4450 West Eau Gallie Boulevard, Melbourne, FL 32934. Corresponding author: P. J. Cosentino, cosentin@fit.edu. Transportation Research Record: Journal of ...
Evaluating Laboratory Compaction Techniques of Reclaimed Asphalt Pavement Paul J. Cosentino, Albert M. Bleakley, Amir M. Sajjadi, and Andrew J. Petersen Reclaimed asphalt pavement (RAP) is a byproduct of roadway resurfacing. A limited amount of RAP can be recycled into new hot-mix asphalt; the rest is stockpiled. Some states allow the use of RAP-aggregate blends as base course material. Because of RAP's low strength and susceptibility to creep deformation, the Florida Department of Transportation (DOT) excludes RAP from being used as pavement base course for high-traffic areas. The research objective was to determine whether the strength characteristics of RAP could be improved through compaction and thereby make its base suitable in high-traffic areas. Modified Proctor, vibratory, and gyratory compaction data were compared. Four RAP sources were used. Specimens compacted by the three methods were tested with the limerock bearing ratio (LBR), unconfined compressive strength, a nd indirect split tensile strength. LBR is Florida 's variation of the California bearing ratio. Specimens were compacted to either a density or a compaction energy level. Vibratory compaction produced the lowest densities and strengths. Modified Proctor produced higher densities and strengths than vibratory, but the LBR strengths for all RAP types were consistently below Florida DOT standards. Gyratory compaction produced the highest de nsities and strengths. Gyratory RAP specimens were two to four times as strong as modified Proctor specimens at the same density. The compaction method did not have as significant an effect on creep, although gyratory-compacted samples produced less creep than modified Proctor-compacted samples.
OBJECTIVE The o bjective of this research was to evaluate the modified Proctor, vibratory, and gyratory compaction effects on RAP through strength and one-dimensional creep testing. RAP, limerock, cemented coquina, and clayey sand were used along with 50:50 RAP- limerock blends. Limerock served as the control material.
LITERATURE REVIEW RAP, which is not reused on site, is typically transported to asphalt pl ants, where it is crushed and stockpiled. Crushing produces a more uniform product. RAP that is not crushed is termed "milled RAP," differentiating it from crushed RAP. Sandin (2) performed a statewide variability evaluation of Florida RAP and determined that the average statewide asphalt content of crushed RAP was lower than that of milled RAP. Montemayor (3) conducted Proctor compaction tests on RAP, finding that it did not produce well-defined maximum-density curves. Montemayor concluded that specifying density as a percentage of the modified Proctor maximum density might not be realistic for RAP. Cosentino and Kalaj ian (4) subjected RAP to static pressures of 2 12,400,700, and 1,000 psi (1,484, 2,800, 4,900, and 7,000 kPa) and found that densities increased approximately 4% per loadi ng interval, while LBR increased significan tly with each interval. The densities achieved were higher than those achieved with modified Proctor. Gyratory compaction (ASTM 06925), used in asphalt mix design, has also been used on various soils. Gyratory compaction of Florida base and subbase soils produced dry unit weights closer to those from field compaction than did either modified Proctor or vibratory compaction methods. Gyratory compaction is most sensitive to the number of gyrations (5- 7), less sensitive to the gyration rate, and no t affected by the gyration angle (5, 6).
Pavement milling produces reclaimed asphalt pavement (RAP), a portion of which can be recycled directly into new hot-mix pavement. The remaining portion, often hauled off site and stockpiled, is available for other highway uses. Although RAP, a granular material, possesses good drainage characteristics and adequate shear strength, it has low bearing strength and under constant stress produces excessive creep. The Florida Department of Transportation (DOT) bases bearing strength on the limerock bearing ratio (LBR). which is cond ucted in accordance with Florida Method 5-515 (1). The LBR, found by dividing the stress at 0.1-in. (2.54-mm) deflection by 800 psi (5,600 kPa), produces values that are 25% higher than California bearing ratios.
RAP AND AGGREGATE SOURCES Four milled and crushed RAP stockpiles were sampled from three asphalt plants. APAC Florida plants in Jacksonville and Melbourne, plus theY. E. Whitehurst and Sons plant in Gainesville, Florida, were sampled. Both crushed and mi lied RAP were obtained from the APAC Melbourne facility, while only crushed RAP was obtained from the APAC Jacksonville plant and milled RAP from the Whitehurst plant. These sources were referred to as Melbourne milled, Melbourne crushed, Jacksonville crushed, and Whitehurst milled.
