NATIONAL BUREAU OF STANDARDS REPORT

4621

THE DEGRADATION OF TWO COATING ASPHALTS

by

Sidney H. Greenfeld

<NBp>

U. S. DEPARTMENT OF COMMERCE

NATIONAL BUREAU OF STANDARDS
U. S. DEPARTMENT OF COMMERCE

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NATIONAL BUREAU OF STANDARDS

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NATIONAL BUREAU OF STANDARDS REPORT

THE DEGRADATION OF TWO COATING ASPHALTS

Sidney H. Greenfeld

Research Associate

Asphalt Roofing Industry Bureau

Floor, Roof and Wall Coverings Section

Building Technology Division

Staff

John P. Falzone

Sidney H, Greenfeld

Shigeru Ishihara

Lawrence R. Kleinschmidt

Jointly Sponsored by

Asphalt Roofing Industry Bureau

The publication, reprinting, or reproduction of this report in any form, either in whole or in part, is prohibited

unless permission Is obtained inwrItingfromtheOfiice of the Director, National Bureau of Standards, Washington

25, D. C. Such permission is not needed, however, by a Government agency tor which a report has been specifically prepared If that agency wishes to reproduce additional copies of that particular report for its own use,

NBS PROJECT

1004-10-1017 April 16, 1956

NBS REPORT

4621

by

and

National B " Standards

U. S. DEPARTMENT OF COMMERCE

NATIONAL BUREAU OF STANDARDS
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THE DEGRADATION OF TWO COATING ASPHALTS

by

Sidney H» Greenfeld

ABSTRACT

The changes that occurred when two coating asphalts,

differing widely in durability, were exposed to heat; heat

and light; heat, light and water and out of doors were

followed by chromatographic and selective solvent analyses.

In all four exposures the asphaltenes and degradation

products increased at the expense of all of the n-pentanesoluble components. However, the magnitudes of the

changes were different for the various exposures.

1, INTRODUCTION

Numerous investigators have reported the results of accelerated (1)* or outdoor (2) exposures of asphalts in which asphalt

has been treated as a single material and its durability expressed in terms of physical changes, primarily cracking. In

two instances the complex nature of asphalt was recognized and

the changes in some of its components (3) reported at relatively

short periods of exposure. However, no systematic study has

been published of the changes that take place in the asphalt

*The numbers in parentheses indicate references listed at the

end of this report.

2

constituents (^) as a function of time, when asphalts are exposed to different environments.

This paper describes the changes occurring in two asphalts

of widely different origin and their components when they are exposed to heat; heat and light; heat, light and water and to the

weather,

2. MATERIALS AND METHODS

2,1 Asphalts

The two asphalts used are described in Table I. They are

typical shingle coating grade asphalts blown from residua from

crudes produced in the United States.

2.2 Specimen Preparation

The exposure specimens were prepared by the hydraulic press

method previously reported (5)<. Each coating was 2^ or 26 mils

thick with a tolerance of ±1 mil. The coatings were nominally

2-1 A by 5-1A inch in width and length, respectively, with permissible variations of 1/8 inch in each. This variation in area

accounted for most of the variation of 0,57 grams in the weight

of the coatings, which averaged 4.65 grams per specimen. All

specimens of each asphalt were prepared at the same time and exposed within 24 hours of their preparation.
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TABLE I.

CHARACTERISTICS OF ASPHALTS

CHARACTERISTIC ASPHALT I ASPHALT II

Softening Point“{ °F 223 224

Penetration—'^at 32°F 10 11

Penetration at 77°F 17 17

Penetration at 115°F 30 26

c / Susceptibility^ 1.16 0.87

Loss on Heating,— $ 0.22 0,03

Pen. after Heating at 77°F 17 17

Specific Gravity at 77°F 1.0015 0.999

Durability,—^ days 43 75

Component Analysis (4)

Asphaltenes, $ 39.0 38.4

Resins, $ 10.3 9.9

Dark Oils, $ 18.2 23.3

White Oils, % 27.4 24.4

Ethanol Extract, $ 2.8 0,7

Recovery, % 97.7 96.7

“ ASTM D36-26.

b/“ ASTM D5-52.

= ^115 - P32

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5I- 9C - 22 hours a day exposure to 51 minutes of

light followed by 9 minutes of light cold (4o°F)

water spray.
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2.3 Specimen Exposure

Six specimens of each asphalt were exposed in an air oven at

l40° 4:5°F.

Seven specimens of asphalt I were exposed in a single arc.

accelerated durability machine, operated at 120-145 volts and

15-17 amperes, for 22 hours a day at l40 it5°F.

