(71 ! I DO ! -.re &e?ea.vdb Information Services

Nations! Bureau of Standards

Bldg. 225, Rm. A4S

Washington, D.C, 20234

NATIONAL BUREAU OF STANDARDS REPORT

4200

MmJ QUARTERLY REPORT

ON

EVALUATION OF REFRACTORY QUALITIES OF CONCRETES

FOR JET AIRCRAFT WARM UP, POWER CHECK,

AND MAINTENANCE APRONS

by

W. L.. Pendergast, E. C. Tuma, R. A c Clevenger

U. S. DEPARTMENT OF COMMERCE

NATIONAL BUREAU OF STANDARDS
U. S. DEPARTMENT OF COMMERCE

Sinclair Weeks, Secretary

NATIONAL BUREAU OF STANDARDS

A. V. Astin, Director

THE NATIONAL BUREAU OF STANDARDS

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

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

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

of the back cover of this report.

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Data Processing Systems. Components and Techniques. Digital Circuitry. Digital Systems.

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Radio Standards. High Frequency Standards. Microwave Standards. • Office of Basic Instrumentation • Office of Weights and Measures
NATIONAL BUREAU OF STANDARDS REPORT

NBS PROJECT NBS REPORT

0903-21-4428 June 30, 1955 4200

QUARTERLY REPORT

ON

EVALUATION OF REFRACTORY QUALITIES OF CONCRETES

FOR JET AIRCRAFT WARM UP, POWER CHECK,

AND MAINTENANCE APRONS

by

W, L e Pendergast, E, C, Tuma, R. A» Clevenger

Refractories Section

Mineral Products Division

Sponsored by

Department of the Navy

Bureau of Yards and Docks

Washington, D. C 9

Reference? NT4-59/NY 4200 008-1

NBS File No 0 9c3/ll34-C

Approved

R. A* Heindl, Chief

Refractories Section

U. S. DEPARTMENT OF COMMERCE

NATIONAL BUREAU OF STANDARDS

The publication, r

unless permission

25, D.C, Such pe

cal ly prepared If

Approved for public release by the

Director of the National Institute of

Standards and Technology (NIST)

on October 9, 201 5.

r In part, Is prohibited

tandards, Washington

eport has been speclfireport for Its own use,

QUARTERLY REPORT

ON

EVALUATION OF REFRACTORY QUALITIES OF CONCRETES

FOR JET AIRCRAFT WARM-UP, POWER CHECK,

AND MAINTENANCE APRONS

TECHNICAL REQUIREMENTS

The technical requirements for the concretes designed with

dense aggregates are the same as those given in NBS Report 3012,

dated December 31* 1953

The technical requirement for the concretes designed with

lightweight aggregates are: (l) they must develop a flexural

strength of 600 psi after curing for 2S days in the fog-room;

(2) the maximum cement content shall not exceed nine sacks per

cubic yard.

1 . INTRODUCTION

The objective of the investigation is the determination of

the physical properties of concretes that will evaluate their

suitability for use in jet aircraft warm-up, power check, and

maintenance aprons,

2. MATERIALS: PREPARATION AND TESTING

2,1 Cements

The permanent length change, the water lost as indicated

by the weight loss, and the decrease in strength as indicated by

Young* s modulus of elasticity (dynamic method) were determined on

specimens fabricated from each of the three types of cement
.
- 2 -

namely portland, Portland pozzolon and high-alumina, bach

t / was mixed with water to a normal consistency ^ and the specimens fabricated from the mix were cured for 28 days in the

fog-room. They were then weighted, measured, and Young’s

modulus determined,, The specimens were then heated to apparent

constant weight at 100° C, removed from the oven, cooled in a

desicator, and the same properties redetermined 0 This operation

was repeated at 100°C intervals to 500°C e

2 0 2, Aggregates

Coarse fractions of the lightweight aggregate, "Rocklite",

are marketed in sizes not comparable to the standard sizes commonly

2/ used in concrete design . The fines are furnished as passing a

No, 8 mesh screen. Since this is a coated material the usual

method of crushing to obtain desired sizes could not be used. It

was, therefore, necessary to screen a comparatively large amount

of this aggregate to recover the needed percentages of the various

sizes. The screening has been completed and the aggregate was

recombined to the finness moduli that would develop the maximum

strength in the trial mixes of concrete,,

The rate of absorption, saturated surface dry, was determined

on the aggregate at 5-minute intervals up to one-half hour. This

information was necessary in order that the amount of free water

available for mixing be known when the aggregate is charged into

the mixer in a dry condition. Having this information is important.

