-HaTT4Hai i^ureau of Standards

iih"raT»v N W RTi^c» DEC1 1 1961

NBS MONOGRAPH 36

Effect of Mortar Properties

On Strength of Masonry

U.S. DEPARTMENT OF COMMERCE

NATIONAL BUREAU OF STANDARDS
THE NATIONAL BUREAU OF STANDARDS

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Office, Washington, D.C.
. UNITED STATES DEPARTMENT OF COMMERCE • Luther H. Hodges, Secretary

' NATIONAL BUREAU OF STANDARDS • A. V. Astin, Director

Effect of Mortar Properties

On Strength of Masonry

Cyrus C. Fishburn

National Bureau of Standards Monograph 36

Issued November 20, 1961

For sale by the Superintendent of Documents, U.S. Government Printing Office Washington 25, D.C. - Price 30 cents
Contents

Page

1. Introduction 1 2. Materials 1 2.1. Cements 1 2.2. Sand 3

2.3. Mortars for wall construction 3

2.4. Concrete masonry units 4

2.5. Brick 5

3. Construction and curing of walls and bond-test specimens 5

3.1. Concrete masonry walls 5

3.2. Composite masonry walls 6

3.3. Curing of masonry walls 8

4. Compressive strength tests , 8

4.1. Test equipment and wall preparation 8

4.2. Loading procedure 9

4.3. Compressive strength of walls '. 10

4.4. Compressive load strain and deflection 12

5. Racking strength tests 13

5.1. Test equipment and method 13

5.2. Racking strength of walls 14

5.3. Racking shear strain 17

6. Flexural strength tests 18

6.1. Test equipment 18

6.2. Method of test 18

6.3. Flexural strength of concrete masonry walls 19

6.4. Flexural strength of composite masonry walls 23

7. Discussion and summary of wall test results 27

7.1. Effects of storage on cement properties 29

7.2. Compressive tests 29

7.3. Racking tests 30

7.4. Flexural tests 30

8. Appendix I. Tabular information 33

9. Appendix II. Construction, curing, and testing of bond-test specimens. 42

9.1. Equipment 42

9.2. Concrete block assemblies 42

9.3. Crossed-brick couplets 43

9.4. Composite assemblies 44
Effect of Mortar Properties on Strength of Masonry

Cyrus C. Fishburn

The physical properties of mortars, the bond strength of the mortars to masonry units, and the structural strength of concrete masonry and composite masonry walls containing

the mortars are discussed and compared. All of the mortars were tempered to as wet a

consistency as could be conveniently handled by the mason. The compressive strength of the walls increased, in general, with the compressive

strength of the mortar. The racking and flexural strengths of the walls increased with the bond strength of the mortar. The strength of bond test specimens tended to increase with

the compressive strength of the wet consistency mortars that were used. However, bond

strength appeared to be the dominant factor affecting the racking and flexural strength of the walls. Increase in both bond strength and wall strength with compressive strength of the mortar was not proportional to the relative compressive strengths of the type N and

type S mortars. The stiffness of walls subjected to compressive and flexural loads increased with the bond and compressive strength of the mortars. However, the stiffness of walls subjected

to flexural loads appeared to be more dependent upon the number of bed joints in the

tensile face and on their extension in bond than upon the bending strains in the masonry

materials.

1. Introduction

The compressive, flexural, and racking strengths

of two masonry wall constructions were measured

to determine the effects on wall strength of using

mortars differing in the kind of cementing materials. Three masonry cements and one laboratory

prepared cement were used. Two of the masonry

cements were blends and one was a masonry ce- Iment as furnished by the producer,

j This work was done as part of the Masonry Reisearch Program, an investigation of portlandjcement base masonry cements, which was con- Wucted at the National Bureau of Standards and

financed through the National Research Council,

National Academy of Sciences. The sponsors and

participants in the program included over 40 manufacturers of Portland cement, most of whom also produced masonry cement. In addition to structural tests of walls in which new and improved

apparatus was used to measure racking and flex- pal strength, a bond test method was developed to

I, measure the strength between masonry mortars

md masonry units. Using this method of test,

the bond strength of small representative speci- mens made with the walls was measured and compared with the flexural strength of the walls. In previous tests of masonry wall constructions

built at the Bureau, the cementing materials in nearly all of the mortars were portland cement and

lime, used either singly or in combination. Relatively few wall constructions were built with mortars containing masonry cement. Of these, the

last was built in 1940 and was reported in BMS

Report No. 53. One hundred and fourteen masonry walls were

constructed, 58 of which were of hollow concrete

masonry. The other 56 walls were of composite

construction, having a brick facing and a concrete masonry backing. A total of 26 walls were tested

in compression, 24 in racking and 64 in flexure. One or more bond test specimens were built with

each wall specimen, using the same mortar and

similar masonry units. ASTM C270 type N and

type S mortars were evenly represented in each

wall construction.

