Publications

Placement of Warm Mix Asphalt on the East Entrance Road of Yellowstone National Park

Previous Chapter « Table of Contents » Next Chapter

8. Production Mixture Testing

During the production of the three mixtures, samples were taken periodically from the windrow. One sample was taken at random for every 770 tons (700 metric tons). These samples were shipped from the project to the Western Federal Lands Highway Division (WFLHD) laboratory in Vancouver, Washington for testing. Based on the produced quantities for the project, 12 mixture samples were obtained for the control mixture, 12 samples were obtained from the Advera mixture, and 10 samples were obtained from the Sasobit mixture. The sand equivalent (SE), percent fracture, and core density values were determined from samples obtained by the contractor as part of the quality control/quality assurance process established in the contract.

Once these samples arrived at the laboratory in Vancouver, they were tested for asphalt content and gradation. Additionally specimens were fabricated for Superpave volumetric testing. Table 5 summarizes the conventional mix properties and Table 6 depicts the Superpave volumetric properties.

Table 5: Conventional mix properties.

	Control		Advera		Sasobit
	Average	Std. Dev.	Average	Std. Dev.	Average	Std. Dev.
1"	100.0	0.00	100.0	0.00	100.0	0.00
1/2"	85.8	2.15	83.2	2.09	85.0	1.92
3/8"	69.2	2.47	67.1	2.54	68.5	2.45
#4	42.8	2.10	43.6	2.22	43.0	2.11
#8	27.6	1.41	28.9	1.56	28.9	1.68
#40	10.5	0.76	11.3	0.86	11.8	0.72
#200	4.6	0.40	5.1	0.44	5.4	0.22
AC Content	5.28	0.296	5.16	0.219	4.88	0.188
SE	66	3.99	66	2.92	65	2.20
% Fracture	99.8	0.24	99.8	0.31	99.9	0.18
Core Density	93.2	1.07	93.9	1.39	93.4	1.20
Moisture Content	0.35	0.16	0.41	0.06	0.53	0.10

Table 6: Superpave mix properties.

	Control		Advera		Sasobit
	Average	Std. Dev.	Average	Std. Dev.	Average	Std. Dev.
Gmb	2.298	0.0147	2.315	0.0160	2.311	0.0159
Gmm	2.438	0.0080	2.440	0.0092	2.452	0.0071
Va	5.8	0.78	5.1	0.92	5.7	0.69
VMA	15.0	0.54	14.3	0.53	14.2	0.60
VFA	61.7	4.22	64.3	5.27	59.8	3.56

The gradations for the three different mixtures were fairly consistent. The most significant difference was that the asphalt content was below the targeted value of 5.3%. There was also higher than normal amounts of moisture content. During production the contractor obtained lower moisture content values due to an oven malfunction and insufficient heating; this unfortunately led to lower asphalt contents. The low asphalt contents also contributed to the high air voids and VMA values that were obtained from the Superpave specimens.

In spite of the low asphalt contents, the core density values indicate that density was achieved in the final placed mat. The standard deviation of the core density values was higher for the Advera and Sasobit, but the average is only marginally higher than the control mixture. Based on the data, the range was greater for the warm mixes than the control mix. Despite lower average asphalt contents, the highest in-place density values were from cores taken from the warm mix sections. Since the same compactive effort was applied in each case, this would suggest that the warm mix additives enhance the compaction of the mixture.

Additional specimens were fabricated for moisture sensitivity testing including tensile strength ratio (TSR), Hamburg rut testing, and Asphalt Pavement Analyzer (APA) rut testing. In order to provide sufficient material for specimen to be fabricated for various moisture sensitivity tests, material was combined from individual samples.

The tensile strength ratio test results were very similar, although one of the Advera WMA results would not pass the nationally established minimum ratio of 0.80. All of the dry strength values were fairly low, averaging approximately 70 psi (480 kPa) primarily due to the relatively soft grade of binder that was used on the project. Tables 7, 8, & 9 contain the data for this testing.

Table 7: Tensile strength ratio data for the control mix.

Control Mixture
	Specimen #	Air Voids	Strength (kPa)		Specimen #	Air Voids	Strength (kPa)
Dry	2	9.6	434	Dry	2	7.6	490
	4	8.8	428		5	7.1	510
	6	9.9	421		6	7.4	490
Wet	1	9.8	338	Wet	1	7.6	400
	3	9.4	365		3	7.1	448
	5	9.3	372		4	7.2	414
	Average Dry		428		Average Dry		497
	Average Wet		358		Average Wet		421
	TSR		0.84		TSR		0.85

Table 8: Tensile strength ratio data for the Advera Mix.

