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NATIONAL BUREAU OF STANDARDS REPORT

6256

A RAPID METHOD FOR PREDICTING THE DURABILITY

OF COATING- GRADE ROOFING ASPHALTS

by

John P. Falzone

and

George D, McDonald

<^B§>

U. S. DEPARTMENT OF COMMERCE

NATIONAL BUREAU OF STANDARDS
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, 1 00 1 , as amended hy Congress in Public Law 619, 1950. These include t lie development and

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

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NATIONAL BUREAU OF STANDARDS REPORT

MBS PROJECT NB9 REPORT

1004-12-1041 January 9, 1959 6256

A RAPID METHOD FOR PREDICTING THE DURABILITY

.OF COATING-GRADE ROOFING ASPHALTS

by

John P. Falzone , and

George D. McDonald

Research Associates

Asphalt Roofing Industry Bureau

Floor, Roof and Wall Coverings Section

Building Technology Division

Jointly Sponsored by

Asphalt Roofing Industry Bureau

and

National Bureau of Standards

IMPORTANT NOTICE

NATIONAL BUREAU OF f Intended for uee within th< to additional evaluation an* Hating of thla Report, elthe the Office of the Director, I however, by the Governmei

to reproduce additional co|

Approved for public release by the

Director of the National Institute of

Standards and Technology (NIST)

on October 9, 201 5.

r progren accounting document!

formally published It U subjected

tg, reproduction, or opendlterature

ilsslon la obtained In writing from

. Such pormlMlon la not needed,

lly prepared If that agency wlahea <NBS>

U. S. DEPARTMENT OF COMMERCE

NATIONAL BUREAU OF STANDARDS
I
A RAPID METHOD FOR PREDICTING THE DURABILITY

OF COATING- GRADE ROOFING ASPHALTS

by

John P, Falzone

and

George D 0 McDonald

5j< ^

ABSTRACT

Twelve coating-grade asphalts, representative of

those commercially available in the manufacture

of roofing were studied to determine whether the

rates of filtration, changes in constituents or

losses in weight could be correlated with their

durability

o

Rates of filtration determined by the method described distinguished between the better and the

poorer weatherers, but a quantitative correlation

was poor although the method proved simple and reproducible o Average rate of changes of total oils, dark oils,

asphaltenes or asphaltenes plus loss in weight

showed excellent correlations, but were inapplicable

to early predictions of durabilities since their

rates of change were not comparable throughout the

exposure cycle 0 Average rate of loss in weight was related to durability,, In addition, the weight change for each

asphalt was nearly linear with time and was comparable in early periods of exposure 0 The loss at

300 hours is consequently recommended as a rapid,

reliable criterion for predicting the durability

of a blown, coating-grade asphalt,,

^ % >|c ^

2

1„ INTRODUCTION

This investigation is part of the long established asphalt

research project jointly sponsored by the National Bureau of

Standards and the Asphalt Roofing Industry Bureau,

It has been known for some time that other factors being equal,

the durability of roll roofings or shingles depends upon the

nature of the asphalt employed in its manufacture. In turn,

the nature of the asphalt is principally a function of the

source of the petroleum crude from which it is derived and,

to a lesser extent, the processing used to convert the

residuum into the coating-grade product having the necessary

physical characteristics. Because of the relatively long

life of even the poorest roofing, a rapid, reliable evaluation of the weathering properties of an asphalt has long

been an objective in the research project. The inherent

chemical and rheological complexity of an asphaltic system

has impeded the attainment of a simple satisfactory solution

to this problem.

Early investigators concentrated their efforts towards developing methods for accelerated weathering. Since the

effects of light, heat and oxygen were recognized as fac- , tors contributing to the degradation of the coating (1, 2)~,

the carbon arc lamp was soon introduced to asphalt studies

(3)o Later developments led to the periodic use of a water

spray. Subsequent work on the effects of current and voltage (*+), exposure temperature ( 5 ) 9 accelerated cycle used

(6), film preparation ( 7 )

,

inspection procedure and end-point

determinations (8, 9) ultimately led to some recommended

practices in accelerated testing of bituminous products.

