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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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tion, National Bureau of Standards. Washington 25. D. C.

NATIONAL BUREAU OF STANDARDS REPORTMBS PROJECT NB9 REPORT1004-12-1041 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 AssociatesAsphalt Roofing Industry Bureau

Floor, Roof and Wall Coverings SectionBuilding Technology Division

Jointly Sponsored byAsphalt 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 Governmeito 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 DURABILITYOF COATING- GRADE ROOFING ASPHALTS

by

John P, Falzoneand

George D 0 McDonald

5j< ^

ABSTRACT

Twelve coating-grade asphalts, representative ofthose commercially available in the manufactureof roofing were studied to determine whether therates of filtration, changes in constituents orlosses in weight could be correlated with theirdurability

o

Rates of filtration determined by the method de-scribed distinguished between the better and thepoorer weatherers, but a quantitative correlationwas poor although the method proved simple and re-producible o

Average rate of changes of total oils, dark oils,asphaltenes or asphaltenes plus loss in weightshowed excellent correlations, but were inapplicableto early predictions of durabilities since theirrates of change were not comparable throughout theexposure cycle 0

Average rate of loss in weight was related to dura-bility,, In addition, the weight change for eachasphalt was nearly linear with time and was com-parable in early periods of exposure 0 The loss at300 hours is consequently recommended as a rapid,reliable criterion for predicting the durabilityof a blown, coating-grade asphalt,,

^ % >|c ^

2

1„ INTRODUCTION

This investigation is part of the long established asphaltresearch project jointly sponsored by the National Bureau ofStandards 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 thenature of the asphalt employed in its manufacture. In turn,the nature of the asphalt is principally a function of thesource of the petroleum crude from which it is derived and,to a lesser extent, the processing used to convert theresiduum into the coating-grade product having the necessaryphysical characteristics. Because of the relatively longlife of even the poorest roofing, a rapid, reliable evalua-tion of the weathering properties of an asphalt has longbeen an objective in the research project. The inherentchemical and rheological complexity of an asphaltic systemhas impeded the attainment of a simple satisfactory solutionto this problem.

Early investigators concentrated their efforts towards de-veloping methods for accelerated weathering. Since theeffects 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 waterspray. Subsequent work on the effects of current and vol-tage (*+), exposure temperature ( 5 ) 9

accelerated cycle used(6), film preparation ( 7 )

,

inspection procedure and end-pointdeterminations (8, 9) ultimately led to some recommendedpractices in accelerated testing of bituminous products.

Unfortunately, the quantitative relationship betweenaccelerated and natural weathering is as yet not satisfac-torily resolved. However, there is sufficient evidence toindicate that the relative order of failure for asphaltshaving significant differences in weather resistance is thesame for both weatherometer and roof exposures (6),

1/Figuresthe end

in parentheses indicateof this report.

literature references at

- 3 -

The purpose of this investigation was to evaluate severalproposed criteria for predicting durability employingaccelerated tests as primary standards, namely

s

(1) The filtration rate of n-pentane solubles throughthe 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 availableasphalts, were submitted by several members of the ResearchCommittee of the Asphalt Roofing Industry Bureau, four fromCalifornia, four from Midcontinent, and three from Venezuelancrudes. An additional Midcontinent sample, blown in alaboratory still to a significantly lower softening point,was included o The lower softening point of this samplerendered difficult the determination of its durability..

2 0 2 Sampling

Enough material was taken from a 5-gallon sample and atleast one inch below the surface so that every determinationthat was made for each asphalt was done on a portion pouredfrom the same melt* This precaution was taken because ofthe recognized susceptibility of asphalts to both reversibleand irreversible changes even at room temperatures* The sur-face of samples in storage for three years, for example, hasbeen 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 asphaltby the Ring and Ball method as prescribed in A 0 S 0 T 0 M 0 Proce-dure D36-26o

- 1+ -

The first specimen was poured immediately prior to castingthe films necessary for accelerated testing, the secondimmediately after, The results presented in Table 1 areaverages of the two 0

2 a b Penetrations

Penetrations at 32% 77° and 115°F were determined for eachasphalt employing A 0 S 0 T„M 0 Procedure D5-#9» The specimensfor these determinations were poured immediately after halfof the necessary films for determining durability were cast.The results are shown in Table 1 0 The susceptibility factoris defined as the ratio of the penetration at 115°F minus thepenetration 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 nor-mally added to a sample in order to precipitate theasphaltenes, Subsequent removal is effected by filteringthrough a tared Gooch crucible, the bottom of which iscovered by an asbestos mat 0 During the separation of 21asphalts (12), Kleinschmidt observed that he could generallypredict the relative order of failure of these samples inan accelerated cycle by arranging them according to thetime necessary for filtration, those taking the least time.failing most rapidly,

