The Potential Use of Tar Sand Bitumen As Paving Asphalt J

2,5,'2:-

THE POTENTIAL USE OF TAR SAND BITUMEN AS PAVING ASPHALT

J. Claine Petersen Distinguished Scientist Western Research Institute larami e • Wyomi ng

. INTRODUCTION

The amount of asphalt used annually is about 30 million tons of which about 24 million tons is used in paving. Thus, the potential exi sts for util i zati on of si gnifi cant amounts of tar sand bi tumen in paving if the bitumen were commercially available and if the properties of tar sand asphalts were suitable for paving use. The commerci a 1 application of tar sand bitumen as a paving material has been limited to the direct use of the tar sand as a surfacing material. Tar sands from the Asphalt Ridge,U~ah, deposit are quarried and blended with dry sand to pave county roads, parking lots, and driveways. Petroleum asphalt is added to limestone tar sands from the Uvalde, Texas, deposit to prepare a pa vi ng materi a 1. Through the 1930' s, crushed tar sand from the Santa

Rosa, New Mexico, deposits were used to pave roads, streets, and airport runways as far away as Seattle, Washington; and during the 1940's tar sands from deposits in Utah, California, and Kentucky were quarried for application as paving materials. The tar sands as obtained from quarri es, however, do not meet exi sti ng specifi cati ons as a hi ghway construction material.

In thi s paper, several past studi es (l-.!) desi gned to evaluate recovered tar sand bitumen as a pavi ng materi a 1 are revi ewed and the

Prepared for presentati on at the 1987 Summer Meeti ng of the Interstate Oil Compact Commission, Coeur d'Alene, Idaho, June 22-24, 1987.

1 results of the studies compared. Considerable data interpretation and some additional data are supplied by the author. The properties of tar sand asphalts prepared from recovered bitumen are compared with those of petroleum asphalts. The properties evaluated are those used for the specification of paving asphalts together with additi.onal properties deemed important to the performance of asphalt in pavements.

MATERIALS EVALUATED

Tar sand asphalts prepared from different material sources and by different recovery methods are discussed in this paper. They are 1) an aspha lt prepared from sandstone deposi ts near San Lui s Obi spo, California (Edna), and recovered using a light oil-assisted, hot

(alkaline) water separation process U); 2) two asphalts prepared by a similar process from Asphalt Ridge tar sand deposits near Price

(Sunnyside) and Vernal (Asphalt Ridge), Utah (~); 3) two asphalts prepared from bi tumen recovered duri n g the Larami e Energy Technology Center's U.S. DOE in situ combustion project (TS-2C) (il conducted at Utah's Northwest Asphalt Ridge deposit (Vernal); and 4) two asphalts prepared from bi tumen recovered duri ng the Larami e Energy Technology

Center's U.S. DOE in situ steamflood recovery project (TS-IS) (~), also conducted at the Utah Northwest Asphalt Ridge deposit. The two asphalts prepared from the in si tu combusti on bi tumen were prepared to grade by the author and supplied to the subsequent investigators (~) for evaluation. Several representative petroleum asphalts, identified in the text, were used for property compari sons. Experimental details

2 necessary for clarity are briefly provided as needed in the text. For additional detail the reader is referred to the original papers.

COMPARISON OF THE TAR SAND AND PETROLEUM ASPHALTS BASED ON PROPERTIES OFTEN USED FOR SPECIFYING PAYING ASPHALTS

Before discussing the specific properties of the tar sand asphalts, a few comments will be made regarding paving asphalt specifications. These specifications, which have evolved over the years, deal with easily measured asphalt properties that define the asphalt's suitability for use in paving mixtures. Consistency measurements (e.g., viscosity or penetrati on) are probably the most important pri mary specifi cati on considerations because they are important in determining the properties of the pa vi ng mi xture duri ng preparati on and duri ng pavement construc tion as well as the properties of the finished pavement. Some specification tests may not be functional with regard to pavement performance. Many important performance properties of paving asphalts such as long-term durabil ity and factors related to pavement moi sture damage are not adequately defined by standard specifications. Thus, additi ona 1 speci a 1 tests are often necessary; however, these speci a 1 tests have not been standardized for use in current paving technology. Although each state or local unit may impose unique restrictions or modifications regarding specifications, general specifications have been adopted at the national level and can be found in readily available publications (2.. ~). Specification-type data cited in the discussions in this paper are those generally accepted by most transportation agencies, although all agencies may not use the same types of data.

