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Effects of Mineral Additives on the

Durability of Coating-Grade Roofing Asphalts

United States Department of Commerce

National Bureau of Standards

Building Materials and Structures Report 147
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UNITED STATES DEPARTMENT OF COMMERCE • Sinclair Weeks, Secretary NATIONAL BUREAU OF STANDARDS • A. V. Astin, Director

Effects of Mineral Additives on the

Durability of Coating-Grade Roofing Asphalts

Sidney H. Greenfeld

Building Materials and Structures Report 147

Issued September 1956

For sale by the Superintendent of Documents, U. S. Government Printing Office, Washington 25. D. C.

Price 20 cents
Contents

Page

1. Introduction 1

2. Materials. _ 1 2.1. Mineral additives 1 2.2. Asphalts.. . 1

3. Procedure - 3

3.1. Preparation of specimens . 3

3.2. Exposure of specimens 4

3.3. Inspection of specimens . 4

4. Results 4

4.1. Effect of softening point of asphalt products on durability 4

4.2. Effect of softening point of asphalt base on durability of coatings containing mineral additives 5

4.3. Effect of degree of mixing of additives with asphalt on durability of coatings 5

4.4. Effect of six selected commercially available additives on

durability of coatings 6

4.5. Effect of the particle-size distribution of the mineral additives on the durability of coatings 9

4.6. Effect of particle shape of additives on durability of coatings. . 10

4.7. Effect of clay, fly ash, and silica from different sources on

durability of coatings 11

5. Summary and conclusions 12

6. References 12

7. Appendix 13

7.1. Volume composition 13

7.2. Specific gravit}’ 13

7.3. Shatter test on coatings 13

7.4. Water absorption of asphalt—disk method 13
Effects of Mineral x^dditives on the Durability of Coating-Grade

Roofing Asphalts

Sidney H. Greenfeld*

The effects of 14 mineral additives on the durability of coatings made from three asphalts were evaluated in accelerated durability machines. It was found that while the durability

of the coating is largely a function of the asphalt used, it increases, generally, with coating

thickness and mineral additive concentration. Additives with flat, platelike particles finer than 75 microns in diameter (U. S. Standard Sieve No. 200) were most effective in producing

coatings of increased durability. Complete dispersion of the adflitives in the base asphalts

is necessary to produce consistent results.

1. Introduction

In the late 1920’s and early 1930’s, the asphaltroofing industry began to use mineral additives in

the asphalt coatings of roll roofing and shingles

in order to stabilize these coatings, i. e., prevent

their flowing, at service temperatures. It was

observed that some of these materials also ajtjtreciably increased the durability of the coatings.

Because little was known of how mineral matter

affected the weathering of asphalts, a project was

started at the National Bureau of Standards by

the Asphalt Roofing Institute ^ to investigate the

effects of adding finely divided mineral matter of various kinds to an asphalt. The results indicated

that many types of minerals up to concentrations

of 35 percent materially improved the durability

of the asphalt [1, 2].^ However, the study left many cjuestions still unanswered.

The investigation was resumed and extended in 1947 to cover concentrations of mineral matter in excess of 35 percent in several different asphalts. In addition, the effects of coating thickness, soft- ening point of the base asphalt, particle-size dis- tribution, particle shape, and some natural variations of the minerals and methods of mixing the

minerals and asphalts are covered by this work.

2. Materials

2.1. Mineral Additives

0. G. vStrieter [2], working with but one asphalt,

found that although many mineral additives en- hanced durability, there were large differences in the magnitude of the increase. Based partly on

his findings and largely on the results of service

performance, six additives were selected for evaluation in three asphalts in this investigation. The

characteristics of these additives are reported in detail in table 1. Figure 1 contains photomicrographs of these materials at convenient magnifications to illustrate their particle shapes. Table 2

lists the properties of other materials used in only one phase of this study. Some of the properties

’Research Associate at the National Bureau of Standards, representing

the Asphalt Roofing Industry- Bureau.

> Now the Asphalt Roofing Industry Bureau.

- Figures in brackets indicate the literature references at the end of this report.

of three of the minerals in table 1 have been re- peated in table 2 in order to facilitate the comparison of these minerals with the others in table 2.

2.2. Asphalts

The asphalts investigated were obtained from

three widely different crudes and are typical of

asphalts used in the manufacture of asphalt

shingles. Eacli crude was commercially processed

into a flux and five asphalt products of different

softening points, as shown in table 3. The fluxes are the residual products of steam- or vacuumrefining processes that had removed the lowerboiling fractions of the crudes. The fluxes were

oxidized with air at about 450° F in industrial

blowing stills. As oxidation progressed, the charge

became harder, and as it attained the characteristics of each of the desired products, that product was removed from the still. (Although rarely

exposed to the same climate conditions, service

performance of the three asphalts indicated that

asphalt II should be the most durable and I the

least. Asphalt 1 II should be close to asphalt II.) To facilitate the differentiation of the various

coating terms, the following designations are used throughout this report:

Asphalt. A ])articular source of asphalt prod-

£ubts, designated bv the numerals I. II, and

^TII.

Asphalt yrod«cf. An asphalt blown to a desired softening point.

Asphalt blend. A mi.xture of two adjacent

products in suitable proportions to have a desired softening point.

Coating. An asphalt blend with or without

mineral matter having a softening point in the range of shingle coatings.

Asphalt coating. An asphalt blciul without

mineral matter having a softening point in the range of shingle coating asphalts, and

exposed for evaluation, designated A, B. and C.

Additive coating. An asphalt blend with added

mineral matter having a softening point

in the range of shingle coatings.

Asphalt base. An asidialt blentl that is mixeil

with mineral matter to produce an additive

coating.

388027—56 1
Table 1. Characteristics of mineral additives

.Additive

Property

Biue-black

slate Florida

clay “ Niagara

dolomite Low-carbonfly ash Tennessee mica Lake Erie ! silica

2.94 2. 64 2. 87 2. 62 3.01 2.68

i.O 97 9 2.0 2.0 2. 7 2. 5 %.. 29.5 63.9 19.4 30.0 97.2 19.5 1 %.. 32. 7 36.4 18.0 33.8 61.5 20.2 %.. 2.

1

11.8 1.8 4.9 0. 9 0.7 %.. 5.4 13.3 43. 7 7.3 4.4 2.5 1 %-. 0.2 2. 7 0. 1 0.4 0.

2

0.2 %.. .00 0.04 .00 5. 90 .46 .00 i %.. .0 .0 '.0 <0.0 .0 .0

Chemical analysis: e SiOd 56 47 6 40 50

1

98+

32 38 1 48 35 CaO+MgO 49 2. 5 1 K'oO-l-'KraoO 4 100.5

- -%-- 2 7.6

Particle size Finer than Lf. S. mils microns Std. Sieve

9 84 250 No. 60 %._ 99.8 100.0 99.9 99. 6 100.0 99.9 ; 6.97 177 No. 80. %.- 99.3 99.9 99.9 98.9 96.0 98,2

5 86 149 No. 100 . %._ 97.9 99.8 99. 6 97.5 91.0 80.8 i 4 92 125 No. 120 %.. 96. 2 99.8 99.3 96.7 85.6 53.7 i 3 47 88 No. 170 . .. %.. 91.3 99. 6 96.6 94.2 65.9 15.3 ! 2 91 74 No. 200 . %.. 86.9 99.3 93.4 92.3 56.8 8. 1 1 2 44 62 No. 230 %._ 83.6 99.

