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51 Chapter 4. Field Measurements (Phase III) 4.1. Introduction During Phase III of NCHRP Project 21-11 we cooperated with selected transportation agencies whereby the recommended protocol was implemented as a âshadow specification.â The data include characterization of different sample sources (e.g., maximum particle size and gradation) along with the measurements of geochemical and electrochemical properties of the samples including resistivity, pH, and chloride and sulfate contents (i.e., the total salt content). The Wenner 4-probe technique (according to ASTM G57 (2012) and Wenner (1915)) was used in the field for measurement of electrical resistivity and representative material samples were collected from the site or from the source to perform electrochemical tests in the laboratory using Texas modified and AASHTO test procedures. In this chapter, we summarize the field and laboratory test results obtained from four active construction projects in cooperation with two owners (Texas and New York DOTs), four different geotechnical testing laboratories (UTEP, McMahon & Mann, NYSDOOT and TXDOT), and four general contractors. The main focus of this chapter is to determine whether the main technical goal of the research project for better characterization of corrosion potential using the suggested protocol as compared to the traditional methods has been met. We also evaluate the practicality and implementation of the suggested protocol through the interaction with laboratories engaged in the electrochemical testing, and suppliers/owners in different states. We present a brief description of the data obtained in pursuit of Phase III in the following section. This is followed by the key results obtained from different test methods in the form of resistivity obtained from the Wenner 4-probe test (used in the field), and laboratory measurements including resistivity pH, and chloride/sulfate contents. Finally, we present a detailed discussion of the trends observed within the data sets and comparison between the field and the laboratory measurements. 4.2. Description of Data Set Two sites in Texas and two sites in New York were included in the field verification study including sites located in San Antonio, TX; El Paso, TX; Buffalo, NY; and Schroon, NY. We sampled materials from the sources and at the sites for laboratory testing. Split samples were sent to The University of Texas at El Paso and state DOT geotechnical laboratories to determine gradation, resistivity, pH, salt and sulfate contents. Table 4-1 summarizes the laboratory tests performed on the samples obtained from the site and the source by the owner and/or the research group at The University of Texas at El Paso.
52 Table 4-1 Laboratory tests performed on the site and source samples. Samples Site Source Owners (state DOTs) - 1 measurements of Ï, [Cl-] and [SO4] content, and pH using Texas modified and AASHTO procedures Research group (UTEP) Texas modified and ASSHTO procedures2 Texas modified and AASHTO procedures 1 No tests were performed by the owners on the site samples. 2 Field resistivity tests were performed using the Wenner 4-probe technique (according to ASTM G57 (2012)). The site in San Antonio, Texas involved construction of MSE walls at the intersection of IH10 East and Ackerman Road (Figure 4-1 (a)), where the MSE wall fill was a coarse, open graded gravel produced locally by Hanson Aggregates (Lehigh Hanson Company 2019). Limestone was mined at the quarry to produce the aggregates for MSE wall fill. Similar to the San Antonio Site, the site in El Paso, Texas involved construction of MSE walls at the intersection of Montana Avenue and Lee Trevino Drive (Figure 4-1 (b)). The MSE fill at this site was a medium grain, well-graded, sand. We selected two quarries from the New York State (NYS) inventory to include in our evaluation; one from the eastern part of the state (Peckham Quarry, NYSDOT Region 1), and one from the western part of the state (Enterprise Stone & Lime, NYSDOT Region 5). The sources from the eastern and western parts of the state were granite and limestone quarries, respectively. The two sources produced well-graded gravels that included significant sand components. These materials meet the requirements for pavement subbase in NYS. The material sourced from NYSDOT Region 5 was used in a bridge reconstruction project in Tonawanda, NY (near Buffalo, NY) along the I290 West where it crosses the Niagara Frontier Transportation Authority Property (Figure 4-1 (c)). The fill was placed as subbase beneath the shoulder backing at the west end of the bridge. The shoulder backing was compacted to a thickness of approximately 12 inches and was approximately 5 feet wide. Although this material was used in an application where corrosivity was not an issue, the NYSDOT sampled and tested the material similar to what is specified for MSE wall fill. Material from NYSDOT Region 1 was also used in a bridge reconstruction project along I87N, near Exit 28 in Schroon, New York (Figure 4-1 (d)). Although this material could potentially be a source of MSE wall fill, for this project material was placed as subbase beneath the shoulder along the approach sections. The material was compacted to a final lift thickness of approximately 15 inches and had been in place for less than a week during our site visit.
