National Bureau of Stand8ro^

DEC 9 '3^^

taken from the library.

BUILDING SCIENCE SERIES

REFERENCE

Natural Weathering of

Mineral Stabilized Asplialt Coatings

On Organic Felt

U.S. DEPARTMENT OF COMMERCE

National Bureau of Standards
NATIONAL BUREAU OF STANDARDI

SEP 2 1 1970

Contents

Page

1. Introduction 1

1.1. Scope of study 1 1

2. Experimental details 1

2.1. Types of specimens 1

2.2. E(iuipment for preparation of specimens 2

a. Smooth-surface, felt-base specimens 2

b. Granule-surfaced specimens 2

c. Back-coater 2

d. Aluminum-base panels 2

2.3. Materials 2

a. Mineral matter 2

b. Asphalts 2

c. Saturated felts 4

d. Aluminum panels 4

e. Granules 4

2.4. Specimen preparation 4

a. Smooth-surface, felt-base specimens 4

b. Granule-surfaced, felt-base specimens 4

c. Smooth-surface, aluminum-base specimens 4

2.5. Specimen exposure 4

a. Felt-base specimens 4

b. Aluminum-base specimens 4

2.(i. Specimen evaluation 4

a. Felt-base specimens 4

b. Aluminum-base specimens 4

o. Progress of deterioration 4

3.1. Smooth-surface specimens 4

3.2. Granule-surfaced specimens 7

3.3. Blistering 7

4. Failure criteria 7

5. Outdoor performance 7

5.1. Smooth-surface, felt-base specimens 7

5.2. Granule-surfaced, felt-base specimens 10

(). Correlation with exposures in accelerated weathering machine 10

7. Conclusions 14

8. References 15
Natural Weathering of Mineral Stabilized Asphalt

Coatings on Organic Felt

Sidney H. Greenfeld

Sixteen years of outdoor weathering of laboratory-prepared smooth-surface and mineralsurfaced, felt-base roofing specimens has provided information on the effects of mineral additives on the durability of coating-grade roofing asphalts. Six finely divided mineral additives (blue black slate, clay, dolomite, fly ash, mica, and silica) were evaluated at concentrations up to 60

percent in California, Mid Continent and Venezuela asphalts. The mineral-surfaced specimens

are all performing satisfactorily, and show only minor degrees of degradation. Of the smoothsurfaced specimens, the Mid-Continent asphalt performed the best and the California asphalt

the poorest. The mica and blue black slate increased the durabilities of all three asphalts at all concentrations and two coating thicknesses. Fly ash, clay, dolomite, and silica were beneficial in some combinations, but had little effect in others. In general, these early results from outdoor

exposure tend to corroborate the results obtained on these coatings exposed in weatherometers. Key words: Additive; asphalt; durability; felt; stabilizer; weathering.

1. Introduction

The most certain w ay to determine how a product

\vill weather in a given geographical area is to expose

the product and observe it over the years. For

materials or systems of low Hfe expectancy, this procedure has been proven extremely satisfactory. For building materials, where the life expectancy is

' of the order of decades, the observed frequently

outlives the observers. Those who design the tests, know their background and appreciate the signifij cance of results, pass out of the picture and are

ii replaced by others who find current work of greater

I interest. In many instances, the current production

I is no longer strictly comparable to that being

observed.

Therefore, it has long been the practice to design

. rapid methods for evaluating materials and simultaneously exposing the same materials to the

weather. The results of the laboratory evaluation

become available in a relatively short period of time; those of the simulated-service tests (outdoor

exposures) get lost in the shuffle and the validity

I of the rapid tests is never proven.

! This study was designed in 1947 by the Research

Committee of the Asphalt Roofing Manufacturers

Association i to include a simulated-service study

and several degrees of accelerated evaluation of the

system: coating asphalt and mineral additives.

The laboratory phase of the work was completed

in 1954 and a series of reports and publications

issued [1, 2, 3] 2. The verification of the conclusions

drawn in these articles will be found in the results .obtained for the outdoor tests. This paper is in the nature of a progress report of the first 15-17 years

of these outdoor tests.

1.1. Scope of Study

The mineral additive—asphalt systems included

in this study consisted of three asphalts and six mineral additives at three concentrations on one

grade of shingle felt. The coatings were applied in two film thicknesses, and were exposed unsurfaced

and surfaced with roofing granules.

1 Formerly the Asphalt Roofing Industry Bureau.

2 Figures in brackets indicate the literature references at the end of tin; paper.

2. Experimental Details

2.1. Types of Specimens

Three types of specimens were included in this study. The basic specimen was a smooth-surface

coated felt. These were exposed with coating thicknesses of 15 and 25 mils,^ were back-coated with

the same coating blend, and were dusted with mica

retained on a No. 100 sieve.

» 1 Mil = 0.025 mm (approx).

The first type of specimen was made on 9- X 12-in^

felts and trimmed to 7 X 11 in prior to exposure

to remove any edge effects. The second type of specimen also had a felt base. In addition to being front and back coated, it was

surfaced with granules. These, too, were trimmed

to 7 X 11 in.

* 1 in = 2.54 cm.

1
The third type of specimen was used for acceler- ated weathering tests. It consisted of the coating on 23,4- X 6-in aluminum panels. The results of these tests were reported earlier [3].

2.2. Equipment for Preparation of Specimens

a. Smooth-Surface, Felt-Base Specimens

Crimped (solder free) gallon cans. Asphalt melting bath.

Six-ounce ladle. Laboratory hydraulic press with 12- X l-l-in cadmiun-plated platens.

Tempered hardboard, 12 X 14 in. Kraft paper, 12 X 14 in. Cellophane, 12 X 14 in. Dextrin-coated paper, 12 X 14 in.

b. Granule- Surfaced Specimens

All of the granule-surfaced specimens were made

on the apparatus shown in figure 1. Its principal

parts are:

A. Hot plate for keeping the base warm during

the pouring of the coating. B. Variable-voltage-controlled, temperature-regulated doctor bar for spreading the coating

and regulating its thickness. C. Granule hopper and fluted granule spreader.

