National Bureau of Standards

APR 171943 *rcm the u.:...

U. S. DEPARTMENT OF COMMERCE

BUILDING

MATERIALS

AND

STRUCTURES

REPORT BMS96

Properties of a Porous Concrete

of Cement and UniformSized Gravel

4^

Perry H. Petersen
BUILDING MATERIALS AND STRUCTURES REPORTS

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BMSl Research on Building Materials and Structures for Use in Low-Cost Housing 10^ BMS2 Methods of Determining the Structural Properties of Low-Cost House Constructions 100 BMS3 Suitability of Fiber Insulating Lath as a Plaster Base ' 10^ BMS4 Accelerated Aging of Fiber Building Boards lOjS BMS5 Structural Properties of Six Masonry Wall Constructions 15^ BMS6 Survey of Roofing Materials in the Southeastern States 15^ BMS7 Water Permeability of Masonry Walls 10^ BMS8 Methods of Investigation of Surface Treatment for Corrosion Protection of Steel 10|S BMS9 Structural Properties of the Insulated Steel Construction Co.'s "Frameless-Steel" Constructions for Walls, Partitions, Floors, and Roofs lOji BMSIO Structural Properties of One of the "Keystone Beam Steel Floor" Constructions Sponsored by the H. H. Robertson Co 100 BMSll Structural Properties of the Curren Fabrihome Corporation's "Fabrihome" Constructions for Walls and Partitions 100 BMS12 Structural Properties of "Steelox" Constructions for Walls, Partitions, Floors, and Roofs

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(List continued on cover page iii)
UNITED STATES DEPARTMENT OF COMMERCE • Jesse H. Jones, Secretary

NATIONAL BUREAU OF STANDARDS • Lyman J. Briggs, Director

BUILDING MATERIALS

and STRUCTURES

REPORT BMS96

Properties of a Porous Concrete of Cement and

Uniform-Sized Gravel

by

PERRY H. PETERSEN

ISSUED MARCH 18, 1943

The National Bureau of Standards is a fact-finding organization;

it does not "approve" any particular material or method of construction. The technical findings in this series of reports are to

be construed accordingly

UNITED STATES GOVERNMENT PRINTING OFFICE • WASHINGTON • 1943

FOR SALE BY THE SUPERINTENDENT OF DOCUMENTS, U. S. GOVERNMENT PRINTING OFFICE

WASHINGTON, D. C. • PRICE lO CENTS
Foreword

This report describes an investigation of physical properties of a porous concrete of cement and uniform-sized gravel, undertaken in

cooperation with the Federal Public Housing Authority to determine

the application of such a concrete in the construction of low-cost

housing.

The technical facts presented provide data from which architects

and engineers can determine whether performance requirements are met.

Lyman J. Briggs, Director.

Ill)
Properties of a Porous Concrete of Cement and Uniform-Sized

Gravel

by PERRY H. PETERSEN

CON

Page Foreword ii

I. Introduction 1 II. Materials 2

1. Cement 2

2. Aggregate 2

III. Preliminary studies 2

1. Mixing the porous concrete 2

2. Placing concrete in wall specimens 2

3. Method of molding cylinders 3

4. Preliminary tests, using grits 3

5. Preliminary tests, using pea gravel 4

6. Preliminary tests, using %-inch gravel 4

IV. Description of specimens and test results __ 4

1. Transverse strength 5

2. Heat-transfer properties 6

(a) Specimens 6

ENTS

Page IV. Description of specimens, etc. —Continued.

2. H eat-transfer properties—Continued.

(b) Test equipment and procedure. 7

(c) Heat-transfer data and results. 8

3. Compressive strength 8

4. Shrinkage and thermal-expansion coefficients 9

5. Water penetration due to capillarity. 11

6. Resistance to rain penetration 11

(a) Specimens 11

(b) Test equipment and procedure. 1

1

(c) Test results 1

1

7. Bond strength 11

8. Resistance to failure by diagonal

tension 13

V. Summary 14

ABSTRACT

The physical properties of a porous concrete consisting

solely of Portland cement, water, and uniform-sized

gravel were investigated. Each of three coarse aggregates, grits (No. 8 to No. 4), pea gravel (No. 4 to %

inch), and %-inch gravel (% to % inch), was used, with

lYi bags of cement per cubic yard in concrete tamped

in place and 3 bags per cubic yard when no compacting was done. Walls, wallettes, beams, and bond pull-out

specimens were tested, as well as 6- by 12-inch control

cylinders. Compressive, transverse, shearing, and bond

strengths are reported, as well as resistance to heat

transfer, water penetration by capillarity, and rain penetration.

I. INTRODUCTION

Plain or with reinforcement, concrete is readily adaptable to most structures, the

strength requii-ements being attained by the

correct proportioning of the ingredients and the

use of proper workmanship. There is beingbrought to the attention of the building industry

at this time a type of porous concrete made

solely of cement, gravel, and Avater, the gravel

being of a uniform size. Smce sand and other

size gravels are excluded in the proportioning of

the ingredients and the cement content is kept

down to about half that of the usual structural

concrete, a highly porous material is obtained.

Certain promising features of such a material were believed to warrant an exammation of its physical properties. In some localities, there is an abimdance of uniform-sized gravel compared

with the supply of the graded aggi'egates used

in regular concrete. Since no excess water is used, bleeding is eliminated and hj^di'ostatic

pressures do not exist, thereby allowing a rougher type of formwork.