53 (a) San Antonio, TX (b) El Paso, TX (c) Buffalo, NY (d) Schroon, NY Figure 4-1 Locations and coordinates of construction sites1. 1 The photos from El Paso, Buffalo, and Schroon sites are older Google Earth images that do not depict construction activities at these locations. Location of the MSE wall 29Â°26â18.7âN 98Â°22â48.2âW 29.438528, -98.380056 Location of MSE wall 31Â°48'03.1"N 106Â°18'52.8"W 31.80086428, - 106.31466715 Location of the shoulder 42Â°59â49âN 78Â°51â34.5âW 42.996944, -78.859583 Location of the shoulder 43Â°52â16.3âN 73Â°45â13.9âW 43.871194, -73.753861
54 In Figure 4-2, we present the gradation curves for the different materials sampled from the sites cited in this chapter. In Table 4-2, we summarize salient details of each sample in terms of aggregate size, grading number, and USCS classification to describe the characteristics of the sample domain used in the field and laboratory tests. Given the details from Table 4-2 (GN and PP#10), and from the suggested protocol (Appendix A - also summarized in Figure 3-14), samples from Buffalo and El Paso should be evaluated using the current AASHTO tests (passing No. 10 sieve) and samples from San Antonio and Schroon should be evaluated using modified procedures, which includes larger particles within the test specimens. Figure 4-2 Gradation curves from different sites. Table 4-2 Summary of gradation from different sources. NMAS 1 (in) PP21/4" (%) PP#10 (%) PP#200 (%) Cu 3 Cc4 USCS classification GN 5 San Antonio, TX 2 0 0 0 1.48 0.97 GP 0.13 El Paso, TX 0.25 94 70 0 6.52 1.04 SW 4.55 Buffalo, NY 1 49 31 0 20.00 0.99 GW 3.07 Schroon, NY 2 17 10 0 11.01 2.51 GW 1.70 1 NMAS = nominal maximum aggregate size 2 PP = percentage passing 3 Cu = Uniformity coefficient ( ð·ð·60 ð·ð·10 ) 4 Cc = Coefficient of curvature ( (ð·ð·30)2 ð·ð·60 Ãð·ð·10 ) 5 GN = grading number
55 4.3. Results 4.3.1 Resistivity â Soil Boxes In Figure 4-3, we show the laboratory measurement of soil resistivity using the modified soil box for the samples retrieved from the sources and the sites included in Phase III. The equipment used for laboratory measurement of resistivity included: 1) Soil Resistance Meter, M.C. Miller, Model: 400D and 2) Potentiostat, Gamry Instruments, Model Reference 600. The potentiostat showed repeatability of about 10% - 15%. The M.C. Miller device showed repeatability of about 1%. Hence, we present the results obtained from the M.C. Miller device in what follows. We present laboratory measurements of resistivity from samples retrieved from sources and sites in Buffalo, NY; Schroon, NY; San Antonio, TX; and El Paso, TX in Figure 4-4. Figure 4-4 includes the results from testing samples, via AASHTO T-288 (2016) and Tex-129-M and data obtained by owners/contractors as well as by UTEP (NCHRP Research Team). The data presented in Figure 4-4 show relatively good agreements between the resistivity measurements from samples retrieved from the sources (tested by UTEP and owners) and those obtained from the sites (tested by UTEP). An exception to this observation is the site sample from Schroon, NY tested via Tex-129-M (resistivity = 9300 â¦-cm in Figure 4-4). This result appears to be low compared to the other test results obtained from the source and tested via Tex-129-M, and is not higher than the results obtained via AASHTO T-288 (2016). This is unusual as measurements of resistivity via Tex-129- M are generally higher than those obtained via AASHTO T-288 with the same sample, as depicted by the bias that was shown in Figure 3-4 and 3-5 and discussed in Section 18.104.22.168. (a) Schematic1 1 C1 and C2 = current terminals; P1 and P2 = potential terminals C1 C2 P2 P1 resistance meter 12â 8â depth = 3.5 â stainless steel plates soil box
