Evaluation of Surface Resistivity Measurements as an Alternative to the Rapid Chloride Permeability Test for Quality Assurance and Acceptance

Transcription

1 Rupnow and Icenogle Evaluation of Surface Resistivity Measurements as an Alternative to the Rapid Chloride Permeability Test for Quality Assurance and Acceptance Submission Date: --0 By: T. D. Rupnow and P. J. Icenogle Tyson D. Rupnow, Ph.D., P.E. (Corresponding Author) Louisiana Transportation Research Center 0 Gourrier Avenue Baton Rouge, Louisiana 00 Ph. -- Fax --0 Tyson.Rupnow@la.gov Patrick J. Icenogle, E.I. Louisiana Transportation Research Center 0 Gourrier Avenue Baton Rouge, Louisiana 00 Ph. --0 Fax --0 Patrick.Icenogle@la.gov Word Count Text Figures 0 Tables 00 Total

2 Rupnow and Icenogle 0 0 ABSTRACT ASTM C 0 tests were conducted at various ages with the corresponding surface resistivity test and the results were compared. Samples tested included field and laboratory prepared samples. The laboratory test matrix tested several mixtures common to Louisiana at a wide range of water to cementitious materials (w/cm) ratios to evaluate the range of the surface resistivity meter. The surface resistivity measurements correlate well with rapid chloride permeability measurements across a wide range of permeability values and sample testing ages. Suitable correlations were found to exist between both the -day and -day surface resistivity values and the -day rapid chloride permeability values. The variability of the surface resistivity meter results are usually less than those from the rapid chloride permeability test. The surface resistivity meter was also able to identify great differences in w/cm ratios for the same mixtures. The surface resistivity meter was determined to be user friendly. The preliminary cost benefit analysis showed that implementation of the device will save the Department about $0,000 in personnel costs in the first year. It is estimated that contractors will save about $. million in quality control costs. The cost benefit ratio for this project is estimated to be about. A Louisiana Department of Transportation and Development (LADOTD) Test Requirements (TR) Procedure, TR, has been developed and implementation of the surface resistivity device has begun.

3 Rupnow and Icenogle INTRODUCTION Many entities currently use permeability specifications in portland cement concrete (PCC) pavements and structures. For those states using permeability specifications, the two test methods generally used are ASTM C0 (rapid chloride permeability) () or ASTM C (boil test) (). This project investigated the use of a surface resistivity device as an indication of concrete s ability to resist chloride ion penetration for use in quality assurance (QA) and acceptance of concrete. Until recently, the rapid chloride permeability test was the only test that quickly determined concrete s ability to resist chloride ion penetration. Recent advances in surface resistivity measurements and their correlations to the rapid chloride permeability results have led many owners to research use of surface resistivity meters for a variety of reasons: the first being low cost of the equipment and the second being a reduction in the number of man hours required to conduct the test. Since Morris et al. showed that concrete can be characterized by its surface resistivity; much work has been completed in this area (). Most recently, an AASHTO Technical Implementation Group (TIG) has approved Provisional Test Method TP -, Surface Resistivity Indication of Concrete s Ability to Resist Chloride Ion Penetration (). Chini et al. showed that a strong relationship exists between the rapid chloride permeability test and the surface resistivity test (). Kessler et al. have competed research in Florida noting the surface resistivity tool can be used as an indicator of chloride penetration resistance at days for concretes that have reached a large portion of their total reaction such as those produced with silica fume or metakaolin (). The authors also noted that concretes containing fly ash or ground granulated blast furnace slag may not lend themselves to testing at days but more likely days. The Florida Department of Transportation used the results from this research to develop a test method (). Hamilton et al. conducted a rigorous study comparing surface resistivity measurements to bulk diffusion, rapid chloride permeability (ASTM C0) measurements, and rapid migration test results (). They showed that a good correlation exists between all test methods at various ages of testing with the best correlations existing between day rapid chloride permeability and the day bulk diffusion test results. Presuel-Moreno et al. characterized over 0 bridges in Florida using the surface resistivity test method (). The results showed that a correlation existed between samples tested in field conditions (i.e., non-saturated) and samples taken to the laboratory and subsequently tested in a wet (i.e., saturated) condition. The correlation showed that the field surface resistivity was generally three times that of the wet conditioned samples. The objectives of this research were to compare the surface resistivity and rapid chloride permeability of hardened concrete produced in laboratory and field conditions at various ages. Concrete samples were produced in laboratory conditions from five mixtures at three different w/cm ratios to produce a wide range of permeability values. The resulting mixtures were tested for both surface resistivity and rapid chloride permeability at,, and days of age. Field cast specimens, generally from the Caminada Bay Bridge project, were also tested for surface resistivity and rapid chloride permeability at and days of age. Other laboratory samples

