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NATIONAL BUREAU OF STANDARDS REPORT

NBS PROJECT

0903-20-4428 July 27, 1959

NBS REPORT

6475

QUARTERLY REPORT

ON

EVALUATION OF REFRACTORY QUALITIES OF

CONCRETES FOR JET AIRCRAFT WARM UP, POWER CHECK,

MAINTENANCE APRONS, AND RUNWAYS

by

W. L. Pendergast, E. C. Tuma, Bruce Foster

Refractories Section

Mineral Products Division

Sponsored by

Department of the Navy

Bureau of Yards and Docks

Reference: NT4-59/NY 420 008-1

NBS File No. 9.3/1134-C

Approved:

Raymond L. Blaine

Chief, Concreting Materials Section

IMPORTANT NOTICE

NATIONAL BUREAU OF

intended for use yvithin to additional evaluation a listing of this Report, eit the Office of the Director however, by the Governm

to reproduce additional c

Approved for public release by the

Director of the National Institute of

Standards and Technology (NIST) on October 9, 201 5.

)r progress accounting documents

i formally published it is subjected

ng, reproduction, or open-literature mission is obtained in writing from

C. Such permission is not needed,

illy prepared if that agency wishes

U. S. DEPARTMENT OF COMMERCE

NATIONAL BUREAU OF STANDARDS

QUARTERLY REPORT

ON

EVALUATION OF REFRACTORY QUALITIES OF

CONCRETES FOR JET AIRCRAFT WARM UP, POWER CHECK,

MAINTENANCE APRONS, AND RUNWAYS

1 . INTRODUCTION

The purpose of this project is the development of criteria for the

fabrication of jet exhaust resistant concretes. Concretes under development are evaluated by exposure to hot gases from a combustion chamber.

The combustion chamber delivers these gases at velocities and temperatures

approaching field conditions.

2. X-RAY EXAMINATIONS OF NEAT CEMENTS

X-ray patterns have been obtained on four specimens of neat port land

cement after the following treatments. Cement was mixed with 27.57o water

and placed in the cylinders of bombs*. One sample was taken from a bomb

after fog-room curing for 12 days. A second sample was taken from a bomb

that had received 12 days fog-room curing and seven days evacuation (constant weight). A third sample was taken from a bomb that had received the

fog-room and evacuation treatments followed by heating to 280° C under

increasing pressures to 1000 psi. The cement from which the third sample

was taken was removed from the bomb and placed in a porcelain crucible and

heated at atmospheric pressure to 300® C. The fourth sample was taken from

this material.

The patterns have not as yet been interpreted.

* A schematic diagram of the bomb appears in Figure 2, NBS Report 5233.
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3. EFFECT OF THE LENGTH OF CURING AND

DRYING PERIODS ON THE RESISTANCE OF

BLAST FURNACE SLAG CONCRETE TO JET

IMPINGEMENT

Panels made with blast furnace slag aggregate, that were cured in

the fog-room for 28 days prior to various drying periods, evidenced no

visible loss in the jet blast test. The panels, and the test results,

were reported in NBS Report 6398; for convenience the test results are

also given in Table I of this report. To determine if similar concrete

with only 14 days moist curing would also resist spalling, three 18x18x6 in.

panels were fabricated. The proportions used were similar to that previously reported. A second shipment of blast furnace slag was required

for the work. The grading, bulk specific gravity, and absorption were

similar to the slag of the first shipment.

The properties of the fresh concrete were as follows:

Proportion, by weight of cement, to fine, to

coarse aggregate 1:1.36:2.04

Cement content, sacks/yd

Vinsol resin, by weight of cement,

Water content, gallons/yd^

W/C ratio, by weight

Air content, gravimetric, percent

Slump, inches

Remarks

7.73

percent 0.01

29.40

0.41

3.9

3.5

good workability

Five 6x6x36 in. beams were also cast from this concrete. Tests made

on these specimens are described in Section 5.

The fog-room curing period for the panels was reduced from 28 to 14

days and the drying periods of the 3 panels were 7, 14, and 21 days respectively. The panel P-BF-5-1 (Table 1), after 14 days fog-room curing

TABLE

1.