1

89.9 90.6 50.3 “ 4

1

1 73 44 No. .32.5 98.9 81.0 84.8 37.8 3.4 [ 1. 57 40 Sedh. 68 97 73 73 65 9

' 54 12 39 60 22 6 ,39 10 Sedi>- 8 2 26 43 4 4

. 16 4 Sedi>- . 2 1 13 15 2 1 1 2 Mixture with asphalt; ‘ Ease of mixing . _ Softening-point increase. . . . ... “F_. Good

15 Poor28 Fair13 Fair to good20 Good40 Good

5

“ Plasticity index, 34. Plastic limit, 34. ASTM Method D424-39.

b Isopropyl alcohol displacement.

' Low-temperature nitrogen adsorption—B. E. T. Method.

<1 ASTM D281-31, using a mineral oil and water instead of the specified oil.

« W. Lerch and R. H. Bogue, Ind. Eng. Chem. 2, 29fi-300 (1930).

< Turns phenolphthalein pink in aqueous solution,

e Supplier’s analyses.

1' Sedimentation in isopropyl alcohol. It should be noted that the results obtained by this method do not necessarily agree with those of the sieve

analysis.

40 percent of additive in product 4 of asphalt III (softening point, 224“ F). See table 3.

TENNESSEE MICA

X 80 Mineral additives. I

LOW CARBON FLY ASH

X 80 Figure 1.

LAKE ERIE SILICA

X 80
Table 2. Properties of clays, fly ashes, silicas, and oyster shell

Property » Florida •> clay Kyanite

Bradbury

clay Low car- bon •> fly- ash Pigh car- bon fly ash

Chicago

fly ash Lake

Erie •> silica

Bank

silica Ottawasilica Special

silica Oyster ' shell

Moisture.. , _ .. . 2. 7 0.0 1. 6 0.4 0.4 0. 4 0.2 0. 1 0.0 0.6 0.4 Loss on ignition at 1.000° F._ 11.8 . 1 4.4 4. 9 22.8 2. 1 . 7 . 2 . 1 , 7 9 Loss on ignition at 1.800° F_. 13.3 . 1 5. 7 7.3 25.9 4. 2 2. 5 . 4 . 2 1.4 43. 5 Water solubility . .

0.0 . 5 1.0 5. 9 4. 9 5.6 0.0 .2 . 1 3.0 0.5 Free alkali -%- .0 .0 0.0 '0.0 '0. 1 '0.6 .0 .0 .0 0.0 '.0

Particle sizes finer than U. S. Standard Sieve: Xo. 60 -%- 100.0 99.9 100.0 99.6 98.7 99. 9 99.9 100. 0 100.0 98.2 97. 7 Xo. 80 -%- 99.9 99.0 99. 7 98. 9 97.4 99. 7 98.2 97.8 99.0 98.

93. 6 Xo. 100 99.8 95.8 99. 1 97. 0 95.5 99.4 80.8 8.5.8 96.8 98.0 88.3 Xo. 120 .% 99.8 91. 9 98.8 96. 7 93.9 99. 1 53. 7 72. 2 90.2 97.8 84.4 Xo. 170 - 99.6 80.3 97.9 94.2 89.2 98.2 15.3 42, 7 65. 0 94.3 75. 5 Xo. 200 99.3 72.4 97.3 92. 3 85.4 97.4 8. 1 .34.3 51.7 91. 2 69. 5 Xo. 230 % 99. 1 65.8 96.8 90. 6 82.5 96. 6 ,5.4 ,30. 8 43.0 87.9 65. 2 Xo. 325 98.9 58.9 95.0 84.8 72. 9 94.0 3.4 19. 9 27.8 83. 1 57.

Mixture with asphalt: <• Ease of mi.xing. . . .. . Poor Good Fair Good Good Good Good Good Good Good Good

Softening point increase ._. _°F.. 28 5 4 20 17 22 5 7 7 20 15

» Refer to table 1 for test 'methods. ^ Reproduced from table 1 for comparison purposes. ' Turns phenolphthalein pink in aqueous solution.

<•40 percent of mineral matter in jjroduct 4 of asphalt III {softening point,

224° F). See table 3.

Table 3. Asphalt products

Product

I

Asphalt

II III

Product 1: Softening point » °F,. 189 190 190 Penetration 6 . . . 28 27 22 Specific gravity ' _ 1.013 0.995 1. 015

Product S: Softening point <> . -°F 201 204 192 Penetration •> 23 23 22

Products:

Softening point “ °F__ 213 217 207 Penetration i> . . 21 20 20

Product i: Softening point » °F__ 218 227 226 Penetration •>_, ___ - . 19 18 17

Products:

Softening point - -°F 230 239 2.32 Penetration ij._ _ 14 15 16 Specificgravitv ' . 1.017 1.003 1.021

Flux: Furol viscosity <• at 210° F. _ . 84 286 595 Flashpoint (CO C) ' °F__ 445 580 620

Softening point, ring, and ball, ASTM Method D36-26.

•> Penetration at 77° F, 100 g, 5 sec (0.1-mm units), ASTM Method D5-52.

Specific gravity at 77° F was determined only on products 1 and 5.

<• Furol viscosity, ASTM Method D88.

« Flash point, Cleveland Open Cup, ASTM Method D92.

3. Procedure

! 3.1. Preparation of Specimens

^ Preliminary to preparing the additive coatings,

• the softening-point increases produced by the

j minerals at their test concentrations were determined. These increases were used to select the

1 asphalt base required for the coating. Suitable

j proportions of the asphalt products straddling

: the softening point of the asphalt base wer(>

I blended to form the base. The blend was mixed

with the desired percentage of mineral matter to

I produce an additive coating with a softening point

I

I

in the range 217° to 227° F. In some instances

the softening point of 227° F was exceeded even though only the softest product was used, because

that particular concentration of that additive re- sulted in a very large softening-point increase.

The selected blend of products was melted, the

mineral matter added, and the mixture stirred

contmually by hand at about 420° to 4.30° F until

the surface became free from foam and bubbles.

When viscosity measurements were desired, the

temperature was increased to 4.50° F and the viscosity measured with a Brookfield viscometer.^

While the temperature was dropping slowly to 190°

F, viscosity measurements were made at intervals of

about 10 deg F after thorough stirring of the mix.

The mix was reheated to its working range for

the preparation of exposure panels ‘‘ by the

hydraulic-press method [3]. The molten coating was poured on a sheet of aluminum , 3 by 6 by 0.064

in., which was fastened to a 6- by 8-in. sheet of kraft paper with masking tape (the tape covered

Yi in. on three sides and }i in. on one of the narrow

sides of the aluminum sheet). A sheet of dextrincoated paper was placed immediately over the

surface of the molten coating and the assembly

put between the heated platens (220° F) of a hydraulic press. The press was closed with sufficient tlirust to cause the coating to flow ami

assume the thickness defined by spacers at two

sides of the platens. After about 30 sec. the

assembly was removed from the press, and the

dextrin paper was soaked from the panel surface.

The masking tape was stripped from the panel, ami

the thickness of the coating was recorded. All acceptable coatings had a deviation of less than

1 mil from the retinireil tliickness. Just prior to making the first panel, two speci- mens for the softening-])oint iletermination and

3 A Furol viscomotor i.-! ousstomarily usihI in asphult work whou no miuonrl nmltor is nrosont.

• '‘I'linols" iiml "spocinu'n.s" ;iiv synonymous.

