Progress Report on Changes in Asphaltic Concrete in Service WILLIAM J . KENIS, SR., Materials Engineer, Delaware State Highway Department This paper describes the experimental asphkltic concrete pavements constructed in Delaware to evaluate the changes in the asphalt and the properties of mixtures during con- struction and in service. Two experimental asphalts from specific sources, each laid over a rigid (old portland ce- ment concrete) and a flexible (old surface treatment) base, were used. The present report includes data from three series of samples, those taken during construction and those taken after one and two years of service. Comparison of results obtained by three different laboratories—Bureau of Public Roads, Asphalt Institute, and Delaware State Highway De- partment—also is provided. At present no specific conclusions can be drawn but laboratory tests indicate that differences in behavior of the same asphalt at various locations in the road may be as great as or greater than differences in the asphalts from the two crude sources used in this study. Other than minor reflection cracking from the concrete base on the rigid sections, no deterioration in the pavements has been noted at any location. • THE AD HOC Advisory Committee of the Highway Research Board, appointed to e^qjlore problems of mutual interest and concern to users and producers of asphaltic materials, has stressed investigations of (a) asphalt test characteristics and (b) the service behavior of asphalts from different sources. In June 1957, all State Highway Departments and the U. S. Bureau of Public Roads were asked to consider sponsoring research projects directed toward obtaining such data. Accordingly, the Delaware State Highway Department undertook the.research pre- sented in this progress report. The report describes the project and shows the trends being developed. Inasmuch as the project will be continued, final conclusions are not yet possible. LOCATION AND DESCRIPTION OF PROJECT The experimental test section is located on FAS road 30 between Rising Sun and Woodside, Del. It was constructed as a part of a resurfacing project, the total length of which is 3.66 mi. The experimental test section is approximately 0.9 mi of this total. This location was selected because of the uniqueness of the existing roadway to be resurfaced. The roadway consisted of a 9-ft lane of portland cement concrete 9 in. thick, adjacent to a 13-ft lane of bank-run sand-gravel base 6 in. thick. The Portland cement concrete had been covered the previous year (1957) with a single surface treatment of RC-3 cutback asphalt and aggregate. The sand-gravel base had been double surface-treated using MC-0 cutback asphalt for the prime application followed by two applications of RC-3 cutback asphalt and aggregate. The surface over the concrete pavement was in excellent condition with very little reflection cracking 39
Transcript
Progress Report on Changes in Asphaltic Concrete in Service WILLIAM J . KENIS, S R . , Materials Engineer, Delaware State Highway Department
This paper describes the experimental asphkltic concrete pavements constructed in Delaware to evaluate the changes in the asphalt and the properties of mixtures during construction and in service. Two experimental asphalts from specific sources, each laid over a rigid (old portland cement concrete) and a flexible (old surface treatment) base, were used.
The present report includes data from three series of samples, those taken during construction and those taken after one and two years of service. Comparison of results obtained by three different laboratories—Bureau of Public Roads, Asphalt Institute, and Delaware State Highway Department—also is provided.
At present no specific conclusions can be drawn but laboratory tests indicate that differences in behavior of the same asphalt at various locations in the road may be as great as or greater than differences in the asphalts from the two crude sources used in this study. Other than minor reflection cracking from the concrete base on the rigid sections, no deterioration in the pavements has been noted at any location.
• THE AD HOC Advisory Committee of the Highway Research Board, appointed to e^qjlore problems of mutual interest and concern to users and producers of asphaltic materials, has stressed investigations of (a) asphalt test characteristics and (b) the service behavior of asphalts from different sources. In June 1957, all State Highway Departments and the U. S. Bureau of Public Roads were asked to consider sponsoring research projects directed toward obtaining such data.
Accordingly, the Delaware State Highway Department undertook the.research presented in this progress report. The report describes the project and shows the trends being developed. Inasmuch as the project will be continued, final conclusions are not yet possible.
LOCATION AND DESCRIPTION OF PROJECT
The experimental test section is located on FAS road 30 between Rising Sun and Woodside, Del. It was constructed as a part of a resurfacing project, the total length of which is 3.66 mi. The experimental test section is approximately 0.9 mi of this total.
