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10 20.0 18.0 -0.8298 y = 36.496x 16.0 2 R = 0.9988 Average Air Voids, % 14.0 12.0 10.0 8.0 6.0 4.0 2.0 0.0 0.0 1.0 2.0 3.0 4.0 5.0 6.0 7.0 8.0 9.0 t/NMAS Figure 8. Relationships between air voids and t/NMAS for 9.5-mm SMA mixes. 4.4 EVALUATION OF EFFECT OF t/NMAS ON 4.4.1 Section 1 DENSITY FROM FIELD STUDY Section 1 was constructed on July 18, 2003, and con- The field test sections consisted of 7 mixes that were to be sisted of a 2.0 to 5.0 t/NMAS overlay of an existing HMA placed on the test track. These mixes had to be verified before layer. This construction was performed adjacent to the NCAT placing on the track; hence, these mixes could be placed Test Track. The mix was a 9.5-mm NMAS fine-graded mix- and tested without significant costs. Some of the mixes did ture. The length of the section was about 40 m, and the width not meet volumetrics and other requirements, but they were was about 3.5 m. On some of the sections the placement judged sufficient for this part of the study because determin- began on the thick side and in some cases the placement began ing the desired thickness range was a relative value based on on the thin side. This technique was used so that there would t/NMAS. be no bias due to the placement of the HMA. On this sec- 20.0 18.0 16.0 y = 29.982x -0.7232 14.0 Average Air Voids, % R2 = 0.9945 12.0 10.0 8.0 6.0 4.0 2.0 0.0 0.0 1.0 2.0 3.0 4.0 5.0 6.0 7.0 8.0 9.0 t/NMAS Figure 9. Relationships between air voids and t/NMAS for 12.5-mm SMA mixes.

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11 16.0 14.0 12.0 y = 27.14x-0.9206 Average Air Voids, % R2 = 0.9974 10.0 8.0 6.0 4.0 2.0 0.0 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 t/NMAS Figure 10. Relationships between air voids and t/NMAS for 19.0-mm SMA mixes. tion the paving began with the thicker portion of the section meet desired requirements for weight and tire pressure, and and the thickness was slowly decreased as the paver moved thus the data generated for the rubber tire roller compacted down the test lane. The desired mat thickness was achieved mixture were omitted from the analysis for this section. The by gradually adjusting the screed depth crank of the paver breakdown rolling was performed with one pass in the static during the paving operation. The weather conditions during mode on the mat at a temperature of about 300F. This was fol- the paving were 84F, overcast, with calm wind. The existing lowed by three passes in the vibratory mode at low amplitude surface temperature prior to overlay was also 84F. and high frequency (3800 vibrations per minute [vpm]) and The roller utilized in this section was an 11-ton steel roller one pass in the static mode. It was determined that this com- HYPAC C778B with a 78-in. wide drum that could operate in paction effort reached the peak density; hence, additional vibratory or static mode. The rubber tire roller available did not rolling was not performed. 8 7 30 sec 6 60 sec Average Air Voids, % 5 90 sec 4 3 2 1 0 0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 t/NMAS Figure 11. Relationships between air voids and t/NMAS for 9.5-mm ARZ mixes.

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12 12 30 sec 10 60 sec 90 sec 8 Average Air Voids, % 6 4 2 0 0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 t/NMAS Figure 12. Relationships between air voids and t/NMAS for 9.5-mm BRZ mixes. A total of 16 cores were obtained from this section and the the air voids increased by 0.5 percent (less than 0.5 percent test results of the cores are presented in Figure 18. The results were considered insignificant). This number is somewhat include the thickness of cores, t/NMAS, and the air voids arbitrary, but it is realistic. Therefore, as shown in Figure 18, determined from the vacuum seal device. the recommended t/NMAS range for 9.5-mm fine-graded A review of the data indicated that a polynomial function mix was 3.4 to 5.8. This does not mean that satisfactory com- provided the best fit line. The best-fit line indicates that the paction cannot be obtained outside of these limits, but it does air voids decreased as the t/NMAS increased to a point where indicate that more compactive effort would be needed. So additional thickness resulted in increased air voids. The rec- this recommended range should only be used as a guide and ommended thickness range was selected as the point(s) where should not be a rigid requirement. The effect of t/NMAS on 9 8 30 sec 7 60 sec 6 Average Air Voids, % 90 sec 5 4 3 2 1 0 0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 t/NMAS Figure 13. Relationships between air voids and t/NMAS for 19.0-mm ARZ mixes.

