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Mathey, Robert G/Investigation of the co QC100 .U56 NO.86-3387 1986 V19 C.1 NBS-P Investigation of the Corrosion of

Aluminum Standing-Seam

Roofing at an Army Facility

Robert G. Mathey

U S. DEPARTMENT OF COMMERCE

National Bureau of Standards

National Engineering Laboratory

Center for Building Technology

Gaithersburg, MD 20899

June 1 986

Prepared for: U.S. Army Corps of Engineers

Construction Engineering Research Laboratory

P.O. Box 4005

Champaign, IL 61820

and

Defense Logistics Agency

Installations Division

eron Station

100 rndria, VA 22314

- U 5 6

86-3387

1986

C. 2

NBS RESEARCH

INFORMATION CENTER NBSIR 86-3387

INVESTIGATION OF THE CORROSION OF

ALUMINUM STANDING-SEAM

ROOFING AT AN ARMY FACILITY

Robert G. Mathey

U.S. DEPARTMENT OF COMMERCE

National Bureau of Standards

National Engineering Laboratory

Center for Building Technology

Gaithersburg, MD 20899

June 1 986

Prepared for: U.S. Army Corps of Engineers

Construction Engineering Research Laboratory

P.O. Box 4005

Champaign, IL 61820

and

Defense Logistics Agency

Installations Division

Cameron Station

Alexandria, VA 22314

U.S. DEPARTMENT OF COMMERCE, Malcolm Baldrige, Secretary

NATIONAL BUREAU OF STANDARDS. Ernest Ambler. Director
.

.

'
TABLE OF CONTENTS

Page

LIST OF TABLES iv

LIST OF FIGURES iv

ABSTRACT v

1. INTRODUCTION 1

1 . 1 Background 1 1.2 Objective and Scope 3

2. OUTDOOR EXPOSURE OF ALUMINUM ROOFING SAMPLES 4

2.1 Description and Properties of Samples 4

2.2 Exposure Tests 4

3. LABORATORY MEASUREMENTS AND OBSERVATIONS 7

3.1 Mass Loss 7 3.2 Microscopic Observations 9

4. SUMMARY 12

5. REFERENCES 13

6. ACKNOWLEDGMENTS 14

iii
LIST OF TABLES

Page

Table 1. Mass Loss of Aluminum Roofing Samples 8

LIST OF FIGURES

Figure 1. Aluminum roofing samples mounted on exposure test rack 5

Figure 2. Exposure test rack attached to fire wall between sections of

roofing 5

Figure 3. Exposed (left) and control (right) specimens 10

Figure 4. Photomicrograph (lOx) of portion of surface area of exposed

sample 11

Figure 5. Photomicrograph (lOx) of portion of surface area of control

sample 11

iv
ABSTRACT

An investigation was conducted to determine the extent of corrosion of an

aluminum standing-seam roofing system exposed to weathering over a period of

nearly three years. The aluminum roofing was installed on three large warehouses at an Army facility in Columbus, Ohio. A high performance elastomeric

sealant was used in forming the standing seams of the roofing system. The

roof slope, about 5 percent, was less than that usually recommended for

unsoldered standing-seam roofing. The roofs were located in a region having a

high level of acid rain.

In this preliminary study, small scale samples of the same material as the

aluminum roofing were exposed on a rack mounted on the roof of one of the

warehouses. The extent of corrosion of the roofing system was determined from

measurements of mass and observations of the exposed small scale aluminum

roofing samples. The change in mass of the exposed samples was compared to

that of the control samples. The average rate of mass loss was calculated to

be 0.038 mg/dm^'day. Low power microscopic observations to determine

the surface condition of the exposed samples after nearly three years exposure

indicated a loss of gloss, an increase in surface roughness, and many small

dark spots. At the dark spots, which were thought to be incipient corrosion,

there was essentially no pitting.