This report deals with a porous concrete such

as is obtained when usmg each of tlnee differ- ent-sized aggregates. The methods of mixing

and placuig that were used are outlined, to- gether with the various tests performed. The

[1]
specimens were tested structurally for compressive, transverse, bond strength, and shear

properties, as well as heat transfer, water capillarity, and resistance to rain penetration.

II. MATERIALS

1 . Cement

The cement used was North American brand

Portland cement.

2. Aggreg.\te

The aggregate was Potomac River gravel of

three different sizes, namely, grits, pea gravel,

and a /4-in. gravel. The grits and pea gravel were obtained commercially as such, but the

'/i-in. gravel was screened at the Bureau from

commercial /4-in. gravel. The sieve analyses

aie given in table 1. The absorption, apparent

specific gi-avity, and the bulk specific gravity on

a surface dry basis are given in tiible 2.

^ABLE 1.—iS'/eiic analyses of aggregates

V. S. standard Sieve

Percentage, passing, by dry weight Fineness modulus

1 in. in. H in. % in. No. 4 No. 8 No. Ifi No. 30

Grits 10098

2

91

2.50

27

2

5

1 20 4.8

r-i. 7

7. 0 Pea gravel. .... .. . 100

'ji-in. gravel 100 9(i 31

Table 2.

Data on ingredients and mixtures

Absorption, percentage by dry weight « Bulk specific gravity, surface dry basis " Apparent specific gravity ^_ Sieve analyses limits (appro.x.) Cement content bags per cu yd Method of placing Dry aggregate per hag of cement lb Water-cement ratio by weight Weight of fresh concrete lb/ft

Grits

0.6

2. 63

2. 66 No. 8 to No. 4

3. 02 Loose

736

0.50

98. 2

2. 45 Tamped

1,075

0. 50 no. 3

Pea gravel

0.7

2. 56

2. 61 No. 4 to }

2. 95 Loose

750

0. 50

97.

1

2. 51 Tamped

1, 085

0.50

113.9

-in. gravel

% in.

3. 16 Loose

770

0. 40

105. 5

0.6

2.61 2.64

to in.

2. 51 Tamped

], 100

0. 44

114. (I

"Determined according to the ASTM Standard Test Method C 127-39,

III. PRELIMINARY STUDIES

A preliminary investigation was conducted

to develop techniques in mixing and placing the

porous concrete and molding representative

cylinders, and to obtain approximate values of

compressive and transverse strengths.

1. Mixing the Porous Concrete

A rotary drum-type mixer was used and

found satisfactory, although the paddle type is recommended by some investigators. In charging the mixer, part of the required water was

put in first, followed about 15 seconds later by

the gravel and cement. By this procedure,

each batch gained some cement adhering to the inside of the mixer from the previous batch,

but lost about the same amount to the following

one. Care was taken to add just enough water

tluring the mixing to produce a sheen to the

cement coating on each particle of gravel so

that, wherever any two particles touched, a

meniscus of cement slurry was formed of considerably greater area than the actual contact

surfaces. The total mixing time was kept between 2}i and 3 minutes.

2. Placing Concrete in Wall vSpecimens

Two methods of placing the porous concrete were used, namely, the loose and the tamped.

The designation loose signifies that the concrete was poured into the forms and allowed to

settle in place without any tamping, rodding,

or other compacting. The designation tamped

signifies that the concrete was compacted in

place with wood tampers of end dimensions 2%

by 4 in. A trial wall, 100 in. high, 56 in. long, and 3

in. thick, was made, using grits as the aggregate. The concrete in the lower half was tamped in place and in the upper half placed

loose. No difficulty was experienced in placing the concrete by either method in a wall of

[2]
this thickness. Upon stripping the foiins, the

surface texture of both halves was simihir to that shown for grits in figure 1. Figure 1 iUustrates the difi'erence in textui'c of the walls made with the three aggregates, the concrete in the specimen on the left in each

group having been tamped, and that on the

right having been placed in the loose condition.

It is to be noted that a surface finish such as

piaster, stucco, or a grout is required for this

type of concrete, in order to prevent unraveling

of the aggregate at the surface when the walls

are subjected to any abuse.

3. Method of Molding Cylinders

Cylinders were molded in two different ways

to correspond to the method used in placing' the concrete in the wall specimens. For the loose

condition, cylinders were made by dribbling

the fresh concrete from a scoop against the in- side face of the mold in small quantities and the

top finished off with a trowel, compacting about

a 2-in. mound of excess material into the cylinder. Tamped cylinders were made by tamping

the concrete 25 times in each of 3 layers, using

a length of pipe with a cap of 2-in. outside

diameter, the whole weighing about 5 lb.

4. Preliminary Tests, Using Grits

Small walls or wallettes, 6 in. thick, 30 in. high, and 30 in. wide were made of grits with

cement contents of 2% and 4 bags per cu yd,

each in the tamped and in the loose condition.

The compressive tests of the wallettes, load

applied to the top (6 by 30 hi.), were made at the age of 7 and 28 days, and the transverse

tests were made at 7 days with the walls in a horizontal position, centrally loaded on a span

of 24 in. The compressive strengths are shown

in figure 2. Two sets of cylinders were molded

from the batches for each compressive-test

wallette, one set placed loose, and one tamped,

regardless of whether the concrete for the wallette was tamped or placed loose. Thus, cylinder strengths are also shown for two othei' cement contents, the cement content beingcomputed from the actual weight of the

cylinders upon stripping the molds 24 hr after molding.

The moduli of rupture of the wallettes at 7

Figure 1. —Walls of porous ccncrelc.

