UTC 2022 Funding - Cycle 2 Research Projects

Project Number: CY2-UTEP-04
Project Title: Microstructure Analysis with X-ray CT Scan Imaging to Develop Enhanced Full-Depth Reclamation (FDR) Mixes Through Optimized Mix Design Compaction Effort
Performing Institution: University of Texas at El Paso,
Principal Investigators: Rajib B. Mallick and Soheil Nazarian
Project Partners: Road Recyclers, LLC. and Cement Council of Texas
Proposed Start and End Date: 11/01/24 to 10/31/25
Project Description: The use of Full Depth Reclamation (FDR) and the development of novel binders have continued to grow over the last three decades in the US. The mix design is conducted through several steps including combining in-place materials, adding pre-mix water, applying and mixing binder, compacting, curing, and testing with or without conditioning. To “harmonize” testing conditions for different “stabilization” methods, agencies often utilize a generic “mix design” system, irrespective of the type of in-place materials and binders. This approach, while convenient, is not the most optimal, as it may not utilize the unique advantages of a specific binder and may also result in an inferior FDR base course. The single most important property that controls the strength of FDR mixes and their potential to deteriorate over time under traffic loading is the efficiency of compaction during the recycling process. Efficient compaction of FDR mixes can result in a favorable microstructure, which increases the density and strength, reduces the potential for moisture damage, and enhances its long-term durability. The microstructure of the compacted FDR is affected by the optimum binder content, which is mostly dictated by the compaction effort (number of gyrations with the Superpave Gyratory Compactor, SGC) that is utilized during mix design. Different research reports recommend different gyration numbers, and at the same time, tests indicate a significant difference in the strengths of samples compacted with different numbers of gyration. Some binders can significantly facilitate compaction at the expense of relatively more sensitivity to compaction effort. Therefore, a pertinent question is, what is the optimized compaction effort that could lead to the formation of the optimized microstructure of FDR mixes that are resistant to deterioration? The answer to this question will result in the development of new specifications to guide the mix designers to develop appropriate optimum binder content and the contractors to utilize appropriate compaction equipment and passes in the field. The research is proposed based on observations from the literature, inferences from the Cycle 1 SPTC study, and interviews with the FDR and cement industry.
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