on a project named "Study on Asphalt Concrete Waterproof Layer". The project was funded by China Railway Corporation. These researches presented a key and comprehensive work on choosing material, asphalt mix design, service performance, structural design, construction technology and quality control, which were accomplished through literature reviews, field investigation, experimental and numerical analysis. The objective of this project was to design new-type asphalt concrete waterproof layer suitable for high-speed railway in cold regions.According to construction and service conditions of asphalt concrete waterproof layer on high-speed railway subgrade in cold regions, the following features were needed which were good waterproofness, low temperature cracking resistance, high temperature stability, durability and integrity, close combination with adjacent structures, convenient construction, easy to control and maintenance. Furthermore, the relevant technique indices were presented in this paper. Through analyzing the types and characteristics of different asphalt mixtures, Mastic Asphalt Concrete (MAC) and Semi-mastic Asphalt Concrete (SAC) waterproof layers were proposed on the basis of gussaphalt and dense-graded asphalt mixtures.Through reference to highway asphalt concrete engineering and theoretical derivation, a conclusion was drawn that modified bitumen was recommended and the grade of bitumen should be PG70-34. For this purpose, the new mastic asphalt binder called PmB (Polymer-modified Bitumen) was specially developed in this paper. By reviewing the mix design theories, the guassasphalt and Marshall Design methods were considered as the basis of the MAC and SAC design respectively and the corresponding asphalt mixtures were designed. Laboratory tests were conducted to evaluate the workability, high temperature stability, low temperature cracking resistance, waterproofness, durability and cooperative performances of MAC and SAC. The results indicated that the service performances of MAC and SAC (with PmB) were favorable. Nevertheless, the SAC (with 90# basic asphalt) couldn’t meet the needs of waterproof layer on high-speed railway subgrade in cold regions.The thermal stress of Mastic Asphalt Concrete Waterproof Layer (MACWL) was investigated to propose the optimal structure by means of the finite element (ABAQUS) numerical analyses of a typical high-speed railway subgrade with a MACWL. The thicknesss, temperature, stiffness modulus, coefficient of linear contraction of MAC as well as elastic modulus of the surface layer of sugrade were taken as the control variables and the thermal stress were taken as the key mechanical parameter. The grey relation entropy analysis method was utilized to analyze the above-mentioned influence factors. These results demonstated that considering synthetically from material properties and economic benefits, the thickness of MACWL should be proposed to 5 cm.Relying on Harbin-Qiqihar high-speed railway trial section, the construction technologies of MACWL including mixing round, transportation, paving as well as detail treatments were studied. Some relevant technique indices were proposed and service performances of MACWL in trial section were tested and evaluated. In trial section, Mastic Asphalt Concrete Waterproof Layer (MACWL) had smooth surface, compact appearance, no surface water seepage and its key service performances met or exceeded the design requirements. This indicated that new-type asphalt concrete waterproof layer performed well, especially in waterproofness and permeability resistance, which should be beneficial to the long-term service of the high-speed railways.