^1, Grits; B, Pea gravel; C, ^i-in. gravel. Specimen on loft, coucrcle was

tamped in pIace;speciinenonright,concretewas placed in loose condition.
1800

1600

1400

to

V 1200 \

.^ 1000

\ 800

I

^ 600

I

400

200

—

/

<lggregah? - ^ //

f- o/ /

/—

f •

/ /a/

ifi / #/ A

/

/

)y —

—

/

• A

?t

.0

p A 1\

ilsjoo

7

o

1

!z Z 2i 3 3k 4 4i S

Cemen/ com'en^, Sags per ca yd of concre/e

Figure 2. —Compressive strength of porous concrete, using grits.

days were, respectively, 44 and 73 lb/in. ^ for 6. Preliminary Tests, Using ^-in. Gravel

the 2K- and 4-bag mixes placed loose, and 78

and 178 Ib/in.^ for the 2/2- tamped in place.

and 4-bag mixes

5. Preliminary Tests, Using Pea Gravel

The same two mixes of 2}^ and 4 bags of cement per cu yd, placed loose and tami^ed,

using pea gravel, were used in the 7-day compressive tests, and the transverse tests were made at 7 days for both the 2)i- and 4-bag mixes

placed loose. Thi-ee cylinders loose and tlu"ee tamped were made along with each wallette,

whether or not the concrete in the wallette was

placed loose or tamped. The compressive

strengths of the wallettes and cylinders are shown in figure 3. The moduli of rupture at 7 days were, respectively, 39 and 72 lb/in. ^ for the

2)^- and 4-bag mixes placed loose.

Tests were also made with the /4-in. gravel in

the same way as was done with the pea gravel.

The compressive test results of wallettes and

cylinders are shown in figure 4. The moduli of

rupture at 7 days were, respectively, 61 and 98

Vofm? for the 2%- and 4-bag mixes placed loose.

IV. DESCRIPTION OF SPECIMENS AND

TEST RESULTS

In these tests, each of the three aggregates was used with a cement content of 3 bags per

cu yd in concrete placed loose, and 2^ bags

per cu yd tamped in place. Records were

kept of batch weights, amounts of water, and

weights per cubic foot of wet concrete; the

latter was determined with a standard cubicfoot measure. These data are shown in table 2.

[4]
1600

li Z Zi 3 3^ 4 4^ 5

Cement con/en/; Sags per coyc/ o/^ co/7C/-e/e

Figure 3.

Compressive strength of porous concrete, using peri gravel.

All the walls were (i in. thick, and the test cylinders were of the standard 6- by 12-in. size. The forms were made of %-in. plywood, with

2- by 4-in. studs, 4- by 4-in. wales, and 2- by

6-in. end forms. To facilitate handling, all the

walls were built on steel channels.

1. Transverse Strength

The wallettes for transverse tests were 6 by

30 by 30 in., as in the preliminary tests, and

four of each mixture were made. Two wallettes were monolithic and two had horizontal

transverse joints at midheight, the top half

being poured 24 hr after the bottom half,

without any grouting or extra preparation of

the bonding surfaces. These wallettes were

left without a surface finish and were tested at 28 days, together with their respective cylinders. The moduli of rupture are given in table 3, together with the compressive strength

of the cylinders. Shown in figure 5 is the %-in.-

gravel wallette, concrete placed loose, with a cement content of 3 bags of cement. The

wallette lies horizontally for the transverse

test on a span of 24 in. between rollers; the load

being applied along the center line.

Table 3.

Moduli of rupture of walls and compressive strength of cylinders of porous concretes

Aggregate- Grits Pea gravel Ji-in. gravel

Normal cement content.- ... bags per cu. yd.».. 3 2H 3 2H 3 2H

Method of placing- _ _ _ Loose Tamped Loose Tamped Loose Tamped

Modulus of rupture of monolithic walls ... _. lb/in.2.. 96 135 82 96 85 101 Compressive strength 'of cylinders... .. .. ..lb/in.2.. 410 590 410 700 580 930 Modulus of rupture of transverse joint walls .

.

. lb/in.2.. 38 22 39 26 54 C) Compressive strength of cylinders ..lb/in.2.. 410 600 390 720 580 C)

" See table 2 for actual cement content. Transverse-joint walls not made.

[5]
X

I

/300

1600

1400

1200

WOO

800

600

400

ZOO

•

jgrec,/Ige -

-7

h. 6/- ays

crve/

•

(

7y y

\oO;

li 2 Zj 3 3k 4 4i

Cemen/ con/er?/, dags per cayd of concre/e

Figure 4.

Compressive strength of porous concrete, using "/n-i n. gravel.

2. Heat-Transfer Properties

(a) Specimens

One wall of each mixture was made for the

heat-transfer tests, the walls being 100 in. high,

6 in. thick, and 56 in. wide. As the walls were

highly porous and offered little resistance to the

transmission of air, they were finished, 2 weeks

after pouring them, with a }^-in. coating of stucco on the weather face and two coats of

cement-water paint on the edges, top, and other

face. The stucco was proportioned 1 :0.2 :.3.0 by dry

weight of North American brand portland

cement, Miracle brand hydrated lime, and

Potomac River building sand. It was troweled on to about }^-in. thickness and, after the

preliminary 'set had taken place, was brushed

with a wet whitewash brush to eliminate the

trowel marks.

The cement-water paint was applied in two

coats, 24 hr apart, the first being in the proportions of 1:0.25:1.0 by dry weight of white

Portland cement, Miracle brand hydrated lime,

and Potomac River building sand passing a No. 30 sieve. The finish coat was 1:0.25 of

white Portland cement and hydrated lime.