P. J. Cosentino. A. M. Bleakley, and A. M. Sajjadi, Florida Institute of Technology, Melbourne, FL 32901 . A. J. Petersen, Creech Engineers, Inc., Suite 232, 4450 West Eau Gallie Boulevard , Melbourne, FL 32934. Corresponding author: P. J. Cosentino, cosentin@fit .edu .
Transportation Research Record: Journal of the Transportation Research Board, No. 2335. Transportation Research Board of the Nat ional Academies, Washington, 0 C., 2013. pp. 89- 98. DOl: 10.3141/2335-10
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The four RAP sources were compared with limerock, cemented coquina, and clayey sand. The limerock and cemented coquina were obtained from Florida DOT- approved base course sources because RAP was being evaluated for potential use as base material (8).
COMPACTION METHODS The gyratory compaction machine could be set for either compactive effort (number of gyrations) or density (sample height). Therefore, modified Proctor specimens were made first and then gyratory specimens were made to match the modified Proctor densities. Regardless of vibration time, vibratory compaction produced densities below those for modified Proctor and gyratory compaction methods and therefore could not be matched.
STRENGTH AND CREEP TESTING Strength testing included LBR, unconfined compression (UCC), and indirect tensile (IDT) testing. Creep testing was performed with one-dimensional confined and unconfined creep tests conducted at a constant stress of 12 psi (84 kPa). Similar-size samples were produced from all three compaction devices. Samples obtained from LBR testing were 6.00 in. (152.4 mm) in diameter and 4.58 in. ( 116.4 mm) high, which is the size of the LBR mold. Samples from gyratory compaction were 5.91 in. (150.00 mm) in diameter, and samples from vibratory compaction were 6.00 in. (152.4 mm) in diameter; however, their sample heights varied. LBR specimens were not soaked to enable direct comparisons between specimens from all compaction methods. The gyratory and vibratory molds do not allow soaking. UCC and IDT tests were conducted on ejected modified Proctor and gyratory specimens to eliminate mold-geometry effects. Unconfined creep tests were performed to investigate the creep of ejected modified Proctor and gyratory specimens. Because of the geometry of the vibratory mold, it was not possible to eject or test vibratory specimens.
DENSITY RESULTS
Modified Proctor Test Modified Proctor moisture-density relationships from the four RAP stockpiles based on third-order polynomials are shown in Figure 1. Cohesionless granular soils produce an "S-curve" moisture-density relationship that typically yielded high densities at both low- and high-moisture contents (9). Three of the four RAP sources produced this S-curve. RAP sampled from APAC Jacksonville followed the typical moisture-density parabola because of the higher percentage of material passing the No. 200 sieve. The highest densities were produced by the APAC Jacksonville crushed RAP, which had a specific gravity (G, ) of 2.604 and the highest percentage fines (7%); the second highest were from the Whitehurst RAP, with a G, of 2.576, while the APAC Melbourne crushed G, was 2.508 and milled G, was 2.524. The higher crushed densities of the Melbourne RAP were probably the result of higher fines content.
Gyratory Test Moisture-density relationships at 75 gyrations are presented in Figure 2. RAP was tested at target moisture contents of 3%, 6%, and 9% to determine whether moisture content had an effect on gyratory compaction. Moisture contents below 9% were used to prevent excess water from leaking into the gyratory compactor. From the results (Figure 2), one can see that three of the four samples showed peak dry densities. Whitehurst milled RAP did not. Polynomial fits were placed through each set of data. The polynomial-fit peak density for Melbourne crushed RAP occurred at 5.1%; for Melbourne milled RAP, near 6.1%; and for APAC; Jacksonville RAP, near 4.6%. The large differences in Melbourne milled RAP densities- from 3% to 5.5% moisture-were attributed to sample variability because these materials were obtained at different times. Peak densities ranged from near 122 and 126Jb/fe (19.1 and 19.7 kN/m 3) for all four sources.
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Dry density versus moisture content for gyratory compaction of RAP .
Vibratory Tests
ing three samples initially decrease in density as moisture content increases and then increase as moisture content increases above 4.0%. The second-order polynomial trend lines shown in the figure yielded the highest regressions. Crushed RAP produced higher densities at higher moisture contents than milled RAP. Similar to the modified Proctor results, the vibratory-test results on APAC Jacksonville crushed, with the highest specific gravity and percentage of fines, produced the highest densities.