56 (b) Test setup Figure 4-3 Resistivity measurement using modified soil box (DAQ = data acquisition system). Figure 4-4 Comparison of resistivity results obtained from modified soil box tests1. 1 The owner (TXDOT) from two of the sites (El Paso and San Antonio) did not provide results from resistivity testing in accordance with Tex-129-M. TXDOT provided data from testing in accordance with AASHTO T 288 for the San Antonio site, but not for the El Paso site. Gamry device M.C. Miller device DAQ soil box digital scale 2400 2200 2100 8600 12000 10700 20600 17300 16700 4000 3300 4400 6400 6300 23000 36000 9300 45300 61300 4700 4300 0 10000 20000 30000 40000 50000 60000 70000 O w ne r/S ou rc e U TE P/ So ur ce U TE P/ Si te O w ne r/S ou rc e U TE P/ So ur ce U TE P/ Si te O w ne r/S ou rc e U TE P/ So ur ce U TE P/ Si te O w ne r/S ou rc e U TE P/ So ur ce U TE P/ Si te Buffalo, NY Schroon, NY San Antonio, TX El Paso, TX R es is tiv ity (â¦ -c m ) AASHTO T-288 Tex-129-M
57 4.3.2 Resistivity â Field Tests using Wenner Technique We performed in-situ resistivity measurements at each site using the Wenner 4-probe technique, as described by ASTM G-57 (2012) and Wenner (1915). In addition, in-situ measurements of moisture content and density were made using a nuclear density gauge (Troxler, Model 3440 â shown in Figure 4-8) and samples were collected from the site for further laboratory investigations. The equipment used for resistivity measurements included: 1) Advanced Earth Ground Tester GEO, Fluke, Model 1625-2, 2) Soil Resistance Meter, Nilsson Electrical Laboratory INC., Model 400, 3) Soil Resistance Meter, M.C. Miller, Model: 400D, and 4) Potentiostat, Gamry Instruments, Model Reference 600. The resistivity values presented in this research are mainly from those obtained from M.C. Miller, Model: 400D, as it provides the most stable resistivity readings. In Figure 4-5 we show the typical test setup for performing the Wenner 4-probe measurement. We used a penetration depth of the probes (âbâ) of 6 inches for all measurements and varied the spacing between the probes, (âaâ) as 6 inches, 12 inches, and 24 inches. The spacing determines the depth covered by the measurements. For resistivity measurements in MSE walls, we selected test locations perpendicular and parallel to the reinforcement strips. For resistivity measurements along the shoulder (or shoulder back) of roads, we selected measurement lines perpendicular and parallel to the pavement. Figure 4-6 is a schematic that depicts the locations, zones, and directions of resistivity measurements at each site. (a) Schematic Soil C1 C2 P2 P1 Resistance meter a a a b Side view
58 (b) Test setup in the field Figure 4-5 The Wenner 4-probe technique. (a) San Antonio, TX Wenner probes Gamry deviceM.C. Miller device DAQ L1 L6 L1L2 L1 to L6 (every 15 feet) MSE wall fill 15 fe et perpendicular to the reinforcements parallel with the reinforcements 5 feet 2 feet edge of concrete panel (reference point) N steel reinforcement 15 feet a (Typ.)
