NATIONAL BUREAU OF STANDARDS REPORT

5989

INSULATING CONCRETES

(Tests of Reinforced Perlite Concrete Slabs)

Interim Report No. 2

by

T. W. Reichard and D. Watstein

Report to

the Departments of

the Air Force, the Army, and the Navy

<nb|>

U. S. DEPARTMENT OF COMMERCE

NATIONAL BUREAU OF STANDARDS
THE NATIONAL BUREAU OF STANDARDS

Functions and Activities

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Inquiries regarding the Bureau’s reports should be addressed to the Office of Technical Information, National Bureau of Standards, Washington 25, D. C.
NATIONAL BUREAU OF STANDARDS REPORT

MBS PROJECT NB8 REPORT

1001-12-1+815 July 23v 1958 5989

INSULATING CONCRETES

(Interim Report No. 2)

T. W. Reichard and D, Watstein

To

the Departments of

the Air Force, the Army, and the Navy

IMPORTANT NOTICE

NATIONAL BUREAU OF

Intended for use within

to additional evaluation 1 lUtlng of this Report, ell the Office of the Olrectoi however, by the Governn

to reproduce additional

Approved for public release by the

Director of the National Institute of

Standards and Technology (NIST)

on October 9, 2015.

or progress accounting documents

Is formally published It is subjected

itlng, reproduction, or open-literature irmleslon Is obtained In writing from

. C. Such permission Is not needed,

cally prepared If that agency wishes

NBS
'.Sts.; ' ,
INSULATING CONCRETES

(Tests of Reinforced Perlite Concrete Slabs)

Interim Report No. 2

by

T. W. Reichard and D. Watstein

A description is given of a series of transverse tests

of perlite concrete slabs reinforced with welded wire fabric.

The purpose of the tests was to determine the properties of

such slabs subjected to short-term and long-term loads. The

effect of the reinforcement and the formboard normally used

with roof slabs of perlite concrete was investigated.

In the short-term tests the slabs were loaded to complete failure, whereas the specimens subjected to the longterm test were loaded with one-half of the estimated maximum

load. The results indicate that the minimum concrete strength

must be about 1+00 psi in order to develop the full strength

of the 1|“ by 4- in. 12/12 ga welded wire fabric used in the

3-in. thick slabs tested on 36-in. span.

The slabs tested under a sustained load for 200 days

showed increases over the instantaneous deflections of about

280 and 350 percent for the 230 psi and the 665 psi concrete,

respectively, although the instantaneous deflections of the

two slabs were nearly equal.

1 . INTRODUCTION

During the past two years the National Bureau of Standards

has been engaged in a study of insulating concretes initiated

as a Tri-Service Project.!/ In view of the current interest

in the usq of insulating concretes in reinforced roof slabs,

the Bureau was asked to include some tests of perlite and vermiculite concrete slabs under short-term and sustained loads

in the study of insulating concretes.

This report presents the data developed in the tests on

perlite concrete slabs reinforced with welded wire fabric. The

investigation included the study of the behavior of slabs under

short-term and sustained loads.

l/ Tri-Service Projects are sponsored jointly by the Departments of Army, Navy, and the Air Force.
'

.

.

*
2. PREPARATION OP SPECIMENS

The test slabs were 24- by 48- by 3~in * slabs and were

designed to be tested as simply supported one way slabs with a 36-in. span. They were reinforced with 4- by 4~i n * welded wire

fabric of 12 ga wire. The fabric was spaced 0.2 in. from the

bottom of the slabs.

The slabs were cast on 1 in. formboard in a plywood form.

Slab Nos. 5, 9, 10, ,11, 12, and 13, were cast with cellophane

between the slab and' the formboard to prevent any bond between

them. Slab Nos. 2, 9, 10, 11, 12, and 13 were tested without

the formboard.

Slab Nos. 6 and 7 bad the wire fabric anchored to 2- by

3-in. galvanized steel angles at each end to prevent slipping

of the reinforcement through the concrete while under test.

The concrete used was a 1:5 perlite mix for all slabs except Nos. 9, 12, and 13, which was a 1:4 perlite mix. Type I

cement was used in sr lab Nos. 1, 2, and 3. Type IH cement was

used in all other slabs.

The two slabs fabricated for the sustained load tests had

steel inserts cast in the top surface as gage points for deflection measurements. All slabs and the 6- by 12-in. control

cyclinders were left in the form for one day covered with vapor

barrier paper. The concrete made with Type I cement was cured

for three days under damp burlap following removal of the form.

The concrete made with Type III cement was damp cured one day

after removal of the, form. The concrete was then air-dried

until tested at 28 days for the Type I cement specimens, or 7

days for the Type III cement specimens.

The formboard for all slabs except No. 8 was a 1-in. thick,

asphalt coated, vegetable fiberboard commonly used as rigid

insulating roof board. The modulus of rupture of the formboard

was 230 psi as determined by flexure tests. The tensile strength

of the board was about 110 psi.