Keywords: Aluminum roofing; corrosion; outdoor exposure; roofing; weathering

v

1. INTRODUCTION

1 . 1 Background

In July 1981, the Defense Logistics Agency (DLA) requested that the National

Bureau of Standards (NBS) and the U.S. Army Construction Engineering Research

Laboratory (CERL) provide technical assistance for a project involving the

installation of aluminum standing-seam roofing on three large warehouses at the

Defense Construction Supply Center (DCSC) in Columbus, Ohio. Both NBS and CERL

were given copies of the plans and specifications for review. At a preconstruction

conference held at DCSC in October 1981, comments from both agencies and details

regarding the aluminum roofing systems were discussed.

Aluminum standing-seam roofing was specified to replace built-up bituminous

roofing on the three warehouses which were each about 160 ft (48.8 m) wide and

1541 ft (470 m) long. Firewalls divided the roof into approximately 11 equal

sections, each about 138 ft (42 m) long. The centrally located ridge of the

roof extended the length of the building. The roof slope from ridge to eaves

was about 5/8 in. per foot (50 mm/m). The aluminum panels used in the roofing

system were 1 ft (305 mm) wide, 0.032 in (0.81 mm) thick, and 80 ft (24 m)

long. They were rolled-formed with a 2-1/2 in. (64 mm) high rib on each side

and two low profile equally spaced intermediate ribs. A strip type sealant was

used in forming the standing seam which joined two panels together. The purpose

of the sealant was to make the seam watertight. Construction of the aluminum

standing-seam roofing at DCSC is described in CERL interim report M-336 [ 1

] *

.

* Numbers in brackets indicate references listed in Section 5.

1
One concern with the aluminum roofing system was the relatively low slope of

the roof. The Department of Defense Manual on Maintenance and Repair of Roofs

states that unsoldered standing-seam roofing should be used with slopes of

3 in. per foot (250 mm/m) or geater [2], In addition, the standing-seam method

for metal (unsoldered seams) roofing illustrated in the Architectural Sheet

Metal Manual [3] is recommended for roofs having a slope of 3 in. per foot

(250 mm/m) or greater. It is noted that the manufacturer of the aluminum

roofing system recommended a minimum slope of 1/2 in. per foot (40 mm/m).

Because of the relatively low slope of the aluminum roofs and also because

Columbus, Ohio is located in an area having a high level of acid rain, DLA

requested that NBS conduct a preliminary assessment of the performance of the

aluminum roofing with regard to corrosion.

In carrying out the DLA aluminum roofing project, CERL had the overall

responsibility to determine the behavior of the aluminum standing-seam roofing

system over two annual cycles and to evaluate its capacity for long-term,

trouble-free performance. The CERL report [1] documents the construction and

instrumentation of the roof system for one of the three DCSC warehouses on

which it was installed. Specific tasks assigned to CERL were to observe and

monitor the construction of the roofing on the warehouses, to observe condition

and performance of the roofing at periodic intervals, to measure deformation

and movement of roof panels at appropriate locations, to measure temperatures

of the metal and existing built-up roofing, and analyze and evaluate the results

of the observations and measurements. The results of the analysis and

evaluation will be documented by CERL in a final report.

2
1.2 OBJECTIVE AND SCOPE

The objective of this study was to conduct a preliminary assessment of the

corrosion of the aluminum roofing system over a three year period using samples

of the same roofing material that were exposed on a rack mounted on the roof of

one of the warehouses. The change in mass of the exposed samples was measured

and low power microscopic observations were conducted to determine the surface

condition and extent of corrosion.

3
2. OUTDOOR EXPOSURE OF ALUMINUM ROOFING SAMPLES

2.1 DESCRIPTION AND PROPERTIES OF SAMPLES

Fourteen pieces, each about 16 in. (40 cm) long, of the 1 ft (30 cm) wide

aluminum roofing panels were obtained and used to prepare samples for the

exposure tests. These 16 in. (40 cm) long pieces were cut from the 80 ft

(24 m) long panels at ventilator locations on the roof. Four samples for

exposure tests were prepared from each of the 16 in. (40 cm) length of panel.

The exposure samples were approximately 4x6 in. (10 x 15 cm) and had a low

profile rib in the center that extended the length of the sample. Figures 1

and 2 show the sample configuration; figure 2 also shows a large area of the

aluminum roofing system.

