The National Academies

NCHRP IDEA 20-30/IDEA 166 [Completed (IDEA)]

Guidelines for the Waste Concrete Fines
[ NCHRP 20-30 (NCHRP-IDEA) ]

  Project Data
Funds: $94,438
Staff Responsibility: Inam Jawed
Research Agency: University of Pittsburgh
Principal Investigator: Julie M. Vandenbossche
Fiscal Year: 2012

This project developed guidelines for using waste concrete fines (and the associated wastewater) in concrete by developing methods to rapidly characterize fines samples and evaluating the performance of concrete using these recycled materials. Unfortunately, a considerable amount of wastewater with high pH, as well as dissolved and suspended solids, is associated with concrete production (clean-up), the rehabilitation of concrete structures, and the recycling of concrete at the end of the structure’s life. Sources of recycled fines were identified and the fines were characterized after mixing them with water to create solutions and suspensions and their indices of refraction, pH, and conductivity determined.  Mortar samples were prepared and their setting times and strengths measured for a range of fines particle sizes and contents. Correlations were established from the collected data to help develop a performance-prediction model for different recycled fines materials. This model was used to develop guidelines for using recycled concrete fines in new concrete mixtures. In the next step, a water recirculation system was constructed, which incorporated in-line (continuous reading) sensors for measuring the index of refraction, conductivity, and pH. Waste materials were added to the recirculation system and evaluated using the in-line sensors to validate the implementation plan and the model. The implementation plan for ready-mix concrete producers when upgrading plants with in-line sensors was finalized along with instructions on applying the guidelines for using recycled fines. Work has continued beyond the IDEA project with support from Northwest Regional Transportation Center. Sensors were installed in the recycled water recirculation system at the Stoneway Concrete plant in Seattle, Washington.  Mixtures with recycled and “city water” were tested and strength test results compared with predictions from the IDEA developed models. Results were presented to the Seattle Department of Transportation (DOT), City of Seattle Department of Planning and Development, and Washington State DOT as part of the implementation efforts. The product implementation is very easy and requires just following the provided user guidelines in the report. A short table that contains physical and chemical properties changes should be helpful for implementation engineers to use that could serve as a checklist to use the concrete fines properly.
The final report is available.

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