- 3 -

especially when concretes containing high-alumina hydraulic

cement are mixed. In such mixes it is necessary to add the required

water at one time due to the rapid initial set of the cement

„

The method used in saturating the aggregate for the concrete

mix wras as follows: It was placed in burlap sacks, and immersed

in water for 8 hours, the sacks and contents were then removed

from the water and drained for 18 hours and weighed,, This method

was found to be the most convenient for the size of batches used*

2,3. Concretes

Five one-cubic foot trial batches, one five-cubic foot and

three 15-cubic foot final batch of concretes were designed and mixed.

The properties of the fresh concretes were determined, and specimens

were fabricated, cured, and those tested which had completed the

curing period,,

Two of the five trial mixes were designed with the lightweight

aggregate, "Kenlite", and Portland cement in one and portland

pozzolan in the other.

The other three trial mixes were designed with the lightv.re/ ght

aggregate, "Rocklite" 0 Portland cement was used in one of the mixes

Portland pozzolan in the second and the high-alumina hydraulic

cement, "Lumnite", in the third 0

Three final 15-cubic foot batches were designed with the "Rocklite"

aggregate and contained either portland, Portland pozzolan, or Lumnite

cement

- 4 -

One final five-cubic foot batch of concrete was designed

with Portland cement and olivine as the aggregate. White Marsh

sand, -30 to -100, was substituted for 50 percent of the fines

of the parent aggregate. The reduction in volume (from 15 to 5

cubic ft,) of this batch was due to a shortage of the aggregate.

In the March 31, 1955, quarterly report information was given

on concretes containing sintered slag. The properties of three

of these concretes containing either Portland, Portland pozzolan,

or the high-alumina cements were determined after curing and after

heat treatments at 250°, 500° and 1000°G respectively.

The properties of the three concretes designed with Portland

cement and containing either crushed building brick, olivine, or

calcined Kentucky flint clay as part of the aggregate were

determined after two curing periods and the same three heat

exposures, White Marsh sand was substituted for 50 percent of the

fines, -30 to -100, in these concretes as detailed also in the

preceding quarterly report,,

3, Results and Discusion

3.1. Cements

Subjecting the neat cement specimens to increasing heat treatments resulted in a continual linear shrinkage. The linear shrinkage for all three cements based on the length of the specimen as

removed from the fog-room after a 28 day curing period, was uniform

to 300°C, The shrinkage up to that temperature of Portland pozzolan

cement was 1.49 pBrcent, that of Portland 1,08 and that of

- 5 -

Lumnite 0.86 percent. From 300° to 500°C the Portland cement

continued to shrink at a uniform rate to a total of 1.9%<> From

300? to 400°C the pozzolanic Portland cement continued to shrink

uniformly to a total of 2.12 percent, but from 400° to 530°C

there was a decided decrease resulting in a final shrinkage of

2.14 percent. The high-alumina hydraulic cement changed very

little from 300° to 500°C, and the total for the entire range

was 0,87 percent.

The percent water lost, as indicated by weight loss, was

based on the weight of the specimens after the 28 day fog-room

curing. It was assumed that the original proportion of mixing

water had not changed. The lumnite cement had lost all the

mixing water at 300°C; the portland pozzolan at 400°G and the

Portland at 500°G.

