NATIONAL BUREAU OF STANDARDS REPORT

3616

LABORATORY STUDIES OF SEVERAL FACTORS

AFFECTING THE BEHAVIOR OF SOME MINERALS

AS STABILIZERS FOR ASPHALT ROOFING

By

Sidney H. Greenfeld

<NBS>

U. S. DEPARTMENT OF COMMERCE

NATIONAL BUREAU OF STANDARDS
U. S. DEPARTMENT OF COMMERCE

Sinclair Weeks, Secretary NATIONAL BUREAU OF STANDARDS

A. V. Astin, Director

THE NATIONAL BUREAU OF STANDARDS

The scope of activities of the National Bureau of Standards is suggested in the following listing of

the divisions and sections engaged in technical work. In general, each section is engaged in specialized research, development, and engineering in the field indicated by its title. A brief description

of the activities, arid of the resultant reports and publications, appears on the inside of the back

cover of this report.

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Standards. Microwave Standards.

^Office of Basic Instrumentation ®Office of Weights and Measures.
NATIONAL BUREAU OF STANDARDS REPORT

NBS PROJECT NBS REPORT

1004-10-1017 August 16, 1954 3616

LABORATORY STUDIES OF SEVERAL FACTORS

AFFECTING THE BEHAVIOR OF SOME MINERALS

AS STABILIZERS FOR ASPHALT ROOFING

By

Sidney H* Greenfeld

Research Associate

Asphalt Roofing Industry Bureau

Floor, Roof and Wall Coverings Section

Building Technology Division

Sponsored by

Asphalt Roofing Industry Bureau

NBS

. S. DEPARTMENT OF COMMERCE

NATIONAL BUREAU OF STANDARDS

The publication, Approved for public release by the

or ln part ' IS prohlblted

unless permissior . XT . , T

. „ Standards, Washington Director of the National Institute of

Standards and Technology (NIST)

on October 9, 201 5.

25, D, C. Such p

cal ly prepared If

report has been specifi-

• report for its own use,

CONTENTS

9|c>(c^c^c3)c4o|c^:

Page

SUMMARY 1

1. INTRODUCTION 2

2 0 MINERAL MATERIALS 3

2.1 Materials Tested as Stabilizers 3

2.2 Asphalts 3

3. EQUIPMENT AND PROCEDURE 3

4. EXPOSURE SERIES 6

4.1 The Effect of the Softening Point

of the Asphalts on Their Durability 6

4.2 The Effect of the Softening Point of

the Base Asphalt on the Durability

of Coatings Containing Mineral

Additives 6

4.3 Selected Minerals ~ The Effect of Some

Natural Variations of Clay, Fly Ash

and Silica on the Durability of Coatings 9

4.4 The Effect of the Degree of Mixing of

Minerals with Asphalt on the Durability of Roof Coatings l4

4.5 The Effect of the Particle-Size Distribution of the Mineral Matter on

the Durability of Coatings 17

4.6 The Effect of Particle Shape of

Minerals on the Durability of

Coatings 23
TABLES

Table No. Page

I. Properties of Minerals ^ - 5

II. Durability of Asphalt Products 7

III. Effect of the Softening Point of

the Base Asphalt on the Durability

of Coatings 8

IV. Properties of Clays, Fly Ashes, and

Silicas 10-11

V. Durability Data 12-13

VI. Mixing Procedures in Asphalt III 16

VII. Particle Size Distribution Series

3 5% Mineral Matter 18-20

VIII. Particle Size Distribution Series

50% Mineral Matter in Asphalt II 22

IX. Fineness Factor 25
LABORATORY STUDIES OF SEVERAL FACTORS AFFECTING

THE BEHAVIOR OF SOME MINERALS AS STABILIZERS

FOR ASPHALT ROOFING

by

Sidney H, Greenfeld

SUMMARY

The effects of a number of variables inherent in asphalts

and minerals available for use in asphalt roofings that were

not reported in "Laboratory Evaluation of Six Selected

Commercially Available Materials as Stabilizers for Asphalt

Roofings" are covered in this report. The influence of softening point of the asphalts; particle sLze distribution of the

mineral matter; particle shape of the mineral matter; natural

variations in three of the minerals; and the thoroughness of

mixing on the durability of the coatings were measured. The

following generalizations resulted:

