In Long Term Pavement Performance (LTPP) assessment process , the specific pavement studies were designed to investigate the factors affecting pavement rehabilitation such as overlay thickness (51 and 127mm), asphalt overlay materials (raw compared with adding 30% reclaimed asphalt pavement (RAP)) and surface curing type before rehabilitation (low and heavy). In this study, data from 4 sites were taken to perform analysis where each site consists of 8 sections (4 sections with raw materials and another 4 sections using 30%RAP). Each section was 152.4 m long and 3.66 m wide. These sites were selected due to their similar climate to Egypt. Four performance indicators were chosen including fatigue cracking, longitudinal cracking, rutting, and roughness. A statistical analysis using the paired t-tests, p-values and analysis of variance (ANOVA) were achieved to determine the priority in performance and the significance in variation. The results that based on practical observations have indicated that the RAP sections achieved similar/ better performance as compared with raw sections especially at higher thickness except for rutting. The climate had no obvious effect on fatigue cracking development while dry climate provided higher longitudinal cracking and roughness progress for RAP sections. Statically, the variation in pre-overlay curing (from low to heavy) had the highest statistical effect on fatigue cracking increasing, while rutting and roughness progresses weren't clearly affected by variation in climate, thickness or curing.

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Alexandria city lies at the north of Egypt on the Mediterranean Sea. The top layers of soil in Alexandria differs from bed rock (Borg El-Arab), sand (near the sea, north Abo-Qir street) to silt and clay (Elsyouf, Smouha, Khorshed, etc..). Thus, a great attention should be considered in the design of pavements on these dissimilar subgrades because the performance of a pavement depends on the quality of its subgrade and subbase layers. The non-linear finite element program MICHPAVE is used in this study to analyze the flexible pavement responses. Displacements, stresses and strains are computed only within the region modeled by finite elements. At the end of the analysis, MICHPAVE outputs an equivalent resilient modulus for each pavement layer. Results from the non-linear mechanistic analysis, together with other parameters, are used as input to two performance models, to predict the fatigue life and rut depth. These performance models are currently restricted to three-layer pavements with asphalt concrete (AC) surface, base and roadbed soil, and four-layer pavements with AC surface, base, subbase and roadbed soil. Analysis of research results has shown that using a reasonable subbase layer reduces the rut depth of pavement while the increase in subbase thickness causes increase in rutting. Total expected rut depth of pavement as well as expected rut depth in the asphalt course increase with the decrease of subgrade stiffness, while fatigue life of pavement increases with the increase of subgrade stiffness.