The method, although it indicates the weight lost after

heating at the various temperature, and a greater part of this

loss is probably water, is not considered too accurate. Some of

the errors that maybe introduced are for example: the mixing water

may not be equally distributed from one specimen to another;

bleeding may occur during or after fabrication; the cements may

gain or lose a small percentage of the water during curing; repeated

handling of the specimens even with utmost care may cause some loss.
-

.
- 6 -

Young’s modulus of elasticity was determined, of each

specimen after each treatment. The modulus for all cements

after the 28 day fog-room curing was above 5,000,000 psi.

Increasing the heat treatments to 500°C reduced this value to

slightly above 1,000,000 psi for the Lumnite, and Portland

pozzolan and 2,000,000 psi for the Portland. This decrease

in modulus of elasticity would indicate a corresponding

decrease in strength.

3.2. Aggregate

The rate of absorption, saturated surface dry^ for the

coarse aggregate sized to the gradation used in the concretes

was as follows:

5 Min. Immersion 2.4 Percent

10 " " 2.6 "

15 " " 3.2 "

30 » " 3*4 " 4/

The absorption-17 for the fine aggregate was as follows:

5 Min. Immersion 11.7 Percent

10 " " 13 o7 "

15 " » 16.3 "

30 " 17.3

The method used in wetting the aggregate resulted in somewhat higher absorption values because the surface water was not

completely removed especially from the fines. The producers of

this aggregate recommend that it be used at 75 percent of its

total absorption and claim to obtain this condition by spraying.
. ,, V: ,

: - v ...

'•

. ^ •

. .

• l''

'

.
- 7 -

3.3. Concret es

Table 1 gives the composition and some properties of the

fresh concretes, together with the flexural strengths after 23

3 3

days of fog-room curing » The trial mixes P-K-G and Z-K-E

contained the +3/4" top-size of the aggregate "Kenlite”. The

flexural strengths given, when compared with those appearing in

table 3 of NBS Report 3B55 ^ December 31, 1954 indicate that this

coarse size of aggregate did not tend to increase the flexural

strength of the concrete. Apparently the strength of the aggregate decreased with increase in size.

Table 1 also gives the composition and some of the properties

of the fresh concretes designed with, "Rocklite" aggregate. The

trial batches identified as P-R-E^, P-R-F^, and P-R-G^ contained

increased amounts of the +1" to +l/2" aggregate. Trial batches

P-R-H^j Z-R-E^, and L-R-E^ contained increased amounts of the

intermediate sizes + 3/8" and +No4. Such variation of the finness

4

moduli resulted in only one concrete (Z-R-E ) f that met the

technical requirement for flexural strength of 600 psi.

The last column of this table gives the flexural strengths of

prisms measuring 3 x 4 x 16 inches. The values for flexr •al

strength when determined on smaller specimens have been consistently

5/

higher than when determined by the ASTM method^ . Most of the

available data on the flexural strengths of lightweight aggregate

concrete was determined on specimens similar in cross sectional

area to the 3 x 4 x 16 inch prisms.

Table

1.

Properties

of

Fresh

Concretes,

Trial

Batches. I

©I

H

H jC P

fillA

psi

740 -A£

770 575 550

OO

c*-

590 690

u-\

Remarks :

Cured

Concrete

mostly

aggregate

fracture

®

t3

® •JS (0 4J 'do® •H © bOg ssl © © O

bO

© ffl W)

£p

K

C P bo O © MH H © ©

large

air

voids;

aggregate

fractured

along

cleavage

lines J 11._

all

aggregate

fractured

all

aggregate

fractured

all.

aggregate

fractured

© 3 2 ..

3.'

© 11 I g | B

•H «H Or;s P ©

•rl b£) © ©

Ch

©

©

•PXt

LA

CV i m

111 | -Ha

605 560 o 505 500 o

^A §

620 o 1 &

.. t

•g

aa « ©

a

p o i %

•g

O >o i3 io

,3 s i1 1 3 t

bO gl. bO h0

ft. &®

® o © 5 3 8

d-a * &© & > © +3 b0 U0 ro £ > >

CV O' IA VA LA

© ft! -H ca -J- CA CA CA CA CA © S © S O K O ^ JZ -P

+2 £ ¥.