The formboard used for slab No. 8 was a 1-in. thick asphalt

impregnated fiberboard. This formboard is made up of two l/2-in.

thick sheets cemented together to make up the 1-in. thickness.

The modulus of rupture was about 380 psi and the tensile strength

was about 260 psi.

2 .
• ,

•
3. TEST PROCEDURE

All slabs were simply supported on two 2-in. diameter

steel pipes spaced 36 in. on centers (see figure l). The

2-in. pipes were seated on a rigid supporting frame and

were free to rotate in the direction of the span. Bearing

plates, 2-in. wide and l/4-in. thick were placed between

the supports and the slabs.

3.1. Short-term tests

For the short-term tests the slabs were loaded in a hydraulic testing machine equipped with a rigid loading

beam centered under a spherically-seated head. The loading

beam was designed to apply the load at the quarter points

of the slab through 2-in. diameter steel pipes. Leather

belting was placed between these pipes and the top of the

slabs .The load was applied at a rate that would allow deflection readings to be taken without interrupting the application of the load. Center deflections of the slabs were

measured with 0.001 in. dial gages until the initial failure.

3*2, Sustained load tests

For the sustained load tests the slabs were loaded by

placing cast iron weights 4 ft long directly on 2-in. diameter

steel pipes at the quarter points of the slabs. The total

load for slab Nos. 11 and 13 was 808 lb and 1008 lb, respectively. These loadsv were approximately half the estimated

maximum loads.

The humidity and temperature in the test room were not

controlled, but throughout most of the test period remained

at I4.O - 10$ R.H. and 72° ± 4° P> (Pig* 6). However, after the

test had been in progress about 200 da^s , the humidity and temperature rose to about 60$ R.H. and 80^ F, This increase was

due to a room, directly under the test room, being filled with

steam.

Changes in the dimensions of the portable deflectomet er

were compensated for by the use of standard surfaces installed

on a steel channel.

3 *
'

"

<

!
I|. RESULTS 4.1.

Type of failure

4. 1 .

1.

Composite slabs (concrete and formboard)

When the eight composite slabs were tested, two distinct

failures occurred in each slab. The initial failure occurred

when the formboard ruptured. The load at this point was the

maximum observed for the test.

The deflection of the composite slab was then continued

until a secondary failure occurred. In all composite slabs

except Nos. 6 and 7> the secondary failure was caused by failure of the bond between the steel wire fabric and the concrete.

Slab Nos. 6 and 7 had positive anchorage for the wire

fabric at each end which prevented excessive slipping of the

reinforcement through the concrete. The secondary failure in

slab No. 6 was by fracture of the wire fabric, while in slab

No. 7 secondary failure was by crushing of the concrete,

4.1.2.

Slabs without formboard

The initial failure of the four slabs tested to failure

without formboard was similar to the secondary failure of

the composite slabs. Slab Nos. 2 and 10 failed through

slippage of the fabric through the concrete. The steel fabric

failed in slab No. 9 which was cast from 885 psi compressive

strength concrete. Slab No. 12 which was made from 400 psi

concrete appeared to fail simultaneously by bond through excessive slip and fracture of the reinforcement.

4.2.

Bond between formboard and concrete

Table 1 gives a summary of the data and figures 2 and 3

show the load-deflection curves for the slabs. With the load

applied at the quarter points, the performance of the slab

is nearly the same as would be expected with a uniformly distributed load totalling the same as the applied machine load.

The deflections given in Table 1 for an equivalent distributed

load of 150 lb per sq ft indicate that the amount of bond between the formboard and the concrete may affect the stiffness

of the composite slabs to some extent although the strength

of the concrete appears to be the main factor.

4 .
• • •

.
1|.3. Bond between concrete and steel wire fabric

The loads at initial failure for slab Nos. 2, 9, 10,

and 12, and the secondary failure load for the composite

slabs give an indication of the effectiveness of the steel

reinforcement. Prom the data available, it appears that

the concrete strength should be about IpOO psi in order to

have sufficient bond between the 4~ by 4-in* 12/12 welded

wire fabric and the concrete to develop the full strength

of the steel.

4.4. Sustained load tests

Figures 4 and 5 show the time-deflection curves for

the two sustained load tests. The instantaneous deflections

caused by application of the test load were about the same

for the two slabs but the increase in deflection with time

was greater for slab No. 11.

Both slabs appeared to have stopped moving at about

200 days although there is some doubt as to the reason. It

was at this time that the humidity and temperature in the

test room had increased above the normal. Prom a study of

the data it is apparent that changes in the relative humidity

affect the deflection of these slabs. The slight drop in the

deflection above the 200 day period coincides with an increase

in relative humidity to 60 percent. It is possible that the

moisture picked up by the concrete had caused the concrete

to expand somewhat, thus causing the deflection to decrease

slightly. It is probable that the deflections will continue

to increase after the ambient relative humidity returns to

normal

5 . PROPOSED TESTS

It is planned to make sustained load tests on vermiculite

concrete slabs. No formboard will be used and the same amount

of reinforcement will be used as in the perlite concrete slabs.