I
one shatter specimen ° were poured. After lialf the panels had been prepared, another shatter

specimen and a water-adsorption specimen (see

footnote 5) were poured. A tliird shatter and two

additional softening-point specimens were poured

after all the panels had been made. On occasions,

ash determinations were made to confirm uniform

mineral distribution in the molten stabilized coating.

3.2. Exposure of Specimens

Six accelerated-durability machines were used

in this investigation. Duplicate specimens were

e.xposed in two different machines in order to obtain an average value of durability that would be

considered more representative. The specimens were supported on aluminiim panel supports, two

to a support, one above the other. The speci- mens and supports, respectively, were inverted on

alternate days.

The accelerated-durability machines were op- erated 22 hr a da^', 7 days a week, during the entire course of exposures. As recommended [4], the

enclosed arcs were operated at 120 to 145 v and

15 to 17 amp. The exposure cycle, identified as 51-9C, consisted of 51 min of radiation, followed

by 9 min of radiation and cold (40° ±2 deg F), demineralized water spray, delivered at 25 ±5 psig.

This cycle was selected for its effectiveness, based on a comparison of numerous combinations of

light, water spraj", and refrigeration [5]. ft provides the frecpiency and quantity of cold water

needed for removal of the water-soluble weathering

products, and also induces frequent thermal

shocks, which make a low-temperature refrigeration period unnecessary [6]. It also has the

advantage of yielding consistent results, regardless

of the part of the cycle in which the inspection is made, providing the panels are dry when inspected.

A thermostat was embedded in an asphalt-coated

panel and rotated with the test specimens. This

thermostat controlled forced-air circulation to maintain the panel in which it was mounted at 140° to 145° F for about half of each cycle. The

panel temperature rose from about 50° to 140° F,

within about 30 min, the exact time being dependent on the number of panels in each machine and

the ambient conditions.

3.3. Inspection of Specimens

The e.xposure panels were examined weekly,

both visually and with a high-voltage probe [7]; spark patterns were taken whenever there was any

break in the coating [8]. The patterns were ex- amined through a transparent grid of 60 squai'es

covering the central 2- by 5-in. portion of the coat- ing in. around the edge of the coating was not

included). When breaks in the coating appeared

in 30 or more squares, the specimen was considered failed and removed from the machine.

* The methods are described in the appendix, page 13.

4. Results

All durability results reported on coatings are the averages of two or more exposures made in two

different accelerated-durability machines. In all cases, the replicate individual specimens failed within 15 percent of their reported average. Of

course, because of the large number of variables

involved in the materials, preparation, and ex- posure of each coating, occasional replicate speci- mens deviated widely from each other. In these

few instances additional sets of four specimens were exposed to obtain additional results from

which more reliable conclusions could be drawn.

4.1. Effect of Softening Point of Asphalt

Products on Durability

Four specimens of each of the asphalt products ® in table 3 were exposed to determine the relationship between softening point and durability. The

results are presented in figui’e 2. For all three

asphalts the durability increased as the softening

point of the products decreased. This characteristic is used to good advantage when mineral

matter is added to asphalts in commercial production, because it permits the use of softer, more

durable asphalt products without the danger of having the coating flow at service temperatures.

® About a year had passed between the time the additive coatings were

exposed and that at which these specimens were made. The change in soft- ening point of each product during storage may be obtained from figure 2 and table 3.

Figure 2. Durability of asphalt products.

25-mil coating thickness. 51 -9C cycle. , products of asphalt I; A, products

of asphalt II; O. products of asphalt III.

4
4.2. Effect of Softening Point of Asphalt Base on Durability of Coatings Containing Mineral Additives

Additive coatings having a common asphalt

base (blend of asphalt II; softening point, 225° F)

\vith 35, 50, and 60 percent of mineral matter were made and compared with additive coatings made

from progressively softer l)lends of the same

asphalt with the same percentages of mineral

matter (variable base). The variable-base coatings were all compounded to have softening

points in the range of 217° to 227° F. As seen in figure 3, with both blue-black slate and dolomite,

the durability of the coatings increased with

mineral-matter concentration, with the “commonbase” coatings appearing slightly, but not significantly. more durable than the “variable-base”

coatings at concentrations below 50 percent and

slightlv less durable above 50 percent. Thus, in

Figube .3. Accelerated-durability data.

25-mil coating thickness. 51-9C cycle. Durability ratio of 1 = 75 days.

Softening points of Softening points of coatings with blue- coatings with dolo- black slate mite

Concentration

1 Common Variable Common Variable

1 base, O base. A base, • base, A

°F °F °F °F

0 225 228 225 228

35.. 231 222 230 225 246 217 236 219

60 270 “ 237 248

Base softening points

.35 . 225 211 225 217

225 202 225 206

60 225 190 225 197

“ See page 3.

the case of this particular asphalt, the increased

durability of the softer products was not manifested significantly, and the softening point of the

asphalt base was not of controlling importance.

The data in figure 3 are plotted on a ratio basis,

i. e., the durability of the coating divided by the

durability of the corresponding asphalt coating.

In this way it is possible to see readily the magnitude of the change in durability produced by the

additive, and the effects of the additives on the

various asphalts are reduced to a comparable

basis.

4.3. Effect of Degree of Mixing of Additives

With Asphalt on Durability of Coatings

The mineral additives investigated had wide

ranges of particle sizes, as shown in table 1. The

effect of the thoroughness of mixing on the durability and uniformity of durability was investigated.

Three mineral additives were used: (1) blue-black

slate, representing a material that mixes readily

and easily with asphalt, (2) Niagara dolomite,

representing a material that is incorporated with

asphalt with moderate difficulty, and (3) Florida

clay, representing a material e.xtremely difficult to mix with asphalt. These materials were mixed in

concentrations of 35, 50, and 60 percent with

asphalt III by three different procedures:

Prolonged hand mixing (P) —The melt was

stirred continually until all bubbling and foaming

ceased, about 1 hr. Continuous mechanical mixing (M)—The mixture was stirred for 30 min with a high-speed

laboratory stirrer after the mineral matter had

been added to the molten asphalt.

Brief hand mixing (B) —Panels were made as soon as the mineral matter was folded into the

asphalt. Only enough stirring was used to keep

the mineral matter suspended.

Figure 4 covers the results of the accelerated

durability tests on these coatings. The data in figure 4 are also plotted on a ratio basis. It can

be seen that with blue-black slate, a mineral that

mixes readily with molten asphalt, the type of

25-miI coatins thickness. 51-9C cycle. Dunthility ratio of 1-7.5 ilays

f.\siihalt III), r. imilonged haiul mixing: .M. 30-min mcclumtol mixing;

n, brief haiui mixing.
mixing had little effect on the average durability

at the two higher concentrations. With only 35

percent of slate, however, prolonged hand mixing

produced more durable coatings than either the

30-min mechanical mixing or the brief handmixing procedure.

The most durable coating at each concentration

of dolomite resulted from a difi'erent mixing procedure: mechanical mixing at 35 percent, prolonged

hand mixing at 50 percent, and brief hand mixing

at 60 percent. Of the coatings containing clay,

only those in which the clay was incorporated by

means of prolonged hand mixing ])roved to be

slightly more durable than the corresponding

asphalt coating without mineral matter; the other

mixing procedures resulted in coatings of significantly less durability. Thus, it may be concluded

that with clay, the mineral matter that was diffi- cult to blend homogeneously with the asphalt

base, the degree of mixing was important. Even

with the blue-black slate and dolomite, thorough

mixing was essential to produce uniform durability

in duplicate specimens. As seen by the solid vertical lines in the center of each bar in figure 4, regardless of the mineral additive used, the differ- ences in the durability among the replicate s])eci- mens were always least when prolonged hand mixing was employed.

