| Considerable progress has been made over the past 50 years in the field of pavement engineering. While much has been learnt about designing and maintaining pavements economically, still there exists a need for improving existing procedures to meet increasing infrastructure needs with limited resources. At present, highway agencies lack adequate information on the influence of pavement drainage on the performance of flexible pavements. There is very limited experimental field data to quantify its influence or effect on the pavement performance. The interactions of the structural factors with other variables such as climate are not well understood and therefore, still needs to be explored in order to improve relationships between pavement performance and response. As a result, controlled field experiments are necessary to answer questions which are currently not explained by the theoretical modeling.; This research documents and presents the results of relative influence of design and construction features on the response and performance of in-service new flexible pavements, included in SPS-1 and SPS-8 experiments of the Long Term Performance Pavement (LTPP) program.; In summary, for pavements in the SPS-1 experiment, base type seems to be the most critical design factor for fatigue cracking, roughness (IRI), and longitudinal cracking-WP. This is not to say that the effect of HMA surface thickness is not significant. In fact, the effect of base type should be interpreted in light of the fact that a dense graded asphalt treated base effectively means thicker HMA layer. Drainage and base type, when combined also play an important role in improving flexible pavement performance, especially in terms of fatigue and longitudinal cracking. Base thickness has secondary effects on performance, particularly in the case of roughness and rutting.; Subgrade soil type seems to be playing an important rote in flexible pavement performance. In general, pavements built on fine-grained soils have shown worst performance, especially in the case of roughness. Also, climate is a critical factor in determining flexible pavement performance. Longitudinal cracking-WP and transverse cracking seems to be associated with Wet Freeze environment, while longitudinal cracking-NWP seems to be the dominant in "freeze" climate.; On average, for pavements in the SPS-8 experiment, those located in WF zone have more fatigue cracking, longitudinal cracking-NWP, and roughness than pavements in other climates. Also, in general, pavements constructed on "active" subgrade (frost susceptible or expansive) soils have more longitudinal cracking-NWP, transverse cracking, and fatigue cracking than pavements on "non-active" soils. Pavements located in "wet" climate, on average, have higher change in IRI than those in "dry" climate. Furthermore, pavements located in WF zone and those built on active soils have higher change in IRI.; Although most of the findings from this research support the existing understanding of pavement performance, the methodology in this study provides a systematic outline of the interactions between design and site factors as well as new insights on various design options. |
