Correlation of Nuclear Density Results with Core Densities

Transcription

1 TRANSPORTATION RESEARCH RECORD Correlation of Nclear Density Reslts ith Core Densities JAMESL. BURATI,JR.,ANDGEORGEB. ELZOGHBI The paper smmaries the findings of a research effort (a) to determine hether correlation exists beteen the reslts of nclear density gages and core densities obtained in the field and (b) to determine hether the se of nclear density gages in lie of cores is arranted. Data ere collected on to rnay paving projects selected by the FAA Eastern Region sing cores and three nclear gages (CPN M-2, Seaman C-75BP, and Troxler 3411-B). The data ere analyed statistically to identify possible correlations among the nclear gages and beteen the nclear gage readings and the core reslts. The reslts indicated that the level of correlation among the core and gage reslts varied from gage to gage and from project to project. There as a higher degree of correlation among the gages than there as beteen the core densities and the gage reslts. It is recommended that nclear gages not simply be sbstitted for core densities if the acceptance limits have been developed for cores becase the gage reslts do not necessarily correlate ell ith the core reslts. If nclear gages are to be sed for acceptance prposes, then appropriate acceptance limits shold be developed for se ith the gages. Dring 1978, the Federal Aviation Administration (FAA) Eastern Region incorporated a statistically based acceptance plan into its bitminos srface corse specification (P-41). This specification provided for the determination of a price adjstment factor based on the relative acceptability of the pavement materials (J). The acceptance plan alloed the se of either cores or nclear gages for pavement density determination. Hoever, the FAA discontined se of nclear gages for acceptance decisions after preliminary research (2) at the National Aviation Facilities Experiment Center (N AFEC) reslted in a lack of confidence in the consistency and accracy of nclear gages. The limited data from the N AFEC project are not sfficient gronds on hich to base a rejection of nclear gages. A thorogh stdy of nclear gage readings obtained nder field conditions as essential if the FAA as to consider sing nclear gages in its acceptance approach for bitminos pavements. To this end, to constrction sites ere selected on hich to gather nclear gage data. The findings of the research effort on these projects are presented in this paper. The objective of the research as to determine hether nclear density gages shold be introdced in the FAA acceptance procedre. The specific objectives of the research ere Department of Civil Engineering, Clemson University, Clemson, S.C To determine hether correlation exists beteen the reslts of nclear density gages and the core densities obtained in the field, and 2. To determine hether to se nclear density gages in the acceptance plan based on the correlations identified. To meet the otlined objectives, the research as condcted in to major phases. First, field data ere gathered on constrction projects sing three nclear density gages (Troxler 3411-B, Seaman C-75BP, and CPN M-2). Next, these data ere analyed statistically to identify possible correlations beteen nclear gage readings and core densities. DATA COLLECTION Data for the research ere gathered on to constrction projects dring The projects ere selected by the FAA Eastern Region. Data ere to have originally been collected on three projects, bt the Eastern Region as only able to identify to sitable projects for hich data cold be obtained. Type of Data For research prposes on the projects stdied, for cores ere collected for determiningjoint density in addition to the for cores normally drilled for mat density determination. Nclear gage readings ere taken at locations here cores ere drilled to identify hether correlations beteen the nclear gages and the core density reslts exist. These correlations can be sed to determine hether nclear gages can be sed as an alternative to cores for acceptance decisions. Nclear gage readings ere also taken at random locations on the joints and ithin the mat. The ease and speed of the nclear gages alloed a large nmber of locations (approximately 3) to be selected from each paving lot. Data Collection Procedres To projects ere selected by the FAA Eastern Region for the collection of field data. The projects stdied ere the Morriston, Ne Jersey, Mnicipal Airport and the Rochester-Monroe Conty Airport in Rochester, Ne York. Data ere collected on the projects by the research staff sing