This location was selected because of the uniqueness of the existing roadway to be resurfaced. The roadway consisted of a 9-ft lane of portland cement concrete 9 in. thick, adjacent to a 13-ft lane of bank-run sand-gravel base 6 in. thick.
The Portland cement concrete had been covered the previous year (1957) with a single surface treatment of RC-3 cutback asphalt and aggregate. The sand-gravel base had been double surface-treated using MC-0 cutback asphalt for the prime application followed by two applications of RC-3 cutback asphalt and aggregate. The surface over the concrete pavement was in excellent condition with very little reflection cracking
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over the concrete joints; there was no evidence of bleeding and the condition of the surface was generally uniform throughout the length of the project.
The sand-gravel or flexible base portion was less uniform than the portland cement concrete side. There were a number of cracked areas resulting from base failures, and bleeding had occurred in the wheel tracks in some areas because of excess asphalt.
Figure 1. F i n i s h e d roadway.
ASPHALT B ASPHALT A
BF BPR BF Al BF DEL AF D E L AF Al AF BPR
BR BPR BR Al BR DEL AR DEL AR A AR BPR
SAMPLE SLAB S E E FIGURE 2 TO: RISING SUN TO: WOODSIDE
FAS NO. 30 T E S T SECTIONS LAID S E P T 15, 1958
F L E X I B L E B A S E ASPHALT A
F L E X I B L E B A S E ASPHALT B
k̂ ^̂ ^̂ ^̂ ^̂ ^̂ ^̂ ^̂ ,'̂ '̂ RIGID B A S E ASPHALT A ' / / / / / / / / / / / ^ y / y y / X RIGID B A S E A S P H A L T B
Figure 2. Delaware t e s t road experimental road t e s t s e c t i o n .
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The entire length of original roadway was to be resurfaced with 3 in. of the State's standard hot-mix, hot-laid asphaltic concrete. The resurfacing consisted of 1% in. of binder course and iVi in. of wearing course. The finished roadway is shown in Figure 1.
The wearing course for the experimental portions of the project was constructed using two asphalts of the 60-70 grade from known crude sources and methods of manufacture.
The entire binder course and the wearing course outside the experimental areas were constructed using an asphalt of 10-85 penetration grade refined from a mixed crude.
Three laboratories are cooperating in making the tests—the Asphalt Institute, the Bureau of Public Roads, and the Delaware State Highway Department.
The plan and detailed location of the experimental sections are shown in
CORE SAMPLES OIVEN SLAB NUMBERS AND FURTHER IDENTIFIED BY NUMBERS I THRU 16
Figure 3. Pavement sampling patte r n .
Figure h- Cored sample from t e s t s e c t i o n .
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Figure 2. Test sections are located on both sides of the pavement to provide comparisons of performance of the surfaces over rigid and flexible bases.
A total of twelve sampling areas have been designated. The special asphalts are referred to as asphalts A and B, respectively. The rigid and flexible base portions are designated as R and F , respectively (slab samples such as B F - A I and BR-AI for any sampling period are always located directly opposite each other). Figure 3 shows the general pattern of sampling in each area.
The 12- by 16-in. blocks were sawed from the pavement immediately after construction and after one year of service; the blocks were then cored in each individual co-operator's laboratory. The cored samples obtained after two years of service were
Figure 5. Typica l slab area a f t e r two years.
