Approved for public release by the

Director of the National Institute of

Standards and Technology (NIST)

on October 9, 201 5.

NATIONAL BUREAU OF STANDARDS REPORT

1926

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FIRE TESTS OF COLUMNS ENCASED IN

PUMICE-AGGREGATE CONCRETE

by

Nf D. Mitchell

and

A. F. Robertson

U. S. DEPARTMENT OF COMMERCE

NATIONAL BUREAU OF STANDARDS
U. S. DEPARTMENT OF COMMERCE

Charles Sawyer, Secretary

NATIONAL BUREAU OF STANDARDS

A. V. Astin, Director THE NATIONAL BUREAU OF STANDARDS

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NATIONAL BUREAU OF STANDARDS REPORT

NB5 PROJECT NBS REPORT

1002-43-1029 October 2, 1952 1926

FIRE TESTS OF COLUMNS ENCASED IN

PUMICEt-AGGREGATE CONCRETE

by

N. D. Mitchell

and

A. F. Robertson

The publication, reprinting, or reproduction of this report In any form, either In whole or in part, Is prohibited

unless permission is obtained In writing from theOffice of the Director, National Bureau of Standards, Washington

25, D, C, Such permission Is not needed, however, by a Government agency for which a report has been specifically prepared If that agency wishes to reproduce additional copies of that particular report for Its own use.

FIRE TESTS OF COLUMNS ENCASED IN

PUMICE- AGGREGATE CONCRETE

ABSTRACT

Fire- endurance tests have been performed on three loaded

6-in. 20 lb steel H section columns protected by 2 in. of

monolithic concrete. The concrete used was mixed in the ratio

of 1:3 1/8:1 1/2 by volume using pumice as the fine and coarse

aggregates. Pumice from a different source was used for preparation of the concrete for each of the specimens. These were

representative of material available in New Mexico, Oregon and

California. It is shown that the particular specimens tested

provided fire-endurance periods of more than four hours. There

was little evidence of differences in performance of the

various aggregates tested.

1. INTRODUCTION

Three 6- in. steel H columns protected by 2 inches of

pumice-aggregate concrete were subjected to fire-endurance

tests 267, 270 and 271, during July and August 1950. Different aggregates were used for each column encasement.

These pumice aggregates were representative of those available in New Mexico, Oregon and California respectively.

Auxiliary fire-endurance tests were made on a wall panel,

268 , and a floor, 269, constructed of the same kind of

concrete. The tests were made at the request of the Office

of the Chief of Engineers, Department of the Army, to develop

information on the behavior of such concretes when exposed

to fire.
2

2. MATERIALS

2.1 Steel Columns

The fabricated columns were made of 6- in. 20 lb stanchion

sections having a cross-sectional area of 5*88 in. The heads

of the columns were restrained for 32 1/4 in. by means of

1/2-in. flange cover plates, leaving an effective column

length of 123 3/4- in. as shown in figure 1. The column ends

were milled square with the column axis, thus allowing direct

loading contact with the 1 7/8- in. steel bearing plates. The

columns were hot riveted. The least radius of gyration of the

columns was 1.50- in. and the £-/r ratio was 82.5*

2.2 Concrete

The pumice concrete used for encasing the columns was

one part portland cement, 3 1/8 parts fine aggregate and 1 1/2

parts coarse aggregate by volume. The aggregate used in the

concrete for encasing one column, the floor, and the wall

panel was from New Mexico. Because of the difficulty of placing

the harsh mix made with this aggregate, an alkyl aryl sulphonate was used as an air entraining agent in the concretes

made with the Oregon and California aggregates for encasing the

other two columns. The proportion of chemical used was 1 part

to 850,000 parts cement. The aggregates were water soaked

before mixing.

After seasoning, the concrete cylinders made with the

aggregate from New Mexico weighed 96 lb/ft^ and had a moisture

content of 18 percent; those made with the aggregate from

Oregon weighed 101 lb/ft^ and had a moisture content of

32 percent; and those made with the aggregate from California

weighed 103 lb/ft8 and had a moisture content of 21 percent.

The moisture contents seemingly indicated the tenacity with

which the aggregates held free water. Sieve analyses and bulk

density measurements of the dry aggregates are presented in

table 1.
3

FIG. I. TESTS 267,270,271. CONSTRUCTION DETAILS OF STEEL COLUMNS. FP2983
- 4 -

Table 1. Sieve analysis and specific density of

pumice aggregates.