Advera Mixture
	Specimen #	Air Voids	Strength (kPa)		Specimen #	Air Voids	Strength (kPa)
Dry	1	8.0	441	Dry	1	7.1	469
	2	7.7	455		4	6.6	531
	4	7.6	476		6	7.6	476
Wet	3	7.9	359	Wet	2	7.2	400
	5	7.6	352		3	6.7	428
	6	8.0	372		5	7.2	420
	Average Dry		457		Average Dry		492
	Average Wet		361		Average Wet		416
	TSR		0.79		TSR		0.85

Table 9: Tensile strength ratio data for the Sasobit mix.

Advera Mixture
	Specimen #	Air Voids	Strength (kPa)		Specimen #	Air Voids	Strength (kPa)
Dry	2	7.1	517	Dry	Only one data set was run
	4	7.2	538
	6	7.6	517
Wet	1	7.3	428	Wet
	3	7.3	441
	5	7.3	448
	Average Dry		524
	Average Wet		439
	TSR		0.84

The Hamburg rut testing also provided very similar performance results between the three mixtures. The specimens were tested at 40 °C in a wet condition. The data indicates that all mixtures would meet current agency maximum rut limits as the maximum rut value observed was 4.00 mm. The plots of all of the rutting data also indicate that stripping is not occurring in any of the mixtures tested. This may be due to the 1% hydrated lime that was a necessary additive in all of the mixtures as an anti-stripping agent as indicated from the mix design.

The Sasobit WMA did show an average rut depth almost 1 mm less than the control; however, with the limited number of samples tested it is difficult to determine the statistical significance. This lower rutting may be attributed to a stiffening of the asphalt binder that was noted earlier. Table 10 provides the data from the Hamburg rut tests.

Table 10: Wet Hamburg rut test at 40 °C.

Mixture	Specimens	Air Void Content	Rut Depth @ 5,000 Passes (mm)	Rut Depth @ 10,000 Passes (mm)	Rut Depth @ 15,000 Passes (mm)	Rut Depth @ 20,000 Passes (mm)
Control	C-1 & C-2	6.6 & 6.2	2.3	2.9	3.61	3.82
Control	C-3 & C-4	8.0 & 7.8	2.5	3.00	3.62	4.00
Control Average =			2.40	2.95	3.62	3.91
Advera	A-1 & A-2	8.0 & 8.2	2.70	3.00	3.62	3.80
Advera	A-3 & A-4	6.1 & 6.4	2.20	2.50	2.90	3.25
Advera Average =			2.40	2.95	3.62	3.91
Sasobit	S-1 & S-2	7.4 & 7.4	2.20	2.80	2.97	3.28
Sasobit	S-3 & S-4	6.8 & 6.6	1.90	2.50	2.59	2.60
Sasobit Average =			2.05	2.65	2.78	2.94

Rut testing was also performed using the Asphalt Pavement Analyzer (APA) rut testing device. The testing was performed in a dry condition and at the temperature of 58 °C in accordance with the binder grade selected for the project.

The rut data parallels the results of the Hamburg rut testing. The Sasobit WMA indicated the best rutting resistance, but none of the mixes performed poorly in the test. All rutting values were low. The fact that the Sasobit WMA provided the best results may again be indicative of the stiffening effect of the binder. The APA rut data is provided in Table 11.

Table 11: Asphalt Pavement Analyzer rut test at 58 °C.

Mixture	Specimens	Average Air Void Content	Average Rut Depth
Control	C-1 to C-6	7.0%	2.6 mm
Control	C-7 to C-12	7.4%	2.4 mm
Control Average =		7.2%	2.5 mm
Advera	A-1 to A-6	7.8%	2.8 mm
Advera	A-7 to A-12	6.4%	2.7 mm
Advera Average =		7.1%	2.8 mm
Sasobit	S-1 to S-6	8.0%	2.1 mm
Sasobit	S-7 to S-12	6.9%	1.7mm
Sasobit Average =		7.5%	1.9 mm

Previous Chapter « Table of Contents » Next Chapter