4.4. Effect of Six Selected Commercially Available Additives on Durability of Coatings

A series of exposures was made to determine the

effects of six commercially available additives on

the durability of asphalts from three crudes. The

investigation included the effects at concentrations

of 35, 50, and 60 percent when exposed in films 13,

25, and 43 mils thick. Because of tl>e difficulty of Table 4. Characteristics of asphalt coatings used as

controls

Test

.Asphalt I Coating A

Asphalt II Coating B

Asphalt III Coating C

Softening point » __°F_. 223 224 227 Penetration i> at 32° F , 10 11 11 Penetration t at 77° F . _ 17 17 14 Penetration b at 115° F.

.

30 26 21 Penetration index 4. 7 4. 7 4. 5 Susceptibility b 1. 16 0. 87 0. 73 Loss on heating = —%.- 0. 22 .03 . 10 Penetration after heating b 17 17 14 Specific gravity at 77° F 1.015 0.999 1.018 Viscosity at 400° F --cp.. 280 420 375 Viscosity <> at 450° F __cp__ 100 140 130 Viscosity 4 at 500° F_

.

_.cp_. 25 53 28 Water absorption * at 28 days .g/ftX. 0. 67 0. 43 0. 34 Shatter resistance < (average) ... in. . 6.3 8.3 2. 7

a ASTM Method D36-26.

b ASTM Method D5-52. Units are 0.1 mm. Penetration index from nomograph in reference [9], and

suseeptibiUty^ggSgh^^tion 115°F- penetration 32° penetration 77° F

« ASTM Method D6-39T.

b Brookfield viscometer.

in a mixed ice and water bath. See appendix for method. 6

handling coatings containing 50 and 60 percent of

Tennessee mica and 60 percent of Florida clay,

| specimens were not made from these compositions, | but exposures were made of all three concentrations of the No. 50 blue-black slate, Niagara

dolomite, low-carbon fly ash, and Lake Erie silica in the three asphalts. I Where possible, each coating was made to a softening point in the range 217° to 227° F, but

in the cases of 60 percent of blue-black slate and

fly ash and 35 percent of mica, a softening point

of 227° F was exceeded, even though the softest ; asphalt products were used.

For control purposes, coatings containing no j additives were made of the three asphalts. The

characteristics of the asphalt coatings that were

exposed are shown in table 4. The durabilities of

these coatings are reported in figure 5 and are used ! as the reference coatings in the durability ratios

in figures 6 to 10. ; In the range of film thicknesses investigated, 13 , to 43 mils, the durability of each of the three ! asj)halt coatings increased almost linearly with | thickness. Coatings of A were less durable than i corresponding coatings of B and C. I The characteristics of all of the coatings, both j with and without additives, are presented in table

5. The softening points and penetrations of the i asphalt bases, as estimated from the proportions ; of the two products blended, and the volume composition and specific gravity, as calculated from | the specific gravities of the components, are pre- j sented for information. The temperature of | preparation and viscosity data are reported as | background information pertinent to the prepara- [ tion of the specimens. The water-absorption and

shatter determinations are related to two factors

FILM THICKNESS, MILS ;

( Figuhe 5. Accelerated durahility data of asphalt coatings. | 51-9C cycle. O, Coating A; V, coating B; A. coating C. I
ADDITIVE CONCENTRATION, PERCENT Figure 6. Coatings containing blue-black slate. 51-9C cycle

Coating thickness

Asphalt O. 13 mils V, 25 mils A, 43 mils

Durability ratio of 1 =

I Days33 Days43 Days72

II 55 75 94

III 61 75 118

Figure 7. Coatings containing Florida clay.

See figure 6 legend.

Figure 8. Coatings containing Niagara dolomite.

See figure 6 legend.

of natural degradation that are not usually considered in accelerated durability tests. However,

because these characteristics may be significant

under certain types of exposure conditions, they

have been included.

The durability of each of the coatings containing additives is presented in table 6 and figures

ADDITIVE CONCENTRATION, PERCENT Figure 9. Coalings containing low-carbon fly ash.

All coatings containing fly ash were examined only visually. See figure 6 legend.

ADDITIVE CONCENTRATION , PERCENT Figure 10. Coatings containing Lake Erie silica. See figure 6 legend.

6 to 10, according to the mineral used. The data

in the figures, again, are on a durability-ratio

basis in order to simplify their interpretation.

At all film thicknesses, the Tennessee mica was

most effective in increasing the durability of asphalts from all three sources. Many of the coatings containing mica were removed before failure, as shown in table 6, but

long after all of the other coatings had failed. Although 35 percent of mica increased the durability of all three asphalts at least 500 percent, it could not Im used at the higher concentrations

selected for these tests, because it increased the

viscosity of even the softest asphalt products to the extent that they became unworkable.

It is evident from the data that different mineral

additives may affect durability to different tle- grees. However, one generality applies. Durability increases with coating thickness both witli and without mineral additives. In some instances

this conclusion may be evident only when the

ratio data are translated into observed durability

in days. For example, in figure 6, the durability

ratio for the 25-mil-thick coating of 50 percent

blue-black slate, in asphalt I was about f.O. whereas for the 43-mil-thick coating it was only

1.6, but the durabilities of these coatings were SI and 116 days, respectively.

Each of the asphalt-additive systems must bo

considered separately in order to interpret the

data accurately. Blue-black slate, which is widely used in commercial rooliitg, improved the

durability of all three asphalts in all three film

thicknesses. However, ii\ asphalt I. there was
Table 5. Characteristics of coatings

Property

.Additive (%) in asphalt I Additive (%) in asphalt II Additive (%) in asphalt III

0 35 50 60 0 35 50 60 0 35 50 60

Blue-black slate

Volume percentage^ __ ... . 0 15. 7 25. 7 34. 1 0 15. 5 25.4 33.8 0 15. 7 2.5.7 34.2

Specific gi'avity of mixture". 1. 015 1.32 1. 51 1 . m 0. 999 1.30 1. 49 1. 66 1.018 1.32 1. 51 1.68 Softening point °F._ 223 222 226 240 224 222 217 237 227 218 221 256 Softening point of base>> °F_. 223 210 202 189 224 211 202 190 227 205 191 190 Penetration of base at 77°Fi> 17 21 23 28 17 22 23 27 14 20 22 22 Temperature of preparation. °F_. 365-428 410-428 410-428 446-482 410-464 437-446 446-464 467-473 401-437 410-437 448-473 464-490 Viscosity at 400°F. . ...cp.. 280 540 1,210 11, 100 420 640 1.480 13.500 375 580 1,450 14, 500

! Viscosity at 450°F cp.. 100 180 580 3, 900 140 290 600 4. 150 130 224 535 6,200 Viscosity at 500°F cj).

.

25 58 260 2, 100 53 130 275 1,850 28 87 240 2, 350 Water absorption at 28 days. g/ft^.. 0. 67 0. 77 0.92 0. 92 0. 43 0. 70 0.91 0. 99 0. 34 0. 53 0. 66 0. 70 Shatter resistance" .in... 6.3 11. 7 18.3 21.0 8.3 12.0 18.

