DEVELOPMENT OF A PROCEDURE FOR THE AUTOMATED COLLECTION OF FLEXIBLE PAVEMENT LAYER THICKNESSES AND MATERIALS: PHASE IIA - EXECUTIVE SUMMARY REPORT

Transcription

1 DEVELOPMENT OF A PROCEDURE FOR THE AUTOMATED COLLECTION OF FLEXIBLE PAVEMENT LAYER THICKNESSES AND MATERIALS: PHASE IIA - EXECUTIVE SUMMARY REPORT FLORIDA DOT STATE PROJECT report prepared by: EMMANUEL G. FERNANDO, PhD., P.E. Texas Transportation Institute Texas A&M University College Station, Texas and KENNETH R. MASER, PhD., P.E. INFRASENSE, Incorporated Cambridge, Massachusetts September 1993

2 ABSTRACT The overall objective of this project is to develop, test, and implement a ground penetrating radar system to supply accurate pavement layer data for the pavement management activities of the Florida DOT. The project has been divided into different phases that successively demonstrate, develop, pilot test, and implement radar technology for Florida pavement conditions. The subject of the present report is the Phase I demonstration of the potential of current GPR technology to estimate pavement layer thicknesses and classify base material type. This demonstration consisted of a sequence of research activities that included the following: 1. selection of test sites for radar thickness evaluation; 2. radar survey of test sites established; 3. blind predictions of layer thickness and base material type made solely on the basis of interpretation and analysis of raw radar data, and visual observation of surface characteristics of test sites selected by the Florida DOT; 4. collection of ground truth information to verify the radar predictions; 5. re-interpretation of radar traces to improve accuracy of thickness predictions using ground truth information; and 6. adjustment of radar predictions by calibrating to a single core. The sites selected covered a variety of Florida pavement materials, with asphalt layers that consisted of multiple lifts. Analysis of the radar measurements made on these sites were divided into 3 different types (blind, adjusted, and calibrated) to assess the accuracy of the radar predictions against the availability of reliable, supporting information. Data collected from ground truth surveys were used to evaluate the accuracy of the radar predictions. The findings from the study demonstrate that existing radar technology can be used with success to predict layer thicknesses and identify base material type. Implementation of this technology for these purposes on a network wide scale is feasible, and will require adaptation of current analysis procedures to handle Florida pavement materials. This will require evaluation of a variety of Florida pavements to develop guidelines for interpreting and analyzing radar data. i i

3 DISCLAIMER The contents of this report reflect the views of the authors, who are responsible for the facts and accuracy of the data presented herein. The contents do not necessarily reflect the official views or policies of the Federal Highway Administration or the Florida Department of Transportation. This report does not constitute a standard, specification, or regulation. iii

4 ACKNOWLEDGEMENTS This report presents the results of Phase I of a 3-phase study sponsored by the Florida Department of Transportation, to demonstrate, develop, pilot test and implement radar technology for estimating pavement layer thicknesses and classifying base material type. The guidance and support of the Florida DOT Project Manager, Mr. Bruce Dietrich, is gratefully acknowledged. We would also like to extend our appreciation to the District 3 Materials Office whose personnel did the coring work for the ground truth surveys conducted herein, and would like to specifically acknowledge Messrs. James Best and Troy Clark for their valuable support. The cooperation and support of the Tallahassee Maintenance Office under the direction of Mr. Mike Roddenberry is also acknowledged. i v

5 TABLE OF CONTENTS PAGE ABSTRACT. ii DISCLAIMER ACKNOWLEDGEMENTS EXECUTIVE SUMMARY 1 CHAPTER 1. INTRODUCTION 3 CHAPTER 2. DESCRIPTION OF RADAR SURVEYS 6 CHAPTER 3. COLLECTION OF GROUND TRUTH INFORMATION 11 CHAPTER 4. RADAR DATA ANALYSIS CHAPTER 5. COMPARISON OF RADAR PREDICTIONS WITH GROUND TRUTH DATA 47 CHAPTER 6. ASSESSMENT OF RADAR PREDICTIONS 58 CHAPTER 7. CONCLUSIONS 62 REFERENCES APPENDIX A - TABLES OF THICKNESS DATA FROM GROUND TRUTH SURVEYS APPENDIX B - BLIND PREDICTIONS OF LAYER THICKNESS PROFILES OF FLORIDA TEST SITES.... APPENDIX C - TABLES OF PREDICTED AND MEASURED THICKNESSES AT INDIVIDUAL CORE LOCATIONS iii iv v

6 EXECUTIVE SUMMARY The overall objective of this project is to develop, test, and implement a ground penetrating radar system to supply accurate pavement layer data for the pavement management activities of the Florida DOT. The project has been divided into different phases that successively demonstrate, develop, pilot test, and implement radar technology for Florida pavement conditions. The subject of the present report is the Phase I demonstration of the potential of current GPR technology to estimate pavement layer thicknesses and classify base material type. This demonstration consisted of a sequence of research activities that included the following: 1. selection of test sites for radar thickness evaluation; 2. radar survey of test sites established; 3. blind predictions of layer thjckness and base material type made solely on the basis of interpretation and analysis of raw radar data, and visual observation of surface characteristics of test sites selected by the Florida DOT; 4. collection of ground truth information to verify the radar predictions; 5. re-interpretation of radar traces to improve accuracy of thickness predictions using ground truth information; and 6. adjustment of radar predictions by calibrating to a single core. The sites selected covered a variety of Florida pavement materials, with asphalt layers that consisted of multiple lifts. Analysis of the radar measurements made on these sites were divided into 3 different types (blind, adjusted, and calibrated) to assess the accuracy of the radar predictions against the availability of reliable, supporting information. Results from comparisons of the radar predictions with corresponding ground truth information are summarized as follows: 1. On average, the means of the blind predictions for asphalt thickness deviated from the corresponding measured means by 0.5 inches. On 3 of the 5 sites considered for demonstration of radar's capability to predict layer thicknesses, the means of the blind predictions for asphalt thickness were within 0.1 inch or 2 percent of the corresponding measured means. The largest discrepancies were obtained in Site 4 where a sand asphalt hot mix (SAHM) layer was observed from the field survey. The reflections from this layer were highly variable due perhaps to local moisture infiltration associated with the relatively high air voids content of this material. Once this condition was recognized and correctly accounted for in the analysis, the discrepancies were reduced to within 10 percent of the measured means. This result reflects the potential improvement in prediction capability that may be obtained as knowledge and experience with Florida pavement materials are accumulated and the analysis software is adapted for these materials. It also 1

7 indicates the potential improvement in accuracy that is possible when supporting information are available for interpreting the radar measurements. This information need not necessarily come from cores. 2. For sites where predictions of base layer thickness were made, the means of the predicted thicknesses were found, on the average, to be within 0.9 inches of the measured means. In one site (Site 6), the mean of the blind predictions was equal to the measured mean. The largest discrepancy between means (2.1 inches, or 23 percent of the measured mean) was obtained for Site 1. This discrepancy was reduced to 1 inch (11 percent of the measured mean) when the layering within the asphalt was correctly accounted for in the analysis. In all cases, the differences between predicted and measured means for base thickness were reduced to within 0.5 inches after calibration. 3. The base material was correctly classified for 4 of the 6 test sites, or for 8 of the 14 classifications that were made (1 in each of Sites 1, 2, 3, and 6; 2 in Site 4; and 8 in Site 5 which had numerous changes in pavement section over a 1.5 mile length). The presence of a concrete base was found to be indi~ated by the appearance of regularly spaced peaks in the dielectric profile of the asphalt layer, attributed to moisture infiltration through transverse cracks on the surface, and by the absence of a clear reflection from the bottom of the concrete base due to the lossy characteristic of this material. On the other hand, the presence of a sand asphalt base was found to be indicated by the variability in the reflections from the base, and by negative and positive reflections at the top and bottom of the layer respectively. These results again show the benefit of knowing certain characteristics of a given material that would leave specific signatures in the radar data which may be used for identification. The task at hand is to establish a data base of base material types and associated radar signatures which may be used to reliably discriminate between limerock, concrete, and "other" base material types. 4. In general, the section changes in Site 5 were successfully detected from the radar measurements. Only 1 section in Site 5 (Section 4) was erroneously identified as being different from the adjacent sections. This was again attributed to the presence of a SAHM base layer which was associated with highly variable reflections in the radar data. This result again shows the benefit of knowing something about a given material that may be used for radar data interpretation. In summary, the findings from the study demonstrate that existing radar technology can be used with success to predict layer thicknesses and identify base material type. Implementation of this technology for these purposes on a network wide scale is feasible, and will require adaptation of current analysis procedures to handle Florida pavement materials. This will require evaluation of a variety of Florida pavements to develop guidelines for interpreting and analyzing radar data. 2