59 (b) El Paso, TX (c) Buffalo, NY (d) Schroon, NY Figure 4-6 Locations, zones and directions for performing soil resistivity measurements. At locations where the soil appeared to be very dry (e.g., in the MSE wall in San Antonio, TX), we added water in small amounts (less than 200 ml) to the soil next to the probes to improve the electrical conductivity between the probes and the soil. In this case, samples for measuring moisture content and electrochemical properties of the soil were collected farther away from the wet region of the soil. These samples were sealed and stored in double ZiplockTM plastic bags to prevent evaporation and contamination. According to Wenner (1915), the resistance reading (R) can be converted to the resistivity (Ï) at different probe penetrations (b) and different spacings (a), using Equation (4-1). L1 L5L5L1 L1 to L5 (every 10 feet) MSE wall fill perpendicular to the reinforcements parallel with the reinforcements 7 feet 1 feet edge of concrete panel (reference point) N steel reinforcement a (Typ.) L1 L10 L10L1 L1 to L10 (every 15 feet) shoulder 2. 5 fe et â 3. 5 fe et perpendicular to the pavement parallel to the pavement 2 fe et 6 inches edge of pavement (reference point) N a (Typ.) Zone 1 Zone 2 a (Typ.)b a (Typ.) c probes perpendicular to the CL of the road probes parallel with the CL of the road Concrete slab Pavement N
60 ðð = 4ððððð¶ð¶ 1 + 2ðð âðð2 + 4ðð2 â 2ðð â4ðð2 + 4ðð2 (4-1) When the penetration depth of the probes is small in comparison to the spacing among them (b < 0.05 a), Equation (4-1) can be simplified as Equation (4-2), which is the formula cited by the ASTM G57 standard (2012). Since the penetration depth in this research (6 inches) is clearly greater than 5% of the spacing between the probes, we used the original formula by Wenner (1915) (Equation (4-1)) to determine the numerical resistivity values in the field. ðð = 2ððððð¶ð¶ (4-2) We show resistivity measurements as a function of depth for different sites at directions parallel or perpendicular to the reinforcements (or pavements) in Figure 4-7. These data include measurements from lines/locations spaced approximately 15 feet apart. Each line/location is a total of 6 feet long and includes resistivity measurements at probe spacings of 0.5, 1.0, and 2.0 feet. At some locations the one- or two-feet probe spacing could not be achieved due to space constraints to place the probes. a) San Antonio, TX â parallel to reinforcements b) San Antonio, TX â perpendicular to reinforcements c) El Paso, TX â parallel to reinforcements d) El Paso, TX â perpendicular to reinforcements 0 0.5 1 1.5 2 2.5 0 5,000,000 10,000,000 15,000,000 20,000,000 25,000,000 30,000,000 35,000,000 D ep th (f t.) Resistivity (â¦-cm) Location 1 Location 2 Location 3 Location 4 Location 5 Location 6 0 0.5 1 1.5 2 2.5 0 5,000,000 10,000,000 15,000,000 20,000,000 25,000,000 30,000,000 35,000,000 D ep th (f t.) Resistivity (â¦-cm) Location 1 Location 2 0 0.5 1 1.5 2 2.5 0 20000 40000 60000 80000 100000 120000 D ep th (f t.) Resistivity (â¦-cm) Location No.1 Location No.2 Location No.3 Location No.4 Location No.5 0 0.5 1 1.5 2 2.5 0 20000 40000 60000 80000 100000 120000 D ep th (f t.) Resistivity (â¦-cm) Location No.1 Location No.2
61 e) Buffalo, NY â parallel to pavement f) Buffalo, NY â perpendicular to pavement g) Schroon, NY â parallel to pavement h) Schroon, NY â perpendicular to pavement Figure 4-7 Results from in-situ testing (determined from Equation (4-1)). Figure 4-7 allows us to compare the data obtained from different sites, and from fills that incorporate metal reinforcements and those that do not. Based on the data shown in Figure 4-7, we made the following observations: â¢ The resistivity measurements from the San Antonio site were very high; greater than 1,000,000 â¦-cm, and within the range of 5,000,000 to 35,000,000 â¦-cm. This is due to the extremely dry conditions at this site. â¢ Data from the MSE wall site in San Antonio show higher variations between measurements taken at different locations compared to the data obtained from the other sites. This might be related to the extremely dry conditions at the site (with moisture content less than 