Sieve Amount retained on sieve

designation

New Mexico Oregon California

Coarse Fine No.l* Fine No. 2* Coarse Fine Coarse Fine

percent percent percent

1 in. 0 0 0 0 0 0 0

3/4 in. 0 0 0 0 0 11 0

1/2 in. 0 0 0 0 0 68 0

3/8 in. 4 0 0 0 0 95 0

No. 4 96 2 0 52 1 99 13

8 97 36 20 87 32 99 42

16 97 69 46 88 59 99 58

30 97 88 77 89 62 99 68

50 97 94 77 89 70 99 76

100 98 95 83 90 71 99 81

Specific 26 39 58 29 38 32 50

density

lb/ft3

New Mexico fines No. 1 used for columns and fines No. 2 used

for slabs.

2.3 Wire and Rods

Steel wire of No. 6 ga (0.192 in. diam) was used for the

spiral reinforcement to bond the concrete to the columns.

Welded steel fabric of 6- by 6- in. mesh by No. 4 ga (0.225 in.

diam) wire was used as reinforcement in the concrete slabs.

Three 3/4- in. diam hot rolled steel rocSs were also used to

reinforce the floor slab.
- 5

-

3o CONSTRUCTION

3 o'l Preparation of Columns for Covering

i The, columns were prepared for covering with concrete by

mounting thermocouples and winding a 6-ga wire (0.192 in.

diam) spirally around the column on 8- in. pitch as shown in

figure 1. The wire spiral had about 1-in. clearance at the

center of the column flanges, leaving a 7/8- in. clearance

between the wire and the outside of the concrete covering.

Each turn of the wire was tack-welded at one of the four points

where it came in contact with the column edges.

3o2 Placement of Concrete

Plywood forms were spaced 2 in. on all sides from the

vertical column shafts 0 Concrete poured into the tops of the

forms was compacted around the columns by vibrating the form

sides with an air hammer. In mixing the concrete for the first

column, the aggregate from New Mexico was incorporated into

the batch as received from the producer Because of difficulties

encountered in handling the concrete prepared in this manner,

the two remaining concretes were prepared with an air entraining

agent and aggregates which had been water soaked for twelve

hours

The two 4- in. thick concrete slabs were also prepared in

wood forms o The wall panel was 4- by 8- ft and the floor, 4- ft

4- in. by 9-ft. Both were reinforced with wire fabric, the

latter with rods as well.

Each concrete batch was mixed for not less than 1 1/2 min

before the water was added and not less than 2 min afterward.

The water content was controlled to produce a slump.

Three 6- in. diam by 12- in. cylinders were cast from each of

the three concretes. Compressive tests were made at the time

of the fire tests of the columns; the results of these tests

are presented in table 2. The low strength of two of the

three cylinders of concrete made with the pumice aggregate

from New Mexico is evidence of the difficulties experienced

when working with this aggregate without previous wetting and

subsequent treatment of the mix.
- 6 -

Table 2. Compressive tests on concrete cylinders

.

Moisture

Aggregate type Compressive strength content of

cylinders

i

r

, 1

lb/in. 2

2 3

' percent

t

t New Mexico ' 1210* 2260 1550* ' 18

Oregon ' 2l40 2100 2090 ' 32

California ' 2200

! 2310 2190 ' 21

1 * Large voids in interior of cylinders probably

caused by rodding of harsh mix during filling

of cylinder molds 0

3.3 Workmanship

The fabrication of the steel columns was of good commercial quality. The concrete was also of good quality for both

the Oregon and California mixes. The difficulties of working

the pumice aggregate from New Mexico in the dry condition

caused some small voids in the column encasement and rough

surfaces on the column and the two slabs. These surfaces were

smoothed by the use of mortar composed of cement with pumice

fines after removal of the forms.

3 A Seasoning of Concrete

The forms for the columns and cylinders were stripped

after one day, and the concretes dampened daily for the next

6 to 13 days, after which the columns were weighed periodically for fifteen days, during which time the laboratory was

heated to about 130°~F at night and allowed to cool to about

85° F during the day. The weight of the concrete column coverings

made with pumices from New Mexico and Oregon remained reasonably

constant after 13 days and 10 days, respectively. However, that

made with pumice from California did not remain constant, but

lost three pounds during the last seven days of seasoning, of

which one pound was lost during the last two days. The column

coverings made with pumice from New Mexico lost 12 pounds and

those made with pumices from Oregon and California lost 13

pounds each during seasoning.
- 7

-

4. EQU PMENT AND TEST METHOD

4.1 Equipment

A gas-fired furnace was used for testing the columns.

