NATIONAL BUREAU OF STANDARDS REPORT

4998

A STUDY OP THE PROPERTIES OF THE

U.S. CAPITOL SANDSTONE

fey

Arthur Ho ckTnan and D. W. Kessler

Report to the

Architect of the Capitol

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 at its headquarters in Washington,

D. C., and its major field laboratories in Boulder, Colorado, is suggested in the following listing of

the divisions and sections engaged in technical work. In general, each section carries out spe- cialized research, development, and engineering in the field indicated by its title. A brief

description of the activities, and of the resultant reports and publications, appears on the

inside back cover of this report.

WASHINGTON, D. C.

Electricity and Electronics. Resistance and Reactance. Electron Tubes. Electrical Instruments. Magnetic Measurements. Dielectrics. Engineering Electronics. Electronic Instrumentation.

Electrochemistry.

Optics and Metrology. Photometry and Colorimetry. Optical Instruments. Photographic

Technology. Length. Engineering Metrology.

Heat and Power. Temperature Physics. Thermodynamics. Cryogenic Physics. Rheology

and Lubrication. Engine Fuels.

Atomic and Radiation Physics. Spectroscopy. Radiometry. Mass Spectrometry. Solid State Physics. Electron Physics. Atomic Physics. Nuclear Physics. Radioactivity. X-rays. Betatron. Nucleonic Instrumentation. Radiological Equipment. AEC Radiation Instruments. Chemistry. Organic Coatings. Surface Chemistry. Organic Chemistry. Analytical Chemistry.

Inorganic Chemistry. Electrodeposition. Gas Chemistry. Physical Chemistry. Thermochemistry. Spectrochemistry. Pure Substances.

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

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

Organic and Fibrous Materials. Rubber. Textiles. Paper. Leather. Testing and Specifications. Polymer Structure. Organic Plastics. Dental Research.

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

Metals Physics.

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

Materials. Constitution and Microstructure.

Building Technology. Structural Engineering. Fire Protection. Heating and Air Conditioning. Floor, Roof, and Wall Coverings. Codes and Specifications.

Applied Mathematics. Numerical Analysis. Computation. Statistical Engineering. Mathematical Physics.

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

Circuitry. Digital Systems. Analogue Systems. Application Engineering.

• Office of Basic Instrumentation • Office of Weights and Measures

BOULDER, COLORADO

Cryogenic Engineering. Cryogenic Equipment. Cryogenic Processes. Properties of Materials.

Gas Liquefaction.

Radio Propagation Physics. Upper Atmosphere Research. Ionospheric Research. Regular

Propagation Services. Sun-Earth Relationships.

Radio Propagation Engineering. Data Reduction Instrumentation. Modulation Systems.

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

Systems Application Engineering.

Radio Standards. Radio Frequencies. Microwave Frequencies. High Frequency Electrical

Standards. Radio Broadcast Service. High Frequency Impedance Standards. Calibration

Center. Microwave Physics. Microwave Circuit Standards.
NATIONAL BUREAU OF STANDARDS REPORT

NBS PROJECT NBS REPORT

1001-30-4810 January 8, 1957 4998

A STUDY OP THE PROPERTIES OF THE

U.S. CAPITOL SANDSTONE

by

Arthur Hockman and D. W. Kessler

To

Architect of the Capitol

IMPORTANT NOTICE

NATIONAL BUREAU OF S intended for use within th< to additional evaluation anr

listing of this Report, eithe the Office of the Director, I however, by the Governmer

to reproduce additional cof

Approved for public release by the

Director of the National Institute of

Standards and Technology (NIST)

on October 9, 201 5.

progress accounting documents

ormally published it is subjected

;, reproduction, or open-literature

ssion is obtained in writing from Such permission is not needed,

1 prepared if that agency wishes

<NBS>

U. S. DEPARTMENT OF COMMERCE

NATIONAL BUREAU OF STANDARDS
. • * . '
Contents

Page

Abstract 1

1+ Introduction 2

2. Physical Tests 3

2.1 Compressive strength 3

2.1.1 Test specimens and procedure 3

2.1.2 Test results 4

2.2 Flexural strength 4

2.2.1 Test specimens and procedure 4

2.2.2 Test results 4

2.3 Shearing strength 6

2.3.1 Test specimens and procedure 6

2.3.2 Test results 7

2.4 Abrasive hardness 7

2. 4-1 Test specimens and procedure 7

2„4.2 Test results 8

2.5 Toughness 9

2.5.1 Test specimens and procedure 9

2.5.2 Test results 9

2.6 Absorption 10

2.6.1 Test specimens and procedure 10

2.6.2 Test results 10

2*7 Bulk specific gravity 11

2.7.1 Test specimens and procedure 11

2.7.2 Test results 12

2.8 True specific gravity and porosity 13

2.8.1 Test specimens and procedure 13

2.8.2 Test results . 13

2.9 Elasticity by sonic method l4

2.9.1 Test specimens and procedure l4

2.9.2 Test results ll|

2.10 Capillarity properties 16

2.10.1 Test specimens and procedure 16

2.10.2 Test results 16

2.11 Effects of freezing and thawing 18

2.11.1 Test specimens and procedure 18

2.11.2 Test results 18

2.12 Petrographic analysis 21

2.13 Chemical analysis 23

3. Studies on Effect of Paint As a Preservative 25

3.1 Observations on the Capitol Building 25

3.2 Observations on the White House 25

3.3 Columns of the U.S. Treasury Building 25

3.4 Bid Patent Office Building 26

3.5 Bulfinch gatehouses 26

3.6 Capitol gateposts 26

3.7 Relation of paint to spalling 26

4. Re commendations 27

5. Summary 27
.

'
A STUDY OF THE PROPERTIES OF THE

U.S. CAPITOL SANDSTONE

'by

Arthur Hockman and D. W. Kessler-::-

Abstract

Various physical tests were made on nine samples of

Aquia Creek sandstone cored out of the exterior walls

of the original portion of the U.S. Capitol c One of

the purposes of the study was to determine If the

sandstone had been affected by weathering to depths

greater than the depths of the spalling. The physical tests were supplemented by chemical analysis . on

3 specimens taken from 3 different depths of one core,

and by petrographic studies on several other cores.

Observations were made on a few structures also of

Aquia Creek sandstone, to determine if repeated

painting has contributed to the spalling of the

Capitol stone.

The results of the laboratory studies indicate that

much of the exterior sandstone of the Capitol is of

poor quality, but the stone has not been seriously

affected by weathering to depths greater than l/2

inch. If this depth is removed by means of suitable

tooling, the sandstone should be serviceable for many

more years. However, it will be necessary to continue

painting the stone In order to prevent further erosion of blocks of inferior quality. An alternative

treatment would be to re-face the old walls with a more durable stone.

It is believed that painting has contributed, indirectly, to the spalling now seen on many blocks,

but in general, it has prevented more serious weathering of the poor quality blocks.

^Consultant, Kessler Stone Research Laboratory,

Washington, D.C.
'
1. INTRODUCTION

At the request of the Architect of the Capitol, a study

was made of the properties of the exterior stone (Aquia Creek

sandstone) in the original portion of the United States Capitol«

Three cores of stone taken from the east side of the

Capitol on August 7, 1956, were submitted to this Bureau for

test. Since this group of samples did not afford enough material for all the tests desired, six additional cores were

requested. Three of the additional samples were cored from

the walls on the west side and three from the east side of the

building. A plan drawing of the Capitol was supplied showing

the approximate locations where the nine samples were cored.

The cores were approximately 2 l/l| In. In diameter and

ranged in length from 6 l/2 in. to 12 in. Table 1 gives the

dimensions, date of removal and approximate location of each

core in the building.

Table 1. Sample Cores Tested

ore

r o Length

' in.