2 54 three different gages (Troxler 3411-B, Seaman C-75BP, CPN M-2). The Troxler and CPN gages have Cesim 137 sorces, hereas the Seaman gage has a Radim 226 sorce. While the Troxler and CPN gages both operate in the backscatter mode, the CPN gage has to backscatter modes, BS or AC. The AC mode is sed on thin-lift asphaltic concrete and the BS mode is sed on deeper lifts. The BS mode as sed in the research becase it provided density vales closer to the core reslts. The Seaman gage operates differently from the other gages. It ses the air-gap ratio method. The air-gap ratio method is sed by Seaman to redce the effect of the chemical composition of the mixtre on the gage density readings. Data for each project consisted of the densities of the compacted pavement materials. The compacted materials ere tested on a lot basis, ith a lot consisting of 1 day's prodction, not to exceed 2, tons. Eight cores ere selected for each lot, for for the mat and for for the joints. The random sampling and testing procedres sed on the projects are otlined in the Eastern Region Laboratory Procedres Manal (ERLPM) (4). A standard cont as taken each orking day for each gage. For the Seaman gage, an air-gap reading as taken for each lot. Care as taken to ensre that gages ere firmly seated at each location here readings ere taken. The pavement srface as very dense and smooth; therefore, no filler material as needed to prevent air gaps. Care as taken to ensre that all manfactrers' operating procedres ere folloed for all readings taken. Readings ere obtained ith each of the three nclear density gages at the exact locations here cores ere to be drilled. The nclear readings ere taken immediately before drilling to garantee no change in pavement density beteen the time of the nclear gage readings and the drilling of the cores. Each individal gage reading as the average of to readings, ith the gage rotated 18 degrees prior to taking the second reading. While one gage as being sed, the other gages ere at least 3 ft a ay to ensre that they old not affect the reading being taken. While the joint density readings ere taken, at Morriston the gages ere oriented so that the radiation sorce and the detector ere aligned longitdinally along the joint beteen the pavement sections. On the Rochester project, to joint readings ere obtained for each sample location, one ith the gage parallel to the joint as at Morriston and one ith the gage perpendiclar to the joint. The individal perpendiclar gage readings ere the average of to readings ith the gage rotated 18 degrees beteen readings. The radiation sorce of the gage and detector ere on opposite sides of the joint beteen the pavement sections for each of the to readings. RESULTS OF DENSITY DATA ANALYSIS After collection, the data ere transferred to the compter in preparation for analysis. Separate analyses ere condcted for each project. The Statistical Analysis System (SAS)(J) as sed for both the data management and the analysis. The reslts of the data analysis procedres are presented and TRANSPORTATION RESEARCH RECORD 1126 discssed in this section. The relationships among the nclear gage reslts are considered first. The correlations beteen the nclear gage reslts and the core density vales are then discssed. In the discssions that follo, density readings (core or nclear) taken at coring locations are referred to as acceptance tests. Nclear gage readings taken at locations here cores ere not drilled are referred to as random tests. Nclear Gage Comparisons One of the objectives of the stdy as to investigate ho ell the three different types of nclear density gages correlated ith each other. This correlation as desired to determine ho each gage performed in comparison ith the other gages. An analysis of the performance of each of the gages ith respect to the core density vales is presented in a later section. This section presents the reslts of the correlation analysis of the three gages ith respect to one another. Scatter Plots Plots of the density vales obtained by each of the gages are presented in Figres 1-3 and 4-6 for the Morriston and Rochester projects, respectively. The mat and joint density reslts are distingished in each of the plots by closed and open circles, respectively. The mat density vales are generally higher than the joint reslts for all of the plots. Figres 1, 2, and 3 present plots of CPN verss Troxler, CPN verss Seaman, and Troxler verss Seaman densiiy resils, respectively, for the Morriston project. As shon in the plots in Figres 1-3, there is generally a linear relationship beteen each of the pairise combinations of gages. The vales fall close to a straight line ith relatively little dispersion abot the line. There appears to be more scatter in the joint density reslts than in the mat density vales. This reflects a higher degree of variability in the joint density vales. Plots similar to those in Figres 1-3 are presented in Figres 4-6 for the Rochester project. There is more scatter in the data for Rochester than is fond in the plots for Morriston. The data are more spread ot and the linear relationship seen in Figres 1-3 is less prononced in Figres 4-6. There appears to be mch less correlation beteen the gage reslts in Figres 4-6 than is present in Figres 1-3. The reason for this difference is not knon, bt may be related to differences in the paving mixes and materials for the projects. Hypothesis Testing To frther investigate the data plotted in Figres 1-6, the TTEST procedre in SAS as sed on a pairise basis to test the assmptions of eqal means and variances beteen the reslts of the gages. The possible pairise comparisons inclde (a) CPN ith Troxler, (b) CPN ith Seaman, and (c) Troxler ith Seaman. These comparisons ere made individally for each of the projects, and for both the joint and mat density reslts. The reslts of the hypothesis tests are presented in Tables 1-4. The Morriston reslts are in Tables 1 and 3, hile the Rochester reslts appear in Tables 2 and 4.

