NATIONAL BUREAU OF STANDARDS REPORT

8511

COMPARISON OF XENON AND CARBON ARCS AS

RADIATION SOURCES FOR LABORATORY WEATHERING OF ASPHALTS

by

Keith Go Martin, Paul G, Campbell and James R. Wright

**-*<” l

i nin' "»*"«—<*-

f-r T~fnrrr^&

U.S. DEPARTMENT OF COMMERCE

NATIONAL BUREAU OF STANDARDS
THE NATIONAL BUREAU OF STANDARDS

The National Bureau of Standards is a principal focal point in the Federal Government for assuring

maximum application of the physical and engineering sciences to the advancement of technology in industry and commerce. Its responsibilities include development and maintenance of the national stand- ards of measurement, and the provisions of means for making measurements consistent with those standards; determination of physical constants and properties of materials; development of methods

for testing materials, mechanisms, and structures, and making such tests as may be necessary, particularly for government agencies; cooperation in the establishment of standard practices for incorporation in codes and specifications; advisory service to government agencies on scientific and technical problems; invention and development of devices to serve special needs of the Government; assistance

to industry, business, and consumers in the development and acceptance of commercial standards and

simplified trade practice recommendations; administration of programs in cooperation with United

States business groups and standards organizations for the development of international standards of

practice; and maintenance of a clearinghouse for the collection and dissemination of scientific, technical, and engineering information. The scope of the Bureau’s activities is suggested in the following

listing of its four Institutes and their organizational units. Institute for Basic Standards. Electricity. Metrology. Heat. Radiation Physics. Mechanics. Applied Mathematics. Atomic Physics. Physical Chemistry. Laboratory Astrophysics.* Radio Standards Laboratory: Radio Standards Physics; Radio Standards Engineering.** Office of Standard Ref- erence Data. Institute for Materials Research. Analytical Chemistry. Polymers. Metallurgy. Inorganic Materials. Reactor Radiations. Cryogenics.** Office of Standard Reference Materials. Central Radio Propagation Laboratory.** Ionosphere Research and Propagation. Troposphere

and Space Telecommunications. Radio Systems. Upper Atmosphere and Space Physics.

Institute for Applied Technology. Textiles and Apparel Technology Center. Building Research.

Industrial Equipment. Information Technology. Performance Test Development. Instrumentation.

Transport Systems. Office of Technical Services. Office of Weights and Measures. Office of Engineering Standards. Office of Industrial Services.

* NBS Croup, Joint Institute for Laboratory Astrophysics at the University of Colorado. ** Located at Boulder, Colorado.
NATIONAL BUREAU OF STANDARDS REPORT

NBS PROJECT NBS REPORT

421 .04-12-4210141 31 July 1964 8511

COMPARISON OF XENON AND CARBON ARCS AS

RADIATION SOURCES FOR LABORATORY WEATHERING OF ASPHALTS

by

Keith G e Martin,, Paul G a Campbell and James R 0 Wright

Organic Building Materials Section

Building Research Division

Institute of Applied Technology

Sponsored, by

National Bureau of Standards

IMPORTANT NOTICE NATIONAL BUREAU OF ST

for use within the Government, and review. For this reason, th whole or in part, is not autho Bureau of Standards, Washingt

the Report has been specifically

Approved for public release by the

Director of the National Institute of

Standards and Technology (NIST)

on October 9, 2015.

:ss accounting documents intended

subjected to additional evaluation

! listing of this Report, either in e Office of the Director, National

1 the Government agency for which

:opies for its own use.

U. S. DEPARTMENT OF COMMERCE

NATIONAL BUREAU OF STANDARDS

COMPARISON OF XENON AND CARBON ARCS AS

RADIATION SOURCES FOR LABORATORY WEATHERING OF ASPHALTS

by

Keith Go Martin^— Paul G 0 Campbell and James R. Wright

1 o INTRODUCTION

Laboratory weathering of coating-grade asphalts by an, accelerated weathering cycle was first described by Stricter in 1930 fj]—'. The equipment

consisted of an enclosed carbon arc radiation source,, a rotating cylinder

to hold test specimens,, vertical water jets to simulate rain^ and lawn

sprinklers for vigorous spraying . The heat produced by the carbon arc maintained a temperature of approximately 60 C, C (140®F) at the surface

of the panels. A refrigerator^ as a separate unlt 5 was used to obtain

sudden temperature changes. Asphalt specimens,, 25-mils thick,, were made

on aluminum, panels and specimen failure was determined by visual inspection.

Data were presented on several asphalts exposed to the accelerated weathering cycle and. to outdoor weather. The results were sufficiently similar

so that Stricter recommended the method as a tentative standard of test.

In 1 933 Stricter °s work was published by ASTM as a ““Recommended Practice

for Accelerated Weathering Test of Bituminous Materials"” [2] and^ although

the test has undergone some modification^, it is widely used at the present

time [3]. The principal modifications have been the use of more cycles

[4]j, a uniform method of sample preparation [5], the use of a single

probe spark-generating instrument for detecting crack failures [6, l] s and a multi-probe defector [8].

Numerous papers have been written over the past 35 years in which the

carbon-arc accelerated weathering test was evaluated per se or the test was used, as a research and development fool [ 9 ]. However^ in none of

of these papers has the test been shown, to correlate with actual weathering beyond the status shown by Strieter in 1930 . Also,, it has not been

shown conclusively that this test can be used to predict asphalt durability. A number, of reasons have been advanced showing why it would be

u

Present address; Division of Building Research,, Commonwealth Scientific

and Industrial Research Organization,, Highett, Victoria,, Australia.

2/

Numbers in brackets refer to the list of references at the end of

this report.

- 2

difficult to obtain a correlation between asphalts exposed to the

accelerated cycle and to outdoor weathering. Those reasons include:

the rigid aluminum panel backing [10], the regularity of the test

method [ll], variations in asphalt -aluminum adhesion [12],, variations

in radiation intensity [13], and differences in the spectra of solar

and carbon arc radiant energy.

Within the past 5 years,, a more realistic radiant energy source be- came available for the laboratory weathering of organic materials.

This source was the xenon arc which has a. radiation spectrum remarkably similar to solar energy in the ultraviolet and visible regions [14].

While this machine has found extensive use in. the plastics, textiles,

and photographic industries, the first published use in asphalt degradation has been reported only recently by Martin [15] and by Wright and

Campbell [16 J„ In both of these references, films 25-p. thick were used

without water spray or thermal, shock.