Both coats of cement-water paint were applied

to the walls made of grits and pea gravel, using a roofers brush. However, on the /4-in.-gravel

walls, a fender brush was used for the first coat and the roofers brush for the second coat. The approximate quantities of the materials

for surface finishes used on each wall are given

in table 4. These values may vary with any

slight increase or decrease in the thickness of

the stucco or with any change in consistency or brushing technique in applying the cementwater paint.

[6]
FiuuKJi 5.—Transverse test.

(b) Test Equipment and Procedure

The heat-transfer tests were conducted in the

shielded hot-box apparatus by the Heat Transfer Section at this Bureau. During the test,

heat flowed from the metering and shield boxes,

which were heated electrically, tlu-ough the

wall to the cold box, which was cooled by a

refrigerating machine. The electric energy

supplied to the metering box and measured by

Table 4.

Quantities of materials used for wall-surface finishes

Aggregate Grits . Pea gravel ?4-in. gravel

Nominal cement content ______ _bags per cu yd »_- 3 3 21,2 3 Method of placing. _ _ Loose Tamped Loose Tamped Loose Tamped

Stucco materials: Cement lb/ft-'..

_ lb/ft2_- 0.53 0. 53 0.59 0.53 0. 80 0.64 Hydrated lime _ . 11 .11 . 12 . 11 .16 . 13 Sand Ib/ft2.. 1.59 1.59 1.76 1.59 2. 40 1.91 Cement-water paint materials:

First coat: Cement-- -- lb/ft W C) .29 .20 .46 .33 Hydrated lime... _ -_ .- lb/ft2-- (») m .07 .05 . 12 .08 Sand.- _lb/ft2_- (•>) CO .29 .20 .46 .33 Second coat: Cement ___ lb/ft! - _ lb/ft2-.

(") (") . 10 .07 . 12 .12 Hydrated lime _ (") (») .03 .02 .03 .03

» See table 2 for actual cement content.

I" Quantities were not obtained.

[7]

511094°—43 2
a watthour meter was taken as closely equivalent to the heat energy transferred through the area of the specimen covered by the metering

box. The temperatures in the metering and

in the shield boxes were the same and kept at 70° ±0.5° F, whereas that in the cold box was

at 0° ±0.5° F. The stucco face, designated as the weather side of the wall, was turned against

the cold box, and the cement-water paint

surface was used at the hot-box side.

(c) Heat- Transfer Data and Results

The results of the observations on heat

transfer are given in table 5, the heat trans- mission of the specimens being expressed in

three ways. Two include the effect of surface

coefficients, and a third is independent of them.

The first result, the observed thermal transmittance, u, is the number of Btu per hour transmitted through each square foot of specimen

for each degree Fahi-enheit temperature differ- ence of the air on opposite sides of the walls. This value includes the observed surface coeffi- cients, and Jo, as shown in the table. The

second value for thermal transmittance, shown

as U, is corrected to agree with the conditions

recommended in the ASHVE "Guide" for 15

mph wind outside and zero wind inside, using

surface coefficients of 1.65 and 6.00 for^? and /o, respectively. The third value, C, the thermal

conductance, represents the number of Btu per

hour transmitted through each square foot of

specimen for each degree Fahi-enheit temperature difference betweea the surfaces of the two

sides of the wall and is therefore independent

of the surface coefficients. The thermal conductivity, k, is equivalent to the conductance

of the material per inch of thickness.

Table 5.

Heat-transfer coefficients

Aggregate,

Nominal cement content bags per cu. yd.''- Method of placing Weight. .lb..l/tt.! Thickness in. Observed thermal transmittance, u

Corrected thermal transmittance, U. Thermal conductance, C. Warm surface film conductance, fi Cold surface film conductance, fo Thermal conductivity, k

Grits

3 Loose

98.2 6.0

0.551 .680

1.43 1.90

1.70 8.6

2\i Tamped

110.3 6.0

0. 561 .702

1.54

1.89

1.66

9. 2

Pea gravel

3 Loose

97.

6.0 0.520

.643

1.28

1.88

1.64

7. 7

21/5 Tamped

113.9 6.0

0. 590

.751 1.79

1.87

1.66

10. 7

5-4-in. gravel

3 Loose

105.5 6.0

0. 618

.786 2.00

1.87

1. 71 12.0

2!.i Tamped

114.9 6.0

0. 671 .874 2.69

1.91 1.68

16.

» Determined by shielded hot-box apparatus. Cold side of wall finished with \i-m. stucco. Warm side of wall finished with 2 coats of cementwater paint.

b See table 2 for actual cement content.

» The definitions of «, U, C. and k, representing the various coeflScients of heat transmission, are: M=number of Btu per hour transmitted through each square foot of specimen for each degree Fahrenlieit difference in tenifjerature between the

air on the 2 sides, as observed under test conditions. U—v. corrected for a 15-mph wind outside and zero wind inside by means of the factors ./i=1.65 and /o=6.00 taken from the ASHVE "Guide." C=number of Btu per hour transmitted through each square foot of specimen for each degree Fahrenheit temperature difTerence between the surfaces of the two sides as observed under test conditions. /c=The thermal conductivity of the material, equivalent to the conductance per inch of thickness.

3. Compressive Strength

Compressive tests at an age of 7 weeks were made with wall specimens of two sizes. The

walls which had been previously tested for heat-transfer properties at 4 weeks were used

as one of the compression specimens. A wallette was also tested in compression at the same

age, this specimen having been made and the

surface finished like the larger wall and at the same time.