4 Rupnow and Icenogle 0 0 from an ongoing ternary cementitious combinations study were also tested at and days of age. MATERIALS AND TEST METHODS Cementitious Materials X-ray fluorescence (XRF) was used to determine the chemical constituents of the cementitious materials used in the laboratory produced concrete. Table shows the results of the XRF analysis in percent of the oxide. Note that all materials are representative of those used on construction projects in Louisiana and conform to applicable ASTM, AASHTO, and LADOTD standards and specifications. TABLE XRF Results for the Cementitious Materials Used in the Laboratory Test Factorial Type I/II Portland Class C Fly Class F Fly Grade 00 Grade 0 Oxide Cement Ash Ash Slag Slag SiO Al O Fe O CaO MgO Na O K O TiO SO LOI Concrete Samples Table shows the laboratory test matrix used for determining the effect of w/cm. Note that TI, C, F, G0S, G00S, and SF stand for type I/II portland cement, class C fly ash, class F fly ash, grade 0 slag, grade 00 slag, and silica fume, respectively. These mixtures were chosen because they are representative mixtures used in LADOTD construction projects, but with w/cm between 0. and 0.. All mixture ID s listed in Table, were batched at 0., 0.0, and 0. w/cm ratios. The mixtures contained lbs/yd ( kg/m ) of cementitous materials with a coarse to fine aggregate ratio of 0:0. Other laboratory produced concrete, about 0 mixtures, was also tested to provide a larger database of results and these mixtures were ternary combinations ranging from 0 to 0 percent portland cement replacement and contained 00 lbs/yd ( kg/m ) of cementitious materials. The coarse aggregate consisted of a # limestone and natural river sand proportioned at a 0:0 coarse to fine ratio.

5 Rupnow and Icenogle 0 0 TABLE Laboratory Test Factorial to Determine Effect of w/cm Mixture ID 00TI 0TI-0C 0TI-0F 0TI-0G00S 0TI-0G0S 0TI-0SF TI-SF Field prepared samples, about lots, either originated in a precast yard or on the construction site from cast-in-place concrete. Samples in a precast yard were match cured with the member(s) and then transported to the Louisiana Transportation Research Center (LTRC) Concrete Research Laboratory for storage in the 00 percent relative humidity room until the age of testing. Cast-in-place cylinders were field cured for about three days and then transported to the LTRC Concrete Research Laboratory for storage and testing. Laboratory produced samples were produced and then cured in a 00 percent relative humidity room until the date of permeability testing. All concrete samples cast and tested in this study were x in. (00 x 00 mm) cylinders. Permeability Test Methods The rapid chloride permeability for each mixture was determined according to ASTM C0. Surface resistivity results were determined according to the provisional AASHTO Test Method TP - Surface Resistivity Indication of Concrete s Ability to Resist Chloride Ion Penetration, (). Figure shows a schematic of how the surface resistivity device works. A current is applied across the outside pegs and the potential (resistivity) is measured on the inside pegs. The result of the test is then displayed in kω-cm. The distance (a) between the pegs will affect the results of the test. For the purposes of this study, the peg distance was fixed at. in. (. cm) for all specimens tested. A CNSFARNELL resistivity meter and a Resipod surface resistivity meter was used for the first half and second half of the study, respectively. All rapid chloride permeability and surface resistivity samples were tested in triplicate. At the age of testing, surface resistivity cylinders were removed from the humidity room and marked as shown in Figure. Surface resistivity measurements were recorded at each of the coordinates twice and averaged for a sample. Figure shows a test being conducted. The surface resistivity test is a non-destructive test therefore the samples were tested for surface resistivity and then prepared for rapid chloride permeability.