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13 12 10 30 sec Average Air Voids, % 60 sec 8 90 sec 6 4 2 0 0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 t/NMAS Figure 14. Relationships between air voids and t/NMAS for 19.0-mm BRZ mixes. the measured density was determined from Figure 18. Data The paving started from the thick portion of the mat and pro- in the figure indicate that the lowest air voids (7.0 percent air gressed toward the thinner portion. The weather conditions voids) occurred at t/NMA 4.4. Table 5 shows the air voids at during the paving were 82F, overcast, with calm wind. The various t/NMAs as related to this minimum. existing surface temperature was 96F. The roller utilized in this section was an 11-ton steel drum 4.4.2 Section 2 roller HYPAC C778B with a 78-in. wide drum that could operate in vibratory or static mode. The rubber tire roller was Section 2 was constructed on August 7, 2003, and the a 15-ton HYPAC C560B with a tire pressure of 90 psi. For the t/NMAS for this overlay ranged from 2.0 to 5.0. The mixture side of the mat utilizing only the steel drum roller, the initial was a 9.5-mm NMAS coarse-graded mixture. The length of rolling was performed with four passes in the vibratory mode the section was about 40 m, and the width was about 3.5 m. at low amplitude and high frequency (3800 vpm) at a mix tem- 12 30s 10 60s 90s Average Air Voids, % 8 6 4 2 0 0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 t/NMAS Figure 15. Relationships between air voids and t/NMAS for 9.5-mm SMA mixes.

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14 12.0 30 s 10.0 60 s 90 s Average Air Voids, % 8.0 6.0 4.0 2.0 0.0 0 0 .5 1 1.5 2 2.5 3 3.5 4 4.5 t/NMAS Figure 16. Relationships between air voids and t/NMAS for 12.5-mm SMA mixes. 12.0 30s 10.0 60s 90s Average Air Voids, % 8.0 6.0 4.0 2.0 0.0 0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 t/NMAS Figure 17. Relationships between air voids and t/NMAS for 19.0-mm SMA mixes. 10. 0 9.0 R2 = 0 . 6 3 9 2 8.0 7.0 Air Voids, % 6.0 5.0 4.0 3.0 0.0 1.0 2.0 3.0 4.0 5.0 6.0 7.0 t/NMAS Figure 18. Relationships of air voids and t/NMAS for 9.5-mm fine-graded mix.