F 8 o O

C- 8 3 OsO

OCV o

O' 8

ii £ © H ft. C

jz> o H

w r § 3 § £ O'rHOrH O'

R 1 B O

fl-C cv CV o 8 OLA cu\

O o O

CO 9

cv 4 o O CV cv o cv rH

© P $ o cvo oC'-

-©• O

IA

O' 5

CAO 3

CV0-

d -3 1 1

LA CA rH CA CV IA CV to s B* I a

<: o

is \

lea s1 O

to vO CV r- o rH O'

"br!CA o 3 sj

to CA IA

eo

p

<D -P £

CA tA

to

H S-e o q bb © § '3 o 1

-Ps 8 8 • c

LA8

500 VA8 8 c 8 £3 30

o. 6 a oc

jb" o ®£ C a

Q> •P 8 OO O

i-j q

R

vOIA

CAqtoo

IA

vO 8 CA & cO A%

O' tod io a1 ®

-p

© bO m ® o tovO

LA

SO

vO sO'

IA

(A •o

_ <H P P g ° g g o o o o o o o o o P £ ° P bb O © a-a*.s <s o

toq

cv

O'*

g s R o R

1—1 r—1 o o H rH o rH o H rH rH rH rH “I

•3

-p3

rH•f -v > *"h if ia

sj

Sd Sd « « « ai 3

0- cL fvl a. CP CP O.

N Ji

®

J 3 I i

The

flexural

strength

as

determined,

after

28-day

fog-room

curing,

on 6x6x

20

inch

beams

(A.S.T.M.

Method

C78-44)

and 3x4x

16

inch

prisms;

(usLng

an

18

inch

ant

13

l/2

inch

span

respectively).

This

type

cement,

Green-bag

port

lard

pozzolan,

was

purchased

with

an

airentraining

agent.

The

mixer

was

charged

with

diy

aggregate.

- 3 -

Table 2 gives the properties of the fresh concretes as

determined on the three final 15- cubic foot mixes e "Rocklite"

was the aggregate in these concretes and the bond either

Portland, Portland pozzolan, or the high-alumina hydraulic cement.

The results indicate the probable variation in the properties

of concrete of the same design that may be expected in laboratory

controlled mixing. Flexural strength determinations on beams

fabricated from the many trial mixes previously reprted indicated

that the maximum strength to be expected would not be greater

than 600 psi, The low average value of 585 psi for the flexural

strength of the concrete designed with Portland pozzolan cement

was caused by the results of a beam fabricated from mix Z-R--1*

This particular mix was too plastic, because of low water content,

to fabricate sound beams for testings

Table 3 gives the composition and some properties of the fresh

concretes, together with the flexural strength of the final batches

designed xfith Portland cement and either crushed building brick,

calcined Kentucky flint clay, or olivine. In designing three

of these concretes, namely P-B-WM, P-C-WM and P-O-WM, white

marsh sand was substituted for 50 percent of the fine parent aggregate, The properties of the concretes that do not contain the

white marsh sand have appeared in previous reports but are again

given to illustrate how the sand effects the properties. Flexural

strength determinations on beams fabricated from trial mixes of the
.

'

.
Table

2.

Properties

of

Fresh

Concretes,-^

Final

Mixes,

with

Lightweight

Aggregate.

Remarks

Cured

Concrete

1 all

aggregate

fractured

all

aggregate

fractured p

j

rH f+3 to CO

psi tOs

UN

to

to, F

_

Remarks j

Freeh

Concrete

slightly

sticky

but

placed

well

placed

well

[

—

slightly

sticky

but

placed

well

sticky

but

placeable i

o

S)&©>

o

x>

i *1 f o o

i 4.8

| a3

od

k

o 1

to u j

jl $3Vi x> 3 —

Water

Cement Ratio

vOc\O

r0^ & J0.35 3 3 j C?O

’ r

Weight

of

Fresh Concrete

c*^ S'* £ “i \ O'

ro O' S

100.43

t-to

O'

O'

1 R

3 O' |

100.00 j

3.00.00

i &

toO'

