National Bureau of Standards

Library, N. W. BIdg.

AUG 1 9 1952

Fire Tests of Gunite Slabs and Partitions

United States Department of Commerce

National Bureau of Standards

Building Materials and Structures Report 131
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UNITED STATES DEPARTMENT OF COMMERCE • Charles Sawyer, Secretary NATIONAL BUREAU OF STANDARDS • A. V. Astin, Acting Dirtctor

Fire Tests of Gunite Slabs and Partitions

Nolan D. Mitchell

Building Materials and Structures Report 131

Issued May 12, 1952

For sale by the Superintendent of Documents, U. S. Government Printing Office, Washington 25, D. C.

Price 15 cents
Foreword

The use of noncombiistible constructions for restricting the spread of fire makes necessary a knowledge of the fire-resistive properties of the materials

used in them.

This paper gives the results of fire tests on gunite concrete in the form of

slabs and partitions. In addition to reporting the fire-endurance limits of

gunite of conventional cement and sand mix, a means of improving the fire resistance of this type of concrete by modifying the aggregate is presented.

Such modification would probably be effective in other types of concrete as well.

A. V. AsTiN, Acting Director.

CONTENTS

Page Foreword

1. Introduction and scope

2. Materials

3. Construction of slabs and partitions

4. Equipment and method. of testing.

_

5. Results of tests

II

11

122

2

5

10

5.1. Slabs

5.2. Partitions

6. Summary and discussion

II
Fire Tests of Gunite Slabs and Partitions

Nolan D. Mitchell

Eight slabs and four partitions made with gunite concrete on wire-fabric reinforcement were subjected to lire-endurance tests at the National Bureau of Standards. The slabs were made with aggregates composed of sand and wood sawdust, the sawdust ranging from 0 to HO percent by volume of the aggregate. The aggregate for two partitions was sand, a third had a minor amount of asbestos added, and that of the fourth consisted of equal volumes

of sand and sawdust. Fire-endurance limits for the slabs increased almost linearly with

increased percentages of sawdust incorporated into the mix. Partitions made with sand

aggregate only in the concrete or with the addition of a small amount of asbestos tiber to the concrete showed early failure by spalling and holing through. The explosive violence

of the disruptions suggested the presence of entrapped water in the dense concrete. A

partition made with a concrete having equal volumes of sawdust and sand as aggi-egates did not spall and failed by a limiting 325 deg F rise of temperature at a single point on

the unexposed side after 70 min of tire exposure, whereas the partitions having asbestos and sand or sand only as the aggregate reached tire-endurance limits through explosive

spalling in 16 to 26 min. Subsequent to the tire-endurance test, the partition with sawdust

successfully withstood the application of the hose-stream test. The effect of the sawdust

is to lower the thermal conductivity of the concrete and increase its porosity, thus making

easier the escape of moisture in the form of vapor.

1. Introduction and Scope

Fire-endurance tests were conducted at the

National Bureau of Standards on eight slabs and

four partitions made of gunite concrete with

welded-wire fabric reinforcement. In addition to

its extensive use as linings for flumes, conchiits, sewers, and reservoirs, gunite has been used as

fire-protective coverings on structural members

and as readily apjilied coatings, such as stucco on

buildings. This type of concrete has also been

suggested as suitable for the construction of fire- resistant curtain w'alls to prevent or reduce the

spread of fire among flammable materials. The

tests described in this report were made to investigate the properties of gtmite in slabs and partitions when subjected to standard fire exposures. Tests on steel columns Avith gypsum fire-protective coverings had shown that a gypsum concrete having wood chips as the aggregate was superior

in fire protection to other types of gypsum encase- ment tested.^ F'or this reason, sawdust was sviggestecl as a substitute for part of the sand

aggregate iit six of the eight gunite slabs and in one of the partitions. The mix for another partition was altered by the addition of fibered asbestos.

2. Materials

Two slabs Avere made from each of four mixes.

The aggregate for one pair of slabs was composed of siliceous concrete sand. For the other

three pairs, sawdust was mixed with the sand in

the amounts of 30, 40, and 50 percent of the vol1 Nolan D. Mitchell, fire tests of columns protectee! with gypsum, BS J Research 10, 737 (1933) RP563.

time of the aggregate. The ratio of cement to aggregate was 1 : 4 by volitme.

Potomac River sand was used in the construction of the partitions. The aggregate for two

partitions consisted of 3 parts of building or mortar sand and one part concrete sand by volume.

The other two partitions had building and concrete sands in equal quantities in the aggregate.

The mix for one partition (125) was modified

by the addition of 6 lb of asbestos fiber to each

bag of cement.- Another f)aitition (139) was made with aggregate consisting of equal volumes

of sand and sawdust.

The sawdust for partition 139 consisted principally of white pine and maple, mostly fine, but

with some planer shavings of size to pass a No.