1%) as the operators had to add water in small amounts to the fill (next to the probes) to improve the electrical connection between the probes and the fill. Addition of water and the high evaporation rate at this site might be the main reasons for the relatively large variations in the resistivity measurements. â¢ Measurements from the San Antonio and El Paso sites depict higher resistivity values from lines orientated perpendicular to the MSE reinforcements compared to the measurements from lines orientated parallel with the reinforcements. This can be explained by the fact that the steel reinforcement provides an easy path for current in the longitudinal direction causing a reduction in the resistivity readings when the alignment of the pins for resistivity measurements are orientated parallel (longitudinal) with the reinforcements. â¢ Considering the measurements from the New York sites that were performed within the shoulder areas of the pavement, measurements with lines perpendicular or parallel to the pavement are similar to each other (no steel reinforcements in the subbase materials). â¢ In general, the resistivity measurements from the site in San Antonio increase with respect to depth, but the data from New York sites generally decrease with respect to depth. This 0 0.5 1 1.5 2 2.5 0 20000 40000 60000 80000 100000 120000 D ep th (f t.) Resistivity (â¦-cm) Location 1 Location 2 Location 3 Location 4 Location 5 Location 6 Location 7 Location 8 Location 9 Location 10 0 0.5 1 1.5 2 2.5 0 20000 40000 60000 80000 100000 120000 D ep th (f t.) Resistivity (â¦-cm) Location 1 Location 2 Location 3 Location 4 Location 7 Location 8 Location 9 Location 10 0 0.5 1 1.5 2 2.5 0 20000 40000 60000 80000 100000 120000 D ep th (f t.) Resistivity (â¦-cm) Location 1 Location 2 Location 3 Location 4 Location 5 0 0.5 1 1.5 2 2.5 0 20000 40000 60000 80000 100000 120000 D ep th (f t.) Resistivity (â¦-cm) Location 2 Location 3 Location 4 Location 5
62 observation may be related to the significantly higher effect of the reinforcements in reducing the resistivity at 0.5 feet depth compared to that at 2.0 feet depth (i.e., having one layer of reinforcement in a 0.5-feet thick material has a more significant charge carrying effect compared to that over a thickness of 2.0). In addition, the measurements at depths of 2.0 feet from the subbases studied at the New York sites reflect the presence of subgrade material beneath the 12 to 15 inches of subbase material that was placed for these projects (i.e., materials at the New York sites are not homogeneous over the two feet depth of measurements). â¢ The resistivity measurements from the site in El Paso remains relatively constant with respect to depth, which is different than the increasing trend observed in the data from San Antonio. This could be attributed to the high moisture content of the fill in El Paso (with the average moisture content of 7.3%), which dominates over the effect of reinforcements (described above). In addition, the lower variations in the resistivity measurements from El Paso can be explained by the higher moisture content of the fill at this site. â¢ Higher resistivities were observed from measurements at the site in Schroon, NY compared to those from the site in Buffalo, NY. This is consistent with laboratory measurements of resistivity. We measured the in-situ moisture contents at the Schroon, Buffalo, and El Paso sites as approximately 3.0, 2.5, and 7.3 percent by weight, respectively. Figure 4-8 shows one of the in- situ moisture content measurement at Schroon, NY, performed by the NYSDOT (the owner) using a nuclear density gauge. UTEP and the NYSDOT tested samples from the sources and sites in accordance with Tex-129-M, which includes the larger soil box and all of the particle sizes in the test specimen. We extrapolated the moisture-resistivity curves obtained from these laboratory tests to moisture contents of 3.0, 2.5, and 7.3 percent as shown in Figure 4-9, and compared these values to the field/in-situ measurements at depths of 6 inches. We obtained a good comparison as shown in Table 4-3. The average error was approximately 11%. Figure 4-8 In-situ measurement of moisture content at Schroon, NY. nuclear density gauge (Troxler, Model 3440)