D. S-rolls for initial embedment of the granules

and removal of excess.

E. Embedding rolls. F. Belt drive for pulling canvas belt through the

machine.

c. Back-Coater

. The felt-base specimens were all back-coated

with the apparatus shown schematically in figure 2.

d. Aluminum-Base Panels

The equipment used in preparing the aluminum

base specimens is described in ASTM D1669, Standard Method for Preparation of Test Panels for Accelerated and Outdoor Weathering of Bituminous

Coatings [1] and in reference [3].

2.3. Materials

a. Mineral Matter

The six minerals used in this investigation were

blue black slate, Florida clay, Niagara dolomite,

low-carbon fly ash, Tennessee mica, and Lake Erie

silica. The properties of these materials are listed in table 1

b. Asphalts

The descriptions and properties of the three

asphalts used in this investigation were reported

previously [3] and are tabulated in table 2.

Figure 1. Ap-paratus for prefaring granule-surfaced specimens.

.\. Heated bed for keeping felts warm while asphalt coating is poured on them.

B. Doctor bar for leveling and defining coating thickness. C. Granule hopper and distributor. D. Granule placement S-rolls. E. Granule pressing, or embedding, rolls.

2
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•3 IN. I. D. IRON

PIPE WITH CAPS

1/3 SAWED OFF.

ADJUSTABLE DOCTOR BAR TO REGULATE COATING THICKNESS

COATING LEVEL

Figure 2. Apparatus for coating tKe backs of the specimens. Each specimen was placed face up on the top of the 11 -incylinder and the crank turned to apply a thin coating on its back.

T.vBLE 2. Characteristics of unstabilized asphalt coatings used as controls

Asphalt

Test Softening point ' T (°C) _

Penetration at 32 °F (0 °C) - .0.1 mm.-

Penetration at 77 °F (25 "C) 0.1mm . Penetration at 115 °F (46.1 °C) 0.1 mm._

Penetration index ^ Susceptibility 2 Loss on heating, 3 Penetration at 77 °F (25 °C) after heating, 0.1 mm-_

Specific gravity at 77 "F (25 "O

Viscosity, cP at 400 °F 1 (204 "C)

Viscosity, cP at 450 °F (232 °C)

Viscosity, cP at 500 "F (260 °C) Water absorption, at 28 days ' g/m -__ Shatter ^ in (cm) (ave)-.

California

223 (106.0)

10

1730

4.7

1.16 0.22

171.015 280

10025

7.2 6.3 (16.0)

Mid-continent

224 (106.5)

111726

4.7 0.87

0.03

170.999 420

140534.6

8.3 (21.1)

Venezuela

227 (107.8)

1114214.5 0.73 0.10

141.018

375

13028

3.7

2.7 (6.9)

' ,ASTM method D36-26. .\STM method D.5-52. P. I. from Nomograph, and S =

» ASTM method D6-39T. N s

' Brookfield viscometer; 1 cP = 0.001

'—.

Pen. 115 °F (46.1 °C) - Pen. 32 °F (0 °C)

Pen. 77 °F (25 °C)

(6)

^ Specimens, 3-in diam X 'ii-in thick, submerged M-in in distilled water at 77 °F (25 °C).

.A ^o-^h \veight was dropped on a 3-in diam specimen, -^iti-in thick, in a mixetl ice and water bath.

c. Saturated Felts

The dry felt was prepared for this project in rolls 12 ± 3^ in wide by 300 ft long and shipped by one

of the sponsoring companies to another of the sponsors for saturation by personnel on the project. The

dry and saturated felts had the characteristics

listed in table 3.

4
Table 3. Characteristics of felt

Dry felt

Furnish, %:

(iauge, lb/480 ff^ 2 Kerosene capacity ' Caliper, mils:

Tensile, ll)/in Ash, %:

Rags

Paper Asplund

Scrap felt

g ker/ir felt:

.53 ± 2 1.90 ± 0.01

.57 ± 3 316.8

Saturated felt

California asphalt Mid-Continent asphalt Venezuela asphalt

Saturation

Percent of

felt weight

177

183 187

Percent of kerosene

capacity

9396

98

1 Burette method ARIB No. 2.125, April 1954.

* 1 lb = 0.45 kg (approx).

Aluminum Panels

The panels, made from S-2 aluminum alloy, were

G in long, 2^4 in wide, and 0.065 in thick.

and a half times the required quantity of coating was distributed over the felt and spacers of the

required thickne.ss (felt thickness plus '.i mils) were

placed along two of the sides of the felt. A sheet of dextrin-coated paper, two sheets of Kraft paper and

a piece of tempered hardboard were successively

placed over the coating, and the assembly was put

into the hydraulic press. The press was closed and

the' pressure raised to about 120 psig. After about

30 s, the panel was removed from between the sheets

of Kraft paper and placed in a water bath at room

temperature, where the cellophane and dextrin

paper soon floated free. The panel was thoroughly

washed and dried and its thickness measured.

When the required number of acceptable panels

had been prepared, the hot coating was ladled from

the melting bath to the back-coater, which had pre- viously been heated to about 450 °F (232 °C).

While one man rotated the roller slowly, another

passed the back of the panel over the roller, picking

up a thin coating. The back coating was dusted with

mica while still warm. Upon cooling, each specimen was cut to 7 X 1 1 in and exposed the next day on wooden roof decks, which had been covered with

smooth-surface roll roofing (facing due south and

at an angle of 45°). An area of 4 X 7 in was exposed,

leaving each specimen a 3-in head lap.

Granules

The granules were of the ceramic type, with the

characteristics listed in table 4. These characteristics were supplied by the granule manufacturer and no

attempt was made to verify them.

