An Analysis of Economization Based Optimization of Flexible Pavement Structural Design

Abstract

Pakistan is a developing country with many budget constraints. Road construction industry acts as a backbone in the progress of any country yet road development needs huge budgets. In developing countries like Pakistan with all the budget constraints, it is important to introduce new cost saving techniques in road design and construction. Pavement thickness is a significant cost factor in any road project. This research work emphasizes on coming up with a cost effective design of flexible pavements by reducing the thickness of asphalt concrete layer without compromising on durability and longevity/service life of the pavement. For this purpose, multilayer pavement approach has been used to make the pavement economical by placing high quality material on top while low quality material on the bottom (base and sub base). Base and sub-base layer thickness will also be increased in order to reduce the asphalt concrete layer thickness; therefore, the strength requirements will be fulfilled. With a focus on ride quality as a major aspect of AC, the multilayer pavement approach can be made more economical by keeping its thickness to a minimum. AASHTO 1993 design guidelines for structural design of pavements are dependent on the application of load by different vehicles directly on pavement layers, depending upon their respective stiffness. Therefore, according to AASHTO design, it can be established that a reduction in thickness of the asphalt concrete layer will directly increase the thickness of base and sub base layers, hence adjusting the respective stresses and stiffness. To make the pavement structure more economical, this technique is very practical in a developing country like Pakistan where very high quality granular material is abundantly available. Due to its high construction cost, the thickness of asphalt concrete layer is a hot issue among highway agencies and engineering consultancies all over the world as asphalt concrete is an expensive material. If there is an appreciable impact on cost with no compromise on stability from the actual AASHTO design, then the AC thickness may be reconsidered and subsequently new local parameters of pavement thickness design may be set to save budget for highway construction using local materials. The existing design practices in road construction in Pakistan are reviewed and suitable recommendations are also provided. Optimization of flexible pavement thickness is carried out by using linear integer programming technique and for this purpose linear integer program solver (LiPs) software was used in order to find the optimal flexible pavement thickness configuration. AASHTO design method was used for pavement thickness design. Iterations were done to reach the desirable values of pavement thickness. Flexible pavement structural design analysis was carried out by using KENPAVE software and in the end a brief comparison is presented between AASHTO flexible pavement structural design and optimize flexible pavement structural design analysis results in order to draw out the final decision matrix. This study will also be a good viable solution for conservation of local materials and to provide a platform for future research and studies into making pavement thickness design economical.