3 The approach used by a 11 of the i nvesti gators to prepare candi date tar sand asphalts was to first prepare a material, by distillation of oi 1 s if necessary, to meet consi stency specifi cati ons (penetrati on or

vi scos;ty). foll owed by the measurement of other properti es to determi ne

how these remai ni ng properti escompared wi th those of speci ncati on

petroleum asphalts.

Tar Sand Asphalts from Hot Water Process

In Table 1 the properties of the three tar sand asphalts recovered

by the hot water process (from tar sand deposits in Edna, California, and Sunnysi de and Vernal, Utah) are compared with the properti es of

three petroleum asphalts prepared from different crude oil sources. The consistency of all three petroleum asphalts was 80 penetration at 77°F (2S·C); penetration values of the Edna, Sunnyside, and Vernal tar sand asphalts were 80, 84, and 64, respectively. Both viscosity and penetration measurements at temperatures other than 77°F (2S0C) for the tar sand asphalts compare favorably with those of the petroleum asphalts and fall within the normal range of variability expected for materials from different sources.

Results of the ash determinations, spot tests, and loss on heating measurements for the tar sand asphalts, however, were different than correspondi ng results for the petrol eum asphalts and requi re further di scussi on. As seen in the table, the ash content of the tar sand .. aspha 1ts was consi derab 1y hi gher than that of the petrol eum asphalts.

Also, ash determinations by direct ashing of the tar sand asphalts was considerably higher than determinations by a filtration method using an asphalt solution (ASTM D4-42). The lower ash content obtained by

4 Tab 1e 1. Compari son of PrQperti es of Tar Sand Asphalts Prepared from Hot WUet-Separated Bitumen with Properties of Several Petroleum Asphalts L

Tar sand asghalts Petroleum as~fia1ts ,~ Edna, Sunnyside, Vernal, Kern Rtver, Oregon Basin, Tampi co, ;- Ca 1i fl Utah 2 Utah 2 Ca 1ifl Califl Mexico 1 '1 1- ! Asphalt yield, % 100 100 94.5 53.0 43.6 72.2 Ash, % 0.53 , 2.04 0.8 3 , 2.14 0.53 , 1.84 03 03 03 I Spot test Positive Posi ti ve Positi ve Negative Negative Negati ve Solubility in carbontetrachloride, % 99.6 100 100 100 100 100 I Specific gravity, 77°F (25°C) 1.087 1.020 1.012 1.012 1.028 1.038 Flash point, of (OC) 505 (263) 460 (238) 505 (263) 550 (288) 570 (299) 510 (266) i Penetration, dmm $ 77°F (25°C), 100g, 5 sec 80 84 64 80 80 80 $• t1l 60°F (15.5°C), 100g, 5 sec 26 32 18 22 26 34 ~ 34°F (1°C), 200g, 60 sec 14 23 11 10 17 26 •il" Viscosity, poise 210°F (99°C) 24.4 62.6 36.7 18.3 33.8 72.6 275°F (135°C) 2.71 7.39 3.93 1.93 3.72 7.31 Ductility, 77°F (25°C), 5 cm/min 100+ 100+ 100+ 100+ Ii § Softening point, of (OC) 116 (47) 123 (51) 121 (49) 111 (44) 116 (47) 121 (49) i Loss on heating, % 0.45 0.40 0.11 0 0 0.2 ,~ 77°F (25°C) Pen of ~ loss on heating residue 66 57 54 71 70 68 1 t '1 1 Data from (1) ~ I 2 Data from ("2) ,/ 3 ASTM 04-42- I 'I Di rect ash j I j ! t I fil trati on ref1 ects the fi neness of the mi nera 1 parti c1 es in the tar sand asphalt. Although most asphalt speci fi cati ons 1 i mi t ash content, sma 11 amounts of mi nera 1 matter in the asphalt may not necessaril y be detrimental. A certain amount of mineral fines are a normal part of a pavement aggregate mixture. Small amounts of ash in tar sand asphalts coul d most 1i kel y be taken into account duri ng the desi gn of the pavement mixtures. The spot test measures the presence in asphalts of components that are not soluble in petroleum naphtha. The test in itself is non functi ona 1 wi th regard to pavement performance and was i niti ally deve loped to detect aspha lts that had been thermally cracked duri ng manufacture. Such asphalts often had poor component compatibility that resulted in poor aging and flow characteristics. The tar sand asphalts probably gave a positive spot test because of the presence of the mineral matter just described. As will be seen later, evidence suggests that tar sand asphalts may actually have better aging characteristics than typical petroleum asphalts. Loss on heating data were obtained from a test in which an asphalt film was exposed to the atmosphere at 325°F (163°C) for a specified period of time. The test detects asphalts with volatile components that might be lost both. during the hot mix operation and possibly during the service life of the pavement. Volatile loss leads to undesirable hardening of the asphalt. The asphalt also hardens from air oxidation during the test. If both volatile loss and oxidation occur simultaneously during the test, it is difficult to assess the relative contribution of each factor to the total hardening of the asphalt. Both the Edna and Sunnyside tar sand asphalts showed relatively high volatile