1

21 2. 7 9. 2 15. 5 21

Florida clay

Volume percentage" .. .. 0 17.3 27.8 36. 6 0 16.9 27. 5 36. 3 0 17.3 27.8 36.7

Specific gravity of mixture" 1.015 1. 30 1.47 1.61 0. 999 1. 28 1.45 1.59 1.018 1.30 1.47 1. 61 223 ^219 226 224 221 220 227 221 227 223 199 189 224 206 191 227 205 190

17 24 28 17 23 27 14 20 22 365-428 410-428 437 410-464 428-455 446-482 401-437 437-464 446-482

280 590 3, 000 420 830 3, 600 375 990 5, 000

100 225 1,400 140 340 1, 550 130 335 2, 100 25 94 570 53 135 700 28 117 850

0. 67 1. 32 1. 96 2. 04 0. 43 1. 42 2. 18 0. 34 1.88 1.99 Shatter resistance^ in. .. 6. 3 8.7 9. 0 12.0 8.3 8.3 15. 7 2. 7 9.3 6.3

Niagara dolomite

Volume percentage^. . 0 16 0 26. 1 34. 7 0 1,5.8 2.5.8 34.3 0 16.0 26. 1 34. 7 Specific gravity of mixture** 1.015 1.31 1. 50 1. 66 0. 999 1. 29 1.48 1. 64 1.018 1.31 1.50 1.66 Softening point ...‘’F.. 223 220 224 226 224 225 219 227 221 222 224 Softening point of base>> °F_. 223 209 205 198 224 217 206 197 227 204 202 194 Penetration of base at 77° Ft 17 22 22 25 17 20 23 25 14 20 21 22 Temperature of jrreparation . .°F._ 36.5-428 428-437 419-45." 455-464 410-464 428-464 392-410 401-419 401-437 437-464 446-482 436-455 Viscosity at 4U0°F cp_. 2-SO 500 780 1,380 420 691) 880 1.380 375 590 900 1,280 Viscosity at 4oO°F cp_. lOO 175 295 485 140 240 360 550 130 222 275 450 AMscosity at 500°F . . . ... cp.. 25 90 125 225 53 100 180 260 28 80 140 230 Water absorption at 28 days. g/ft*.

.

0. 67 0.88 1.07 1.30 0. 43 0. 86 1. 15 1.41 0. 34 0.91 1. 15 1. 26 Shatter resistance"... . in.. 6.3 6.3 5.8 14.0 8.3 15. 7 15. 5 18.3 2. 7 7.3 8.3 12.0

Low-carbon fly ash

Volume percentage" 0 17. 2 27.9 36.8 0 17.0 27.6 36.4 0 17.3 28.0 36.8

Specific gravity of mixture". 1.015 1.29 1.46 1.60 0. 999 1. 27 1. 44 1..58 1.018 1.29 1.46 1. 60 Softening point .. . °F . 223 223 219 256 224 219 225 253 227 224 224 266 Softening point of basei> °F . 223 205 189 189 224 205 197 190 227 205 191 190 Penetration of base at 77°Fs 17 22 28 28 17 23 25 27 14 20 22 22 Temperature of preparation. .°F__ 365-128 410-473 437-455 464-482 410-464 435-464 437^55 428-437 410-437 419-446 457^75 509-527 Viscosity at 400° F. . . .. ..cp . 280 4P0 1. 500 18, 500 420 560 375 820 2, 200 33, 000 Viscosity at 450°F . .cp 100 205 590 7, 750 140 200 130 320 860 14, 500 Viscosity at 500° F . . . .cp.

.

25 96 255 4, 300 53 120 28 94 365 5, 700 Water absorption at 28 days.g/ft*.. 0. 67 0. 95 1. 12 1. 14 0. 43 0. 88 1.08 1 23 0. 34 0.70 0.93 1.08 Shatter resistance' in. .. 6.3 7.8 11. 5 8.3 7.3 12.0 21.0 2. 7 5.3 10. 7 12. 7

Tennessee mica

Volume percentage" .. 0 15.4 25.2 33.6 0 15.2 24.9 33.2 0 15. 4 25. 2 33. 6 Specific gravity of mixture". . .. 1.015 1.33 1. 52 1.69 0. 999 1.31 1.50 1.67 1.018 1.33 1. 52 1.69 Softening point. . _.°F 223 270 224 270 227 270 Softening point of base>>. .. ..°F.. 223 189 224 190 227 190 Penetration of base at 77°Fi> 17 28 17 27 14 22 Temperature of preparation. °F. 365-428 428-446 410-464 482-491 401-437 491-518 Viscosity at 400°F. .. cp.. 280 420 375 Viscosity at 450°F cp.. 100 140 130 Viscosity at 500° F cp 25 53 28 Water absorption at 28 days . g/ft*.

.

0. 67 2. 05 0. 43 0. 83 0. 34 0. 52 Shatter resistance" in.

.

6. 3 21 8. 3 21 2. 7 21

! Lake Erie silica

Volume percentage** 0 16.9 27. 5 36.2 0 16. 7 27. 2 35.8 0 16.9 27. 5 36.2

Specific Cavity of mixture" 1.015 1.30 1.47 1.62 0.999 1. 28 1.45 1. 60 1.018 1.30 1.47 1.62 Softening point .. °F 223 226 4217 224 4217 4217 222 227 226 227 222 Softening point of baset °F.. 223 213 208 196 224 207 200 197 227 206 205 191 Penetration of base at 77°Fb . 17 21 22 25 17 23 24 25 14 20 20 22 Temperature of preparation.,°F.. 365-428 410-419 410-437 419^46 410-464 383-401 392-410 383-419 401-437 401-410 419-446 446-464

A iscosity at 40n°F cp 2S0 600 790 420 480 860 375 600 1 140 A'iscosity at 450°F cp 100 200 250 140 220 300 130 215 485 Viscosity at ,500°F. . . cp.. 25 50 53 92 190 28 65 200

AA-'ater absorption at 28 days.g/ft^.. 0. 67 0. 64 0. 73 0. 73 0. 43 0. 56 0. 62 0. 65 0. 34 0. 63 0.59 0. 59 Shatter resistance" in. .. 6.3 7.3 14. 7 16. 7 8.3 11. 7 20.0 17. 7 2. 7 6.3 7.3 8.3

“Calculated. Estimated. Penetration units=0.1 mm. ' 3- by 516-in. disk. .Average of 3 specimens. a Rate slow—probably 3 to 4 deg F higher. 8
Table 6. Durabiliti/ ratio “ of coatings containing So

percent of mica

Coating

thickness

Asphalt

I II III

^fils

132543

5. 7 13.3

t'>13. 9

6.7

>>>13. 3 b>10. 6

6. 6 >>>13.3

>>>8.5

» See caption of figure 6 for durability-ratio figures.

i> Removed at 1,000 days (before failure).

little dift’erence in durability between 35 and 50

percent blue-black slate and in asphalt III, almost no difference in durability between 50 and 60

percent; in the 13-mil coating all three concentrations were of about the same durability. The

greatest relative improvement was observed in

the 25-mil coating.

Florida clay behaved as an extender in asphalt

I. leaving the durability almost unchanged in all concentrations. In asphalt II, similar results were observed, although some slight increase in durability could be seen. Although improvement

was shown in asphalt III in the 43-mil film, there was almost a corresponding decrease in durability

at 13 mils.

Niagara dolomite, in all three concentrations,

improved the durability of asphalt I slightly, and

that of asphalts II and III appreciably more,

especially in the 25- and 43-mil coatings.

