Materials, Specifications, and Construction Techniques for Heavy-Duty Flexible Bases: Literature Review and Status Report on Experimental Sections (0-4358-1)

For the majority of the Texas highways the granular base layer is the main structural component of the pavement system. Project 0-4358 was initiated to provide TxDOT guidelines to improve its base specifications in order to better withstand the demands of future traffic loads. This report provides the results of a literature search and a survey of the performance of experimental heavy-duty base pavements recently constructed in Texas. Base specifications and construction practices from eight U.S. DOTs and two overseas countries were compared with TxDOT current and proposed specifications. Currently, TxDOT is the only agency that does not control the amount of fines (minus 200 fraction) in its bases. Research studies have indicated that high levels of minus 200 can severely impact both moisture susceptibility and cold weather performance. The newly proposed TxDOT specifications with limits on the fines content are in line with the practices of other agencies in similar climates. The results from three experimental sections on US-281, US-77 and FM-181O provide several important observations about current base performance. The use of small amounts of stabilizer to upgrade marginal materials does not always guarantee a top-quality base. Better methods of selecting optimal stabilizer content are needed. Furthermore, the flexible bases with high fines content appear to have high initial field stiffnesses that decease rapidly with time.