3 Brati and Eloghbi ~ >- f- (iii 14 LlJ Cl LlJ Cl 135 <l Cl CD ,,. '"""' -. rs... o ::.-r.:j..t,ffo ~\~o4:::s 9:.~ o ~ : o 8'. 9:1g oo&o o.". ls CD e e o ~~ ~ O O ocffig o o ~ 8:, o oooo 8Ql)~o~o oo o~ o o o <So og SAMPLE STATISTICS: HEAN () STD DEV ( ) HEAN () STD DEV () CPN I 4.1 \ CORRELATION COEFFICIENT (e ) CORRELATION COEFFICIENT (O) TROXLER TROXLER GAGE DENSITY (PCF) FIGURE 1 Plot of CPN verss Troxler gage density reslts for the Morriston project. ~.. LEGEND, e - INDIVIDUAL HAT DENSITY VALUES - INDIVIDUAL JOINT DENSITY VALUES 15 ~~ ~ r. - :'I... -~. 145 ~ -. >- ~ a.~ f- 14 iii LlJ Cl o 8 oooo8i cwo LlJ 135 ~ oca,g o Cl OOOO~J'8 o 9c<!. otffi 8 S o taa, SAMPLE STATISTICS CPN SEAMAN.. 13 MEAN (e ) I STD DEV (e ) gn HEAN () ' 125 STD DEV () CORRELATION COEFFICIENT (e ) 82 CORRELATION COEFFICIENT () & SEAMAN GAGE DENSITY (PCF) FIGURE 2 Plot of CPN verss Seaman gage density reslts for the Morriston project. Visal inspection of the statistics in Tables 1 and 2 identifies a trend in the relative magnitdes of the mat density means of the three gages. On both projects, the Seaman gage prodced the largest mean vale, folloed by the Troxler and then the CPN gages. If the t-statistics are considered, the Seaman mean at Morriston is not significantly different from the Troxler mean at the.11 level of significance. There is little consistency in the standard deviation vales for the mat density reslts. The Seaman gage had the largest (.1 level of significance) standard deviation for Morriston, bt had the smallest (.16 level of significance) standard deviation for Rochester. The hypothesis test reslts for joint density are presented in Tables 3 and 4. As ith the mat density reslts, the CPN gage had the loest mean (.1 level of significance). The Seaman mean as larger than the Troxler mean at the.3 significance level. On the Rochester project there ere no significant differences among the standard deviations for the

4 56... il. >- I- <ii (!) <f 13!i (!) Cl'....J x 13 Cl'. I FIGURE 3 - LEGEND: e - INDI\'1L 1 1\L ~l,\t DENSin' VALUES () - l ND I \'1 D~AL JOI NT DENS l T\' \'ALUES ~ o..-..., a ~- -. :.~r:.~,. «r..lit::, ~.o o 125 ooch~~-og, oog ~ o o o OO 'f?ov~ o Q o'?l o oo<no~~g> -o~o ~ o o SAMPLE STATISTICS: MEAN ( ) STD DEV ( ) MEAN () STn OF.V () TRANSPORTATION RESEARCH RECORD TROXLER 148. l 4. I 38. I SEAMAN GAGE DENSITY (PCF) SEAMAN I CORRELATION COEFFICIENT C l. 85 CORRELATION COEFFICIENT () 89 Plot of Troxler verss Seaman gage density reslts for the Morriston project il >- I- ; "' <.::> <f <.::> 138 il LEGEND: - I ND IV lduai. MAT DENS I TY VALUES - INDIVIDUAi. JOINT DENSITY VALUES MEAN (e ) STD DEV ( ) MEAN () STD DEV \) CPN CORRELATION CO EFFlCIENT ( ) CORRELATION COEFFICIENT () TROXLF.R I TROXLER GAGE DENSITY (PCF) FIGURE 4 Plot of CPN verss Troxler gage density reslts for the Rochester project. gages. For Morriston, the Seaman standard deviation as larger than the Troxler vale at the.4 significance level, bt as not significantly larger than the CPN vale at the.11 significance level. It is not possible to establish trends ith only to projects. Hoever, it can be conclded from Tables 1-4 that the three gages ill not alays prodce the same mean reslts, and that the variability may differ from gage to gage. Correlation Analysis Becase all three gages ere sed to obtain density vales at each location, it is possible to correlate the individal vales on a pairise basis beteen the gages. Tables 5 and 6 present the reslts of the correlation analysis. Table 5 presents the correlation coefficients for mat and joint density for each