It was the objective of the present work tos (a) make a direct comparison of the carbon-arc weatherometer and the xenon-arc weatherometer as devices for the laboratory weathering of coating-grade asphalts using

the ASTM Daily A cycle and the spark-generating apparatus to detect

failure, (b) to measure, by infrared , analysis, the photooxidation rates

of the same asphalts upon exposure to both radiation sources, and (c) to

determine the role of thermal shock in asphalt degradation.

2 . EXPERIMENTAL

2.1 Materials

Ten commercial coating-grade roofing asphalts (Nos. 2, 3, 6, 8, 9, 11, 16,

18, 19, and 22) were used in this study. Asphalts 2 and 22 were of Venezuelan origin, asphalts 6 and 8 were of Southeastern USA origin, asphalts

3, 9, and 18 were of California Coastal origin, and asphalts 11, 16, and

19 were of Mid-Continent USA origin. The physical properties of these

asphalts are given in Table I.

2.2 Apparatus

The xenon-arc radiant energy source was an Atlas Weather -Ome ter, Model

60-WR, equipped with a constant wattage transformer to operate a 6000-

watt high pressure water cooled lamp. The water jacket assembly con- tained an outer cylinder of pyrex glass which filtered out all wavelengths below approximately 275, mu.. A specimen rack, 37-3/4 in. diameter,

was employed and this rack is rotated at one revolution per minute. For

- 3

-

experiments requiring a water spray,, the machine was modified with a specimen spray unit employing four No. 50 nozzles capable of delivering 4.4 to

5.2 pints per minute. The nozzles were 3 inches from the plane of the

specimen surface. The asphalt panels exposed to the water spray were mounted normal to the xenon-arc source. For experiments requiring

constant temperature and humidity with no water spray,, the automatic

temperature-humidity controlling devices of the machine were utilized.

The carbon-arc radiant-energy source was an Atlas Weather-Ometer,

Model SMC, with a single enclosed carbon arc. The spray unit was the same as that used in the xenon-arc weatherometer . A standard specimen

rack, 30 in. in diameter, was employed. In all experiments using

either 25 p or 625 p (25 mils) asphalt, films, the asphalt specimens were mounted on the drum in the area of greatest radiant energy flux

(see Appendix).

2.3 Exposure of Asphalt Films

The asphalt films of approximately 625-p thickness (25 mils) were prepared by the hydraulic-press method described in Standard Method for

Preparation of Test Panels for Accelerated and Outdoor Weathering of

Bituminous Coating (D 1669-62) [17 j. Triplicate samples of each

asphalt were exposed in the weatherometer s at a black panel temperature

of 60°C and the test conditions followed Daily Cycle A in the Recommended

Practice for Accelerated Weathering Test of Bituminous Materials (D 529-

62) [3]. The test conditions used in this cycle were as follows: 51 min.

of light only (black panel temperature 60 ±2°C), followed by 9 min. light

and spray (spray water temperature 7 ±2°C at the nozzle). The cycle con- sisted of 22 periods at these conditions, daily. The cracks in the

weathered asphalt film were determined by the spark-generating method

described in Tentative Method of test for Failure End Point in Accelerated

and Outdoor Weathering in Bituminous Materials (D 1670-62T) [18]. The

clear plastic grid, used in these experiments was that described by

Kleinschmidt and Greenfeld [19] and it consisted of 60 equal rectangles

in an area approximately 2 in. wide and 5 in. long.

The method used to measure the photooxidation of 25-p thick films of

asphalt was based on changes in the infrared spectra at 1700 cm"' due

to exposure to xenon-arc radiant energy. Detailed procedures for

the preparation, irradiation, and infrared analysis of these films

have been reported previously [12], Briefly, the method used in the

present work is as follows: the asphalt films are prepared by pressing

vacuum-dried, solid samples of asphalt between sheets of dry

unlacquered cellophane in a hydraulic press with platens heated to
.
- 4 -

121 c C 0 The films obtained are measured for thickness with a dial thickness gage, suitable exposure areas are mapped,, and the films are separated from the cellophane by soaking in distilled water„ The

films are then mounted on aluminum holders, 3/8 in, by 1/4 in. by

2 in., with an opening 5/16 in. by 13/16 in„, and allowed to dry overnight. at room temperature. The infrared spectrum of each film is

recorded,, and the films are exposed to xenon-arc radiation at chamber

conditions of 49° C and 40% R.H.

At the desired time, the exposed samples are removed from the exposure

chamber and rescanned in the infrared spectrophotometer. The change

in absorbance, AA, in the carbonyl band (1700 cm"1) is calculated

and used as a measure of the oxidation that has taken place during a given exposure period. The photooxidation rate is obtained by ex- posing a sufficient number of samples of a given asphalt for varying

durations of time.

2.4 Temperature Cycle Measurement

Each of the weatherometers was equipped with a black panel thermometer

unit. This unit acts as a standard specimen to enable correlation of

temperatures between weatherometers, and the temperature so indicated

is the maximum temperature of the artificial weathering cycle. This

panel temperature is not that of the asphalt coatings, although the

variation may not be great. Also, the unit does not permit a continuous

record of temperature.

In order to obtain a continuous measure of the temperature of an asphalt

coating during a weatherometer cycle, a thermocouple junction of copper

and constantin wires was gently embedded into the surface of a 625 -i_l specimen of asphalt coating on an aluminum panel. The thermocouple was previously calibrated against ice and boiling water. Connections from

the asphalt coating on the weatherometer drum to a millivolt recorder,

of response time one second, were made through the hollow shaft upon

which the drum was mounted. Twisting of the insulated connecting wires

occurred in the hollow shaft with each revolution, but did not prevent

the recording of two complete hourly cycles.

2.5 Chemical Dosimetry

The relative incident radiant flux in each weatherometer was measured

with the chemical actinometer, potassium f errioxalate-phenanthroline

[20]. When exposed to radiant energy of less than 510 mp wavelength,

solutions of the ferrioxalate reduce to the ferrous state which forms

a very stable compound with the phenanthroline and has a strong absorption band at 510 mp. The amount of ferrous iron formed is determined

by spectrophotometry. Details of the procedure and discussion of the

applicability of the method to asphalt irradiation have been given previously [13, 15].