Load was applied to the columns by means of a hydraulic jack

under the furnace floor. It was maintained by a pump which

supplied oil to the jack at constant pressure. The movable

section of the floor of the furnace was supported on a

spherical bearing block resting on the jack piston.

Temperatures in the furnace combustion space were

measured by 12 thermocouples protected by iron tubes. These

tubes projected from the furnace walls and roof. The temperatures at 28 points in the steel column were measured by

thermocouples made from No. 24 ga duplex chromel-alumel wire.

The wires were protected with an insulation of woven glass

impregnated with silicone varnish. The ends of the pair of

wires were twisted and welded together and the resulting

junction inserted to a depth of about 1/8- in. in a hole in

the steel column and secured therein by swaging the steel

around the hole. The junctions were arranged with seven thermocouples at each of the four levels of the column as indicated

by positions B, N, M and T, in figure 2.

The concrete floor vs tested in a furnace having a

combustion space 4- ft 10- in. w de , 8- ft long, and 3- ft high.

he six thermocouples were protected by iron tubes as in the

column furnace. Temperature measurements in the steel rod

reinforcement were obtained by means of thermocouples inserted

into each rod at mid-length. The leads of these thermocouples

were cast into the concrete floor to emerge on the unexposed

side. Surface temperatures were measured at six locations on

the top of the concrete floor. The junctions and a short

length of the termocouple leads were placed under 6- in.

square by 0.4-in. thick felted asbestos pads.

The concrete wall panel was tested in a furnace with a

combustion space 4- ft 8- in. wide, 10-ft high, and 2-ft deep.

The furnace temperatures were measured with nine chromelalumel thermocouples protected in iron tubes. Surface temperatures were measured with six thermocouples held in

contact with the unexposed wall surface by felted asbestos

pads.

- 9

-

k.2 Test Specifications

The tests were conducted in accordance with the Standard

Methods of Fire Tests of Building Construction and Materials,

A.S.T.M. Designation E119-V7, except that the floor and wall

were of substandard size. These methods require that one side

of the wall, the underside of the floor, and the complete external surface for at least 9- ft of column length be exposed

to a fire controlled to conform closely to the time temperature

curve defined by the following points:

1,000°F at 5 min

1,300°F at 10 min

1 ,550°F at 30 min

1,700°F at 1 hr

1,850°F at 2 hr

and rising 75 degrees F per hr thereafter.

The specifications require that during the fire test the

column be subjected to the normal working load or, alternatively

tested without load but with the temperatures measured in a

prescribed manner. The fire-endurance limit is considered as

being reached when the column fails to support the applied

load or, in the alternate test, when the average temperature

of the steel at any one level in the column reaches 1000°F

(538°C) , or the temperature of the steel at any one of the

measured points reaches 1200°F (6 1+9°C).

Walls and floors are considered to have reached their

fire-endurance limit when flame breaks through the structure,

when gases hot enough to ignite cotton waste pass through,

when the average temperature rise of five or more locations

on the unexposed surface amounts to 250 degrees F, or the increase of temperature at any one of the locations becomes

325 degrees F.

4.3 Bearing of Columns

Steel bearing plates were bolted to each end of the columns.

The lower plate- was 20- in. square and 1 7/8- in. thick. The 25-

by 27- by 1 7/8- in. top plate was fastened to the column with

fourteen 7/8- in. bolts, and it in turn was bolted to the overhead structure of the loading device. Three-fourths inch of

grout was used between the bottom bearing plate of the column
10 -

and the furnace floor. As the floor rested on a well- lubricated

ball and socket joint whose center of curvature fell on the

center line of the column at its lower end, the column can be

considered as having one spherical end bearing.

4.4 Restraint of Columns

The method of fastening the column head gave substantially

effective restraint against bending of the upper 32 1/4- in. The

upper end of the 10- ft 3 3/4- in. length can be considered as

fixed, figures 1 and 2.

'4o 5 Loads on Columns

The load applied to the columns during test was computed

from a formula recommended by the American Institute of Steel

Construction, as follows:

P = A 17,000 -, ,0.485

' in which P is the total load on the column, A is the

cross sectional area of the steel shaft, its effective

length, and r its least radius of gyration. For these

columns, the values are:

A = 5»88-in. 2 = 123 3/4- in.

r = 1 . 50-in.