5 Brali and Eloghbi SA."'IPLE sratlsrlcs : CPN ~EAN ( l STO Of.V ( e ) ) 7!-1F.AN () l41. 8 STD DEV () 4. CORRELA T lon COEFF I CIENT C l CORRELATION CUfff" 1 C l>:n r () SEA."lAN I ) I )9.19 LL >- I- Vi '-' <t '-' LEGEND: - INDIVTDUAL MAT DENSITY VALUES - INDIVIDUAL JO I NT DENSI TY VALUES " SEAMAN GAGE DENSITY (PCF) FIGURE S Plot of CPN verss Seaman gage density reslts for the Rochester project. LL.. >- I- Cii '-' Cl '-' a:...j x ~ LEGEND - INDIV I DUAL ~ I AT DENSITY VALU ES I ND f V IDUAL JOI NT DENS I TY VALUES i cm 8. ~ SAHPLF. STATISTICS: MEAN ( e ) STD DE V ( e ) MEAN () STD DEV () TROX LF.R I CORRELATION COEFFICIENT (e ) CORRELATION COEFFIC I EN T () SEAHAN I ) I.6 ) SEAMAN GAGE 145 DENSITY (PCF) FIGURE 6 Plot of Troxler verss Seaman gage density reslts for the Rochester project. gage combination for the Morriston project. Table 6 presents similar reslts for Rochester. The correlation coefficients among the gage combinations are similar for each project hen considered individally. Hoever, the coefficients for Morriston are consistently larger than the ones at Rochester. For Morriston, the mat density coefficients are.81,.82, and.85 for the CPN- Troxler, CPN-Seaman, and Troxler-Seaman comparisons, respectively. For Rochester, the coefficients are.58,.59, and.6 for the same comparisons. Similar reslts are exhibited for the joint density correlations. The joint density correlations for Rochester are not as niform as the joint density reslts for Morriston. They are, hoever, still consistently loer than the Morriston joint density reslts.

6 TABLE I RES UL TS F PAIR WISE HYPOTHESIS TESTS ON NU CLEAR GAU GE MAT DENSITY RESULTS FOR THE MORRISTOWN PROJECT Gage No. Mean Std. Dev. F-Statistic (Prob > F)* t-statistic (Prob>ltl)# CPN Troxler Seaman CPN (.711) (. 42) (.95) (.1) (.115) (. 1) * - probability of obtaining an F vale as large as the one shon if the variances are actally eqal # - probability of obtaining a t vale as large as the one shon if the means are actally eqal TABLE 2 RESULTS OF PAIRWISE HYPOTHESIS TESTS ON NUCLEAR GAUGE MAT DENSITY RES UL TS FOR THE ROCHESTER PROJECT Gage No. Mean Std. Dev. F-Statistic (Prob > F)* t-statistic (Prob>ltl)# CPN Troxler Seaman CPN (.53) (. 169) (.1) (.1) 7.38 (.1) (.1) * - probability of obtaining an F vale as large as the one shon if the variances are actally eqal # - probability of obtaining a t vale as large as the one shon if the means are actally eqal TABLE 3 RESULTS OF PAIRWISE HYPOTHESIS TESTS ON NUCLEAR GAUGE JOINT DENSITY RESULTS FOR THE MORRISTOWN PROJECT No. Mean Std. Dev. F-Statistic t-statistic CPN Troxler Seaman CPN * (.621) (.2) (.4) (.437) (.118) ( 8) - probability of obtaining an F vale as large as the one shon if the variances are actally eqal # - probability of obtaining a t vale as large as the one shon if the means are actaly eqal

7 Brati and Eloghbi 59 TABLE 4 RESULTS OF PAIRWISE HYPOTHESIS TESTS ON NUCLEAR GAUGE JOINT DENSITY RES UL TS FOR THE ROCHESTER PROJECT Gage No. Mean Std. Dev. F-Statistic t-statistic CPN Troxler Seaman CPN (.418) (.1) (.994) (. 31) (.422) (.1) * - probability of obtaining an F vale as large as the one shon if the variances are actally eqal # - probability of obtaining a t vale as large as the one shon if the means are actally eqal TABLE 5 CORRELATION COEFFICIENTS BETWEEN NUCLEAR GAUGES FOR MAT AND JOINT DENSITIES ON THE MORRISTOWN PROJECT (192 OBSERVA TIONS) Type CPN Troxler Seaman CPN Mat Joint.9.87 Troxler Mat Joint.9.89 Seaman Mat Joint NOTE - the probability that any individal coefficient in the table old be obtained if the tre correlation is ero is 1 It appears that the gages correlate eqally ell ith one another, bt that the level of correlation may vary from one project to the next. Gage Verss Core Comparisons If nclear density gages are to be considered for se in acceptance decisions, it is desirable to investigate ho ell their reslts compare ith the method that is crrently sed for this prpose, that is, the se of core densities. The core and nclear density reslts on each of the projects ere analyed to determine ho ell the gage reslts correlated ith the core densities. Scatter Plots Plots of the density reslts for each gage verss the core density reslts are presented in Figres 7-9 for Morriston and Figres 1-12 for Rochester. The mat and joint density reslts are distingished in each of the plots by closed and open circles, respectively. Figres 7, 8, and 9 present plots of the CPN, Troxler, and Seaman reslts, respectively, against the corresponding core densities. The data in Figres 7-9 are more scattered than the corresponding plots for each of the nclear gage reslts against each other gage that are presented in Figres 1-3. The linear relationships beteen the gages in Figre 1-3 are not apparent in the gage verss core plots (Figres 7-9) becase of the increased spread among the data vales. It