(1) The durability of the three asphalts decreased

as their softening points increased,

(2) The greater durability of the lower softening

point asphalts was readily apparent with mineral concentrations of 50% or greater,

(3) None of the three clays evaluated had any

appreciable effect on the durability,

(4) Fly ash samples could not be evaluated on the

same basis as other samples because the spark method

of determining failure could not be used.. The indications are, however, based on visual determination of

failure, that the effect of fly ash on durability is

variable, that sample being designated as "low carbon"

being least beneficial,

(5) Of the four silicas- only the special silica,

characterized by its relatively greater fineness,

(and with Asphalt II, Ottawa Silica) increased the

durability of the asphalts,,

(6) Thorough mixing is necessary to obtain the most

uniform and optimum benefits from the use of minerals

as stabilizers*

(7) Commercial blue black slate, Niagara dolomite

and Lake Erie Silica were fractionated into a number

of particle size ranges and reconstituted into five
- 2 -

synthetic size distributions. The durabilities of

coatings made from 35# of each of these with each

of the asphalts were in the following descending

order

Classification with U. S. Standard Sieves

Passing 200 mesh

Commercial Gradation

Passing 325 mesh

Equal Size (approximately equal weights

on each sieve)

Uniform Size (Passing 140 * Retained on

230 )

Passing 60 - Retained on 200 mesh

(8) Minerals with flat, plate-like particles

(blue black slate, mica, and oyster shell) were most

. beneficial as stabilizers.

1. INTRODUCTION

During the planning of the mineral stabilizer research

program it was recognized that there were several variables

involved in stabilization of asphalts against degradation- . that were not covered by the exposures of the main series*'

to be made. Supplementary exposure series were planned to

determine whether any relationship could be established

between some of these properties of the materials and durability and between some processing variables and durability.

The following series of exposures were made*

(1) The Effect of Softening Point on the Durability of Asphalt.

(2) The Effect of the Softening Point of the

Base Asphalts on the Durability of Coatings* Containing Mineral Additives.

Greenfeld. S. H.. "Laboratory Evaluation of Six Selected

Commercially Available Materials as Stabilizers for

Asphalt Roofing" , Sept. 23, 1953*
- 3

-

(3) Selected Minerals - The Effect of Some Natural

Variations of Clay, Fly Ash, and Silica on the

Durability of Coatings

„

(b) The Effect of the Degree of Mixing of Minerals

with Asphalt on the Durability of Coatings,

(5) The Effect of the Particle-Size Distribution of

the Mineral Matter on the Durability of Coatings.

(6) The Effect of the Particle Shape of the Mineral

Matter on the Durability of Coatings,

With the exception of the Selected-Materials and

Particle-Shape Series, all of the properties studied are

of the type that can be modified in the laboratory or

plant

2, MINERAL MATERIALS

2.1 Materials Tested as Stabilizers

Because of the numerous materials tested as stabilizers

and the limited number of tests performed on each, the

mineral materials will be described in connection with the

series of exposures with which each is connected. Table I

is a general tabulation of the properties of some of these

minerals

2.2 Asphalts

The asphalts used were the same as those reported in

"Laboratory Evaluation of Six Selected Commercially Available

Materials as Stabilizers for Asphalt Roofing", The asphalt

products were blended to produce a base asphalt which, when

mixed with the desired mineral matter, resulted in coating

with a softening point in the range of 217 to 227°F.

3, EQUIPMENT AND PROCEDURE

The equipment and procedures for making the exposure

panels and exposing and evaluating the coatings were as

described in the above-mentioned report.
TABLE

I.

PROPERTIES

OF

MINERALS

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Method described in "A Survey of Materials Available

for Use as Mineral Stabilizers’*, A.R.I.B., Oct. 1952.

b/

“Isopropyl Alcohol Displacement.

sJ

Nitrogen Adsorption - B.E.T. Method.

d/

A.S.T.M. Method D281-31, Using Primol D and Water.

e/

Sedimentation in Isopropyl Alcohol.

f/

Supplier’s Data for Typical Material.