2. Materials

All materials used in the wall constructions were

ivailable commercially and were representative of

those commonly used in building construction.

2.1. Cements

a. Masonry Cements

The masonry cements were representative of

!he brand name products made in 1953. They

lontained about 50 percent by weight of portland

lement or portland cement cUnker interground

Rfith about 50 percent of a supplementary material such as limestone, raw mix or other predominately calcarious material. All contained an air entraining additive, some contained water repellants such as stearate and oleate. Three bags of each of the 43 masonry cements

included in the Masonry Research Program were

received at the Bureau in 1953. Reserve supphes

of each cement were placed in sealed containers

and were stored at the mills. A selection of the

cements to be used in two blends for wall tests was made after initial studies had been completed

on all cement samples. The reserve supplies of

these selected cements were sent to the Bureau

1
and were received in good condition during the

spring of 1957.

The two blends of masonry cements used in the

wall constructions were designated as cements B

and C. Masonry cement D, weighing 75 lb per

bag, was also used in the construction of some

walls built for flexural strength tests. In so far as possible, the 5 cements in each blend were selected to be similar in composition and

compatible with each other in the properties of

their Federal Specifications SS-C-181c mortars.

Blended cement B was intended to produce mortars of moderate compressive strength and high

water retention. Similarly, cement C was in- tended to produce mortars having a relatively

higher compressive strength, moderate water re- tention, and a relatively lower air content. All

of the masonry cements weighed 70 lb per bag and

each blend contained equal weight proportions of

its component cements.

After blending, the cements were stored in

sealed containers until used in the wall constructions. The physical properties of the individual

cements in the blends were measured in 1953, in

accordance with the current requirements of Federal Specification SS-C-181c. These properties

are listed in tables 1 and 2 (appendix I, Tabular

Information).

b. Laboratory Cement E

A laboratory prepared cement, designated as cement E was used in the construction of 12 walls,

tested in flexure, to obtain comparative information on the efjpects of using a mortar of rela- tively high compressive strength, high water retention and low air content on the flexural strength of

the walls. Cement E was a blend of materials

commonly used in building constructions. It yielded wall test mortars having an air content of

1 percent or less, by volume.

c. Portland Cement

A Portland cement meeting the requirements of

Federal Specification SS-C-1 92(b) and ASTM

Standard C150-56, for type I portland cement was used with cements B, C, D, and E for the

preparation of ASTM C270 type S mortars.

Some of the physical properties of this portland

cement are listed in table 3.

d. Cements Used in Type N and Type S Wall Construction Mortars ASTM C270 type N and type S mortars were

used in the wall constructions. The cements used

in the type S mortars were the same as those used

in the type N mortars except that they contained an addition of 50 percent by volume of portland

cement. The proportions by weight of the components of each cement used in the type N and

type S mortars are listed below

Proportions by weight of cement

Mortar

designation

BNCN_

DN_

EN.

BS_

CSDS_

ES-

%

100

59. 8

100

59. 8

D

%

100

61. 4

%

100

60. 5

Portlail

i

40

40.' 38.! 39.

n

e. Tests of Cements Used in the Wall Constructions,

All of the cements used in the wall constructio],< were tested for conformity with the requirement

of Federal Specification SS-C-1 81c. The phy

ical properties of the masonry cements used in tli type N wall mortars were measured in 1954 ar in 1959. The properties of the cementing mat

rials used in the type S wall mortars were measiu-(i

in 1959. All of the data obtained are listed table 4. The cements were placed in sealed contain©

as soon as received at the Bureau, early in 19^

The data (table 4) show that storage for 5 y

from 1954 to 1959, did not greatly affect tl physical properties of the cements. Some increa' in the residue in the No. 325 sieve and a reductio

of about 1 percentage point in the water requiri

ment for normal consistency were noted.