63 Figure 4-9 Extrapolating the moisture-resistivity curves to determine the resistivity at in-situ moisture content for the site in Buffalo, NY. Table 4-3 In-situ (Wenner 4-probe) and laboratory (modified soil box) measurements1. In-situ range (â¦-cm) Laboratory (â¦-cm) El Paso, TX 8000 - 22,000 11,600 Buffalo, NY 30,000 - 54,000 38,400 Schroon, NY 60,000 - 115,000 95,000 4.3.3 Other Electrochemical Properties We present laboratory measurements of chloride and sulfate contents from samples retrieved from sources and sites in Buffalo, NY; Schroon, NY; San Antonio, TX; and El Paso, TX in Figure 4-10 and Figure 4-11, respectively. These graphs include the results from testing samples via AASHTO T-290 (2016), AASHTO T-291 (2013) and Tex-620-M. The data show good agreements between measurements from samples retrieved from the sources and those obtained from the sites. In most cases the chloride and sulfate contents determined by Tex-620-M are lower than those obtained by AASHTO test procedures. An exception to this observation is seen with the source from Buffalo, NY, where the sulfate content from Tex-620-M appears to be higher than that from AASHTO T- 290 (2016). However, the measurement of sulfate content via AASHTO T 290 for the site sample is higher compared to the results from testing the source. The measurement of sulfate content via AASHTO T 290 from the source sample appears to be anomalous and too low and is not considered in the comparisons of results. We show the results of electrochemical tests performed on the samples retrieved from the sites and from the sources in Table 4-4. The laboratory results of the resistivity tests were discussed in 1 Because of the unusually high resistivity measurements at the San Antonio site (Figure 4-7 (a) and (b)), we did not include the comparisons between laboratory and in-situ measurements in this Table. y = 239758x-1.374 RÂ² = 0.993 y = 112488x-1.172 RÂ² = 0.997 0 10000 20000 30000 40000 50000 60000 70000 80000 90000 100000 0 5 10 15 20 R es is tiv ity ( â¦ -c m ) Moisture Content (%) at NYSDOT laboratory at MMCE Ï = 38400 2.5% (in-situ)
64 Figure 4-4. Considering the AASHTO requirements for fills in MSE walls (presented in Table 1), the material from Buffalo, NY, is characterized as corrosive but other materials are noncorrosive. Table 4-4 Characterization of corrosion potential1. Protocol Resistivity (â¦-cm) pH [Cl -] (mg/kg) [SO4] (mg/kg) Corrosive San Antonio, TX Modified Tests 53,300 9.0 1 1 No El Paso, TX AASHTO 3,650 9.0 49 40 No Buffalo, NY AASHTO 2,233 7.7 14 311 Yes Schroon, NY AASHTO 10,433 8.3 15 53 No Note: The values marked in red do not meet current AASHTO requirements for MSE wall fill. Figure 4-10 Comparison of chloride content results obtained from samples collected from the sites and sources. 1 The presented values in this Table are average of site and source. 16 11 5 26 8 4 54 45 8 5 1 1 1 1 47 33 0 10 20 30 40 50 60 UTEP/Source UTEP/Site UTEP/Source UTEP/Site UTEP/Source UTEP/Site UTEP/Source UTEP/Site Buffalo, NY Schroon, NY San Antonio, NY El Paso, NY Ch lo rid e co nt en t ( m g/ kg ) AASHTO T-291 Tex-620-M
65 Figure 4-11 Comparison of sulfate content results obtained from samples collected from the sites and sources. 4.4. Comments and Suggestions from Owners We exchanged information with the New York State DOT (NYSDOT) geotechnical and environmental engineering laboratories and noted their comments and suggestions for proper implementation of the proposed protocol. Since the Texas DOT participated in the development of the modified test procedures, they offered no additional comments. We summarized the main comments/suggestions that we received from NYSDOT below: 1. When testing compacted specimens, add increments of moisture after removing the specimens from the box and use a mixer (similar to Figure 4-12) to obtain a good distribution of moisture throughout the specimen (i.e., do not add water directly to the compacted specimen within the soil box). 2. The moisture increment corresponding to 100 percent saturation is easily obtained from weight measurements of the compacted soil specimen after each increment. The increment at which the wet weight of the material begins to decrease occurs near saturation. 