6 loss (Table 1) compared with the petroleum asphalts. Thi sloss undoubtedly contributed to the relatively high drop in 77°F (25°C) penetration for the tar sand asphalts (80 to 66 and 84 to 57) during the loss on heating test. Support for thi s explanation can be found by examination of the relatively lower drop in penetration (64 to 54) for the less volatile Vernal asphalt. Volatile components found in the laboratory-prepared asphalts may not represent an inherent deficiency of the tar sand bitumen but may reflect the presence of components introduced by the the method of bitumen recovery and/or the inefficiency of the laboratory distillation. The previous investigators estimated

(2) that approximately two percent of the fuel oil diluent used in the recovery process remained in the bitumen. This may have contributed to the volatility observed.

Tar Sand Asphalts from In Situ Steamflood

Data in Table 2 compare the properties of two tar sand asphalts prepared from bi tumen obtained by in si tu steamf100d (.±.' 6) whi ch meet the consi stency requi rements of AC-5 and AC-30 pa vi ng asphalts. The properties are compared with Table 1 and Table 2 ASTM specifications for the corresponding grades of petroleum asphalts. Table 2 specifications are more restrictive than those of Table 1. The data show that the tar sand asphalts easily met both sets of speci fi cati ons. The hi gh 77 of

(25°C) penetration value for the tar sand AC-5 asphalt suggests that it has a low temperature suscepti bil i ty in the lower temperature range.

This property could be desirable since it often relates to better pavement resistance to low-temperature cracking. The relatively high ductility for the AC-30 tar sand asphalt also suggests the potential for good low temperature flow properties.

7 Table 2. Comparison of Properties of Tar Sand Asphalts Prepared from Utah In Situ Steamflood-Bi-tumen-wlth SpeeHi-eationsfor Paving Asphaltsl

AC-5 Asphalt AC-30 Asphalt ASTM ASTM TS-1S !~ Specifications TS-IS Specifications +600°F (+316°C) l for AC-5 Bitumen for AC-30 residue I Yield from TS-IS Bitumen, % 100 93 i Solubility in trichloroethylene, % 99.0 (min) 99.7 99.0 (min) 99.7 I Flash point, C.O.C., of (OC) 350 (177) (min) 450 (232) 450 (232) (min) 511 (266) 00 I Penetration, 77°F (25°C), 100g, 5 sec 1202 , 140 3 (min) 223 50 (min) 63 ! Viscosity, poise i 140°F (60°C) 500±100 515 3000±600 2800 275°F (135°C) 1.102 , 1.753 (min) 1.70 3.50 3 (min) 3.40 Thin-film oven test residue, I Viscosity, 140°F (60°C), poise 2500 (max) 2032 15000 (max) 4290 2 ,3 3 I Ductility, 77°F (25°C), 5 cm/min 100 (min) 105+ 40 (min) 105+ 1 # ~ 1 Data from (4) 2 ASTM D-3381~ Table 1 3 ASTM D-3381, Table 2 l! I Tar Sand Asphalts from in Situ Combustion In Table 3 the properties of two tar sand asphalts prepared from bitumen obtained by in situ combusti on (l,.. 2.) are compared wi th the properties of a petroleum asphalt routinely used as a laboratory standard by the i nvesti gators (1.). The two tar sand asphalts were prepared to AC-IO grade, one by vacuum di sti 11 ati on and the other by fl ash evaporati on. Ash contents of these asphalts were hi gh at near

fi ve percent. Thi s hi gh ash content is refl ected in the tri chl oro ethylene solubility data and possibly in the spot test results. Note that the laboratory standard petroleum asphalt also showed a positive

spot test. yet this asphalt typically performs well in the field.