*C Mineral Matter in Asphalt III (S.P. = 223°F).
- 6 -

EXPOSURE SERIES

4 0 1 The Effect of the Softening Point of the

Asphalts on Their Durability

Coatings, 25 mils thick, were made from each of the

asphalt products and exposed in the accelerated durability

machines to determine the effect of softening point on

the durability of the asphalts 0 The durabilities of these products are tabulated in

Table II and shown graphically in Figure 1. The general

trend is for the durability to decrease as the softening

point of the asphalt increases D It must be stated, however,

that there was an occasional specimen that deviated from

the general trend with an abnormally low or high durability.

Some differences in durability were the result of exposing

half of the panels in one machine (odd ones) and half in

another (even ones) 0 In most cases the agreement was good,

but in two instances, there was considerable divergence

between the results of the two exposures 0 4 q 2 The Effect of the Softening Point of the Base

Asphalt on the Durability of Coatings

Containing Mineral Additives

Table III and Figure 2 are comparisons of coatings

made from a common base (Product C of Asphalt II) asphalt

with those made to a definite softening point range, employing progressively softer asphalt as the quantity of

mineral additive was increasedo The coatings containing

the common base seemed to be slightly more durable in the

lower mineral concentrations, but the difference was very

small and of the same order of magnitude as the differences

found in replicate panels exposed at the same time. Thus,

variation in the softening point of coatings containing

mineral additives seems to be less significant than in

asphalt coatings without additive

Q
- 7

-

TABLE II. DURABILITY OF ASPHALT PRODUCTS

PRODUCT A B c D E

Asphalt I

Softening Point, °F

Penetration at 25°C

192 205 215 224 237

2b 21 19 17 15

Acc. Dur., DaysM/

Panel No. 1 bb 37 29 29 28

Panel No. 7 30 37 29 29 28

Panel No. 2 52 38 36 36 28

Panel No. 6 52 38 36 29 28

Average 44 37 33 31 28

Failure Pattern—/ C C c C C

Asphalt II

Softening Point, °F 196 212 225 234 239

Penetration at 25°C 25 20 17 17 15

Acc. Dur., Dayss/

Panel No. 1 108 83 82 81 482/

Panel No. 7 83 83 69 61 81

Panel No. 2 100 84 84 83 83

Panel No. 6 100 84 84 63 83

Average 98 83 80 72 82

Failure Pattern^/ CA A AC EA AED

Asphalt III

Softening Point, °F

Penetration at 25°C

195 195 208 235 239

19 19 19 15 15

Acc. Dur., Days a/

Panel No. 1 95 95 81 85 64

Panel No. 7 86 95 81 85 57

Panel No. 2 87 87 46 37

Panel No. 6 87 87 ltl£/ 46 37

Average . 89 91 81 66 48

Failure Pattern-^/ AC AC -

11 TP Ai1 A

a/

Odd numbered panels were in one machine; even in another,

Patterns are described in "Laboratory Evaluation of Six

Selected Materials as Stabilizers in Asphalt Roofing".

^Jot counted in average.
- 8 -

TABLE III. EFFECT OF THE SOFTENING POINT OF THE BASE

ASPHALT ON THE DURABILITY OF COATINGS^/

CONCENTRATION OF

MINERAL, $

PANEL.

no.£/

COMMON

SOFT. PT.

°p

BASE MIX

BASE

DUR.

DAYS

VARIABLE

SOFT. PT.

° F

o f

BASE MIX

BASE

DUR.

DAYS

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7

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2

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Ave. it it 80 it it 75

35$ B.B.s. 1

ii 231 177 211 222 145

7

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6

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50$ B.B.S. 1

it 246 211 202 217 169

7

ii H 211 n ii 2

•i it 209 it ii 215

6

it n 198 ti it Ave. ii ii 209 ti n 192

60$ B.B.S. 1

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7

ti ii 227

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ii ii 224 ii it Ave. n ii 227 ii it 238

35$ N. Dol. 1

it 230 152 217 225 98

7

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6

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ii 236 152 206 219 142

7

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numbered ones, in another.
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80

70

60

50

40

30

20

10

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FIGURE

2

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- 9 -

4.3 Selected Minerals - The Effect of Some Natural

Variations of Clay, Fly Ash and Silica on the

Durability of Coatings (All coatings tested in

this series were 25 mils thick and contained

25% mineral matter.)