The aluminum panels has a nominal thickness of 0.032 in. (0.81 mm) and a textured

finish described by the manufacturer as "stucco embossed." The average density

of the aluminum roofing panels determined from tests of 42 specimens was

171.12 lb/ft^ (2.74 g/cm^). The manufacturer reported the panels to be corrosion

resistant Alclad 3004* and they were furnished in mill finish.

2.2 EXPOSURE TESTS

Thirty samples were mounted on a rack and exposed at the same angle as the

roofing. Figures 1 and 2 show the exposure rack mounted on the firewall of one

of the warehouses at DCSC. The exposure rack faced west.

Each of the aluminum roofing samples was supported by six porcelain Insulators.

The method of support allowed for expansion and contraction of the samples

* This description was used to identify the aluminum roofing material, it does

not represent an endorsement or disapproval by the National Bureau of Standards.

4
Figure 1. Aluminum roofing samples mounted on exposure test rack

Figure 2. Exposure test rack attached to fire wall between sections of

roofing

5
without introducing stress in them. The samples were not in contact with any

other material. Round slots in the insulators where the samples were supported

(figure 2) allowed some movement of the samples and still maintained their

adequate attachment. The insulators were held in place by screws attached to

the wood rack. The distance between the samples and the wood rack was about

7/8 in. (22 mm)

.

The cleaning of the samples for their initial weighing and exposure consisted

of soaking them in acetone for 10 to 30 minutes and rinsing them in ethyl

alcohol. It is noted that this initial cleaning was found to be unsatisfactory.

Because of this, the average rate of mass loss of the exposed samples was

determined from a second exposure period. The samples for exposure were

chemically cleaned before and after the second exposure period. Of the 56

samples included in the tests, 30 were selected for exposure and 26 were used

as control samples. The control samples were stored in the laboratory in

polyethylene bags and protected from light, moisture, and sources of

contamination.

After 20b days of exposure (first exposure) the samples were returned to the

laboratory, and both the exposed and control samples were weighed, chemical Ly

cleaned, following the methods in ASTM Gl-81 [4], and weighed again. The

exposure surfaces, or tops, of the samples were subjected to low power microscopic examination. The samples were then reinstalled on the exposure rack

and exposed for 797 days (second exposure). After this second exposure they

were returned to the laboratory and weighed, chemically cleaned, and weighed

again. They were also examined visually and by using a light microscope

at lOx.

6
3.

LABORATORY MEASUREMENTS AND OBSERVATIONS

3.1 MASS LOSS

The samples were initially installed for exposure at DCSC on August 10, 1982,

and removed for laboratory tests and observations on March 3, 1983 (first

exposure). The samples were reinstalled on the exposure rack at DCSC on

May 23, 1983, and removed for the second time for laboratory tests on

August 1, 1985 (second exposure).

The samples were weighed before and after cleaning prior to the initial exposure

and for each of the two times that they were returned to the laboratory for

testing. The initial cleaning consisted of soaking them in acetone for 10 to

20 minutes and rinsing them in ethyl alcohol. When the samples were returned

to the laboratory after exposure at DCSC they were chemically cleaned essentially

as described by ASTM Gl-81 for aluminum alloys [4], The chemical cleaning of

both the exposed and control samples was conducted as follows:

step

1.

Samples were dipped in the following mixture:

Chromic acid (CrOg)

Phosphoric acid (H3 PO4 , sp gr 1.69)

Water to make

Temperature of the mixture

Time in the mixture

20 g

50 ml

1 liter

80° C ( 176° F)

6 to 7 minutes

2. Rinse sample in distilled water 6 to 7 minutes

3. Scrub specimens lightly with a bristle brush under running water

4. Rinse specimens in distilled water 6 to 7 minutes

5. Place specimens in methyl alcohol 6 to 7 minutes

After cleaning and weighing the samples after their second exposure (May 23,

1983 to August 1, 1985) at DCSC, 4 exposed and 4 control samples were cleaned

7
again as described above and then weighed. The reason for this second cleaning

of these 8 samples was to determine the effect of the cleaning on mass loss.