21/4 screen, and weighed about 101/2 Ib/'ft^

The Avelded-Avire fabric used for reinforcing

in both the slabs and partitions was of 4- by 4-in. mesh made with No. 6 galvanized Avire. Oiled ply.Avood sheets were used to support the

Avire fabric and served as backing panels against

Avhich to project the gunite during the construction of the slabs and partitions. The frames for

the gunite slabs as Avell as the supporting members

of the plyAvood backing-up forms, Avere of ordinary lumber.

3. Construction of Slabs and

Partitions

The slabs and partitions Avere constructed by

bloAving the gunite mix against plyAvood held as a

= S. H. Tnfrberg and N. D. Mitchell : results of these tests were summarized in NBS Report BMS71, fire tests of wood- and nietalfi-anied partitions (1941). 985311—52 1
2

backing within the construction or fire-test frames.

The water was added as the mixture left the nozzle.

Wire fabric was placed in these frames so as to be

in the midplane of a slab or partition. The slabs,

made in the shops of the Cement Gun Company

of Allentown, Pa., were shipped by truck to the

National Bureau of Standards with the wood

frames still attached. These frames were removed

after delivery. The partitions were made at the

National Bureau of Standards in the movable

steel test frames of the furnace in which they were

to be tested. The concrete was placed with a cement gun having a 3-bag batch capacity. One bag of cement

(94 lb) was considered as one cubic foot. The

weight of one cubic foot of sand varied with the

moisture content, ranging from 73 to 100 lb/ft ^. Six of the slabs and one partition, 139, had sawdust mixed with the sand aggregate. The ratio

of cement to aggregate was 1:4 by volume, but

varied considerably in proportion by weight be- cause of differences in the moisture content of the

sand and the low density and varied amounts of

sawdust. Wlien the gunite had been deposited to the required thickness, its surface was leveled and

finished with a float. Two groups of slabs made up of one from each

mix were placed for drying, the one consisting of

odd-numbered slabs before the fan outlet of a highpressure-steam unit heater, the other on the floor of the laboratory building. To determine the con- dition of dryness, the slabs were weighed periodically. The first fire-endurance test was made

after the slabs had aged for a period exceeding

4 months.

Inasmuch as dryness also affects their fire re- sistance, the seasoning time of the partitions was

prolonged to assure normal dryness. Partitions

124 and 125 were kept moist for 4 days, after which

they were dried 8 weeks in a heated laboratory.

Partitions 138 and 139 were left in their frames

and dampened for 7 and 10 days, respectively, and

were subsequently aged 4 months in the heated

laboratory before testing.

The slabs were 30 in. square and nominally 2.75

in. thick. The partitions were nominally 2.5 in. thick, 16 ft long, and 10 ft high, filling the opening of the test frames for the wall-testing furnace.

Other characteristics of the slabs and partitions are given in section 5.

4. Equipment and Method of Testing

The equipment for constructing the partitions was supplied by the manufacturer of the cement

gun.

The slabs and partitions were placed to form

one wall of the combustion chamber of each of

two gas-fired furnaces. Details of the furnace

used for testing the partitions are shown in figure

1. Temperatures in the combustion chamber of

this furnace were measured with nine thermocouples. A smaller furnace used in the slab tests had four thermocouples for the same purpose.

In order to control the fire exposure in conformity Avith the standard reference curve, furnace

temperatures were determined at 5-min intervals

during the first hour of a test and at 10-min intervals thereafter, if the test continued. This standard requires furnace temperatures of 1,000° F at

5 min, 1,300° F at 10 min, 1,550° F at 30 min,

1,700° F at 1 hr, and 1,850° F at 2 hr, etc.^ Temperatures on the unexposed surfaces of the

slabs were measured at three locations, and on the

partitions at nine locations. The surface thermocouples were covered with 6- by 6- by 0.4-in. asbestos felt pads secured to the surface. The disposition of the thermocouples on the unexposed face

of a partition can be seen in figure 2. The fire exposures were continued beyond the

time when the first criterion of failure in the

test had been observed to determine the effects of additional exposure. Failure occurred when

one of the following conditions limiting fire re- sistance was attained: (a) Fire damage sufficient to allow the passage of flame or gas hot enough

to ignite cotton waste on the unexposed surface, or (b) the transmission of heat through the partition to raise the average temperature 250 deg

F (139 deg C) on the unexposed surface or 325

deg F (181 deg C) at one point on the unexposed

surface. The tests of the partitions were con- ducted in accordance with the Standard specification for fire tests of building construction apd

materials, ASA No. A2-1934. The tests of the

slabs, except for size, followed the same general procedure.

All but slab 2 were set within a strong struc- tural frame to give restraint against expansion

in the plane of the slabs. The partitions were

similarly restrained. No load was applied to

either the slabs or partitions during the test.