T A B L E 1
Property Asphalt A Asphalt B Penetration grade 60-70 60-70 Crude source Venezuela (Lagunillas) Middle East (Safaniya) Type distillation Vacuum or tube Vacuum or tube Date sampled (gal) Sept. 15, 1958 Sept. 15, 1958 Sample quantity (gal) 10 (AI) 10 (AI)
5 (DEL & BPR) 5 (DEL & BPR)
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T A B L E 2
PROPERTIES OF ORIGINAL ASPHALTS
Asphalt A Asphalt B
Del. BPR AI Del. BPR AI
Specific gravity, 77 F 1.023 1.023 1.024 1.030 1.030 1.030 Penetration, 100 g, 5 sec, 77 F 60 62 61 65 66 66 Softening point, R i B {°F) 118 123 125 118 124 124 Ductility, 5 cm/min, 77 F (cm) 100 250 150 100 250 150 Flash point ("F):
c . o . c . 585 580 610 610 570 595 P . M . - 505 - - - -
Solubility in CCI4 (%) 99.9 99.9 99.2 99.9 99.8 99.9 Inorganic matter insol (7o) - 0.10 0.03 - 0.22 0.02 Furol viscosity at 275 F (sec) - 279 - - 285 -Oliensis spot test Neg. Neg. - Neg. Neg. -Loss on heating at 325 F (̂ 0) 0.04 0.02 0.03 0.03 0.02 0.03 Pen residue, 100 g, 5 sec, 77 F ("/̂ 56 55 55 60 59 60 Orig. pen (%) 93 89 90 92 89 91 Film oven test, Ve-in. film,
5 hr, 325 F : Loss (̂ o) - 0.09 0.08 - 0.08 0.11 Penresidue, lOOg, 5sec, 77 ¥{J^ - 40 40 - 42 41 Orig. pen (7o) - 65 66 - 64 62 Soft point of residue ("F) - 133 132 - 135 134 Duct. r e s . , 77 F , 5 cm/min (cm) - 250 150 - 140 150
T A B L E 3
AGGREGATE CHARACTERISTICS
Characteristic BPR AI Del.
Los Angeles percent of wear 24.7^ 21.6^ 27.5b Sodium sulfate soundness loss (7o) 4.6 - -Specific gravity:
Sand equivalent 86 83 -^ased on grading C, AASHO Method T96. °Based on grading A, AASHO Method T96.
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taken from the roadway before removal of the blocks (Figs. 4 and 5). Wearing course specimens were sawed from the binder course in the laboratory.
MATERIALS
Asphalts The two special asphalts used in the study were sampled at the plant during the mix
ing operation. The samples were sealed in 1-gal containers and shipped to the individual cooperators for testing purposes. Pertinent information and sample identification are given in Table 1.
Test characteristics of each asphalt as determined by each cooperator are given in Table 2. It is apparent from this table that there is little difference in the usually-measured physical characteristics of the two asphalts. Both asphalts had about ttie same resistance to hardening in the thin-film test, although the BPR results did indicate some difference in the ductility of the thin-film residue. However, the significance of differences at such high values of ductility is not known.
Aggregate
The aggregate was crushed limestone and screenings from Downingtown, Penn. A 3,000-lb portion of the combined hot aggregate was obtained by dry mixing weighed components from each hot bin and dumping into a clean truck. The first batch was wasted to clean the pugmill. The second batch was dumped from the truck to a concrete platform and bagged by random sampling. Ten 100-lb bags of the aggregate were then prepared for each cooperator.
Aggregate characteristics are given in Table 3. Variations in percent of wear as indicated in the table may possibly be attributed to the different methods used by the cooperators. The Bureau of Public Roads value of 24. 7 percent was based on grading C d AASHO Method T 96 and the 27. 5 percent value determined by Delaware was based on grading A. Grading A requires a 1/a-in. maximum size aggregate in contrast to a ^s-in. maximum size aggregate of grading C . The low value of 21.6 percent wear was determined by the Asphalt Institute using grading C .
ASPHALT CONTENT BY D I F F E R E N T DESIGN METHODS
The actual grading of the aggregate and percentage of asphalt used in the asphaltic mix was established from similar mixes that, through years of service, have performed satisfactorily.
^ased on effective specific gravity of aggregate, 2.802, for BPR tests and apparent specific gravity, 2.8II4 , for AI tests.
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However, it was of interest to compare the results of design studies, conducted by different laboratories using various methods. Three methods of design (Marshall, Hveem, and immersion-compression) were used. All laboratories made studies with the Marshall method; the Bureau of Public Roads and the Asphalt Institute conducted studies using the Hveem method, and the Bureau of Public Roads also conducted studies using the immersion-compression method.
Aggregates used in this study were proportioned to practically identical gradations by each cooperating laboratory. This was done by separating the aggregate into sieve-size fractions, down to the No. 20 sieve and recombining. The grading used in the design studies was determined from an average of 15 routine hot bin, dry gradations and 17 extracted aggregate dry gradations. It was agreed that the average of the 32 gradations would be used in the design studies to approximate as closely as possible field conditions.
Table 4 shows the design gradations used and the gradations of samples shipped to the individual cooperators. It indicates the normal variations to be expected in conducting aggregate gradation analysis, and also shows that for this aggregate there was little variation between washed and dry analysis.