6 Rupnow and Icenogle FIGURE Schematic of the surface resistivity meter (0). FIGURE Cylinder markings ().

7 Rupnow and Icenogle 0 FIGURE Surface resistivity test being conducted. RESULTS AND DISCUSSION Permeability Test Method Comparison The ASTM C0 results were as expected for this study. In the laboratory test matrix, the increased w/cm mixtures showed increased permeability at all ages. Note that the increase in cement replacement percentage led to a decrease in permeability as expected for the ternary mixtures tested. The raw data used in the analysis can be found in Rupnow et al. (). To validate the relationship between rapid chloride permeability and surface resistivity, as suggested by others (-), the average surface resistivity results were plotted against the average ASTM C0 results for all samples tested as shown in Figure. Note the relationship is very good with a correlation coefficient of 0.. Figure also shows the data fit the AASHTO recommended penetrability classes well.

8 Rupnow and Icenogle 0 FIGURE Relationship between surface resistivity and rapid chloride permeability at all ages and for all samples tested. Upon determining that the relationship was valid, the research team then plotted the average -day surface resistivity results versus the average day rapid chloride permeability results to further evaluate the proposed correlation. The results are shown in Figure. Note the correlation coefficient was reduced slightly from 0. to 0., but is still very good. The laboratory matrix included samples to be tested at a very early age of days. The day surface resistivity results were plotted against the day rapid chloride permeability results and are shown in Figure. Note the correlation still is good, but the correlation coefficient dropped from 0. to 0.0.

9 Rupnow and Icenogle FIGURE Relationship between the average -day surface resistivity and the average - day rapid chloride permeability results.

10 Rupnow and Icenogle FIGURE Relationship between the average -day surface resistivity and the average - day rapid chloride permeability results. The results of this study show that the proposed correlation is valid across a wide range of permeability values. The results also show that the correlation is valid across several different testing ages. The early age correlations contradict Kessler et al. () in that the mixtures tested in this study still had significant hydration yet to be completed at days of age, yet they still correlated well with the -day rapid chloride permeability results. The surface resistivity results show that the device can be used effectively as a quality acceptance and quality control tool for prediction of concrete permeability. Although the study shows that a valid correlation exists at days of age, the authors suggest using the -day correlation for simplicity. Samples are routinely tested at days of age for strength. Since the surface resistivity test is a non-destructive test, the same samples cast for strength can also be used for determination of permeability. Although the results were comparable in permeability classes, the variability of the surface resistivity test results appear to be lower than the variability of the rapid chloride permeability test results. This led to a lower percentage of re-tests due to failing samples with the surface resistivity test method compared to the rapid chloride permeability test method for this study. A failed sample is a sample that exceeds the LADOTD limit.

11 Rupnow and Icenogle 0 Effect of w/cm Ratio The effect of w/cm on the results of the surface resistivity measurements was investigated. Figure shows the effect of w/cm on the average -day surface resistivity results for the laboratory test matrix. Note the effect is as expected for all mixtures; an increase in w/cm leads to a decrease in surface resistivity indicating a more permeable concrete. Note the results show that the surface resistivity meter can be used to indicate a w/cm for a given mixture if past performance has been documented. The results shown in Figure also show the effect of increasing supplementary cementitious materials (SCMs) for each w/cm. As the percentage of portland cement replacement is increased the surface resistivity increased indicating a less permeable concrete. Note the mixtures containing silica fume at lower percentage of portland cement replacement exhibit better surface resistivity values due to the increased pozzolanic action associated with the use of silica fume. 0 FIGURE Effect of w/cm on the average -day surface resistivity results for the laboratory test matrix. The authors observed numerous issues regarding the design of the original surface resistivity meter. Non-rechargeable batteries led to erratic readings due to low battery level. Maintenance of the cord and wooden pegs was also an issue. These issues have been resolved with a redesign of the meter. Taking the above issues into account, the users of this meter were