The three types of materials investigated in this series

(described in Table IV) are representative of the wide variety

of each type available. Despite the fact that the three

clays tested varied from a disordered kaolinite (Florida

Clay) to a mullite, there was little difference in their

effects on the durability of any of the asphalts (Table V

and Figure 3). 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 in the Kyanite, which

was mixed easily with the asphalts, there was no appreciable

improvement in durability. In general, therefore, all three

clays produced no decrease in the durability of asphalts II

and III and only a small decrease in asphalt I.

Fly ash contains some components which are conductors

of electricity; therefore, the high voltage probe could

not be used to determine failures in coatings containing

fly ash. Therefore, all end-point determinations on coatings

containing fly ash were made by visual inspection.

Because fly ash is a by-product of the combustion of

coal, its composition, both physical and chemical, varies

with the source of the coal, the way it is burned, and the

efficiency of the combustion. Therefore, its effect on
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the durability of asphalt roofing varies considerably.

The three samples of fly ash tested varied from one produced

under very efficient combustion conditions (2% loss on ignition) to one with almost 18$ loss on ignition. All three

materials were very finely divided and had appreciable amounts

of water-soluble material present 5 only two had small amounts

of free alkali. Because failure was determined visually on

these coatings , their durability cannot be compared directly

with the unstabilized asphalts or the other coatings in which

failure was measured by means of a high voltage probe. (Where

comparisons between the two methods for determining failure

are possible, visible inspection always results in a somewhat

longer coating life.) Therefore, only comparisons among the

fly ash specimens can legitimately be made. The material

designated as Low Carbon Fly Ash contributes the least to

the durability of the coatings.

Two of the samples of silica tested were in their natural

form while the other two (Ottawa and Special) had been processed through a grinding and sieving operation. Further,

the Special Silica had been used to polish plate glass and

in addition to- the small particles of glass present, the

corners and edges of the particles were rounded. With the

exception of this material* which was appreciably soluble in

water, the silicas were rather coarse and inert.

None of the silicas affected the durability of asphalt

both of the processed silicas and Lake Erie Silica increased the durability of asphalt II 5 and only the Special

Silica appreciably increased the durability of asphalt III.

The efficacy of the Special Silica is probably due to its

fine degree of subdivision, 82% being minus M+ microns

( 325-mesh sieve).

4 A The Effect of the Degree of Mixing of Minerals

with Asphalt on the Durability of Roof Coatings

The effect of the thoroughness with which the mineral

matter was mixed with the asphalt on the durability of the

coating was investigated. Three mineral additives were

useds 1) Blue black slate, representing a material which

mixes readily and easily with asphalt 5 2) Niagara
DURABILITY,

DAYS

FIGURE 3

EFFECTS OF SELECTED MATERIALS ON DURABILITY

35% MINERAL MATTER

25 MILS THICK

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FLY ASH

- 15 -

dolomite, representing a material which is incorporated

with asphalt with moderate difficulty; and 3) Florida

Clay, representing a material extremely difficult to mix

with asphalt. These materials were mixed in concentrations

of 35, 50, and 60% with asphalt III by three different procedures:

1) Prolonged Hand Mixing - The melt was stirred

continually for about one hour until all

bubbling and foaming ceased.

2) Continuous Mechanical Mixing - The mixture was

stirred for 30 minutes with a high-speed laboratory stirrer after the mineral matter was

added to the molten asphalt.

3) Brief Hand Mixing - 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.