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15 TABLE 5 Relationship of air voids and tire roller. The effect of t/NMAS on the measured density t/NMAS for 9.5-mm fine-graded HMA was determined from Figure 19. Data in the figure indicate compacted with steel roller that the lowest in-place air voids (10 percent air voids for t/NMA Percentage points the steel wheel roller only and 10.5 percent air voids for the above lowest steel and rubber tire rollers) occurred at t/NMAS of 4.7 for 4.4 (lowest air voids, 7.0 %) 0.0 2 2.5 the steel wheel roller and 3.8 for the rubber and steel wheel 3 1.0 roller. Table 6 shows the air voids at various t/NMAs as related 4 0.1 to this minimum. 5 0.1 4.4.3 Section 3 perature of about 300F. This was followed with four passes in the static mode. For the side of the mat that used a rubber Section 3 was constructed on July 25, 2003, and consisted tire roller as an intermediate roller, the breakdown rolling was of a 2.0 to 5.0 t/NMAS overlay of an existing HMA layer. performed with four passes in the vibratory mode operated at The mix was a 9.5-mm NMAS SMA. The length of the sec- low amplitude and high frequency (3800 vpm). This was fol- tion was about 40 m, and the width was about 3.5 m. The lowed with five passes of the rubber tire roller and one pass paving started from the thick portion of the mat and pro- of the steel roller in the static mode. gressed to the thinner portion. The desired mat thickness A total of 15 cores were obtained from the side that uti- was achieved by gradually adjusting the screed depth crank lized only a steel drum roller and 16 cores from the side that of the paver during the operation. The weather conditions used the rubber tire roller. The relationship of air voids during the paving were 95F, partly cloudy, with calm wind. measured from the vacuum seal device and t/NMAS was The existing surface temperature was 115F. evaluated for each rolling pattern. The results are illustrated The roller utilized in this section was an 11-ton steel drum in Figure 19. roller HYPAC C778B with a 78-in. wide drum that could A review of the data indicated that a polynomial function operate in vibratory or static mode. The rubber tire roller was provided the best fit. As the thickness increased, the air voids a 15-ton HYPAC C560B with a tire pressure of 90 psi. For decreased until a point where additional thickness resulted in the side of the mat utilizing only the steel drum roller, the ini- increased air voids. The plots also suggest that the side uti- tial rolling was performed with one pass in the static mode lizing only a steel drum compactor had better compaction. followed by five passes in the vibratory mode operated in low To determine the desired thickness, it was decided to use air amplitude and high frequency (3800 vpm) on the mat having voids 0.5 percent larger (a void level less than 0.5 percent dif- a mix temperature of about 320F. This was followed with ferent was not considered significantly different) than the two passes in the static mode for the finish rolling. For the minimum air voids from the best-fit line. Therefore, as shown side of the mat that used a rubber tire roller as an intermediate in Figure 19, the desired t/NMAS range for 9.5-mm coarse- roller, the breakdown rolling was performed with one pass in graded mix was 3.5 to 5.9 for compaction with a steel wheel the static mode and four passes in the vibratory mode oper- roller and 2.9 to 4.6 for compaction with the steel and rubber ated in low amplitude and high frequency (3800 vpm). This 14.0 13.0 12.0 Steel/Rubber Tire Roller 2 11.0 R = 0.5115 Air Voids, % 10.0 9.0 Steel Roller 2 R = 0.68 8.0 7.0 6.0 5.0 0.0 1.0 2.0 3.0 4.0 5.0 6.0 7.0 t/NMAS Figure 19. Relationships of air voids and t/NMAS for 9.5-mm coarse-graded mix.

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16 TABLE 6 Relationship of air voids and t/NMAS for 9.5-mm coarse-graded HMA compacted with steel roller and with steel and rubber tire rollers Steel roller Steel and rubber tire rollers t/NMA Percentage t/NMA Percentage points above points above lowest lowest 4.7 (lowest air voids, 10.0 %) 0.0 3.8 (lowest air voids, 10.5 %) 0.0 2 2.5 2 2.0 3 1.0 3 0.5 4 0.5 4 0.0 5 0.0 5 1.0 was followed with eight passes of the rubber tire roller and 4.4.4 Section 4 two passes of the steel wheel roller in the static mode. A total of 12 cores were obtained from the side that utilized Section 4 was constructed on August 12, 2003, and con- only the steel drum roller and another 12 cores from the side sisted of a 