Shown in figure 6 is the wall made of %-in. gravel, using 3 bags of cement, the concrete placed in the loose condition. During the compressive test, deformation readings were taken

with a 20-in, Whittemore strain gage on three

vertical lines, on each face of the wall, for uniform increments of load. The average secant modulus of elasticity at an applied stress of 200

lb. /in.- is given in table 6, together with the

maximum compressive strengths of walls and

cylinders. The dispersions of the strength

values of the individual cylinders from the mean

were greater than is usual with workable

dense concretes. Figure 7 shows the 30-in. wallette set up for

compressive test. The face shown is stuccoed, ans the edge and back face are cement-water

painted. The top and bottom were capped

previous to the test with a Lumnite cement

mortar.

[8]
Figure 6.

Compression test of 100 by 56 by 6 in. wall

4. Shrinkage and Thermal-expamsion

Coefficients

For determining the amount of shrinkage

and the coefficients of tliermal expansion, one

30-in. wallette was built for each mixture. On

botli faces, there were four 20-in. gage hues,

two horizontal and two vertical, each 5 in. from the edges of the walls. Observations

were made approximately once a week with a Whittemore strain gage. The specimens were

allowed to remain in the laboi-atory, where

neither temperature nor humidity was controlled. After they had aged at least 3 months,

they were stored in a drying room, kept at 95°

to 100° F, and after drying them, a set of

observations was taken. Then, they were

Table 6.Compressive strength and secant modulus of elasticity

Aggregate.

Nominal cement content bags per cu. yd.» Method of placing Compressive strength: Walls 56 by 100 by 6 in lb/in 2 Cylinders lb/in 2 Wallette 30 by 30 by 6 in.... _ _ lb/in 2 Cylinders lb/in 2 Secant modulus of elasticity at 200 lb/in Wall 56 by 100 by 6 in lb/in 2

• See table 2 for actual cement content. [9]

Grits

3 Loose

647

491

714

1, 010, 000

21-^ Tamped

665

582 995

1,130, 000

Pea gravel

3 Loose

504 447

551 380

830, 000

2}2

Tamped

667

645

918

654

1, 210,000

H-in. gravel

3 Loose

621 520

700

1, 670, 000

2H

Tamped

835 930

1,090

947

2, 080. 000
Figure 7.

Compression test of 30- by 30- by 6-iti. wallette.

transferred to a cold room with a temperature

between 8° and 12° F and, when the temperature of the walls reached that of the room, a set of observations was made. After one more

cycle of the hot and cold storage, the wallettes were returned to the drying room and the final observations taken after reaching temperature

equilibrium. Shown in table 7 are the coefficients of thermal expansion of each of the walls,

together with the maximum amounts of shrinkage corrected for temperature, as evidenced in

the drying room and in the laboratory prior to drying them. These slu-inkages are the changes

in length, based on original readings taken at an age of 2 or 3 days.

Table 7.

Shrinkage and thermal—expansion coefficients

Aggregate Grits Pea gravel ?4-in. gravel

Nominal cement content . bags per cu yd > 3 2M 3 3 2H

Method of placing Loose Tamped Loose Tamped Loose Tamped

Coefficient of thermal expansion per °F t . . _ . 6.1X10-6 6. 1X10-6 6. 1X10-6 6.0X10-» 6. 1X10-9 5.9X10-6 Total shrinkage: Laboratory storage. % 0. 038 0. 026 0.029 0. 025 0. 012 0. 007 Drying-room storage _ % .052 .037 .041 .033 .015 .009

a See table 2 for actual cement content.

^ Determined in the range of 10° to 100° F.

= Corrected for temperature.

[10]
Table 8.— Rise of water due to capillarity

Aggregate Grits Pea gravel M-in. gravel

Nominal cement mixture.- _ _ _ bags per cu yd".. Method of placing, _ . _ . Loose

1.25

1. 00

91/ Tamped

1.50

1. 25

3 Loose

0. 90

1. 00

Tamped

1.00

1. 00

3 Loose

1.50

0- 50

Tamped

0. .50

. 75

Rise in 1 hour: Specimen 1.

_

.in.. Specimen 2.. in.. Average .... . . . 1.1

3. 00

1.60

1.4 1.0

1.75 1.50

1.0 1.0 0.0 Rise in 21, hours: Specimen 1 in 2. 00

2. 00

1.75 1.50

1.75 2,00

1..50 Specimen 2. 1.75

.

... .in.

Average. . . . . . 2.2 2.0 1.6 1.6 1.9 1.6

Rise in 7 days: Specimen 1... in 6. 75

6. 25

5. 00

4. 50

3. 25

2. 50

3. 25

2. 50

3. 50

4. 00

.3.25 Specimen 2... _. . .. in. 3. 50 Average ... .... ...... 6.5 4.7 2.9 2.9 3.8 3.4

" See table 2 for actual cement content.

5. Water Penetration Due to Capill.arity

From the broken halves of the transverse-test

walls, specimens 6 in. thick, 10 in. wide, and

15 in. high were stood vertically in pans containing )i in. of water. This was done in a room

where the relative humidity was 80 to 85 per- cent and the temperature 72° to 75° F. The maximum rise of water in the specimens was observed at 1 hr, 24 hr, and at 7 days,

and these values are given in table 8. Two

specimens of each set were used, one from a monolithic wall, and the second from a transverse-joint wall.

