Evaluation of Resistivity Meters for Concrete Quality Assurance, Project TR201414
Abstract
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.
Table of Contents
Executive summary -- Literature review -- Materials -- Mixture designs -- Lab mixing and test methods -- Field test methods -- Precision and bias -- Lab results and discussion -- Field results and discussion -- Sealer testing and results -- Conclusions and future research -- Appendix A. MODOT section 501 concrete -- Appendix B. Proposed MODOT EPG surface resistivity standard -- Appendix C. Resistivity testing -- Appendix D. Other testing -- Appendix E. Field testing
Degree
M.S.