A quantitative method to measure this filtration rate wasdeveloped with the aid of a pressure filter designed bythe Johns-Manville Research Laboratories, The instrumentwas essentially an all metal cylinder having a fitted, re-movable stopcock assembly at the bottom so that a Whatman#50 paper filter disc could be inserted and a fitted caphaving a lead-in tube so that a suitable inert gas couldbe introduced for increasing the pressure. The latter wasregulated 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 weightconcentration of asphalt was pipetted into 90 ml 0 ofn-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., theensuing 90 seconds were used to transfer the sample into thepressure filter tube, fitting the cap into place and ele-vating the pressure to one p.s.i, using nitrogen gas forthis purpose.

The stopcock was opened allowing the filtrate to flow intoa suitable graduated cylinder. The times required forsuccessive 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 = KTfairly closely, where V = volume of filtrate in ml. andT = time in minutes. Taking the logarithm of both sidesand rearrangement of the result yielded

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

Consequently, volume was plotted against time on logarithmicgraph paper, A line having the slope = 1/2 was fitted to theexperimental points and extrapolated to T = 1. The valueof V thus obtained, when squared, evaluated K according tothe above expression.

Two values of K were obtained for each asphalt. The firstwas derived employing a 10$ solution of each asphalt inbenzene. A second filtration rate, designated Ks

,was de-

termined in which the amount of asphaltenes precipitatedwas calculated to be the same for all samples. The levelarbitrarily chosen was that amount of asphaltenes obtainedwhen an aliquot of the 10$ benzene solution of the asphalthaving the lowest initial asphaltene concentration was used.

- 6 -

2 0 6 Durability by Accelerated Weathering

Since the primary standard employed in this study was theweatherometer test, every reasonable precaution was taken toobtain reliable ratings 0 Five replicate specimens of eachasphalt were cast in uniform films of 25 mils ±1 mil on6- x 2-3/4- in„ aluminum panels (7)° Essentially these wereexposed to accelerated conditions as proposed by A 0 S o T o M o

Method D529-39To To offset possible differences in thecarbon arc machines, two specimens of each asphalt wereexposed in one weatherometer and the remaining three inanother

o

The 51-9C cycle, consisting of 51 minutes of dry light andheat 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 duringeach cycle was comparable.

Failure determinations were made by obtaining spark photo-graphs using the high voltage crack detector technique (8,9) The coating was removed as a final failure when thephotograph showed that at least 5

0

% of the specimen ! s areahad cracks.

The specimens were inspected regularly twice each week, morefrequently when failure appeared to be imminent,, The in-spections were standardized as follows?

At the end of 51 minutes of dry light and heat, the specimenswere removed, permitted to cool to room temperature and in-spected preliminarily. Those coatings which showed pronouncedsparking were put aside for further evaluation. Twenty min-utes after they were removed from the machine, spark photo-graphs of these specimens were made, The failed coatingswere removed and the time to failure was recorded..

.

.

I

II

j

I

- 7 -

2o7 Hate of Change of Components

A primary separation of the asphalts was obtained bychromatographic analysis (11) 0 This consisted of filter-ing off the n-pentane insolubles (asphaltenes

)

5and

further separating the solubles (maltenes) into whiteoils, dark oils and resins by absorbing them on activatedFuller's earth in a chromatographic column and elutingwith 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 em-ployed to obtain successive fractions,.

An individual specimen of each asphalt was fractionatedbefore exposure, at 200 hours, at a second estimatedintermediate point and at final failure „ Thus, changesin every component with time could be followed „ Theaverage rate of change of each desired constituent wasobtained by dividing the total change by the time ofexposure »

2,8 Loss in Weight

Data for this study were obtained by weighing the repli-cate specimens of each asphalt at approximately 200-hr,intervals and computing their average. Since this is asurface phenomenon, actual losses in weight and not per-centages were compared since the surface area of eachspecimen was the same. Similar to the constituent changestudy, loss in weight for each asphalt was plotted againsttime of exposure. Average rate of loss in weight was com-puted by dividing the total loss by its durability.

.

.

