Microstructure Analysis with X-ray CT Scan Imaging to Develop Enhanced Full-Depth Reclamation (FDR) Mixes Through Optimized Mix Design Compaction Effort

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 Southern Plains Transportation Center (SPTC) study, and interviews with the FDR and cement industry. The objective of the proposed research is to investigate the effect of mix design compaction effort on the microstructure, density and strength, and thereby develop an optimized mix design procedure for mixes with different binders. The scope of work consists of preparing FDR specimens with different binders, using different compaction efforts, measuring their conventional laboratory properties, characterizing their microstructure using X-Ray Computed Tomography (X-ray CT) scan, and correlating microstructure to the strength and stiffness of FDR mixes. Building on Cycle 1 findings, the matrix of materials will consist of one FDR blend of RAP and granular materials and two binders which are proven to be most promising in terms of strength and performance under accelerated loading and testing from Cycle 1, i.e., CSS1H emulsified asphalt, and high Yield emulsified asphalt. Three different laboratory levels of compaction will be used. The test results will include phase identification, density, porosity, damage evaluation from X-ray CT scan, as well as indirect tensile strength and stiffness with and without conditioning. The proposed research will be carried out in five tasks spread over a 12-month period. Task 1: Design FDR mixes using 50, 75, and 100 SGC gyrations per TxDOT specifications Tex-113-E and Tex-241. Task 2: Conduct Indirect Tensile Strength (per Tex-226-F), and stiffness (per AASHTO T307) tests on dry and moisture-conditioned specimens. Task 3: Carry out X-ray CT scan, conventional density test (Tex-113-E), and Indirect Tensile Strength (Tex-226-F) at different loading levels on samples compacted at optimum binder contents and different gyration levels. Task 4: Correlate microstructure and the extent of damage to strength and stiffness. Task 5: Prepare and submit the final report.

• Record URL:
  • https://www.sptc.org/cy2-utep-04

Language

• English

Project

• Status: Active
• Funding: $133,739.00
• Contract Numbers:

  CY2-UTEP-04

  69A3552348306

• Sponsor Organizations:

  Office of the Assistant Secretary for Research and Technology

  University Transportation Centers Program
  Department of Transportation
  Washington, DC  United States  20590
• Managing Organizations:

  Southern Plains Transportation Center

  University of Oklahoma
  202 W Boyd St, Room 213A
  Norman, OK  United States  73019
• Project Managers:

  Dunn, Denise

• Performing Organizations:

  University of Texas El Paso

  El Paso, TX   
• Principal Investigators:

  Nazarian, Soheil

  Mallick, R

• Start Date: 20241001
• Expected Completion Date: 20250930
• Actual Completion Date: 0
• USDOT Program: University Transportation Centers

Subject/Index Terms

• TRT Terms: Binder content; Compaction; Full-depth reclamation; Microstructure; Mix design; Tensile strength; Tomography
• Geographic Terms: Texas
• Subject Areas: Design; Highways; Materials; Pavements;

Filing Info

• Accession Number: 01941691
• Record Type: Research project
• Source Agency: Southern Plains Transportation Center
• Contract Numbers: CY2-UTEP-04, 69A3552348306
• Files: UTC, RIP
• Created Date: Jan 1 2025 5:15PM