2.4. Specimen Preparation

a. Smooth-Surface, Felt-Base Specimens

The asphalts were melted in a double-boiler, consisting of a one-gallon can, wrapped in aluminum

foil to prevent contamination, sitting in a twogallon bucket half full of asphalt. The temperatures

of both the asphalt under investigation and the

asphalt in the bath were watched constantly to prevent any overheating. When the temperature

of the test asphalt was in the range of 400 to 450 °r

(204 to 232 °C), any required mineral matter, pre- heated to 300 °r (149 °C), was stirred into it with

a large chromium-plated ladle. The mixture was

continually stirred at 450 °F (232 °C) until it no

longer frothed. All compositions were made and are reported on a weight-percent basis. The saturated felts, cut into 9- X 12-in sheets, were heated in an air oven at 300 °F (149 °C) to warm them and to eliminate moisture. They were

ready for use when the saturant, which came to the

surface as the felts were heated, was completely

reabsorbed.

When the felts and coating were in working condition, a felt was removed from the oven and placed on a sheet of cellophane backed by a double thick- ness of 12- X 14-in Kraft paper and a 12- X 14-in piece of tempered hardboard. Approximately one

Table 4. Characteristics of granules

Base Rock: — 10 + 35 mesh Wausau, Wisconsin graystone (Argillite).

Chemical Anab'sis

Component Percentage

Si02 70.0 AUG 3 17.4 Fe20s 5.7 MgO 1.5 CaO 0.3 NajO 4.8 CO2 0.6 HcO (at 105 °C) 0.04

Pigments: Chromium oxide and phthalocyanine green, bonded

with sodium silicate.' Granules:

Acidity: Extract from 25 g is equivalent to 0.1 ml of O.l.V acid. Color fixation: 30 percent pigment loss. Wettability: 80 percent.

Oil absorption: 6 lb/ton « (3 g/kg).

Particle Size (Tyler)

Sieve No. Percent

Retained on 10 0.7

Retained on 14 33.9 Retained on 20 36.0

Retained on 28 21.6 Retained on 35 7.2

Passing 35 0.5

Granules were oiled with 5 lb per ton (2.5 g/kg) of lightweight paraffin

oil, complying with the following specification: Sp. Gr.

Viscosity at 100 °F (37.8 °C) Flash point (COCl

Fire point (COC)

Pour point

26-30 ° API

96-105 S.U.S. 350 °F (177 °C) min. 395 °F (202 °C) min. 25 °F ( - 3.9 °C) max.

' U.S. Patent No. 2,417,058.

2 Basis of test not reported.

5
b. Granule-Surfaced, Felt-Base Specimens

The asphalt and felts were prepared as in 2.4a. The hot plate (A) on the laboratory roofing machine

(fig. 1) was heated to about 250 °F (121 °C) and the

doctor bar (B) to 450 °F (232 °C). The canvas belt was threaded through the machine and a sheet of

12-in wide Kraft paper three feet long was fastened

to its end, about 4 in in front of the doctor bar. In

order to be assured that the doctor bar was at the

proper distance from the machine bed, a blank run was made in which no granules were used. When

cool, the thickness of the coated panel was measured.

In a normal run the felt panel was fastened with

masking tape to the Kraft paper on the hot plate.

About one and a half times the required coating was distributed over the panel. The motor was

started and the panel was pulled under the doctor

bar (B) and granule hopper (C); then the motor was stopped for 2 min to permit the panel to cool and the granules to become firmly set. Then the

panel was drawn through the S rolls (D) and embedding rolls (E). The panel was removed from the belt and passed backwards through the embedding rolls again. Because of the heavy gear on one side of the

embedding rolls and because the rolls were not crowned, this procedure was necessary to make the

embedment of the granules more uniform. The

panels were backcoated as in 2.4a.

c. Smooth-Surface, Aluminum-Base Specimens

The smooth-surface, aluminum-base specimens were prepared as in ASTM D 1669, which is based on work reported in reference [3].

2.5. Specimen Exposure

a. Felt-Base Specimens

Within 24 hr after their preparation the felt-base specimens, both smooth and granule surfaced, were

exposed outdoors on the roof of the Industrial

Building at the former NBS Washington site, facing due south and at an angle of 45 deg. The

7- X 11-in specimens were mounted by nailing

shingle fashion on protected decks with 4- X 7-in tabs exposed to the weather. The decks for the

smooth-surface specimens were protected with 55-lb

roll roofing, which also served as the under-layment

for- these specimens; the granule-surfaced specimens

had a 90-lb mineral-surfaced roll roofing as underlayment and deck cover.

b. Aluminum -Base Specimens

The aluminum-base specimens were exposed in two weatherometers to cycle 51-9C of ASTM D 529, , within 24 hr of the time they were prepared. A detailed account of the apparatus and procedure is given in reference [3].

2.6. Specimen Evaluation

a. Felt-Base Specimens

The 4- X 7-in exposed portions of the specimens were examined through a transparent grid with 98

squares [0.40 X 0.40 in] covering the central 33^-

X Q}4-'m area. The areas around the edges [0.325 in wide] of the 4- X 7-in area were excluded from the

examination to eliminate the edge effects. The numbers of squares with cracks and spalled coating were

counted and recorded during each inspection. In- spections were made every three months during the

first two years of exposure and semiannually thereafter. The semiannual inspections were made in March and September.

b. Aluminum-Base Specimens

The aluminum-base specimens were examined

with a high voltage probe in accordance with ASTM

D 1670. Spark photographs were taken of all speci- mens with three or more breaks in the coating. These

photographs were examined through a transparent

60- rectangle grid covering the central 2- X 5-in portion of the specimen. Only failures by cracking were rrcorded for this type of specimens.

3. Progress of Deterioration

3.1. Smooth-Surface Specimens

When the smooth-surface specimens were first prepared, they had a matte finish corresponding to the texture of the dextrin-coated release paper used on them. After short periods of exposure, the surfaces

became glossy. Continued exposure produced eleva- ted ridges, followed by thinner connecting ridges.

