Optimization of Cement Modified Recycled Base (CMRB) Mixture Design
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Optimization of Cement Modified Recycled Base (CMRB) Mixture Design

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  • Creators:
  • Corporate Creators:
    Clemson University
  • Contributors:
  • Corporate Contributors:
    South Carolina. Department of Transportation
  • Subject/TRT Terms:
  • Publication/ Report Number:
    FHWA-SC-24-04
  • Resource Type:
    Tech Report
  • Geographical Coverage:
    United States
  • Edition:
    Final July 2020 – Aug 2023
  • Corporate Publisher:
    South Carolina. Department of Transportation
  • Abstract:
    SCDOT is focused on improving the design of Cement-Modified Recycled Base (CMRB) to enhance the long-term durability and performance of pavements. The current approach emphasizes using unconfined compressive strength (UCS) and other parameters such as optimum moisture content (OMC) and maximum dry density (MDD) along with treatment depth in designing CMRB treatment. However, the current design process does not address durability parameters such as resistance to wetting-drying cycles, freeze-thaw cycles, or shrinkage-induced cracking, as well as the impact of content and size of Recycled Asphalt Pavement (RAP) in the mix or the influence of soil type on CMRB design. The present study was conducted to evaluate the influence of a range of parameters on the performance of CMRB. Findings from this study show that the base soil type can have a significant influence on the cement content needed to achieve desired performance characteristics. Introduction of RAP particles larger than ¾ inch as well as RAP content up to 35% in the mix did not significantly influence UCS, allowing greater flexibility in RAP size and content in the mix. The study also recommended refining sampling practices, which included smaller intervals in sampling base material, and focusing on samples with the highest clay content as the reference material. The slurry method in preparing UCS samples was also recommended for enhancing the mixing and compaction process in the lab setting, although field construction issues need to be considered. Methods to evaluate the drying shrinkage of CMRB are also suggested, with a maximum allowable deviation of moisture content of no more than 1% to 2% from the Optimum Moisture Content (OMC), depending on the base soil type. The study recommends several modifications to the current Full-Depth Reclamation (FDR) mixture design to enhance the efficacy and performance of CMRB. These adjustments include sampling at smaller intervals, allowing RAP particles larger than ¾” without significantly impacting UCS, allowing testing at higher cement content levels for clay-rich base soils, exploring the slurry method in preparing UCS samples, incorporating drying shrinkage in mix design, ensuring in-situ moisture content not to deviate by more than 1% to 2% from the OMC, implementing stringent quality control procedures, modifying soaking duration for durability assessment under wet-dry cycling, and establishing shrinkage thresholds for each soil type.
  • Format:
    PDF
  • Funding:
    SPR No. 754
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