3. For AASHTO T-288 and Tex-129-M compare the resistivity measurements obtained when the specimen reaches saturation (Ïsat) to the minimum resistivity (Ïmin) obtained by increasing the moisture content until reaching the absolute minimum resistivity. However, for moisture contents in excess of those needed to achieve 100 percent saturation, we are not testing a compacted specimen, rather we are testing a slurry. This comparison provides useful information to estimate the behavior of the material in the worst-case scenarios and to determine the possible underestimation/overestimation of the reported resistivity. 4. Resistivity tests with coarse samples in the 20 lb. box and preparing the samples and testing in accordance with Tex-129-M was feasible (required a reasonable amount of time and effort). 97 311 46 61 15 24 43 35 169 133 15 9 1 1 35 29 0 50 100 150 200 250 300 350 UTEP/Source UTEP/Site UTEP/Source UTEP/Site UTEP/Source UTEP/Site UTEP/Source UTEP/Site Buffalo, NY Schroon, NY San Antonio, NY El Paso, NY Su lfa te co nt en t ( m g/ kg ) AASHTO T-290 Tex-620-M
66 5. A bottle roller is not standard equipment for a geotechnical lab and other methods of mixing should be implemented for measuring salt contents and pH in accordance with Tex-620-M. 6. Mixing times for the tests on leachates for measurements of pH and salt contents should be kept to a maximum of 30 minutes. 7. Use a template to properly align pins for performing the Wenner 4-probe test. 8. The Wenner 4-probe test is relatively easy to implement and can be used on active construction projects. Resistivity meters built specifically for this test, similar to the M.C. Miller Resistivity Meter, should be employed due to their ease of use, field ruggedness and efficiencies (i.e., although the results obtained from the Gamry device were in good agreement with the M.C. Miller device, it was a relatively time consuming process to make a measurement with the Gamry device). Figure 4-12 A mixer used at Soils Engineering Laboratory of NYSDOT. 4.5. Conclusions We made the following observations from the data we collected in cooperation with owners/contractors as part of Phase III: â¢ We observed higher variations in results between laboratories that were testing similar samples compared to the variations observed from resistivity measurements made with samples retrieved from the sources before construction, and from the site during construction. This is because, in general, samples retrieved from the site or the source were similar. â¢ The variations we observed during the field studies included in Phase III were higher than the variations that we observed from testing replicates with the same operator/laboratory during Phase II. This is expected because of variabilities that exist between laboratory practices and the errors due to variations between samples. We intentionally limited the bucket containing the sample and added water electric motor
67 variations between samples when we implemented the laboratory test program for Phase II, which mitigated the sampling error. â¢ Reinforcements affect the in-situ measurements of resistivity from MSE wall fills. â¢ Reinforcements appear to have the least effect on measurements of resistivity if the lines for the Wenner 4-probe test are orientated perpendicular to the reinforcements. â¢ We observed good correspondence between laboratory and field measurements of resistivity when the laboratory tests are conducted on compacted specimens with the same particle sizes, gradation and moisture content as the in-place fill, and considering the in- place moisture content of the fill. The experience and data collected from implementing the proposed protocol on active construction projects indicate that the modified test procedures and the test protocol for improved characterization of corrosion potential are easier to implement compared to the traditional methods. The owners/contractors were able to perform the modified test procedures, and with few exceptions could acquire the equipment needed to perform these tests.