8 CHAPTER 1. INTRODUCTION Knowledge of asphaltic pavement layer thickness and properties is important in many areas of pavement management. Accurate thickness data is needed throughout the roadway network to improve pavement performance predictions, to establish structural load carrying capacities, and to develop maintenance and rehabilitation priorities. On a project level, accurate knowledge of pavement thickness is required for overlay design and to interpret the results of structural tests, such as Dynaflect and FWD. For new construction, it is important to assure that the thickness of materials being placed by the contractor is close to specification. Layer thicknesses may be determined from historical records. However, records are often highly inaccurate or nonexistent. The only presently acceptable methods for pavement thickness measurements are through core samples and test pits. These are time consuming, destructive to the pavement system, dangerous to field employees, and intrusive to traffic. Ground penetrating radar is a non-contact technique which has the potential for surveying pavement thickness while operating at highway speed. Until recently the radar data required qualitative interpretation and these techniques were not well established or understood. But, recent research has now automated data interpretation and allowed verification. The present study evaluates the applicability of current ground penetrating radar (GPR) technology to estimate pavement layer thicknesses and classify base material type for the pavement management program of the Florida Department of Transportation (FDOT). PREVIOUS RADAR APPLICATIONS Ground penetrating radar equipment has been available for the past 15 years. The initial applications of this equipment were to geological and geotechnical investigations. In these applications, the radar data is collected by dragging an antenna along the ground surface. The resulting radar data is displayed graphically and interpreted manually by someone with expertise in radar data interpretation. The application of radar to pavement evaluation is more recent. This capability has been suggested in a number of research experimental studies (1,2) and specifically suggested as a means for improvement of FWD backcalculations (3). In fact, an ASTM specification exists (4) for the measurement of pavement thickness with radar. In these applications r however, the radar technology used was identical to that developed for geotechnical purposes. Recently, systematic investigations have been carried out in Texas and Kansas which compared predicted to actual thickness for a range of conditions. The radar technology used in these investigations was very different from the original geotechnical approach. The equipment used was a non-contact horn 3

9 antenna suspended from a moving vehicle. Data interpretation was automated using software based on an electromagnetic model of the pavement layer structure that is used to obtain quantitative results for asphalt thickness from the raw radar data. In the Texas study (5,6), results from four SHRP asphalt pavement test sites based on 50 cores showed the accuracy of the radar predictions for asphalt thickness to be within ± 5% (± 0.31 inches). When one calibration core was used per site, the accuracy was improved to ± 0.11 inches. The accuracy of the radar predictions for base thickness was within ± 1.0 inch. The nominal layer thicknesses at these sites ranged from 1 to 8 inches of asphalt and 6 to 10 inches of base. Moisture content in the base was also predicted to within 2 percent by weight, and the results also showed that the radar predictions were independent of survey speed (from 5 to 40 mph) and were repeatable. In the Kansas study (7,8), 14 sites were selected to represent the population of pavement types present in the state. The radar results showed substantial variations in asphalt thickness within each 1000 foot test section, and, in general, higher values of asphalt thickness than were reported in available records. The radar predictions, when correlated with data from 73 ground truth cores, show an accuracy of ± 5% to ± 10%, depending upon the treatment of the data. The asphalt thicknesses encountered in this study ranged from 2.5 to 20 inches. Other reported applications of radar include void detection underneath concrete pavements and bridge deck evaluation. In a study done for" the Houston office of the Texas DOT, radar was successfully used to detect voids underneath jointed concrete slabs, and thus locate areas where grouting was needed (9). In this study, radar measurements taken at a spot on the pavement with known moisture filled voids were used in establishing a reference with which to interpret radar measurements taken along the concrete roadway for the presence of voids. In New Hampshire, a radar-based bridge deck evaluation system has been developed for the state DOT by INFRASENSE (10,11). The system, known as OECAR for DEck ondition 8ssessment using Radar, was evaluated through network surveys covering 44 bridge decks. It was shown that the system can be successfully implemented on a production basis, and reliably used to measure bridge deck deterioration. OBJECTIVES AND SCOPE The review of radar applications presented above point to the potential of using GPR technology for estimating pavement layer thicknesses on a network-wide basis. The overall objective of this study is to provide for the systematic implementation of GPR technology, within the Florida DOT, for inventory of pavement layer thicknesses and base material types. This is evident in the approach adopted for this study, which has been divided into distinct phases covering: 4

10 1. a demonstration of the applicability of using radar to predict layer thicknesses and classify base material type (Phase I); 2. a pre-production survey (Phase IIA), and radar system development and pilot, implementation (Phase lib); and 3. a statewide radar survey (Phase III). The subject of the present report is the Phase I demonstration of the potential of current GPR technology to estimate pavement layer thickness and classify base material type. This demonstration consisted of a sequence of research activities that included the following: 1. selection of test sites for radar thickness evaluation; 2. radar survey of test sites established; 3. blind predictions of layer thickness and base material type were made solely on the basis of interpretation and analysis of raw radar data, and visual observation of surface characteristics of test sites selected by the Florida DOT; 4. collection of ground truth information to verify the radar predictions; 5. re-interpretation of radar traces to improve accuracy of the thickness predictions using the ground truth data collected; and 6. adjustment of radar predictions by calibrating to a single core. The next series of chapters document the research efforts made and the results obtained, beginning with a description, in Chapter 2, of the surveys made on the selected test sites. This is followed by separate chapters presenting, the ground truth surveys conducted (Chapter 3); the blind interpretation and analysis of the radar data (Chapter 4); the comparison of the blind predictions with ground truth information and the adjustments made to improve the agreement with the observed (Chapter 5); a summary assessment of the radar predictions (Chapter 6); and the Phase I conclusions (Chapter 7). 5

11 CHAPTER 2. DESCRIPTION OF RADAR SURVEYS The data analyzed in this report was collected at 6 sites selected for evaluation by the Florida DOT. Data was collected using radar equipment leased from Pulse Radar, Incorporated of Houston, Texas. Ambient temperature during data collection was in the mid-90's. The area had received daily rainfall during the month preceding the survey. However, there was no rainfall during the day of the surveyor during the preceding day. TEST SITES SURVEYED Originally, there were 5 test sites established by the Department for the Phase I demonstration study. The locations of these test sites are shown in Figure 1 and are identified as follows: 1. Site 1 - located on the eastbound outer lane of US 27 near the intersection with SR 59; 2. Site 2 - adjacent to Site 1 and located on the westbound outer lane of US 27 near the intersection with SR 59; 3. Site 3 - located on the westbound outer lane of US 27 near the Chaires crossing; 4. Site 4 - adjacent to Site 3 and located on the eastbound outer lane of US 27 near the Chaires crossing; and 5. Site 5 - located on the westbound outer lane of West Tennessee Street along US 90 from Appleyard to intersection with SR 263 (Capitol Circle). During the day of measurements, a sixth site was established that represented original pavement construction. Radar data collected on this site were used in the equipment demonstration conducted the following day at the Florida DOT office in Tallahassee. This site is on the Westbound outer lane of Mahan Drive along US 90, beginning alongside a sidewalk manhole located past the intersection of Mahan Drive and West Bacon Drive, and ending just prior to the intersection of Mahan Drive with Phillips Road. The lengths of the selected test sites are as follows: 1. Sites 1 to 4 approximately 0.3 miles; 2. Site miles; and 3. Site 6 approximately 420 feet. 6