As previously seen for the in situ steamflood tar sand asphalt. both of the in situ combustion tar sand asphalts showed relatively high

77°F (25°C) penetration values of 196 and 208 compared with the minimum of 70 and 60 shown in the ASTM Table 1 and Table 2 specifi cati ons. respectively. Penetration values measured at 39.2°F (4°C) were also relatively high. indicating a softer asphalt at lower temperatures.

Softening points of the asphalts. on the other hand, were relatively hi gh, i ndi cati ng greater resi stance to flow at somewhat hi gher temperatures.

Viscosity data at 275°F (135°C) show that the viscosity temperature suscepti bil i ty of the tar sand asphalts was re 1ati ve 1y hi gh at hi gh temperatures. This is evidenced by a relatively low viscosity (below specifications) in this temperature region. This temperature region is used during mixing and pavement 1aydown.

Finally. the results of the thin film oven test show that both tar sand asphalts lost weight on heating as a result of volatile loss. while

9 Table 3. Comparison of Properties of Tar Sand Asphalts Prepared from In Situ COlllbustion Process Bitumen with Properties of Laboratory Standard Petroleum Asphaltl

TS-2C Vac TS-2C Flash ASTM Lab standard distilled tar evaporated tar Speci fi cati ons 2 petroleum sand asphalt sand asphalt for AC-10 asphalt Ash, % about 5 about 5 Spot test Positive Positive Posi ti ve Solubility, trichloroethylene, % 94 95 99.0 (mi n) 99.9 Flash point, of 568 (298) 562 (294) 425 3 , 450 4 (min) 697 (369) (OC) (219) (232) Specific Gravity, 77°F (25°C) 0.998 0.995 1.02 Penetration, dmm 77°F (25°C), 100g, 5 sec 196 208 70 3 , 60 4 (min) 118 60°F (I5.5°C), 100g, 5 sec 55 67 o 39.2°F (4°C), 100g, 5 sec 14 12 4 39.2°F (4°C), 200g, 60 sec 55 65 26 Viscosity, poise 77°F (25°C) 2.6x105 2.3x10 5 5.8x105 140°F (60°C) 1070 960 1000±200 1580 275°F (135°C) 1. 36 1. 29 1.503 , 2.50 4 (min) 3.8 Ductility, 77°F (25°C), 5 em/min 53 60 150+ Softening point, of (OC) 127 (53) 121 (49) 107 (42) Thin film oven test Loss on heating, % 1.5 2.1 Negative Pen of residue, 77°F (25°C) 88 94 68 Due of residue, 77°F (25°C) 62 101 50 3 , 75 4 (min) 150+ Vis of residue, 140°F (60°C) 3400 3800 5000 (max) 3050

Data from (3) 2 ASTM D-338C 3 Table 1 4 Table 2 the petroleum asphalt showed negligible loss. As mentioned previously,

these volatiles may be present because of inefficient laboratory dis

tillation during bitumen recovery. The higher volatile loss for the two

asphalts is seen for the asphalt that was obtained by the relatively

inefficient flash evaporation procedure. In spite of the relatively

high volatile losses during heating, the 140°F (60°C) viscosities of the

tar sand asphalt resi dues after heati ng (3400 and 3800 poi se) were sti 11

below the maximum allowed by the specifications. Volatile losses of the

magnitude seen produce significant hardening of the asphalt and probably

account for the major portion of the hardening seen during the thin film

oven test, thus suggesting that the tar sand asphalts are inherently

resistant to oxidative hardening. Oxidative hardening will be discussed

1 ater in more detail. The ductil i ty values of the tar sand asphalt

resi dues from the thi n fil magi ng test were hi gher than the ductil i ty \., _., values measured before thin film aging. These results are highly

unusua 1 and suggest desi rab 1e agi ng characteri sti cs for the tar sand

asphalts.