The loss of mass of the aluminum roofing samples after each of the two exposure

periods is given in table 1. The average value of the mass of the control and

exposed samples is given for the samples after the first period of exposure and

chemical cleaning. It can be seen from the mass loss data in table 1 that

there was considerably more loss of mass of the control specimens after the

shorter, first exposure, period than for the longer, second exposure, period.

This may possibly be due to the initial cleaning of the specimens (acetone and

alcohol) not removing as much adhered material from the samples as compared to

the chemical cleaning procedure. The estimate of mass loss due to exposure

reported herein is therefore based on the second exposure period since the

samples were chemically cleaned before and after this exposure period.

Table 1. Mass Loss of Aluminum Roofing Samples

Type of

Sample

Mass of Samples After

First Exposure!/ (g)

Mass Loss After

First Exposure!/ (g)

Mass Loss After

Second Exposure!/ (g)

Hi aA/ Hi aA/ oA/

Control 35.7280 0.4878 0.0055 0.0009 0.0012 0.0003

Exposed 35.9003 0.5554 0.0188 0.0035 0.0485 0.0091

1/ First exposure period was August 10, 1982 to March 28, 1983 (206 days).

!/ Second exposure period was May 28, 1983 to August 1 , 1985 (797 days).

A/ Average value of 30 exposed and 26 control samples.

A/ Standard deviation.

8
The surface area of the 4x6 in. (10 x 15 cm) samples is estimated to be

25.14 in. ^ (0.016 m^) t since the samples have a low profile rib that extends

along the center of the longitudinal direction. The average effective width

of the samples, including the rib, was determined to be 4.19 in. (10.6 cm) from

measurements of six samples. Using data from the second exposure period (X =

0.0485 g) the average rate of mass loss was calculated to be 0.038 mg/dm2»day.

It was noted earlier that after cleaning and weighing the samples after the

second exposure, 4 exposed and 4 control samples were again chemically cleaned

and weighed to determine the effect of cleaning on mass loss. There was

essentially no change in mass of the control samples after the second chemical

cleaning of the samples from the second exposure, however, for the exposed

samples the mass loss averaged 0.0016 g.

3.2 MICROSCOPIC EXAMINATIONS

ASTM Standards Gl-81 [4] and G48-76 [5] were considered in examining and

determining the extent of corrosion. It can be seen from the photograph (figure

3) of a typical exposed and control sample, that the exposed sample on the left

has less gloss and greater surface roughness than the control sample on the right.

Also, it can be seen that the surface of the exposed sample contains many small

dark spots. It is thought that these dark spots represent incipient corrosion.

Photomicrographs (lOx) of a portion of the surfaces of typical exposed and

control samples after the second exposure are presented in figures 4 and 5,

respectively. The dark spots on the exposed sample seen in figure 3 are shown

in more detail in figure 4. At the dark spots (incipient corrosion) there was

essentially no pitting. The total time of outdoor exposure at DCSC of the

exposed samples was 33 months and 26 days.

9
10

Figure

3.

Exposed

(left)

and

control

(right)

specimens
Figure 4.

Figure 5

Photomicrograph (lOx) of portion of surface area of exposed sample

. Photomicrograph (lOx) of portion of surface area of control sample

11
4 . SUMMARY

Aluminum roofing samples, 4x6 in. (10 x 15 cm) in size were exposed to outdoor

weathering for nearly three years on a rack mounted on one of the roofs of the

buildings at the Defense Construction Supply Center (DCSC) in Columbus, Ohio that

were reroofed with an aluminum standing-seam roofing system. The samples were

of the same material as the roofing system. The objective of the study was to

conduct a preliminary assessment of the extent of corrosion of the aluminum

roofing over a period of nearly three years. Changes in mass of the exposed

samples were measured and the average rate of corrosion was calculated to be

0.038 mg/dm^'day. Photographs and photomicrographs of exposed and control

samples indicated a loss of gloss, increased surface roughness, and dark spots

(incipient corrosion) at many locations on the surface due to the outdoor

exposure. Observations of the surface of the exposed samples indicated that

essentially no pitting occurred.