USC0MM-NBS-DC
.

'
Table

1.

Properties

of

Perlite

Concrete

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Slab

Nos. 6

and 7

bad

wire

fabric

welded

to2- by

3*in.

l8

ga

GI

angles

at

both

ends

of

slabs.

2/

Porraboard

used

for

slab

No. 8

was

the

stronger

asphalt

impregnated

type.

FIG 1

LOADING

ARRANGEMENT

FOR

SHORT

TERM

TESTS > z

<1 111 -) I - ^ Ci A

CE. -1 uj 5 oH2: LlI

UJ

(HZ<

cr

cr<zQ<oJ

U'

DEFLECTION

MEASURING

MACHINE

LOAD,

LBS

EQUIVALENT

DISTRIBUTED

LOAD,

LB/FT

MACHINE

LOAD,

LBS

FIG. 2 SHORT TERM TEST

CENTER DEFLECTION VS. APPLIED LOAD FOR PERLITE CONCRETE SLABS

EQUIVALENT

DISTRIBUTED

LOAD,

LB/FT

MACHINE

LOAD,

LBS

EQUIVALENT

DISTRIBUTED

LOAD,

LB/FT

MACHINE

LOAD,

LBS

FIG. 3 SHORT TERM TEST

CENTER DEFLECTION VS. APPLIED LOAD FOR PERLITE CONCRETE SLABS

WITHOUT FORMBOARD

EQUIVALENT

DISTRIBUTED

LOAD,

LB/FT

FIG.

4

SUSTAINED

LOAD

TEST

TIME

VS.

CENTER

DEFLECTION

FOR

PERLITE

CONCRETE

SLABS

Nl £ -OI ‘NOI103“ld3a d31N30 1V101

TIME

.

DAYS

FIG.

5

SUSTAINED

LOAD

TEST

TIME

VS.

INCREASE

IN

CENTER

DEFLECTION

FOR

PERLITE

CONCRETE

SLABS o

o

roO

O

(Si

O

o

N0l±031d3a Sn03NV±NV±SNI 30 %

l N0llD31d3a U31N30 Nl 3SV380NI

TIME,

DAYS

FIG. 6

SUSTAINED

LOAD

TEST

TIME

VS.

RELATIVE

HUMIDITY

AND

TEMPERATURE

SLAB

NO.

II

(SLAB

NO.

13

WAS 7

DAYS

BEHIND) o

30

40

60

80

100

200

300

/ I

u. s. Department of commerce

^

Sinclair Weeks, Secretary

NATIONAL BUREAU OF STANDARDS

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

The scope of activities of the National Bureau of Standards at its headquarters in Washington,

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

divisions and sections engaged in technical work. In general, each section carries out specialized

research, development, and engineering in the field indicated by its title. A brief description of

the activities, and of the resultant publications, appears on the inside front cover. WASHINGTON, D. C.

Electricity and Electronics, Resistance and Reactance. Electron Devices. Electrical Instru- ments. Magnetic Measurements. Dielectrics. Engineering Electronics. Electronic Instrumentation. Electrochemistry.

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

Technology. Length. Engineering Metrology.

Heat. Temperature Physics. Thermodynamics. Cryogenic Physics. Rheology. Engine

Fuels. Free Radicals Research.

Atomic and Radiation Physics. Spectroscopy. Radiometry. Mass Spectrometry. Solid State Physics. Electron Physics. Atomic Physics. Neutron Physics. Nuclear Physics. Radioactivity. X-rays. Betatron. Nucleonic Instrumentation. Radiological Equipment.

Chemistry. Organic Coatings. Surface Chemistry. Organic Chemistry. Analytical Chemistry. Inorganic Chemistry. Electrodeposition. Molecular Structure and Properties of Gases. Physical Chemistry. Thermochemistry. Spectrochemistry. Pure Substances.

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

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

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

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

Metal Physics.

Mineral Products. Engineering Ceramics. Glass. Refractories. Enameled Metals. Concreting Materials. Constitution and Microstructure.

Building Technology. Structural Engineering. Fire Protection. Air Conditioning, Heating,

and Refrigeration. Floor, Roof, and Wall Coverings. Codes and Safety Standards. Heat

Transfer.

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

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

Circuitry. Digital Systems. Analog Systems. Application Engineering.

• Office of Basic Instrumentation. • Office of Weights and Measures. BOULDER, COLORADO

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Gas Liquefaction.

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Propagation Services. Sun-Earth Relationships. VHF Research.

Radio Propagation Engineering. Data Reduction Instrumentation. Modulation Systems.

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

Radio Systems Application Engineering. Radio Meteorology.

Radio Standards, High Frequency Electrical Standards. Radio Broadcast Service. High

Frequency Impedance Standards. Calibration Center. Microwave Physics. Microwave Circuit

Standards.
NBS