Because fly ash conducts electricity, coatings

made with it could not be inspected with the aid

of the high-voltage probe; they were inspected

visually. Because the majority of the other coatings failed electrically before they would have

failed by visual inspection, the durabilities of the

fiy-ash coatings were probably less than reported.

It is not possible to estimate the magnitude of this

effect; therefore, these data must be considered

without attempting to compare them, with those

of the other minerals. In asphalt I, the fly ash

apparently had little effect on the durability. In

asphalts II and III, the fly ash seemed to improve

the durability at concentrations of 35 and 50 percent, but less so at 60 percent. Fly ash was the

only additive in which the 60 percent coatings were consistently less durable than the coatings

with 35 and 50 percent of additives.

The Lake Erie silica decreased the durability of

asphalt I at the lower concentrations, but had

almost no effect at 60 percent (except in the 13-mil

coating). In both asphalts II and III it decreased

the durability in the 13-mil films and increased it in the 43-mil films. It improved the durability of

asphalt II about the same at all three concentrations in the films 25 mils thick, but did not change

the durability of asphalt III at concentrations

lower than 60 percent.

Thus all six additives increased or did not appreciably alter the durability of asphalts II and III

at all three concentrations in films 25 and 43 mils

thick. Blue-black slate and mica also improv'cfl

the flurability of asphalt I ajjyfreciably in all film thicknesses and concentrations. In those instances

in which the 13-mil additive coatings behaved ir- regularly this effect may f)c attributed to the pres- ence of additive particles afjproximaf ing in diameter the thickness of the coating.

4.5. Effect of the Particle-Size Distribution of

the Mineral Additives on the Durability of

Coatings

Because the particle-size distribution is one of the attributes of the arlditives that may affect ])erformance and one that may be modified, its effects on durability were evaluatefl in all three

asphalts. Three minerals, blue-black slate, Niagara dolomite, and Lake Erie silica, were sieved

into 8 fractions and reconstituted into 5 different

synthetic size distributions, designated as follows

and reported in detail in table 7; + 200 mesh -Material retained on U. S. Standard Sieve Xo. 200. — 200 mesh —Material passing a U. S. Standard Sieve No. 200. — 825 mesh—Material passing a U. S. Standard Sieve No. 325. — 140 +325 mesh—Material passing a U. S. Standard

Sieve No. 140 but retained on a No. 325. “l+jual” size—Approximately equal weights retained on

U. S. Standard Sieves Nos. 120, 170, 230, and 325.

Table 7. Particle-size distributions

U. S. Standard

Sieve No.

Particlo

size

1 Size distribution »

Regular +200 -200 -325 1 +325

Equal

size

Blue-black slate finer than Standard Sieve

Mils

hO 9.8 99.8 99. 1 100.0 80 7. 0 99.3 94. 7 .... i i66.

98. 7 100 5.9 97.9 85.0 100.0 94.

95. 1 120 4.9 96. 2 74. 1 99.9 92. 4 90.2

170 3.5 91.3 35.2 99.9 72. 9 66. 6 200 2.9 86.9 5. 7 99.3 40. 2 54. 5

230 2. 4 83.

1.0 95.4 1.3. 5 42. .s 325 1. 7 76.7 0. 7 85. 5 100. 0 4. 1 21.7

Niagara dolomite finer than Standard Sieve

^

60 9.8 99.9 99. 6 80 7.0 99.9 98. 6 UK). 0

100 5. 9 99.6 95.8 97. 9

120 4.9 99. 3 91. 1 100. 0 11X1.0 94.5

170 3. 5 96. 6 61. 4 99.9 93. 0 79. 8 200 2.9 93.4 20. 5 99.9 74. 1 70. 0

230 2. 4 89.9 5. 9 97.9 41.2 50. 0

325 1. 7 81.0 0.7 87.0 UXl. 0 9. 5 19. 1

Lake Erie silicst finer than Standard Sieve

60 9.8 99. 9 100. 0

80 7. 0 98. 2 99. 3 100. 0 UHl. 0

100 5. 9 SO. S 92. 7 99. 9 97. 9

12(1 4.9 ,53.7 76.

9<9. 9 UX). 0 93. 1 170 3.5 L5.3 26. 5 7 4Ii 7 71.2

200 2. 9 8. 1 7. 7 98. 2 18.8 5lv 5 230 2. 4 5. 4 l.S 85. 7 7.3 4u 7 325 1. 7 3.4 1. 1 52. 5 Itxui 1.2 28 2

«A more comploto descriptiou of ihoso distribution.^ is in the to\t. Breiuso of ttu> uiu'ort'.iiutios involvoil in sopuratini: <rr\'s:ul:ir (Wtidos by moans of sieves witit stiuaro oitenintrs. ttio distributions deviate somewhat

from their desisinations.

J)
ASPHALT I ASPHALT H ASPHALT HI

Figure 11 . Effect of particle-size distribution on durability.

35 percent mineral matter. 25-mil coating thickness. 51-9C cycle.

-\sphalt Durability

ratio of 1 =

I)ai/s I 43

11 75

III 75

Exposures were made of coatings (all 25 mils

thick) containing 35 percent of additives with

each of the above distributions. Average durability figures are shown graphicallv in figure 11. The data are presented as a ratio of the durability of the additive coating divided by that of the corresponding asphalt coating. The results obtained with the regular commei'cial-size distri- butions are also presented for comparison.

In asphalt I, only the coating with —325-mesh

blue-black slate proved to be superior to that with

the regular particle-size distribution, and in asphalt II and III, many of the distributions were approximately ec^ual. In general, the coatings containing —200-mesh materials were some- what more effective in increasing the durability of the asphalts and those with the -b 200-mesh additives less effective. Additional exposures were made from asphalt

II and 50 percent of the +200- and —200-mesh

portions of each of these three minerals in film

thicknesses of 13 and 25 mils. The results are shown in figure 12. Film thickness was of ex- treme importance when an experimental gradingsuch as the +200-mesh materials was used. In

every instance the 13-mil films containing 50 per- cent of +200-mesh material did not weather as

well as the 13-mil films without additives, but in

the 25-mil films, the durability was considerably

improved bv this coarse material as well. However, when the —200-mesh material was used,

there was an improvement of about the same magnitude in both the 13-mil and the 25-mil films. To generalize for coatings 25 mils thick containing 35 percent of additive, the —200-mesh

fraction increased the durability most and the

Figure 12 . Effect of particle-size distribution on durability.

60 percent of mineral matter. 51-9C cycle.

Film thickness Durability ratio

of 1 =

Mils Days

13 55

25 75

+200-mesh material was least effective, whereas

the regular, —325, equal size, and uniform size (—140 +230) follow the —200 in descending

order, with little difference between consecutive

distributions. \^Tien higher concentrations of

mineral additives are used, the maximum particle size should be considerably less than the

coating thickness in order to obtain greater

durability.

4.6. Effect of Particle Shape of Additives on

Durability of Coatings

Because particle shape was one property of the

minerals studied that seemed to be related to the

efficacy of their stabilizing action, some quantitative method of expressing particle shape was

sought. A relationship between a bulk density

and the true density of the minerals seemed worth

considering for this purpose. Franz Popel [10], in 1929, proposed a relationship of this type, which

he called “fineness factor,” and defined as density — compacted weight.

compacted weight

where the compacted weight is an empirical

bulk density determined under any set of conditions that would yield reproducible results. The bulk density used was obtained by fluffing

the mineral matter b}^ letting it flow slowly

through a column of 1-in. inside diameter, 21 in. long. Baffles set at an angle of 45° were placed

12 and 16 in. from the top of the column and the

column was constricted to a diameter of % in. at the bottom. The column discharged into a

100-ml, weighed and calibrated cylinder from a

point % in. above the cylinder. In practice the

mineral matter was poured slowh^ into the col- umn until it just overflowed the receiver. The

excess was struck off level with the top of the

receiver and the receiver and contents weighed.