Cl ’ 12

C2 t 12

C3 ’ 11

c4 ’ 11

c5 ’ 10 1/2

C6 ’ 12

C7 ’ 9 l/2

c8 ’ 9 1/2

C9 ’ 9 1/2

’ r

f Location in Capitol ! taken ’ t _ — -j — “ ‘ — “ ~ “ ~T

8/7/56 1 Genter steps, south exposure ’

t 1 8-7-56 ’South portico pier, east exposure ’

t t

8-

7-56 ’South central portion, east exposure’

t 1

9-

11-56’ Central portion, west exposure ’

1 t 9-11-56’ Central portion, north exposure ’

? f 9-11-56’ Central portion, west exposure ’

t t 9-11-56’ Southeast portion, east exposure ’

t 1 9-11-56’ Southeast portion, south exposure ’

l ! 9-11-56’East portion, east exposure ’

f t

--The core numbers in table 1 and In the following tables cor

respond to the numbers supplied by the Architect’s Office.

All the samples, except C7 and C8 , were received in sound

condition. Sample C7 was split into two pieces along its long

dimension and C8 was broken into approximately 3 1/2 and 6 in.

2 .
»*

.

'
lengths * However, parts of these broken cores were usable inmany of the tests.

Seven cores were used in the flexural strength tests before they were cut into smaller test specimens for compression,

absorption, specific gravity, etc. Pour cores were cut into

1-in. lengths and then re-cored into smaller specimens, 1 in.

in diameter in order to study the properties of the stone in

relation to the distance from the weathered surface. It was

necessary to reduce the size of some of the samples by recoring them to a smaller diameter (1 3/4 in.) to adapt them

to the test method for sonic modulus of elasticity. The latter cores were also used for capillarity and freezing and

thawing tests. (Figure 1)

In order to obtain some information on the value of paint

as a preservative for Aquia Creek sandstone, studies were made

on the performance of this stone in the U.S. Capitol and other

old Government structures. In this connection, use was made

of some studies made previously on the White House and on the

old columns (now replaced) in the U.S. Treasury building.

This report presents in detail data obtained from physical, chemical and mineralogical tests, with brief descriptions

of the methods and procedures. Standard procedures were followed wherever possible and references to published standards

are given. Conclusions are drawn and appropriate recommendations are made wherever - definite indications are obtained. A

summary Is included to present the main findings in brief

form.

2. PHYSICAL TESTS

2.1 Compressive strength

2.1.1 Test specimens and procedure

Cores Cl, C2, and c5 were cut into 1—in. sections which

were re-cored into smaller cores, 1 in. in diameter for compressive strength and other determinations at various distances from the exposed surface to the back ends of the sample

cores. It was not possible to make such detailed studies on

all the samples, but portions of cores C3, C6, and C8 were

also tested for compressive strength as shown in table 2.

The ends of the test specimens were ground until they

were flat, parallel to each other, and perpendicular to the

side of the cylinder.

3 .

After- the specimens were dried in an oven at 105 deg C

and cooled to room temperature, they were tested in a BaldwinSouthwark 75 , 000-lb capacity hydraulic testing machine. The

load was applied at a rate of 100 lb per sq in. per sec until

failure occurred. Except for the smaller size of the specimen

the test method was essentially the same as the ASTM Standard

C170-50, Compressive Strength of Natural Building Stone.

2.1.2 Test results

The compressive strength, C, of each specimen was calculated as follows:

C = w

A

whe re

,

¥ = total load in lb

A = calculated area of bearing surface in sq in.

Table 2 gives the compressive strengths of the various

specimens cut from sections at different distances from the

painted surface as indicated. Since these test specimens

were cut with their lengths parallel to the lengths of the

original cores, the direction of loading was parallel to the

natural bedding of the stone and therefore the values are

probably somewhat less than the strength of the stone as it

is loaded in the building.

Table 2. Compressive strength

, „ , Distance of specimen from painted surface in inches-x-

’Sam-’ ^ ^

< pie; 1 2 3 4 b 6 7 b 9

1

" ~r TK3-1 psi !! nsT” f "nan t rvai t tici-I f a ? t tvq ? f nsi f rva

- v psi f psi ’ p,si ’ psi ' psi * psi ’ psi ’ psi ’ Cl 1 0 <m 0 0

1

1 0 r- 0 0

I

—

1

10,700’ 11,400’ 0 c, 0 0

1

—

1

10,200’ 10,100’ 9,400*9,500’

t I ! 1 t t ? t t t C2 t 3,400' 2,500’ 3,ooo» 3,600’ 3,000* 3,ooo» f i _ t

*

I I 5 ? t I t t t C3 1 t 4,900’ 6,100’ 6,600’ i 1 --- ’

i I s t I 1 i t t t c5 1 2,200’ 2,300’ 1,600’ 2,000’ 1,800’ 2,000’ 1,900’ 2,000’ — '

t ! 1 1 1 I t t t t C6 t —~ I 1 1 3,000 s 2,900* 2,800

t „„„ t t

t I ? ! I t t T t 1 c8 1 — ’ I 3,500' 2,300’ 3,100’ cm

o-. cm OO 3,5oo> — > It t I I I I I It

-::-The distances from the painted surface given in this and subsequent tables are approximate and represent the distance of the

ends of the specimens furthest from the painted surface.

4 .
'

.

.
The large variation in strength values among the individual

samples obtained in this test gives some information on the variation in quality of the stone. For comparison purposes, the compressive strength of one of the most widely used sandstones from

Amherst, Ohio, averages 9,000 psi; whereas, the average strength

value obtained for all specimens of the Capitol stone tested was

4 , 600 psi. This value is in the range of compressive strengths

for high quality concrete.

There is little indication in the strength tests that the

stone near the painted surface is weathered more than that 8 or

9 in. back from this surface.

2.2 Flexural strength

2.2.1 Test specimens and procedure

Flexural strength tests were made on seven of the nine cores

submitted. These tests were made on the original sample cores

before they were cut up for the other tests, such as compression,

absorption, etc. Two tests were made on each of cores C2 and C3

by loading them off-center on short spans, as shown in figure 2.

In this manner flexural strength values were obtained at various

distances from the painted surface, the closest being 3 in. and

the furthest 8 in., as indicated in table 3»

After the specimens were dried for 24 hr at 10£ deg C and

cooled to room temperature, they were tested in a BaldwinSouthwark 60, 000-lb capacity hydraulic testing machine. The

cylindrical specimen was laid on supporting knife edges with the

bedding of the stone perpendicular to the direction of loading.

The load was applied at approximately 1000 lb per min until

failure occurred. A similar test method Is described In ASTM

Standard 099^52, Modulus of Rupture of Natural Building Stone.

2.2.2 Test results

The modulus of rupture, R, in lb per sq In. of each speci

men was calculated as follows:

whe re

,

R _ 8WL

d3

W - breaking load In lb

L = length of span in in.

d - diameter of the specimen in in.

3 ,

Table 3 gives the flexural strengths (modulus of rupture) of

the seven samples tested*

Table 3« Flexural strength

I

t

» Sample

No.

t 5 t

} Spark ’

f r ?

Distance

fracture

painted

of

from

end

!

t

? Modulus of rupture

t

?

?

f ? in. ? in. ! psi ?

t Cl » 10 8 3

f 1,900 ?

t ? i ! f

t C2 t 9 ? 4

t 1,130 t

? ? ? f 1

T C2 » 6.3 5 8 ? 94o ?

1 f 1 J t

1 C 3

f 6 * 3

T 1 ,890 ?

I ! ! ? V

t C3 ' 5.5 ' 6 1 1,800 f

1 ? J 1 f

1 ck i 9! 3f 360 s

1 t ! f !

T C6 * 10 1 3

1 3k 0

?

t J ? ? !

! C8 » 6 * 3t 830 J

? t ! ! ?