These ridges were the result of expansion of the

surface as it became oxidized. As oxidation progressed; the surface became progressively more water

soluble; material was dissolved by rain outdoors or water spray in the weatherometers, and the glossy,

ridged surface assumed a matte appearance. With

time, widely spaced cracks appeared. These cracks

usually penetrated the felt-base specimens fairly

rapidly through the coating to the felts. In the

aluminum-base specimens, the cracks frequently

remained on the surface for relatively long periods

of time and failure was evidenced by pinholing in noncracked areas or at crack intersections. In the felt-base specimens, widely spaced cracks

became interlaced with narrower cracks until spalling of the small areas surrounded by cracks began.

As coating spalled from the specimens, the substrates were exposed to the weather. In the aluminum-base

specimens, exposure was usually discontinued prior

to the spalling phase of weathering. In the felt-base specimens, the spalling permitted the saturated-felt

to be degraded rapidly by the weather. Photo6
3 oxidation rapidly destroyed the saturant and per-

] mitted water to enter the felts and, through

alternate wetting and drying, shrink and distort

|| them. Finally, the weakened tabs were blown away.

3.2. Granule-Surfaced Specimens

The granule-surfaced specimens have shown only

the early stages of deterioration during the 15 years they have been exposed to the weather. Changes

observed early in the exposure period consisted of

! small losses of granules in most of the specimens and

heavier losses of granules in the few specimens in which poor granule adhesion was measured prior to exposure. After about 12 years of exposure, cracks

began to appear in the coatings. About a cjuarter of the specimens had cracks in 5 percent of their surface

areas (five grid areas) after 12 and a half years. No

.spalling of the coatings has been observed in any of these specimens since their exposure in 1952. However, in the normal course of events, as weathering

progresses, generally more granules will be lost, more

cracking will occur and, finally, the coatings will spall off the saturated felts, just as in the smoothsurface, felt-base specimens. The granules protect

the coating from solar radiation and greatly delay

the later stages of deterioration.

3,3. Blistering

Early in the exposure of the smooth-surface, felt- base specimens some small blisters were observed.

These were principally around the edges, but in some

of the specimens made with Mid-Continent and Venezuela asphalt, blisters appeared well within the areas

inspected. Only a very few specimens made with

California asphalt had any blisters; none had more

than three. While blistering contributes to poor

appearance, it does not interfere with the essential function of roofing, which is to keep the structures weatherproof. Therefore, blistering is not normally

considered as a criterion of failure. However, blisters can act as centers of stress concentration and lead

to earlier cracking and .spalling of the coating. Thus,

the effect of blistering is manifested in the reported

cracking and .spalling. The only other comment that can be made concerning blistering is that the largest

incidence of blistering was associated with the coatings made from the more durable asphalts.

The aluminum-base specimens and the granulesurfaced, felt-base specimens experienced essentially no blistering.

4. Failure Criteria

When a product exposed to the weather no longer

performs the function for which it was designed, it

j has failed. However, it has become customary to

,! replace roofing for reasons other than, and earlier

; than, complete failures. Quite frequently, shingles

i are replaced because they no longer have an acceptable appearance; on other occasions failure can be

II anticipated in the near, but indefinite, future. Cont sequently, certain standards of failure were arbitrar-

; ily selected by the sponsors of this program.

I These failure criteria appear in table 5.

f 5. Outdoor

!j

I 5.1. Smooth-Surface, Felt-Base Specimens

The results of 200 months (16% years) of exposure

of the smooth-surface, felt-base specimens to the

weather are summarized in tables 6 and 7. Infor- mation on crack development is presented along

with the observations of spalling. The ratio of the

II time in which an asphalt coating w ith mineral matter

j in it reaches a given level of deterioration to the

\ time in which the same asphalt alone reaches that

it same level of deterioration is also reported. This

{ ratio is frequently more signihcant than the actual

|i number of months of exposure, for this comparison

of a coating with mineral additives to its base

asphalt tends to compensate for variations in the

weather, or climate. This technique was used in

'i reference [3], where the results of the accelerated

' weathering on these coatings were discussed. (A

T.VBLE 5. Failure criteria

Specimen type Criterion of failure

Smooth-surface, felt base Spalls in 25 grid areas (25%).

Granule-surfaced, felt-base 50% Granule loss in 49 grid areas (50%) or spalls in 25

grid areas (25%).

Aluminum-base Cracks in 30 grid areas (50%)

Performance

few of the coatings 15 mils thick (table 6) and many

more of those 25 mils thick (table 7) had not reached some of the levels of deterioration reported. This

condition is indicated by dashes in both tables).

At every level of performance and in both thick- nesses the jMid-Continent asphalt outperformed the

Venezuela asphalt, which, in turn, outperformed the

California asphalt. The mica-stabilized coatings out

performed all the others; only one coating had

deteriorated to any of the selected levels in tables 6

and 7 in 200 months. The 15-mil California coating

with 35 percent mica exhibited its first spalled areas

in 164 months.

Before discussing specific performances, however,

a word of explanation is in order concerning the

mechanism of cracking and why cracking, though

ultimately contributing significantly to shingle

7
Table 6. Smooth surface specimens i

15 Mil (0.38 mm) Thickness

' o8.tinjj (1 Gpcri p t loii 257c, Cracked 50% Cracked Initial Spall 25% Spalled 50% Spalled

Ratio Alonths Rat io jMonths Ratio Months Ratio A/TrtntViQ

r-" I'f \ 1 oU 15 1 .0 15 1.0 35 1.0 49 1.0 55 1 .0

1 'i^or Rms; 18 1 .2 18 1 .

71 2^0 104 2.116 2.

_l_ ^f\C/ RRS 38 2.5 40 2! 7 101 2^9 139 2_S 145 2.6

-1- f\()or RRS 99 6.6 140 9 .