5. Results of Tests

5.1. Slabs

Before proceeding to give the results of the

tests, it may be well to call attention to the lack

of uniformity in the thicknesses of the slabs. At

the locations where the thermocouples were placed,

the thicknesses, which were intended to be 2.75

in., ranged from 2.56 to 3.06 in. The density of

these slabs ranged from 134 lb/ft * for slabs with

sand aggregate to 92 lb/ft ^ for those having equal

volumes of sand and sawdust for the aggregate.

These data on thickness as well as the average

3 See Appendix A of BMS71.
3

of the thicknesses and the principal results of

the tests are given in table 1. The relatioris of composition and thickness to time to failure for the eight tests of slabs are shown in figure 3. It should be observed that

the time to failure for slabs varied with the composition and the average thicknesses at the points

where the surface temperatures were measured.

The time to reach limiting surface temperatures

in previously reported fire tests of solid paititions

of both neat and sanded plasters varied, for a

given composition, approximately as the 5/3

power of the thickness. Assuming that the same

relation applies for gunite specimens, curves

SECTION LONGITUDINAL SECTION HALF ELEVATION

Figure 1. Details of wall-testing furnace.

A, Furnace chamber; B, burners; C, thermocouple protection tubes ; D, pit for debris ; E, observation windows ; F, air inlets • Vj, nue outlets and dampers; H, firebrick furnace lining; I, reinforced-concrete furnace sheU ; K, gas cocks; L, control valve-' M, ladders and platforms to observation windows; N, movable test frame; O, test wall; P, felted asbestos pads covering
4

1-"I(;ui:k -. Fnititiun l.i'i after 1-lir crintsurc of tin n/itiositi ftirr to tin [in

showing the relation between thickness and time

to failure have been drawn for each aggregate

composition. These given a fair approximation

of the performance to be expected from fire tests of slabs of similar compositions and of thick- nesses in the range 2 to 3 in. By interpolation,

dashed lines have been inserted to indicate the

results to be anticipated from fire tests of slabs

having, respectively, 10 and 20 percent of sawdust

in the aggregates. Some of the data from the

tests of partitions have also been plotted to show

the relation of the results of these tests to those

derived from the tests of the slabs. Early in tests of slabs 1 and 2—the slabs with

sand aggregate—steam condensed on the unex- posed faces. Slab 1 showed minor cracking during the test, together with spalling of a small sec- tion at one corner, due to expansion of the slab

in its frame. However, slab 2 did not crack on

either face until cooling occurred, at which time

Table 1. Slabs made of gunite concrete^

Composition, by volume

Average

Thickness of slabs at thermocouple

locations Weight of slabs Time for limiting temperature rise "

Slab Cement Sawdust Sandthickness

at edges Upper

north

quarter

Upper

south

quarter Center Average As re- ceived

After drying

Exposure

Average Maxi- mum

12

3

4

5

6

78

0

01.2

1.2

1.6

1.6

2

2

4

42.8

2.8

2.4

2.4

2

2

in.

2, 62

2. 56

2. 5

2. 56

2. 69

2. 5

2. 56 2.5

in.

2. 69

2. 62

2.62

2. 88

2. 88

2. 62

2. 75

2. 88

in.

2. 69

2. 75

2. 75

2. 56 3.06

2. 62

2. 75

2. 88

in.

2. 88

2. 69

2. 88

2. 88

3.0

2. 69

2. 75

3. 06

in.

2. 75

2. 69

2. 75

2. 77 2.98

2.64

2. 75

2. 94

lb203

197

170

169

168

168 152

158

lb 193

189

155

156

149

142 134

142

Percent

96

102

101 108

10199

101

101

min

38

39

7166

88

70

85

103

min

53

5177

75

97

76

94 107

< Limiting rise of temperature under asbestos pads on surface; average 250 deg F (139 deg C), maximum 325 deg F (181 deg C).
5

JOO

2.25

2.00,

1 / /

/ /

/ / /

/

/

4/

/

,3 139

/°5 8 7

i2e

2

/ /

/

/ /

/

-r- 6/

139 K1AX

/

138/

/ /

/

—r

/ / /

/

/

/ /

/

/

/ /

/ 4 4^

20 40 60 80 100 TIME, MINUTES Figure 3. Effects of composition and thickness of gunite on time for limiting temperature 7-ise.