-1o3

i &

to

1 O'

Slump inches 1.75 CJ

OJ O

3

to

:•

2.37 Oto

Cv> otoO

8

NO

8

H /c

Air

Content

Gravimetric Method

percent 2.83 1.73 otoH C^v 5

rH

COCO

1—

CO

£>• mO'

C^s

Water

Content

©

-P©

1

o

CH O' O

un

c^\ 3TO H03W)

37.3 35.5

i

41.8

OJ3

CJto

CM

25.2 O

Vinaol Resin

by

Weight

of

Cement

percent 0.005

VO8

to8 a

o

c

odod

0.005 S.

to8

Cement

Content

sacks/yd-^

of

concrete

S.77

8.81 to

to 8

O' 8O'

r

O

O'

9.17 £jcA O'

Proportion

by

Weight

of

Cement

to

Coarse

and

to

Fine

Aggregate

1

:

1.01

:

0.73

o

T3 o

'Oo8

i—

rH

o

T3 od

CMt>O

£>

O'o

rH

o

Tf 8

•a

"80a1

25

|

P-R-l

OJ

1

d.

di

l to

H

4 Z-R-2

—

Z-R-3 1

rH

05A

L-R-2 L-R-3

i

oj a

U o

•P rH © X.' n C -p -p illx: c

to ftj

'd H Vj

i ?* r*

xi a s

E S £ * .

O k © k

mill

'ol ^al

concretes, containing some sand, indicated that an increase in

cement would be necessary to maintain the specified strengths

The substitution of sand in concretes P-C-WM, and P-O-WM

resulted in a higher air content.

The sand, when introduced in the design of concretes P-B

and P-C, reduced the lubricating effect of the fine parent aggregate, This produced a harsher mix and necessitated reducing the

ratio of coarse to fine aggregate to obtain workable concretes.

In general the properties of the fresh concretes indicated

that sand might be substituted for all the fines without adversely

effecting their properties.

Table 4 gives the properties of the cured and heat-treated

concretes. The results indicate that sand may be substituted for

part of the fines of the parent aggregate. The use of sand did

not seriously affect the strength, resistance to abrasion. Young 3 s

modulus of elasticity or ithe shrinkage of these concretes when

tested after two different curing treatments or the heating at

250°C, When, however, specimens were tested either after the 500°C

or 1000°C heat treatment, the results indicate that the sand was

the cause of a reduction, in the strength of the concrete, its

resistence to abrasion, and an increase in the expansion.

Table 5 gives the properties of three cured and heat-treated

concretes designed with sintered slag aggregate and either Portland

Properties

of

Cured

and

Heat-Treated

Concrete;^

with

Sand

Substituted

for

Portion

of

Fines. 3a " 8.

$1

Jr

at

?! 3 8II

li 6 . " 8*5 s „-s s i «° &1 E E “5 a

“•

.. ° 5

-? ° " ll-g

r-l <> - g'S -O fsp

tn&

il5!

Ifi

fill jpf

pi I Sij 5 r3 ? a a I § 6 s-s t +S & Xt • ? a -13 gas

s'9 ! B s a 1 f* ! a a S .i

•9Hnbh : ^ ^

Efeg i;S

3M;! a .a| J r t. % t i 1 £aIss 1I

r.a

>>8. |oaaa 3 2 s °3

'ol

Tabid

5.

Properties

of

Cured

and

Heat-Treated

Concretes

with

Ligitweigit

Aggregate,

Total^ Weight Change

{

2 O rH H 45 t0 O CN © H H

G + 1 + 1 1 1 !