To compute void contents of compacted bituminous mixtures by use of conventional formulas accurately, the specific gravity of the aggregate, which takes into account the absorption of asphalt, must be known. An aggregate effective specific gravity between the bulk and the apparent specific gravity would normally be the most accurate specific gravity for use in determining void values. The limestone aggregate used in this study has low water absorption characteristics approximately 0. 5 percent; this indicates that void contents, obtained by using apparent and effective specific gravities, have negligible differences. The Public Roads data in Table 3 sliowed a difference between the apparent and bulk specific gravities of 0.05 and the Asphalt Institute and Delaware tests showed differences of 0.02. The latter is within the tolerance prescribed by the standard method for determination of specific gravity by AASHO test procedures.
Marshall Method
Marshall design methods were studied by all three cooperators. In Delaware and Public Roads design tests, the 50-blow mechanical compactor was used with the flat-type head. Hand-operated equipment was used by the Asphalt Institute. Void values obtained using the Marshall procedure are based on apparent specific gravities of the aggregate as determined by each individual cooperator.
Tables 5 and 6 show normally-expected trends for each cooperator. However, Asphalt Institute bulk specific gravity values are somewhat higher than bulk specific gravity values determined by the other two cooperators. The higher stability values determined by the Asphalt Institute are in agreement with their higher values of bulk
T A B L E 8
HVEEM STABILOMETER AND COHESIOMETER TEST RESULTS OF LABORATORY PREPARED MIXTURES, ASPHALT B
Asphalt Content Specimens Specific Gravity * ^ a Stabllometer Cohesiometer Asphalt Content Specimens
Theoretical* * ^ a Stabllometer Cohesiometer Cooperator Mix Basis per Test Bulk Theoretical* Voids Value Value (after Cooperator
^ased on effective specific gravity of aggregate, 2.811, for BPR tests and apparent specific gravity, 2.8li4, for AI tests.
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15
m a
CE
8 a.
I 2 AGE OF PAVEMENT-YEARS
ASPHALT A - F L E X I B L E BASE
15
CO o > 10 ct < u. o
!• J-r
I 2 AGE OF PAVEMENT- YEARS
ASPHALT A-RIGID BASE
D E L B P R
A I
15
M O
5 tol
15
CO o 5 , 0 c < II. o
0 1 2 3 AGE OF PAVEMENT- YEARS
ASPHALT B - F L E X I B L E BASE
I 2 AGE OF PAVEMENT-YEARS
ASPHALT B-RIGID BASE
Figure 7. Percent of air voids, with years of service.
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specific gravity. These higher bulk specific gravity and stability values could be attributed to the use of hand-operated equipment.
Hveem Method The Hveem Method of design was studied by the Bureau of Public Roads and the
Asphalt Institute. Testing procedures used by each cooperator were essentially those of ASTM method D-1560.
Void percentages, however, were computed differently—Asphalt Institute void computations are based on the apparent specific gravity of the aggregate and Bureau of Public Roads void computations are based on the effective specific gravity, of aggregate as determined by the Rice vacuum saturation procedure.
Table 7 and 8, Hveem stabilometer test results, show trends similar to the trends given in Tables 5 and 6. Hveem stabilometer and cohesiometer values are in accordance with the densities shown.
Immersion-Compression Method
The results of the immersion-compression design method, conducted by the Bureau
T A B L E 9
SUMMARY DESIGN VALUES
Asphalt A Asphalt B
Del. BPR AI Del. BPR AI
Marshall method: Design asphalt content mix basis (̂ o by
wt) for: Maximum density Maximum stability 80 percent voids filled 4 percent air voids^ Avg.
Bulk specific gravity at design asphalt content
Hveem method: Design asphalt content mix basis (% by wt) for stabilometer value of 35
Bulk specific gravity at design asphalt content 1̂
Air voids at design asphalt content (̂ o) Immersion compression:
Design asphalt content mix basis {% by wt) for percent voids
^ased on apparent specific gravities of aggregate as given m Table 3. Based of effective specific gravities as given m Table 7 or 8 for BPR and apparent
specific gravity for AI. °Based on effective specific gravity of 2.801 for asphalt A mixture and 2.803 for asphalt B mixture. "̂ Ratio of wet strength after h days immersion in water at 120 F compared to in i t ia l dry strength.