? C9 ' 5-5 1 3

! 1,800 I

1 J ? t ?

The flexural strength values were rather low when compared

with those of most sandstones. For the two cores, C2 and C3s

which were broken at different distances from the painted surface , the results for greater depths were lower than those closer

to the weathered face. Such results may be attributed to natural

variations In the stone. It Is also possible that the stone was

originally laid with the better faces of blocks exposed to the

weather.

2.3 Shearing strength

2.3.1 Test specimens and procedure

Because of the relatively large size of the specimen required for this test and the scarcity of sample material, only

one core (two specimens) was tested for this property.

6 .
'

•

.

,
The specimens were rectangular bars, 5 in. long, 1.6 in.

wide and 1/4 in. deep (figure 1-B) . After the specimens were

dried in an oven at 105 deg C for 24 hr and cooled to room

temperature, they were tested in a Baldwin-Southwark 60, 000-

lb capacity hydraulic testing machine with the aid of the

modified Johnson shear tool. This method Is described In

A STM Standard 0102-36, Shear Testing of Natural Building Stone.

2. 3° 2 Test results

The shearing strength, S, in lb per sq in. was computed

by the formula:

whe re

,

s = JL.

2A

W -- maximum load in lb indicated by the

testing machine

A = area in sq in. of the center section

of the specimen

Table 4 gives the shearing strengths in psi of the two

specimens tested:

Table 4« Shearing strength

t

?

!

t

?

!

I

Sample

No.

c4-i

C4-2

?

f Location in core ,

T 4 in. from painted end

t

* 10 in. from painted end

f

T Shearing

? strength

» psi

' 1+36

!

» 46o

?

!

t

I

II

V

?

A knowledge of the shearing strength of the stone may

be of value in the event that metal anchors are used in facing

the stone with a veneer.

2.4 Abrasive hardness

2.4.I Test specimens and procedure

This property was determined on cores Nos. 5 and 9 y using the standard method for testing the abrasive hardness

of stone as developed at the National Bureau of Standards.

This method usually employs a 2~by 2- by 1-In. rectangular

specimen. However, because of the cylindrical shape of the

sample cores, test specimens were prepared in the form of

disks, 2 l/8 in. in diameter and 1 in. thick (figure 1-C)

.

These were cemented to 2- by 2- by 1/2—in. wooden blocks In

order to adapt them to the testing machine.

\

In this test, the stone specimens are held on a revolving

cast iron disk under a constant pressure of 2 kg (4*4 lb) and

made to revolve for 4 min at half the speed of the grinding

disk. The abrasive is artificial corundum No. 60, which is

fed to the disk at a constant rate. The amount of wear is

determined by weighing the oven-dried specimens before and

after the test.

This method is described in detail In ASTM Standard C24l~

4l, Abrasion Resistance of Stone Subjected to Foot Traffic.

2.4®2 Test results

The abrasive hardness values, (Ha ), were computed by the

formula:

H = 10 (W g + 2,000) G

a 2,000 Wa where

,

W- - the original weight of the specimen

Or = bulk specific gravity

Wa = loss of weight In grams

Table 4 gives the abrasive hardness values (Ha ) of several

specimens cut at various distances from the painted surface of

each of the two samples tested.

Table 4« Abrasive hardness

t f Dis t ance of spe cimen from painted surface , in. 1

’ Sample l- — r

} No. » 1

t 2 i 3 4

? 4

t 6 ? 7

' 8

!

i ? Ha

t Ha

t Ha ' Haj Ha

i Ha

» Ha

’ Ha

f

t t t s t t t ! t

’ c4 1 1.3 i 1.4 ! 1.4 1.2 j 1.2 t 1.3 i 1.2 ? 1.2 T

t t t T i t t T

t C9 ' 6.9 i 6.9 ! 7.2 7.1 t 6.6 ? —

t t

t t T t i t t ! r I

8 .
. >

.
The results obtained on sample C5 indicate a very low

resistance to abrasion, whereas, the results obtained on sample G 9 are equal to values obtained on good quality building

stone. Tests made on specimens cut at different distances

from the paint show no significant variations.

2.5 Toughness

2.5*1 Test specimens and procedure

This property, also referred to as impact resistance,

was determined on seven of the nine sample cores submitted.

The test specimens were cylinders 1 in. in diameter and 1 in.

high, the same size as those used in the compression test

(figure 1-A) . The ends of the cylinders were ground flat and

parallel

.

After the specimens were dried in an oven at 105 deg C

for 24 hr and cooled to room temperature they were tested on

a Page impact apparatus. In this machine the specimen is

mounted on a heavy cast iron base. A steel plunger with the

lower end rounded rests on the specimen, and a 2 kg weight

is dropped on the plunger by a motor driven sprocket chain.

The height of the first drop is 1 cm and each succeeding drop

is increased by 1 cm until failure occurs. Since the force

of the impact is concentrated on the center of the specimen

by hemispherical contact of the plunger, the specimen usually

breaks in three or four approximately equal segments.

This method Is described in ASTM Standard D3~l8,

Toughness of Rock.

2.5.2 Test results

Table 6 gives the toughness values of the specimens cut

at various distances from the painted surface of each of the

seven samples tested.

Table 6. Toughness

T Sample 1 No. »

Distance

1 2

Hei

of

£ht

specimen

3 4

of drop

from painted surface,

5 6 7

causing failure, cm

in.

8

t t ¥ t t t f C2 * 2 t 2 T 3

1 3

T 3

f 3

! — t -

c.3 ' - 1 “ t J 5

t 4T 5

I - t -

cil * Q t 2 1 2 » 1 r 2 » 2 t - Co » - 1 — I — T 3

1 2 » 2 T - C7 T 4

r 3

T 4

f 4

f 4

* 5

t 5

1 5

C8 ' T - T - 1 2 r 3

T 3

t 3

! - G9 1 6 t 6 t 8 t 7

t 61

I - 9
i‘

’

.
The values obtained in this test give an indication of the

tenacity of the stone. Results obtained on samples C3» C7> and

C9 are reasonably high for sandstone, whereas, the other values

are low. There appears to be no significant change in values

from the painted surface to greater depths in the core.

2.6 Absorption

2.6.1 Test specimens and procedure

This property was determined on all of the nine cores

submitted. Most of the test specimens were cylinders 1 in.

in diameter and 1 in. high, while the others were disks

approximately 2 l/Lj. in. in diameter and 1 in. thick (figure

1-A,C). Specimens were cut from cores Cl, C5? and C7 at one

inch intervals from the exposed ends to the back. Many of the

specimens used for the absorption studies were utilized later

for the compressive strength and hardness tests.

The test specimens were dried in an oven at 105> deg C,

and after being cooled in a desiccator to room temperature

were weighed to the nearest 0.01 gm. They were then immersed

in distilled water at room temperature for 48 hr, surface

dried, and weighed again.

Except for the small size of the specimens, the test is

the same as that described in ASTM Standard C97“47? Absorption

and Bulk Specific Gravity of Natural Building Stone.

2.6.2 Test results

The percentage of absorption, by weight, of each speciemen was calculated as follows:

where

,

Absorption [%) ~ ..jUjLOQ

A

A = weight of the dried specimen

B - weight of the specimen after immersion

Table 7 gives the absorption values of the specimens

cut at various distances from the painted surface of each

of the nine samples tested.

10 .
'

v
Table 7- Absorption

1 Sam-

' pie

* No,

t

* Cl

!

' C2

i

t

Distance of specimen from painted surface, in,

1 ? 2 3 4 6

543* 5-67' 5-66' 5-37* 5-73* 5-8l*

i t t ? — *11.90*12.03*12.11*

t t ? f — » 7 .23* 7 48’ — ’

7 8

w

5-98*

9

~~fo * 6 . 02 *

' C6

C7

C8

C9

T

t

t f '11.55'

C3

04

c5

? i

» 13 ol8' 13,34

T t

* 12 . 50 * 12.58

t t

? t

' 11.38'11.48

t !