2.0 to 5.0 t/NMAS overlay of an existing HMA that used the rubber tire roller. To determine the range of rec- layer. The mix was a 12.5-mm NMAS SMA. The length of ommended t/NMAS for this mix, the relationship of air voids the section was about 40 m, and the width was about 3.5 m. The from the vacuum seal device and t/NMAS was evaluated for paving started from the thinner portion and proceeded toward each rolling pattern. The results are illustrated in Figure 20. the thicker portion of the mat. The weather conditions during The best-fit lines indicate that the air voids decreased as the paving were 80F, overcast, with calm wind. The existing the thickness increased to a point where additional thickness surface temperature was 85F. resulted in increased air voids. The plots also suggest that the The roller utilized in this section was an 11-ton steel drum side utilizing only the steel drum compactor had higher den- roller HYPAC C778B with a 78-in. wide drum that could sity. Rubber tire rollers are not used on SMA mixtures and operate in vibratory and static modes. The rubber tire roller these data confirm that there is no need to use the rubber tire was a 15-ton HYPAC C560B with a tire pressure of 90 psi. roller. As shown in Figure 20, the recommended range for For the side of the mat utilizing only the steel drum roller, t/NMAS for the 9.5-mm SMA mix is 3.8 to 5.3 for the com- the initial rolling was performed with four passes in the paction with a steel wheel roller and 2.6 to 5.1 for compaction vibratory mode operated at low amplitude and high frequency with a steel and rubber tire roller. The effect of t/NMAS on (3800 vpm). The mat temperature was approximately 320F. the measured density was determined from Figure 20. Data in This was followed with three passes in the static mode includ- the figure indicate that the lowest in-place air voids (8.5 per- ing finish rolling. For the side of the mat that used a rubber cent air voids for the steel wheel roller only and 10.3 percent tire roller as an intermediate roller, the initial rolling was per- air voids for the steel and rubber tire rollers) occurred at formed with four passes in the vibratory mode operated at t/NMAS of 4.5 for the steel wheel roller and 3.8 for the rubber low amplitude and high frequency (3800 vpm). This was fol- and steel wheel roller. Table 7 shows the air voids at various lowed with four passes of the rubber tire roller and one pass t/NMAs as related to this minimum. of the steel roller in the static mode. 14.0 13.0 Steel/Rubber Tire Roller 12.0 2 R = 0.1864 11.0 10.0 Air Voids, % 9.0 8.0 Steel Roller 7.0 2 R = 0.8335 6.0 5.0 4.0 3.0 0.0 1.0 2.0 3.0 4.0 5.0 6.0 t/NMAS Figure 20. Relationships of air voids and t/NMAS for 9.5-mm SMA mix.

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17 TABLE 7 Relationship of air voids and t/NMAS for 9.5-mm SMA mix compacted with steel roller and with steel and rubber tire rollers Steel roller Steel and rubber tire rollers t/NMA Percentage t/NMA Percentage points points above above lowest lowest 4.5 (lowest air voids, 8.5 %) 0.0 3.8 (lowest air voids, 10.3 %) 0.0 2 5.5 2 1.2 3 2.0 3 0.2 4 0.2 4 0.0 5 0.2 5 0.5 A total of 21 cores were obtained from the side that uti- rollers) occurred at t/NMAS of 4.5 for the steel wheel roller lized only a steel drum roller and 21 cores from the side that and 4.8 for the rubber and steel wheel rollers. Table 8 shows used the rubber tire roller. To determine the recommended the air voids at various t/NMAs as related to this minimum. t/NMASs for this mix, the relationship of air voids from the vacuum seal device and t/NMAS was evaluated for each rolling pattern. The results are illustrated in Figure 21. 4.4.5 Section 5 The best-fit lines indicate that the air voids decreased as the thickness increased to a point where additional thickness Section 5 was constructed on July 16, 2003, and consisted resulted in increased air voids. The plots also suggest that the of a 2.0 to 5.0 t/NMAS overlay of an existing HMA. The mix side utilizing only the steel drum compactor had higher den- consisted of a 19.0-mm NMAS fine-graded HMA. The length sity. As shown in Figure 21, the suggested minimum t/NMAS of the section was about 40 m, and the width was about 3.5 m. for 12.5-mm SMA mix is 3.8 for compaction with steel wheel The paving started on the thin end of the section and pro- roller and 4.6 for compaction with steel and rubber tire roll- ceeded to the thicker portion. The desired mat thickness was ers. For these mixes, the density increased as the t/NMAS