vp -.4 ON CM OJ C- rH cn^tANOtnino OC\»ON<0 0'r,

+ I + i i i i

ntNir, pv rH CNsO 4O r, « vO -4 m

O CN O tO CN O oqi + 1 3 1 1 1

1

3 j

II

percent

-0.000 -0.020 +0.020 -0.031 -0.052 -0.090 +0.462

© 0$3000H4

? 199999 a

CN rH O O t0 CN O

SSSiSSpm

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w

t>vO O'- O s© N-sQ -4- CM O^lMAOlA^n £*, WiACVC^^tObMA

-4’-4'-4'-4, CMrH*-HrH \CQ XirH

'O® ONCN>0 ON -4 'nCVsOO^QtQCN

IN- ~4r Cm n© cn a) H H

CM -4 -4 -4- on CV’ CM rH

lAOf-isO UN UN O xO vOWN^ffvOON -4 tO CN UN tO CM tO UN H CN CN CM CV H

8;

c

O, O s S3 S 2C

m -4* H ~± cn »^

o q ooo

•S do odd

<Q CN O t0 vO 33O O O O H

O O OOO

^5 | 88 SSS

do ooo | •H52

•5 - &<*H "m HOP E Q S

® OlA lAlfcO H »ntO CM vO Q

2 Q <0 lAQN

hb -4- UN r> <S> <0CN

un Q un O Q -4 -4- ON O

-4 un cnH« -4 CN nO CN £*-

ir\ 88 3«8 j

nC*

j

£

vj01

50$

pull-outs;

50$

aggregate

fracture

f

ev

pull-outs;

mostly

aggregate

fracture

90$

pull-outs

90$

pull-outs

all

pull-outs

©1

g

«H

«JW)

<d

P UN g .. |f |1!

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+> J c O I e e

© ©

<d «? bO tiy 2 £

bo ^

© ©

UN O CM UN o ca © © ©

1i1§ "§ § P

? ? ? ? ? it ill

UN CM UN cd

Flexural s

e£

•rH un o mmun ® o r- cn -4- -4 G un sO -4cnH

VSN UN UN O Q to O'- rH CM ON -4t> nO UN r-J O UN P UN O C^CM O sQ tO -4t> O -4

1©

OT©

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UN

UN

UN3O

© "H ©1 Ji -s

aJ o © S 2

&<

Eh £

rHCMCN-4UNNOt>0 rH CM ON-4-UNnO ©-to r-l CM CN -4 UN v© tN-tO

Proportion

by

Weight

of

Cem®t 5

•O flJ S 5P © & sl

3 © °-5

O fr, +>

rHON

.4&« rH

rH

£-

UN

rH

CO<n

rH

rH

CMUN

rH

toUN

rH

rH >

4

i

c

1 2

J

0

1

1

3 s

9 sN

0 o>

3 *

I

© © © * 3 $

| . 2 & a * *

CO ? & c? c?

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s & a "a s, „ © P Orl OXJ-P

rH CO H H ‘H V p *8 $2 I

% csle^fjgg •H © © Q © c> Ch to U £i V W'rt'rt

cl *H © © © ©O ffl H Vc -O © U

'ol < ffi «

- 10 -

Portland pozzolan, or high-alumina hydraulic cement, as the bond.

The results indicate that this type of aggregate may be used in

the design of concretes that will meet the specified technical

requirements. It was, however, necessary to use from eight-andone-half to nine sacks of cement to develop the specified strength.

After curing for 28 days in the fog-room these concretes developed

a flexural strength of well over 650 psi. After the seven day fogroom curing plus the 21-day laboratory storage, these concretes

developed equally as much strength as any of those designed in this

investigation.

After heat treatments at 250°C and 500°C, the concretes

retained a considerable percentage of their original strength. After

the treatment at 1000°C, however, the strength and resistance to

abrasion were reduced materially and nodules of lime were noted in

the concrete. These nodules were up to one-half inch in diameter

and occured most frequently at the surface of the specimens causing

some cracks to develop. Although the source and method of preparation

of this aggregate was traced, no apparent reason for the lime has

been uncovered

- 11 - REFERENCES

1/

2/

3/

y

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ASTM C187-49

ASTM C136-46

ASTM C127-42

A modification of the ASTM method C128-42, suggested by the

laboratories of the Public Roads Administration, and

described in detail in NBS Report, "Investigation of Lightweight Aggregate Concrete", by Kluge, Sparks, Tuma, Clevenger,

and Robinson - December 2, 1949

ASTM C78-49

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.