The weight of the mineral matter divided by its volume is termed the “fluffed bulk densitv” or

I

I

I

t

I

I

10
simply, the “fluff density.” A correlation of durability with fineness factor ' is presented in figure

13. The individual points are tabulated iii table 8. The only points that deviated considerably

from the curves were those for oyster shell and

mica, both being materials characterized by flat, platelike particles. Because the deviations are

The durabilities of the coatings with mica, although not shown in figure

13. are considerably greater than would be e.\pected from linear e-xtrapoLation

of the curves.

Figure 13. Accelerated durability data.

35 percent of mineral matter. 25-mil coating thickness. 61-9C cycle. •, Coatings with asphalt I; X, coatings with asphalt II; O, coatings with

asphalt III.

Table 8. Effect of fineness factor on the durability of additive coatings {25 mils thick)

Additive

Particle shape Density

Fluff denFineness

Durability, 35 % of mineral in asphalts

(vis- ual)

sity factor

I II III

Mica Fpa

glcm3

3. 01 0. 29 9.7 Days

572 Days

>1,000 Days

>1,000 —200 blue-black FP 2.94 .68 3.3 65 157 182

slate. Blue-black slate... FP 2.94 .73 3.0 68 152 174 Oyster shell AP 2.68 .72 2.7 115 198 193 Special silica BR 2. 58 .78 2.3 45 123 155 Low-carbon fly H 2. 62 .62 2.2 46 116 119 ash. —200 dolomite BS 2. 87 .94 2.

43 99 127 —325 dolomite BS 2. 87 .93 2.

37 93 111 -f200 blue-black FP 2.94 .99 2.0 62 133 110

slate. Niagara dolomite. BS 2. 87 1.03 1.8 52 101 115 Kyanite. ... I 3.60 1.34 1.7 43 98 96 Florida clay I 2.64 1.04 1.5 38 86 70

-(-200 dolornite BS 2. 87 1.29 1.2 43 90 107 Lake Erie silica... BR 2.68 1.31 1.1 37 105 76 “FP — Flat plates; BR = blocky, rounded corners; FI = heterogeneous; AP=acicular plates; BS = blocky, sharp comers; I = indefinite (requires higher magnification than on light microscope).

in the direction of greater flurability than indicated by the lines, the lines may be taken as conservative indications of durability.

Despite the fair correlations indicated in figure

13, it must lie emphasized that these data were

obtained for specific materials under very specific

test conditions and that the results may vary

under other conditions. The fact that a different

line is plotted for each asphalt emphasizes the

importance of the asphalt itself in respect to durability.

4.7. Effect of Clay, Fly Ash, and Silica From

Different Sources on Durability of Coatings

All coatings tested in this series were 25 mils

thick and contained 35 percent of mineral matter. The materials investigated (flescribed in table

2) are representative of the wide variety of each

type available. Although the three clays tested

varied from a disordered kaolinite (Florida clay)

to a mullite (Kyanite), there was little difference

in their effects on the durability of any of the

asphalts (fig. 14). Because of the flocculated

nature of the Florida and Bradbury clays, the

reported size distributions are probably not

accurate. These clays were not dispersed readily

in the asphalts. However, even with Kyanite,

which was mixed easily with the asphalts, there was no appreciable improvement in durability.

In general, therefore, all three clays produced a small increase in the durability of asphalts II and III and a small decrease in asphalt I. As previously mentioned, fly ash contains some

components that are conductors of electricity;

Figure 14. Effects of selected materials on d: -ab-'iry. Specimens containing fiy sish were inspcctoil only visually See figure 9 legeiui.

ll
therefore, the high-voltage prohe could not he

used to determine failures in coatings containing

fly ash. All end-point determinations on coatings

containing fly ash were made by visual inspection.

Because the durability based on visual inspection

is generally greater than that based on inspection

with the high-voltage probe, the durability ratios

reported in figure 14 must be considered mdy as approximations and the following discussion eval- uated accortlingly.

Because fly ash is a byproduct of the combustion

of coal, its composition, both physical and chemical, varies with the source of the coal, the wav it is burned, and the efficiency of the combustion.

Therefore, its effect on the durability of asphalt

roofing varies considerahly. The three sami)les of

ffy ash tested varied from one produced under

very efficient combustion conditions (2% carbon)

to one with almost 23 percent of carbon. All three additives were very finely divided and had

appi-eciahle amounts of water-soluble material

present; two had small amounts of free alkali. The low-carbon ffy ash (actually 4.9% carbon),

with no free alkali, apparently did not increase

the durahilitv of asphalt I, hut seemed to increase

that of II and III. However, the high-cabon fly

ash apparently increased the durability of all of the asphalts, dlie Chicago fly ash also increased

the durability of all three asphalts, slightly for asphalt I and appreciably for asphalt III. Two of the samples of silica were in natural

form, and the other two (Ottawa and Special) had

been processed through grinding and sieving operations. Because the special silica had heeii used

to polish plate glass, the corners and edges of the

particles were rounded. In addition, small particles of glass were present. With the exception

of this additive, which contained 3 percent of

material soluble in water, the silicas were rather

coarse and inert. None of the silicas affected the durability of asphalt I; both of the processed silicas and Lake

Erie silica increased the durability of asphalt II

;

and only the special silica appreciably increased

the diu-ability of asphalt III. The efficacy of the

special silica is probably due to its fine degree of subdivision, being 82 percent less than 44 microns

(325-mesh sieve).

5. Summary and Conclusions

A number of variables pertinent to the durability of 3 asphalts in combination with 14 mineral

additives were investigated under accelerated ex- posure conditions, dlie results follow: As the softening point of a blown asphalt coat- ing is increased, its durability is decreased. In additive coatings, the greater durability of the asphalt bases of the variable-base coatings

compared with those of the constant-base coatings was not significant.

Concentrations of up to 60 percent of selected

additives resulted in substantially increased durability in all three asphalts.

Thorough mixing of the mineral additives with

the asphalts was of primary importance for unifoi-m results. The durability of all coatings increased with

coating thickness in the range of 13 to 43 mils.

Although the additives produced effects of I varying magnitude in the three asphalts, in ' general, mica, oyster shell, and blue-black slate were most effective in increasing durability; dolomite and fly ash of less influence ; and silica and

clay, least. In other words, minerals with platelike jrarticle shapes were most effective in increa,°-

ing durability.

Blue-black slate, dolomite, and silica were more j effective at higher concentrations in thicker coatings, but fly ash was less effective. Satisfactory ^ specimens with 50 or 60 percent of mica or with 60 , percent of clay coidd not l)e produced with the | facilities availalfle. The particle-size distributions of the mineral ; additives had significant effect on the durability i of coatings. !| Clays of three different types all produced nearly | the same small effect on the durability of all three

asphalts. Three samples of fly ash all produced I some increase in durability. Only special silica, |, of the four silicas evaluated, produced a significant

increase in durability (especially in asphalt III).