12 Figure 1. Location of Radar Test Sites.

13 For all sites except Site 5, the beginning and ending locations of each site were marked with paint stripes sprayed on the shoulder together with the corresponding site number. For Site 5, the middle of the intersection of West Tennessee Street with Appleyard was designated as the start of the site, while the middle of the intersection with SR 263 (Capitol Circle) was designated as the end of the site. Sites 1 to 4 are located in a somewhat rural area east of Tallahassee. For the purpose of locating these sites, it is noted that Sites 3 and 4 are approximately 6.4 miles east of the intersection of US 27 and US 319, and that Sites 1 and 2 are approximately 7 miles east of Sites 3 and 4. SURVEY PROCEDURE Radar measurements were made starting with the sites farthest east of Tallahassee. Traffic control for the measurements was provided by the Springhill Road Maintenance Office. For Site 1, a lane closure was initially set up for the eastbound outer lane. Metal plates placed on the pavement surface at the beginning and ending locations (Figure 2) provided reference markers in the radar data with which to identify radar signals taken within the site. The radar van from Pulse Radar was driven continuously along the test site, with measurements being initiated prior to the beginning of the site and terminated past the end of the site. A chaser vehicle also followed the van during the measurement process. The above procedure proved to be efficient enough to eliminate the need for lane closure to conduct the radar measurements on the other test sites. Consequently, Sites 2, 3, 4, and 6 were surveyed using only the chaser vehicle equipped with an arrowboard to direct traffic to the passing lane of each test site. The metal plates were set down by FOOT personnel prior to the passage of the radar van, and removed after passage of the van. Measurements were made at a speed of about 10 mph, which, for the data acquisition capability of the Pulse Radar system, provided approximately one radar waveform every foot. For Site 5, which was selected to assess the capability of current radar technology to detect changes in pavement section, no metal plates were used, and the van was driven at the normal traffic speed which ranged from 0 to 30 mph. For this site, measurements were initiated when the van was about at the middle of the intersection of Appleyard and West Tennessee Street, and terminated at about the middle of the intersection of West Tennessee with SR 263. The chaser vehicle was still used to direct traffic to the passing lane during the survey of this site.- Radar data were collected along the centerline of the test lane at Sites 1 and 2, and along the left wheel path at the other test sites. Additionally, at the suggestion of the Florida DOT, radar measurements were made along the right wheel path of the test lanes for Sites 3 and 4. All data were collected directly to the hard disc of the 386 8

14 Figure 2. Metal Plate Used to Identify Site Limits. 9

15 microcomputer housed inside the Pulse Radar van. Data were subsequently copied to floppy diskettes for further analysis by INFRASENSE and TTl. For the purposes of this analysis, two sets of calibration tests, consisting of a plate reflection, end reflection, and time calibration tests were carried out during the survey. The first set of tests was conducted after completion of the radar measurements on Site 1, to take advantage of the lane closure set up for this site. The second set of tests was conducted in a parking lot after measurements were made on all test sites. 10

16 CHAPTER 3. COLLECTION OF GROUND TRUTH INFORMATION In order to verify the blind radar predictions as well as to provide information for re-interpreting the radar measurements on selected test sites, field cores were taken to determine actual asphalt thicknesses, to measure actual base thicknesses from the core holes, and to identify the type of base material for each test site. The blind predictions of layer thicknesses will be presented in Chapter 4. Adjustments of these predictions were later conducted to improve the agreement with the measured core thicknesses. These adjustments were made based on information obtained from the cores which were useful in re-interpreting and re-analyzing the radar measurements. The steps taken to improve the accuracy of the thickness predictions are presented in Chapter 5. The present chapter is devoted to discussing the efforts made to collect information for verifying the radar predictions and documenting the pertinent data collected. SAMPLING PLAN FOR GROUND TRUTH SURVEY For the ground truth survey, a sampling plan was initially developed to establish the number and locations of cores at each site. This sampling plan is presented in Table 1. The choice of sample size, or number of cores to take from each site, was guided by the following considerations established in consultation with the Florida DOT Project Manager for this study: 1. the capability of current GPR technology to predict layer thicknesses will be evaluated through comparisons of the radar predictions with the ground truth data collected from Sites 1, 2, 3, 4, and 6; and 2. the capability of current GPR technology to detect changes in pavement section will be evaluated using data collected from Site 5. The first consideration necessitated that a sufficient number of cores be taken from Sites 1, 2, 3, 4, and 6 to enable statistical inferences to be drawn concerning differences between the means of the predicted and measured layer thicknesses. However, from a practical point of view, the volume of traffic on a particular site was also considered in establishing the sample size. This was particularly important for Sites 5 and 6 where the volume of traffic was high, making it particularly necessary to minimize the length of time a site was closed to traffic due to coring operations. The high volume of traffic on Site 5 was a factor that influenced the decision to use the site primarily for evaluating the capability of current GPR technology to detect changes in pavement section. Based on the radar data, there were 7 predicted changes in pavement section on this 1.5 mile long site, which would have required an impractically larger sample size than was proposed if statistical comparisons of means of predicted and measured layer thicknesses had to be made for the different sections comprising the site. Consequently, for Site 5, cores were generally taken to bracket changes in pavement section identified from the radar data and from the straight line 11

17 Table 1. Proposed Coring Plan Site Number of Wheel Core locations referenced Cores Path from start of test site 1 9 Centerline 200, 300, 390, 590, 790, 990, 1190, 1290, & 1440 ft Centerline 30, 130, 240, 300, 400, 580, 600, 780, 1050, 1390 ft. 3 8 Left 50, 140, 270, 420, 640, 950, 1090, & 1470 ft. 100, 300, 400, 490, 610, 690, 790, 920, 990, 1260, & Left ft. (Take concrete cores at 100, 790, and 1390 ft.) 4 9 Right 200, 300, 490, 590, 690, 890, 990, 1090, & 1290 ft Left 640, 1190 ft. 1340, 1440, & 1560 ft. (If 5-2a 3 Left base is PCC, take concrete core at 1440 ft.) >. 5-2b 1 Left 1640 ft. 1880, 2210, 2470, 2870, & 3170 ft. (If base is PCC, 5-2c 5 Left take concrete core at 2470 ft. ) Left 3280, 3460, & 3610 ft. 3810, 3960, & 4160 ft. (If Left base is PCC, take concrete core at 3960 ft.) Left 4260 & 4400 ft Left 4480 (at transition between 5-5 and 5-6) 4700, & 5940 ft. 6 4 Left 50, 150, 250, & 350 ft. TOTAL 73 (73 asphalt cores plus possibly 6 concrete cores) Cores/site 12 (12 asphalt cores per site) 12

