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Development Of Mix Design And Testing Procedures For Cold Patching Mixtures

The objective of this study is to address the use and performance of homemade and containerized patching maintenance mixtures for repairs in cold and wet weather. The Texas Department of Transportation (TxDOT) reported problems relating to the durability, workability, and shelf life of homemade patching mixtures under these conditions. TxDOT requires an improved mix design procedure to develop patching mixtures with a durability of at least 6 months that accounts for traffic volume. Various failure mechanisms pertaining to the use of cold patch mixtures were identified and current mix design, materials, performance evaluation, and field application procedures were assessed. Based on results from screening experiments, a preliminary mixture design procedure was developed. A laboratory experiment was developed to evaluate the performance of patching materials by investigating the influence of pertinent material characteristics, including gradation, aggregate type, binder viscosity and content, compaction temperature, curing time, and use of admixture. The materials selected for homemade mix design in the laboratory are consistent with those used by the Lubbock district in its homemade mix design. The Cold Patch Slump Test (CPST), a slump-based laboratory workability test, was developed to quantify workability for cold patch materials. It is an inexpensive and quick test and shows correlation between laboratory and field values. The Hamburg Wheel Tracking Device (HWTD) was used for stability testing on cold patch mix, which was first cured and then compacted at elevated temperatures. Indirect Tensile Strength (ITS) and stripping tests will be conducted on the homemade mixes. The initial field evaluation included six containerized medium-curing products, three homemade mixes made by district maintenance yards in the Lubbock district, and one commercially produced stockpile mix in Lufkin. The study area for the field evaluations is the Lubbock and Lufkin districts of TxDOT. The results of the field evaluation are still being collected and will be reported in the coming year. A preliminary evaluation of the effectiveness of various cold patching mix containers was also conducted and guidelines for further durability testing in the laboratory were developed.