174 5 0

_L PInv 19 lis 19 l!3 42 l!2 60 1.2 66 1.2

9 0.6 9 0.6 42 1.2 79 1.6 91 1.7

18 1 .18 1 .

37 1 .

55 1 .

61

H- 50% Dolomite 24 1 .

24 1 6 37 1 .

55 1 .

58 J + 60% Dolomite- 24 1 6 24 1 6 40 1

'. 1 61 1.2 69 1 .

-1- "^^^7 PIv- AqIi g 0.6 9 0.6 49 1.4 65 l!3 77 1 .

y 0.6 9 0.6 52 1 .

85 l!7 93 1 .

28 1 .9 28 1 .9 100 2^9 133 2.7 139 2.5

164 4^7

_L 'It^i':^ ftilipn 23 1 5 23 1 .

48 1 [4 63 1 3 79 1 .

-J- 'lO'^ f^ilirn ] 9 1 3 19 1 .54 1.5 72 1 5 78 1 .

-4- fint^ Silinn 48 3 2 48 3 .

72 2'. 1 90 1 .8 102 1 .9

32 1 .0 32 1 .0 82 ] .0 120 1.0 130 1.0 94 2.9 109 3.4 ] 18 1 .4

-J- .^n<^ URS 71 2.2 100 3 .142 1.7 155 1.3 176 1 .4 fiO^ RRS 2 201 - 6 3

_|_ Tt^PT, Plnv 29 0^9 32 1.0 79 1.0 102 0.9 113 0.9

-1- r»n'^ piflv 26 0.8 29 0.9 72 0.9 98 0.8 107 0.8

53 1 .

56 1 8 88 1 .

130 1 .

139 1 .

+ 50% Dolomite 56 1 8 59 1 8 144 1 .8 152 1 3 159 1 2 + 60% Dolomite -- 62 1 .9 68 2 .

105 1 .3 157 1 3 166 1 3

4- ."^5^ FIv A*;h 38 1 .2 38 1 .

113 1 .4 140 1 .T T

36 I I 44 1 4 88 1 .

143 1.2 148 1 .

-1- fiO<v^ Flv Assh 62 1 .

100 3 1 96 1 .2

-1- H5*^ Minn

-i- 3,5% Silica 3

1 0 38 1 .

41 0 5 148 1 .. 54 1 2

31 1 .0 34 1 .

93 1 .158 1 3 173 1 .3

-1- fiO^ Silir-n 34 ] J 37 1 2 80 1 .

161 1 .181 1 4

27 1 .0 27 1 .0 55 1 .0 91 1 .0 101 1.0

_I_ 'i'^Cy RR<i 36 1 .

36 1 3 101 1 8 156 1 7 166 1.6

_i_ r^nor RRH 54 2 0 57 2 .

95 1 .

159 1 .190 1 .9

J- fiOOT RRS 60 2 2 73 2 ,

133 2 4

4- '^5^ Pinv 17 0^6 17 o!6 54 i]o 84 0.9 94 0.9

_(_ (^(1%. PInv 17 0.6 17 0.6 60 1 .

96 1 .

113 1.1

-1- .'^'i^ Dnlnmil-P 21 0.8 21 0.8 66 1.2 101 1.1 113 1.1 + 50% Dolomite _ 23 0.9 23 0.9 57 1.0 100 1.1 115 1.1 + fiO% Dolomite 29 l.I 30 1 .

63 1.1 114 1.3 126 1.2 + 35% Kly Ash 20 0.7 20 0.7 96 1.7 152 1.7 155 1.5 + 50% FIv Ash 27 1.0 27 1.0 66 1.2 152 1.7 155 1.5 + 60%, Fly Ash 3 + 35% Mica + 35%o Silica 16 0.6 16 0.6 51 0.9 79 0.9 91 0.9 + 50%, Silica 16 0.6 16 0.6 60 1.1 91 1.0 97 1.0 + 60%, Silica ]9 0.7 19 0.7 53 1.0 99 1.1 lU 1.1

' Average of two specimens.

- One specimen only. Inspection sheets lost. — Specimens have not progressed to this failure le\ el after 200 months of expos\ire. T Tab torn off.

failure, cannot be used as an early warning of impending failure. While early cracking of the

coating on shingles may be startling to an uninformed

observer, the data in tables (i and 7 for smoothsurface specimens show the lack of correlation

between early cracking and failure. Thus, cracking

has not been used as one of the criteria of failure. Cracking of coatings on shingles results from the

large differences in thermal coefficient of linear expansion between the saturated felt and the shingle

coatings. Data on these materials are difficult to obtain, but a few order-of-magnitude figures have

been published. These are listed in table 8. It is evident from the above data asphalt moves

roughly 25 times as much as the saturated felt does

in the cross direction and 50 times as much as the

saturated felt in the machine direction as the temperature changes. At the higher end of the range of temperatures encountered by roofing during exposure, the asphalt can accommodate the differential

movements by flow, but at the lower end of the

temperature range flow is not rapid enough and

partial accommodation results by the curling of the

shingle tabs. When this movement can no longer

cope with the stresses, cracking occurs. These cracks

usually run at right angles to the greatest differ- ential movement.' In the exposure of the smoothsurface specimens, all early cracking first occurred in the cross direction. These occurred very early in the

exposure period, in some instances during the first winter, but the specimens continued to perform well

for many years. There was no relationship between

any of the levels of cracking and spalling. Therefore,

nothing more will be said about cracking, for spalling has been set as the criterion for failure. Returning to the performances of specific systems,

it can be seen that many of the specimens containing

blue black slate have not deteriorated to the 25 per- cent spalled level after 17 years of exposure. For

these systems, just as with the asphalts without

8
Table 7. Smooth surface specimena ^

25 Mil (0.64 mm) Thickness Outdoor Exposures

25% Cracked 50% Cracked Initial Spall 25% Spalled 50% Spalled

Months Ratio Months Ratio Months Ratio Months Ratio Months Ratio

10 1.0 10 1.0 46 1.0 80 1.0 95 1.0 21 2.1 25 2.5 95 2.0 136 1.7 T

88 3.8 58 5 8 116 2.5 T T

121 12!l 149 3^2 — —

11 1.1 11 1.1 63 1.4 100 1.2 115 1.2 26 2.6 29 2.9 72 1.6 127 1.6 142 1.5

18 1 .