Twenty-seven specimens of asphalt I and 26 specimens of asphalt

II were exposed concurrently with those above to 22 hours per day

in the accelerated durability machine followed by one hour of soaking in distilled water. This wash period was divided into 45

minutes in one pyrex container and 15 minutes in a second. The

water was changed whenever specimens were removed for analysis.

This procedure is termed the 22-1 cycle. During the remainder

of each day, the specimens were at ambient conditions.

Eighteen specimens of each asphalt were exposed on the roof

of the Industrial Building of the National Bureau of Standards

facing due South at an inclination of 45°. Thus, 58 specimens of

asphalt I and 50 specimens of asphalt II were exposed in all.

In all of the accelerated durability machine exposures, the

specimens were exposed two to an aluminum specimen holder, one

above the other. On alternate days the specimens and the holders

were inverted. in order to approximate uniform exposure for all of

the specimens.
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2,h Component Analysis

Before and periodically during exposure all of the specimens

were weighed and from one to three were removed for analysis.

These were separated into component groups: asphaltenes, resins,

dark oils, white oils (4).

During exposure three types of products of degradation were

formed. One was volatile, and escaped. Another was water-soluble

and was removered readily. The third was soluble in ethanol, but

insoluble in water and pentane. This material remained on the

asphaltenes when they were extracted with n-pentane. However,

extraction of the asphaltenes with ethanol removed the major portion of this product. In some asphalts a slight colored film still

remained on the surface of the asphaltenes after extraction with

ethanol, but any solvent that removed the entire film dissolved

appreciable quantities of the asphaltenes as well. Hence, ethanol

was used to extract the major portion of the degradation products

that were not soluble in water.

One gram of asphaltenes was placed in a 150 ml beaker with

100 ml of ethanol and heated to about 70°C on a covered steam bath

for three hours. The extracted asphaltenes were filtered from the

solution in a weighed Gooch crucible, with an asbestos mat covered

with a disc of filter paper, and dried and weighed. The quantity

of ethanol extract was obtained by difference.*

*Prolonged extraction in an soxhlet extractor produced the same

results

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The components of the asphalt have been described by

Kleinschmidt (4). Briefly, they are:

Asphaltenes - Black, brittle solids insoluble in n- pentane.

Water-white oils - Colorless, viscous oils not adsorbed

from n-pentane solution by fuller's

earth.

Dark oils - Highly viscous, reddish-brown oils eluted from

the fuller's earth with methylene chloride.

Resins - Glossy, dark brown solids eluted from the fuller ®s

earth with methyl ethyl ketone.

The changes that occur in each of these components as the

asphalt is degraded are most easily followed if the component always is expressed as a percentage of the original weight of the

asphalt. This common denominator permits direct subtraction at

different periods of exposure. All component analyses in this

paper are presented in this manner.

3. RESULTS

3.1 Weight Changes - 22-1 Cycle

When asphalt is degraded by light, heat and water it undergoes a loss in weight that increases with exposure. Figure 1

illustrates the losses that occurred when the two asphalts were exposed simultaneously to the 22-1 cycle in an accelerated durability

machine. The first two points for each asphalt are each averages of

26 specimens. Following points are of progressively fewer specimens,

for specimens were periodically removed for analyses, until the
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EXPOSURE,

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last two panels. It was observed that even though the specimens

were rearranged daily, there was a consistent variation in their

weight changes. This variation, the extremes of which are represented by the dotted curves in Figure 1, were in no way related

to the differences of ^1 mil in coating thickness or ^1/8-inch

in each of the other coating dimensions. The coatings that lost

relatively more weight during the early periods of exposure continued to do so during the entire exposure and, conversely, those

initially with low losses continued low. While the differences

among replicate specimens were small in relation to the weight

losses after a short period of exposure, they are significant

and indicative of variations that should be considered normal in

this type of exposure.

In the enlarged sections of Figure 1, it can be seen that

during the early exposure both asphalts exhibited a net gain in

weight, despite the daily soaking. However, by the end of six

or seven days of exposure the specimens were all back to their

initial weights, and they continued to lose weight thereafter.

This loss amounted to for asphalt I and l6.6^ for asphalt II

at 3500 hours of exposure. Asphalt I failed mechanically (6) at

1550 hours} asphalt II failed at 4l50 hours.
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3.2 Component Changes - 22-1 Cycle

Figures 2 and 3 are graphical presentations of the changes

that took place in these two asphalts during exposure. Each

point, except the last, is the average of analyses of three sped

mens. The weight loss curves on these two figures are of the par

ticular specimens analyzed in each case, but they always agreed

with the general averages in Figure 1 within 0,3^.