Entering these in the above formula gives the value of

P as 80,500 lbs total load on A, equivalent to a stress

of 13,700 lbs/in.

This load, which was applied before starting the test

fire, was maintained during test until rapid yielding of the

column occurred. Load was removed when the yield of a column

from its maximum expansion amounted to about 0.6 in. , or

about three-fourths of its thermal expansion.

4 0 6 Measurement of Deformations

Changes in length of the column were indicated by obser-

•vations of a dial micrometer arranged to measure movements

of the piston of the hydraulic loading jack. Movement
- 11 -

of the framework supporting the overhead bearing . plate , due

to expansion, was small in comparison with the expansion of

the exposed portion of the column. No measurements of lateral

deflections were made during the tests.

4.7 Mounting of Floor

The floor was mounted on the furnace with each end

bedded on 3/4- in. of portland cement mortar. No load was

applied during the test, but deflections were measured at

two locations at the midspan of the floor. These deflections were measured between' a stationary beam>and the top

of the floor by means of a rule.

4.8 Mounting of Wall

The wall was mounted in a steel and concrete frame

which supported it at the front of the furnace. It was

held in the frame by 5/16- in. bolts, spaced about 18-in.

apart, in contact with the wall surfaces along each vertical edge. This method of mounting served to restrain the

wall somewhat against lengthwise bending. Deflections were

measured at the center of the panel surface and at 12-in.

each side thereof along the horizontal center line.

5. RESULTS OF TESTS

5.1 Columns (General)

Although shrinkage cracks developed in the concrete

encasements, they remained in place even after load failure

of the columns. These cracks are evident in the photographs of

the tested columns, figures 3 and 4. None of the cracks in the

concrete exceeded o/8-in. and most of them were less than

1/8 in. -wide. The test results on the individual columns are

presented in the first section of table 3 and the following

test logs.
12

-Column

after

test.

Fig.

4

—

Column

after

test
- 13 -

5.2 Test 26 7 Column, New Mexico Pumice Concrete

5.2(a) Test Log

Time Observations

hr : min

0:00 Test started 10:54 A.M. , July 3l, 1950.

0:05

Initial temperature 86°F.

Corners of column red.

0:15 Column is dull red.

0:30 Cracks on north and east sides.

0:42 Two cracks on north, 3-ft and 1-ft in

0:52

length; many fine cracks on other sides.

Large cracks on all sides about l/l6-in.

1:21

wide and 6- to 12- in. in length.

Cracks larger on all sides.

1:32 Crack on north continuous for almost

2:00

entire column length.

Cracks on south about 1/8- in. wide.

3:06 Very large crack on north, column bright

3:57

orange.

Some cracks on east about 1/4- in.

4:45 Oil supply to jack shut off.

4:47 Gas off.

Examination of the column after test indicated that the

covering had been well distributed around the column. The

thickness of the shrunken concrete over the steel averaged

1.9- in. with a maximum deviation of 3/l6-in.

5.2(b) Temperatures

Furnace and column temperatures are shown in figure 5*

Temperatures of the steel column are plotted as (a) the

highest at any level (b) the minimum average at any level

and (c) the average at level N.

The rapid rise of temperature of the steel to 212°F

(100°C) within 10 min at level B was probably caused by a

fault in the concrete covering. It may, however, have been

caused by the separation of a thermocouple from the steel.
- lb -

0o‘3dniVd3dW31

o

o

ro o o

0001 o o o O o o o O

CM o o o o O o o o O

— CD 00 CO in ro 00

00

IsCO

ID

ro

CM

o

CO

ID

ro

CM

3o ‘3dniVd3dlAI31

TIME,

HRS.

FIG.

5.

TESTS

267

AND

270.

TEMPERATURES

DEVELOPED

IN

COLUMNS

AND

CONCRETE

ENCASEMENTS

MADE

WITH

PUMICE

AGGREGATES

FROM

NEW

MEXICO

AND

OREGON.

FP2983
- 15 -

The average temperature at level N reached 1000° F at

4 hr 21 min and thus represents the limit as defined by an

average temperature at one level. The temperature of 1200°F

at one thermocouple was reached after 4 hr 51 min fire exposure. The fire exposure during the test, as represented

by the area under the curve of average temperatures, was

101 percent of that under the standard reference curve.