The cementing materials used in the type

and type S wall mortars were also tested as m

sonry cements using blended Ottawa sand aggr

gate for conformity with the requirements

Federal Specification SS-C-181c. The tests we

made in 1953 and 1959 for masonry cement 1 and in 1956 and 1959 for masonry cement blen(

B and C. Tests of the laboratory prepari

cement E were made only in 1959. The data a

listed in table 5. The type N mortar (DN), containing masom

cement D had a high air content and was ; strong or stronger than was the low air, hi^

water-cement ratio mortar EN, which containd

the laboratory prepared cement E. Howeve

when the two cements were tested in type 5 mortars by the. addition of portland cement ar sand, this strength relationship was changed ai

the water requirement of mortar ES was reduce over 10 percentage points below that of morti

EN; see table 5. Storage of the masonry cements for 5 yr (19ii to 1959) resulted in some small changes in tl physical properties of the cements when tested I accordance with Federal Specification SS-C-I81

as blended sand mortars. The air content of th mortars was reduced 1 or 2 percentage point

As a result, the compressive strengths of tli

Dp

2
nortars were increased and the water retention

iT-alues were reduced. The amount of reduction n water retention ranged from 2 to 4 percentage

laJ )oints. 2.2. Sand

A mason's sand from the Philadelphia, Pa., area

va,s used in mortars for wall constructions. The

and was used while in a damp condition and was

tored in an unheated concrete bin, covered with

1 cellophane vapor barrier.

Two shipments of sand from the same source

aid having the same specific gravity and absorp38|jlion were received in 1957. The grading and

iither physical properties of the sands are listed

'n table 6. The amount of sand passing the No.

lO and No. 100 sieves was greatest for the sand in

tionsiihe first shipment, received in June 1957. The

Qortar in walls built prior to November 10, 1957,

ontained sand from the first shipment. Mortar

lOfD walls built after that date contained sand from

pliy7[he second shipment.

intKij Five determinations of the weight of dry sand

^aiier unit volume of loose damp sand were made

atljii sand contained in the first shipment. The

iraiaeasurements were made using a % ft^ measm-e

|.nd the shoveling procedure listed in section 7 of

^STM Method C29-55T. The data are listed mdow.

Weight of aggregate

ill Moisture Weight of Weight of content of dry sand in Date loose damp damp sand a cii ft of sand by weight dam.p sand

of dry sand

July 1957 Ib/ft^ % lb 79. 6 4. 6 76. 1 85. 8 4. 5 82. 1

5

75. 3 4. 2 72. 3

78. 8 4. 2 75. 7

4 80. 5 3. 8 77. 6 Avg 80. 0 4. 3 76. 8

2.3. Mortars for Wall Construction

a. Proportions

. m The mortars were proportioned by volume but

'..m\he measurement of materials used in a batch of wTtportar was by weight. The type N mortars conrpe i&ined one part of cementing material to 3 parts of

BtaBEOose damp sand by volume. Type S mortar was

rdwicher and contained I/2 parts of cementing mateeducff-ial to 4 parts of loose damp sand by volume.

For the volume proportions, a cubic foot of loose

amp sand was assumed to contain 80 lb. of sm'face

itry sand. The data listed in section 2.2 indicate

jhat a cubic foot of loose damp sand usually conained less than 80 lb of dry sand. Since the

portar materials were measured by weight, the

oftiifbove listed volume proportions of cement to sand

re in error and the mortars were slightly leaner

ol t|han indicated.

To permit the use of all mortar in a batch Avithin a reasonably short time, the size of the mortar

batches was controlled to that amount which the mason could use without waste within .30 to 40 min

after completion of the mixing. The weights per

bag (ft^) of each cementing material and the batch

weights of dry materials in tlie mortars used for the construction of the walls are listed in table 7. The amount of water used in each batch of mortar was adjusted to produce a mortar having as wet a consistency as could be conveniently handled

by the mason. The judgment of the mason was

depended upon to determine the proper mortar

consistency and he occasionally suggested changes

in the amount of water used in similar mortar

batches.

b. Preparation

Loose damp sand was taken from the stock pile

and placed into 30-gal capacity cans fitted with

covers and brought into the laboratory where its moistm'e content was measured. The solid materials needed for each mortar batch were weighted

and stored in sealed containers until used.