Unfortunately, the quantitative relationship between

accelerated and natural weathering is as yet not satisfactorily resolved. However, there is sufficient evidence to

indicate that the relative order of failure for asphalts

having significant differences in weather resistance is the

same for both weatherometer and roof exposures (6),

1/ Figures

the end

in parentheses indicate

of this report.

literature references at

- 3

-

The purpose of this investigation was to evaluate several

proposed criteria for predicting durability employing

accelerated tests as primary standards, namely

s

(1) The filtration rate of n-pentane solubles through

the insolubles of an asphalto

(2) The rate of changes in components 0

(3) The rate of losses in weighto

2 0 EXPERIMENTAL PROCEDURES

2d Asphalts

Twelve samples, representative of commercially available

asphalts, were submitted by several members of the Research

Committee of the Asphalt Roofing Industry Bureau, four from

California, four from Midcontinent, and three from Venezuelan

crudes. An additional Midcontinent sample, blown in a laboratory still to a significantly lower softening point,

was included o The lower softening point of this sample

rendered difficult the determination of its durability..

2 0 2 Sampling

Enough material was taken from a 5-gallon sample and at

least one inch below the surface so that every determination

that was made for each asphalt was done on a portion poured

from the same melt* This precaution was taken because of

the recognized susceptibility of asphalts to both reversible

and irreversible changes even at room temperatures* The surface of samples in storage for three years, for example, has

been shown to change as much as 8% in pentane insoluble

(asphaltene) content (10),

2 0 3 Softening Points

Two softening point determinations were made for each asphalt

by the Ring and Ball method as prescribed in A 0 S 0 T 0 M 0 Procedure D36-26o

- 1+ -

The first specimen was poured immediately prior to casting

the films necessary for accelerated testing, the second

immediately after, The results presented in Table 1 are

averages of the two 0

2 a b Penetrations

Penetrations at 32% 77° and 115°F were determined for each

asphalt employing A 0 S 0 T„M 0 Procedure D5-#9» The specimens

for these determinations were poured immediately after half

of the necessary films for determining durability were cast.

The results are shown in Table 1 0 The susceptibility factor

is defined as the ratio of the penetration at 115°F minus the

penetration at 32°F to that at 77°F for a given asphalts

2,5 Filtration Rate

In the primary separation of an asphalt into asphaltenes,

white oils, dark oils and resins (11), n-pentane is normally added to a sample in order to precipitate the

asphaltenes, Subsequent removal is effected by filtering

through a tared Gooch crucible, the bottom of which is

covered by an asbestos mat 0 During the separation of 21

asphalts (12), Kleinschmidt observed that he could generally

predict the relative order of failure of these samples in

an accelerated cycle by arranging them according to the

time necessary for filtration, those taking the least time

.failing most rapidly,

A quantitative method to measure this filtration rate was

developed with the aid of a pressure filter designed by

the Johns-Manville Research Laboratories, The instrument

was essentially an all metal cylinder having a fitted, removable stopcock assembly at the bottom so that a Whatman

#50 paper filter disc could be inserted and a fitted cap

having a lead-in tube so that a suitable inert gas could

be introduced for increasing the pressure. The latter was

regulated by a simple manostat in series with a manometer.
I

.

.

.
- 5 -

The general procedure employed was as follows?

Ten ml. of a benzene solution having the desired weight

concentration of asphalt was pipetted into 90 ml 0 of

n-pentane previously measured into a suitable glass bottle 0 After swirling , the bottle was stoppered and the system was

allowed to stand for 20 hours at room temperature

.

The mixture was again swirled. Timed with a stopwatch., the

ensuing 90 seconds were used to transfer the sample into the

pressure filter tube, fitting the cap into place and elevating the pressure to one p.s.i, using nitrogen gas for

this purpose.

The stopcock was opened allowing the filtrate to flow into

a suitable graduated cylinder. The times required for

successive 5 ml, volumes to flow were recorded.

The filtration rate was obtained as follows?

The flow rate was found to follow the expression V

2 = KT

fairly closely, where V = volume of filtrate in ml. and

T = time in minutes. Taking the logarithm of both sides

and rearrangement of the result yielded

In V = 1/2 In T + 1/2 In K.

Consequently, volume was plotted against time on logarithmic

graph paper, A line having the slope = 1/2 was fitted to the

experimental points and extrapolated to T = 1. The value

of V thus obtained, when squared, evaluated K according to

the above expression.