18 diagram provided by the Florida DOT after blind predictions of layer thicknesses and base material type were made and reported to the Department. For the other sites, the sample size was established such that the difference between the mean of the core thicknesses and the true universe mean for a given site would be within a certain tolerance for a given probability level. The universe mean, herein, is defined to be the mean that would be obtained if one were able to measure asphalt thicknesses at all points within a given site, a task that is not practically possible since it would require an extremely large sample size. Thus, the universe mean must generally be estimated by sampling the thicknesses at a number of locations, determining the mean of the sampled thicknesses, and establishing the interval about the sampled mean within which the universe mean may be expected to occur with a given probability. For this study, a maximum permissible deviation of 0.25 inches between the sampled mean and the universe mean was used in establishing the number of cores to take from a given site. Assuming a probability level of 95 percent, the sample sizes for Sites 1, 2, 3, 4, and 6 shown in Table 1 were determined. For each site, the locations of cores were established so as to cover the range in asphalt and base thicknesses that were seen from the radar data. Cores were proposed to be taken along the path(s) the radar antenna tracked when the measurements were made. The only exception was Site 3 where it was proposed to take cores only at the left wheel path, even though radar measurements were made on both wheel paths as recommended by the Department. However, analysis of the radar data on this site showed that the layer thicknesses are very similar for both wheelpaths. Consequently, in order to minimize the number of cores that need to be taken, it was proposed to take cores only at the left wheelpath of Site 3. This aspect of the sampling plan was brought to the attention of the Florida DOT Project Manager who raised no objections, and who later revealed that there was actually no difference in pavement cross sections at the left and right wheel paths of Site 3. This site is actually adjacent to Site 4 where the right wheel path is on a widened section of the test lane. The recommendation to survey both wheel paths of Sites 3 and 4 was made merely to make less obvious to the research team the site where there was an actual difference in pavement cross section at the left and right wheel paths (Site 4). In addition to the cores, the sampling plan called for taking dry samples of base and subgrade materials at selected test pit locations in Sites 1, 2, 4, and 5. The proposed test pit locations, shown in Table 2, were established based on the radar data. For example, it was proposed to take base and subgrade samples from Site 1 at the locations shown in the table since analysis of the radar data indicated a higher base dielectric constant at the second test pit location, i.e., 780 feet, than at the first test pit location, i.e., 350 feet. Moisture content and dielectric measurements on base and subgrade samples were made in the materials laboratory at TTl to provide data to support or substantiate the results of the radar analysis. 13

19 Table 2. Proposed Sampling Plan for Base & Subgrade Materials. Site Number of Wheel Test pit locations Test Pits Path referenced from start of test site 1 2 Centerline 350, & 780 ft. 2 2 Centerline 260, & 890 ft. 4 2 Right 710, & 1310 ft Left 600 ft ft. (will be done if 5-2a 1 Left cores show base is not regular concrete) Left 4300 ft Left 4950 ft. TOTAL 10 14

20 FIELD DATA COLLECTION PROCEDURE Each site was initially closed to traffic prior to commencing the coring activities, with traffic control being provided by the Tallahassee Maintenance Office. Core and test pit locations were then laid out with a measuring wheel, and marked on the pavement surface with spray paint. Once this was done, 6-inch diameter cores were taken from the designated core locations by wet coring. The thicknesses of individual lifts in a given core were then measured after the loose core was pulled out from the pavement. In addition, the total thickness of the asphalt concrete layer was measured from inside the hole whenever a core was broken. Measurement of base thickness was accomplished by initially removing the base material inside a core hole using a post hole digger. Removal of the base material was facilitated by attaching the post hole digger to a power tool that rotates it. This technique helps in loosening the base material inside the core hole, and was particularly useful for removing limerock which was found to be generally stiff. Once the base material has been removed, and the subgrade exposed, the base thickness was measured from inside the hole. Measurements of core and base thicknesses were made by the coring crew from the District 3 Bituminous Section at Chipley. All measurements were recorded on appropriate forms. At the designated test pit locations, a crew from the Tallahassee Maintenance Office used a jack hammer to remove the asphalt surface layer so that dry samples of base and subgrade materials can be obtained. Base samples were taken from the top, middle, and bottom of the base to check for significant differences in moisture content with depth in the base layer. Subgrade samples were obtained from the top of the subgrade. Base and subgrade samples for moisture content determinations were placed inside plastic Ziploc bags. In addition, approximately 55 pounds of material from each of the base and subgrade layers were placed in separate cloth bags for laboratory measurements of dielectric constants of molded soil samples prepared at ~ifferent moisture contents. Cores and soil samples were placed inside boxes for shipment to TTl at the end of each work day. Labels were affixed to each bag of soil sample that identified the type of sample, i.e., base or subgrade, and the location where the sample was taken, i.e, site number, wheelpath, and test pit location. In addition, for base samples on which moisture content determinations were planned, the label identified where in the base the sample was taken, i.e., top, middle, or bottom. Cores were also placed inside 6-inch diameter PVC pipes for added protection during shipping. Each pipe was 12 inches long, with a vertical cut along its length to accommodate the core, and a label for recording the appropriate information on site number, wheel path, core location, and total core thickness. This label was filled up prior to placing a core inside a PVC pipe. All test pits and core holes from the ground truth survey were patched by a crew from the Tallahassee Maintenance Office. 15

21 SUMMARY OF GROUND TRUTH DATA Table 3 shows computed means and standard deviations of asphalt and base thicknesses measured at the different test sites. Measured layer thicknesses at the individual core locations are presented in Tables A.1 through A.7 of Appendix A. The range in measured asphalt thicknesses is shown graphically in Figure 3 for each test site. The mean of the measured thicknesses is also shown by the horizontal tick mark within each vertical line representing the range of asphalt thickness for a given site. The widest range in asphalt thickness is seen in Site 5 where the core data reveals several changes in pavement cross section within the site. The high end of the range for asphalt thickness was measured towards the end of Section 5 of Site 5 (at a footage of 4481) where there is a localized thickening in the asphalt layer that was also observed from the radar data for this site. Likewise, the widest range in base thickness is also seen in Site 5, where, as shown in Figure 4, the base layer varies from a low thickness of 5 inches to a high of inches. It was also observed that the cores generally consisted of different lifts, as illustrated in Figures 5 through 10. The lift thicknesses shown in the figures are the means of the corresponding individual lift thicknesses recorded by the coring crew from the District 3 Bituminous Section. The identification of the type of material in each lift is based on information from the coring log and from pavement design sheets provided by the Florida DOT after blind radar predictions have been made and reported to the Department. The thicknesses of individual lifts of cores from the various test sites are documented in Tables A.8 through A.14 of Appendix A. It is important to recognize the layering observed in the different test sites since this will usually cause overlapping of the radar signals which must be considered in the analysis. The type of base material observed in each test site is summarized in Table 4. It is observed that, from Section 1 to Section 3 of Site 5, there are 4 different changes in base material which mirror the segmentation of the site into Sections 1, 2a, 2b, 2c, and 3. The sand asphalt hot mix (SAHM) base from Section 3 to Section 6 of Site 5 was found to be a material characterized by high air voids and low dielectric constant, as evident from Table 5 which shows laboratory measured values of air voids content, bulk specific gravity, and dielectric constant for this material. This characteristic may be useful in identifying sand asphalt hot mixes from radar measurements. Laboratory measured values of moisture content, for soil samples taken from test pits, are presented in Table 6. The measurements indicate that the moisture content does not vary significantly with depth in the base layers of sites where samples were collected. 16

22 Table 3. Means and Standard Deviations of Measured Layer Thicknesses at Test Sites. Site Wheel Mean Thickness (inches) Std. Deviation (inches) Path Asphalt Base Asphalt Base 1 Centerline Centerline Left Left Right Left a Left b Left c Left Left Left Left Left Left

23 14~ ~ ex>..- CI) Q.).c () c: --- CI) CI) Q.) c: ~ ().c ~ Q.) \ l. "...,...,...,...,.... ~ 4... I- 2 o~--~------~------~------~------~------~------~--~ L, Site 4R 5 6 Figure 3. Range in Measured Asphalt Thicknesses for Each Site.