Effect

of

Curing,

Drying,

and

Jet

Impingement

on

Panels

Designed

with

Portland

Cement

and

Blast-Furnace

Slag

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and 7 days drying, showed a loss measurable by methods 1, 2, and 3, appearing under column, "Jet Impingement Test". Panels 2 and 3, for which the

drying periods were 14 and 21 days respectively, showed no loss. These

data indicate that a concrete made with blast furnace slag may be expected

to resist the jet blast when fog-room cured for 14 days and dried, at

50% humidity and 73°F, for the same period of time. £

The appearance, disappearance, and reappearance in a different location, of pale pink areas, approximately two inches in diameter, noted in

the column headed 'Remarks", Table I, is a phenomena as yet unexplained.

It is noticeable only in concretes that show no visible loss in the jet

impingement test and occurs after a duration of about one minute of the

test.

Repeated jet impingement tests on successive days on panel P-BF-5-3

affected the temperature gradient in the top 1/4 inch. The curves shown

in Figure I give the results of temperature measurements on and within

the same panel during three successive jet impingement tests.

The difference between surface temperatures and those one quarter inch

below the surface at the end of each time interval was greater during the

first test than during subsequent tests. We attribute this to the presence

of more moisture in the concrete available for cooling by evaporation during

the first test.

The studies that were made of the effect of reducing the angle of

impingement of the jet stream from 90 to 15° did not materially alter the

temperature pattern. Temperature data at other positions and depths during

the three tests gave similar results.
-

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TEMPERATURE

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TIME,MINUTES

FIG. I -TIME -TEMPERATURE CURVES AT CENTER SURFACE

AND ONE QUARTER INCH BELOW CENTER SURFACE OF

TEST PANEL DURING THREE JET IMPINGEMENT TESTS.

-4-

4. EVALUATION OF WATER REPELLANTS

To evaluate the merit of surface water-repelling treatments in

reducing the water absorption of concrete during exposure to moisture,

rainfall or high humidities, and thereby improving the concrete's ability

to resist jet impingement, two 18x18x6 in. panels were fabricated using a

Portland diabase concrete. Five, 36x6x6 in., beams were also fabricated

from the same mix. The tests made on these beams will be described later

in Section 5 of this report.

The concrete was a seven- sack mix with 65% coarse diabase and 35%

fine. The W/C ratio was 0.48 resulting in a slump of 6 in. A more detailed description of this concrete was given in NBS Report 5123. Since

it was believed that vacuum-processed concrete has a more open structure

than conventionally placed concrete, this method was used in placing the

panels. These panels were fog-room cured for 21 days. The drying period

prior to the jet blast test was shortened to 14 days with the expectation

that an untreated panel would show some spalling. One panel was treated

with a silicone water repellant at the end of the drying period and permitted to dry for four hours. Both panels were subjected to the equivalent

of a two inch rainfall for 24 hours; and immediately exposed to the jet blast

for 10 minutes. The untreated panel gained weight during the rainfall

exposure, 0.17%; the treated panel did not, but there was a slight increase

in weight from the silicone treatment. During the jet blast test, the

treated panel evidenced some spalling, the untreated none. However, after

I a cooling period of several hours the untreated panel did show some pop-off

failure. This latter type of failure is common when refractories are
'
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subjected to a thermal spalling test. As a result of this limited test we

have concluded that (1) our effort to choose a control concrete that would

show appreciable spalling failed; (2) a longer period of time should elapse

between application of the water repellant and rainfall exposure, and (3)

the concrete should be alternately wetted and dried through several cycles

before exposure to the jet test.

5. ASSESSMENT OF THE EFFECT OF STEAM PRESSURE

AND THERMAL PROPERTIES ON THE FLEXURAL

STRENGTH AND BEHAVIOR IN THE JET BLAST TEST

The resistance to jet blast of room-dry beams was compared to that of

oven-dry beams, with the thought that only thermal stress would be involved

in the latter, while thermal and steam pressure stresses would occur in the

former* The beams, previously mentioned in this report, sections 3 and 4,

were cured in the fog-room, sealed on all but the top surface, as cast, and

dried at 50% relative humidity and 73°F. The seal was removed when the beams

completed this drying period. Some of the beams were further dried to

apparent constant weight at 110°C. The length of the beams, 36 inches,

permitted two tests to be made on 18 in. spans with each beam. Five of

the ten beams were fabricated using blast furnace slag as the aggregate

(see part 3 for batch mix), the other five were fabricated using diabase

aggregate (see part 4 for batch)

.

