Early Characterization and Performance of a Flexible Thick Lift Pavement

Abstract

The South Carolina Department of Transportation (SCDOT) has recently been experimenting with thick lift paving to increase construction speed and facilitate faster access to traffic. However, there has been limited research and practice with thick lift paving. South Carolina has successfully placed a pavement in two lifts of 4.5 inches thick each. However, what happens if instead of two lifts, only one thick lift is placed? Thick lift paving within this thesis is defined as pavements that were placed in one single lift of 6 inches or greater. Thick lift paving’s major concerns and risks include placing a pavement with relatively unknown constructability, cooling curve predictability, and long-term structural and field performance. With such a knowledge gap in this particular construction technique, a test section at the National Center for Asphalt Technology (NCAT) Pavement Test Track was constructed to analyze whether thick lift paving is a viable alternative to conventional multi-lift paving. There are many benefits to placing a thick lift pavement such as the rapid speed of construction, the elimination of tack between layers, the lower cost of labor with faster construction speed, not switching between mixtures while paving multiple lifts, and reducing the need to rotate construction equipment. Despite these benefits, there are still many concerns with this procedure due to limited research and unproven implementation. Section S9 at the Test Track was designed as a thick lift pavement in an effort to address some of these concerns. To ensure that the major benefit of rapid construction was an option, the section was subjected to temperature analysis during construction. The analysis included determining if conventional means of measuring temperature at a construction site was adequate for a pavement of this thickness, if software such as MultiCool was able to predict the cooling curve accurately, and if the cooling rates were fast enough for overnight construction and opening to traffic in the morning. The results illustrated that the best time to pave a thick lift pavement would be in evening, as the lifts laid during this time required the shortest cooling times. Also, the evening in-situ cooling results were more consistent when comparing results to the MultiCool software. Another major concern is the performance and structural integrity of the section under traffic application. To address this concern, instrumentation such as asphalt strain gauges (ASGs), earth pressure cells (EPCs), and temperature probes were embedded into the pavement during construction. Along with these instruments, weekly field testing was done to analyze the pavement’s performance. The analysis during the construction of the thick lift pavement did illustrate that controlling roughness was an issue and this problem was resolved using diamond grinding immediately following the paving. Overall, based on early data from the embedded instruments and weekly field testing, the thick lift pavement did have similar performance to conventional pavements. Section S9 was subjected to full-scale analysis to ensure that the benefits of utilizing thick lift pavements were viable and that the associated risks could be mitigated. From all construction, cooling curve, field performance, and structural results, it is recommended that thick lift pavements be implemented when speed of construction is a concern. This method could be utilized to place a single thick lift structure including the surface layer and use diamond grinding to control smoothness. Another strategy would be to use the thick lift construction method to place the base layers in one lift and place a thin wearing layer on top that could improve smoothness without diamond grinding.