Vibratory compaction tests were conducted in accordance with ASTM D4253. They did not produce well-defined optimum moisture contents. Moisture-density plots (Figure 3) show that three of the four materials produced peak densities through linear and secondorder polynomial fits, at extremely high moisture contents, while the Whitehurst milled RAP produced a curve similar to the modified curves. Moisture contents higher than 9% could not be produced with the vibratory equipment because water vibrated out of the mold during compaction. The vibratory compaction correlations (Figure 3) between dry density and moisture content were inconclusive and varied by source. Whitehurst milled RAP appears to show a conventional relationship in which dry density peaks at approximately 111.0 lb/fe (17.4 kN/m3) at an optimum moisture content of 4.0%. The remain-
RESULTS OF STRENGTH TESTING: LBR TESTS After the modified Proctor, vibratory, and gyratory compaction testing, unsoaked LBR tests were conducted on 116 samples from all four RAP stockpiles. Unsoaked tests, which would produce higher
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Unsoaked LBR versus dry density for modified Proctor compaction.
LBRs than soaked tests, were conducted because the vibratory and gyratory mold geometries prevented soaking.
Error typically associated with sample variation and LBR testing most likely produced the large scatter.
Modified Proctor-LBR Correlation
Vibratory-LBR Correlation
Unsoaked LBR from the modified Proctor compaction test are presented as LBR versus dry density in Figure 4. Of the 32 tests, nine were with Melbourne crushed, eight with Melbourne milled, seven with Whitehurst milled, and eight with Jacksonville crushed RAP. Unsoaked LBR values rose as dry density increased. The general trend among all data points indicated a linear relationship, which produced a regression coefficient of .57. LBR increased 0.58 for each 1lb/ft3 (0. 157 kN/m 3) increase in dry density. The highest unsoaked LBR of24 from the modified Proctor was well below Florida DOT's specified LBR of 100 for base course or of 40 for subbase material.
The LBR values obtained from vibratory compaction are presented as LBR versus dry density in Figure 5. The vibratory LBRs were all well below the Florida DOT- specified subbase LBR of 40. Of the 32 tests, 10 were with Melbourne crushed, seven with Melbourne milled, eight with Whitehurst milled, and seven with Jacksonvi lle crushed RAP. For the vibratory compaction method , LBR values increased slightly as dry density increased. The general trend from all points indicated a weak linear relationship with a regression coefficient of 0.1 7. LBR increased 0.24 for each 1 lbtfe (0.157 kN/m3) increase in dry density, which is less than half the rate obtained from the modified Proctor.
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Unsoaked LBR versus dry density for vibratory compaction.
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Unsoaked LBR versus dry density for gyratory compaction.
Gyratory- LBR Corre lation
inftuence on LBR. LBR increased linearly 0.4 1 per gyration, with a strong positive linear correlation coefficient of .70. Two outliers, one at I00 gyrations and o ne at ISO gyrations, produced LBR values approximately 30 below the trend line. These outliers were considered to be from experimental error in the LBR test. Four spec imens compacted at ISO gyrations produced LBRs of or g reater than I00. All samples compacted for 75 or more gyrations produced LBR values greater than 40. Five samples with densities greater than 125 lb/fe (1 9.6 kN/m 3) produced unsoaked LBR values slightly greater than I 00, whi le samples with densities above l l6 lb/ft3 (18.2 kN/ m3) produced LBR values g reater than 40. Samples compacted for less than 25 gyrations did not achieve an LBR of 40. In conclusion, gyratory compaction of RAP produced the highest LBRs of the three compaction methods.
The results for LBR versus dry density from the gyratory compaction are presented in Figure 6. The 52 tests included 12 with Me lbourne crushed, eight with Melbourne milled, 14 with Whitehurst milled, and 18 with Jacksonvi lle crushed RAP. LBR values from gyratory compaction were significantly higher than those achieved with the other compaction methods. LBR increased linearly 2.75 for each I lb/ft3 (0.1 57 kN/m 3) increase in dry density (Figure 6). This rate was much higher than the rates associated with either modified Proctor or vibratory compaction. The R2 of .62 was similar to the coeffi cient produced by the modified Proctor testing. Figure 7 is a plot of LBR versus the number of gyrations to show whether extra compactive effort from additional gyrations had any
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COMPARISON OF GYRATORY AND MODIFIED PROCTOR STRENGTHS
peak value on the stress-versus-deflection plot was used as the UCC strength. Of the 12 specimens, five were compacted by using modified Proctor energy, four with the gyratory energy at 75 gyrations, and three with gyratory energy heights set to match the modified Proctor densities. The results for UCC strength versus dry density are shown in Figure 9. Linear trend lines were fitted to the data. Regression coefficients are not shown because of the limited number of data points. Similar to the strength variations found from LBR tests, UCC strengths for gyratory specimens were three to four times as high as the modified Proctor specimens, and dry density increased as the number of gyrations increased. Figure 9 shows that the UCC strength of the gyratory-compacted specimens increased linearly from about 25 to l 05 psi ( 172 to 723 kPa) as density increased, while the UCC strength of the modified Proctor specimens remained constant at about 20 psi (138 kPa).