8

18 1 8 58 1 3 79 1.0 101 1 .

1

9 0^9 9 o!9 61 l!3 88 i!i 103 i!i 23 2.3 26 2.6 61 1.3 88 1.1 101 1.1 8 0.8 8 0.8 61 1.3 91 1.1 109 1.1

14 1.4 14 1.4 58 1.3 94 1.2 118 1.2 27 2.7 31 3.1 97 2.1 130 1.6 142 1.5 —

9 —0.9 —9 —0.9 —63 —

1.4 —87 —

1.1 —100 —1.1 9 0.9 9 0.9 75 1.6 103 1.3 126 1.3

g 0.8 3 0.8 145 3 .

2

145 1 .

8

145 1 .

5

28 1.0 36 1.0 1.56 1.0 174 1.0 200 1.0

121 4.3 135 3.7 157 1.0 — — — —

81 2.9 108 3 0 201 1 .

3

36 1.3 39 103 0.7 —

143 —

0.8 —151 —0.8

34 1.2 39 1.1 109 0.7 166 1.0 176 0.9

44 1.6 50 1.4 117 0.8 177 1.0 — —

72 2.5 83 2.3 107 0.7 — — — —

62 2.2 80 2.2 99 0.6 178 1.0 — —

38 1.4 38 1.1 165 1.1 — — — —

50 1.8 65 1.8 171 1.1 — — — —

62 2.2 100 2.8 96 0.6 — — — —

—

33 —

1.2 —

38 —

1.1 —

123 —

0.8 —195 —1.1 —

— —

—

32 1.1 38 1.1 105 0.7 — — — —

35 1 .

2

4

1

1 .

1

95 0.6

25 1.0 33 1.0 101 1.0 1.59 1.0 167 1.0 48 1.9 58 1.8 107 1.1 171 1.1 79 3.2 94 2.8 151 1.5 — —

88 3.5 139 4 .

2

97 1.0

21 0.8 21 0.6 ' 86 0.9 2 144 0.9 = 149 0.9

12 0.5 12 0.4 68 0.7 2 144 0.9 = 149 0.9

21 0.8 21 0.6 57 0.6 159 1.0 166 1.0 29 1.2 31 0.9 72 0.7 162 1.0 166 1.0 37 1.5 39 1.2 65 0.6 149 0.9 159 1.0 28 1.1 28 0.8 108 1.1 171 1.1 187 1.1 23 0.9 29 0.9 107 1.1 32 1.3 32 1.0 107 1.1 202 1.3

16 0.6 16 0.5 84 0.8 152 1.0 159 1.0

16 0.6 18 0.5 123 1.2 159 1.0 180 1.1

16 0.6 16 0.5 78 0.8

Coating description

.\sphalt__. BBS

BBS BBS

Clay

Clay

Dolomite,

Dolomite- Dolomite,

Flv Ash_-

Flv Ash,.

Fly Ash,_ Mica

Silica

Silica

Silica

California + 35% + 50% + 60% + 35% + 50% + 35% + 50% + 60% + 35% + 50% + 60% + 35% + 35% + 50% + 60%

Mid-Continent Asphalt. + 35% BBS + 50% BBS + 60% BBS + 35% Clay + 50% Clay + 35% Dolomite + 50% Dolomite + 60% Dolomite + 35% Flv Ash + 50% Fly Ash + 60% Flv Ash + 35% Mica + 35% Silica + 50% Silica + 60% Silica Venezuela + 35% + 50% + 60% + 35% + 50% + 35% + 50% + 60% + 35% + 50% + 60% + 35% + 35% + 50% + 60%

Asphalt-, BBS BBS

BBS

Clay

Clay

Dolomite- DolomiteDolomite.

Fly Ash,,

Fly Ash,,

Fly Ash.. Mica

Silica Silica

Silica

• Average of two specimens.

- One specimen only. — Specimens have not progressed to this failure level after 200 months of exposure. T Tab torn off.

additives, the thicker films are performing better and

the asphalts are tending to fall in the same order of

durability. It is also apparent, with one exception,

that coatings with higher concentrations of blue

black slate are deteriorating more slowly than those

with lower concentrations.

For materials with other than those with platelike particle shapes, the response to mineral additives cannot be discussed in general terms [3]. The

other additives used tended to have blocky to spherical shapes; their performances were varied

in the three asphalts.

Fly ash was the next best performer in that it increased the durability of some coatings as much

as 170 percent and in no instance were coatings

containing fly ash less durable than the asphalt with

which they were made. The higher concentrations

again produced the best performers and the thicker

films lasted longer than the corresponding thinner

ones. Most of the IN'Iid-Continent coatings with fly

Table 8.

