Case study for rehabilitation and reconstruction works of the existing asphalt roads in R.Macedonia

摘要

Dimensioning of the pavement structure is a complex engineering problem. The influential factors are numerous, different and variable during the exploitation period (i.e. stress-deformation state of pavement structure in exploitation). Besides the problem of bearing capacity and usability in different operational conditions (climatic influences and field conditions), the pavement structures must meet the criteria for flatness and friction-adhesion in order to ensure safe and comfortable driving. The rehabilitation of the existing roads in R.Macedonia is required due to the fact that roads are in use more than 30 years. On these roads tests are preformed (sampling of asphalt and soil) in order to determinate thickness of asphalt layers. For obtaining information for each road section, points of profiles are set up at distance of maximum 2 m. The traffic load considered for the operating period of 10-20 years is concerning for the time period of developments of the projects, the change in economic conditions and other factors that influence traffics as well. The analysis of the pavement structures for the asphalt layers is done by empirical formulas based on which specialized software are developed. Recently used softwares are based on finite element method that simulates the behaviour of pavement structure during exploitation period. Asphalt mixture is an elastic-viscous material and its characteristics depend on the material components (for pavement layers) and the factors (load and temperature) on which the pavement is subjected during the period of exploitation. One important factor for the road condition is the temperature. Especially significant is the variation of the temperature i.e. in winter less than -30°C and in summer more than 45°C, which has direct impact of the modulus of the asphalt layers. Because the roads referred in this paper are constructed more than 30 or 40 years ago, the aging of asphalt on these roads results with occurrence of cracks (mostly fatugue cracks on the asphalt layers). For stabilization and prevention of propagation of cracks on the surface asphalt layers polymer grids are used. The polymer grids increase the resistance on pavement deformation by absorbing the tension forces. Most used standard for dimensioning of pavement structures is AASHTO, which is based on empirical formulas and regression methods obtained on the basis of long-term tests. AASHTO is used starting from 1972, reviewed (additions) in 1981 and 1986 and as definite edition the guidelines are published in 1993, while in 1998 it was verified using geosynthetics. With the use of polymer grids in the asphalt layers, a longer operating life of the pavement structure is achieved and the properties of new pavement are improved. The polymeric grids especially reduce the propagation of cracks from the old existing asphalt on new pavement surface (fatigue and cracks due to temperature variation in asphalt) and cracks on interfaces with rigid concrete elements.