24 14.0~ ~ CJ) (l) ,...,...,...,..., c ,...,... () c CJ) CJ) (l) c ~ ().c f goof - (l) CJ) co co I ~--,l ~I------~I ~I------~I------~~------~I-----, L 4R 5 6 Site Figure 4. Range in Measured Base Thicknesses for Each Site.

25 6~ ~ N 0 -(j) (]).c u c --.- (j) (j) (]) c ~ u.c I- ~...J o -' f Site 1 Core Lifts Binder 8lEE Crack relief _ Type I ~ Leveling ~ Type II overbuild ~ FC-2 & Type S Figure 5. Observed Layering in Site 1 Cores.

26 ~ (/) Q) H-f-+HH-I-H-I-t++t++H+H++-I++-I l c 0 c 4... ~~~yyyyy<.,.~~~~~~~y<,...<a (/) (/) Q) c ~ 0..c r- N ~.....J 3... YY'~vYY~~~~~~..,I<..IV<~~~oVQ J;<.A~~~~yyyyy<.,.~~~~~~VQ O--L Site 2 Core Lifts SAHM ~ Type II ~ Leveling 8llE Crack relief ~ Type II overbuild ~ FC-2 & Type S Figure 6. Observed Layering in Site 2 Cores.

27 , N N en ~ ~.... C ~I~.... en ~ H-H-t--H+++-H-+--t-'i-+t H+t H.... ~ ~~.....c I- ~ J Site 3 Core Lifts ~ Type S ~ Leveling EEW Crack relief ~ ~ype II overbuild ~ FC-2 & Type S Figure 7. Observed Layering in Site 3 Cores.

28 ~ 7"""""",,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,~~ """".'"'''.''''''''...''''''...''''''''...'''''''..''... '..'''''''..- CJ) Q)..c..: ().- -- CJ) c 5 6 """,.. "",,,,,,,,,..,,,,,,,,,,,,,,,,,,,,,,,,,,,'''''''.,...'''~ "".".".,,,..."...,,...,,..,',.,","'...'.".""'''''''''.. '"..., CJ) Q) 4"",,,,,,,'"'''' c ~ (,,)..c ~ ~ :..J 2,,,,..,,,,,.,..,,,,..,,, N w 1 """,",.".. ","",... ',',',.".,"",..,'.. """,',"""".. ~ffi~~ftwm~~ftwffi~~ftw~"" " '.. '.. """ ".. "'''.. '''' '''' """",."".. "."""""" Site 4 Core Lifts (LWP) ~~~~~ Type II & SAHM ~ Leveling HW Crack relief ~ Typ~ II overbuild ~ FC-2 & Type S Figure 8. Observed Layering in Site 4 Cores Taken Along Left Wheel path.

29 ... 8~ ~ 7 ~ U) 6 Q)..c g 5 en en Q) c ~ (.)..c r- ~...J Site 4 Core Lifts (RWP) ~~~~ Type II & SAHM ~ Leveling ~ Crack relief ~ ~ype II overbuild ~ FC-2 &.Type S Figure 9. Observed Layering in Site 4 Cores Taken Along Right Wheel path.

30 3.5~ ~ N (Jl -Cf) Q).c () c --- Cf) Cf) Q) c ~ () c ~ ~ ~ 171'777 'z Z 'z Z Z Z Z 1?? 17 '7 '777. '77 '77... / '7 I7 I7777 ' /VV;A,vV;N.vc;.;<"NV..,.<..,vV;N.vc;.;<"NV..,.<..,vV;A,v;.;<"N.vc;.A "' A.-'V'... """""""...,....A.-'V''"''-IV''''''''''''''''''''''"...,....A.-'V''"''-IV'''''''''''''''''''''''./V''-'''I.. 77 '77 ' '7 '7 ~z. '7 'Z 1 7 "'.7?.77T7 ~7 '7 '77777?? '77 '7 '7 '77777 '7/ 'Lt "'.7 Site 6 Core Lifts Figure 10. Observed Layering in Site 6 Cores.

31 Table 4. Base Material at Different Test Sites Identified from Ground Truth Survey. Site Wheel Base Materi a 1 Path 1 Centerline Limerock 2 Centerline Limerock 3 Left Limerock 4 Left Portland Cement Concrete 4 Right Soil Cement 5-1 Left Limerock 5-2a Left Reddish brown sand 5-2b Left Limerock 5-2c Left Reddish brown sand 5-3 Left SAHM 5-4 Left SAHM 5-5 Left SAHM 5-6 Left SAHM 6 Left Limerock 26

32 Table 5. Laboratory Measured Values of Air Voids Content and Dielectric Constant for SAHM Base Material. Site Location Air Voids Bulk Specific Dielectric (feet) Content (%) Gravity Constant Mean: Std. Deviation:

33 Table 6. Moisture Contents of Soil Samples from Test Pits. Site Location Moisture Content (% of dry weight) (ft) Base Subbase Subgrade To~ Middle Bottom R R a

34 CHAPTER 4. RADAR DATA ANALYSIS Prior to presenting results from the blind interpretation and analysis of the radar data, a review of basic principles of GPR data analysis is provided in an effort to provide the reader with a basic understanding of how the technology works. This includes an example illustrating the basic procedure for analyzing raw radar waveforms. PRINCIPLES OF GROUND PENETRATING RADAR Ground penetrating radar operates by transmitting short pulses of electromagnetic energy into the pavement using an antenna attached to a survey vehicle (see Figure 11). These pulses are reflected back to the antenna with an arrival time and amplitude that is related to the location and nature of dielectric discontinuities in the material (air/asphalt, asphalt/base, etc). The reflected energy is captured and may be displayed on an oscilloscope to form a series of pulses that are referred to as the radar waveform. The waveform contains a record of the properties and thicknesses of the layer within the pavement. Figure 12 shows the relationship of the layer thicknesses to the radar waveforms. Figures 13 and 14 show typical pavement waveforms collected during this project. The pavement layer thicknesses and properties may be calculated by measuring the amplitude and arrival times of the waveform peaks - corresponding to reflections from the interfaces between the layers (see Figure 12). The dielectric constant of a pavement layer relative to the previous layer may be calculated by measuring the amplitude of the waveform peaks corresponding to reflections from the interfaces between the layers. The travel time of the transmit pulse within a layer in conjunction with its dielectric constant determines the layer thickness, as follows: Thickness = velocity x (time/2) ( 1 ) Since the measured time between peaks represents the round trip travel of the radar pulse, the thickness computation is based on time divided by 2. The radar velocity can be computed from the dielectric constant of the medium,, using the formula: velocity 11.8 { (inches/nanoseconds) (2) 29

35 Antenna Figure 11. Illustration of Radar Survey Vehicle. 30

36 Vo I tage Antenna CJ tc-reflected <D rays surface T t AC 1 (2) Asohal t Q) Base Subgrade Tlme(ns.) Radar Waveform Pavement Cross Section Figure 12. Model of Radar Pavement Data. 31

37 4SPJMLT LAVER5 : ".'... '" '",....,... I ",' I... '.' o to :... : :... : : : :--~ \...-" > OJ OJ 4- ~ -4ee OJ w u. N c: C'O +> Vl 'r ' ~-.~~.,---~..., :... ~~