Material Coefficient of

linear expansion

Temperature

Range

Source

°c-' °c

Asphalt saturant 6.1 X 10-< 15-60 (7) .\sphalt coatins 5.9 X 10-< 15-60 (7) Petroleum asphalt and fluxes 6.3-6.8 X 10-J 0-230 ' (7) Asphalt

various sources 5.8-6.2 X 10-J (8) Organic felt

machine direction 1.1 X lO-'' ( - 34)-( - 1) (9) Organic felt

cross direction 2.4 X 10-- ( - .34)-{ - 1) ' (9) Aluminum alloys 2.4-2.6 X 10-5 ' (10)

' Converted to metric system.

ash have not failed. The Venezuela coatings 25 mils

thick with 50 and 60 percent fly ash are just beginning to fail, and the California-fly ash coatings have

all failed in 1.1 to 1.5 times the durabilitj^ of the
California asphalt without additives. Thus, the

pattern established by the unstabilized asphalts has

been carried through to the coatings containing fly ash.The effects of clay, dolomite, and silica on the

durability of the smooth-surface specimens were more variable than those of blue black slate, fly ash,

and mica. The silica was most beneficial in the California asphalt, for it increased its durability (25

percent coating spalled) as much as 80 percent. In

all instances it increased the durability by at least 10 percent. Similarly, in the Mid-Continent asphalt

it also increased the durability of the asphalt by at

least 10 percent; the 25-mil coatings with 50 and 60

percent silica have not failed after 200 months, or a

15 percent greater time than the straight asphalt

specimens. The specimens made from the ^'^enezuela asphalt-silica system again were in between those

with Mid-Continent and California asphalts, but

the inprovement in durability by the silica was not

as consistent as in the other two asphalt systems.

Three of the coatings performed only as well as the

asphalt alone, one not quite as well, one a little better, and the one with 60 percent silica 25 mils

thick is still performing well after 200 months.

In only a few combinations containing clay or dolomite were improvements in durability of more

than 20 percent observed. Fifty percent clay in- creased the durability of the California asphalt in both thicknesses by 60 percent. Fifty percent dolomite improved the thin films of both Mid-Continent

and Venezuela asphalt by 30 percent. However, the

other combinations performed within 20 percent

of the dui'ability of the straight asphalts.

Thus, in summary, the Mid-Continent asphalt was more durable than the Venezuela asphalt, which was more durable than the California asphalt. The

mineral additives either improved the durability

or had little effect. Mica and blue black slate always

improved the durability of the three asphalts. Fly

ash, silica, dolomite, and clay improved the durability to a lesser extent and only in specific combinations of composition and coatings thickness.

Figure 3 is a photograph of some of the specimens

made with Mid-Continent asphalt after 163^ years

of exposure. The test specimens are the five in each

column under the identification tags, as identified

in figure 3. The variation of performance with composition

and coating thickness is evident in this photograph.

5.2. Granule-Surfaced, Felt-Base Specimens

Prior to exposure, samples of all of the granulesurfaced specimens were subjected to granule adhesion tests. The procedure used was ARIB Index

No. 1.119 [10], using the electrically operated equipment. As recommended in the procedure, the average

weight loss for 10 2- X 10-in specimens when

abraded dry must be in the range of 0.2 to 0.7 g. The only composition that produced specimens that

did not fall A\ithin this range was 60 percent blue

black slate in Venezuela asphalt. A second set of specimens was made, but it also did not pass the

test. Both sets of specimens were exposed and both

experienced large losses of granules early during

their exposure. The California specimens containing

clay passed the test marginally. They, also, lost some granules early during exposure. However, none

of these .specimens has failed by the established

criteria. Figures -1 and 5 are photographs of California and

Venezuela specimens after 15 years of exposure. The

unstabilized asphalt coatings show noticeable losses of granules and cracking of the coatings. Cracking

of the coatings is also evident in the California

coatings containing clay. However, all of the granule-surfaced specimens are still performing well

after 15 years and should give many more years of protection from the weather.

6. Correlation With Exposures in Accelerated Weathering Machine

Because most asphalt-prepared roofing is exposed

as granule-surfaced material, the ultimate correlation

must be between the granule-surfaced specimens

exposed outdoors and the specimens exposed in the

accelerated weathering test. Because none of the

granule-surfaced specimens has failed by any of the

established criteria for failure, a discussion of correlation would be meaningless. However, many

of the smooth-surface, felt-base specimens have

failed. While no quantitative correlation can be

made until more specimens fail, certain parallels can be seen in figure 6 between the performances of these specimens and their corresponding aluminumbase specimens exposed in the w eatherometer. The

dots represent the average durability of four speci- mens on aluminum panels exposed in the weatherometers and the bars represent the average durability

of two felt-base specimens exposed outdoors.

Based on those specimens exposed outdoors that

have failed, it is quite apparent that many of the

findings in the weatherometer test [3] can be cor- related with the exposures outdoors.

The California asphalt (Asphalt I in reference

[3]) produced the least durable specimens. The

Venezuela asphalt (Asphalt III in ref. [3] produced

the next more durable specimens, and the MidContinent asphalt (Asphalt II in ref. [4] )the most

durable specimens. However, for some systems

there was little or no difference in the durabilities

of corresponding coatings made from the latter two

asphalts.

For all three asphalts, mica (shown in tables 6 and 7, but not in fig. 6) made the greatest improvement in performance. Blue-black slate was also

beneficial to all three asphalts. And dolomite, just as in the weatherometer tests, did not appreciably

affect the durability of the three asphalts. On" the

other hand, clay, fly ash, and silica all are performing

10
FiGVRE 3. Smooth-surface, felt-base specimens after 16]/2 years of exposure '

Column 1 Column 2 Column 3

Coating composition Thickness Coating composition Thickness Coating composition Thickness

mils mils mih 35% Mica 25 60% Fly Ash 25 60% Fly Ash 25 60% Blue Black Slate ^ 15 35% Fly Ash = 15 50% Fly Ash 15 60% Blue Black Slate 15 35% Fly Ash 15 50% I'ly Asli 15 60% Blue Black Slate 25 35% Fly Ash 25 50% Fly Ash 25 60% Blue Black Slate 25 35% Fly Ash 25 50% Fly Ash 25

' Mid-Continent Asphalt.