While the weight losses were measures of the water soluble

and volatile, or gaseous, products of degradation formed, there

was a third product of degradation that remained with the asphalt

the ethanol extract of the asphaltenes. There was some ethanol

soluble in the asphaltenes before weathering, possibly formed

during the "blowing" operation in the manufacture of the

asphalt, but during exposure it increased, went through a broad

maximum around 1000 hours and then slowly decreased. This material may well be an intermediate in the formation of the other

degradation products.

During the early stages of exposure there was a rapid increase in the asphaltene content of both asphalts. This was

followed by a slower increase in asphalt ligand in asphalt I,

by a long period of constant value followed by a slow decrease.

The resins in both asphalts also increased for the first

^00 hours, but then began to decrease at about the same rate as

the dark oils, which had undergone a rapid decrease during the

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early exposure. The white oils also decreased progressively

during exposure. Thus, after some early changes, the degradation

process seemed to be a gradual attrition of the entire n-pentanesoluble portion of the asphalt.

3.3 Component Changes - Dry Light

Exposed simultaneously with the above were a number of specimens of asphalt I which were not subjected to washing, termed dry

light exposures. The results of these exposures are shown in

Figure 4. A number of differences between these curves and those

in Figure 2 are readily apparent. The most obvious is that the

initial weight increase was greater and was continued for about

1200 hours (instead of 125 hours). At 3000 hours, when these exposures were discontinued, the loss amounted to only 0.5^, compared to 22,6^ when the coatings were washed.

As might be expected, because no material was removed as

water solubles, the ethanol extract continued to increase with

time to over 6^ at 3000 hours. Some of this material was undoubtedly water soluble also.

The rapid changes in the components that occurred during the

first 200 hours of exposure also too]f place in these dry exposures,

but for the next 1000 hours the composition remained static. After

1200 hours the normal changes were resumed and the asphaltenes increased to higher concentrations than when washing occurred.
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3.4 Heat Exposures

When light was omitted and specimens of the two asphalts were

exposed to heat alone, in an air oven at l4o°F , the changes that

occurred were again very different; they are presented in Figures

5 and 6, There were, of course, no water-soluble products removed. There was no weight change in either asphalt for the

first 200 hours. Asphalt I then lost weight progressively until

its exposure was discontinued at 1320 hours; the total loss

amounted to only 0.1^, Asphalt II, however, gained weight between

400 and 600 hours and then leveled off at a gain of 0,2^. The

ethanol extract remained at a very low value. Instead of the

rapid rise in asphaltphe content previously observed, there was

no change during the first 200 hours. Then the rapid change

occurred and was followed by a period of decreasing value in

asphalt I and constant -value in asphalt II. The resins increased

slightly and the dark oils decreased comparably. The white oils

decreased slightly in asphalt I, but remained constant in asphalt

II, Because each of the values in Figures 5 and 6 represents a

single determination, there is slightly more scatter of these

points than in the previously reported exposures.

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3.5 Out -of -Door Exposures

Figures 7 and 8 present the results of the out-of-door exposures on the roof of the Industrial Building at the National

Bureau of Standards, During the first 24 months of exposure the

changes that took place were similar to t^iose that occurred in the

22-1 cycle in the accelerated durability machineSo However, the

timing ratio of all of the changes was not the same. At three

months, the asphalts had already lost a little weight, the

possible weight gained being overlooked because no weighings

were made during the first three months. The ethanol extracts

increased as weathering progressed and appear to be reaching

maxima at about l8 to 24 months.

In asphalt I, the asphaltenes went through a maximum value

of about 42,5^ at 9 months, but in asphalt II, they were still

increasing at 24 months (comparable trends existed in the 22-1

cycle). The resins in both asphalts went through the same maximum

values as in the 22-1 cycle. In asphalt I, both the white and

dark oils decreased rapidly for six months and then much more

slowly, but in asphalt II, the white oils remained constant

for six months, decreased rapidly for the next six months, then,

with the dark oils, remained almost constant for the following

year. All of these changes are similar to those that occurred

in the 22-1 cycle, but because of the much slower rate of change

of the asphalt, are somewhat subdued.