38 w xe ,. 1.\, I: \ l(\ ~..:.. /":\...;...:... :... :...;...;... :... : 11,'<', ' I" : l '.: : : : : : : : III ', I., 1. 1>---. -'. I. II" '.. I "'''~ ~..r---.. _.,...~ ; ~ ' -..., I II i I I~ "\ : I ".--..!,....:-, -.".---,- : : ---: ~.. _-----'"--+ I. III I~III I, 'I :1 ' / l'.a\... : : '... _ : - : \,iii I' ll, 'J'.' : : ;..., :. \ lt.. ~.. '\.... t,... r......'. ".-": '".... :... \.,.. " I JI:',. '. ~ I" 'o': :""".".-'... : " (r I; I \" "'. III I','1... r..: : :----"... : ----'.... :,... I I' \ 1 \ \ v:"... ~ '... ~ '..",", ''''---.: --Po- :..._,;..:. \ "I I., 1 '" '... II' ',', ~ ~ ""'7---~ '"... ' t ~I II ~... :,I 1',:/ "--J: : :..... _ : : :.. \.,I L~ I : '\~ '-..'-.:/ (.'. '".., : _---r-.. "..: l-... "II.. I Ll Il~ \ \" I: ("'!.. II,-,.!" : : :... : : '~'-\..-'-'-': I nji'-i\,.. ' 'I.. ".,..-..._.. r!" nl I.-' 'I, \... II l. ',....,... ~ ,..,..,..'-.... I II. 1\... I..(-... ~ : : : '.""./:... ':'.... -=-~~-... ~-~,... "II' l... \ " \ " /,'"... : : ~: -----: : : : \ "I II II: \ \ """ \ / I" \ ~ : l _...-: : -,.-; _-...' r,.~.---;... II Il--, I'.,. "\'--.1: III... \1, 1...-:-. :.._ : : : : _ :-- :.,...,.'1/1: \\ '''', \ :,' I '/.-...\ : '!'"'-" : ; : ;-"' ; : \... / J';.~ 'i ~... ",' ~.,;J IL I (' \I l -~....,( ~...!...:..,"'"",-...:...:...,_... :, I II" I I \,. I I \. --. J ". -.. \ " 1III : 'I I..., \\ /,,/.... ". : : : ;--- "'--... ~ : -. ' '.;'_.-"" : "... I~,..I, I~ "'-.'" 'It,,'-.,r' : :... : --: : _. : \ I I:~, \ \:,' I" ~ I l :.-.. ;..-_ "'--_.'._. - ' '.. :.-- :, " 'i" II' I" '" i"' '. '. "~ I. I \ '--a... I I "I' :.-..; , /..: :--... "..... " I'~' I "... rl... I.~, : :....,.,... : :.. \ ".,I \ I L ~,. :.. 'Z~ I "~ ~.'. '-"..."-,,,-",. :-...--:'"7-:--:--: :,r' : '),""-.... l ~ ',' (,,'~" -..." _... r.,... '"I '-' L J I \ -....~,,.~ -., "",.' --.. " 11 ria I "'...'-. I I,... '. '..c. ~ - : -... \.../:11',,1;"\ 1,\1... \...:...,/...", \'1.~.. I '\..... r ----:..._--.-!'-....._.. ~-. ~.,;"'" '\,jj ; / I,'1, '.. " "p' -. " 1'11"" \ '11/-.. It -..'".-~, ~ : , 11'11"1 I ')1,I'...- -"9'_- --- ""'\ ~ - '. J "I i t, 11'\'. ".'. ':"I'~. r~,. V ~..."':"" ~... :.-... \,... ' I I : II...,... II I \... : : : -: : --: '''''- "'~ : \ ) I,'" \, of I" ~--'----;'----' - ~ ' ' ---'" \.,., III i : "11\..." \. ~l " \ ~/-... /... : : : ~' :.'-..-)..;...--.; " I J/ "....".J. '...'.... \ )I t~ \ \' /,'",,; : : : '-... \..~ II I: 1\ '.._... "/,,.,..., \ : " : -; "'!'--.-~ :--... )" I I Il\ l~',... ~ : 1/ \ t~., ~.t ;.-... : : : "---', '"': : ~. \. hit Jo J, 1 ~":.. J,,~a;a,'--',.,,' '.'.----:,, "'-"~';-"'..-..;-: ;-: ;.. 0: ,.,.,' 11111r..\1, I. "--." ~.. } II ,.,: : : '---/: -- ' : ,.;..-, tll'll\ ',', I,... ',--'P _ \. II IJI: III ' "1 l.""', \ / :...,..---.~ "':"~-"'''-''''''':'''''.'-''''''\..~ : '.....,Ir... \..... : /,.... \ : I' '\ Ill"\ (\.. 1/,,_., : : : --: :..-'-" "j.l,..(... \. 'III~ ~ \ ~... \.J/ /,I r " '\\. : : ~.---: :--/ "..,: \... 1 I~~( I' ~.. "'.. '.."'f'.. ~,L.~..i!.... ; i....;...'-;-...:...: w... : " "I'. I 1\ '" '. 0/ "., ~.._-"'_.r..! -- "'!'--....',.... " I I : I L', I,.:.' _ I.: j., p ~--.. _-...:... "... : I "., "~,' /... '-r'. :.---' : "'".,../ " ~I IL'... _ '- -' _ \ Lli : I :/ll" \, "'" :... ~-... "....-"":" i--~.., ~ '1'....--:.11_1.\...,. ".r _.. --~.... " ' '...."... : / -.:, '..-.", '. IJ ":J " I.. r..-" _. '"1\ "'~-'" '(-J.: \ ".' '1'.. :...:,... ~.-. ~ :.-: ~... ~~ " >...,,...' I... "'-~ II I... r '''~''''':.,',.' l... 1, t... oo...j.,.... : \, '''.-'. ".' 1 Figure 14. Sample Radar Waveforms for Site 6, LWP. xe0

39 where 11.8 is the radar velocity in free space in inches/nanosecond. Combining equations (1) and (2), one obtains Thickness (5.9 x time) IE (inches) (3) where time is measured in nanoseconds. Computation of the surface layer dielectric constant can be made by measuring the ratio of the radar reflection from the asphalt to the radar amplitude incident on the pavement. This ratio, called the "reflection coefficient", can be expressed as follows: Reflection coef (1-2) (F, -;;:) (F, + r;;) (4) where the subscripts 1 and 2 refer to the successive layers. The incident amplitude on the pavement can be determined by measuring the reflection from a metal plate on the pavement surface, since the metal plate reflects 100%. This is why a metal plate reflection test is conducted as part of a radar survey. Using the data obtained rearranging equation (4), and noting that the dielectric constant of air is 1, one obtains the asphalt dielectric constant, c a ' as follows: (5) where A ApI amplitude of reflection from asphalt surface amplitude of reflection from metal plate (= negative of incident amplitude) A similar analysis can be used to compute the dielectric constant, cb' of the base material. The resulting relationship is (6): C - C ~ F - R2J2 b a F + R2 (6) 34

40 where: F 4F. (1 - fa) R2 ratio of reflected amplitude from the top of the base layer to the reflected amplitude from the top of the aspha It. The above equations are used to compute asphalt and base layer thicknesses from the radar data. An example illustrating the application of the equations in determining layer thicknesses is given in Figure 15. Similar calculations were made on the radar data collected from the different sites. A typical result is shown in Figure 16 which shows the predicted asphalt and base thickness profiles for the left wheel path of Site 3. Additional aspects of radar data analysis are discussed in the following sections. ANALYSIS OF ASPHALT LAYERS In the above discussion it is assumed that there is one homogeneous layer of asphalt overlying a base material. In fact, most asphalt pavement structures are composed of several asphalt layers. These may be the result of successive pavement overlays and/or of particular pavement design specifications. As shown in Chapter 3, the FOOT pavements tested in the program had 4-5 distinct layers ranging in thickness from 0.2 to 5 inches. Most of these layers appeared to have been placed as part of the design. In some cases, the dielectric properties of the asphalt layers are similar enough to allow the asphalt to be treated as a homogeneous layer. In other cases, including those of the Florida DOT pavements, the layer property differences are significant and must be considered in the data analysis. When the asphalt layers are thick, i.e., greater than 2.5 inches, the analysis of the asphalt layers is relatively simple. The second layer of asphalt can simply be treated as if it were the base material, and the analysis method described above for the base can be used for the second asphalt layer. When the layers are thin, however, it is sometimes difficult to clearly distinguish one from the other in the raw data, since the reflections overlap. Distinguishing and accounting for thin layers adds to the complexity of the analysis. INFRASENSE has implemented a procedure in its PAVLAYER software for distinguishing thin asphalt layers, and this procedure was used in the analysis of the Florida DOT data. The procedure involves the removal of early reflections to reveal the presence of secondary layers. Figure 17 illustrates the results of this procedure. Figure 17 shows the same data for Site 6 as shown in Figure 14, but with the surface reflection 35