12
5. REFERENCES

1. Rosenfield, Myer J. , "Construction of Aluminum Standing-Seam Roofing at an

Army Facility," U.S. Army Corps of Engineers Construction Engineering

Laboratory Interim Report M-336 , November 1983.

2. "Facilities Engineering Maintenance and Repair of Roofs," Army TM 5-617,

Navy NAVFAC MO-113, Air Force AFM 91-31, and Marine Corps MCO P11014.9,

January 1974.

3. "Architectural Sheet Metal Manual," Sheet Metal and Air Conditioning

Contractors National Association, Inc., Third Edition, Vienna, VA, 1979.

4. "Standard Practice for Preparing, Cleaning, and Evaluating Corrosion Test

Specimens," ASTM Designation Gl-81, 1982 Annual Book of ASTM Standards,

Part 10, American Society for Testing and Materials, Philadelphia, PA.

5. "Standard Recommended Practice for Examination and Evaluation of Pitting

Corrosion," ASTM Designation G48-76 (Reapproval 1980), 1981 Annual Book

of ASTM Standards, Part 10, American Society for Testing and Materials,

Philadelphia, PA.

13
6 . ACKNOWLEDGMENTS

This study was sponsored by the U.S. Army Corps of Engineers Construction

Engineering Research Laboratory and the Defense Logistics Agency. Special

thanks and appreciation are expressed to Myer J. Rosenfield, CERL, Marvin U.

Dubois, DLA, and William J. Smith, DCSC, for their assistance in carrying out

this study.

14
NBS-114A (REV. 2-80

U.S. DEPT. OF COMM.

BIBLIOGRAPHIC DATA

SHEET (See i nstruction s)

1. PUBLICATION OR

REPORT NO.

NBSIR 86-3387

2. Performing Organ. Report No,

746

3. Publication Date

MAY 1986

4. TITLE AND SUBTITLE

Investigation of The Corrosion of Aluminum Standing-Seam Roofing at An Army Facility

5. mm. Mathey

6. PERFORMING ORGANIZATION (If joint or other than N BS, see in struction s)

national bureau of standards

DEPARTMENT OF COMMERCE

WASHINGTON, D.C. 20234

7. Contract/Grant No.

8 . Type of Report & Period Covered

9.

SPONSORING ORGANIZATION NAME AND COMPLETE ADDRESS (Street. City. State. ZIP)

U.S. Army Corps of Engineers Defense Logistics Agency

Construction Engineering Research Laboratory Installations Division

P.O. Box 4005 Cameron Station

Champaign, IL 61820 Alexandria, VA 22314

10.

SUPPLEMENTARY NOTES

] Document describes a computer program; SF-185, FIPS Software Summary, is attached.

11.

ABSTRACT (A 200-word or less factual summary of most significant information . If document includes a significant

bibliography or literature survey, mention it here) An investigation was conducted to determine the extent of corrosion of an aluminum

standing-seam roofing system exposed to weathering over a period of nearly three year

The aluminum roofing was installed on three large warehouses at an Army facility in

Columbus, Ohio. A high performance elastomeric sealant was used in forming the stand

ing seams of the roofing system. The roof slope, about 5 percent, was less than that

usually recommended for unsoldered standing-seam roofing. The roofs were located in

region having a high level of acid rain.

In this preliminary study small scale samples of the same material as the aluminum

roofing were exposed on a rack mounted on the roof of one of the warehouses. The extent

of corrosion of the roofing system was determined from measurements of mass and

observations of the exposed small scale aluminum roofing samples. The change in mass

of the exposed samples was compared to that of the control samples. The average rate

of mass loss was calculated to be 0.038 mg/dm^.day. Low power microscopic observations to determine the surface condition of the exposed samples after nearly three

years exposure indicated a loss of gloss, an increase in surface roughness, and

many small dark spots. At the dark spots, which were thought to be incipient corrosion, there was essentially no pitting.

12.

KEY WORDS (Six to twelve entries; alphabetical order; capitalize only proper names; and separate key words by semicolon s) Aluminum roofing; corrosion; outdoor exposure; roofing; weathering.

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