5.89'

t t ! !

' 13 . 28 * 13 . 33 * 13 - 49 * 13029 ’ -*

t ! ! ! !

* 12 , 56 * 12 . 67 * 12 . 55 * 12 . 59 * 12 , 34 * 12 . 50 *

t t f r r f t

» — * 11 . 93 * 11 . 94 { 12 . 03 * 11 . 98 * 11 . 94 * 12 . 01 '

f » ? ! t ? ?

* 11 . 28 ' 11 . 41 'll . 36 'll. 35 * 11 . 34 * 11 . 05 *

f f t t f t ! — * — 1 1346 ’ 13 . 32 ' 13 . 21 '

? ? ! ? J ! 8 . 29 * 8 . 42 ' 8 . 15 * 8 . 07 ' 8.09' —- '

r t ? f t t

?

»

t

The values obtained on samples Cl, C3? and C9 are near the

average values for sandstone but the results obtained on the

remaining specimens are quite high. Tests made at different

depths from the weathered surface afford no definite indication

that the stone is in better condition several inches from the

paint than at about 1 in. therefrom.

2.7 Bulk specific gravity

2.7.1 Test specimens and procedure

This property was determined on all nine samples submitted.

The test specimens were the same 1-in. and 2 l/4-in. cylinders

used in the absorption test. After drying for 24 hr at 105 deg

C and cooling in a desiccator the specimens were weighed to

the nearest 0.01 gm for the dry weight in air. They were then

soaked in distilled water for 48 hr, surface dried and weighed

for the wet weights in air, after which they were weighed suspended in water to determine their volumes.

11 .

2.7*2 Test results

The bulk specific gravity values were computed from the

formula:

Bulk specific gravity = A—

B ~ C

where

,

A - weight of the oven-dried specimen

B - weight of the soaked and surface-dried specimen

C = weight of the soaked specimen in water

Table 8 gives the bulk density results obtained on specimens cut at various distances from the painted end of each of

the nine samples tested.

Table 8. Bulk specific gravity

in,

Sample

No.

Dis tan

1 * ce of specimen from painted surface 2»3 t 4*5 s 6»7 t

1 gm/ml

Cl

G2

G3

ck

C5

C6

C7

C8

C9

2 . 090 * 2 . 091 ’ 2 . 089 * 2 . 090 » 2 . 075 ’ 2 . 072 * 2 . 065 1 2 . 062 * 2 . 056 '

t 1.872» -

T T f t

* 1.851’ 1.848* 1.852*

1 1 ? t

? * 2.026’ 2. 017 T

! r

!

»

!

t

t

f

1.839*

1

?

» t 1 . 784 * 1 . 785 * 1 . 784 * 1 . 78 6 * 1 . 782 1 1 . 789 ’

t ! 1 t ! f 840 » 1. 835» 1.831 1 1.837' 1.833' l. 837 1 1.833* — t 1 t r t ? t —. r t —_ *1.844*1. 818*1. 834*1. 836»1. 840*1. 840

1 t t f f ? t r 1.863* 1.848’ 1.856 '1.852 *1.853*1. 8 60 *1.856 *1.862* — ? t t ! ? t 793*1.791*1.799*

T t t *1f

T

t

? 1.989’ 1.988* 1.996* 1.999*2.000*

t T t ? t

The bulk specific gravity values obtained on all the specimens tested are somewhat low, indicating a lower unit weight for

this stone as compared to that of most of the common sandstones

used for building purposes. Generally, the better grade of

sandstones have higher bulk specific gravities than obtained

on these specimens.

12 .

2.8 True specific gravity and porosity

2.8.1 Test specimens and procedure

These properties were determined on three of the nine

samples submitted. Since jjorosity is derived from the bulk

and true specific gravity values, it was necessary first to

determine the true specific gravities.

These determinations were made on 55-00 gm powdered samples by determining the volumes with Le Chatelier flasks.

First, about 200 gm of fragments representative of each core

were ground in a porcelain mortar until all of the 200 gm

passed a No. 100 sieve. The powdered material was dried in a shallow glass dish for 2lp hr at 105 deg C, and stored in a desiccator until tested.

Briefly described, the test method consists of taking an

initial reading of a volume of kerosene in the Le Chatelier

flask, adding the 55-00 gm of sample, removing entrapped air,

followed by a final reading of the volume. Each test was made

over a 24 hr period at constant temperature, the latter never

varying more than 0.1 deg C between the first and last volume

readings

.

The difference between the first and final readings taken

on the Le Chatelier flask, represents the volume of liquid

displaced by the weight of sample used in the test.

2.8.2 Test results

The true specific gravity was calculated as follows:

True specific gravity = weight of sami

displaced volume in ml

Porosity values, P, were computed from the bulk specific

gravity and true specific gravity by the formula:

where, Da and are respectively the true specific gravity

and bulk specific gravity. This method gives the total pore

space regardless of whether the pores are open or closed.

13 -
>

'

'
Table 9« True specific gravity and porosity

r Sample No. 1

r

True specific ! gravity ’

r Porosity

r gm/ml ? percent

* Cl f

f 2.494 ’

\ 16.72

» C3 t

f 2.503 ?

f 19.26

1 c5 t 2.547 1 27.92

j 1

The porosity values obtained for samples Cl and C3 are

near normal for sandstone; however, the value for sample C5

is quite high.

2.9 Elasticity by sonic method

2.9.1 Test specimens and procedure

The dynamic modulus of elasticity by sonic methods was

determined for six of the nine samples submitted for test.

The specimens were in the form of cylinders, approximately

2 1/2 in. long and 1 3/4 in* in diameter (figure 1-D) . This

property was determined wherever possible on specimens taken

near the painted and back ends of each core tested. The

specimens were first tested in an oven-dried condition, and

later four of the six samples were tested after 10 and 20

cycles of freezing and thawing.

The test procedure followed was essentially that as

outlined in ASTM Standard C2l5-55Tj Tentative Method of Test

for Fundamental, Transverse, Longitudinal and Torsional Frequencies of Concrete Specimens.

2.9.2 Test results

The dynamic modulus of elasticity, E r

, using the longitudinal velocity was computed by the equation:

E

d = (2nl) 2 /9

where

,

n = longitudinal frequency

1 = length of specimen in in.

P = weight/in. 3/g, g = 386 in./sec"1

14 .
'
Table 10 gives the modulus of elasticity values determined

for samples in the original condition and after 10 and 20 cycles of freezing and thawing.

Table 10. Dynamic modulus of elasticity

(longitudinal vibrations)

’ Position of * Specimen’ specimen f Original T After 10 f After 20 ’ No. f in core ! ’ freezings ! freezings T

t ! t J T

f ? ! psi

A

' psi

6 A

» 1.56 x 10 6

' P Sl /

t

t C2-a 1 near paint f 1.48 x 10 1 1.57 x 10 fe t

! t ? j t t

t C2~b f near back ! 1.49 > 1.54 ’ 1.55 !

f 1 T ! t J

f C3-a 1 near paint ? 2.54 » 2.8l ’ 2.77 T

! t ? t ? ?

r C3-b » near back ? 2.30 ! 2.60 * 2.56 f

t t » t t t

? C4-a * near paint ? O .887 * „„„ f

T

1 » ! ? ! f

? C4-b ? near back ! O .887 » ___ t = —t

? r t ? f T

t C6-a f ne ar paint 1 1.67 ' » 1.71 » 1.71 !

t ! t t t I !

f C6-b * near back I 1.58 » 1.61 » 1.61 1

t t t T t 1

f 07 -a-::- ! near paint f 2.25 ? t t

» T T ! t J

1 C7-b ’ near middle J 2.15 ? t f

1 1 ! t 1 I

t 07-c ’ near back ! 2.23 ? „„„ t ___ !

r t ? t t »

t c8-b ' near back t 1.23 1 1.39 * 1.36 f

t t ? t ? ?