41 ~ 4.88 a x 2.88 VI +J..- 0 > QJ en m J..- 0 > ',' 'f 'J ';" ~... f. I"! i I 1...TJH.! 2.64 i4.0 i -~" ~" ICMi.~.5~5 cp. ITJIIHI ~.l"!~--':""'"... I j 0.19 Ia\ i i 1 i! T r '... r HIHHIII:HH IIHI:IHI Time (Nanoseconds x 2) /. Z'/l I/~) [ ; + J -!'-. (, I i rvit) fl.,) 5. 'j.a t'j fj-. t) (2. l'l) I{ = :: 5.'18 J. I fl:: i.i ~ t :;' b I 1 ~ J"tt'U....~ c~~tl,,4- fr<-1..1-~ F = = 'fj:;:;:; R.2.:: r/~/ t:b - f~ Ab/A ::: [F~RL r 5.(" F + Rz.., - 5 l~1 f). I'! /",S)'5 - ~.Ob - t!.h [- :l. C(. -(l...(.. v -"'.3' r f-o.:3/' :: il.;) 7 N:..;t S; Lj Lltb '.1 Jr:?b,b-.1 (If) /.( Ili,17 I 3 1/ 'fj, '" Figure 15. Sample Radar Waveform and Thickness Calculations. 36

42 Base o ~~~~~~~~~~~~~~~~~~~~~~~ o Distance (feet) Figure 16. Predicted Layer Thickness Profiles for Site 3, LWP.

43 xe0, t. : ': ,... i'... : w co xe0 Figure 17. Radar Waveforms for Site 6, LWP, After Removal of First Surface (Note Appearance of Two Asphalt Layers).

44 removed. The result reveals a two layer asphalt structure, with an analysis that yielded a surface layer over a lower layer. In fact, the cores revealed a similar structure, as shown in Figure 18. INTERPRETATION OF BASE MATERIAL TYPE The predicted layer thicknesses, and base material type for the different sites surveyed are summarized in Table 7. For the purpose of identifying the base material, the following general categories were used: 1) limerock; 2) old concrete pavement; and 3) other base material. In all cases, the asphalt/base interface was visible in the radar data facilitating calculation of asphalt thickness. As discussed below, the base/subgrade interface was not clear in all cases. Layer material interpretation was based on the estimated layer thickness, the dielectric constant, and its spatial variation. In general, layers detected below the surface layer, with predicted thicknesses of 3 inches o~ less, and dielectric constants of 8 or less were assumed to be asphalt layers. Thicker layers with dielectric constants greater than 8 indicate granular, stabilized, or concrete layers. The following items were considered in the effort to classify the base materials of the different test sites: 1. The ability to detect the base/subgrade interface through a thick base layer suggests a granular base, since radar transmission through such layers is fairly good. 2. The inability to detect the base/subgrade interface suggests (a) a clay or concrete layer, since transmission through these materials is generally poorer, or (b) the base and subgrade materials may be similar so that no base/subgrade interface can be detected. 3. The presence of regularly-spaced transverse cracks at the pavement surface and the appearance of strong reflections at regular spacings in the radar data suggest the presence of an old concrete pavement beneath the asphalt material. In an effort to get more information with which to differentiate between limerock, and a base material falling into the 1I 0 ther ll category, laboratory measurements of the dielectric constants of molded limerock samples at different moisture contents were conducted at TTl. Limerock material for these tests was provided by the District Materials Engineer of District 3 who indicated that the material was typical of those used on roadways in northwest Florida. The results of these measurements are shown in Figure 19 where it is seen that the measured dielectric - constants vary from about 8 to 20 for a range of moisture contents between 6 and 14 percent. The general trend observed from the figure is an increase in the dielectric constant with increasing moisture content. In addition, analysis of radar data taken from the Florida DOT parking lot in Tallahassee (which has a limerock base) showed dielectric constants ranging from 11 to 19, which suggest field moisture contents of between 10 to 14 percent based on the laboratory results. These moisture 39

45 3.5 Asphalt Thickness (inches) - - Firat Layer (FC-1) I Second Layer (T-11) - Total Asphalt Thickness EE FC-1 Core o T-11 Core ~ Total Core Thickness I I I,. I I. I 0 I 0 I I. I I I. D I II I ~ I.1 I I II.. I. I II. I I I... I I I,... " 'I I I'", #A,.." \ r I,t. \,. CD - -- "E ~. tf-i.l--' -,.. " I.5 a Distance (ft) Figure 18. Plot of Predicted Layer Thicknesses versus Core Thicknesses, Site 6.

46 Table 7. Summary of Layer Thicknesses and Base Material Type Predicted Blind. Site Distance Average Total Base Material (feet) Thickness (inches) Type Aspha 1t Base 1 all imerock 2 all * old concrete (or other material, perhaps clay) 3 (LWP) all limerock 3 (LWP) all imerock 4 (LWP) all old concrete 4 (RWP) all other 5-1 o other 5-2a other 5-2b other 5-2c other imerock other limerock end imerock 6 o imerock * Predicted using radar data for first 500 feet of test site. 41

47 20.0, _--_...-.._......_..._._.._- -ffi ,. 1i5 c o ~ c t5 Q) Q) _ o 1 o ~--~----~----~----~--~~--~----~ Moisture Content (percent) Figure 19. Measured Dielectric Constants of Molded Limerock Samples.

48 contents may be reasonable considering the amount of rainfall the Tallahassee area has received prior to the week of the survey. It is realized that other base materials may have dielectric constants in the same range as those measured for limerock. However, in the absence of any other information other than what were available, and considering that limerock is used widely as a base material in Florida, it was decided to classify a base as limerock whenever the predicted dielectric constant was 8 or greater, and the material was identified to be granular based on the considerations given above. Obviously, further investigations have to be made to establish guidelines for determining whether a material is limerock, or some other granular or stabilized material. In the succeeding phases of this project, a laboratory evaluation using TTl's dielectric probe will be used to obtain dielectric properties for a range of base and subgrade materials. DETECTION OF CHANGES IN PAVEMENT SECTION The 1.5 mile survey of Site 5 was carried out in order to test the capability of radar to identify changes in pavement layer structure. The identification was carried out by examining the raw radar data, and by noting locations where significant changes in the radar pattern occurred. Examination of the raw radar data was carried out in two ways: (I) examination of groups of raw radar waves; and (2) examination of a colorized presentation of the radar data. Figures 20 and 21 show examples of waveform presentations which reveal an abrupt change in pavement structure. Figure 22 shows a colorized presentation of the same change as that shown in Figure 20. SUMMARY OF BLIND RADAR PREDICTIONS The thickness analysis for Sites 1 to 4, and Site 6 was carried out at 4 foot longitudinal increments. More detailed analyses at 1 foot increments were carried out on Site 4 and on selected sections of Site 2 to reveal details and spatial pattern of reflection anomalies. Site 5 was analyzed at 10 foot longitudinal intervals. The results of these analyses can be summarized in terms of the mean values and standard deviation of the thicknesses computed for each detected layer. These results are presented in Table 7. The classification of base material type into the three categories of "1 imerock", "concrete", and "other" was based on an interpretation of the thickness and dielectric constants of the layers, and on knowledge of possible occurrences in pavement construction as noted earlier. The predicted thickness profiles for all sites are presented in Appendix B. / 43