The first number in the proportions shown indicates Portland

cement, the second sawdust, and the last sand, that is, 1 : 1.2 : 2.8 equals 1 part of Portland cement, 1.2 parts of sawdust, and 2.8 parts of sand, by volume.

fine edge cracks developed. Bowing of either slab

ainonnted to less than 14 in. The limiting aver- age temperature rise of 250 deg F was reached on

slab 1 at 38 min, and on slab 2 at 39 min. The

maximum one-point rise of 325 deg F occurred at 53 and 51 min on slabs 1 and 2, respectively. The

thicknesses of the slabs at the points of maximum

rise were 2.88 in. on slab 1 and 2.69 in. on slab 2. Although steam issued from each of the six slabs

made with sawdust in the aggregate, in no case was condensation observed on the surface. Upon

cooling, each slab developed a few cracks.

Slabs 3 and 4, with 30 pei^cent of sawdust in the

aggregate, showed a little steam and a small quantity of smoke, more or less acrid, at the surface

of the panels. Fire-endurance limits for slab

thicknesses of 2.75 and 2.77 in., by average 250 deg

F rise of temperature, occurred at 71 and 66 min

and by maximum one-point rise of 325 deg F at 77 and 75 min for slabs 3 and 4, respectively. No

spalling was apparent on either slab. In substituting 40 percent of sawdust for an

equal volume of sand, slabs 5 and 6 gave results

similar to those obtained with aggregate containing 30 percent of sawdust. A small quantity of

steam and smoke was generated but there were no

cracks. The time to the fire-endurance limits by

temperature rise on the unexposed surface showed

a further increase, particularly in slab 5. The

limiting average temperature rise on slab 5 oc- curred at 88 min and on slab 6 at 70 min. The

respective limiting one-point temperatui*e rises were reached at 97 min and 76 min, with the re- spective thicknesses measured at 2.88 and 2.62 in. Slabs 7 and 8, having aggregate composed of

equal volumes of sand and sawdust, showed greater

fire resistance than that of the other slabs. Only

negligible quantities of steam and smoke appeared.

The limiting average temperature rises were

reached at 85 and 103 min, and the limiting maximum temperature rises at one point were observed

at 94 and 107 min. The average thicknesses at thermocouple locations were 2.75 and 2.94 in. for

the respective slabs and where maximum surface

temperatures were observed the thicknesses were

2.75 and 2.88 in. Time-temperature curves for slabs 2, 3, and 7

ai'e shown in figure 4, which gives the curves

of average temperatures and the one-point max- imum temperature on the unexposed surfaces.

The three slabs were of nearly the same average

thickness. Also shown is the standard furnace

curve and the curve (F) of the average funiace

temperatures for each test. The fire exposures

for these three slabs were approximately 100 per- cent of the standard. The fire exposure is meas- ured by the ratio of the area under the curve of

furnace temperature to that under the standard

reference curve and both above the base temperature of 68° F (20° C) expressed as percent.

5.2. Partitions

The partition tests Avere performed in two

groups. The first group included partitions 124

and 125, the second, made several months later after the tests of the slabs had indicated the

effectiveness of the sawdust admixture in the aggregate, included 138 having only sand as the

aggregate and 139 in which the aggregate was

a mixtui;e of sand and saAvdust.

The principal characteristics of the partitions

of both groups and a summary of the results of

the tests are given in table 2.

Table 2. Partitions made with gunite concrete

Composition,

parts by volume

AverTest data

Parti- age

tion thick- Failure Ce- Saw- Sand ness Kind of Expo- ment dust test sure Time Kind

124

125

138

139

1

1

1

1

0

0

«2

a 4

4

4

2

in.

2.5

2. 5

2.5

2. 75

Fire en- durance, do

do

[ do

]Fire and

hose

(. stream.

Percent

97

96

86

100

min

1 26

1 36

16

26

26

/ 70

\ 80

Hole

through. Temp avg. Hole

through. Do. Glow in cot- ton waste. Temp max.'' Temp avg. No failure in hose stream

test.'

« Because of different degrees of dampness of sand used in the gunite mixes,

the proportions of cement to sand by weight were, respectively, 1:4. 25; 1:3. 4; 1:3. 1; and 1:1.63.

i> Six pounds of asbestos fiber per bag of cement was added to mix.

' The 2 volumes of sawdust weighed 22 percent of the weight of 1 volume of cement. The thickness of the partition where the maximum rise of surface temperature was observed was 2.5 in.

' The hose stream was applied to the heated surface at the end of 82 mm

of fire exposure.
6

bJQ

O

H

Z

uO

(0

bJ

bJtco

bJO

bJCCD

I-<

bi

Q.s

bJI1300

1200

1100

800

700

500

200

Figure 4.

I I ''4 TIME IN HOURS

Time-temperaturc curves for slabs 2, 3, and

Partition 124 was made with a mix consisting of

1 part of Portland cement to 4.25 parts of di-y sand

by weight, or 1 : 4 by vohime.

Spalling of the fire-exposed surface accompanied by explosive reports began within 6 min after

the start of the test and continued at frequent in- tervals to the end. By 11 min, about half of the

fire-exposed area had spalled, some places reaching

depths of 1 in. The panel failed by the explosive

formation of a hole blowing through at 26 min.