6. Resistance to Rain Penetration

(a) Specimens

Th(> si.x specimens used for the water-pern- c- ability tests were about 51 in. high, 41 in. wide,

and 6 in. thick, with each of the three aggregates represented with the concrete tamped or placed loose. They were built on supporting

channels with a 2-in. m.ortar base containing a copper flashing projecting at the back, which

collected any water penetrating the face during

test. Simihir to the heat-transfer walls, the

front face, edges, and top were finished with

y% in. of stucco. Tliese walls were aged at

least 1 month indoors before being tested. The walls made of grits are shown in figure 8. On the left is the face of the tamped wall to which the stucco was later applied, and on the

right may be seen the back of the wall with the concrete placed loose and the flashing embedded

in the 2-in. mortar base.

(6) Test Equipment and Procedure

The water-permeability test is described in BMS82, Water Permeability of Wafls Built of

Masonry Units. The walls were given a pre- liminary test of 2 days, and then put in a drying room until they had reached constant weight

before the final test. The specimens were supported on metal skids, and when clamped in position, the exposed face formed one side of a

pressuie chamber. An air pressm-e of 10

Ib/ft^ above atmospheric was maintained in the chamber, and water from a perforated tube was sprayed near the top edge of the exposed

face at the rate of 40 gal/kr.

The following observations were made during

the test: Time requii'ed for the appearance of

moisture (dampness) and of visible water on the

backs of the walls; time for leakage of water

from the flashing, and the maximum rate of

leakage; extent of damp area on the back,

including that produced by the capillary rise of inoistiu'e from water on the flashings.

(c) Test Results

The arbitrary method of rating the per- foimance, as given in BMS82, was employed.

All the walls were judged to be exceflent, since

they had no visible water above the flashings

in 1 day, no leakage, and less than 25 percent

of the wall area was damp m 5 days.

7. Bond Strength

Bond pull-out specimens were made to deter.mine the value of the bond of porous con-

[11]
Figure 8. — Water permeability speci?ners of porous concrete containing grits and before stuccoing. On the left is face of wall of tamped concrete; on the right is back of wall of loose concrete.

Crete as compared with that of the usual structural concrete. Porous concrete tamped in place, and made with pea gravel, using 2}^ bags

of cement per cu yd, was compared with an

ordinary concrete with a compressive strength

of 2,500 lb/in.2 in the proportions of 1:2.8:3.2,

by volume of cement, sand, and /4-in. gravel.

The steel used in both sets of specimens was the

%-in. round deformed bar made by the Atlantic

Steel Co.

Tliree siDecimens of each type of concrete were made, 6 by 6 by 12 in. long, the bar being

centered in the molds as shown in figure 9. The specimens were made with the bar in the

horizontal position; the porous concrete was tamped in place, and the regular concrete compacted with an electric vibrator. Tkree

compressive-test cylinders of each type of concrete were made. All the specimens were stored

in air in tlie laboratory and tested at the age

of 28 days.

For testing, the bond specimens were set up

as shown in ligiue 10. The plaster-capped base was in contact with a spherical bearing block

having a 1-in. hole in the center, and a 0.0001-

in. micrometer dial was used to measure the

amount of slip of the bar at the free end.

Loads were applied to the bar, and the

amount of slip as shown by the mici'ometer

dial was recorded for various loads. The

average bond stresses for each bar \|ere computed for a first slii) of 0.0001 in. and for the

ma.ximum load and are given in table 9. For the porous concrete, the yield pctint of the

steel had not been reached at bon^l failure,

whereas in the ordinary concrete the yield point

of the steel was exceeded. All specimens failed

by splitting longitudinally through the center

[12]
Figure 9.

Bond pull-oul Ivnl specimens.

in tho plane parallel to the finished surface in

tlie position they were molded.

8. Kesistance to Failure by

Diagonal Tension

To determine resistance to diagonal tension,

six beams were made of pea gravel, using 2^

bags of cement per cu yd, the concrete being

tamped in place. The beams were 4 ft 10 in. long, 6 in. wide, 13^ in. deep, with reinforcing

steel at a depth of 12 in. Two %-in. round

deformed bars, hooked at each end, were used

as reinforcement, the bars in three of the beams

behig given a coating of cement grout immediately before placing them; in the other three

beams the reinforcing was placed as delivered.

In the tests a 4-ft span was used with the

beam loaded at midspan. The maximum load was recorded, as was the load for the appearance

of the first crack. The observed data are given

in table 10, and it is to be noted that specimen

3, using the uncoated steel, failed by yielding of

the tensile reinforcement, whereas the other five failed principally by diagonal tension.

Table 9.Bond strengths as determined by pull-out specimens

Specimen... __ Bond stress: At slip of O.DUOl in lb./in.2_. At maximum load _lb./in.2._ Compresswe strength: Cylinders lb./in.2..

Porous concrete

214-has mix, tamped, pea gravel

14B 313

551

2 3

221 177 376 306

594 530

avg

181 332

Regular concrete

1:2.8:3.2 by volume

221 934

2, 430

2 3

279 226

(') 930

2,680 2,760

242

930

2, 620

Loading discontinued at yield point of steel.

[13]
Table 10.

Resistance to diagonal tension in beams

S|ji'cinicn

Computed shearing

stresses

First crack Maximum

load

Compressive strength of cylinders

BARS ITNCOATED

12

3

Iblinfi 28

30

36

31

lb/in.- 56

74

10077

Iblin.'- 546 639

759 Average 648

BARS COATED WITH CEMENT OROl'T

1 39

40

3538

85

83

7180

709

821 824

785

23._.A verage . - _ .

Figure 10.- I'd/mis-concrete specimen in bond pull-out

test.