TEMPERATURE SUSCEPTIBILITY OF TAR SAND ASPHALTS

The suscepti bi 1 ity of asphalt to physi ca 1 property change wi th

varying temperature is an important performance-related variable. In

general, a high susceptibility to a change in consistency with

temperature is undesirable because this can lead to unstable pavements

at high temperatures, which may deform or rut; and to highly brittle

pa vements at low temperature, whi ch may crack from therma 11y-i nduced

11 stress. The temperature susceptibilities of the tar sand asphalts were computed by a number of different methods (l) and compared with corresponding calculated data for several petroleum asphalts. The results of these calculations are shown in Table 4. The vi seosi ty temperature suscepti btl i ty through the temperature range of 140 OF (60°C) and 275 OF (135°C) is shown by data in the fi rst two line entries of Table 4. Greater numerical values indicate greater temperature susceptibility. In general, data for the tar sand asphalts were similar to data for the petroleum asphalts, except for the two in situ combustion asphalts (TS-2C vacuum residue and TS-2C flash residue) which showed higher temperature susceptibilities. The possibility exists that the high mineral fines contents of these asphalts may contribute to the increased viscosity temperature susceptibility of these asphalts in the hi gh temperature range. In the mi dtemperature range, the viscosity temperature susceptibilities of the two tar sand in si tu combusti on asphalts were si mil ar to that of the 1ab standard asphalt, as seen by data in the third line entry of Table 4. The penetration ratio (fourth line, Table 4), calculated from penetration determinations at 39.2°F (4°C) and 77°F (25°C). indicate that the two in situ combustion asphalts may have lower temperature susceptibilities in the low temperature range than the other tar sand asphalts and most of the petroleum asphalts. Lower numerical values for penetration index and data in the remaining line entries in Table 4 indicate lower temperature susceptibilities. Data in the fifth line entry (penetration index) show that the two in si tu combusti on asphalts ex hi bit reduced temperature susceptibilities compared with all other asphalts as calculated from the penetration at 77°C (25°C) and the softening

12 Table 4. Comparison of Temperature Susceptibilities of Tar Sa.nd Asphalts with Temperature Susceptibilities of Petroleum Asphaltsl , Tar sand aSEhalts Petroleum aSEhalts Sunny- TS-2C TS-2C Kern Oregon Edna, si de, Vernal, TS-IS TS-IS Vac Flash Ri ver, Basi n, Tampi co, Lab ! Parameter Calif Utah Utah (AC-5) (AC-30) resi d resid Calif Calif Mexico standard :1 VTS2,3 (140, 275·F) 3.68 3.77 4.22 4.23 3.45 I ( 60, 135·C) I VTS4,3 (210, 275·F) 3.57 3.00 3.42 3.83 3.41 3.22 ( 99, 135·C) I VTS5,3 (77, 140·F) 3.50 3.52 3.61 I (25, 60·C) I w Penetration ratio6 ,7 17.5 27.4 17.2 28 31 12.5 21.2 32.5 22 I } Penetration index8 ,7 -0.92 0.28 -0.74 4.3 3.7 -1. 73 -0.92 -0.14 -1.4 9 I Pen/vis number ,7 -1.05 0.49 -1.27 -1.20 -1.20 -1.55 -0.58 -0.75 -0.10 f 1 1 Parameters calculated from data in (2) and (3); methods of calculation found in (3) 1 2 Viscosity temperature susceptibility-:- calculated from viscosities at 140 (60) and-275·F (135·C) 3 Greater numbers mean greater temperature susceptibility I 4 Viscosity temperature susceptibility, calculated from viscosities at 210 (99) and 275·F (135·C) 5 Viscosity temperature susceptibility, calculated from viscosities at 77 (25) and 140·F (60·C) 6 Calculated from penetrations at 39.2 (4) and 77·F (25·C) I 7 Lower numbers mean greater temperature susceptibility 1 8 Calculated from penetration at 77·F (25·C) and softening point, ·F i 9 Calculated from penetration at 77·F (25·C) and viscosity at 275·F (135·C)

I! I ;{ j Il I, ! I

I point. Calculated pen/vis numbers in the last line entry in the table, obtained from penetration data at 77°F and viscosity data at 140°F

(60"C) - midrange temperature determinations - show that the temperature

susceptibilities of all asphalts were within the same general range.

In summary, the tar sand asphalts, except for the two in situ

combusti on asphalts, showed S1 mil ar temperature suscepti bi 1 i ties to

petY'ol eum asphalts. The two in si tu combusti on tar sand asphalts, on

the other hand, seemed to have greater temperature susceptibility in the

hi gher temperature range and lower temperature suscepti bil i ty in the

lower temperature range.'