---Specimens C 7 , a,b,c, were rectangular bars 2 l/2 by 5/8 by 3/8

in. All other specimens were cylinders 2 to 3 in. in length

and 1 3/4 i- n » i- n diameter.

The values of modulus of elasticity shown in table 10 are

quite low and variable. The fact that the values increased

slightly after 10 and 20 severe cycles of freezing and thawing

is contrary to the usual findings and could not be accounted

for in this case. When two specimens of the same sample were

tested, one near the paint and one near the back, no significant

differences were obtained.

15 .
II.I’
2.10 Capillarity properties

As a further means of comparing the condition of the stone

near the painted surface with the stone at depths of about 12

inches back of the weathered surface, it was decided to apply

a test for capillarity properties. This test had been used in

experiments on mortars and a few types of stone, and the results reported in NBS Building Materials and Structures Report

No. 139, "Studies of Stone-Setting Mortars," page 22.

2.10.1 Test specimens and procedure

The specimens were 1 3/U in. in diameter and the lengths

varied from 2 to 3 inches. These were prepared by coring the

original samples down to a smaller diameter, and the lengths

varied because in some cases it was not possible to make them

all 3 in. long.

The conditions of the tests are illustrated in figure 3?

A and B. Test A determines the absorption when the specimen

is standing on one end on a plastic sponge which is immersed

in water nearly to the top. In test A absorption takes place

entirely by capillary suction. Test B measures the absorption

for the same period (one minute) when the specimen is in contact with water on bottom and sides, i.e., all faces except

the top are Immersed. The areas in contact with water in each

case are determined for comparison with the absorption results.

2.10.2 Test results

The weights of water in grams absorbed during test B are

divided by the corresponding weights absorbed during test A.

These ratios are compared with the area ratios in contact with water in tests A and B. Such comparisons are believed to afford some information on the nature of the pores

of the stone, i.e., whether the pores communicate and form

continuous channels or whether there are numerous dead-end

channels

.

Table 11 gives the capillarity values obtained on two

specimens of each of 4 cores.

16.

Table 11.

Capillarity test values on 4 cores (original condition )

? Specimen

* No.---

T

1 Test A

t

’ Test B

?

X Absorption » ratios B/a ’ Area ratios 1 a 2/a

!

!

r I gm » gm ? ? X

\? i i i— o CVI ! 4.10

1

0 0 1— C\J C\J i 5.4 1 7.8 X

f X J X 1 f

t C2-3 ? 3- 94 » 23 *65 ? 6.0 » 8.0 T

t t X f ! X

i C3-1 t .69 ! 7.43 X 11.8 » 7°3 X

t ? ? 1 t X

T C3-3 X *97 ' 8.74 S 9c 0 * 7.0 t

f f ? ! ! 8

t C6-1 t 3.14 r 22.49 8 7.2 » 7.8 »

! t ! ? f 8

t C6-3 X 5.45 * 18.30 ! 3.4 ’ 6.7 8

r ? X ? t 8

t C8-1 X • 91 > 10.53 X 11.6 * 5.9 I

f ! t ! 1 f

? C8-3 t 2.03 > 16.08 8 7*9 1 7.5 X

r X X ? t 8

---Specimen 1 of each core represents the stone near the painted

surface while specimen 3 represents the stone 9 to 12 inches

back of the exposed surface.

When the B/A ratios are considerably less than the corresponding a2/a

l ratios it is indicated that there is some

retardation of the rate of absorption per unit of area in test

B as compared to that in test A. The reason for such retardation is that the air in the pores of the dried specimen, which

escapes through the top of the specimen in test B, has difficulty in finding its way out when absorption is taking place

from the other faces. In materials that show such retardation

there is apt to be more damage from frost action because the

pores do not always act as continuous passages.

One specimen, 06-3 in table 11, gave such indication

while all others show reasonably close agreement between the

b/a and a 2/a i ratios. Similar indications are also shown in

tables 2, 6 and 7 that sample C6 was of somewhat better quality

near the weathered face that at greater distances back of that

face

.

17 -
> • 1 '
2.11 Effects of freezing and thawing

These tests were made to determine if specimens taken near

the painted surface would show more deterioration in this test

than specimens at greater distances from that face. This was

done as another means of determining whether the surface stone

has undergone more severe deterioration in the building than

that at considerable depth.

2.11.1 Test specimens and procedure

The specimens were the same as those used in the capillarity tests reported in table 11.

The freezing procedure consisted of soaking the specimens

for hours, then placing them in trays containing about 1 in.

of water in the freezing chamber. The freezing temperature

was -10 deg C and the specimens were left in the chamber until

the water was entirely frozen. Thawing was done slowly by

removing the trays from the freezing chamber and standing them

in the room at about 23 deg G until the ice was entirely

melted. This is a severe test, and the specimens were subjected to 20 cycles.

2.11.2 Test results

Since a limited number of freezings does not, ordinarily,

produce visible deterioration, the changes in capillarity,

sonic elasticity, absorption, and bulk specific gravity were

used as criteria for judging the amount of injury produced by

the freezing cycles. Comparison of the results obtained on

the specimens cut from near the painted surface with those

obtained on specimens near the back ends of the cores gives

some information on the weathering that had occurred near the

surface of the building. In making this comparison, it was

assumed that the stone in the Capitol 9 in. or more from the

surface had not been appreciably affected by weathering and,

hence, represents the stone in its fresh condition.

18
’

’

'

•

.
Table 12.

Changes in capillarity tes t

Capillarity test

values before

freezing

Test A*Test B* B/k

values after freezing and thawing cycles

! Capillarity test 1 Capillarity test

~ values after ' values after 1

» 10 freezings ' 20 freezings ' ’Test A'Test B*

? i v

T 1

* Spe ci-*

'men ?

* No. »

i t b/a 1 Test A'Test B ' b/A '! J ? '\

f C2-1 *

* C2~3 *

» ?

* C3**l !

gm ' gm ' 4.10 * 22.01 ' 5*4

t ? 3.94 * 23.65 * 6.0

! ? .69 * 7-43 1 11.8

gm gm gm gm

C3-3 » .97 1 8.74 1 9.0 * 1.03 * 8.61 * 8.4 * 1.18 * 8,91 *

C8-1 ' .91 *10.53 *11.6

5.30 *22.51 ' 4.2 * 5.47 *22.95 *

4-70

.70

?*24.03

t

' 7.25

T

5.1 »

10.4

4*90

,82

*24.18

T

* 7*69

?

» C6-1 * 3.14 *22.49 * 7«2 » 4.28 *22.36 » 5-2 * 4.86 *22.18

C6-4 * 5*45 *18.30 * 3.4 * 6.30 *18.12 * 2.9 * 6.65 *18.13 '

? ! 1.10 *10.80 *

? t 9.8 * 1.49 '11.44

C8-3 * 2.03 *16. 08 * 7.9 * 2.90 * l5°62 * 5.4 * 3q12 *16.50 *

4.2

4*9

9.4

7.6

4 » 6

2.7

7.7

5.3

Table 13.

?

1

T

t

!

I

T

t

!

t

!

t

!

?

t

r

!

t

t

Specimen

ho.

C2-1

C2-3

C3-1

C3-3

C6~l

C6-4

C8-1

C8-3

Calculated percentage changes in capillarity

test values after 20: freezing and thawing cycles

* Changes ' Changes * Changes *

' in Test A * in Test B * in b/a *

* values * values ’ ratios ' 1”"” percent ' percent * percent '

* +334

t +4*3 -22.2 '

1

* +24.4

r

* +18.9

t

* +21.7

t

* +54°

8

t

* +22.0

* +2.0

1

' + 3*5

?

* +1.9

!

» -1.4

!

* - .1

* -18.3

?

» - 20.4

!

* -15.6

t

* -36.1

f

* -20.6

t

!

?

f

r

t

t

v

t

1

?