V. SUMMARY

Specimens of porous concrete consisting of

cement and each of three uniform-sized gi-avels as aggregates (grits, pea gravel, ^i-m. gravel) were made and tested after preliminary studies

into the tecliniques of mixing and placing had

been completed. The strengths obtained in

these preliminary studies led to the use of two

mixtures for the tests, namely: 3 bags of cement

per cu yd in concrete placed loose and 2)^ bags

of cement in concrete tamped in place. A

summary of the results of the various tests performed, follows: ^ The weight per cubic foot tended to in- crease with increase in size of aggregate, with

a range of 97 to 105 Ib/ft^ for that placed loose

and 110 to 115 Ib/ft^ for that tamped in place.

The water-cement ratio, by weight, however,

decreased with increase in size of aggregate,

ra:iging from 0.50 to 0.40 for the loose and

0.50 to 0.44 for the tamped concrete. The modulus of rupture for the monolithic

walls was about 100 lb/in. ^, tending to be

slightly less than this value for the concrete placed loose and more for concrete placed by

tamping. This value is about one-fourth of that expected for a dense concrete with a. compressive strength of 2,500 Ib/iir'. The

transverse strengths of walls containing a

horizontal construction joint were considerably

less than for walls with no joints; with the

tamped porous concrete, the strength of the

joint averaged less than 25 jjercent of that of the

monolithic wall. The compressive strength of the tamped

cylinders ranged from 600 to 900 lb/in. ^, and

was a fair indication of the strength in walls

' 'l"he indications of this data on strength, shrinkage, resistance to rain

IK'uctration, and heat transfer are similar to those reported by the Building Research Board of Great Britain, namely: "The optimum proportion of cement to aggregate was found to be sur- prisingly low, a ratio of 1 part of cement to 18 parts of aggregate graded from 'ii in. to % in. being found sufficient to cover the stones and develop

a compressive strength at three months of over 400 lb/in. ^ with either gravel or dolerito. "In respect of drying, shrinkage, and expansion on wetting, the opentextured concrete does not differ significantly from typical dense 1:2:4 concrete. "Rendered panels of open-textured concrete 9 in. thick proved quite

resistant to rain penetration. The thermal conductivity was closely similar to that of solid brickwork and dense concrete, a result which was

not anticipated, the high proportion of pore space being expected to improve the thermal insulation." From report of the Director of Building Research for the year 1939, page 45 (His Majesty's Stationery Office, London).

[14]
8 ft high and of the same mixture. When the concrete was placed loose, the walls yielded

strengths of 500 to 650 lb/in. ^, these values

being 50 to 150 lb/in. ^ higher than the strengths

of their respective cylinders. The values for secant modulus of elasticity at a stress of 200

lb/in.- ranged between one and two million

lb/in. ^, tending to increase with increased size of aggregate.

Resistance to heat transmission decreased

as the size of aggregate increased, the values of

thermal transmittance, U, varying from 0.64

to 0.87 Btu/hr ft^ °F for 6-in. walls, these

being the corrected values for a 15-mph wind

outside and zero wind inside, the standard

test condition recommended by the ASHVE

"Guide." The "Guide" lists U values of 0.77

to 0.88 for dense concretes of various ages and

mixtures.

Resistance to rain penetration of walls to which )i-in. stucco was applied was excellent. The coefficient of thermal expansion averaged

0.000006/° F, approximating that of the gravel

used as aggregate.

The amount of shrinkage ranged from 0.009

to 0.052 percent for the dry walls and seemed

to decrease with increase in size of gravel and

with the amount of compacting.

The rise of water by capillarity in walls of

porous concrete ranged from 3 to 6% in. at

7 days, the greater value occurring in the concrete with grits placed loose. The bond stress at first slip between reinforcing steel and tamped porous concrete made of pea gravel and 2}^ bags of cement per cu yd was

about three-fourths of that obtained for a i-egular concrete with a compressive strength of 2,500 Ib/in.- However, the maximum bond

sti-ength developed by the pull-out specimens of

porous concrete was only about one-third that

of the ordinary concrete. Tim computed shearing stress in the beams at

failure was about 80 lb/in. ^, this value being

about one-half of that expected for a regular concrete with a compressive strength of 2,500

ll>/in.^ The resistance to failure by diagonal

tension did not change appreciably when the

reinfoi'cing bars were coated with a cementwater grout immediately before placing.

The assistance of the Federal Public Housing

Authority, represented by A. M. Korsmo and

B. M. Thorud, in planning the investigation,

supplying information on methods of mixing

and placing concrete, and in analyzmg the

results of the preliminary studies is gz'atefully

aclvuowledged. Mr. Korsmo also reviewed the

marniscript of the report and made valuable

suggestions for its improvement.

The heat-transfer properties were determined

by H. E. Robinson, of the Bureau's Heat

Transfer Section; the water-permeability properties by C. C. Fishburn, of the Masonry Construction Section.