3* RESULTS AND DISCUSSION

3.1 Rate of Filtration

The softening points, penetrations, rates of filtrationat two concentrations and the durabilities for the 12asphalts are presented in Table 1. For ease of comparisonthe 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 fil-tration at either concentration and the durability of theasphalt* It should be borne in mind that the conditionsfor this determination were selected on the basis of alimited study of the effects of varying the concentrationof the benzene solution of the asphalt and settling periodof the precipitate after transfer to the pressure filter.They constitute a compromise designed to minimize erraticresults and compression of differences among the asphaltsinduced by lower concentrations while at the same timeoffsetting inordinate running times and similar com-pressive effects brought about by longer settling periods*It is conceivable that an extended study of these variableswould indicate other conditions to be more favorable forthe measurement of this property* The method is simplewhile the reproducibility of duplicate determinations is

±3f*.

However, changes in constitutents and losses in weightstudies were favored because of the promising nature ofthe results obtained*

3.2 Changes in Components

The fractions obtained with the separation employed wereasphaltenes, while oils, dark oils and resins. As eachasphalt degraded during exposure, the overall patternwas quite similar; asphaltenes and resins increased andlosses in weight became evident as the dark and white oilswere depleted* Thus, it might be expected that the rateof change of one or more of these fractions would be re-lated to durability* A previous report on 20 asphalts had

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shown a good correlation to exist between acceleratedweathering and (1) the average rate of change of asphaltenes,(2) the average of rate of change of total oils (white plusdark oils), (3) the average rate of change of asphaltenesplus weight loss (10)„ These conclusions have been re-affirmed in the present study 0 Figures 1, 2 and 3 show therelationships.. In addition, the average rate of change indark oils also correlated well with weather resistance(Figure 4)„

In order to determine whether these data could be trans-lated into a practical, reliable method for predictingdurability, it was necessary to establish whether thesame relative order of change was maintained in eachasphalt during the early periods of exposure 0 The datacompiled for this purpose are shown in Table 2 0 Thus,the change in asphaltenes, white oils, dark oils, resinsand weight loss of each asphalt was followed in themanner illustrated by Figures 6 and 7 Tor three of thesampleSo A direct graphical comparison of all asphaltenecomponent changes with time established that the samerelative order of change was not maintained throughoutthe exposure (Figure 8;„ A similar study of total oilchange during exposure for each asphalt likewise showedthat an interchange of relative position took place whichwas different from that obtained by comparing the calcu-lated average rates of change,, Consequently, predictionsbased on early rates of change of these constituents couldlead to serious discrepancies,

3o 3 Loss in Weight

Losses in weight data were analyzed in an identical mannerto those involving changes in components. Thus Figure 9showed a good correlation with durability by acceleratedweathering. Additionally, the loss for each asphalt duringthe early periods was nearly linear with time. Figure 10indicates that the relative position assumed by eachsample could be attributed to the length of time elapsedbefore it actually started to show a loss, i 0 e„, itsinduction 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 andplotted against its durability*, The result is shown inFigure 11 which may now be employed as a calibrationcurve to predict durabilities of other asphalts if theloss at 300 hours is known*,

This development is entirely consistent with the factsknown about the general degradative pattern in asphaltand to a limited extent elucidates the role of oils andasphaltenes with respect to durability,, Specif ically

,

asphalt degrades under the influence of heat and ultra-violet light, the former leading predominantly to anincrease in asphaltenes, the latter to oxygenated, waterextractable and volatile degradation products,, Both ofthese general reactions result in the depletion of thetotal oils,, The data in Table 1 show that the asphalteneincrease had either ceased or tapered to a nominal valuewell before the coating had weathered to final failure,,Evidently, then, the controlling reaction was the light-induced one which continued to deplete the availableoils to a level sufficiently low so that the crackedcoating could no longer heal itself under thermalinfluence,, 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 200-300hours of exposure was an effective measure of the rela-tive rates of this reaction for the asphalts studied,,

Those asphalts having the greater durability had thelonger induction period, the slower rate of loss inweight and lost weight linearly throughout the exposurecycle,, The less durable asphalts had extremely shortinduction periods, the greater rate of loss in weightand evidenced more deviation from linear loss during thedetermination of their durability. The latter effectwas apparently a result of such a rapid depletion of thereactants that the amount made available by the coatingfor continuation of this surface phenomena diminished witht ime 0