COMPOSITION-RELATED PROPERTY COMPARISONS

Limited composition data are available comparing tar sand and

petro 1eum asphalts. Table 5 summari zes vanadi urn, sulfur, and nitrogen

contents of several of the study asphalts together with data on

component analyses as determi ned from sol ubil tty and chromatographi c

characteri sti cs. The vanadi urn content of the two in situ combusti on

aspha lts was low at near 4 ppm. Many petrol eum asphalts have hi gher

vanadium contents than this, sometimes exceeding 1000 ppm. The sulfur

content of the Cal iforni a tar sand asphalt was 3.24 %, in the mi drange

region for petroleum asphalts, while the Utah tar sand asphalts showed

low sulfur contents of 0.50 and 0.38%. The nitrogen contents of the tar

sand asphalts generally were one percent or greater, which is usually

the upper limit for petroleum asphalts, whose typical range is from

about 0.2 to about 0.6% nitrogen.

14 Table 5. eom~ar.t~Q.l!.rr~~-eq-l)flIlT5tttnrr__ Related P-rQpertlesof Tar sand Aspfialts with COrresponding Properties for Petroleum Asphaltsl

Tar Sand asphalts Petroleum asphalts Oregon Edna, Sunnyside, Vernal, TS-2C TS-2C Kern Ri vert Basi n, Tampi co, Property Calif Utah Utah Vac resi d Flash resid Calif Calif Mexico __ 2 __ 2 Vanadi um, ppm 3.7 4.2 __ 2

Sulfur, % 3.24 0.50 0.38 1.23 4.81 6.12 __ 3 __ 3 __ 3 Nitrogen, % 1. 23 0.96 1.2 1.2 1.1 01

Oil s, % 44 31.0 32.0 46.5 46.0 42.5

Resi ns, % 33 48.0 49.5 40.5 33.5 27.5 Aspha1tenes, % 23 23 15 21.0 18.3 13.0 20.5 30.0

1 Data from (1-3) and records of author 2 Not determined. Typical range for most petroleum asphalts is from a few to over 1000 ppm 3 Not determined. Typical range for most petroleum asphalts is from 0.2 to 0.6% Component analyses, as reflected in the oil, resin, and asphaltene determinations that are reported in Table 5, are similar for both tar sand and petroleum asphalts. The significance of component analyses wi th regard to asphalt performance has not been estab 1i shed. Thi sis not surpri si ng si nce the data report only wei ght percents offracti ons and not information on the chemical composition of the fractions.

AGING CHARACTERISTICS OF TAR SAND ASPHALTS

Age-hardening of asphalts in pavement service, primarily from reaction of the asphalt with atmospheric oxygen, is a major factor contri buti ng to reduced durabi 1 i ty, poor performance characteri sti cs, and a shortened servi ce 1 i fe of asphalt pavements. Data presented earlier suggested that some tar sand asphalts might exhibit better-than usual aging characteristics. Data in Table 6 show the properties of the two Utah in situ steamflood asphalts and four petroleum asphalts before and after being subjected to the thin film accelerated aging test (TFAAT). The TFAAT was specifically designed to match, in the laboratory, the level of oxidative aging and the level of volatile loss normally experienced by an asphalt in a typical pavement after 10-15 years of service. In the test, a thin asphalt film (0.16 mm) is exposed at 235°F (113°C) to air under conditions of restricted volatile loss for a period of 72 hours, followed by recovery of the asphalt for evaluation. Because volatile loss is controlled, data obtained on asphalts from this test should be more indicative of actual pavement aging than data obtained from the thin film oven test in which volatile