8 6 TR ANSPOR TATION RESEARCH RECORD 1126 TABLE 6 CORRELATION COEFFICIENTS BETWEEN NUCLEAR GAUGES FOR MAT AND JOINT DENSITIES ON THE ROCHESTER PROJECT(27 OBSERVATIONS) Type CPN Troxler Seaman CPN Mat Joint Troxler Mat.58.6 Joint Seaman Mat.59.6 Joint NOTE - the probability that any individal coefficient in the table old be obtained if the tre correlation is ero is.1 " a.. 16,.. 15 t:: () a:: """ 138 SAMPLE STATISTICS : CORE MF.AN < l S rn DEV < l 3. '.'iean (Q) STO DEV () 3,q CORRELATION C FFlClENT (e ) CORRELATION COl::Ff'ICLF.NT () CPN I 4. I 136. s 5, q 49 JS oe.. o ~... ~ o...-.<i o o LEGEND 1 e - INDIVIDUAL ~lat DENSITY VA LUES o.-- MAT DENS I TY REGRESSION LINE - lndlvidual JOINT DENSITY VA LUES JOINT DENSITY REGRESSION LINE CPN GAGE DENSITY ( PCF) FIGURE 7 Plot of Joint and mat density regression lines for core density verss CPN gage density for the Morriston project. appears that there is a mch higher degree of correlation beteen the gages than there is beteen the gages and the core densities. Plots similar to those in Figres 7-9 are presented for the Rochester project in Figres The plots for the Rochester data appear to be even more scattered than those for Morriston. Hypothesis Testing To frther investigate the relationships beteen the gage densities and the core reslts, the TTEST procedre as sed to test the hypotheses that the means and variances of each of the gages ere eqal to the core vales. F-statistics and t-statistics ere determined individally for the mat and joint density reslts for each gage for each project. The reslts of the hypothesis tests are presented in Tables 7-1. The Morriston reslts appear in Tables 7 and 9. The Rochester reslts are in Tables 8 and I. The mat density reslts for the projects are presented in Tables 7 and 8 for Morriston and Rochester, respectively. For both Morriston and Rochester, for each of the three gages both the means and variances are statistically significantly different from the core reslts at the.3 level of significance. These reslts, along ith visal inspection of the plots, indicate that the nclear gages provide loer mat density vales than are obtained from cores. It also appears that for mat density the nclear gage reslts are slightly more variable than the core reslts. The hypothesis test reslts for joint density are presented in Tables 9 and 1 for the Morriston and Rochester projects, respectively. For Morriston (Table 9), all of the gages

9 Brati and Eloghbi SAMPLE STATISTICS: CORE MEAN ( > s ro DEV (e ) 3.o TROXLF.R HEAN () STD DEV () J 5. 7 G:' a.. CORRELATION COEFFICIENT (e ) CORRELATION COEFF!ClENT (O) '66.44 >- 15 t: Vl UJ a UJ Ir...og.,,.oo,...,9,.,,..,,.. LEGEND: e - INDIVIDUAL MAT DENSITY VALUES - INDIVIDUAL JOINT DENSITY VALUES 14 MAT DENSITY REGRESSION LINE JOINT DENSITY REGRESSION LINE TROXLER GAGE DENSITY (PCF) FIGURE 8 Plot of joint and mat density regression lines for core density verss Troxler gage density for the Morriston project ;;:- a.. 16 SA.~PLE STATISTICS: CORE SEAMAN MEAN ( e ) STD DEV ( e ) 3.o 4. 6 MEAN () 14~ STD DEV (), CURRF.1.AT!ON CUEFFlClENT (e ). 59 CORRf.1.ATION COEFFICIENT (O). 52 >- 15 t: Vl UJ a UJ ~ INDIVIDUAL MAT DENSITY VALUES - INDIVIDUAL JOTNT DENSITY VALUES 14 MAT DENSITY REGRESSlON LINE 138 JOTNT DENSlTY REGRESSION LINE 12D SEAMAN GAGE DENSITY (PCF) FIGURE 9 Plot of joint and mat density regression lines for core density verss Seaman gage density for the Morriston project. provided statistically significantly loer mean vales (.1 level) and higher variance vales (.1 level) than the core joint density reslts. This trend as not fond in the Rochester data. For Rochester, the CPN and Seaman mean joint density vales ere significantly different at the.22 level than the core mean. The CPN mean as smaller than the core mean, hereas the Seaman mean vale as larger than the core mean vale. The Troxler mean vale as not significantly different from the core mean vale at the.44 level. On the Morriston project, the nclear gage joint density readings ere obtained ith the gages oriented parallel to the joints. On the Rochester project, to nclear gage joint density readings ere taken at each location ith each gage, one ith the gage parallel to the joints and one ith the gage perpendiclar to the joints. Table IO presents the reslts for the readings taken ith the gages perpendiclar to the joints. To investigate hether the Rochester joint nclear gage reslts ere closer to the core reslts becase of the different