Modified Proctor and gyratory strengths at the same densities were compared. Testing included LBR, UCC, and IDT tests. Both UCC and IDT tests were on extruded samples.
LBR Results Values for LBR versus density from gyratory and modified Proctor tests are shown in Figure 8. Although both methods show an increase in LBR with density, gyratory compaction yielded significantly higher LBR values than the modified Proctor method at similar densities. Florida DOT's State Materials Office (SMO) confirmed these results by performing LBR tests on two modi fied Proctor-compacted samples, three gyratory-compacted samples given 75 gyrations, and four gyratory-compacted samples that matched the maximum modified Proctor density. Figure 8 shows that gyratory compaction yielded LBR values several times those of modified Proctor compaction at similar densities. The modified Proctor linear regression indicated a 0.58 increase in LBR for every 1.0 lb/ff (0.157 kN/m3) increase in dry density with a regression coefficient of .45 (medium correlation). The gyratory linear regression indicated a much larger LBR increase of 2.71 for every 1.0 lbtfe (0.157 kN/m 3) increase in dry density with a regression coefficient of .40 (medium correlation). The slopes and regression coefficients in Figure 8 differ from those in Figures 4 and 6 because of the additional data provided by Florida DOT's SMO.
lOT Results IDT tests were also performed on specimens extruded from modifiedProctor and gyratory molds. Results for lOT versus dry density are shown in Figure 10. Ten tests were conducted, four compacted by means of modified Proctor, three compacted at 75 gyrations, and three compacted with the gyratory compactor to match the modified Proctor densities. As was the case for both the LBR and UCC tests, gyratory testing yielded IDT strengths two to three times that of the modified Proctor specimens. Some modified Proctor specimens crumbled during mold extraction and therefore produced zero tensile stre ngth. IDT strengths of specimens compacted by both methods increased linearly as density increased.
UCC Results UCC tests were performed on samples extruded from both modified Proctor and gyratory molds. ASTM standards specify a 2: 1 lengthto-diameter ratio to minimize end effects; however, the size of the modified Proctor and gyratory molds prevented this. Both the modified Proctor and gyratory samples were approximately 4.5 in. (114.3 mm) tall by 6 in. ( 152.4 mrn) in diameter. As both molds had the same relative proportions, the results were comparable. The
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FIGURE 8 Unsoaked LBR versus dry density comparison between modified Proctor and gyratory compaction for all RAP stockpi les.
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comparison, LBR and IDT tests were performed on three readily available pavement materials without asphalt. Three samples of limerock, cemented coquina, and clayey sand were prepared for each test. Figure 11 shows the ratio of strengths between the gyratory and the modified Proctor compaction. Additional test results from 50:50 blends of Melbourne milled RAP and limerock are included. This figure shows that the strength ratio decreases from the upper levels near 4 to about 2 with the blends and finally to 1 for conventional soils. These ratios are near I, which indicates that gyratory compaction does not improve strengths of these conventional soils.
were tested to eliminate any effects resulting from the different geometry of the Proctor and gyratory molds. The modified Proctor specimens-4 in. (101.6 mm) in diameter and 4.584 in. (1 16.43 mm) high-were prepared first. Gyratory specimens with slightly different diameters [3.94 in. (100 mm)] and heights [4.72 in. (1 20 mm)] were then prepared (about 0.15% difference in dimensions). Tests were conducted on limerock and Melbourne milled RAP. Data, the average from two tests on each specimen, are presented as displacements versus the log time so as to allow the slope of the plots [M/Mog(t)], termed the creep strain rate (CSR), to be used for evaluation purposes.
UNCONFINED CREEP BEHAVIOR OF GYRATORY AND MODIFIED PROCTOR SPECIMENS
Creep of Limerock Although extensive confined creep testing on conventional aggregates produced undetectably low levels of creep (9), these unconfined specimens showed extremely low but measurable creep. Figure 12 shows the average modified Proctor and gyratory results,
Unconfined creep tests were conducted on ejected gyratory and modified Proctor specimens to determine whether gyratory compaction affected creep performance as well as strength. Unconfined specimens
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