The three minerals are described in Table I. Table VI

and Figure 4 cover the results of the accelerated durability

tests on these coatings. The data in Figures 4 and 5 are

plotted on a ratio basis, i.e., the durability of the coating

divided by the durability of the corresponding asphalt without

mineral additives. In this way, it is possible to see at a

glance the magnitude of the change in durability produced by

the additive, and the effects of the additive are reduced to

a comparable basis. It can be seen that with blue black slate,

the mineral which mixes readily with asphalt, there was little

difference in the durability of the panel made by the three

procedures. The same was true of the coatings containing dolomite, except that there was a little more spread among the

three procedures. However, with clay, the material that is

difficult to mix with asphalt, the only procedure that yielded

coatings as durable as the unstabilized asphalt was the prolonged hand mixing, i.e., thorough mixing. Despite the fact

that the average durability was not appreciably changed by the

degree of mixing in most cases, the data show that with both

the 30-minute mechanical mixing and with the brief hand mixing,

the spread in durability of replicate panels exposed in different machines was greater than with prolonged hand mixing.

Therefore, it must be recommended strongly that thorough mixing

be employed to obtain the most uniform and optimum benefits

from a mineral additive.
16

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- 17 -

4.5 The Effect of the Particle-Size

Distribution of the Mineral Matter

on the Durability of Coatings

Because the particle-size distribution is one of the

attributes of mineral matter which may seriously affect its

performance, its effects on durability were evaluated in

all three asphalts. Three minerals, blue black slate,

Niagara dolomite and Lake Erie silica, were sieved into

eight fractions and reconstituted into five different

synthetic size distributions, as follows

s

1) +200 Mesh - Coarse material retained on a No. 200

U. S. Standard Sieve.

2) -200 Mesh - Material passing a No. 200 U. S.

Standard Sieve.

3) 4325 Mesh - Material passing a No. 325 U. S.

Standard Sieve.

4) Uniform Size - Material passing a No. l4o but retained on a No. 230 U. S. Standard

Sieve.

5) Equal Size - Approximately equal weights retained

on a square-root of two series of

U.S. Standard Sieves.

The geometry of irregular particles being separated by means

of sieves with square openings introduced some deviations

from the distributions desired.

Exposure panels (25 mils thick) were made from coatings

containing 35 per cent of materials containing each of these

distributions. The particle-size distributions are recorded

along with the accelerated durability data in Table VII.

Average durability figures are shown graphically in Figure 5°
- 18 -

TABLE VII. PARTICLE SIZE DISTRIBUTION SERIES*

BLUE BLACK SLATE

ASPHALT None Kf|U- + 200 -200 -325

-146

+ 230

Equal

Size

Asphalt I

Panel No. 1, Dur., Days 52 61 5§ 58 75 53 52

" "7, Dur., Days 52 -- 58 58 75 59 52

" "2, Dur., Days 34 75 65 72 80 55 54

" "6, Dur., Days 34 65 72 80 42 54

Average 43 68 62 65 77 52 53

Durability Ratio 1 1.58 1.44 1.51 1.79 1.21 1.23

Crack Pattern C BG B G G BC C

Softening Point, °F 219 222 226 220 222 227 230

Base Soft. Point, °F

Base Pen. at 77°F

219 210 220 207 20 7 212 214

18 21 18 21 21 20 20

Asphalt II

Panel No. 1, Dur., Days 74 146 131 161 149 140 122

" " 7, Dur., Days 74 --- 131 161 128 133 129

" "2, Dur., Days 76 158 131 147 --- 182 152

" "6, Dur., Days 76 --- 138 161 191 168 153

Average 75 152 133 157 156 158 143

Durability Ratio 1 2.01 1.77 2.09 2.08 2.11 1.91

Crack Pattern AC C A A A A A

Softening Point, °F 228 222 225 227 224 225 220

Base Soft. Point, °F

Base Pen. at 77°F

228 211 217 215 211 21

7

215

17 22 19 19 22 19 19

Asphalt III

Panel No. 1, Dur., Days 66 188 122 185 1 77 145 153

51 "7, Dur., Days 69 --- 122 171 163 138 133

11 "2, Dur., Days 81 159 120 198 161 !34 149

" 11 6, Dur., Days 81 - = - 100 173 154 134 129

Average 75 174 116 182 164 137 l4l

Durability Ratio 1 2.32 1. 56 2.43 2.19 1.83 1.88

Crack Pattern F A A AH A A A

Softening Point, °F

Base Soft. Point, °F

Base Pen. at 77°F

22 7 218 226 221 227 223 223

22 7 205 221 205 207 205 209

14 20 17 20 20 20 20

%> Passing U. S. 60

80

100

120

170

200

230

. 3^ _

99.8

99.3

97.9

96.2

91.3

86.9

83.1

,76 -y.