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of Public Roads, are given in Table 9. .Void values were based on effective specific gravities of the aggregate as determined by the Rice vacuum saturation procedure.
Summary of Design Results
Table 9 summarizes the design values determined by each testing procedure. The table includes the individual asphalt contents determined for each of the four criteria used in setting the MarshaU design value. The Marshall method design asphalt contents determined by Delaware, Bureau of Public Roads, and Asphalt Institute, were 5. 5, 5. 5, and 5.1 percent, respectively, for asphalt A, and 5. 5, 5. 5, and 5. 2 percent for asphalt B ; These asphalt contents are in accordance with the bulk specific gravities given.
The design asphalt contents determined by the Hveem Method by each laboratory are in closer agreement than the asphalt contents determined by the Marshall method. Design asphalt contents for both asphalts A and B range in value from 5.0 to 5. 2 percent.
The immersion-compression design procedure was studied by the BPR only. The optimum asphalt content using this procedure was 4.6 percent for both aspnalts, significantly lower than the optimum contents indicated by the other methods. There is no apparent explanation for this. Al l earlier work by the Bureau of Public Roads has indicated that the three methods should produce essentially the same design value.
PAVING MIXTURES
Samples of the mixtures were taken from the paver immediately before resurfacing. Results of gradation tests on the extracted aggregate are given in Table 10. The table indicates a maximum difference of two percentage points, between cooperators' results, in the amount of niaterial passing the No. 200 mesh sieve. Also, Asphalt Institute and the Bureau of Public Roads percentages of material passing the No. 200 sieve are consistently higher than the percentages reported by Delaware. These slight differences could be due to the fact that Delaware's results are based on dry gradations in contrast to the wet gradations as used by the other two cooperators.
TABLE 10 AGGREGATE GRADATIONS AND BITUMEN CONTENTS OF LOOSE MIX
^tepresents mixture used ui pavement of BPR sampling area. IWet gradations. g r y gradations, AASHD Method T-30. Tlepresents mixture used in pavement of Delaware Sampling area.
T A B L E 11
AGGREGATE GRADATION AND BITUMEN CONTENTS OF WEARING COURSE DilMEDLATELY AFTER CONSTRUCTION (1958)
Delaware* Bureau o l PubUc Roads'" Aaphall I n a l l t u l e ' ' ' ' Percent Paflslng
'/i-In y . - I n No * No 10 No 20 No 40 No 80 No Percent
AC ' A - I n y . - l n
Percent Paaslng Percent
No 4 No 10 No 20 No 40 No 60 No 200 AC ' / . - I n y . - I n No t
Percent Paaatng Percent No 10 No 20 No 40 No 60 No 200 AC
too 87 9 60 2 41 1 22 5 15 0 10 9 8 1 S S fpry gradfttlon ^ e t gradaUon. AASHO Method T-30
Gradatlona made on composite samples
T A B L E 13
AOCHEGATE GRADATION AND BITUMEN CONTENTS OP WEARING COURSE AFTER TWO YEARS (1960)
Delaware Bureau of Public Roads
Sample Percent Passing Asphalt InsUtutefc.g
Percent -y . - I n y . - I n No 4 No 10 No 20 No 40 No 80 No 200 AC ' / . - I n y . - I n No 4
Percent Paaslng Percent Passing
y . - I n No 4 No 10 No 20 No 40 No 80 No 200 A F - l AF-3 AF-3 AP-4 Avg AR-1 AR-2 AR-3 AR-4 Avg B F - 1 BF-S BF-3 BF-4 Avg BR-1 BR-2 BR-3 BR-4 Avg Avg
avg 2.357 21 93 4 8.2 2 402 26 95 2 6 5 2 385 24 94 5 7.1 ^ a s e d cai l a b o r a t o r y b u l k s p e c i f i c g r a v i t i e s g i v e n i n Table 19-° B a s e d on v a l u e s o f MTD g i v e n i n Tab le 1 9 .