Two values of K were obtained for each asphalt. The first

was derived employing a 10$ solution of each asphalt in

benzene. A second filtration rate, designated Ks , was determined in which the amount of asphaltenes precipitated

was calculated to be the same for all samples. The level

arbitrarily chosen was that amount of asphaltenes obtained

when an aliquot of the 10$ benzene solution of the asphalt

having the lowest initial asphaltene concentration was used.

- 6 -

2 0 6 Durability by Accelerated Weathering

Since the primary standard employed in this study was the

weatherometer test, every reasonable precaution was taken to

obtain reliable ratings 0 Five replicate specimens of each

asphalt were cast in uniform films of 25 mils ±1 mil on

6- x 2-3/4- in„ aluminum panels (7)° Essentially these were

exposed to accelerated conditions as proposed by A 0 S o T o M o Method D529-39To To offset possible differences in the

carbon arc machines, two specimens of each asphalt were

exposed in one weatherometer and the remaining three in

another

o

The 51-9C cycle, consisting of 51 minutes of dry light and

heat per hour followed by 9 minutes of light and cold (40°Fo ) water spray, was employed,,

A maximum panel temperature, 144° ±2°F, , was attained in

each machine o The variation in coating temperatures during

each cycle was comparable.

Failure determinations were made by obtaining spark photographs using the high voltage crack detector technique (8,

9) The coating was removed as a final failure when the

photograph showed that at least 5

0

% of the specimen ! s area

had cracks.

The specimens were inspected regularly twice each week, more

frequently when failure appeared to be imminent,, The inspections were standardized as follows?

At the end of 51 minutes of dry light and heat, the specimens

were removed, permitted to cool to room temperature and inspected preliminarily. Those coatings which showed pronounced

sparking were put aside for further evaluation. Twenty minutes after they were removed from the machine, spark photographs of these specimens were made, The failed coatings

were removed and the time to failure was recorded..
. . IIIjI
- 7

-

2o7 Hate of Change of Components

A primary separation of the asphalts was obtained by

chromatographic analysis (11) 0 This consisted of filtering off the n-pentane insolubles (asphaltenes

)

5 and

further separating the solubles (maltenes) into white

oils, dark oils and resins by absorbing them on activated

Fuller's earth in a chromatographic column and eluting

with increasingly polar solvents, namely, n-pentane,

methylene chloride and methyl ethyl ketone.

Two modifications of the procedure cited were mades

(1) The Fuller's earth was activated at l4o°

for 18-20 hours.

(2) A volume of 250 ml, of each solvent was employed to obtain successive fractions,.

An individual specimen of each asphalt was fractionated

before exposure, at 200 hours, at a second estimated

intermediate point and at final failure „ Thus, changes

in every component with time could be followed „ The

average rate of change of each desired constituent was

obtained by dividing the total change by the time of

exposure » 2,8 Loss in Weight

Data for this study were obtained by weighing the replicate specimens of each asphalt at approximately 200-hr,

intervals and computing their average. Since this is a surface phenomenon, actual losses in weight and not percentages were compared since the surface area of each

specimen was the same. Similar to the constituent change

study, loss in weight for each asphalt was plotted against

time of exposure. Average rate of loss in weight was computed by dividing the total loss by its durability.
.

.
3* RESULTS AND DISCUSSION

3.1 Rate of Filtration

The softening points, penetrations, rates of filtration

at two concentrations and the durabilities for the 12

asphalts are presented in Table 1. For ease of comparison

the listing appears in the order of increasing durability,,

It is immediately evident that, except for a general trend,

a good correlation does not exist between the rate of filtration at either concentration and the durability of the

asphalt* It should be borne in mind that the conditions

for this determination were selected on the basis of a limited study of the effects of varying the concentration

of the benzene solution of the asphalt and settling period

of the precipitate after transfer to the pressure filter.

They constitute a compromise designed to minimize erratic

results and compression of differences among the asphalts

induced by lower concentrations while at the same time

offsetting inordinate running times and similar compressive effects brought about by longer settling periods*

It is conceivable that an extended study of these variables

would indicate other conditions to be more favorable for

the measurement of this property* The method is simple

while the reproducibility of duplicate determinations is

±3f*.