- 5

-

In brief, three milliliter lots of 0.15 molar potassium ferrioxalate

solution, were placed in a light-tight holder , equipped with a manual

shutter to allow the solution to be exposed for a timed duration to

the radiation to be measured „ Two-minute exposures were made with the

shutter normal to and at a distance of 27 in. from each arc. The

carbon arc was operated, at the 5A voltage setting (approximately 1.8

KW power consumption) and the xenon arc was operated at various power

settings between 5.5 and 6.0 KW according to the age of the arc. One

set of 4 exposures was made with the carbon arc and 1 1 sets of 4 expo- sures were made with the xenon arc. This latter program was designed

as a check on the decay of intensity of the xenon arc, exposures being

made at the beginning and end of each period at a particular power

setting (approximately 500 hr. or 23 days of 22 hr. cycling). The

exposed solutions were transferred to volumetric flasks and reacted

with aliquots of 0.1 percent, solution of o-phenanthroline at pH 3„5

(sodium, acetate-sulfuric acid buffer). The reactions were carried out. in a dark room and.,, after standing 45 minutes, the absorbance of the

solutions determined at 5 SO mp, with a spectrophotometer, Beckman Model

DU. These results were then, calculated in terms of millimoles per liter

of ferric iron reduced by use of a calibration curve previously established for known, amounts of ferrous iron.

3. RESULTS AND DISCUSSION

3.1 Daily A Cycle Exposures - Carbon-Arc Weatherometer

The artificial weathering of the asphalts used in this study were previously reported by Greenfeld and Wright [21 1. The carbon-arc weatherometer was used and the number of days (22 hours) for both a Wet. and a

““Dry” inspection of the ratings for cracks was reported. Failure was defined at the 50 percent level of cracking according to a 60 -square grid

count. Four of the asphalts were selected for repeat testing and these

results together with those previously reported are given in Table II,

The repeat testing involved inspection of the coatings at the middle of an hourly cycle and gave results in good agreement with, those previously

inspected 20 minutes after the end of the spray period.

3.2 Daily A Cycle Exposures - Xenon-Arc Weatherometer

The results obtained from the exposure of the asphalt coatings to the A

cycle in the xenon-arc weatherometer are given in Table III. The data

are presented as the number of squares of. the exposed asphalt surface,

out of 60 possible, having cracks. Periods of exposure duration are

given in terms of 22 hours of Daily A cycling. (Twenty-two hourly

cycles comprise one day's exposure in the carbon-arc weatherometer)

Generally, regular increases of the incidence of cracking with

increased exposure duration were noted,, and the occasional decreases in

the cracking were attributed to variation in operation of the spark

probe and to the grid method of counting cracks. Some of the data in

Table III are plotted in Figure 1 to indicate the patterns of rate of

crack formation.

It is apparent that the level of crack formation selected as the

failure condition will influence the relative rating of the asphalts.

For instance, in Figure 1 the decreasing order of durability of the

asphalts in the xenon-arc weatherometer is 11, 19, 16, 22, 2, 9, 18, 3,

6, and 8 at the 50 percent level of cracking, but 19, 16, 11, 2, 22,__9,

3, 18, 6, and 8 at the 25 percent level of cracking. It is interesting

to note that the changes of order take place within groups of common

source of asphalts only; there is no cross over of asphalts of different

sources. As shown in Figure 1, the 50 percent level of cracking represents a generally well-defined condition in that most of the asphalts

show a rapid crack growth at this level of exposure. However, Figure 1 also illustrates that this definition of failure is an arbitrary one.

3.3 Comparison of Carbon- and Xenon-.Arc Weather ometers

Table IV gives the results for each of the carbon-arc and xenon-arc

weatherometer durabilities of the asphalts. The carbon-arc results

are those reported for wet inspection (table II) of the asphalt coatings

at the 50 percent level of cracking. Also, it may be observed in Table

IV that the overall correlation of durabilities of asphalts from the same source exposed In the two weatherometers is poor. Within each of the

four sources the trend of durabilities of the asphalts examined is the

reverse for the carbon arc compared to the xenon-arc machine. This is

attributed to the arbitrary nature of the failure point, and the method

of detection of the incidence of cracking. Concerning the latter

aspect, some of the panels were subjected to both .the single probe detection method of Hunter, et al. [7] and the multi-probe method of Jobes [8].

The results are shown in Table V and indicate a significant improvement

in the crack detection ability of the multi-probe unit.

In particular, it was noticed, on occasions that the single probe detector

missed cracks near the edge of the specimen. When insulating tape was placed over the edge of the asphalt coating to prevent the single probe

from sparking to the aluminum panel adjacent to the test specimen, most

of these cracks were detected as indicated in Table VI.

- 7

-

When, the asphalts of similar source are considered in. groups, the over- all correlation of the weatherometer results shown, in Figure 2 is good,

except for asphalts 6 and 8, These two Southeastern USA asphalts failed

earlier in the xen.on.~arc weatherometer than predicted from the carbon-arc

weatherometer results., Similar ly, anomalous behavior of these asphalts

was observed previously in photooxidation rate experiments [12] 0 Repeat

testing of asphalts 6, 8, and 9 were therefore made in the xenon-arc

weatherometer and the results are given .in Table VII 0 Asphalts 6 and 9

behaved very similarly to the earlier tests,, but asphalt 8 showed very

poor reproducibility. At the 33 days exposure duration of the repeat

tests, it was observed that very large cracks had formed in the asphalt

8 coatings After this stage, the rate of development of new cracks was much slower than observed in .the previous tests. Figure 3, the photograph of panels of asphalt 8, illustrates the differences in the type

of film crack failure found in the initial, and repeat tests.

Concerning the general correlation between, the two weatherometers as shown in Figure 2, it is of interest to note that the xenon-arc weatheroraeter takes 1.2 times more exposure time than the carbon-arc weatherometer to fail the asphalts. In actual time involved, the advantage

of the essentially continuous operation of the xenon-arc compared to

week-end and daily shutdowns of the carbon-arc weatherometer more than

offsets the slower artificial weathering of the former machine. This

factor becomes particularly significant when it is realized that the

xenon source has a spectral energy distribution very similar to that

of solar energy while that of the carbon arc is unrealistically intense

in the ultraviolet region and lacks intensity throughout the visible

and infrared regions (see figure 4)

3,4 Daily A Cycle = Temperature Measurements

The results of the measurements of asphalt -coating temperature during

weatherometer cycling are illustrated in Figures 5 and 6 for the carbonarc and xenon-arc machines, respectively. It is believed that these are the first continuous records of the temperature cycle in weatherometers

to which asphalt panels are subjected. Both machines gave similar temperature cycles, the only minor difference was that the coatings spent

a longer time in the spray of the carbon-arc machine (7 to 8 seconds)

than in that of the xenon-arc machine (5 to 6 seconds) and, consequently,

the former coatings reached a lower temperature after nine contacts with

the water spray. The minimum temperatures reached were 8.9 C (48 a F) and

12,8®G (55°F) e Maximum asphalt temperatures in both machines were 3 to

4

& C (5 to 7®F) higher than the 60®G ( H 40 ° F ) indicated by the black panel

dial thermometers and both machines took 20 to 25 minutes to regain maximum temperature after the spray period.