In general, the asphalt was the most important i constituent in a stabilized coatitig in determining

durability, but the durability was improved

appreciably by tlie judicious incorporation of selected mineral additives. , j

i 6. References i

[1] (). G. Strieter, The effect of mineral fillers on the

serviceability of coating asphalts, Proc. Am. Soc. Testing Materials 36, part II, 486 (1936). j [2] O. G. Strieter, Weathering tests of filled coating

asphalts,!. Research NBS20, 159 (1938) RP107.3. j [3] S. H. Greenfeld, A method of j)reparing uniform films : of bituminous materials. Am. Soc.' Testing Materials Bui. 193, 50 (195.3). ! [4] Am. Soc. Testing Materials Method D529-39T, )' Accelerated weathering test of bituminous materials. 1 [51 L. R. Kleinschmidt and S. H. Greenfeld, Influence of t exposure conditions on the accelerated durability

' testing of asphalts, Am. Soc. Testing Materials '' Bui. 214 (April 1956).

[6] S. H. Greenfeld, Effects of thermal shock on the

durability of asphalt coatings under accelerated |' test. Am. Soc. Testing Materials Bui. 193, 46 I

^ (1953).

[7] A. H. Boenau and L. A. H. Baum, The design and

application of a spark-gap instrument for detecting '

: crack failures of asphalt coatings during weathering tests. Symposium on Accelerated Durability I Testing of Bituminous Materials, Am. Soc. Testing

Materials (1949). (ij [8] J. B. Hunter, F. C. Gzemski, and L. Laskaris, A new

method for evaluating failure of bituminous mate- ' i rials due to weathering. Symposium on Accelerated Durability Testing of Bituminous Materials, Am.

Soc. Testing Materials (1949) : [9] J. P. Pfeiffer, The properties of asphaltic bitumen,

p. 157 (Elsevier Publishing Co., New York, N. Y., 1950). [J

[10]

F. Popel, Der Moderne Asphalstrassenbau, Stiassen- ^ bau-Verlag Martin Boerner (Halle, 1939). ;;i 12
7. Appendix

7.1. Volume Composition

Several calculated quantities are reported in table o along with the measured data. The volume

composition was calculated from the weight composition and the specific gravities of the components as follows:

d'* 5 (by volume),

where 5=stabilizer, ir=weight, V=volume,

specific gravity, and the subscripts A= asphalt,

S= stabilizer, and r'= coating.

7.2.

Specific Gravity

The specific gravitv of each stabilized asphalt

coating was calculated from the composition of the coating and the specific gravity of the individual components, as follows:

, ir.+TT; tt:,+it;

d. 4

In order to check these calculations, a number

of specific-gravity measurements were actually

made on some of the stabilized coatings. The cal- culated and observed specific gravities for 13

coatings are presented in table 9. Table 9. Specific gravities

1 =

Asphalt Composition

Specific gravity

Calculated Observed

(50% blue-black slate... . . 1.51 1.50 35% clay 1.30 1.30

J 50% clay. . . 1.47 1.48 160% dolomite . . 1.66 1.66 35% silica .. ... . .. ... 1.30 1.29 150% silica 1.47 1.47 (50% blue-black slate 1.49 1. 50

1 50% fiv ash . _ _ 1.44 1.39 |35% silica 1.28 1,24 150% silica. 1.45 1.43 (50% clay 1.47 1.47

III <50% dolomite.. 1. 50 1. 49 (60% silica . .. 1.62 1.62

7.3.

Shatter Test on Coatings

Preparation of Specimens.

Several disks of asphalt 3 in. in diameter and

Ke in. thick are cast, using a suitable glycerinecoated brass mold.

Test Method.

The test apparatus provides a means for droj)-

ping a constant weight from a variable and

measured height on the cast disk and for i-ecordiiig

the height of drop required to split the disk in one

or more places, each split extending from the

center to the edge of the specimen.

The apparatus consists of a 21 -in. vertical brass

tube, 1 in. in internal diameter; a solenoid sliding

within the tube and adjustable to any height up

to 21 in.; an electric connectio/i to a standard

110-v line (either a-c or d-c) with the solenoid i/i series with a 60-w lamp and a switch for shorting

the solenoid; a falling steel weight, in. in diameter, and weighing lb; ami a stationary

steel contact rod, in. in diameter, weighing

K lb, and having a hemispherical end contacting

the asphalt. In operation the specimen is brought to a temperature of about 40° F by submersion in a bath of ice and water for a period of not less than

1 hr. It is then placed under the vertical brass

tube, being submerged in water at 40° F during the

test, and the contact rod placed in the tube and

in contact with the center of the specimen. The

circuit is closed and the K-lb weight raised to a height of 1 in. l)y means of the solenoid holding it. The solenoid is then shorted, the weight allowed

to drop, and the specimen cjuickly examined for fracture. If it has not si)lit, the weight is raised

to 1}^ in. and the drop again made. This procedure

is repeated with K-in. increments in height until

the specimen fails. With subsequent specimens

the weight should be released from a height 1 in. below the failing height of the first test. At least three determinations are made on each asphalt.

Results. Failure is recorded when the specimen splits, in one or more places, from the center to the edge.

Fractures that do not extend to the edge of the

disk are ignored. The average height of drop

required to break the specimen is recorded as its shatter resistance.

7.4.

Water Absorption of Asphalt—Disk

Method

Application

This method is applical>le to all asphalts having

softening points (ring and ball) of 170° F or over. Apparatus and Materials Required.

1. Brass mold Ke-in. -thick, 3-in. -diameter hole.

2. Brass plate, 4 by 4 in.

3. Glycerine.

4. Hotplate.

5. 100 g of asphalt to be testetl.

6. Pyrex-glass tray, II2 in. deep, any convenient

length and width.

7. Distilled water. Preparation of Specimen.

Apply glycerine to the surfaces of the clean

brass plate and mold, which will come in contact with the asjthalt. Assemble the mold and phu'c

it on the brass plate. Heat the sample of asphalt

to be tested until fluid and free from air bubbles.

If the sample contains mineral matter, it shouhl

13
be stirred slowly with a piece of stiff wire to keep

the matter properly suspended without incorporating air bubbles.

Pour a sufficient amount of the sample to fill the

mold. The pouring must be done in a manner such

that air bubbles are not occluded. The surface

may be flamed lighfly to remove a few that might

form. Not more than in. of the sample should

show above the top of the mold. After the

specimen has cooled thoroughly, remove it from

the mold and wash it to remove the attached

glycerine. Allow the specimen to dry and mark

identification on both sides. Procedure.

Weigh the specimen to 0.001 g and record the

weight. Place the specimen in the glass tray and

fill it with sufficient distilled water to submerge

the specimen at least K in. Place the glass tray

and specimen in a dark cabinet at room temperature. Make periodic weighings in the following manner

to determine the amount of water absorbed:

Remove the specimen from the water at the

end of each specified period. Do not wipe, but

blot both sides and edges carefully until each

surface is as uniformly dry as possible. Weigh

the specimen and record the weight. Return the

specimen to the distilled water tray. Renew with

fresh water at each weighing.

Compute the water absorbed, and convert the

result to grams of water absorbed per square foot

of asphalt surface exposed, including the edges of the disk.

This program was jointly designed and

sponsored by the National Bureau of Standards

and the Asphalt Roofing Industry Bureau. The

author thanks the members of the Floor, Roof,

and Wall Coverings Section for their advice and

cooperation, and William H. Appleton, John

Marchi, and Robert F. Jackson for their help in obtaining the original data. George Clarvoe,

Johns-Manville Corp., supplied the water-absorption and shatter-resistance procedures.

Washington, March 28, 1956.

14

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