However, changes in constitutents and losses in weight

studies were favored because of the promising nature of

the results obtained*

3.2 Changes in Components

The fractions obtained with the separation employed were

asphaltenes, while oils, dark oils and resins. As each

asphalt degraded during exposure, the overall pattern

was quite similar; asphaltenes and resins increased and

losses in weight became evident as the dark and white oils

were depleted* Thus, it might be expected that the rate

of change of one or more of these fractions would be related to durability* A previous report on 20 asphalts had

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shown a good correlation to exist between accelerated

weathering and (1) the average rate of change of asphaltenes,

(2) the average of rate of change of total oils (white plus

dark oils), (3) the average rate of change of asphaltenes

plus weight loss (10)„ These conclusions have been reaffirmed in the present study 0 Figures 1, 2 and 3 show the

relationships.. In addition, the average rate of change in

dark oils also correlated well with weather resistance

(Figure 4)„

In order to determine whether these data could be translated into a practical, reliable method for predicting

durability, it was necessary to establish whether the

same relative order of change was maintained in each

asphalt during the early periods of exposure 0 The data

compiled for this purpose are shown in Table 2 0 Thus,

the change in asphaltenes, white oils, dark oils, resins

and weight loss of each asphalt was followed in the

manner illustrated by Figures 6 and 7 Tor three of the

sampleSo A direct graphical comparison of all asphaltene

component changes with time established that the same

relative order of change was not maintained throughout

the exposure (Figure 8;„ A similar study of total oil

change during exposure for each asphalt likewise showed

that an interchange of relative position took place which

was different from that obtained by comparing the calculated average rates of change,, Consequently, predictions

based on early rates of change of these constituents could

lead to serious discrepancies,

3o 3 Loss in Weight

Losses in weight data were analyzed in an identical manner

to those involving changes in components. Thus Figure 9

showed a good correlation with durability by accelerated

weathering. Additionally, the loss for each asphalt during

the early periods was nearly linear with time. Figure 10

indicates that the relative position assumed by each

sample could be attributed to the length of time elapsed

before it actually started to show a loss, i 0 e„, its

induction period, in addition to its difference in slope

(rate). The loss in weight of each asphalt after 300
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hours of weathering was obtained from this graph and

plotted against its durability*, The result is shown in

Figure 11 which may now be employed as a calibration

curve to predict durabilities of other asphalts if the

loss at 300 hours is known*,

This development is entirely consistent with the facts

known about the general degradative pattern in asphalt

and to a limited extent elucidates the role of oils and

asphaltenes with respect to durability,, Specif ically

,

asphalt degrades under the influence of heat and ultraviolet light, the former leading predominantly to an

increase in asphaltenes, the latter to oxygenated, water

extractable and volatile degradation products,, Both of

these general reactions result in the depletion of the

total oils,, The data in Table 1 show that the asphaltene

increase had either ceased or tapered to a nominal value

well before the coating had weathered to final failure,,

Evidently, then, the controlling reaction was the lightinduced one which continued to deplete the available

oils to a level sufficiently low so that the cracked

coating could no longer heal itself under thermal

influence,, Hence, the faster the rate of this reaction,

the more rapidly did the coating attain final failure,,

It appears that the weight loss obtained after 200-300

hours of exposure was an effective measure of the relative rates of this reaction for the asphalts studied,,

Those asphalts having the greater durability had the

longer induction period, the slower rate of loss in

weight and lost weight linearly throughout the exposure

cycle,, The less durable asphalts had extremely short

induction periods, the greater rate of loss in weight

and evidenced more deviation from linear loss during the

determination of their durability. The latter effect

was apparently a result of such a rapid depletion of the

reactants that the amount made available by the coating

for continuation of this surface phenomena diminished with

t ime 0

- 11 -

The length of the induction period was not determined

quantitatively for each asphalt . However, one of the

less durable asphalts required only forty hours of exposure

before it lost weight while a more durable coating required 160 hours under the same conditions* Further work