- 8 -

It is of importance to note that the initial thermal shock (i„e. rate

of temperature decrease for a given duration) , due to the first con- tact of the cold water spray with the heated asphalt coating, is

different for each position in the weatherometer drum. This difference

is slight for most of the panels,, However, the thermal shock may be

greatly different for that panel first contacted when the water spray

comes on and the remaining panels, if the first panel is not sprayed

for the full contact time 0-27 The two extremes are illustrated in

Figure 5. In case A, the coating with the embedded thermocouple made

contact with the cold water spray about !0 seconds after the spray

switched on and little temperature drop occurred between spray~on and

the first direct contact of spray with coating „ In case B, however,

the spray switched on to immediately contact the coating for approximately 4 seconds and caused a considerable drop in the temperature

before the first complete contact of spray with coating „ While the

rate of temperature drop is about the same for all panels on first

spray contact, the total drop varies greatly with spray-contact time.

For the carbon arc, the extreme case, of partial spray-contact time,

would not be serious because the machine is serviced daily and sample

rotation is interrupted. In the xenon-arc weatherometer this effect

would be significant because the machine is serviced on a weekly basis.

Figure 6 illustrates a case in the xenors-arc weatherometer where the

period between switching-on of the spray and first complete contact

with the coating was approximately 50 seconds without any partial

initial contact.

It is apparent, when the extreme case is included, that the variability

of thermal shock is so great between specimens in any one machine,

that any variability between machines is overshadowed, particularly in

the xenon-arc weatherometer. Furthermore, the major thermal shock

experienced by the asphalt coatings in the weatherometer s is much more

severe than that occurring in practice. The order of maximum thermal

shock in the weaiherometers is 39 G in 4 to 6 seconds whereas from actual

measurements, Cullen [22 j has reported a figure of 44'"C in 2 hours for

asphalt coatings on model built-up roofs. Measurements of surface temperatures of asphalt coatings on actual roofs in Australia indicate

maximum short-term decreases of about 8°C in the first minute [23].

3 /

The exact same shock treatment could be were sprayed simultaneously.

obtained only if all samples

3.5 Thermal Fatigue

Since the temperature cycle experienced by the asphalt coatings in the

Daily A Cycle is variable and is much more severe than that encountered

in actual practice,, a test series was set up to determine what effect

the temperature cycling alone had upon the asphalts,, Asphalts 3, 6, 8,

9, 16, and 18 were exposed to temperature cycling without irradiation

in a carbon-arc weatherometer in which the arc was surrounded with a blackened metal cylinder. The temperature cycle duplicated that found

in the Daily A Cycle,

The samples were exposed to eighty 22-hour cycles (51 minutes of heating,

9 minutes of heating and cold water spray). At the end of this exposure

period, none of the asphalts had any cracks as could be detected by the

spark generating apparatus. The only noticeable effect was that of some surface dulling. Thus, thermal shock alone, without ultraviolet and

visible radiant energy, was not effective in cracking the 625-p asphalt

films.

3,6 Radiant Energy Intensity

Table VIII gives the results of the incident radiation fluxes as determined by chemical dosimetry for the carbon and xenon arcs and also includes data, previously obtained for solar radiation. [15], The results

are expressed in terms of millimoles per liter of ferric iron reduced

during the 2-minute exposure period, and corrected values have been

included to account for the drum radii of the carbon-arc (15 in.) and

xenon-arc weatherometer s (19 in,) in which the asphalt coatings were

exposed,^/ It is apparent that the specimens in the carbon-arc

weatherometer receive on average about five times more radiant energy

of wavelength less than 510 mp than the specimens in the xenon-arc

weatherometer. Radiation intensity in the latter machine closely

resembles that of solar radiant energy measured at noon on a clear

July day in Washington, D, C.

4/

Maximum and. minimum values were obtained for the xenon arc over a 2000 -hour burning time. Conversely, all measurements on the carbon

arc at the 5A position were made within an elapsed time of 10 minutes.

- 10 -

More detailed results concerning the decay of intensity of radiant

energy from the xenon arc are illustrated in Figure 7. Each point

represents the average of four determinations and has been corrected

for drum radius. Despite a pre-burning of 100 hr„, the lamps give a marked peak in their intensity when initially installed. Power stepups at approximately 500-hr. intervals cause much smaller increases

in the intensity and do not completely compensate for the decay of the

lamp with age. However,, the overall decay is relatively small compared,

for example, to the fluctuations of solar radiation intensity at noon

on cloudless days, which are also indicated in Figure 7. It should be

noted that a power step-up was omitted at the 78-day exposure point;

the result recorded represents two sets of readings taken before and

after the weekly cleaning of filters and replacement of cooling water.

This maintenance did not alter the intensity of the lamp as recorded

by the dosimeter.

Figure 8 illustrates the initial decay of intensity of a new lamp

(100 hr. pre-aged), each point being the average of duplicates. It

is apparent that the decay is initially rapid and that the peak of

radiant energy output would influence only one day of artificial

weathering.

4. PHOTOOXIDAT ION RATES

Photooxidation rates, produced by carbon-arc irradiation, were determined

previously by Wright and Campbell [12] for all of the asphalts used in

the present study except asphalts 18 and 11. Martin [ 1 5 ] measured the

photooxidation rates of asphalts 8, 11, 18, and 22 upon exposure to

carbon-, xenon-, and solar radiant energy. In the present study, this

work was extended to include photooxidation rate determinations, as produced by xenon-arc exposure, on all asphalts exposed to the Daily A

cycle. Exposures for the rate determinations were made with the thin

films (25 microns) exposed for varying durations at 49 C and relative

humidity of 40 percent. The extent of oxidation was measured by infrared

spectroscopy.

The oxidation values obtained on the six asphalts not previously evaluated in [ 1 2 ] and [ 1 5 3 ate presented in Table IX. The results are ex- pressed as AA values at 1700 cm* - (carbonyl absorbance at various exposure durations to the xenon arc.

11

In Figure 9, curves are plotted for the photooxidation rates of asphalts

9, 2, 6, and 19. These asphalts are from four different crude sources.

