Guidelines for Use of Waste Concrete Fines

Mortar mixtures were used to investigate the effects of a wide range of recycled concrete fines, both sources and amounts, on set time as well as early and long-term strength. The recycled concrete fines were evaluated by measuring the index of refraction, conductivity and pH so that results could be applied to other sources and amounts of recycled concrete fines in concrete mix water. A variety of cementitious materials combinations were also investigated in conjunction with these fines sources. These cementitious materials were characterized as to their calcium content and calcium-ratio so that the results could be applied to cementitious materials not used in this study. Models relating set time as well as percentage of the control strength (both 3- and 28-day) were developed. These models predicted that two concrete mixtures produced in the laboratory with unknown (but characterized by conductivity and pH measurements) would meet ASTM C 1602 set time and strength requirements at significantly above the optional limits. A follow-up field implementation study in which temporary instrumentation was installed in the mix-water weigh tank at a commercial ready-mix plant. Model refinement performed as a part of this study produced predictive equations, based on pH and conductivity measurements of the mix water, that include the variability of the prediction (standard error) for 3- and 28-day compressive strength. These predictive equations correctly identified a mixture prepared at a ready-mix concrete plant that did not achieve 90% of the 28-day control strength even though the amount of fines in the mix water met the ASTM C 1602 Table 2, Part D limits. The variability of the 3-day strength model was unacceptably high. However, all mixtures in a follow-up field implementation study achieved at least 90% of the control strength; even the mixture that failed to achieve 90% of the 28-day control strength. The model refinement identified a need for additional data (either mortar or concrete mixtures) with recycled concrete fines at higher pH and conductivity values. All four of the false negative predictions were for mixtures that had pH values measured in the mix water that were above the range used in the dataset to develop the equations.

  • Record URL:
  • Supplemental Notes:
    • This Highway IDEA project was conducted by University of Pittsburgh.
  • Authors:
    • Dufalla, Nicole
    • Vandenbossche, Julie M
    • Janssen, Donald J
  • Publication Date: 2014-7

Language

  • English

Media Info

  • Media Type: Digital/other
  • Edition: Final Report
  • Features: Appendices; Figures; References; Tables;
  • Pagination: 141p
  • Serial:
  • Publication flags:

    Open Access (libre)

Subject/Index Terms

Filing Info

  • Accession Number: 01674935
  • Record Type: Publication
  • Files: TRIS, TRB, ATRI
  • Created Date: Jul 11 2018 1:29PM