,

99.1

94.7

85.0

74.1

35.2

5.7

1.0

. o«7.

100.0

100.0

100.0

99«9

99.9

99.3

95.4

85^5 100.0

100.0

100.0

94.7

92.4

72.9

40.2

13.5

4.1

100.0

98.7

95.1

90.2

66.6

54.5

42.8

21.7

35% Mineral Additive Exposed in Films 2 5 mils thick on Aluminum*,
FIGURE

5

EFFECT

OF

PARTICLE

SIZE

DISTRIBUTION

ON

DURABILITY I-

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REG.

+200-200-325-140

E.S.

REG.

+200-200-325

-140

E.S.

REG.

+200-200-325-140

E.S.

+230

+230

+230

- 19 -

TABLE VII, PARTICLE SIZE DISTRIBUTION* ( C ONT g D

)

ASPHALT

Regular

NIAGARA

+200 -200

DOLOMITE

~l4o

-325 +230

Equal

Size

Asphalt I

Panel No. 1, Dur., Days 45 ^3 43 38 36 35

II II y

II II 36 38 36 35

II II p II II « 59 42 5° 37 36 35

II II II II 42 42 37 36 35

Average 52 43 43 37 36 35

Durability Ratio 1.21 1.00 1.00 0.86 0.84 0.81

Crack Pattern C B c BC C C

Softening Point, °F 220 226 221 218 223 224

Base Soft. Point, °F

Base Pen. at 77° F

209 219 211 207 212 214

21 18 20 21 20 20

Asphalt II

Panel No. 1, Dur., Days 98 87 88 99 91 99

it ii yii ti -- 80 88 87 84 99

it li p

* it il 103 89 114 93 83 85

it ii £,

ii II 103 104 93 90 78

Average 101 90 99 93> 87 91

Durability Ratio 1.35 1.20 1.32 1.24 1.16 1.21

Crack Pattern A AC AE A A A

Softening Point, °F 225 223 226 219 223 223

Base Soft. Point, °F

Base Pen. at 77°F

217 214 219 214 2l4 221

19 19 18 19 19 18

Asphalt III

Panel No. 1, Dur., Days 122 112 !34 109 95 87

ii ii yii ii 112 134 102 95 87

tl ft O * !! II 9 108 108 128 116 98 no

ii ii £ii ii 94 110 116 98 76

Average 115 107 127 111 97 90

Durability Ratio 1.53 1.43 1.69 1.48 1.29 1.20

Crack Pattern A A A A A A

Softening Point, °F 221 226 220 223 222 223

Base Soft. Point, °F

Base Pen. at 77°F

204 219 215 206 210 214

20 18 19 20 20 19

%o Passing U.S. 60

80

100

120

99-9

99°9

99o6

99.3

99.6

98.6

95.8

91.1

100.0

100.0

100.0

100.0 100.0

100.0

97.9

94.5

170 96.6 61.4 99.9 93.0 79.8

200 <j3 .4 20.5 99.9 74.1 70.0

230

fc?

41.2 50.0

325 §Lo 100.0 9.5 19 ol

*35% Mineral Additive Exposed in Films 2 5 Mils Thick on Aluminium
20 -

TABLE VII. PARTICLE SIZE DISTRIBUTION SERIES* (C ONT 'D)

LAKE ERIE SILICA

ASPHALT Regular + 200 -200 -325

-l40

+230

Equal

Size

Asphalt I

Panel No. 1, Dur., Days 33 28 49 41 29 37

u ii y

ii n —

.