As with carbon-arc exposure, the overall oxidation rates varied as a function of crude source, but the order based on increasing stability

was California, Venezuela, Southeastern USA, and Midcontinent USA. The

change in radiant energy source, i.e., from carbon arc to xenon arc,

reversed the relative positions of the Venezuela and Southeastern USA

asphalts. Martin [15] showed a similar reversal in order using other

asphalt samples from the same four sources.

Although the overall oxidation rates were different for each asphalt,

the rate curves were similar in general appearance, but unlike those

obtained from carbon-arc exposures. Rather than an induction period,

the xenon-arc irradiation induced definite breaks in the steady rates

of oxidation for all four asphalts. Martin [15] characterized the

photooxidation in the xenon source by initial and secondary oxidation

rates, and by exposure time to cause failure of the asphalt film due to

cracking. The curves in Figure 9 may be characterized in a similar

manner. Also, it may be noted that with only one of the four asphalts.

No. 6, does the straight-line initial oxidation rate pass through the

origin, even though the origin is a valid point on each curve. The

reason for this anomaly is not readily apparent.

In Table X the initial and secondary oxidation rates are shown, as AA/hour, for the four asphalts. Also, the times required to reach

the inflection point, and to develop film failure due to cracking,

are shown. It may be observed, except for the California asphalt No. 9,

that the steady oxidation rates of the asphalts are of similar values.

Greater stability in the Midcontinent USA asphalt is shown by a longer

time to reach the inflection point and a correspondingly greater time

to film failure.

For comparative purposes, the steady oxidation rate values and failure

times are given in Table X for exposures of the same four asphalts to

the carbon arc. The pronounced differences in the response of these

asphalts to the two radiant energy sources may be observed in Figure

10a and 10b. This effect was previously observed by Martin [15] and

by Wright and Campbell [16] when various asphalts were exposed to

solar, xenon-, and carbon-arc irradiance in air [15] and in an ozone- enriched oxygen atmosphere [16].

12

5. CONCLUSIONS

From the results of this investigation, in which the xenon- and carbonarc weatherometers were compared as radiant energy sources for the

laboratory weathering of coating-grade asphalts,, it was observed that:

1. The xenon-arc source requires an average of 1„2 times greater exposure duration than the carbon arc to fail 625-p (25-mil) asphalt

films by the Daily A Cycle, but a shorter total elapsed time period

is needed since the former source operates on a near continuous

basis.

2. The order of durability of asphalts from a single geographical source

was reversed for the carbon arc compared to the xenon-arc machine.

However , when asphalts of similar source were considered in groups,

the overall correlation was good. The order of increasing durability

for asphalts from four sources when exposed to the xenon arc were:

Southeastern USA, California, Venezuela, and Midcontinent USA. The

order for carbon-arc exposure was: California, Southeastern USA,

Venezuela, and Mi dcontinent USA.

3. Asphalt durability to Daily A Cycle exposure was influenced greatly

by the test method. An arbitrary 50 percent failure level gave an order of durability different from that at the 25 percent failure

level for the ten asphalts studied. The number of cracks detected

in the asphalt films by the spark generating apparatus increased as much as 14 percent when the aluminum panel edges were insulated and

by as much as 25 percent when a multiprobe detector was used in

place of the single probe type. The width of the cracks formed,

presumably a function of asphalt -aluminum panel adhesion, affected

final durability results.

4. Continuous measurement of asphalt coating temperatures in the Daily

A Cycle revealed that the initial thermal shock due to cold water

spray, while similar in both machines, was slightly different for

each position on the sample drum, and greatly different for the

first panel contacted when the spray came on if that panel received

less than the full spray period. The major thermal shock in the

weatherom.et.er was much greater than that observed in actual practice. Thermal shock, alone, without, ultraviolet and visible radiant

energy, was not effective in cracking the 625-p, asphalt films.

- 13

5 „ The incident radiant energy flux,, as measured by chemical dosimetry,

was an average five times greater for specimens exposed to the

carbon arc than for those exposed to the xenon arc which,, in turn,, was of similar intensity to noontime solar irradiance on a clear

summer day. The decay of irradiance intensity fox the xenon source, over a 2000-hour burning period, was gradual and of small proportion

after the first few hours of lamp use, Much greater variation was observed with solar radiation on a clear , summer day.

6. Photooxidation, rates of 25-p asphalt films, as measured by infrared

spectroscopy, produced the same increasing order of stability for

the xenon and solar sources, namely, California, Venezuela, Southeastern USA, and Mid continent USA and, also, rate curves of the same general appearance with, an initial oxidation rate, an inflection

point, and a secondary oxidation rate » The carbon-arc source reversed

the relative order of the Venezuela and Southeastern USA asphalts and

produced rate curves unlike those from the other sources. The curves from carbon-arc irradiance showed an induction period followed by a single steady oxidation rate to failure of the asphalt film. The

five-fold higher intensity of the carbon arc over the xenon-arc did

not proportionately reduce film failure time. With most asphalts,

exposure durations needed to cause failure from xenon irradiance

were approximately twice those required by the carbon axe.

7. The radiant energy source appears to be the rate controlling factor

in the photooxidat ion and cracking of asphalt films of 25-ji. thickness, the xenon source producing results much like those from solar

irradiance and the carbon arc giving different results. The effect

of radiant energy source on the durability of 625 -p. films exposed to

the Daily A Cycle, evaluated by the spark probe method, is not readily

apparent because final results are influenced greatly by other factors

involved in the test method. Even so, the xenon source with its

"solar8

" spectral energy distribution should provide laboratory

weathering results more closely related, to natural weathering than

could be expected from the more intense but less realistic carbonarc source.

6. ACKNOWLEDGMENT

The authors are grateful to Mr. S. H. Greenfeid of the Asphalt Roofing

Industry Bureau for technical assistance in the exposure and evaluation

of the 25-mil asphalt films.

- 14 -

7. REFERENCES

[1] 0. Go Stricter,, "Accelerated Test of Asphalt",, Journal of Research , National Bureau of Standards, Vol Q 5, No„ 2 , pp. 247-253 (1930).

[2] "Proposed Method for Accelerated Weathering Tests of Bituminous

Materials", Proceedings , Am, Soc. Testing Mats., Vol. 33, Part I,

p. 381 (1933),

[3] "Recommended Practice for Accelerated Weathering Test of Bituminous

Materials (D529-61)", 1964 Book of ASTM Standards, Part II, pp. 244-

246.

[4] H. R 0 Snoke and B. L. Gallup, "Accelerated Weathering Tests of

Mineral-Surfaced Asphalt Shingles", Journal of Research , National

Bureau of Standards, Vol. 18, No. 6, pp, 669-683 (1937).