5.2(c) Expansion of Column

The changes in column length are shown in figure 6.

The column reached its maximum length in expansion after

4 hr 35 min of fire exposure. The load was removed after

4 hr 45 min fire exposure at which time the column length

had been reduced by about 0.1- in. Through inadvertence

,

the test was terminated at this time, estimated as about

10 min before the usual limit of yield of 0.6- in. in compression would have occurred; therefore the time of failure

of this column under load is recorded as 4 hr 55 min.

’est 270 Column, Oregon Pumice Concrete

5.3(a) Test Log

Time Observations

hr: min

0:00 Test started 9:49 A.M. , August 4, 1950.

Initial temperature 77° F.

0:10 Fine cracks outlined by moist darker

areas

0:20 Corners of column red.

0:30 Prominent cracks on west about 3-to 4-

ft up.

0:35 Larger crack on east 3-ft up

0:47 Cracks better defined over the column

surface.

1:26 Pronounced vertical crack on north.

l:4l Vertical crack on south.

1:50 Cracks a little larger; no evidence of

moisture

2:15 Crack on north side about l/l6-in. wide

(column web lies in north south plane).

2:30 Cracks on north and south about 1/8- in.

wide
EXPANSION

IN

INCHES

- 16 - TEMPERATURE °F

200 400 600 800 1000

TEMPERATURES

FIG. 6. TESTS 267,270,271. EXPANSION OF LOADED COLUMNS

WITH INCREASING TEMPERATURES. FP2983
- 17 -

Time

hr : min

Observations

6:11 1/2

6:10

6:00

5:50

5:10 Cracks on south about 1/4- in. wide.

North windows of furnace opaque.

Column has stopped expanding.

Small yellow flame on column surface

about 6-ft up. Evidently gases coming

from large horizontal crack are burning.

Oil shut off after about 0.6- in. contraction of column. Load failure.

Gas fire off.

Examination of the column after the test showed the

concrete covering to be denser than that for test 267 . The

aggregates had become vitrified to a depth of 1 /2- in. from

the surface. After the test, the thickness of the shrunken

concrete was measured at 19 locations along the column

edges and found to average 1 . 9- in.

5.3(b) Temperatures

Temperature data are presented in figure 5* The average

temperature of 1000°F occurred at level N after 5 hr 23 min

fire exposure. A maximum of 1200°F occurred at level B after

6 hr 2 min fire exposure.

The fire severity during the test period was 100 percent of the prescribed normal.

5.3(c) Expansion of Column

Data on the expansion of the column along its length

are presented in figure 6 . The column reached its maximum

expansion in length after 5 hr 50 min fire exposure. The

load was removed after 6 hr 10 min of exposure, at which

time the column length had been reduced by 0.6 in.

,

marking

its failure under load.
18 -

5 A Test 271 Column, California Pumice Concrete

5.4(a) Test Log

Time Observations

hr : min

0:00

0:15

0:28

0:32

0:35

0 AO

1:13

1:23

1:53

2:15

3:35

3:54-

4-: 50

5:20

5:30

5:55

5:57

Test started 9:4-7 A.M. , on August 9,

1950. Initial temperature 8l°F.

Small cracks visible on west side 4— ft

up.

Small crack 3- ft up on east side.

Small cracks near bottom of east and

south sides.

Network of fine cracks on north.

One crack on east 1/32- in. wide;

others finer.

Many horizontal cracks.

Crack on south about 1/16-in. Most

are horizontal on south and east;

craze cracks on north and west.

Cracks on north and west better

defined; vertical cracks on north

and west developing.

Vertical cracks north and west.

Cracks a little wider and better

defined.

Cracks on south about 1/8- in. wide.

Some cracks about 1/4- in. wide.

Cracks on east appear to be 3/8- in.

wide.

Column not expanding.

Load removed from column.

Gas off.

Examination of the column after the test showed the

covering to be compact and well supported with a small

amount of vitrification. Measurements of the concrete at

24- locations along the column edges indicated an average

thickness after shrinkage of 1.95- in. > with a maximum

deviation of 3/l6-in.

5A(b) Temperatures

Temperature data for this test are presented in figure

7. The average temperature of 1000°F occurred at level B

after 5 hr 25 min fire exposure. A maximum of 1200°F occurred
TEMPERATURE,

19

2400

2300

2200

2100

2000

1900

1800

1700

1600

1500

Ll 1400

1300

1200

MOO

1000

900

800

700

600

500

400

300

200

100

0 01 2345678

TIME, HRS.