10 62 TRA NSPORTA TION RESEARCH RECORD : a.. >- >-- iii a:!3 125 LEGEND: - INDIVIDUAL MAT DENSITY VALUES - lndivldual JOINT DENSITY VALUES MAT DENSITY REGRESSION LINE JOINT DENSITY REGRESSION LINE SAMPLE STATISTICS: MEAN (e ) STD DEV (e ) CORE I MEAN () STD DEV () 4. 1 CORRELATION COE,.ICIENT ( e ) CORRELATION COEFFlGIENT () CPN 146. ) J I J CPN GAGE DENSITY ( PCF l FIG URE l Plot of joint and mat density regression lines for core density verss CPN gage density for the Rochester project. 15 SMPLE STAT\ST!CS: CORE MF.AN < > I SD. 7 STD DEV (e ) 2. I MEAN () 14 J. J S rd DEV () 4. J TROXLEK J.2 14] I ll a.. >- >-- iii a: COKRELATlON COUFICIENT ( e ) COKKF.LATION COEFFICIENT () LEGEND : - INDIVIDUAL MAT DENSITY VALUES - INDIVIDUAL JOINT DENSITY VALUES MAT DENSITY REGRESSION LINE JOINT DENSITY REGRESSION LINE TROXLER GAGE DENSITY ( PCF) FIGURE 11 Plot of joint and mat density regression lines for core density verss Troxler gage density for the Rochester project. orientation of the gages hile readings ere taken, an analysis of gage readings taken parallel to the joints on the Rochester project as also condcted. The reslts of this analysis are presented in Table 11. As can be seen in this table, for each of the gages the readings taken perpendiclar to the joints ere higher than those taken parallel to the joints. Becase the core vales ere higher than the gage reslts, it old appear that the perpendiclar gage orientation provides reslts that are closer to the core densities. Regression Analysis To investigate the relationships beteen each of the gages and the core densities, regression analyses ere condcted on the data. Linear regression analyses ere condcted on the data from each project and for each gage individally. The analyses ere performed to determine ho ell each gage predicted the core density reslts. The reslts of the regression analyses are presented in Tables Tables 12 and 13

11 Brati and Eloghbi SAMPLE STATISTICS: MEAN (e ) STD DEV (e ) MEAN ( ) STD DE V ( ) CORE SE AMAN l so. 7 l so.o 2. l ) 4. J l ;:;: >- 14 f- en ~ Cl 135 ~ CORRELATION COEFFICIENT ( e ) CORRELATION COEFFICIENT ().12.4 co LEGEND' e - INDIVIDUAL MAT DENSITY VALUES - INDIVIDUAL JOINT DENSlTY VALUES MAT DENSITY REGRESSION LINE JOI NT DENS!TY REGRESS ION LI NE SEAMAN GAGE DENSITY ( PCF) FIGURE 12 Plot of joint and mat density regression lines for core density verss Seaman gage density for the Rochester project. TABLE 7 RESULTS OF HYPOTHESIS TESTS FOR PAIRWISE COMPARISONS BETWEEN CORE AND NUCLEAR GAUGE MAT DENSITY RESULTS FOR THE MORRISTOWN PROJECT Sorce No. Mean Std. Dev. F-Statistic t-stati stic (Prob > F)* (Prob > lt l )# Core CPN (. 3) (.1) Troxler (. 4 7) (.1) Seaman (. 3) (.2) * - probability of obtaining an F vale as large as the one shon if the variances ar e actally eqal # - Probability of obtaining a t v a le as large as the one shon if the means are actally eqal present the mat density reslts for the Morriston and Rochester projects, respectively. The joint density reslts appear in Tables 14 and 15. The tables present the regression eqations sing each of the gage reslts as the independent variable and the core density reslts as the dependent variable. The slopes and intercepts for the regression lines are presented along ith the t-statistic for testing the hypothesis that the vales (slope and intercept) are eqal to ero. The R 2 vales presented in the tables are measres of ho ell the variation of the dependent variable is described by the variation in the independent variable. As can be seen in Table 13, the R 2 vales for mat density for Rochester are mch smaller than the vales in Tables 12, 14, and 15. The small R 2 vales presented in Table 13 are the reslt of the greater variability for the mat density data. at Rochester. To illstrate the spread in the data and the relationships of the regression eqations to the data, Figres 7-12 sho plots of the regression eqations for each gage for each project ith the mat and joint density vales also shon. Figres 7-9 sho the Morriston reslts, and Figres 1-12 sho the reslts from Rochester. There is no consistency beteen the projects ith respect to the plots. For Morriston, the mat density regression lines have steeper slopes than the correspondingjoint density lines.