12 Rupnow and Icenogle 0 0 very pleased with the timeliness and accuracy of the results and the ease in which it can be operated. Comparative testing was completed between the old and new meter designs yielding similar results between the two. Therefore, the remainder of the study was completed with the new meter. Since completion of this study, a TR Procedure, DOTD TR -: Test Method for Surface Resistivity Indication of Concrete s Ability to Resist Chloride Ion Penetration, has been developed (). A specification has been drafted incorporating the surface resistivity test into the standards and specifications. In the interim, LADTOD has changed its permeability testing procedures for quality assurance purposes to reflect the change in specification. Table shows the LADOTD permeability classes based on surface resistivity measurements as defined by the AASHTO equation noted in Figure. The ASTM C0 values are included for reference and the surface resistivity values are valid for -day surface resistivity measurements. TABLE LADOTD Surface Resistivity and Permeability Classes for x Inch Cylinders -Day Rapid Chloride Permeability -Day Surface Permeability Charge Passed Resistivity Class (Coulombs) (kω-cm) High >,000 < Moderate,000 -,000 - Low,000 -,000 - Very Low 00 -,000 - Negligible < 00 > Cost-Benefit A cost-benefit analysis was completed to estimate the effect of implementing the surface resistivity meter. Table shows the input parameters for the cost-benefit analysis. The initial cost of each device is noted. The number of testing hours was estimated from LTRC Concrete Laboratory experience with both test methods. Note that the number of testing hours required for testing includes sample preparation, data acquisition and entry, and preparation and distribution of a test results report to interested parties. The technician hourly wage is that of an Engineering Technician III and includes fringe and benefits. The $00 cost per test is the cost for the Department or a contractor to contract the rapid chloride permeability testing to an outside laboratory within Louisiana. TABLE Input Values for the Cost Benefit Analysis Initial Cost ($) Number of Testing Hours Required Technician Hourly Wage or Cost per Test ($) Equipment ASTM C 0 $, $00.00 Surface Resistivity $, $.

13 Rupnow and Icenogle Table shows the estimated cost savings to LADOTD for the first year of implementation. Note that, in an average year, LADOTD currently tests about 0 lots for quality acceptance purposes on about three projects being constructed within the state. As the permeability specifications are implemented statewide, this number is expected to increase by several orders of magnitude. The number of hours required for conducting the test was determined by taking the number of man hours required for each test times the number of lots. The technician costs were determined by taking the hourly wages times the number of hours required for each test. The total costs were derived by summing the technician costs and the initial cost of the equipment. The cost per lot was determined by dividing the total cost by the number of lots. TABLE Comparison of One Year Quality Acceptance Costs for the Surface Resistivity and ASTM C0 tests Number Technician of Testing Hourly Cost Per Number Hours Wage Tech. Cost Total Cost Lot Test Method of Lots Required ($) ($) ($) ($) ASTM C $. $,.0 $0,.0 $. Surface Resistivity 0. $. $,0. $,0. $. SAVINGS $0,. The preliminary cost benefit analysis results showed that implementation of surface resistivity measurements in lieu of rapid chloride permeability tests will save the Department about $0,000 in personnel costs in the first year of implementation. The savings in technician costs in the first year of implementation alone will pay for the purchase of 0 additional meters for the District Laboratories and the Central Materials Laboratory. Table shows the estimated costs savings for contractors conducting quality control testing. The differences show the savings associated with the contractor purchasing the surface resistivity meter versus contracting the rapid chloride permeability testing to an independent laboratory. For the purposes of this analysis, it is assumed that the contractors are sending the ASTM C0 samples to an independent laboratory for testing at a conservative (i.e., cost for testing only) cost of $00 per sample. Note the estimated cost savings total about $. million which should indirectly benefit the Department. The estimated combined savings (benefit) for the Department are about $. million in the first year of implementation. The cost of the project was $0,. The estimated cost benefit ratio is about. Any ratio greater than two is considered excellent. The preliminary analysis shows that the Department will save money by switching to the newer, faster, surface resistivity test method.