on this phase should prove of great interest*

4* CONCLUSIONS

The rate of filtration as determined under the conditions

described in this report did not correlate strictly with

durability although it did distinguish between the less

durable and the more durable asphalts*

The average rate of change of total oils or dark oils or

asphaltenes correlated well with accelerated durability*

However, these constituent changes could not be employed

as criteria for prediction of durability because they

did not change comparably In every asphalt during exposure*

The average rate of loss in weight correlated well with

durability by accelerated weathering* Moreover, the loss

in weight was nearly linear with time during the first

several hundred hours of exposure* Determination of the

loss in weight at 300 hours appears to afford a simple,

reliable method for the prediction of durability of a coating grade asphalt*

An induction period, during which no loss in weight occurs,

apparently furnishes a means for determining the relative

positions of the loss in weight curves for each asphalt

in a series. Further study of this phenomenon is

indicated *

12

5„ REFERENCES

(1) V. Vojtech, "Light Action on Asphalts", J. Soc. Chem 0 Ind „ , 654 (1906)o

(2) Errera, J. , "Light Sensitivity of Asphalts" , Trans,

Farado Soc., 314-17 (1923).

(3) Strieter, 0 o G. , "Accelerated Tests of Asphalt", J 0 Reso NBS 247-253 (Aug. 1930), RP197*

(4) Kolb, W. C. , "The Characteristics of the Carbon Arc.

How the Properties Vary with Voltage and Current",

Electrical Engineering 53, 1173-9 (193*+) , 56, 319-24

(1937)<.

(5) Weetman, B. , "Accelerated Weathering of Bituminous

Materials - Operating Variables", Proc. A.S.T.M. 43 . 1154-64 (1943)o

(6) Kleinschmid t , L. R. and Greenfeld, S. H. , "Influence

of Exposure Conditions on the Accelerated Durability

Testing of Asphalt", A.S.T.Mo Bulletin No. 213 (April

1956)o

(7) Greenfeld, S a H. , "A Method of Preparing Uniform Films

of Bituminous Materials", A 0 S 0 T 0 M 0 Bulletin No 0 193,

50-2 (Oct. 1953)o

(8) "The Design and Application of a Spark-Gap Instrument

for Detecting Crack Failures of Asphalt Coatings

During Weathering Tests", (issued as A.S.T.M. STP

No. 94) Sympo on Accelerated Durability Testing of

Bituminous Materials, American Society for Testing

Materials, p. 153 (1949).

(9) Hunter, Jo B, , Gzemski, F. C. and Laskaris, X. , "A

New Method for Evaluating Failure of Bituminous

Materials Due to Weathering", Symp G on Acc, Durability

Testing of Bit* Materials, American Society for Testing Materials, p 0 144 (1949) (Issued as A.S,T.M, STP

No. 94)o

- 13 -

(10) Falzone, J„ P„ , "Relation of Rate of Component

Changes in Asphalts to Accelerated Durability",

N 0 B 0 S 0 Report No. 5935 (June 20, 1958)o

(11) Kleinschmidt , L 0 R„ , "Chromatographic Method for

the Fractionation of Asphalts Into Distinctive

Groups of Components", J„ Res„ NBS , 163-166

(1955).

(12) Greenfeld, S 0 H. , "Report on the Evaluation of 21

Coating-Grade Roofing Asphalts", N.B.S. Report No„

4732 (July 1, 1956).
,* .
AVERAGE

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U. S. DEPARTMENT OF COMMERCE

Lewis L. Strauss, Secretary

NATIONAL BUREAU OF STANDARDS

A. V. Astiti, Director THE NATIONAL ICUREAIT OE STANHAIt OS

The scope of activities of the National Bureau of Standards at its headquarters in Washington,

D. C., and its major laboratories in Boulder, Colo., is suggested in the following listing of the divisions and sections engaged in technical work. In general, each section carries out specialized

research, development, and engineering in the field indicated by its title. A brief description of

the activities, and of the resultant publications, appears on the inside front cover. WASHINGTON, O. C.

Electricity and Electronics. Resistance and Reactance. Electron Devices. Electrical In- struments. Magnetic Measurements. Dielectrics. Engineering Electronics. Electronic Instru- mentation. Electrochemistry.

Optics and Metrology. Photometry and Colorimetry. Optical Instruments. Photographic

Technology. Length. Engineering Metrology.

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State Physics. Electron Physics. Atomic Physics. Neutron Physics. Radiation Theory.

Radioactivity. X-rays. High Energy Radiation. Nucleonic Instrumentation. Radiological

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Chemistry. Thermochemistry. Spectrochemistry. Pure Substances.

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and Scale. Capacity, Density, and Fluid Meters. Combustion Controls. Organic and Eihroaas Materials. Rubber. Textiles. Paper. Leather. Testing and

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