FIG. 7. TEST 271. TEMPERATURES DEVELOPED IN COLUMN AND CONCRETE ENCASEMENT

MADE WITH PUMICE AGGREGATE FROM CALIFORNIA. FP2983

1000

900

1300

1200

MOO

800

700

600

500

400

300

200

100

Oo

TEMPERATURE,
20 -

at level N after 5 hr 56 min fire exposure. Thus these both

represent column fire resistance periods as limited by temperature of the steel in accordance with the alternate method

of test.

5.4(c) Expansion of Column

Longitudinal expansion data for the column are presented

in figure 6. The column reached its maximum length after

5 hr 30 min fire exposure. A total contraction of about

0.6- in. had taken place at 5 hr 55 min, marking failure of

the column under load, whereupon the load was removed.

5.5 Test 268

Exploratory test of New Mexico Pumice Concrete Wall Panel

5.5(a) Test Log

Time Observations

hr : min

0:00

0:24

0:28

0:45

0:50

1:10

1:27

2:25

2:30

3:00

3 : 46

4:50

5:08

Test started 9:30 A.M. , August 1, 1950.

Initial temperature 86° F.

Small crack across panel outlined by

damp area.

Small amount of water bubbling from

crack on unexposed surface.

Water stopped bubbling from crack.

Fine cracks appear in exposed surface

of panel.

Additional cracks, including two on

fire exposed side.

Horizontal crack near bottom appears

to extend through wall.

Steam from cracks.

Initial cracks now l/l6-in. wide.

Many cracks on exposed surface some of

which seem to pass through slab.

Original horizontal crack now dry.

Cracking sounds.

Gas off.

During the test, the supporting frame bowed out at

both ends from 1-to 2- in. from the front of the furnace.

The panel naturally followed the frame curvature. After

the test the frame resumed its normal plane shape and
21

the panel likewise straightened out leaving almost no sign

of cracks on the unexposed surface. Figure 8 shows the fine

network of cracks on the fire-exposed surface after, the test.

5.5(h) Temperatures

Furnace and surface temperatures are presented in figure

9.

The limit of surface temperature rise was reached after

4 hr 48 min fire exposure when thermocouple No. 4 showed a

rise of 325 degrees F. This thermocouple was located directly

over one of the larger cracks which evidently was the cause

for early failure. The average surface temperature rise limit

of 250 degrees F was reached after 5 hr 6 min of fire exposure.

The severity of the fire exposure was 100 percent of the

normal specified by the A.S.T.M. standard test methods.

5.5(c) Deflections

Deflections as measured during the test were minor and

of no particular significance because of the restraint furnished by the mounting frame.

5.6 Test 269

Exploratory test of New Mexico Pumice Concrete Floor Panel

5.6(a) Test Log

Time Observations

hr: min

0:00 Test started 9:18 A.M. , August 2, 1950=

Initial temperature 88°F.

0:09 Cracking sounds. Fire exposed surface

has two spalled areas about 1/4 in. deep.

0:11 Cracking continues; one reinforcing

rod partly exposed to fire.

0:l6 Loud cracking. About 1/3 length of center reinforcing rod now exposed to fire.

0:l8 Cracking sounds frequent. About 1-in.

thickness of ceiling spalled off.

0:26 About 1/3 width of under surface of

floor had spalled off.

0:30 Crack and moist areas across floor'

surface.

0:37 Spalling appears to have nearly stopped.
2

2

Fig. 8—Fire-exposed surface after test
d 0 ‘3dnitfU3dlAI31

TIME

,

HRS.

FIG.

9.

TEST

263.

TEMPERATURES

DEVELOPED

IN

THE

FIRE

TEST

OFA

WALL;

DETAILOF

THE

WALL

CONSTRUCTION

AND

LOCATIONS

OF

THE

THERMOCOUPLES.

FhP.983
Time

hr : min

Observations

0:44 A large crack formed through the concrete near the south and at the east

reinforcing rod.

0: 46 Spalled area 2- in. deep in spots, wire

fabric visible.

0:49 Most of top surface cracks now dry.

1:13 All moist spots and most of the cracks

on the top surface are near the west

side of the floor.

1:19 Steaming has stopped.

1:58 Large cracks on fire exposed surface.

West reinforcing rod exposed.

2:21 Large crack across ceiling.