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4. SUMMARY AND CONCLUSIONS

The degradation of asphalts varies with the source of the

asphalt and in accordance with the exposure conditions. Different

mechanisms of degradation seem to exist for thermal, dry light, and

light and water exposures. Under normal exposure conditions, where

light, heat and water enter into the degradation of asphalt, two

types of products were isolated. These products were formed from,

and the asphaltenes increased at the expense of, the three components

of the pentane- soluble portion of the asphalt as degradation progressed . Out-of-door exposures produced changes in components similar

to those that occurred in the 22-1 cycle.

12

REFERENCES

(1) Strieter, 0. G. and Snoke, H, R. , "A Modified Accelerated

Weathering Test for Asphalts", J. Res. NBS 481-5 (1936).

Walther, H. , "Influence of Weathering on Bitumen", Mitt.

Dachpappen Ind., 135-52 (1938).

Zapata, J. , "Laboratory Accelerated Weathering", Proc. Assoc.

Asph. Paving Tech. 154-73 (19^8).

Fair, W, F., Jr., Beck, H. R. , and McKee, B. K. , "Accelerated

Weathering of Pitches and Asphalts", ASTM Spec. Tech. Pub.

No. 9^, 109-21 (1949).

(2) Oliensis, G. L. , "Ten Years Outdoor Exposure of Filled Asphalt

Coatings on Saturated Felts", ASTM Bulletin No. l44, 32-48,

(Jan. 1947).

Williams, D. M. , "Correlating Laboratory and Outdoor Weathering Tests", ibid., 49-56.

Kirshbaum, L, , Cubberly, R, H. , and Yeager, F. W. , "Mineral

Stabilizers in Asphalt Roofing", ASTM Spec. Tech. Pub. No. 94,

122-136, (19^9).

(3) Thurston, R. R. , "Constituents of Asphaltic Materials vs.

Accelerated Weathering" , Proc. ASTM 569? (1937)-

Marcel, L. , "Study of the Evaluation of Bitumens", Comptus

Rendus, 2^2, 84-6, (195D.
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REFERENCES (Continued)

(4) Kleinschmidt , L. R. , "Chromatographic Method for the Fractionation of Asphalt Into Distinctive Groups of Components"

J. Res. NBS ^4, No. 3, 163-166, 1955 (RP2577).

(5) Greenfeld, So H. , "A Method for Preparing Uniform Films of

Bituminous Materials", ASTM Bulletin No. 193? 50-53, Oct.

1953.

(6) Greenfeld, S. H. , "The Effects of Thermal Shock on the Dura

bility of Asphalt Coatings Under Accelerated Test", ASTM

Bulletin No. 193, 46-50, Oct. 1953* (Cracking to the metal

in half the exposed area.

)

THE NATIONAL BUREAU OF STANDARDS

Functions and Activities

The functions of the National Bureau of Standards are set forth in the Act of Congress, March

3, 1901, as amended by Congress in Public Law 619, 1950. These include the development and

maintenance of the national standards of measurement and the provision of means and methods

for making measurements consistent with these standards; the determination of physical constants and properties of materials; the development of methods and instruments for testing materials,

devices, and structures; advisory services to Government Agencies on scientific and technical

problems; invention and development of devices to serve special needs of the Government; and the

development of standard practices, codes, and specifications. The work includes basic and applied

research, development, engineering, instrumentation, testing, evaluation, calibration services, and

various consultation and information services. A major portion of the Bureau’s work is performed

for other Government Agencies, particularly the Department of Defense and the Atomic Energy

Commission. The scope of activities is suggested by the listing of divisions and sections on the

inside of the front cover.

Reports and Publications

The results of the Bureau’s work take the form of either actual equipment and devices or published papers and reports. Repor.ts are issued to the sponsoring agency of a particular project or program. Published papers appear either in the Bureau’s own series of publications or in the

journals of professional and scientific societies. The Bureau itself publishes three monthly periodicals, available from the Government Printing Office: The Journal of Research, which presents

complete papers reporting technical investigations; the Technical News Bulletin, which presents

summary and preliminary reports on work in progress; and Basic Radio Propagation Predictions,

which provides data for determining the best frequencies to use for radio communications throughout

the world. There are also five series of nonperiodical publications: The Applied Mathematics

Series, Circulars, Handbooks, Building Materials and Structures Reports, and Miscellaneous

Publications.

Information on the Bureau’s publications can be found in NBS Circular 460, Publications of

the National Bureau of Standards ($1.25) and its Supplement ($0.75), available from the Superintendent of Documents, Government Printing Office. Inquiries regarding the Bureau’s reports and

publications should be addressed to the Office of Scientific Publications, National Bureau of

Standards, Washington 25, D. C.