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TABLE 18 COMPRESSIVE STRENGTH TESTS OF CORES FROM ASPHALTIC PAVEMENT BY PUBUC ROADS
After One Year After Two Years Immediately After Construction Bulk Specific Compressive Bulk Specific Compressive
Identilicatlon Bulk Specific Compressive Gravity Strength Gravity Strength Gravity Strength
^ a s e d on Rice saturation vacuum precedure. Based on mixture containing 5.5 percent asphaltj used i n computing percentage of laboratory
density for pavement samples. ^fJL used Marshall bulk s p e c i f i c grav i t i e s to compute percent compaction. Del. and AI values based on 5.5 percent asphalt i n mixture and apparent s p e c i f i c grav i ty
of aggregate.
T A B L E 20 PROPERTIES OF ASPHALTS RECOVERED FROM WEARING COURSE
Immediately After Construction After One Year (1959) Alter Two Years (1960)
Sample Pen 100 g, 5 sec, 77 F
Softening Point (°F)
Ductility 77 F , 5 cm/min
Pen 100 g, 5 sec, 77F
Softening Point (°F)
DuctiUty 77 F , 5 cm/ min
Pen. 100 g 5 sec, 77 F
Softening Point (°F)
Ductmty 77 F , 5 cm/min
Del. AI BPR Del. AI BPR Del AI BPR Del AI BPR Del. AI BPR Del AI BPR Del AI BPR Del AI BPR Del. AI BPR
As previously indicated, the primary objectives of the research are to measure the chaises occurring in characteristics of the pavement and asphaltic binder during service and to establish specific relationships between the various characteristics.
To accomplish this, pavement samples were taken immediately after construction, and after one and two years of service. Further periodic tests will be made until the conclusion of the study.
< P 3 0
I 2 AGE OF PAVEMENT-YEARS
ASPHALT A-FLEXIBLE BASE
30
I 2 AGE OF PAVEMENT- YEARS
ASPHALT A-RIGID BASE
D E L BPR
AI
0 1 2 3 AGE OF PAVEMENT-YEARS
ASPHALT B-FLEXIBLE BASE
0 1 2 3 AGE OF PAVEMENT-YEARS
ASPHALT B-RIGID BASE
Figure 8. Penetration of recovered asphalt, with years of service.
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The b l o c k samples shown i n F i g u r e 3, w e r e used f o r e x t r a c t i o n tests and tests on r e c o v e r e d asphal t .
Gradat ions
Grada t ions w e r e made on the aggregate f r o m each i n d i v i d u a l b lock sample by D e l a w a r e and the B u r e a u of Pub l i c Roads. The tes t values r e p o r t e d by the Aspha l t Ins t i tu te a re r e s u l t s of composi te b lock samples f o r s amp l ing pe r iods 1 and 2. T h i r d s amp l ing
2iS K t
160
z u kJ
8 g
1201 I- \-v\
AGE OF PAVEMENT-YEARS ASPHALT A-FLEXIBLE BASE
I 2 AGE OF PAVEMENT-YEARS
ASPHALT A-RIGID BASE
DEL BPR
A l
180
0 1 2 3 AGE OF PAVEMENT-YEARS
ASPHALT B-FLEXIBLE BASE
180
Ob
i i Z U i 5 u j
160
120 -H- -tr
- i -4 n
0 1 2 3 AGE OF PAVEMENT-YEARS
ASPHALT B-RIGID BASE
Figure 9. Softening point of recovered asphalts, with years of service.
60
70
65
6 0
55
50
45
4 0
(jj Q. 30
25
20
15
PENETRATION VERSUS SOFTENING POIN ASPHALT A
T PENETRATION VERSUS SOFTENING POIN ASPHALT A
• •
• A •
• •
^ A
• • " 5 afA^
i i • A A
•
# Deloware
• Bu. Publ
V Asphalt
c Rds
Inst
120 125 130 135 140
SOFTENING POINT
145 150 155
Figure 10. Penetration vs softening point, asphalt A.
61
70
65
6 0
55
50
45
4 0
z UJ Q. 3 0
25
20
PENETRATION VERSUS SOFTENING POIN ASPHALT B
T PENETRATION VERSUS SOFTENING POIN ASPHALT B
• V
• < •
• ( ̂ : •
# Delaware
A Bu. Pub!
V Asphalt
c Rds
Inst
120 125 130 135 140
SOFTENING POINT •
145 150 155
Figiire 11. Penetration vs softening point, asphalt B.