14 Rupnow and Icenogle TABLE Comparison of One Year Quality Control Costs for the Surface Resistivity and ASTM C0 Tests Test Method Number of Lots Number of Testing Hours Required Hourly Wage/Cost per Test ($) Tech. Cost/Test Cost ($) Total Cost ($) Cost Per Sample ($) ASTM C $00 $,00,000 $,00, $00.00 Surface Resistivity $. $, $,.0 $. CONCLUSIONS SAVINGS $,,0.0 The results of this study warrant the following conclusions. The surface resistivity measurements correlate well with rapid chloride permeability measurements across a wide range of permeability values and sample testing ages. Suitable correlations were found to exist between both the -day and -day surface resistivity values and the -day rapid chloride permeability values. The surface resistivity meter is also able to identify great differences in w/cm ratios for the same mixtures. The surface resistivity meter is very user friendly even when several issues arose with the operation and maintenance of the surface resistivity meter. The issues have since been resolved with a redesign of the meter. The preliminary cost benefit analysis indicates that implementation of the device will save the Department about $0,000 in personnel costs in the first year. It is estimated that contractors will save about $. million in quality control costs which will indirectly benefit the Department. The cost benefit ratio for this project is estimated to be about. RECOMMENDATIONS The authors recommend immediate implementation of the surface resistivity test method. A training program should be developed for training personnel and it should include at a minimum a video and proficiency exam. A special provision should be drafted allowing for widespread use of the new test method within LADOTD construction projects. Observations indicate that surface resistivity meter results generally have less variability than rapid chloride permeability results. A precision statement needs to be developed for the surface resistivity test. A study needs to be completed looking at in-situ applications of surface resistivity measurements. ACKNOWLEDGEMENTS The authors would like to thank the Federal Highway Administration, Louisiana Department of Transportation and Development, and the Louisiana Transportation Research Center for sponsoring this research. The efforts of Randy Young, Matt Tircuit, Shane Laws, Scott Reech, Benjamin Shearer, Jacob Newgard, Anthony Saladino, Brandon Pitre, and Brennon Hughes in the concrete laboratory are greatly appreciated. The efforts of Mike Bailey are greatly appreciated for the chemical and physical testing of the cementitious materials used in the

15 Rupnow and Icenogle laboratory test matrix. The authors would like to thank Mike Ricca for his effort in coordinating field samples for inclusion in this study. The authors would like to thank Holcim, LaFarge, Buzzi Unicem, and Headwaters for providing the cementitious materials for use in the laboratory concrete. The opinions, findings and conclusions presented here are those of the authors and do not necessarily reflect those of LADOTD or the Federal Highway Administration. REFERENCES. ASTM C0 Standard Test Method for Electrical Indication of Concrete s Ability to resist Chloride Ion Penetration. Annual Book of ASTM Standards, Vol. 0.0, ASTM, Philadelphia, PA, 00.. ASTM C Standard Test Method for Density, Absorption, and Voids in Hardened Concrete. Annual Book of ASTM Standards, Vol. 0.0, ASTM, Philadelphia, PA, 00.. Morris, W., Moreno, E.I., and Sagues, A.A. Practical Evaluation of Resistivity of Concrete in Test Cylinders Using a Wenner Array Probe. Cement and Concrete Research, Vol., No., pp. -,.. AASHTO Technology Implementation Group. Provisional AASHTO Test Method TP -, Standard Test Method for Surface Resistivity of Concrete s Ability to Resist Chloride Ion Penetration. 0.. Chini, A.R., Muszynski, L.C., and Hicks, J.K. Determination of Acceptance Permeability Characteristics for Performance-Related Specifications for Portland Cement Concrete. Final Report, July 00.. Kessler, R.J., Powers, R.G., Vivas, E., Paredes, M.A., and Virmani, Y.P. Surface Resistivity as an Indicator of Concrete Chloride Penetration Resistance. 00 Concrete Bridge Conference, St. Louis, MO, May -, 00.. Florida Method of Test for Concrete Resistivity as an Electrical Indicator of its Permeability. (Designation: FM -) Vivas, E., Boyd, A., and Hamilton, III, H.R. Permeability of Concrete Comparison of Conductivity and Diffusion Methods. Final Report, Report No. 00- (000), June 00.. Presuel-Moreno, F., Suarez, A., and Liu, Y. Characterization of New and Old Concrete Structures Using Surface Resistivity Measurements. Final Report, August, Proceq SA. Resipod Operating Instructions. Schewerzenbach, Switzerland, 0.. Rupnow, T. and Icenogle, P. Evaluation of Surface Resistivity Measurements as an Alternative to the Rapid Chloride Permeability Test for Quality Assurance and Acceptance. Final Report, Report No. FHWA/LA./, July, 0.. DOTD TR Test Method for Surface Resistivity Indication of Concrete s Ability to Resist Chloride Ion Penetration. LADOTD, Baton Rouge, LA, 0. Electronically accessible at: final.pdf.