The limiting average rise of temperature on tlie unspalled remaining portions of the partition did

not occur until 36 min. At this time the partition

had a very large center deflection. The fire was

continued to 1 hr. Practically all of the fire-ex- posed surface had spalled off during the test. Steam began issuing from cracks at 15 min after

the start of the test and continued throughout the

test. At the conclusion, much of the reinforcing

fabric in the lower third of the partition was ex- posed. Figure 2 shows the condition of the partition after 1-hr fire exposure of the opposite side. Partition 125 had 1 part of portland cement to 4 parts of damp sand by volume or to 3.4 parts of

dry sand by weight. Six pounds of asbestos fiber for each bag of cement was added to the mix.

Prior to starting the test, shrinkage of the gunite

had opened a %2"ii^- space between the partition

and test frame at the ends and top. However,

there were no visible cracks in the fire-exposed face

until explosive spalling commenced at about 10

min after the start of the test. At 16 min, an

explosion tore a hole about 4 ft' in area through

the partition. This constituted failure. The fire was continued, however, for 20 min after start of

the test. A considerable volume of steam issued

from numerous cracks formed in the partition in

the latter part of the test. The condition of the

badly spalled fire-exposed side of this partition can

be seen in figure 5. Time-temperature curves for partitions 124 and

125 are shown in figure 6. In addition to the temperatures on the unexposed surface, curves 1 and

1 max show those for thermocouples at the reinforcing wire in the midplane of a partition. The

temperature rise at this location is given as information but is not to be interpreted as affecting the

criterion of failure.
Figure 5. Fire-exposed side after 20-niin fire test of partition 125.
8

Partition 138 consisted of 1 part of })ortlan(i

cement to 4 parts by volume of wet sand or 3.1 parts of dry sand by weight. This partition dif-

•fered from 124 in its richer mix and longer drying time. At 6 min, steam issued from several

cracks. A minute later explosive popping began,

and after 18 min considerable areas of the fire- exposed surface had spalled. The panel failed at 26 min by the transmission of sufficient heat to cause glow in waste on the unexposed surface.

Also, at this time, a hole 14 by 21/2 ii^- was opened

at the edge of a previously spalled area. The limiting maximum temperature rise at one point oc- curred at 28 min, the limiting average rise in 36

min. The test fire was continued to 40 min.

Large cracks developed, but there was little addifine cracks began to form in the unexposed surface. At 9 min, water droplets formed as con- densate from steam issuing from cracks. This

continued until the test had progressed for al- most 1 hr, when the wet spots disappeared and

the steam was succeeded by small quantities of

smoke. At 1 hr 12 min, there were no surface

cracks over in. wide. Three minutes later, the

first milcl-to-moclerate popping sounds occurred.

These were not of sufficient intensity to suggest

explosive disruption of the partition. The fire ex- posure was continued to 1 hr 22 min, although the

end point of fire endurance had occurred at 70

min, when the limiting rise of temperature at one

point on the unexposed side was attained. The

limitino; average rise occurred at 80 min.

FiGUKE 7. Exposed side of pav:

tional steaming. The deflection of the partition

away from the fire amounted to 61/2 in. at the time

of failure and to almost 8 in. at the conclusion of

the fire exposure. The condition of the fire-ex- posed side of this partition after the test is shown

in figure 7. The mix for partition 139 was also 1 : 4 by vol- ume of cement to aggregate or 4.5 parts of cement, one part of sawdust, and 6.9 parts of sand by

weight of dry materials. The aggregate consisted of equal volumes of sand and sawdust.

Before the test, it was noticed that tJiere were

several sag ci*acks up to % in. wide in the exposed

face of the partition. A number of fine cracks

followed the horizontal and vertical reinforcing

wires. Three minutes after the start of the test.

ition 138 after 40-min fire test. At the conclusion of the fire-endurance test, the

j)anel successfully withstood the application of a IVg-in.-diameter hose stream at SO-lb/in.^ pressure. The water was applied for 2 min 24 sec to the side that had been exposed to the fire. There was no passage of water through the gunite

concrete, the unexposed face remaining dry. This

partition met the requirements for a 1-hr fire- resistance rating.

The condition of the exposed side of the partition immediately after the fire-endurance test can

be seen in figure 8. Figure 9 shows the same sur- face of the partition after the application of the

hose stream. The impact of the cold water had

little erosive effect.
9
10

uo

z

til o

0)u

u

DCO

uo

u

c3

<

C

u

CLs

111 I1300

1200

1100

1000

300

200

TIME IN HOURS

Figure 10. Time-temperature curves for partitions 138 and 139.

Time-temperature curves, including those for

the furnace and the unexposed surfaces of partitions 138 and 139, are shown in figure 10.