[5] S. H. Greenfeld, "A Method for Preparing Uniform Films of Bituminous

Materials", ASTM Bulletin, No. 193, p. 182 (1953).

[6] A. H. Boenau and L. H. 'Baum, "The Design and Application of a SparkGap Instrument for Detecting Crack Failures of Asphalt Coatings

During Weathering Tests", ASTM STP No. 94, Am, Soc. Testing Mats.,

Po 153 (1949).

[7] J. B. Hunter, G. C„ Gzemski and L. Laskaris, "A New Method for

Evaluating Failure of Bituminous Materials Due to Weathering",

ASTM STP No. 94, Am„ Soc. Testing Mats., p. 144 (1949)

„

[8] P. Mo Jones, "Comparison of Two Spark-Gap Testers for Asphalt Films",

Materials Research and Standards , Vol. 3, No. 4, p. 293 (1963).

[9] H. Abraham, Asphalt and Allied Substances, Method of Testing : Manufactured Bituminous Products , 6th ed. Vol. V, D„ Van Nostrand,

Co., Inc., New York, New York, Chap. 5 (1963).

[10] G. Lo Oliensis, "Ten Years Outdoor Exposure of Filled Asphalt

Coatings on Saturated Felts", ASTM Bulletin, No, 144, p. 32 (1947).

[ 1 1 ] Jo Zapata, "Experience with Radiation in Accelerated Durability

Tests on Bituminous Materials", ASTM STP No. 94, Am. Soc. Testing

MatSo, p. 164 (1950).

C

1 2 ] J„ Ro Wright and P. G. Campbell, "Determination of Oxidation Rates

of Air-Blown Asphalts by Infrared Spectroscopy", Journal of Applied

Chemistry (London ) , Vol„ 12, p 0 256 (1962).

- 15 -

[ 1

3

] Jo R. Wright, P. G. Campbell, and T„ L. Fridinger, "The Effect of

Carbon-Arc Intensity on Asphalt Oxidation", Journal of Applied

Chemistry (London)

,

Vol. 14 , p. 30 (1964) „ Also, "Relationship

Between Intensity of Carbon Arc and Asphalt Oxidation", ASTM STP

No. 347., Am„ Soc. Testing Mats.;, (In Press).

[14] Atlas Fade-Ometers and Weather-Ometers Brochure, Atlas Electric

Devices Co.,, Chicago, Illinois,, p. 1 1 (1962).

[ 1 5 1 K. Go Martin, "Influence of Radiant -Energy Source on Asphalt

Oxidation",, Journal of Applied Chemistry (London) , (In Press)

f 1

] Jo R. Wright and P. G. Campbell., "Photooxidation of Asphalt, in the

Presence of Ozone";, Journal of Research , Nat. Bureau of Standards,

(In Press) .

[17] 1964 Book of ASTM Standards, op. cit., p. 525

[18] 1964 Book of ASTM Standards, op. cit., p. 529.

[19] Lo Ro Kleinschmidt and S, H. Greenfeld, "Influence of Exposure

Conditions on the Accelerated Durability Testing of Asphalt",

ASTM Bulletin, No. 213, p. 69 (1956).

[20] Co G. Hatchard and C. A. Parker, "A New Sensitive Chemical

Actinometer II. Potassium Ferrioxalate as a Standard Chemical

Actinometer", Proceedings, Royal Soc. (London), Series A, Vol. 236,

p. 518 (1956).

[21 ] S. Ho Greenfeld and J. R 0 Wright, "Four Methods for Predicting the

Durability of Roofing Asphalts", Materials Research and Standards . Vol. 2, No. 9, p. 738 (1962).

[22] Wo Co Cullen, "Solar Heating, Radiative Cooling, and Thermal Movement - Their Effects on Built-Up Roofing", U. S. Dept, of Commerce,

Nat. Bureau of Standards Technical Note 231, Dec. 16, 1963.

[23] E. Ro Ball.ant.yne and J 0 W. Spencer, "Temperatures of Bituminous

Roof Surfaces", ASTM Bulletin, No. 223, p, 69 (1957)

„

8 0 APPENDIX

8.1 Irradiance Distribution in Specimen Drums

To measure the irradiance distribution in the xenon- arc weatherometer

relative to drum height, the difference in carbonyl absorbance (AA at

1700 cm"'*} of exposed 25 ~\i films of a Midconfinent USA asphalt, at

different drum positions, was used as a (monitoring) dosimeter . The

specimen drum in the xenon-arc weatherometer is 19-1/2 in 0 in height

and is 19 in. in radius. The xenon arc is centrally located with regard

to drum, height. Two specimen holders (9x3 in.) cover the height of

the drum from approximately 1/2 in. to 9-1/2 in. and 10 in. to 19 in.,

respectively. Eight films were distributed, equidistant on the specimen

holders and were exposed to xenon-arc radiation for 40.5 hours at a black

panel temperature of 60 c C. Four films were exposed at each of the eight

positions relative to the drum height. The irradiance distribution is

shown in Figure 1 1 and is based on the changes In absorbance (AA at

1700 cm"*) of the asphalt films versus drum height.

The same procedure was used to measure the irradiance distribution in

the carbon-arc weatherometer. The specimen drum is 17-1/2 in. In

height and is 15 in. in radius. A specimen holder covers the height of

the drum from 1 in. to 13.5 in. Six asphalt films were mounted equidistant on a specimen holder. Four films were exposed at each of the

six positions relative to the drum height. The films were exposed to

carbon-arc radiation for 14 hours at. a black, panel temperature of 6Q c C.

The changes in absorbance (AA at 1700 cm"®) of the asphalt films versus

drum height are also shown in Figure 11.

USCOMM-NBS-DC

TABLE I

PHYSICAL PROPERTIES OF ASPHALTS

Asphalt Softening Penetration

Flash

Poinj:, Specifi<

No. Source Point at 25°C, COC, Gravity

°C 1/10 mm °C at 25°C

2 Tia Juana-Lago Colon 104 16 310 1.017

3 California coastal

(catalyzed) 105 18 252 1.032

6 Talco 110 17 288 1.040

8 Talco 105 15 299 1.036

9 California coastal

( fluxed) 110 20 238 1.026

11 Kansas, Lyons 94 21 307 1.000

16 Illinois-KangasOklahoma 117 15 343 1.008

18 Los Angeles blend 99 18 241 1.022

19 Kansas 106 16 327 1.005

22 Laqunillas 107 14 277 1.030

a Ring and Ball Method,

b Cleveland Open Cup Method.