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300
200
• 100 90
Q 80 70
60
50
40
30
20
P E N E T R A T I O N V E R S U S D U C T I L I T Y A S P H A L T A
A V
10
• Delaware
• Bu. Public Rds
V Asphalt Inst
15 20 25 30 35 40
PENETRATION
Figure 12. Penetration vs ductility, asphalt A.
X 45
63
300
200
d 100 9 0
Q 80
70
60
50
4 0
30
20
10 L -15
P E N E T R A T I O N V E R S U S D U C T I L I T Y A S P H A L T B
Y •
A
L
• Delawore
A Bu Public Rds
Y Asphalt Inst
I 20 25 30 35
PENETRATION
4 0 45
Figure 13. Penetration vs ductility, asphalt B,
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p e r i o d tes t values r e p o r t e d by the A s p h a l t Ins t i tu t e a re averages of fou r b l o c k samples . A l l De laware aggregate gradat ions w e r e unwashed, whereas washed gradat ions w e r e used by the Bureau of Pub l i c Roads and the Aspha l t I n s t i t u t e .
Tables 1 1 , 12, and 13 g ive the gradat ions and asphal t contents of the pavement s a m p l e s . A n a l y s i s of these ind ica te that sec t ion A R i s low i n percentage of aggregate pass i n g the No . 200 mesh s ieve as compared w i t h the other three sec t ions .
StabiUty
T h e c o r e d spec imens w e r e used f o r v a r i o u s s t a b i l i t y t es t s . De laware p e r f o r m e d only M a r s h a l l t es t s . B u r e a u of Pub l i c Roads p e r f o r m e d M a r s h a l l and imconf lned c o m p r e s s i o n tes ts , and the Aspha l t Ins t i tu t e p e r f o r m e d M a r s h a l l and H v e e m tes t s . The De laware and Aspha l t Ins t i tu te M a r s h a l l values a re averages of f o u r tes ts . B o t h t m -conf ined compres s ion and Hveem tes t specimens w e r e made f r o m s tacked co re s .
The r e s u l t s of M a r s h a l l tes ts a re g iven i n Tables 14, 15, and 16. F i g u r e 6, w h i c h shows the r e l a t i o n of s t a b i l i t y and age f o r each e:q>erimental sec t ion , indicates increases i n s t a b i l i t y over the t w o - y e a r p e r i o d i n a l l sec t ions . On the o ther hand, tests i n the H v e e m apparatus (Table 17) and compres s ive s t r eng th values (Table 18) show h ighe r s t a b i l i t i e s a f t e r the f i r s t yea r bu t decreas ing s t a b i l i t y a f t e r the second yea r . F i g u r e 7 shows a de f in i t e r educ t ion i n a i r voids over the f i r s t yea r p e r i o d , w h i c h i s i n l i ne w i t h the increase i n s t a b i l i t y , bu t average values f o r the t w o - y e a r samples a re e r r a t i c . The gene ra l t r end i s f o r a l e v e l i n g o f f , bu t i n some cases the t w o - y e a r averages w e r e s l i g h t l y h igher than the one-year va lues .
Tab le 19 g ives the s e v e r a l spec i f i c g r a v i t i e s used by the three coopera tors i n c o m put ing voids and percent of l a b o r a t o r y densi ty f o r the preceeding tab les . The d i f f e r e n c e s i n t e s t r e s u l t s between the coopera to rs a re p a r t i a l l y due to the use of d i f f e r e n t s p e c i f i c g r a v i t i e s . However , the p r i m a r y reason f o r d i f f e r e n c e s i s p robably due to e x p e r i m e n t a l e r r o r o r to ac tua l d i f f e r e n c e s i n the pavement s amp l ing a reas . I n the f u t u r e i t i s planned to interchange samples to es tab l i sh the e f f e c t of d i f f e r e n c e s i n s amp l ing areas .
Changes i n Aspha l t C h a r a c t e r i s t i c s
Tab le 20 g ives the n o r m a l changes evident f r o m yea r to yea r . E v e n though the re a r e some incons is tencies ( d u c t i l i t y tes t r e s u l t s ) , t he re seems to be subs tan t i a l ly good agreement among l a b o r a t o r i e s .