6. Summary and Discussion

In each of the tests of slabs, failure occurred

through average rise of temperature on the unex- posed surface before the limiting rise of temperature at one point was reached. The slabs with no

sawdust failed by 250 deg F rise in 38 and 39 min.

The substitution of an equal volume of sawdust for

30 percent of the sand increased the fire-endurance

limits to 66 and 71 min. By substituting sawdust

for 40 percent of the sand, limits of 70 and 88 min

were attained. With the largest quantity of sawdust used in the tests of slabs (50 percent by vol- ume of the aggregate) limiting average temperature rises were reached at 85 and 103 min. The

time required to reach the limiting maximum temperature rise at one point ranged from 51 min

for a slab with no sawdust to 107 min for a slab

having 60 percent of the sand replaced by sawdust.

The increase of fire resistance of 2.75-in.-thick

5 30

139

6/5

/7 8

a,/ 3

1 /2,125 a 138 20 40 60 80 100 TIME.MINUTES Figure 11. Effect of comtiosition of aggregates on the

fire resistance of 2.75-in. -thick gunite slabs and partitions.

gunite slabs resulting from increasing percentages

of sawdust in the aggregate is shown in figure 11. The values for tests of partitions 125 and 138 are those from the rise of surface temperatures in areas where previous spalling of the fire-exposed

surface had not occurred. The values derived
Errata

Building Materials and

Fire Tests of Gunite

Sheet

Structures Report 131

Slabs and Partitions

The Formula on page 11 should read:

S T = 7.3 (1 + 2.3p) t3

11

from tests have been projected to the 2.75-in. thick- ness on the basis of the fire resistance, varying as the 5/3 power of the thickness of the slab. The partitions without sawdust failed early in

the fire tests by the formation of holes through

them. This occurred in 26, 16, and 26 min for

partitions 124, 125, and 138, respectively. In

addition, partition 138 failed by transmission of

heat sufficient to cause glow in waste on the un- exposed side at the same time that a hole was

formed elsewhere on the partition. Addition of

asbestos fiber to the mix, as for p)artition 125, did

not enhance the fire resistance; rather, this partition failed in less time than did any of the

others. However, when the aggregate consisted

of half sand and half sawdust, as in partition

139, a fire-endurance limit of 70 min, detennined

by the rise of maximum temperature at one point, was achieved. The limiting average rise of temperature was reached at 80 min. Not only were

the fire-endurance limits greater for this partition, but there were none of the disruptive ex- plosive effects which characterized the tests of

the other three partitions.

An empirical formula suitable for estimating

the time required to raise the surface temperature

of gunite slabs or partitions 250 deg F, provided

that spalling is avoided, has been developed from

the derived data and from data obtained in pre- vious tests with partitions of other aggregates

having a greater range of thickness.* This formula is applicable to gunite composed of 1 part

of Portland cement to 4 parts of aggregate composed of silica sand and sawdust. The amount

of sawdust is limited to not more than one-half

of the total of aggregate. The formula is r=7.3(l + 2.3p)^f(l +2.3;?)^|,

where

7'=the time in minutes to reach the average

rise of 250 deg F under asbestos pads on the unexposed surface.

;{= the thickness in inches of the wall or slab

in the range 2 to 3 in. p=the proportion of sawdust by volume in

the aggregate in the range 0 to 0.5. Gunite, as usually made with concrete sand aggregate, was found to be generally unsatisfactory

for fire-resistive constructions. The spalling that

* See BMS71, p. 32, Tests Nos. X 1 and X 2.

caused the early failure in the partitions was ac- companied by explosive violence endangering

those in the nearby area. Failure of the gunite by

spalling was attributed to expansion stresses and

the Avater retained in the dense material. UnaVjle

to escape and with little space for expansion, the

water became heated during the fire test and in- creased in pressure until it attained a force suffi- cient to disrupt the thermally strained concrete. Absence of violent spalling in the two slabs made

without sawdust was considered to be the result

of a somewhat lower density concrete (134 lb/ft ^) and a more thorough drying than had been ac- corded the partitions. To eliminate the possible

presence of excessive free water, the drying time

of one partition having only sand aggregate was

greatly increased over those previously tested,

however, little diminution of spalling was apparent in the fire test. Perhaps the dense structure of gunite concrete prevented the escape of water

within a reasonable drying period.