The mbcer was an electrically driven rotating

blade, horizontal axis Muller plaster and mortar

mixer of 2-ft^ capacity. Preliminary tests with

the mixer indicated no significant change in air content of mortar when the mixer was operated

through the range of full capacity to less than half

capacity. The yield of mortar per batch varied

from about K to the capacity of the mixer (0.65

to 1.0) ft^ depending upon the air and water content of the mortar and the amount of sand used.

During a previous investigation, an accelerated

rate of stiffening was noted at early ages on mortars similar to those used in the wall constructions.

The effects of this early stiffening on mortar consistency were greatly alleviated by using a waiting

period for the mortar followed by final remixing

with the addition of water. A similar procedure was followed in the preparation of the wall mortars. Ninety-five percent of the mixing water was

used in the initial mixing. The remaining five

percent of water was added after the waiting

period. Directions for mixing the mortar were as follows

I. Place one-half of the major portion of the

mixing water (about 47}^ percent of the total mixing water) in the mixer. Start the mixer and add

one-half of the sand. Continuing, add all of the

cementing material, the remainder of the sand and

the remainder of the major portion of the mixing

water. Continue the mixing for 3 min after all of these materials have been added.

II. Stop the mixer and cover it with a vapor

proof sheet. Let the mortar stand in the covered

mixer for 10 min.

III. Kemove the cover from the mixer and start the mixer. Add the remainder of the mixing water

(approximately 5% of the total water). Continue

mixing for a total of Iji min.

IV. At the end of the final mixing period dump

all of the mortar from the mixer to a clean damp

3
mortar board. Do not mix the fresh mortar with

old, unused mortar from the previous batch. Use

the mortar in the wall construction preferably

within 30 min and at no longer than 40 min after completion of its final mixing. Discard mortar

not used at the expiration of the 40-min time

interval. (Examination of laboratory time rec- ords indicates that the elapsed time between the

preparation of successive mortar batches was usually less than 35 min.)

V. Clean the mixer with clean wash water before

preparing a new mortar batch.

c. Measurement of Physical Properties of Mortars

Tests of the physical properties of the mortar

were made on one of the mortar batches used in each concrete masonry wall. Tests of two mortar

batches were made for each composite masonrj^

wall. A representative sample sufficient for all mortar

tests was placed in the 10-qt capacity mixing bowl

of a Hobart ClOO mixer immediately after the mortar was dumped from the mixer to the mortar

board. The physical tests on this mortar were made as described in the following order.

Initial flow oj mortar. The flow table and flo w

mold conformed with the requirements of the Tentative Specification for Flow Table for Use in

Tests of Hydraulic Cement (ASTM Designation

C230-57T). The procedure followed for measure- ment of the initial flow was in accordance with the

requirements of section 9 of the Tentative Method

of Test for Compressive Strength of Hydraulic

Cement Mortars (ASTM Designation Cl0V54T).

The mortar used for measurement of the initial flow was discarded and not returned to the mixing

bowl. The mortar was often of such a wet consistency that 25 drops of the flow table could not

be attained. In such cases, the initial flow for 25 drops was estimated by extrapolation, as follows • Corrected initial flow= observed flow -j- 2 [25

minus the number of drops].

Water retention. The water retention apparatus conformed to the requirements of section 27

of the Standard Specification for Masonry Cement

(ASTM Designation C91-57). Immediately after measuring the initial flow, the mortar remaining

in the bowl was remixed at medium (No. 2) speed

of the Hobart ClOO mixer for 15 sec. The flow

after suction and the water retention were then

determined in accordance with the requirements

of ASTM" C91 except for some mortars a lesser number than 25 drops of the flow table was used.

In all cases, the water retention was taken to be

the ratio of the flow after suction to the initial flow, each being measured at the same number of

drops and corrected, if necessary, for 25 drops.

Air content. The apparatus used to' measure

the air content of the mortar conformed to the

requirements of ASTM C91-57, section 24. The

procedure followed was similar to that of C91-57

except that the mortar consistency was not nece, sarily that given in the specification (flow of 1: ±5 percent). The value Sa (specific gravity

the sand) used in calculating the air contei

equaled that determined for the sand used in tl mortar.