TABLE II

CARBON-ARC WEATHEROMETER RESULTS

DURABILITY

Daily A Gyelon (22 hfa.) £0 Failuf©a No. From Reference 21 Present Work

b c d

6 46 41 _ 8 53 46 41, 47, 54

3 53 44 <» 9 32 32 - 18 45 40 36, 37

2 69 65

22 60 63 63, 64

11 104 94 92, 95

16 102. 93 -• 19 95 90

a 507» failure level (30 out of 60 possible squares with cracks)

b Machine turned off 48 rain, after end of spray; values are average

of four specimens • c Machine turned off 20 min. after end of spray; values are average

of four specimens • d Machine turned off 30 min. after end of spray; each value is that

a single asphalt specimen.

o

CO cni un

UOin

cv CM CM|0|

CO|<}-|

CM

CM vo vo in

ro cm cm

O'co n

M H H

coo

0- col col col vClMcol

col col co 1 co|co|<3 I

O >—i o O ^

O' *—• O o O m n O cv

oo | OlinlOl

in

CO • CO co &

«t3 CO co t: CM

CM vC o

v_^ u

in o

w CO

1 w r>- £>

in u

2D o •r-4 o 2

CJ co

CJ in CO

•

. < 0)

'—i u < m Ctf hJ 0 M O cr < in co o

CJ U-< r/ 1 O' o < <t

1 w u

<L» o r^

CO s K o 3 X Cu SS X in

col cm | co in co co ooo ooo ooc <HcO|CM CM m O' O' co co oo

—< in vo

m}- m

in N ON CM CO 00

co in m cm o cm

m| r^>» vo cm <f- in

co I co| in in m <t •—< «—< •—

^ CO CO(CM|<t CM CO <f- cm cm in in| in| m ’—' »—<

>

1

co co o in O n coo r^l moo CO CO sJ- i—I i—I CO CM CM CO I o<? iDlolinl <t co <j-| —i co co <H<j-|in| H CM ^ CM O in id <t id rv rv cm co m cm o

CM '—'CM i—< CM »—' »—' •—

O in ml h co co co <j- oo cm <r cm m m <j-| <t in •—1 cm

nloloo cm I co ovl

co| <t| rH co | in co |

<f H <f

r—-I r—I r—

MOO CM CM O

in cm ov M H

in vol m

cm <r| CM

ctf • rd O a s

n) ,0 o m ^ u

v£> co

aj o nj ,n u nj y rt 43 u w ,o u

00 CM CM f-H r-1 CM r—

507,

failure

level

used

(30

out

of

60

possible

squares

with

cracks).

Underlined

value

for

each

entry

represents

I

ai

lure

TABLE IV

COMPARISON OF CARBON-AND XENON-ARC WEATHEROMETER RESULTS

Asphalt

No.

DURABILITY

Daily A Cycles (22 hrs.) to Failure

b c Carbon Arc Xenon Arc

6 41 31

8 46 28

3 44 40

9 32 46

18 40 46

2 65 ' 75

22 63 78

11 94 122

16 93 104

19 90 104

a 507o Failure level (30 out of 60 possible squares with cracks)

b Machine turned off 20 min. after spray; values are average of

c Machine turned off 30 min. after spray; values are average of

specimens

specimens

TABLE V

COMPARISON OF CRACK RATINGS OF

ASPHALT FILM SURFACES USING SINGLE AND MULTI- PROBE TESTERS

3

Asphalt

No.

Spark Generating Apparatus

Single Probe Multi- Probe

Difference

%

8 32 40 25

44 51 15.9

11 53 53 0

18 54 60 11.1

54 60 11.1

22 59 60 1.7

54 58 7.4

Ratings presented as number of squares out of a possible 60 with

cracks due to carbon-arc exposure.

See reference No. 7.

See Reference No. 8.

TABLE VI

EFFECT OF TAPING ALUMINUM PANEL - EDGE ON CRACK RATINGS OF ASPHALT FILMS

^

Asphalt Squares Cracked Difference

No. Edge Untaped Edge Taped 7.

2 13 14 7.7

15 17 13.3

15 15 0

17 17 0

18 19 5.3

9 41 45 9.8

8 50 57 14

18 57 59 3.5

6 51 58 13.7

Cracks detected by single probe tester. Ratings presented as number of squares out of a possible 60 with cracks.

TABLE VII

REPEAT XENON-ARC WEATHEROMETER EXPERIMENTS

Exposure - Daily A Cycles (22-Hra.

)

Asphalt

No. 20.5 23 26.5 30.5 33 37.5 40.5 43 45 48 52 56.5

Number of Squares with Cracks

01

6 a

0 1 12 18 48

b. 0 3 7 19 33

c

0 2 18 32 51

8 a . 0 4 18 24 23 28 28 33 34 39

b. 8 9 17 21 22 ’ 22 22 23 25 52

c2 8 8 11 11 13 13 14 21 36

9 a . 0 5 7 16 23 27 35 43

b. 0 0 3 15 21 26 33 42

c. 0 3 3 8 19 23 26 42

50% failure level used (30 out of 60 possible squares with cracks).

Underlined value for each entry represents failure.

a

TABLE VIII

CHEMICAL DOSIMETRY: EFFECT OF RADIANT

ENERGY FLUX ON FERRIOXALATE SOLUTIONS

Radiant

Energy

Source Ferric Iron Reduced, Millimoles per Liter^'

b c

Carbon arc 0.094 0.304

Xenon arc Maximum 0.036 0.073

Minimum 0.025 0,051

Solar

Maximum 0.067 0.067

Minimum 0.038 0.038

Based on exposure of 1.0 sq. cm. area of 0.15 M for

2.0 min at a distance of 27 in. from the source (carbon and xenon).

Values are average of 4 determinations.

Experimental value at exposure distance.

Corrected to exposure distance of asphalt panels; 15 in. for carbon

arc and 19 in. for xenon arc.

5A voltage adjustment switch setting.

TABLE IX

CHANGES IN CARBONYL ABSORBANCE AT 1700 cm. OF ASPHALTS EXPOSED TO XENON ARC

a

Exposure

Time

Hr

A A at 1700 cm

-1

3 9 2 6 19 16

4 0.089 0.076 0.026 0.010 0.017 0.015

8 0.139 0.109 0.035 0.030 0.025 0.018

12 0.179 0.149 0.051 0.041 0.038 0.025

16 0.249 0.184 0.052 0.054 0.045 0.030

20 0.343 0.248 0.077 0.066 0.055 0.054

24 0.426 0.295 0.096 0.086 0.065 0.051

28 0.432 0.298 0.112 0.117 0.073 0.068

32 0.115 0.136 0.083 0.090

36 0.150 0.148 0.106 0.097

40 0.180 0.169 0.117 0.115

44 0.129 0.130

48 0.165 0.154

52 0.185 0.177

a Irradiated in Arias 60-WR Weather- Ometer at 49 °C and 40% R.H.

for time periods indicated. Each value reported is average of a

2 or more values.