' +63.8 ?

t !

* +53*8 *

+8.6

+2 .

6

» -33.6 ’

t ?

* -33°0 ’

19 .

Table 14 ° Changes in absorption and bulk specific gravity (G)

after freezing and thawing cycles

1 * Test values before ' Test values after * Test values after !

t Spe ci

8 freezing cycles * 10 freezing cycles ’ 20 freezing cycles 8

* TMen ’Absorption’ G ’Absorption’ G ] Absorption’ G

I Nn. i 8 f 8 8 8

T ? percent ? « percent t ? percent t ?

? C2 --1 ’ 12.20 ’ 1.,842 8 11.67 ’ 1..839 5 12.04 » 1.,837 !

?

» t ? 1 f ? f

f C 2 --3 ? 11.88 ’ 1.,840 ’ 12.04 ’ 1<,839 8 12.03 ’ 1,,838 t

f ? ? ? 5 ? ? t

! C 3

--l 1 6 . 64 8 2,.037 s 6.90 » 2,,033 ‘ 6.92 8 2,.031+ r

f ? t ! 1 1i t 1

! C 3

--3 1 7.05 ’ 2.,022 8 7 = 32 8 2,,022 8 7.28 ’ 2,,022 ?

I T ! ? ? V

» C6--1 8 11.20 ’ 1,.853 1 11.10 ’ 1. CO co ’ 11.13 » 1,,848 t

t t t t ? ? t 1

? C6*”4 f H .53 8 1,.849 88 11.29 ’ 1,.848 8

1 11.36 8 1,,846 !

0

? ? 1

f t 1! ? ?

t C8--l 8 12.64 8 1,.795 '

' 12.98 ’ 1,,791 88 12.90 8 1,>793 !

t ! 1

1 ? ? t I

J C8-=3 * 12.80 8 1.>793 1' 13.17 ’ 1,,791 8 13° 06 8 1,.790 1

Table l 4 ° Percentage changes in absorption and volume

after freezing and thawing cycles

’Sped- 8 Changes in absorption after 8 Volume increases after 8

5 men — — — —T——— —— " 8

’ No,

t

8 C2-1

i

8 C2-3

?

8 C3-1

?

8 G 3“3

10 freezings 8 20 freezings * 10 freezings’ 20 freezings*

T percent

0. 16

.04

.20

.00

°27

.04

.22

.11

» C6~l »

» C6-4 »

I t

» c8-l ’

t !

’ c8~3 ’

percent

-4-3

+ 1.3

+3 o 8

+3 «

8

+1.0

+ 2.1

+2 .

6

+2.9

percent

-1.3

+1.3

+4.1

~3°3

. 6

-1.4

+2.0

+2.0

percent

0.27

.11

.14

.00

°27

.16

.17

.04

20 .

The results In tables 12 and 13 show that the test A values changed considerably faster due to freezing than the test B

values. This resulted in the b/a ratios becoming smaller. All

of the B/A ratios changed less for core© cut furthest from the

painted surface than for those cut adjacent thereto. Changes

in absorption during the freezing test were small and erratic.

Volume changes as indicated by bulk specific gravity determinations Indicated that appreciably greater swelling occurred for

specimens cut next to the painted surface than those from considerable depth within the stone (tables lip and l5)-»

Since none of the other physical tests such as compression, flexure, toughness, absorption* density, etc. show any

definite progressive weathering from the painted surface. to

greater depths, it must be assumed that there has bden no serious weathering, due to the long exposure, to depths greater

than the depth of spalling.

2.12 Petrographic analysis

A petrographic examination was made on all of the nine

samples submitted for teste The investigation consisted in

determining:

1. Identification and relative abundance of mineral

constituents present

2. Identification and relative bonding of the cementing agents holding the minerals together

3. Alteration of the minerals

4« Textural differences

5. The effect of paint on the surface of the stone

The identification of the mineral constituents was accomplished using microscopic methods and oil immersion techniques

supplemented with X—ray analysis. Thin sections were made

from specimens cut from core No. Cl to determine the structure

and cementing agents present In the sto»ne. Specimens approximately 1 in, square and l/4 in. thick cut from each of the nine

samples were studied under the microscope and photographed.

Background data concerning Aquia Creek sandstone was

obtained from various scientific publications dealing with

the geologic and mineralogic formation of the rocks from which

the stone was quarried. The four most important of these publications are Bulletin IV, Virginia Geological Survey 1912,

The U.S. Geological Survey’s Annual Report (1893-94) ? Bulletin

Geological Survey No. 141? 1894? and Johns Hopkins University

Circular Vol. XV, 1895.

21 .

The nine samples submitted show considerable variations,

both in composition and in texture* In general, the color of

the specimens when observed on a fresh surface is light gray

with occasional stains of brownish yellow. These stains were

produced by the alteration of minerals containing iron, forming hydrous iron compounds. The variation in textures of the

samples can be readily observed from the photographs of the

nine specimens, magnified 10 times, representing each of the

nine samples (figures l\~A s B and C) . The difference In the

textures of the specimens is due primarily to a difference in

specimen porosity. In some specimens it appears that large

voids were formed at the time of lithification of the deposit,

as exemplified in figure 4 “B (C-5 )- In other specimens many

of the voids may be there as a result of leaching of soluble

constituents after the sandstone had lithified as shown in

figure I4.-A (C-2 ).

The samples showed some variations in their mineral content but, in general, the constituent minerals have an average

estimated value of the following in volume percent:

Quartz [j. 5$

Feldspar - = 2:£$

Kaolin -------------- 20$

Magnetite, sphene, garnet,

micaceous material and hornblende 10$

Quartz is the major constituent of the sandstone. The

individual quartz grains are gray, milky or clear in color,

and have an average size range of l/l6 to l/32 in. in their

longest diameter. Geometrically the grains tend to have rounded

surfaces suggesting abrasion from water action. Feldspar and

its major decomposition product, kaolin, with minor amounts of

magnetite, sphene, micaceous materials and hornblende make up

the remainder of the constituents. For the most part, the

feldspars are badly altered to kaolin and, in many areas, the

feldspar grains are completely decomposed. In figure 5 one

can observe the decomposed feldspar areas as fine-grained

birefringent portions of the photograph. Figure 6 shows the

typical alteration products of the feldspar under 200 diameter

magnification. The clear grains are quartz with some micaceous

materials, while the darker, cloudy areas consist of the clay

mineral, kaolin.

The major cementing agent holding the individual grains

together appears to be a secondary silica deposited by circulating ground waters. Under the microscope the silica appears

to be amorphous in character. Small amounts of hydrous Iron

oxide with some calcium carbonate were observed intersti tially

between grain boundaries. In many areas where the feldspar

has been badly altered, micaceous materials are present at

22
.
the grain boundaries and possibly act as cementing agents. In

general, the cementing agents may be described as poor to fair,

for in some specimens the stone was so friable that it could

easily be broken between the fingers. In other specimens the

stone was quite firm and could not be broken easily.

The painted surface of the stone was examined carefully

to determine any possible mineralogical alteration caused by

the paint or volatile oils which may have penetrated the interior of the stone. Some of the specimens examined contained

11 coats of paint which had the appearance of adhering firmly

to the stone. There was slight discoloration for a distance

of about l/l6 in. in the stone’s interior, apparently caused

by the paint oil; otherwise, the stone’s interior had a fresh

appearance. It does not appear, from the specimens examined,

that the paint had any adverse effect on the constituent minerals or the cementing agent in the stone.

2.13 Chemical analysis

Sample No. C3 was selected for a complete chemical analysis. For this purpose, three specimens, each 2 l/2 in. in

diameter and 3/8 in. thick were cut from the painted surface,

middle and back end of the core. Table 16 gives the results

of the chemical analysis obtained for the three specimens of

sample C3»-':‘

---The analysis was made by Lee C. Peck and Edwin G. Tomasi of

the U.S. Geological Survey, Denver, Colorado.