achieved by gradually adjusting the screed depth crank of increased even at the thicker portions. Also the curve did not fit the paver during the operation. The weather conditions dur- the data as well as desired, so the data points were actually used ing the paving were 90F, clear, with calm wind. The existing to select the suggested t/NMAS number. Note in the plots that surface temperature was 96F. the data points continue downward with increasing t/NMAS to The roller utilized in this section was an 11-ton steel roller a point and then the air voids remain relatively constant as HYPAC C778B with a 78-in. wide drum that operated in the t/NMAS increased. vibratory and static modes. The rubber tire roller used did not The effect of t/NMAS on the measured density was deter- meet the tire pressure requirements and the results were omit- mined from Figure 21. Data in the figure indicate that the low- ted from the analysis for this section. The breakdown rolling est in-place air voids (4.7 percent air voids for the steel wheel was performed with four passes in the vibratory mode oper- roller only and 7.5 percent air voids for the steel and rubber tire ated in low amplitude and high frequency (3800 vpm). The 19.0 18.0 17.0 16.0 15.0 14.0 13.0 12.0 Steel/Rubber Tire Roller Air Voids, % 11.0 2 R = 0.77 10.0 Steel Roller 9.0 2 R = 0.87 8.0 7.0 6.0 5.0 4.0 3.0 2.0 1.0 0.0 0.0 1.0 2.0 3.0 4.0 5.0 6.0 t/NMAS Figure 21. Relationships of air voids and t/NMAS for 12.5-mm SMA Mix.

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18 TABLE 8 Relationship of air voids and t/NMAS for 12.5-mm SMA mix compacted with steel roller and with steel and rubber tire rollers Steel roller Steel and rubber tire rollers t/NMA Percentage t/NMA Percentage points points above above lowest lowest 4.5 (lowest air voids, 4.7 %) 0.0 4.8 (lowest air voids, 7.5 %) 0.0 2 11.3 2 6.5 3 3.3 3 3.5 4 0.3 4 0.5 5 0.5 5 0.0 mat temperature was approximately 300F. Three passes in 3.5 m. The paving started from the thinner portion of the mat the static mode and one pass for finish rolling followed this and proceeded to the thicker portion. The weather conditions initial rolling. during the paving were 79F, cloudy, with calm wind. The A total of 20 cores were obtained from this section. To existing surface temperature was 84F. determine the minimum t/NMAS for this mix, the relationship The roller utilized in this section was an 11-ton steel drum between air voids (from the vacuum seal device) and thickness roller HYPAC C778B with a 78-in. wide drum that could was evaluated. The results are illustrated in Figure 22. operate in vibratory and static mode. The rubber tire roller was The best-fit line indicated that the air voids decreased as a 15-ton HYPAC C560B with a tire pressure of 90 psi. For the the thickness increased to a point where additional thickness side of the mat utilizing only the steel drum roller, the initial resulted in increased air voids. As shown in Figure 22, the rec- rolling was performed with four passes in the vibratory mode ommended t/NMAS range for the 19.0-mm fine-graded mix operated at low amplitude and high frequency (3800 vpm). was 3.1 to 4.6. The effect of t/NMAS on the measured density The mat temperature was approximately 300F. This initial was determined from the figure. Data in the figure indicate that rolling was followed with six passes in the static mode. For the the lowest in-place air voids (6.2 percent air voids) occurred at side of the mat that used a rubber tire roller as the intermedi- t/NMAS of 3.8. Table 9 shows the air voids at various t/NMAs ate roller, the initial rolling was performed with four passes in as related to this minimum. the vibratory mode operated in low amplitude and high fre- quency (3800 vpm). This initial rolling was followed with four 4.4.6 Section 6 passes of the rubber tire roller and two passes with a steel wheel roller in the static mode. Section 6 was constructed on August 6, 2003, and consisted A total of 22 cores were obtained from the side that utilized of a range of 2.0 to 5.0 t/NMAS overlay of an existing HMA. only a steel drum roller and 16 cores from the side that used The mix was a 19.0-mm NMAS coarse-graded HMA. The the rubber tire roller. To determine the minimum t/NMAS for length of the section was about 40 m, and the width was about this mix, the relationship between air voids from vacuum seal 10.0 9.0 2 R = 0.77 8.0 Air Voids, % 7.0 6.0 5.0 4.0 3.0 0.0 1.0 2.0 3.0 4.0 5.0 6.0 t/NMAS Figure 22. Relationships of air voids and t/NMAS for 19.0-mm fine-graded mix.