The curing and drying periods together with the flexural strength

and behavior during the jet impingement tests for the five beams fabricated

with blast furnace slag are given in Table 2. Although this type of concrete, with a comparatively short period of curing and drying, will withstand exposure to jet blast without spalling, the flexural strength is

materially affected. Data, given in Table 2, indicate that slow heating
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- 6 -

to 110 o C, and apparent constant weight, does not affect flexural strength.

Upon jet impingement portions of beams that had been dried at 73°F and

50% relative humidity decreased in flexural strength 45% while those also

dried at 110°C decreased in strength but 25%. As shown in Table 2 column

“Jet Impingement Test, Loss”, drying at 110 did increase the resistance

of this concrete to jet impingement. The specimens with additional drying

also showed no evidence of cracking during jet impingement (see Figure 1,

NBS Report 6398).

The results of tests on the five beams fabricated using concrete made

with diabase aggregate appear in Table 3. The proportions of this concrete

were given in part 4 of this report. Drying at 110°C, after 28 days fogroom curing, and storage at 73°F and 50% relative humidity, increased the

flexural strength of this type of concrete by 30%; jet impingement decreased

the strength of those dried at 50% relative humidity and 73°F by 20%, and of

those receiving the additional drying at 110°C by 30%. The beams of this

set showed little or no spalling during jet impingement regardless of

previous treatments. In those not dried at 110°C there was cracking at the

center of the jet impingement area and evidence of water being forced from

the cracks during the test.

These tests were suggested when it was found that beams subjected to

the jet blast on the top surface, as cast, and those broken in flexure with

loading on the side of the beam, showed much greater loss in strength than

could be accounted for by the small depth of material undergoing temperature

change during the jet blast. The tests are limited in number and are not

conclusive. It appears, however, that the flexural strength test is not
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suitable to assess damage resulting from jet blast. It is presumed that

while only a relatively thin layer of concrete undergoes appreciable temperature rise during the jet blast, damage from thermal expansion in the form

of small cracks extends to greater depths. Such damage might not result

where the jet blast is directed on a large slab, and if it did occur, might

not be permanent because of the possibility of autogenous healing.

6. PERMEABILITY

Earlier work on this project has indicated that concretes made with a

fine grained trap-rock aggregate show better performance in the jet blast

test than concrete with other dense aggregates. Recently it was found that

concretes made with blast furnace slag, a relatively porous and light-weight

material, also performed well. It is evident, that while specifying a

dense, fine grained aggregate may lead to a more satisfactory product, such

a requirement is unduly restrictive and other properties of the aggregate,

or of the resulting concrete, may be of equal or greater importance. Jet

blast tests on evacuated concrete have indicated that permeability to fluid

flow is one of these important properties. An apparatus to measure this

property is being assembled. This apparatus was used by Mong and Massengale

in their work on the air permeability of refractories*. A study of the results in this publication and literature on the permeability of concretes indicated that the air permeability of concrete falls within the range of this

apparatus

.

* Permeability and Some Other Properties of a Variety of Refractory Materials,

1 and 11, J.A.C.S., Vol. 36, No. 7 & 8, July and August, 1953.
’

*
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7 . MISCELLANEOUS

Differential thermal analysis and thermal gravimetric analyses were

made on the three samples of rock submitted by your laboratory at Port

Hueneme. All samples exhibited a gradual loss of weight, in addition to

the initial loss of free water. The weight losses for Napa Quarry, Napa

Basalt, and Juarez Basalt at 500°C were 1.25, 1.5 and 2.87. respectively.

All three aggregates show an exothermic reaction at approximately 30(f C

with some indication that this reaction is accompanied by weight gain.

The thermal conductivity of blast furnace slag concrete was determined

by the NBS Heat Transfer Section. At a mean temperature of 118. 3° F it was

4.29 Btu-in/hr-ft z - T. The density of the specimen tested was 125.2 lbs/ft .

The value for thermal conductivity falls mid-way between those reported for

dense and light-weight aggregate concrete.
.V ' V/-.

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