28 49 4l 36 30

ft ft 9* »! II 4l 42 35 26 29 30

ii ii ^u ii — 35 35 40 29 30

Average 37 33 42 37 31 32

Durability Ratio 0.86 0.77 0.98 0.86 0.72 0.75

Crack Pattern C BC C

r\O C c

Softening Point, °F --- 222 226 22 7 223 225

Base Soft. Point, °F

Base Pen. at 77°

F

213 212 210 208 213 213

20 20 21 21 20 20

Asphalt II

Panel No. 1, Dur., Days 91 68 132 112 93 120

ii ii y

ii ii -- 68 132 112 93 109

U II p

* II II 117 84 118 112 93 101

II II £>

II II --- 98 132 112 93 101

Average 104 80 128 112 93^ 107

Durability Ratio 1.39 1.07 1.71 1.49 1.24 1.43

Crack Pattern AC AC A A A A

Softening Point, °F 217 219 223 227 225 226

Base Soft. Point, °F 207 214 215 217 215 216

Base Pen. at 77°F 23 19 19 19 19 19

Asphalt III

Panel No. 1, Dur., Days 80 93 122 108 95 100

ii "7 n it -= 93 122 108 87 100

it it p

* ii it 72 81 143 123 105 103

ii ii £it it — 81 136 123 105 103

Average 76 87 129 115 93 102

Durability Ratio 1.01 1.08 1.72 1.53 1.31 1.36

Crack Pattern A A A A A A

Softening Point, °F 226 222 223 224 226 219

Base Soft. Point, °F

Base Pen. at 77°F

206 215 210 20 7 216 210

20 19 20 20 19 20

% Passing U. S. 60

80

100

120

99.9

98.2

80.8

53.7

100.0

99.3

92.7

. 76.9

100.0

100.0

99.9

99.9 100.0

100.0

97.9

93.1

170 15.3 26.5 99.7 *+3.7 71.2

200 8.1 7.7 98.2 18.8 56.5

230 5.4 1.8 85.7 7.3 46.7

22? 3A_ 1.1 52.5 100.0 1.2 28.2

*35$ Mineral Additive Exposed in Films ;25 Mils Thick on Aluminum.
21

The durability was a function of both the asphalt and

the mineral additive. However, the results will be discussed primarily in terms of the minerals. While the finer

distributions of blue black slate increased the durability

more than the coarse ones in asphalts I and III, in asphalt

II the durability was independent of the size distribution.

The coatings made with silica, however, indicated that the

finer distributions yielded the more durable coatings.

The indecisive nature of the above results led to the

conclusion that the quantity of mineral matter present was

insufficient for the effect of particle-size distributions

to be observed in coatings 25 mils thick. Accordingly, the

two extreme size ranges, +200 and -200, were formulated at

a concentration of 5

0

%> in asphalt II and exposed in films

13 and 25 mils thick. The results are presented in Table

VIII and Figure 5®

The effects of size distribution were clearly evident

with 50% mineral matter in coatings 13 mils thick. For

example, +200 blue black slate lasted only b2%> as long as

the asphalt alone, but the coating with the -200 blue black

slate was three times as durable, making it produce over

seven times the durability of the +200 material. At 25 mils,

the same trend, though not so extreme, was maintained, the

-200 mesh material producing a coating twice as durable as

the +200 mesh. With dolomite, there was a factor of about

two in both cases, but in the thin film it shifted the durability from below to above that of the asphalt alone. In

the case of silica, however, the increase in durability produced by going to the finer size was small.

In summary, the -200 mesh fraction of blue black slate,

Niagara dolomite, and Lake Erie silica seem to be most

effective in increasing the durability of asphalt roof coatings in concentrations of 35 and 50 percent. The material

retained on the 200 mesh sieve is the least effective, while

the regular (commercial), - 325 ? equal size, and uniform size

(_llf0 +230) follow in descending order, with little difference between adjacent distributions.
- 22 -

TABLE VIII „ PARTICLE-SIZE DISTRIBUTION SERIES

50% MINERAL MATTER IN ASPHALT II*

MINERAL

BLUE BLACK

SLATE

NIAGARA

DOLOMITE

LAKE ERIE

SILICA

Size Range

Softening Pt.,°F

13 Mils Thick

No. 1, Dur. , Days

No. 7, Dur

.