The use of wood sawdust as part of the aggregate of the gunite increased the time to failure by

temperature rise on the unexposed side and obviated explosive effects. The sawdust, by increasing the porosity of the concrete, allowed the oc- cluded water, together with the distillation products of the wood, to escape as vapor. As the

greater temperature rise occurred on the fire-ex- posed side of the test structure, the vapors tended

to issue first on that side. Thus the sawdust serves

to provide channels for the escape of the water re- tained in the concrete and prevent spalling. It

also slows the rise of temperature on the unex- posed side by the early transfer of heat-absorbing

vapor to the fire side of the test structure. As is true for other lightweight aggregates, the

use of sawdust reduces the strength of the concrete. However, the current and proposed uses of gunite as a fire-protective covering or in cur- tain-wall constructions are such that great

strength is often of minor importance. Chemically treated or inert sawdust should have little deleterious effect on the portland cement of the

mix.

The improvements achieved by increased proportions of sawdust to sand in the concrete mixes

described in this report suggests that the optimum

proportions for fire protection had not been

reached.

Washington, September 13, 1951.

U. S. GOVERNMENT PRINTING OFFICE: 1952



BUILDING MATERIALS AND STRUCTURES REPORTS

[Continued from cover page ii] BMS34 Performance Test of Floor Coverings for Use in Low-Cost Housing: Part 1 15j5 BMS36 Structural Properties of Wood-Frame Wall, Partition, Floor, and Roof Constructions With "Red Stripe" Lath Sponsored by The Weston Paper and Manufacturing Co 10(i BMS38 Structural Properties of Two "Dunstone" Wall Constructions Sponsored by the W. E. Dunn Manufacturing Co 10|i

BMS39 Structural Properties of a Wall Construction of "Pfeifer Units" Sponsored by the Wisconsin Units Co 10(S BMS42 Structural Properties of Wood-Frame Wall and Partition Construction with "Celotex"

Insulating Boards Sponsored by The Celotex Corporation 15^ BMS43 Performance Test of Floor Coverings for Use in Low-Cost Housing: Part 2 15^ BMS44 Surface Treatment of Steel Prior to Painting 10^ BMS47 Structural Properties of Prefabricated Wood-Frame Constructions for Walls, Partitions, and Floors Sponsored by American Houses, Inc 20j5 BMS48 Structural Properties of "Precision-Built" Frame Wall and Partition Constructions

Sponsored by the Homasote Co 15(5 BMS49 Metallic Roofing for Low-Cost House Construction 200 BMS50 Stability of Fiber Building Boards as Determined by Accelerated Aging 10^ BMS51 Structural Properties of "Tilecrete Type A" Floor Construction Sponsored by the

Tilecrete Co 100 BMS52 Effect of Ceihng Insulation Upon Summer Comfort 150 BMS53 Structural Properties of a Masonry Wall Construction of "Munlock Dry Wall Brick"

Sponsored by the Munlock Engineering Co 100 BMS54 Effect of Soot on the Rating of an Oil-Fired Heating Boiler 100 BMS55 Effects of Wetting and Drying on the Permeability of Masonry Walls 100 BMS58 Strength of Soft-Soldered Joints in Copper Tubing 100 BMS59 Properties of Adhesives for Floor Coverings 150 BMS60 Strength, Absorption, and Resistance to Laboratory Freezing and Thawing of Building

Bricks Produced in the United States 300

BMS61 Structural Properties of Two Nonreinforced Monolithic Concrete Wall Constructions. _ 100 — BMS62 Structural Properties of a Precast Joist Concrete Floor Construction Sponsored by

the Portland Cement Association 150 BMS63 Moisture Condensation in Building Walls 150 BMS64 Solar Heating of Various Surfaces lOe BMS65 Methods of Estimating Loads in Plumbing Systems 150 BMS66 Plumbing Manual 350 BMS67 Structural Properties of "Mu-Steel" Prefabricated Sheet-Steel Constructions for Walls, Partitions, Floors, and Roofs, Sponsored by Herman A. Mugler 150 BMS68 Performance Test for Floor Coverings for Use in Low-Cost Housing: Part 3 200 BMS69 Stability of Fiber Sheathing Boards as Determined by Accelerated Aging 100 BMS70 Asphalt-Prepared Roll Roofings and Shingles 200 BMS71 Fire Tests of Wood- and Metal-Framed Partitions 200 BMS72 Structural Properties of "Precision-Built, Jr." Prefabricated Wood-Frame Wall

Construction Sponsored by the Homasote Co 100 BMS73 Indentation Characteristics of Floor Coverings 100 BMS74 Structural and Heat-Transfer Properties of "U. S. S. Panelbilt" Prefabricated SheetSteel Constructions for Walls, Partitions, and Roofs Sponsored by the Tennessee

Coal, Iron & Railroad Co 200

BMS75 Survey of Roofing Materials in the North Central States 150 BMS76 Effect of Outdoor Exposure on the Water Permeability of Masonry Walls 150 BMS77 Properties and Performance of Fiber Tile Boards 100 BMS78 Structural, Heat-Transfer, and Water-Permeability Properties of Five Earth-Wall