16 Table 6. Aging~Characteristics of Asphalts Aged Using the Thin Film Accelerated Aging Test (TFAAT)l I 1

Tar sand as~ha1ts Petroleum as~ha1ts I1 TS-1S TS-1S As~halt A .. As~halt B 1 (AC-S) (AC-30) AC-S AC-20 AC""S AC-20 i I Viscosity,2 unaged 4.S9xl02 2.11xl0 3 6.81x102 2.53x10 3 5.14x102 2.S3x10 3 Vi scosity,2 aged 5.68x10 3 1. 74x10 4 9.02x104 1. 79x10 6 1.65x10 4 4.44x10 5 I I " Agi ng i ndex 3 12.4 8.3 132 708 32 175 It Log viscosity increase on agi ng4 2.09 1.92 3.07 3.85 2.51 3.24 I ~ 1 Specialized laboratory aging test run at 23SoF (113°C) in which both the level of oxidation J 7, and volatile loss are controlled to match 10-lS years of pavement aging l 2 Complex dynamic shear viscosity, measured at 140°F (60°C) between 25 mm parallel plates ! ~ spaced 1.0 mm apart, sine wave loading at 50% strain, unaged and aged viscosity ! readings at 15.9 and 0.126 radians/second, respectively I 3 Viscosity after aging divided by viscosity before aging i 4 Log viscosity after aging minus log viscosity before aging 1 q

I i ~ ,I \f :! I I I ! I, ! ! j loss is significantly greater than that which occurs during pavement service. From the viscosity data in Table 6, the log viscosity increase on agi ng and an agi ng index (vi seosi ty after agi ng di vi ded by vi scosi ty before aging) were calculated and are reported in the table. As seen in the table, the vi scosity increase of the tar sand asphalts on agi ng was significantly lower than the viscosity increase of the petroleum asphalts. The aging index data al so suggest superior aging characteristics for the tar sand asphalts. As will be seen in the next section, tar sand asphalts recovered from laboratory-prepared pavement mixtures also showed superior aging characteristics. The reduced hardening rate, together with favorable ductility in aged tar sand asphalts, as mentioned previously, suggest that tar sand asphalts should exhibit excellent durability in pavement service.

PROPERTIES OF ASPHALT-AGGREGATE MIXTURES PREPARED USING TAR SAND ASPHALTS

Asphalt pavement mixtures were prepared in the laboratory (3) using the two TS-2C in situ combusti on asphalts and the 1aboratory standard petrol eum aspha 1t. The 1aboratory mi xtures were prepared usi ng graded gravel and limestone aggregates which met specifications for paving mix tures. The wet and dry strengths of standard specimens fabricated from these mi xtures are shown in Table 7. Tensil e strengths of dry mixtures prepared usi ng the petrol eum asphalt were hi gher than those prepared from the tar sand asphalt; however, thi sis not unexpected because of the higher initial viscosity of the petroleum asphalt (Table 3). Values

18 Table 7. Wet and Dry Strength Properties of Laboratory Pavement Mixtures Prepared from Tar Sand Asphaltsl

Tensile strength2 Tensi 1 e strength Asphalt Aggregate Dry After soak3 ratio'+

TS-2C Gravel 70 100 1.43 Vac' resid Li mestone 85 120 1.41 TS-2C Gravel 70 73 1.04 Flash resid Li mestone 85 110 1.29

Petro~eum Gra ve 1 110 100 0.91 1ab standard Li mestone 150 90 0.60

1 Data from (3) 2 Tensile spll'tting test, 68°F (20°C), 2 in./min displacement rate 3 After soaking vacuum-saturated specimen in water for seven days at 68°F (20°C) '+ Tensile strength after soak divided by dry tensile strength

for the mi xture prepared from the tar sand asphalt are acceptable. Of

particular significance, however, are the tensile strengths of the

specimens after soaking in water for seven days at 68°F (20°C). All

specimens prepared using tar sand asphalts actually increased in

strength after exposure to water, while the specimens prepared using the

petroleum asphalt decreased in strength. The relative differences in strengths of the wet and dry samples are shown in the table as tensile

strength ratios. Tensi 1 e strength rati os for the tar sand asphalt

mixtures ranged from 1.04 to 1.43 compared with values of 0.91 and 0.60 for the petroleum asphalt mixtures.

Most petrol eum asphalt pavement mi xtures lose strength when wet.