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19 TABLE 9 Relationship of air voids and t/NMAS Table 10 Relationship of air voids and t/NMAS for 19.0-mm fine-graded mix compacted with for 19.0-mm coarse-graded mix compacted with steel roller steel and rubber tire roller* t/NMA Percentage points t/NMA Percentage points above lowest above lowest 3.8 (lowest air voids, 6.2 %) 0.0 4.5 (lowest air voids, 5.7 %) 0.0 2 3.1 2 1.8 3 0.6 3 0.6 4 0.0 4 0.1 5 1.3 5 0.1 *The steel wheel roller alone was not used because it produced too much scatter in the data device and thickness was evaluated for each rolling pattern. The results are illustrated in Figure 23. The best-fit lines indi- cate that the air voids decreased as the thickness increased to HMA and utilized a modified asphalt. The length of the sec- a point where additional thickness resulted in increased air tion was about 40 m, and the width was about 3.5 m. The voids. The plots also suggest that the side utilizing the rubber paving started from the thicker portion of the mat and pro- tire roller had higher density. As shown in Figure 23, the rec- ceeded to the thinner portion. The weather conditions dur- ommended minimum thickness for 19.0-mm coarse-graded ing the paving were 90F, clear, with calm wind. The existing mix was 3.0 for compaction with the steel and rubber tire surface temperature was 120F. rollers. There is too much scatter in the data to make a good The roller utilized in this section was an 11-ton steel selection of a recommended value for compaction with a steel drum roller HYPAC C778B with a 78-in. wide drum that wheel roller. could operate in the vibratory and static modes. The rubber The effect of t/NMAS on the measured density was deter- tire roller was a 15-ton HYPAC C560B with a tire pressure mined from Figure 23. Data in the figure indicate that the low- of 90 psi. For the side of the mat utilizing only the steel est in-place air voids (5.7 percent for the steel and rubber tire drum roller, the initial rolling was performed with four passes roller, the steel wheel roller alone was not used because it pro- in the vibratory mode operated in low amplitude and high fre- duced too much scatter in the data) occurred at t/NMAS of 4.5. quency (3800 vpm). The mat temperature was about 330F. Table 10 shows the air voids at various t/NMAs as related to This was followed with another five passes in the vibra- this minimum. tory mode operated at low amplitude and high frequency (3800 vpm). There was one additional pass with the steel 4.4.7 Section 7 wheel roller in the static mode to finish the mat. For the side of the mat that used a rubber tire roller as an intermediate Section 7 was constructed on August 14, 2003, and con- roller, the initial rolling was performed with two passes in sisted of a range of 2.0 to 5.0 t/NMAS overlay of an existing the vibratory mode operated at low amplitude and high fre- HMA. The mix consisted of a 19.0-mm NMAS coarse-graded quency (3800 vpm). This was followed with ten passes with 11. 0 10. 0 Steel Roller R2 = 0.1601 9 .0 8 .0 7 .0 Air Voids, % 6 .0 5 .0 4 .0 3 .0 Steel/Rubber Tire Roller R2 = 0.4489 2 .0 1 .0 0 .0 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5 6.0 6.5 7.0 t/NMAS Figure 23. Relationships of air voids and t/NMAS for 19.0-mm coarse-graded mix.