Constructions 250 BMS79 Water-Distributing Systems for Buildings 200 BMS80 Performance Test of Floor Coverings for Use in Low-Cost Housing: Part 4 150 BMS81 Field Inspectors' Check List for Building Constructions (cloth cover, 5 x 7}i inches) 300 BMS82 Water Permeability of Walls Built of Masonry Units 250 BMS83 Strength of Sleeve Joints in Copper Tubing Made With Various Lead-Base Solders... 150 BMS84 Survey of Roofing Materials in the South Central States 150 BMS85 Dimensional Changes of Floor Coverings With Changes in Relative Humidity and

Temperature 100 BMS86 Structural, Heat-Transfer, and Water-Permeability Properties of "Speedbrik" Wall

Construction Sponsored by the General Shale Products Corporation 150 BMS87 A Method for Developing Specifications for Building Construction—Report of Subcommittee on Specifications of the Central Housing Committee on Research,

Design, and Construction 200 BMS89 Structural Properties of "Precision-Built, Jr." (Second Construction) Prefabricated Wood-Frame Wall Construction Sponsored by the Homasote Co 150 BMS90 Structural Properties of "PHC" Prefabricated Wood-Frame Constructions for Walls,

Floors, and Roofs Sponsored by the PHC Housing Corporation 150

[List continued on cover page iv]
BUILDING MATERIALS AND STRUCTURES REPORTS

[Continued from cover page iii] BMS92 Fire-Resistance Classifications of Building Constructions 300 BMS93 Accumulation of Moisture in Walls of Frame Construction During Winter Exposure. _ 10^ BMS94 Water Permeability and Weathering Resistance of Stucco-Faced, Gunite-Faced, and

"Knap Concrete-Unit" Walls 15^ BMS95 Tests of Cement-Water Paints and Other Waterproofings for Unit-Masonry Walls 25^ BMS96 Properties of a Porous Concrete of Cement and Uniform-Sized Gravel 10^ BMS97 Experimental Dry-Wall Construction With Fiber Insulating Board 100 BMS98 Physical Properties of Terrazzo Aggregates 150 BMS99 Structural and Heat-Transfer Properties of "Multiple Box-Girder Plywood Panels" for Walls, Floors, and Roofs 150 BMS100 Relative Slipperiness of Floor and Deck Surfaces 100 BMS101 Strength and Resistance to Corrosion of Ties for Cavity Walls 100 BMS102 Painting Steel 100 ^MS103 Measurements of Heat Losses From Slab Floors 150 BMS104 Structural Properties of Prefabricated Plywood Lightweight Constructions for Walls,

Partitions, Floors, and Roofs, Sponsored by the Douglas Fir Plywood Association. _ 300 BMS105 Paint Manual With Particular Reference to Federal Specifications $1. 25 BMS106 Laboratory Observations of Condensation in Wall Specimens 100 B MS108 Temperature Distribution in a Test Bungalow With Various Heating Devices 100 BMS109 Strength of Houses: Application of Engineering Principles to Structural Design $1. 50

BMSllO Paints for Exterior Masonry Walls 150 BMSlll Performance of a Coal-Fired Boiler Converted to Oil 150 BMS112 Properties of Some Lightweight-Aggregate Concretes With and Without an Air- Entraining Admixture 100 BMS113 Fire Resistance of Structural Clay Tile Partitions 150 BMS114 Temperature in a Test Bungalow With Some Radiant and Jacketed Space Heaters 250 BMS115 A Study of a Baseboard Convector Heating System in a Test Bungalow 150 BMSlie Preparation and Revision of Building Codes 150 BMS117 Fire Resistance of Walls of Lightweight Aggregate Concrete Masonry Units 200 BMS118 Stack Venting of Plumbing Fixtures 150 BMSllO Wet Venting of Plumbing Fixtures 200 BMS120 Fire Resistance of Walls of Gravel-Aggregate Concrete Masonry Units 150 BATfel21 Investigation of Failures of White-Coat Plasters 250 BMS122 Physical Properties of Some Samples of Asbestos-Cement Siding 150 BMS123 Fire-Tests of V/ood-Framed Walls and Partitions With Asbestos-Cement Facings 150 BMS124 Fire Tests of Steel Columns Protected With Siliceous Aggregate Concrete 150 BMS125 Stone Exposure Test Wall - 300 BMS126 The Self-Siphonage of Fixture Traps 200 BMS127 Effect of Aging on the Soundness of Regularly Hydrated Dolomitic Lime Putties 150 BMS128 Atmospheric Exposure Tests of Nailed Sheet Metal Building Materials 200 B MS129 Fire Endurance of Shutters for Moving-Stairway Openings 100 BMS130 Methods and Equipment for Testing Printed-Enamel Felt-Base Floor Covering 150 BMS131 Fire Tests of Gunite Slabs and Partitions 150