23 .
,*
Table 16. Chemical analysis core C3

3

r

1

i

f Location

? Near paint 3

t ? percent i

3 Si0 23 83.81 3

t

I 3

3 °o 3 8.01 3

t 2 3 3 3

t

T Ye ^ °3 f

r .47 3

3

t Fe 0 r .12 J

f t 3

t Mg 0 3 .11 3

3 3 3

I Ca 0 3 .14 3

! 3 3

t Na2

0

i .10 3

t t 3

3 K

2

0 3 3.13 3

3 ? 3

3 H

2 0 - t 1.25 3

1 t 3

3 h2

0+ T 1.88 3

1 3 3

3

! °2 3

3 .50 f

3

!

f CM OO

I

3 .00 33

*

3 P2 °5 33 .02 3

1

3 Mn 0 3 9 0 0 3

of specimen

Middle 1 percent

~

8)4.0 07 !

1 7 089 J

? .49 !

t .10 *

oil '

3 oil f

3 *13

f 3.12 '

3 1.46 »

* 1.66 !

t .46 *

t .01 *

t .02 *

.00

in core

Near back

percent

84.39

7.82

.48

.12

.11

ell

.15

3.16

1.39

1.60

.42

.00

.02

.00

t

3

*

?

t

3

3

t

*

?

t

3

j

3

t

?

?

?

3

s

!

3

3

3

J

!

3

J

3

»

3

The chemical as well as the mineralogi cal studies reflect

the nature of this stone. It is an "Arkose" sandstone formed

from the talus of a decaying granite. The feldspars, in passing over to kaolin due to weathering are responsible for the

light color of the stone. Being formed near tidewater, it

pprobably never had sufficient overburden to compact the layers into dense stone.

There are no indications in either the chemical or

mineralogical analyses that the stone has been injured by the

paint. One interesting finding in the microscopic studies is

that the sample examined showed only eleven coats of paint.

The records are reported to show that the building has been

painted 34 times. This may be interpreted to mean that some

of the paintings did not cover the entire building.

3. STUDIES ON EFFECT OF PAINT AS A PRESERVATIVE

3«1 Observations on the Capitol Building

The Capitol shows a large amount of spalling which pits

the surface to various depths, usually about l/8 in* but sometimes 3/8 in. and more. Usually the pitting is confined to

individual blocks which are probably the poorer grades of

stone o Apparently all of the stone from the quarry was used

as it was taken out regardless of quality, but evidence was

obtained In the tests that the better faces of the blocks were

turned outward to expose the ones of better appearance. A

considerable number of the blocks in the building show no pitting, and these may have performed well without any paint.

This last statement is based mainly on the results of observations on other uses of the same stone where it was not painted.

3.2 Observations on the White House

The following statements are based on an examination made

eight years ago. The exterior stone in the White House is the

same as that in the Capitol and it evidently came from the same

quarry, i.e., the Government quarry located on an island in

the estuary of Aquia Creek near the Potomac River. Sample

cores were taken from the White House at the time of this study

but all these cores were taken from the part that was said to

have been exposed to the most severe part of the fire of I81I4..

Tests on these cores Indicated that the stone was in sufficiently good condition to be kept in service. There were no replacements of stone In the restoration of the building. No

pitting of the stone in the White House was found like that

exhibited in the stone of the Capitol. Statements obtained

indicated that the exterior had been painted every four years.

However, it was found that occasional replacements of weathered blocks had been made from time to time.

3«3 Columns of the U.S. Treasury Building

The old columns of the U.S. Treasury Building were originally of Aquia Cneek sandstone. These were replaced with

granite columns about 42 years ago. It Is recalled that the

sandstone columns were deeply eroded but this erosion was confined to relatively small areas. A large part of the stone

showed little weathering. These columns were not painted.

It seems likely that areas of deep erosion would have developed on the Capitol stone if painting had been omitted, since

so much of the stone appears to be of poor quality. A similar inference can be drawn from recent observations on the

sandstone gateposts described in section 3.6.
.
3*li Old Patent Office Building

The exterior of the original portion of the old Patent

Office Building was faced with Aquia Creek sandstone,, The

south and north walls of this portion can still be seen. The

south wall shows only slight weathering but some blocks in the

north wall are scaling considerably* Deep erosion as noted in

the old Treasury columns was not found on this building* The

sandstone on the south face has weathered less than the marble

wings which were constructed at least 12 years later* No definite conclusions could be drawn from observations made on this

building except that where the sandstone is of good quality it

performs well without paint*

3«5> Bulfinch gatehouses

The Bulfinch gatehouses , formerly on the Capitol grounds

and presently located on Constitution Avenue at l£th and at

17th Streets., are constructed of Aquia Creek sandstone* It is

probable that these two buildings were never painted* Photographs were taken of them and reproduced here to illustrate

the good condition of the stone (figures 7> 8 and 9)* There

is not much evidence of weathering except near the ground and

at occasional small pits or vugs which may have been filled

originally with friable, clayey material which was later removed by weathering*

3.6 Capitol gateposts

The gateposts once situated on the Capitol grounds and

now located on l5th and Constitution, are examples of badly

deteriorated Aquia Cpeek sandstone* Figures 10 and 11 illustrate this condition in two of the gateposts* Since some of

the blocks in the Capitol have been shown by tests to be of

inferior quality, it is likely that such blocks would have

eroded very much like the gateposts if no painting had been

done on the Capitol stone.

3<>7 Relation of paint to spalling

The question has been raised as to whether painting

could have contributed to spalling* No evidence was found

in either the chemical or mineralogical studies to indicate

that there had been injury to the stone due to mineral alterations near the paint. If there had been any chemical Injury

due to the paint it is evident that it would have occurred

over the entire surface. Most of the spalls are small and

thin and many blocks are not spalled*

26 .
’

*

'
When this stone is painted the oil penetrates at least

l/l6 inch and forms a rather effective seal 0 This greatly reduces the absorption of rain water but in a large building it

is almost certain that water can find places to enter, such as

defective joints between blocks or at the tops of walls. If

water Is admitted at places It will spread through the walls

and the paint prevents evaporation at the surface . Under such

conditions there is apt to be spalling due to frost action.

Gases are known where spalling of stone occurred after the

stone had been coated with waterproofing materials.

No definite reasons can be given as to why the stone in

the White House has resisted weathering better than that in

the Capitol. The beveled blocks In the Capitol may have contributed to absorption but It seems more likely that painting

of the White House has been done more thoroughly.

4, RECOMMENDATIONS

Since none of the physical tests other than freezing

tests showed any significant differences between the stone

near the surface and that represented by the depth of the

cores, I.e., 9 to 12 inches within the stone , it must be assumed that there has been no prominent deterioration to depths

greater than the depths of spalling. It is believed, therefore, that if about l/2 inch of the stone is removed by suitable tooling that the walls would be serviceable for many

years. It would be necessary to continue painting to prevent

erosion of the inferior blocks. It would probably be more

satisfactory to re-face the old stone with a more durable

stone where it is to be left exposed to the weather.

SUMMARY

Physical tests made on nine samples of sandstone taken

from the exterior walls of the U.S. Capitol show a large range

in quality of the stone. Only three of the nine samples

could be regarded as good quality stone, whereas the other

six ranged from medium to poor.

An effort was made to determine if the weather has seriously affected the stone to appreciable depths. Small speci~

mens 1 inch long were tested in order to give some data on

progressive deterioration from the painted surface to the

depths represented by the lengths of the sample cores. Such

tests as compressive strength, toughness, abrasive resistance,

absorption, specific gravity and elasticity did not: reveal any

consistent differences between the specimens taken near the

27 -

surface and those at considerable depths. For this reason,

freezing and thawing tests were made on four samples in which

one specimen from each sample was cut from the painted end of

the core while the other was cut from the opposite end to represent the stone furthest from the weathered surface. Four

pairs of these specimens were subjected to 20 cycles of freezing and thawing, of a severe nature, to determine if the surface

material would be deteriorated more in the test than the stone

9 to 12 in. within the blocks.