In fact, poor pavement performance from the detri menta 1 effects of

moi sture is a major problem inmost parts of the country. Further confirmation of the ability of tar sand asphalts to produce asphalt-

19 aggregate mixtures with superior resistance to moisture damage is shown by the test results in Table 8. In the test (~. sma 11 bri quets are prepared from asphalt-aggregate mi xtures in whi ch a uniform aggregate size is used to allow water to easily penetrate the briquet and also to maximize the effect of the asphalt-'aggregate adhesive bond properties on briquet stabil ity. These bri quets are submerged in water. suspended on a stress pedestal. and subjected to freeze-thaw. warm water-soak cycling until the briquets fail from cracking. In the study from whi ch the results in Table 8 were taken. a moisture-sensitive limestone aggregate was u.sed. Note that the br; quets prepared us; ng the four petroleum asphalts failed in from one to seven freeze-thaw cycles. However. briquets prepared using the two tar sand asphalts failed after 10 and 14 repeated freeze-thaw cycles. Results of this test using other materials have shown a fair correlation with results of moisture tests on laboratory mixtures (~) and with field pavement results (11).

Table 8. Susceptibility of Asphalt-Aggregate Briquets 1 to Moisture-Induced Damage2

Freeze-thaw Asphalt 3 Type cycles to failure B-2959 Petroleum 1 B-3036 Petroleum 2 8-3051 Petroleum 7 B-3602 Petrol eum 2 TS-2C Vac resi d Tar sand 14 TS-2C Flash resid Tar sand 10

1 Briquet prepared using a high calcium limestone 2 Data from (9) 3 All asphaltS; AC-10 grade

20 Asphalts used in the laboratory-prepared mixtures (1) described in

Table 7 were recovered from these mixtures by solvent extraction, and

physical properties were determined for the recovered asphalts. Results are shown in Table 9. Of particular significance are the aging indexes

calcu.lated from the viscosities at 140·F (60·C) before and after the

aging. The aging occurred during specimen preparation and

conditioning. The tar sand asphalts showed lower aging indexes than the

petroleum asphalt. Although the level of aging is relatively low for

these asphalts compared to the 1eve 1 of agi ng of the asphalts from the

TFAAT described earlier, the results do again suggest good aging

characteri sti cs for the tar sand asphalts. The softening point and

penetration data shown in Table 9 are less useful in evaluating the

changes on agi ng because non-Newtoni an flow beha vi or domi nates these

measurements; however, nothing about these data suggests abnormal aging

characteristics for the tar sand asphalts.

SUMMARY AND CONCLUSIONS

The properties of several tar sand asphalts prepared in past

studies by several different investigators were compared with each other and with the properties of petroleum asphalts. These results were

revi ewed and di scussed wi th regard to the potential use of tar sand bitumen in pavement applications. The data show that tar sand bitumens

ha ve good potenti a 1 for use in hi ghway pa vements that meet today IS performance requirements. No deficiencies in the tar sand asphalts were found that would be expected to seriously affect performance. On the

21 '\ 9

Table 9. Comparison of Properties of Asphalts Recovered from laboratory Pavement Mixtures with Properties of Initial Asphaltsl

TS-2C Vac TS-2C Flash Lab distilled tar sand asphalt evaporated tar sand asphalt standard petroleum asphalt Recovered from Recovered from Recovered from Initial Gravel Limestone Initial Gravel Limestone Initial Gravel limestone Penetration. 77°F(25°C). dmm 196 101 103 208 91 120 118 55 53

N 5 5 5 6 5 6 6 N Viscosity. 77°F(25°C). poise 2.6x10 7.0x105 4.0x10 2.3x10 1. Ox10 4.0x10 5.8x105 3.9x10 3.8x10 Viscosity. 140°F(60°C). poise 1.07x10 3 1.70x10 3 1.92x10 3 9.6x10 2 1.78x10 3 1.36x10 3 1.58x10 3 4.63x10 34.32x10 3 Softening point. °F(OC) 127(53) 138(59) 150(66) 121 (44) 149(65) 141(61) 107(42) 129(54) 128(53) Viscosity aging index2 at 140°F (60°C) 1. 59 1. 79 1.85 1.42 2.93 2.73

1 Data from (3) 2 Vi scosi ty oT recovered asphalt divi ded by vi seosi ty of i ni ti a 1 aspha 1t other hand, the data indicate that some tar sand asphalts may have superior aging characteristics, being relatively resistant to oxidative age hardening compared with typical petroleum asphalts. Asphalt- aggr'egate mixtures prepared usi ng two tar sand asphalts also showed acceptab le strength p.roperti es and excell ent resi stance to moi sture- induced damage.

ACKNOWLEDGMENT

The author expresses thanks to the United States Department of

Energy for fundi ng the preparati on of thi s paper under Cooperati ve

Agreement Number DE-FC21-83FE60177.

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