49 xe0...;...:...:... :... ;...: :... ~ :.. "-... ~~..-.:::~---~: : : Figure 20. Waveform Presentation of Major Change in Pavement Structure. xe0

50 M...,'\1.. xe t~;. ~'~111 ~'WI,oJ I I': I ~ I,~_. -..' 3\0\~\ /t}:~j:~~ ~~~~~~~~:. ~::III,"I:~:; ~'~~II ~ \~::~::~~:~:~., ::::,... ~.i~~~~-:~ =:.... "'... -'~~::.::~.-----: =-----:------~----:~ _...,....~ 1<., ',"'," ",'0 '\...,.. :--~-.-_!.. ",,-:-, ' ,... ~ ~~....._:--1, '\:I-})\I l~' 111.: t~ -----:---=::::...:... _::;:_.,/ /--~..: ;:.~--~_ ;---- : : : '" ''''~I I,'.,.".-. (...-~,- ' 00,'", \\ ",,1 U," '," :......,/ : ~ _...---~ ~,/' ~-.; ; ',II /1 fir. I I,'I '-' I I...-,'Irpo- ~--~.,' : --...\\11... II),I"~ I,''w-''.' rj :::\,_l l... "''''',,'... '/ )"., ""...', ;1 \f... _l /I.r-~ I /' : _>~.( _ -.:1\:\... {~ll I...,1 './..--~......: :-;~..... ~..-""-'--.~~ /~.~.-..:.---- ;. --"----: I, 'I, I.J,,v- (I. ~'::-.' _.-J- ". '...- : _~. ",.'.'. ---: ' : ---. ":'., I,\~' ;~ ('':'''~'':~l:',i~:''''':~j:'''' ;,.~... ~.-:,.~"'"...:... ;,... ~l.-z~-:...:.;.~""""" ':'.._.:...:..~:-...~-.-.: :.:-... ~-""...:. ~.::,...-~ ~ ;..._......, I /:1 I J J,l, ::;''' :._.-~..-:.. ~---"'==::...:...',.;':.::c...: _.---.."..:.-. --_ :.., ~,. ~,, It , ".1 ~ I' \'.'_~-..A'<: ~~ ;...,,.' "-,:-... ~""-----"" ' ~t' "~:::::"'.' ~ ': --"', \ I~'... f' ~., ,...,'"-.. -.,",",' ~"I~\...,~... ~...;...:.--..:"'... )o~~...-:- ~-...;t.' (:...""~.. ~~~ -~., I, \.J { II '. ' "::.~..-_--...~ _--:---,"-. _.--:....._-:r-::::-j _... I, " I',..._.._... l'''- _... r--_:::: ~ -----: ----:. : _ : l,.': '... : "...'.. I ~ I,, /1, ~... :- ; ,,-... ~- 7'-.001'",.' X : -: ", III, I ~I., I,', - /l _...-."..._... ~------w... "'::-... ~_... l '.,,',... 1Jf. 'n I....J/.,., _---. :'-'..:,.....-:...---~...."" : """'-.._... ;.' "".~:-'"--;------: ',',', / Ir,II:"..., -.../ ~ ""'~,',," ,, -".:'\'" 11.1~~.'' , '-:- \'\...-:- _: ~..,:..._... ~ ----_...' :,1 t...\. : : _". <II,"~ ~'lr'l ':....- ~..,.."_.--.". :...- '.~\...",.~~--:--- _ ~::: : --.../:,1, 'y. :.1.:fJJt... ~'(~'I.\...,'/..,.....r VI:,...,.--.., ~-., '... ~~...,,J.~..'... ','"....-.~\~.\1 ~.:::..., :/'..,...-.~.-:-..\ ~... ~.--~-: ,.~ ll....,\ ~ : ~ ""Ill \ ),...., :-... ~\... ' _---"'---r "-".,., ~.-. ' :..- \,. ~~.I ~ ----;:1;..., t... "\' ~..., :... JI-... : \..-.."---:---~':~ t...-"""------:... ~,' I,'.~\l~i'--... (".,......,..,... \...,...---~,.;.--- :""....:--:::---. /-,~( '~-' : -.""~ ~ I I' X'~'...--.! :', \~-- /..', :...:...".-.,-":', "l'-.':,' :...-:-.. ~\~~.} "1, ~:I'I.~~..:.:..-:~.~::~.. "'>..:.. ~~.I. '''/.. :-:=:-:-..:... :..,.~..:... =r-:.... ~:-.:.,~~...:l... ~~ ~~ _ ~ --.. ~',.. 1', ~'_., \. -~, ~... ','...'.... \ -- :- ~. -". \',..., ~~ ~, \... ~ \ -: : '=--::-:---'i'''-:''~'''' ""<. ;,...-'--::::...---: t : \. \\\..J 1"... :'~"...: ~." \... : :...-.-~---- : -... 'I I I" \ q ", "' /" -'t..".', , , --. '.. I, I~' '\ \...'.. ; _- \ : ~... I: / : --...;. -~~--- : -..., \\..., (11J,,-..,... : ';.~''''... :... ~..... L-r'... --:--- _.:.--- ~ :..,=--: " I r I', ;,.-... \ '.~.~.. ";".,...-"'---...,, "r,','\',l~t'l.'~... -,.:l; ~"... / ~...::. :.~ :-... ~.. :.. ~ ",.,-~.:.-. ~::::'::tl '\= :::~\\~~::::::T:;:::~:::::~:~j:.:::~= -t::;?;~;~::f~:::=--.-~ -~ ~--=-~. :_=_-==~j ~It, III ~I... ".,'..' , ~. J",",-",.., ~ ' ~. ". f' 1 r,'"... "...,.,-. -, (... \. ~ \1, '-I' ~{~II""..._... I',~., \". ~ ;..._"',"... ~..---~_...---~ : !"-----: ""~' I ~'. r.,,\.. 'I'll..., ',~... \; :...,\... } : ',I" \ "-~,,"""~i.:::':...;...:.. '~;..-:...:...,...--:... ~~.. I ~,. "'~.~.:.-~..--..:.-~"""'~-7"'--'...- ~-" _ "I,,. ' ~I. I',... lj..(..... ", " "... ".... _---_ ~-- --_. ~: I,... /'1,' ;..._... :~.t;...: --=:-:-- : --. _ : :.._. '". ~. ~',..._.' N,... " t ,J' ". r --..' _- -""" l',. /"".'I. ',.~ '. I,'..., , ". LI ~II"':'"''... ".l.... I...""-"::... --_ ---' '.( ~- ----, ,"", '~: ','" - /) l _ ", "' -' ~.: ~"-",I' "'. --." _ : : :. ":.._.. I.,',. I. ',\ t:j1 ("...." " I.~... ~' ';\..:. t\... ~...'L'r,' 1:.;~--:--:'.~-_~~"'7..,(... :..::.,:,~... _:-...,.:...,...; : *-.-r_--..: -.. ',I, J ly. '\ '" - 't '..., \~::::::} ~ \~::::::~: ~. ~ ~ ~ - ~ : : : : 1. Figure 21. Waveform Presentation of Localized Thickening of Asphalt Layer in Site 5. xe0

51 GROUND-PENETRATING RADAR SURVEY U.S. Highway 90, Tallahassee, Florida FLORIDA DOT - SECT S-L - August 7, 1991 B! )I't ', " t'l I J II " I' I,! 2455' *Each TIC mark = 1" Travel Distance -+-+! 3198' T 4129' Feature Description Location (ft.) Depth (in.) SU A B T Pavement Surface Asphalt Base Interface Base/Subbase Transition o Green Dark Blue Dark Blue NOTE: After the Transition asphalt base and base/subbase are both positive interfaces Figure 22. Colorized Representation of Radar Data Showing tne Chanqe from Sectior: 2 to Section 3 of Site 5. 46