As a criterion for judging the effects of the freezing

cycles, absorption, density, elasticity, and capillarity tests

were made before and after 10 and 20 freezing and thawing

cycles. The absorption and elasticity tests indicated no consistent differences in the effects obtained on the specimens

from near the surface and those from the back ends of the cores.

However, the specific gravity and capillarity tests did indicate that specimens representing the first 3 inches of stone

from the exposed surface were deteriorated somewhat more than

those at 9 to 12 inches back. It is believed that these differences are not serious.

Chemical and mineralogical examinations indicate that the

stone is an arkose sandstone which was rather poorly compacted

and, hence, quite porous. Chemical alteration of the feldspars has produced considerable amounts of kaolin which, in

Isolated areas, is responsible for the soft spots occurring in

the stone.

A study was made of the effects of painting the stone.

This was done by studying the effects of weathering on the

Capitol and the White House, both of which have been painted

at frequent intervals, and on other old structures made of the

samfe stone that had not been painted. The results indicate

that, where a structure contains blocks of poor stone, it is

better to paint at reasonable intervals in order to prevent

deep erosion on the less weather-resistant parts. Since tests

have proven that the stone in the Capitol ranges from poor to

good, it appears that painting has been advantageous. The

relatively good preservation of the stone in the White House

is believed to be due to thorough painting.

Although painting helped to preserve inferior blocks of

stone in the Capitol, it contributed indirectly to spalling

of the surface. Over most of the surface the paint formed a seal which greatly reduced the absorption of rainwater but it

also interfered with evaporation in cases where water entered

the walls through defective joints between blocks. The freezing of wet stone, with the surface sealed, caused spalling of

the surface.

28 .
’* ' ' IIIII .
Chemical and petrographic studies failed to show that the

paint had any adverse effects on the stone or any of its constituent minerals.

The writers believe that the sandstone is sufficiently

sound to justify further service if about l/2 in. of the

surface is removed by tooling. However* if this is done and

the stone is to be left exposed to the weather* it woulck.be

necessary to keep it painted as has been done in the past.

A preferable treatment and probably a less costly one over a period of several years would be to re-face the old walls with

a more durable stone. The old stone is sufficiently sound to

anchor a new facing thereto but metal anchorage should be provided.

The writers acknowledge the assistance of Alvin Van

Valkenburg, Jr. of the Bureau* s Mineral Products Division

who made the petrographic studies described in section 2.12.

29

Pig. 1. Test specimens used in the determination of the physical

properties of the U. S. Capitol sandstone:

(A) Compression, absorption, specific gravity, toughness.

(B) Shearing strength.

(C) Abrasive hardness, absorption, specific gravity.

(D) Elasticity, capillarity, freezing cycles.

FIGURE

2.

DIAGRAM

SHOWING

METHOD

OF

LOADING

CYLINDRICAL

TEST

SPECIMENS

IN

FLEXURAL

STRENGTH

TEST. 0 cr

q 1 i i

C/5 c*0T3O

30O

O z

•T1 m

piaom

05 o X 3D o o ^ 05 — CO z

G5 C/5 mo

CD

33m

r>

CDmo ozon o o

~n <r

CD 2

“•

O

O 3D m o

C/5 33PIOSm

in co r~ O T) O

JO >>2 o O cn cd > H 2 >

T» 5* m 0

~n

pi1 i °m $H O m z

COH 03

03

XO

JO

LOAD

LOAD

LOAD

FIGURE

3.

DIAGRAM

SHOWING

CONDITIONS

OF

TESTS A

AND B

IN

THE

DETERMINATION

OF

CAPILLARY

PROPERTIES

OF

THE

SANDSTONE

SAMPLES. o k > 2 o m H

CO *5

-i ~n>om $>Hm O"0

T)mom ^ o > — “n r~ H r~ I CO

s£

G c > 0 H H ^ m m h ^ 2 o r u oo

COc

“n> > o o m

CO 05 C 13 0 m >

0505

C - I C- 2

Pig. 4~ A - Photographs of sections of samples C-l, C-2, and C-3,

showing the variation in texture of the U. S. Capitol

sandstone. (magnification, 10 X)

Pig. 4“®* Photographs of sections of samples C-lp, C-5>> and C-6,

showing the variation in texture of the U 0 S. Capitol

sandstone, (magnification, 10X)

Pig, 5. Photograph of thin section of Sample C-l showing the decomposed feldspar areas as fine-grained birefringent

crystals, exemplified in the two circled areas,

(magnification 10 X)

Pig. 6. Photograph of powdered specimen, representing material

from samples of the Capitol sandstone, showing typical

alteration products of the feldspar. Encircled clear

grains are quartz; dark areas are kaolin,

(magnification 200 X)

Pig. 7. View of Bulfinch gate house at Constitution Avenue an

17th Street, Washington, D. C. Photqgraph shows t e excellent state of preservation of the unpainted Aquia

Creek sandstone after about 125 years of exposure.

Fig'. 8. View of Bulf inch gate house at Constitution Avenue and

15th Street, Washington, D. C. Photograph shows the

excellent state of preservation of the unpainted Aqui

Creek sandstone after' about 125 years of exposur-.

Pig. 9. Close-up view of a section of the east side of the

gate house described in Fig. 8.

Pig. 10. View of gatepost at the southeast corner of Constitution

Avenue and l^th Street, Washington, D. C. illustrating the

advanced state of disintegration of unpainted Aquia Creek

sandstone after about 125 years of exposure.

Fig. 11. View of gatepost at the southwest corner of Constitution

Avenue and l§th Street, Washington, D. C. illustrating the

advanced state of disintegration of unpainted Aquia Creek

sandstone after about 125 years of exposure.

THE NATIONAL BUREAU OF STANDARDS

Functions and Activities

The functions of the National Bureau of Standards are set forth in the Act of Congress, March

3, 1901, as amended by Congress in Public Law 619, 1950. These include the development and

maintenance of the national standards of measurement and the provision of means and methods

for making measurements consistent with these standards; the determination of physical constants and properties of materials; the development of methods and instruments for testing materials,

devices, and structures; advisory services to Government Agencies on scientific and technical

problems; invention and development of devices to serve special needs of the Government; and the

development of standard practices, codes, and specifications. The work includes basic and applied

research, development, engineering, instrumentation, testing, evaluation, calibration services, and

various consultation and information services. A major portion of the Bureau’s work is performed

for other Government Agencies, particularly the Department of Defense and the Atomic Energy

Commission. The scope of activities is suggested by the listing of divisions and sections on the

inside of the front cover.

Reports and Publications

The results of the Bureau’s work take the form of either actual equipment and devices or published papers and reports. Reports are issued to the sponsoring agency of a particular project or program. Published papers appear either in the Bureau’s own series of publications or in the

journals of professional and scientific societies. The Bureau itself publishes three monthly periodicals, available from the Government Printing Office: The Journal of Research, which presents

complete papers reporting technical investigations; the Technical News Bulletin, which presents

summary and preliminary reports on work in progress; and Basic Radio Propagation Predictions,

which provides data for determining the best frequencies to use for radio communications throughout

the world. There are also five series of nonperiodical publications: The Applied Mathematics

Series, Circulars, Handbooks, Building Materials and Structures Reports, and Miscellaneous

Publications.

Information on the Bureau’s publications can be found in NBS Circular 460, Publications of

the National Bureau of Standards ($1.25) and its Supplement ($0.75), available from the Superintendent of Documents, Government Printing Office. Inquiries regarding the Bureau’s reports and

publications should be addressed to the Office of Scientific Publications, National Bureau of

Standards, Washington 25, D. C.