F i g u r e 8 shows the r e l a t i o n of the penetra t ions of r e c o v e r e d asphalts f r o m pavement samples w i t h yea r s of s e r v i c e . F o u r plates a re shown, each r ep resen t ing an e x p e r i m e n t a l condi t ion ; that i s , asphalt A over a f l e x i b l e o r r i g i d base, and asphalt B f o r the same cond i t ion . The data p lo t t ed i n the graphs a re the average r e s u l t s obtained by each coopera tor f o r each cond i t ion . A l though there a re some d i f f e r e n c e s i n the p a t t e r n obtained by the d i f f e r e n t l a b o r a t o r i e s , the data obtained a f t e r two yea r s indicate good agreement between coope ra to r s ' r e s u l t s . T h i s may be a t t r i b u t e d t o be t te r s t anda rd iza t i o n of the tes t methods used by each coopera tor o r i t may indicate that e a r l y d i f f e r e n c e s i n d i f f e r e n t sect ions of the pavement tend to disappear w i t h t i m e . Aspha l t Ins t i tu te r e s u l t s f o r z e r o and one yea r a r e values f o r composi te b lock samples (that i s , a sample cons i s t ing of A F - 1 , 2, 3, and 4 ) , whereas Delaware and Bureau of Pub l ic Roads r e su l t s a r e averages of separate de te rmina t ions f o r each b lock . T w o - y e a r samples w e r e tes ted by the Aspha l t Ins t i tu t e i n the same manner as the other coopera t ing l a b o r a t o r i e s . The method of e x t r a c t i o n was changedby De laware f o r the two-yea r samples . P r e v i o u s l y , ex t r ac t ions were p e r f o r m e d by c e n t r i f u g i n g (AASHO Method T164) . T w o - y e a r samples w e r e tes ted by the r e f l u x method (Fau lwe t t e r e x t r a c t o r ) , i n accordance w i t h AASHO method T184 . T h i s was an a t tempt to l i m i t the amount of dust be ing in t roduced in to the ex t r ac t ed asphal t to a m i n i m u m . The asphalt s o l u t i o n f r o m Method T164 and T184 was not supe rcen t r i f uged .
F i g u r e 9 shows i n gene ra l the n o r m a l increases expected except f o r the unusual ly h igh r e s u l t s obtained by De laware f o r the one-year samples . T h i s may be e x p e r i m e n t a l e r r o r r e s u l t i n g f r o m h igh dust content i n the r e c o v e r e d sample .
F i g u r e s 10 and 11 show the r e l a t i o n of pene t ra t ions to so f ten ing points of r e c o v e r e d asphalts f o r bo th asphalt A and B r e spec t i ve ly . C o m p a r i s o n of the slopes of the two p lo ts shows that asphalt A has a s l i g h t l y g r ea t e r negative s lope.
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F i g u r e s 12 and 13 a re p lo t s of d u c t i l i t y vs pene t ra t ion . T h e r e i s cons iderable sca t t e r i n the data points bu t a close look at these p lo ts Indicates that the data f o r each l a b o r a t o r y tends to es tab l i sh a p a r t i c u l a r c u r v e . The cu rves es tabl i shed by each c o -opera to r a re a p p r o x i m a t e l y p a r a l l e l .
T r a f f i c
The e f f e c t of t r a f f i c on the e x p e r i m e n t a l sec t ion has not shown any d e f i n i t e t r ends ; however , c e r t a i n i n d i v i d u a l samples ind ica te g r ea t e r dens i t ies and s t a b i l i t i e s f o r b locks 3 and 4 . T h i s may be due to t r a f f i c hugging o r even c r o s s i n g the centerUne . The annual average 24 -h r t r a f f i c i nc lud ing a l l veh ic les d u r i n g 1960 was app rox ima te ly 1,050.
CONCLUSIONS
A t p resen t no s p e c i f i c conclusions can be d r a w n , but the l a b o r a t o r y tests i nd ica t e . that va r iances i n behav ior of the same asphal t a t d i f f e r e n t locat ions i n the r o a d may be as g rea t as o r g r ea t e r than var iances i n the asphalts f r o m the d i f f e r e n t c rude sources used i n t h i s s tudy. Other than m i n o r r e f l e c t i o n c r a c k i n g f r o m the concrete base on the r i g i d sec t ions , no d e t e r i o r a t i o n i n the pavements has been noted at any loca t ions .