Washington, December 19, 1942.

o

[15]



BUILDING MATERIALS AND STRUCTURES REPORTS

[Continued from cover page ii] BMS32 Structural Properties of Two Bric-Concrete-Block Wall Constructions and a Concrete- Block Wall Construction Sponsored by the National Concrete Masonry Association. 10j5 BMS33 Plastic Calking Materials 10^ BMS34 Performance Test of Floor Coverings for Use in Low-Cost Housing: Part 1 10^ BMS35 Stability of Sheathing Papers as Determined by Accelerated Aging 10^ 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(5 BMS37 Structural Properties of "Palisade Homes" Constructions for Walls, Partitions, and

Floors, Sponsored by Palisade Homes 10(5 BMS38 Structural Properties of Two "Dunstone" Wall Constructions Sponsored by the W. E. Dunn Manufacturing Co 10^ BMS39 Structural Properties of a Wall Construction of "Pfeifer Units" Sponsored by the Wisconsin Units Co lOji BMS40 Structural Properties of a Wall Construction of "Knap Concrete WaU Units" Sponsored

by Knap America. Inc 10(5 BMS41 Effect of Heating and Cooling on the Permeability of Masonry Walls 10(5 BMS42 Structural Properties of Wood-Frame Wall and Partition Constructions with "Celotex"

Insulating Boards Sponsored by The Celotex Corporation 15^ BMS43 Performance Test of Floor Coverings for Use in Low-Cost Housing: Part 2 lOjS BMS44 Surface Treatment of Steel Prior to Painting 10(5 BMS45 Air Infiltration Through Windows 10^ BMS46 Structural Properties of "Scot-Bilt" Prefabricated Sheet-Steel Constructions for Walls,

Floors, and Roofs Sponsored by The Globe-Wernicke Co 10(5 BMS47 Structural Properties of Prefabricated Wood-Frame Constructions for Walls, Partitions,

and Floors Sponsored by American Houses, Inc

--

10(5 BMS48 Structural Properties of "Precision-Built" Frame Wall and Partition Constructions

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

Tilecrete Co 10^ BMS52 Effect of Ceiling Insulation Upon Summer Comfort . 10(5 BMS53 Structural Properties of a Masonry Wall Construction of "Munlock Dry Wall Brick"

Sponsored by the Munlock Engineering Co 10(5 BMS54 Effect of Soot on the Rating of an Oil-Fired Heating Boaer 10(5 BMS55 Effects of Wetting and Drying on the Permeability of Masonry Walls 10(5 BMS56 A Survey of Humidities in Residences 10(5 BMS57 Roofing in the United States—Results of a Questionnaire 10(5 BMS58 Strength of Soft-Soldered Joints in Copper Tubing 10^ BMS59 Properties of Adhesives for Floor Coverings --- 10^ BMS60 Strength, Absorption, and Resistance to Laboratory Freezing and Thawing of Building

Bricks Produced in the United States 15^ BMS61 Structural Properties of Two Nonreinforced Monolithic Concrete Wall Constructions.-. 10^ BMS62 Structural Properties of a Precast Joist Concrete Floor Construction Sponsored by the Portland Cement Association lOi

BMS63 Moisture Condensation in Building Walls 10(5 BMS64 Solar Heating of Various Surfaces 10^ BMS65 Methods of Estimating Loads in Plumbing Systems 10^ BMS66 Plumbing Manual 20^ BMS67 Structural Properties of "Mu-Steel" Prefabricated Sheet-Steel Constructions for Walls,

Partitions, Floor, and Roofs Sponsored by Herman A. Mugler 15^ BMS68 Performance Test for Floor Coverings for Use in Low-Cost Housing: Part 3 15(5 BMS69 Stability of Fiber Sheathing Boards as Determined by Accelerated Aging 10(5 BMS70 Asphalt-Prepared Roll Roofings and Shingles 15^ BMS71 Fire Tests of Wood- and Metal-Framed Partitions 20(5 BMS72 Structural Properties of "Precision-Built, Jr." Prefabricated Wood-Frame WaU Construction Sponsored by the Homasote Co 10(5 BMS73 Indentation Characteristics of Floor Coverings 10(5 BMS74 Structural and Heat-Transfer Properties of "U. S. S. Panelbilt" Prefabricated Sheet-

, Steel Constructions for Walls, Partitions, and Roofs Sponsored by the Tennessee

Coal, Iron & Railroad Co 15^ BMS75 Survey of Roofing Materials in the North Central States - 15^ BMS76 Effect of Outdoor Exposure on the Water Permeability of Masonry Walls 15(5 BMS77 Properties and Performance of Fiber Tile Boards 10^ BMS78 Structural, Heat-Transfer, and Water-Permeability Properties of Five Earth-Wall

Constructions 20(5 BMS79 Water-Distributing Systems for Buildings 15^ BMS80 Performance Test of Floor Coverings for Use in Low-Cost Housing: Part 4 15^ BMS81 Field Inspectors' Check List for Building Constructions (cloth cover, 6 x 7^4 inches) 20(5

[List continued on cover page iv]
[Continued from cover page iii] BMS82 Water Perraeability of Walls Built of Masonry Units 200 BMS83 Strength of Sleeve Joints in Copper Tubing Made With Various Lead-Base Solders 10^ BMS84 Survey of Roofing Materials in the South Central States 15^ BMS85 Dimensional Changes of Floor Coverings with Changes in Relative Humidity and

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

Construction Sponsored by the General Shale Products Corporation 150 BMSS7 A Method for Developing Specifications for Building Construction—Report of Subcommittee on Specifications of the Central Housing Committee on Research, Design,

and Construction 100 BMS88 Recommended Building Code Requirements for New Dwelling Construction with Special Reference to War Housing 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 BMS91 A Glossary of Housing Terms 150 BMS92 Fire-Resistance Classifications of Building Constructions 250 BMS93 Accumulation of Moisture in Walls of Frame Construction During Winter Exposure 100 BMS94 Water Permeability and Weathering Resistance of Stucco-Faced, Gunite-Faced, and

"Knap Concrete-Unit" Walls 100 BMS95 Tests of Cement-Water Paints and Other Waterproofings for Unit-Masonry Walls 150 BMS96 Properties of a Porous Concrete of Cement and Uniform-Sized Gravel 100