TABLE X

OXIDATION - RATE DATA FOR CARBON - AND XENON -ARC RADIANT ENERGY SOURCES

3

Xenon - Arc Exposures Carbon-Arc Exposures

Asphalt

Inflection

Point

Oxidation Rates

A A/hr. x

10" 2 Film

Failure Oxidation Rate

_ 9

Film

Failure

No. Hrs

.

Initial Secondary Hrs. A A/hr . x 10 Hrs

.

9 16 0.90 1.40 28 2.44 8

2 20 0.31 0.50 40 1.13 18

6 20 0.34 0.52 40 1.21 16

19 32 0.21 0.51 52 1.01 24

a All exposures made at 49 °C and 407o R.H

_LJ 1_ ,_i. L

m

m

om

in o in

rO

J i 1 L 1 J i O in o m

rO <nj co — O if) O

SIHOVidO hum saavnos jo uaswnN

LF.

EXPOSURE

IN

THE

XENON-ARC

WEATHEROMETER

ON

THE

RATE

NUMBER

OF

CYCLES

XENONARC

WEATHEROMETER

DURABILITY,

DAYS

0 20 40 60 80 100

CARBON-ARC WEATHEROMETER DURABILITY,

DAYS

FIGURE 2. CORRELATION OF ASPHALT DURABILITIES FROM XENON- AND CARBON-ARC EXPOSURES

(DAILY A CYCLE) OF 625|J FILMS.

FIGURE 3„ FILMS OF ASPHALT NO„ 8 AFTER EXPOSURE TO THE DAILY

A CYCLE IN THE XENON- ARC

WEATHEROMETERo

^

K> CVl — o

A1ISN31NI 3AI1VT3M

300

400

500

600

TOO

800

900

1000

SI00

1200

1300

WAVE

LENGTH

IN

MILLIMICRONS

FIGURE

4.

SPECTRAL

DISTRIBUTION

OF

SOLAR,

XENONARC,

AND

CARBON

-ARC

RADIANT

ENERGY,

Do 3UniVd3dlN31

co

UJ

b"

ID

UJ

2

H

FIGURE

5.

ASPHALT

TEMPERATURE

IN

THE

DAILY

A

CYCLE

IN

THE

CARBON-ARC

WEATHEROMETER.

IN

CURVE

A,

WATER

SPRAY

CAME

ON

10

SEC.

BEFORE

CONTACT

WITH

PANEL

SURFACE

IN

CURVE

B,

SPRAY

ON

AND

PANELSURFACE

CONTACT

WERE

SIMULTANEOUS

„

Do 3idniVU3dWI31

O O O O o o o

io 3afUVH3dlM31

FIGURE

6.

ASPHALT

TEMPERATURE

IN

THE

DAILY

A

CYCLE

IN

THE

XENON-ARC

WEATHEROMETER

0-040

T T

] -T- [—T—[

rrUJ2

23

to

into

UJQ

-J g O _1 to o

zo

S

Q

<

tr

cc<

UJ

_im

<

«r<>

z

o

o

z

o

Q

z

o

o

X

N «

UJ <

5

1 I . .1

CLs

<

5

UJz

I <

CL3

0.UJ

I—to

crUJo

a.

•CD

H

Q

UJz

<

UJ

_lo

to

CEUJb

u.

o

M-

! O

H CJ

O

: O

o

CD

O

tD

i o

-1 O

C\J H

J L

co

UJ

-1o

>-o

<LO

li_ o

ccUJ

CD

o

CMO

ino

6

(•UJUJ- UJO-I) /IAIUJ ‘a3Dna3d

& NOdl 0ldd3J

DECAY

OF

INTENSITY

OF

XENON

ARC

DURING

WEATHEROMETER

EXPOSURES

„

0900

O

o

o

o

o

o

?

rvj

O

lO

6

o

o o o

in rO o o o

6 6 6

(ujuj-Luo-i) /iaiw ‘asonasu

o

CMO

6

o

9

6

NOHI 0ldd3d

co

or3

o

X

UJ

CD

cr3

CD

FIGURE

8,

INITIAL

DECAY

OF

INTENSITY

OF

THE

XENON

ARC.

A

A

at

1700

CM"

1

FIGURE 9. EFFECT OF XENON-ARC EXPOSURE (49°C, 407. R.H. ) ON THE CHANGE IN ABSORBANCE

AT 1700 cm' 1 OF FOUR COATING-GRADE ASPHALTS.

0-2

20

b CVj CD CM tD <

T* 6 6 6 6

1 a Z Z 2 Z

to< A

,-W0 0011 i D vv

FIGURE

10a„

RELATIVE

EFFECTS

OF

CARBONAND

XENON-ARC

EXPOSURES

(49°C

J>

40%

R.H„)

ON

TH]

CHANGE

IN

ABSORBANCE

OF

VENEZUELA

ASPHALT

(

,

)

AND

SOUTHEASTERN

USA

ASPHALT

(

A

, A

).

0-300

r t t

UJo

ce3

o

CD

>-e>

CE

Hiz

U1

o

CE<

o

m

CE

<1o

o

tE<

2

o

CD

CE

<tO

O C. K Q <

O

z

UJX

|-Ifl0 00ZI W VV

FIGURE

10b.

RELATIVE

EFFECTS

OF

CARBONAND

XENON-ARC

EXPOSURES

(49°C,

407.

R.H.)

ON

THE

CHANGE

IN

ABSORBANCE

OF

CALIFORNIA

(O

, •

)

AND

MIDCONTINENT

USA

0180

TOP

OF

DRUM

BOTTOM

OF

DRUM o o o o o o o o

CO OJ o 00 CD CM • • o O o O 6 o o 6 6 6 6 6 ooo&o

GOoN

a.O o O S oc 8 s o <x ^ hc/} o Q M IL. o 9 vo

CM 0s* oo

I-IAIO OOZI

W vV

FIGURE

11.

EFFECT

OF

DRUM

HEIGHT

ON

THE.

XRRADIANCE

DISTRIBUTION

IN

THE

CARBONARC

AND

XENONARC

WEATHEROMETERS