9 Days

No. 2, Dur. 9 Days

No. Dur. , Days

Ave . 9 Dur. 9 Days

Durability Ratio

Crack Pattern

25 Mils Thick

No. 1, Dur. 9 Lays

No. 7, Dur. , Days

No. 2, Dur. , Days

No. 6 5 Dur. , Lays

Ave

,

B 9 Dur. 9 Days

Durability Ratio

Crack Pattern

+ 200 -200 + 200

220 ; 226 219

23 178 5b

23 178 61

23 167 53

23 160 48

23 171 5b

0.42 3*10 0.98

A A A

120 225 110

135 230 110

145 223 102

120 233 102

129 228 106

1.72 3.04 1.4l

A EG A

-200 + 200 -200

217. 219 223

10b 64 80

90 50 86

93 5° 71

102 43 64

97 52 75

1.76 0.94 1.36

A A A

144 134 129

139 120 129

137 98 113

143 98 113

Ibl 112 121

1.88 1.49 1.61

E A A

*Durability of Asphalt II; 13 Mils - 55 Days

25 Mils - 75 Days
- 23 -

4„6 The Effect of Particle Shape of Minerals

on the Durability of Coatings

Because particle shape was the one property of the

minerals studied in the Principal Seriesi/ of exposures that

seemed to be related to the efficacy of their stabilizing

action, some quantitative method of expressing particle shape

was sought. A relation between a bulk density and the true

density of the minerals seemed worth considering for this

purpose . Franz Popel,^/ in 1929 ? proposed a relation of this

type , which he called "fineness factor", and defined as

^ _ density - compacted wt„ = d-b

compacted wt. b

where the compacted weight is an empirical bulk density determined under any set of conditions that would yield reproducible

results o Rather than a compacted weight, the bulk density used was

obtained by fluffing the mineral matter by letting it flow

slowly through a column of one-inch inside diameter, 21 inches

long. Baffles set at an angle of *+5° were placed 12 and 16

inches from the top of the column and the column was constricted to a diameter of 3/b inch at the bottom. The

column discharged into a 100-ml, weighed and calibrated,

graduated cylinder from a point 1/b inch above the cylinder.

In practice the mineral matter was poured slowly into the

column 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

1/

"Laboratory Evaluation of Six Commercially Available Minerals as Stabilizers for Asphalt Coatings", S. H. Greenfeld.

2/

Franz Popel, Der Moderne Asphalstrassenbau (StrassenbauVerlag Martin Boerner, Halle 1929)

.
- 2b -

matter divided by its volume is termed the "fluffed bulk

density" or simply, the "fluff density", A correlation

of fineness factor based on this bulk density is presented in Figure 6, The individual points are tabulated

in Table IX,

It is readily seen that for each asphalt this factor

correlated well with durability. The only materials that

deviate considerably from the curves are oyster shell and

mica, both being materials characterized by flat, platelike particles. Since the deviations are in the direction

of greater durability than indicated by the lines, the lines

may be taken as conservative indications of durability.

Despite the rather good correlations indicated by

Figure 6, it must be 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 (fpr

each asphalt emphasizes the importance of the asphalt

itself in respect to durability.
TABLE

IX.

FINENESS

FACTOR

25

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0 -—

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i—I i—

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0 C/} >

CP

cpcPCPCPpq&qcococpcoi-iMcopq

Pin fx, <q pq pq pq ip, pq pq pq

0

p

0

P

p

o

o

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0H 0

P P

0 p O

0 O 0

-p pc; p 0 0

i—

l

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1

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i—

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o 0 cd CP >N o

0 •H <q O o M P

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1

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i—

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0 O -P P pq CO 1—

1

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H 0

0 pq P Q q pq -P cd Q CO (p pq CP P 0 • O •H —

1

•H 0 o -p o o O UNO to P o O • II li li s o o CO 0 0 o O CM o 0 0 O w

•H CM pq >> Ph • CM rO CM •H o CM • CP pq s 1 pq o CO hi 1 1 4- w + hi fp pq CP
FIGURE

6

DURABILITY

VS.

FINENESS

FACTOR

I

3

I

(3T0A0 06- IS) SAVG ‘AllH8Vdna

FINENESS

FACTOR
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