2:29 Piece of cotton fabric placed on a hot

spot about 10- in. south of center floor

2:30 Cotton scorched.

2:31 Cotton burst into flame.

3:17 Fire visible through crack at hot spot.

3:30 Large crack near northwest corner of

floor

.

4:00 Cracks larger.

4:23 Gas off.

It was obvious that this floor slab would have failed

much sooner if it had been loaded. Figure 10 shows the

spalling and cracking of the fire exposed side of the floor.

5.6(b) Temperatures

Figure 11 shows the temperatures of the one steel

reinforcing rod that remained protected by the concrete.

The temperatures in the central rod, which was exposed to

the flame shortly after the start of the test, rose very

rapidly, and after 25 min were about the same as those

measured by the furnace thermocouples.

Figure 11 also shows average and maximum surface temperatures. It is evident that during the test the hot spot

mentioned in the test log was at a much higher temperature

than any of the surface thermocouples. A piece of cotton

placed on this spot 2 hr 29 min after the start of the test

caught fire and burned in about 2 min, thus defining the end
25

Fig.

10—

Test

269.

Exposed

surface

of

floor

after

test.
26

CO

CLX

^ LU

rO

c\J

o

do‘3UniVd3dlAI3±

FIG.

II.

TEST

269.

TEMPERATURES

DEVELOPED

IN

THE

FIRE

TEST

OFA

FLOOR

;

DETAILS

OF

THE

FLOOR

CONSTRUCTION

AND

LOCATIONS

OF

THE

THERMOCOUPLES.

FP2983
- 27 -

point for this test. The limiting temperature rise of

325 degrees F occurred at one thermocouple location after

3 hr 11 min of fire exposure. The limit of average surface

temperature rise of 250 degrees F occurred after 3 hr 45 min

of fire exposure.

The severity of fire exposure was 101 percent of that

specified by the A.SoT.M. standard test method.

5.6(c) Deflections

An abbreviated table of deflections at the mid- span of

the floor are tabulated below;

Deflections

Time East of center West of center

hr ; min in. in.

0; 00 0.0 0.0

0:30 0.8 1.3

1:00 1.1 1.2

1:30 1.9 2.4

2:00 3.0 3.8

2:30 4.3 5.8

3:00 4.9 7.3

3:30 5.6 9.1

3:45 5.9 10.0

4:00 6.3 10.8

Although no load was applied to the floor during this

test, the deflections began early and became excessive after

3 hr 45 min fire exposure, at which time the limiting rise

of average surface temperature, 250 degrees F (139 degrees C)

was reached. An unfortunate arrangement in the placement of

the steel fabric at the middepth of the slab instead of

below the rod reinforcement is thought to have not only contributed to the rapid deflection of the slab but also to

have been a factor in inducing early spalling of the ceiling

surface to expose the reinforcing rods.
TABLE

1/

SUMMARY

OF

DATA

FROM

FIRE

TESTS

OF

PROTECTED

STEEL

COLUMNS

- 28 -

NBS

Building

Materials

and

Structures

Report

BMS

124
29 -

60 DISCUSSION

6,1 Type of Aggregate

Table 3 summarizes the data from the column tests and

from three previous series of tests » Those data are presented which fit the following requirements:

lo The column shafts were of H section.,

2 0 The cross sections were either square

or nearly square

3o The thickness of the covering over the

steel was 2 in 0 (note two exceptions ),

Examination of the data reveals that with one exception

the fire exposure time to the ®end of the expansion was

greatest for the columns protected by the pumice concrete

The exception is the column protected by the wood-fibered

gypsum concrete, column 1, reference 1, table 3° This column

initially had 1/2 in D greater thickness of protection than

the columns protected by pumice concrete; it was also subjected to higher unit stress during the test. If fire

resistance is proportional to the 1 0 7 power of the covering

thickness, this 1/2 in, additional thickness of insulation

would more than compensate for the observed difference in

fire exposure time required to produce the full column

expansion However, in that test the 1/2 in, of sanded

gypsum plaster fell from place early and could no longer be

considered effective,. Even considering this, it can be said

that for .a. given thickness, the pumice concrete seems to

provide thermal protection for the steel shaft approximately

equal to any of those llstedo

The difference in fire-exposure time between the end

of the expansion period and failure under load is greater

for the limestone concrete and other dense concrete

coverings than for' the other coverings tested. It is evident that this additional fire resistance results from 'the

fact that this concrete carries a large portion of the

applied load, which was not the case with the pumice concrete, the gypsum concrete or gypsum block coverings shown

in table 3 o *

Tests 28, 28a and 30 of reference 2 show greater fire

resistance for the limestone-concrete covered column than

for those protected by the pumice concrete „ The difference
- JO -

between the 8- in. 34 lb H sections of these three test

columns and the 6- in. 20 lb H sections of the pumice

concrete protected columns has a marked effect on the

fire resistance of the columns.