* Tabs partially torn off.
Fir.i'RE 4. Crraniile-surfaced, felt-base Venezuela specimens after lo years of exposure

(Initial granule coverage approximately 25 lb/100 sq ft (1.22 kg/m ))

Column 1 Column 2 Column 3

Composition Coating

thickness Composition Coating

thickness Composition Coatingthickness

mils mils mils 60% Blue Black Slate 25 50%, Blue Black Slate 25 35% Florida Clay 25 60% Blue Black Slate 25 50% Blue Black Slate 25 35% Florida Clay 25 35% Blue Black Slate 25 35% Blue Black Slate 25 60% Blue Black Slate 25 35% Blue Black Slate 25 357o Blue Black Slate 25 60% Blue Black Slate 25

12
Fiox'RE 5. Granule-surfaced, felt-base California specimens after 15 years of exposure

(Initial granule coverage approximately 25 lb/100 srj ft (1.22 l;g/m ' ))

Column 1 Column 2 Column 3

Composition Coating Composition Coating Composition Coating

thickness thickness thickness

mils mils mi's 60% Dolomite 25 100% Asphalt 25 100% Asphalt 45 50% Dolomite 25 50% Blue Black Slate 25 100% Asphalt 45 50% Dolomite 25 50%, Blue Black Slate 25 100%, Asphalt 25 35% Dolomite 25 35% Blue Black Slate 25 60% Blue Black Slate 25 35% Dolomite 25 35% Blue Black Slate 25 60% Blue Black Slate 25

13
200

100

^ tu 300

200

100

300

2 00

100

CALIFORNIA

CO CO AY AY _i _] 1 _] CJ o

m as _i _i o O 1 O < < < _l _] CO QD as o o Q Q 1 u. (7) </) &^

in o o

^°

If) ^

o if) g o Jl 5^O O f) b

ro in CD rO tn rO If) CD rO If) CD rO If)

MID-CONTINENT

VENEZUELA

better than anticipated from the results of the

weatherometer tests. Whereas, in a few of these

systems in the weatherometers the coatings with

additives were 20 percent less durable than their

corresponding straight asphalt coatings, none exposed

outdoors was less durable than its corresponding

asphalt coating. In the extreme cases, such as 60

percent silica in the 15 mil coatings of all three

asphalts, the specimens exposed outdoors were more

durable than the corresponding straight asphalt

specimens and the specimens in the weatherometers

were roughly half as durable. Thus, where the results of the weatherometer tests have not corresponded

with those obtained with the exposure outdoors,

they have been on the conservative side. The 25-mil thick coatings were more durable than

the 15-mil coatings of the same mixes, but in many

instances not 40 percent more durable. Both of these conditions were also apparent in the results of the weatherometer tests.

Figure 6. Durability of smooth-surface specimens. The outdoor exposures are represented by bars and the Aveatherometer exposures by dots. Where there are no tops on tlie bars, the specimens have

not failed after 200 months of exposure.

7. Conclusions

After 16 and a half years of exposure of smoothsurface and granule-surfaced roofing in Washington,

D.C., the following conclusions can be drawn:

(1) All of the granule-surfaced specimens are per- forming satisfactorily. A few, which failed or were borderline in the granule-loss test, have

lost noticeable (}uantities of granules during

exposure.

(2) Of the smooth-surface specimens, those with

35 percent mica and 35, 50, and 60 percent

blue black slate in all three asphalts have

consistently outperformed the corresponding

asphalt specimens without additives. The

systems containing fly ash, dolomite, clay,

and silica gave variable performances; each

combination must be considered separately.

(3) The thicker coatings are outperforming the

thinner coatings.

(4) There were differences in durability among

the specimens made with the three asphalts,

with the Mid-Continent asphalt being the

most durable and the California the least. When mineral additives were mixed with the

asphalts, corresponding differences in durability were observed.

(5) Based on the smooth-surface specimens, the

results in the weatherometer tests in most

instances predicted the relative durabilities of the coating. Where the weatherometers

were different, the difference was in the conservative direction. This work was sponsored by the Asphalt Roofing

Manufacturers Association at the National Bureau

of Standards. The author is grateful to the members

of the Research Committee for their help in designing and monitoring this program and to William H.

Appleton, Robert F. Jackson, John Marchi,

Shigeru Ishihara, John P. Falzone, Jefferson C. Weeks, Thomas R. Davis, Royce E. Stine, and

Thomas Crowe for their help in perparing the

exposure specimens and making the periodic inspections during 16% years of exposure. The author

wishes to express his gratitude, also, to the members

of the staff of the National Bureau of Standards

who helped make this work possible.

14
I

8, References

|3I

|4|

Greenfeld, S. H., A method of prepaiinfi unifurm

films of iHtumim.us materials, ASTM Bui. 193, 50

(1953). Adopted as ASTM Standard Method D

1669-62 and USA Standard A 109.40 - 1965. Greenfeld, S. H., Effects of thermal shock on the

durability of asphalt coatings under accelerated

test, ASTM Bui. 193, 46 (1953). Greenfeld, S. H., Effects of Mineral Additives on the Durability of Coating-Grade Roofing Asphalts, NBS

Building Materials and Structures Report 147, (Sept. 1956). ASTM D 225-65, Asphalt Shingles Sui-faced with Mineral Granules.

[5] Pfeilfer, J. P., The P)'((perfies of Ashpallic liilumen,

pp. 157-15S (I'llsevier Publishing ('o., Xew V'ork, 1950).

|61 Abraham, H., Asphalts and Allied Substances, 6tli ed.,

4, pp. 163-169, (D. Van Xostrand Co., Xew York,

1962).

|7| Hoiberg. A., IJituminous Materials 1, 47 (Interscience

Publishers, Xew York, 1964).

|S| Cullen, W. C, Effect of thermal shrinkage on built-u|)

roofing, XBS Monograph 89 (1965).

|9] Handbook of Physics and Chemistry, 42d edition, 1528, (Chemical Rubber Publishing" Co., 1960).

10] Manual of Test Procedures for Roofing Granules,

Asphalt Roofing Industry Bureau, (1956).

15

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Announcement of New Publications in

Building Science Series

Superintendent of Documents,

Government Printing Office,

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Dear Sir: Please add my name to the announcement list of new publications to be

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(Notifipation key N-339)
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