- 11 -

The length of the induction period was not determinedquantitatively for each asphalt . However, one of theless durable asphalts required only forty hours of exposurebefore it lost weight while a more durable coating re-quired 160 hours under the same conditions* Further workon this phase should prove of great interest*

4* CONCLUSIONS

The rate of filtration as determined under the conditionsdescribed in this report did not correlate strictly withdurability although it did distinguish between the lessdurable and the more durable asphalts*

The average rate of change of total oils or dark oils orasphaltenes correlated well with accelerated durability*However, these constituent changes could not be employedas criteria for prediction of durability because theydid not change comparably In every asphalt during exposure*

The average rate of loss in weight correlated well withdurability by accelerated weathering* Moreover, the lossin weight was nearly linear with time during the firstseveral hundred hours of exposure* Determination of theloss in weight at 300 hours appears to afford a simple,reliable method for the prediction of durability of acoating grade asphalt*

An induction period, during which no loss in weight occurs,apparently furnishes a means for determining the relativepositions of the loss in weight curves for each asphaltin a series. Further study of this phenomenon isindicated *

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 DurabilityTesting of Asphalt", A.S.T.Mo Bulletin No. 213 (April1956)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 Instrumentfor Detecting Crack Failures of Asphalt CoatingsDuring Weathering Tests", (issued as A.S.T.M. STPNo. 94) Sympo on Accelerated Durability Testing ofBituminous Materials, American Society for TestingMaterials, p. 153 (1949).

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

,"A

New Method for Evaluating Failure of BituminousMaterials Due to Weathering", Symp G on Acc, DurabilityTesting of Bit* Materials, American Society for Test-ing Materials, p 0 144 (1949) (Issued as A.S,T.M, STPNo. 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 DistinctiveGroups 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).

,* .

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U. S. DEPARTMENT OF COMMERCELewis L. Strauss, Secretary

NATIONAL BUREAU OF STANDARDSA. V. Astiti, Director

THE NATIONAL ICUREAIT OE STANHA ItOSThe 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.

Heat. Temperature Physics. Thermodynamics. Cryogenic Physics. Rheology. Engine Fuels.

Free Radicals Research.

Atomic and Radiation Piiysics. Spectroscopy. Racliometry. Mass Spectrometry. Solid

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

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

Equipment. '

Chemistry. Organic Coatings. Surface Chemistry. Organic Chemistry. Analytical Chemistry.

Inorganic Chemistry. Electrodeposition. Molecular Structure and Properties of Gases. Physical

Chemistry. Thermochemistry. Spectrochemistry. Pure Substances.

Mechanics. Sound. Mechanical Instruments. Fluid Mechanics. Engineering Mechanics. Mass

and Scale. Capacity, Density, and Fluid Meters. Combustion Controls.

Organic and Eihroaas Materials. Rubber. Textiles. Paper. Leather. Testing and

Specifications. Polymer Structure. Plastics. Dental Research.

Metallurgy. Thermal Metallurgy. Chemical Metallurgy. Mechanical Metallurgy. Corrosion.

Metal Physics.

Mineral Products. Engineering Ceramics. Glass. Refractories. Enameled Metals. Concreting

Materials. Constitution and Microstructure.

Building Techmoingy. Structural Engineering. Fire Protection. Air Conditioning, Heating,

and Refrigeration. Floor, Roof, and Wall Coverings. Codes and Safety Standards. Heat Transfer.

Applied Mathematics. Numerical Analysis. Computation. Statistical Engineering. Mathe-

matical Physics.

Data Processing Systems. SEAC Engineering Group. Components and Techniques. Digital

Circuitry. Digital Systems. Anolog Systems. Application Engineering.

• Office of Basic Instrumentation. * Office of Weights and Measures.

BOULDER, COLORADOCryogenic Engineering. Cryogenic Equipment. Cryogenic Processes. Properties of Mate-

rials. Gas Liquefaction.

Radio Propagation Physics. Upper Atmosphere Research. Ionospheric Research. Regu-

lar Propagation Services. Sun-Earth Relationships. VHF Research. Ionospheric Communication

Systems.

Radio Propagation Engineering. Data Reduction Instrumentation. Modulation Systems.

Navigation Systems. Radio Noise. Tropospheric Measurements. Tropospheric Analysis. Radio

Systems Application Engineering. Radio-Meteorology.

Radio Standards. High Frequency Electrical Standards. Radio Broadcast Service. High

Frequency Impedance Standards. Electronic Calibration Center. Microwave Physics. MicrowaveCircuit Standards,