In general, the pumice concrete coverings protect

columns by their high thermal- insulation properties. The

protection afforded by limestone and other denser concretes

results from moderate insulation properties coupled with

the comparatively high load- carrying ability of the

covering even when exposed to high temperatures.

6.2 Floor and Wall Panels

Table V presents a summary of the data from the tests

on the floor and wall panel of pumice concrete and from one

test on a wall of denser concrete. The time required for

failure in this case is governed by the temperature rise of

the unexposed wall surface. Both pumice concrete specimens

showed greater fire resistance than that exhibited by the

dense concrete wall previously tested. This again emphasizes

the good thermal protection afforded by the pumice-aggregate

concretes

.

Table 4. Summary of data from fire tests of floor

and wall panels

Test' Structure 1 t Exposure ,

'

Temnerature limits

No. ' i Material ' percent 1 ’Type Thick- 1 ! of ' Avg Max

ness

. . !_

r tL. standard 1L_ surface surface

i in. » t 1 hr : min hr: min

268 -Wall

i

i

i

4 ' 1:3 1/8: » '11/2 »

' pumice »

' concrete »

100

1

1

i

1

1

5:04 4:48

269 | Floor 4

1 11 '

1 1 101 1

t 3:^5 2:29*

E2** ' Wall

t

1

1

»

1

4 ' 1:2 1/2: » '3 1/2

1 Potomac '

' river '

1 grave.l; '

1 concrete '

100 1

t

1

1

1

1

1:18 1:15

* Localized hot spot caused by spalling

**Previously unpublished data
- 31 -

During tests of the cylinders, it was notice^ that a

shell of about 1/2 in, thickness around the outside of the

cylinder appeared dry while the central core of the cylinder

was darker in color and seemed damp, Samples were therefore

removed from both the surface and interior of the cylinders

and dried in an oven heated to 220°F (lO^C). An attempt was

made to select the samples in such a manner that they would

be representative of the cylinder as a whole rather than

either the surface or the interior,. The weight loss of the

samples was 18 , 32 and 21 percent of the weight of the dried

concrete made from aggregates from New Mexico, Oregon and

California, respectively,.

The effectiveness of the coverings in providing protection was probably influenced by the amount of free water

retained during the seasoning period „ Therefore, the

differences in protection provided by the concretes made

with the three pumice aggregates can be attributed in part

to the differences in moisture remaining in the column

encasements o Since the failure time of the columns protected

by the concretes made with pumice aggregates and the moisture

contents of these concretes were in the same order, it may

be concluded that the differences in time of failure of these

columns can be attributed in part to the differences in

moisture content, and that there is likely to be little

difference, in the fire-resisting properties of the concretes

made with the three pumice aggregates , The low strength and

porous nature of the New Mexico pumice cylinders, as shown

in table 2, are evidence of the poor workability of the

concrete without the air entraining agent and soaking of the

aggregates before mixing the concrete

,

7 o CONCLUSIONS

The high moisture content discovered in testing the

cylinders, while probably representative of conditions in the

concrete coverings for the columns, is not considered representative of conditions to .be expected in buildings which have

been in service for several years. Consequently , the fireresistant performance observed in these tests was higher than

would be expected from aged installations. This has been recog

nized in arriving at the following conclusions;

1, A column of 6 in, H section steel protected by pumiceaggregate concrete as described will resist fire for b hours

or more before failure occurs under load.
- 32 -

2. Protection of steel columns afforded by pumiceaggregate concretes is mainly of a thermal character. It is

probable that the concrete does not carry a significant

portion of the load at the time of failure from fire exposure.

3. Taking into consideration lower moisture content

and the harsh mix characteristics of the concrete made with

the pumice from New Mexico, it will be found that there is

likely to be little, if any, difference in the fire resisting

properties of concretes made with the pumices from New Mexico,

Oregon or California.

TG10215-1:FP2983 - a

Tests Nos. 267? 270 and 271


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

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