An investigation of roughness trends in asphalt pavement overlays

Pavement smoothness is the key indicator of pavement serviceability and highway user satisfaction. Current public opinion indicates that governments should be increasing spending on highway infrastructure with pavement smoothness being a priority. This need is reinforced by the Federal Highway Administration (FHWA), which indicates that the construction of smooth pavements is a key factor for maintaining quality pavements in the 21st century. The task of providing smoother pavements requires a better understanding of pavement roughness. To accomplish this, data from the Canadian Long-Term Pavement Performance (C-LTPP) test sections and the Long-Term Pavement Performance (LTPP) test sections are examined to investigate roughness trends in asphalt pavement overlays.; An analysis of initial pavement roughness (i.e. pavement roughness immediately after rehabilitation) and long-term roughness is performed to quantify the effect of constructing asphalt overlay pavements with different initial roughness. The examination involves both a literature review and examination of pavement data, which involves individual test projects, the combined data from 3 pavement studies, data located in freeze environments and data with outlier values removed. The effect of constructing pavements to different initial roughness levels is quantified as the differential roughness remaining after approximately 8 years of service. It is shown that approximately 100 percent of any differential initial roughness remains after 8 years. Confidence limits for the relationships are also provided.; To control initial pavement roughness, transportation agencies use smoothness specifications as part of their quality assurance program. In developing these specifications, transportation agencies need to understand the factors that influence initial pavement roughness. To ensure compliance with these specifications, contractors also need to understand these influences. Surface preparation, overlay thickness, type of overlay material, and the pavement roughness prior to rehabilitation are examined through the use of various statistical techniques. All of the factors except for type of overlay material are shown to influence initial roughness at a strong statistical significance level.; This research also develops a series of models for predicting pavement deterioration in the C-LTPP test sections, which serve as a benchmark of pavement performance across Canada. Both within site and between site factors are incorporated into the analysis. Overlay thickness and total cracking prior to rehabilitation are determined to influence pavement deterioration at a 99 percent statistical significance level. Six other variables are shown to contribute to various models but have weak statistical relationships.; This research provides pavement engineers and contractors with valuable information about the effect of initial pavement roughness on long-term roughness and the factors affecting initial pavement roughness. The pavement deterioration models provide a pavement design tool and foundation to enhance current pavement design procedures that do not incorporate the prior cracking in a pavement and do not consider the effect of overlay thickness on both initial roughness and the rate of pavement deterioration.