12 TABLE 8 RESULTS OF HYPOTHESIS TESTS FOR PAIRWISE COMPARISONS BETWEEN CORE AND NUCLEAR GAUGE MAT DENSITY RESULTS FOR THE ROCHESTER PROJECT Sorce No. Mean Std. Dev. F-Stat-istic t-statistic (Prob > F)* (Prob > ltl)# Core CPN (.1) (.1) Troxler (.1) (.1) Seaman (.2) (. 3) * - probability of obtaining an F vale as large as the one shon if the variances are actally eqal # - probability of obtaining a t vale as lar g e as the one shon if the means are actally eqal TABLE 9 RESULTS OF HYPOTHESIS TESTS FOR PAIRWISE COMPARISONS BETWEEN CORE AND NUCLEAR GAUGE JOINT DENSITY RESULTS FOR THE MORRISTOWN PROJECT (PARALLEL) Sorce No. Mean Std. Dev. Core CPN Troxler F-Statist ic (Prob > F)* 2.29 (.3) 2.13 (. 6) t-statistic (Prob > I ti)# (.1) 9.33 (.1) Seaman (.2) 9.49 (.1) * - probability of obtaining an F vale as large as the one shon if the variances are actally eqal # - Probability of obtaining a t vale as large as the one shon if the means are actally eqal TABLE 1 RESULTS OF HYPOTHESIS TESTS FOR PAIRWISE COMPARISONS BETWEEN CORE AND NUCLEAR GAUG E JOINT DF:NSJTY RESULTS FOR THE ROCHESTER PROJECT (PERPENDICULAR) Sorce No. Mean Std. Dev. F-Statistic t-statistic (Prob > F)* (Prob > \t\)# Core CPN (.411) (.13) Troxler (.638) (.448) Seaman (.642) (.22) * - probability of obtaining an F vale as large as the one shon if the variances are actally eqal # - probability of obtaining a t vale as large as the one shon if the means are actally eqal

13 TABLE 11 RESULTS OF HYPOTHESIS TESTS ON PERPENDICULAR AND PARALLEL GAUGE ORIENTATIONS FOR JOINT DENSITY READINGS FOR ROCHESTER PROJECT (72 OBSERVATIONS FOR EACH ORIENTATION) Gage Perpendiclar Parallel F-Statistic t-statistic Mean Mean (Prob > F)* (Prob > ltj)# (Std Dev) (Std Dev) CPN ( 4. 6) (S.O) ( 489) (. 1) Troxler (4.S) (S.O) (.367) (.1) Seaman S S (4.6) (S.4) (.174) (. 9) * - probability of obtaining an F vale as large as the one shon if the variances are actally eqal # - probability of obtaining a t vale as large as the one shon if the means are actally eqal TABLEl2 RESULTS OF REGRESSION ANALYSIS ON GAUGE AND CORE MAT DENSITY RESULTS FOR THE MORRISTOWN PROJECT (4 OBSERVATIONS) Gage Slope t-statistic Intercept t-statistic R-Sqare (Prob> It I)* (Prob>ltl)* CPN a.sos (.1) (.1) Troxler S (.1) (.1) Seaman O.S S.7 O. S94 (.1) (.1) * - probability of obtaining a t vale as large as the one shon if the tre slope or interest is actally ero TABLE 13 RESULTS OF REGRESSION ANALYSIS ON GAUGEANDCOREMATDENSITY RESULTS FOR THE ROCHESTER PROJECT (72 OBSERVATIONS) Gage Slope t-statistic (Prob>ltl)* Intercept t-statistic (Prob>ltl)* R-Sqare CPN (.11) (.1) Troxler S.81 (.87) (.1) Seaman (.17) (.1) * - probability of obtaining a t vale as large as the one shon if the tre slope or intercept is actally ero

