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Evaluation of resistivity meters for concrete quality assurance.

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      This research evaluated a series of MoDOT concrete mixtures to verify existing relationships between surface resistivity (SR), rapid

      chloride permeability (RCP), chloride ion diffusion, and the AASHTO penetrability classes. The research also performed a precision

      and bias evaluation to provide acceptable limits should SR be implemented for quality assurance and to refine language in the AASHTO

      test standard. In the precision and bias determination concrete was produced from three field sites and tested at both UMKC and

      MoDOT labs. Field mixtures included a paving mixture, a bridge deck mixture, and a structural mixture. Eleven other mix designs were

      produced in the lab and evaluated for RCP correlation and included paving, bridge deck, structural, and repair mixtures per Missouri

      Department of Transportation requirements. Additional testing included surface resistivity testing on sealed samples and an existing

      bridge deck. Results showed excellent correlation between SR and RCP which matched existing relationships provided by AASHTO

      and other state DOTs. The structural mixture containing 50% Class F fly ash had the best performance with “very low” chloride ion

      penetrability at 90 days. A ternary paving mixture with 20% Class C fly ash and 30% slag replacement for cement also demonstrated

      low permeability as well as high compressive strength with an average value of over 9,000 psi at 90 days. The two repair mixtures

      showed moderate to low penetrability readings and high early strength consistent with their desired purpose. Tests were also performed

      on a series of slab samples to evaluate SR as a tool for evaluating sealer application. The presence of silane and lithium silicate were

      able to be detected by the SR test. As value added to the laboratory research, field testing was attempted on a bridge deck with the goal

      of providing non-destructive insight to the steel condition in the field. Due to the condition of the bridge conclusions could not be drawn

      other than making recommendations for future bridge deck evaluations. The extensive amount of surface resistivity testing (>4500 tests)

      on 14 concrete mixtures at ages from 3 hours to 90 days using multiple labs, equipment, operators, and curing conditions has verified

      RCP relationships and allowed refinement of a testing procedure for a MoDOT standard in the Engineering Policy Guide. Surface

      resistivity presents an opportunity to improve MoDOT concrete mixtures and specifications to increase durability without adding

      significant additional testing costs.

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