14 66 TRANSPORTATION RESEARCH RECORD 1126 TABLE 14 RESULTS OF REGRESSION ANALYSIS ON GAUGE AND CORE JOINT DENSITY RESULTS FOR THE MORRISTOWN PROJECT (4 OBSERVATIONS) Gage Slope t-statistic Intercept t-statistic R-Sqare (Prob>\t\)* (Prob>\t\)* CPN (.1) (.1) Troxler (.1) (.1) Seaman (.1) (.1) * - probability of obtaining a t vale as large as the one shon if the tre slope or interest is actally ero TABLE 15 RESULTS OF REGRESSION ANALYSIS ON GAUGE AND CORE JOINT DENSITY RESULTS FOR THE ROCHESTER PROJECT (72 OBSERVATIONS) Gage Slope t-statistic (Prob>\t\)* Intercept t-statistic R-Sqare (Prob>\t\)* CPN (.1) 1.1 (.1) 6.9 (.1) (.1) (.8) (.69) Troxler Seaman, * - probability of obtaining a t vale as large as the one shon if the tre slope or intercept is actally ero The opposite is tre for Rochester here the mat density regression lines have shallo slopes. These shallo slopes are indicative of little relationship beteen the gage densities and the core densities. Use of Nclear Gages for Acceptance Before the se of nclear gages is considered for acceptance decisions, it shold be noted that any conclsions and discssions presented in this paper can apply only to the gages sed in this stdy. They can not necessarily be applied to a particlar manfactrer's gages in general becase there is bond to be some degree of variability among the gages prodced even by a single gage manfactrer. The reslts of this research have shon that the readings of the three gages can be significantly different statistically from one another and also from the core reslts. Frthermore, it as fond that there is no consistency ith respect to ho the gages ill perform ith respect to one another from one project to the next. If the intent of sing nclear gages is to provide an estimate for, or to correlate ith, the core reslts, then the findings of this research do not spport the se of nclear gages for acceptance decisions. The se of nclear gages in lie of coring, bt ith the same acceptance limits that ere developed based on core reslts, is not appropriate. The se of nclear gages, hoever, has some distinct advantages over the se of cores. These advantages are related to the nmber of tests that can be condcted nondestrctively ith the nclear gages in a short period of time. Sch advantages allo for a large nmber of acceptance tests at random locations that can more thoroghly sample the total area of the paving lot. The nclear gages allo the acceptability of the lot to be determined ithot having to ait for the cores to be transported to the laboratory and tested. This continos feedback aspect of nclear gages has led to their poplarity as qality control devices by paving contractors. Becase it as fond by this research that the nclear gages did not consistently correlate ith the core reslts from project to project and for mat and joint densities, it is important that a test strip be sed if nclear gages are to be considered for acceptance. The particlar gage that ill be sed on the project can be sed on the test strip to determine the maximm density that is attained on the test strip. This approach of sing the same gage that ill be sed on the project on a test strip that is constrcted ith the same mix

15 Brati and Eloghbi and materials that ill be sed on the project shold eliminate some of the variability that as fond among the projects stdied in the crrent research. RESEARCH FINDINGS The major findings of the research effort to investigate the se of nclear density gages for acceptance prposes are as follos: 1. Statistically significant differences ere fond in the nclear gage reslts for both projects stdied. Both the means and variances ere fond to differ significantly among the gages on both projects, bt the differences in the means ere more prononced. 2. In all cases for both projects the gage reslts had statistically significantly loer mat mean density vales than the core mean vale. The same general trend as also fond in the joint reslts ith the exception of the Seaman gage at Rochester that as significantly larger than the core joint vales. 3. When nclear gages ere sed for determining joint density, it as fond that orienting the gage perpendiclar rather than parallel to the joint provided reslts that ere closer to the joint core density vales. 4. Regression analyses indicated that the predictive ability of the nclear gages ith respect to the core reslts varied from project to project. For Morriston, mat density regression eqations yielded R 2 vales of.493,.655, and.594 for the CPN, Troxler, and Seaman gages, respectively. The corresponding R 2 vales for mat density on the Rochester project ere.13,.81, and Use of nclear gages shold not simply be sbstitted into crrent acceptance plans in place of cores if the crrent acceptance limits and procedres ere developed from historical core data. This shold not rle ot the development of acceptance procedres specifically for nclear gages to take advantage of the large sample sies and rapid reslts that are possible ith nclear gages. ACKNOWLEDGMENT The research and field ork reported herein ere spported by the FAA. REFERENCES I. J. L. Brati and J. H. Willenbrock. Acceptance Criteria for Bitminos Corses on Civil Airport Pavements. Final Report, FAA, U.S. Department of Transportation, R. J. Warner. Bitminos Pavement Testing With Nclear Gages. Proc., FAA Airport Engineering, Environmental Protection Reqirements, and Aircraft Disaster Conference, Hershey, Pa., March SAS User's Gide: Basics, 1982 Edition. SAS Institte, Inc., Cary, N.C., Laboratory Procedres Manal. FAA Eastern Region, U.S. Department of Transportation, Ne York Pblication of this paper sponsored by Committee on Flexible Pavement Constrction and Rehabilitation. 67