Compressive strength. The equipment used || make the mortar cubes and to determine the

compressive strength conformed to the requirj

ments in the appropriate section of ASTM ClO^

54T. The molds were filled in accordance wi

the requirements of section 10 of C109.

The mortar cubes were cured in a damp clos until tested in accordance with the requiremen

of ASTM C270-57T, section 10(b)2 with tl exception that type S mortar cubes were immersf

in water after 7 days storage in air. Yield per bag. The yield of mortar in cubic fej per bag of cementing material was calculated fro the batch weights and the weight of 400 ml

fresh mortar as follows :

j

Yield per bag=

Total weight of sand, cement ai) water per bag of cement

Weight of cubic feet of mortarc

2.4. Concrete Masonry Units

The Solite aggregate used in the concrete m

sonry units was a rotary kiln, expanded sla' aggregate. The high -pressure steam cured co

Crete masonry units were made at the Belt Boul'

vard plant of the Concrete Pipe and Produ<

Co., Richmond, Va., and were donated to tl work by the Southern Light Weight AggregaJ

Corp., Richmond, Va. The sieve analyses of t|

aggregates used in the concrete masonrv unit

the batch weights and other data pertaining

their manufacture, their shape, size and physio

properties are listed in tables 8, 9, and 10. Tl' concrete masonry units are shown in figure

Their physical properties (table 10) were dete

mined in accordance with the requirements

ASTM Standard Method of Testing Concre^

Masonry Units, ASTM Designation C 140-56.

When used in the wall constructions, the co: Crete masonry units were conditioned to equili

rium in temperature and relative humidity wii the laboratory air. The equilibrium relative h^ midity of the blocks was determined with appartus similar to that described in the Tentati""

Method of Test for "Moisture Conditions ^ Hardened Concrete by the Relative Humidii

Method," ASTM Designation C427-58T. Te_^

indicated that the equilibrium relative humidii^

of blocks selected at random was usually withini to 4 percent of the relative humidity of the air ^ the laboratory which was maintained at a dai' mean relative humidity of not less than 50 perceri

The moisture content of the blocks in terms fl'tin the maximum possible moisture content was lo' and was usually between 10 and 12 percent of tl possible maximum. '

m

h
imih

Cffi

rtar

COi(

,0 tt:!

ITsltl

uie

Figure 1. Concrete masonry units.

2.5. Brick

The solid side-cut clay brick used in the composite walls were made in a tunnel kiln at the

Colon, N.C., plant of the Sanford Brick and Tile

Co. The units in this carload shipment of 20,000

brick were unusually uniform in dimension, absorptive properties and strength. The physical properties of the brick are listed in table 11 and were

determined in accordance with the ASTM standard method of testing brick, ASTM Designation

C67-57.

3. Construction and Curing of Walls and Bond Test Specimens

All walls were supported on rolled steel channel

ections and were built by an experienced mason,

rhey were built in running bond using typical

!onstruction techniques, which are described.

E'hat face of the wall nearer to the mason was kept

1 alinement by him and was designated as the

uter, exposed, face of the waU. The mortar

oints in this face were tooled with a rounded

Pooling iron. The far face of the wall was designated as the inner wall face. The mortar joints n the inner face were cut flush and were not tooled.

I'Vith the exception of a tew special walls, a full nortar bed was laid on the supporting channel at

I he bottom of each wall. Plain ended blocks were

Vsed at the ends of all courses containing concrete

jnasonry units. The interior blocks in the con-

;rete masonry walls were open ended.

One and sometimes two 2-block assemblies were Wade as bond-test specimens with each concrete

jbasonry wall. Four crossed- brick couplets and a

|;omposite assembly were made as bond -test speci- mens with each composite masonry wall. The

onstruction, curing, and testing of the bond-test

pecimens are described in appendix II. The

trengths ot the bond- test specimens are discussed

Q the text and are listed in the tables of appendix

which also list the strengths of the waJl constructions together with other properties of the mortars.

ecoi qiii 3.1. Concrete Masonry Walls

a. Typical Construction Details

Bed joint mortar was applied only to the tops

f the face shells of the units starting first at one md at the far face of the wall for the full length

jjjlf the course. Bed joint mortar at the near wall

jpj^ace was then applied. Both mortar beds were

jjj([jt)i|sually started from the same end of the course.

j(l^nt required 30 to 60 sec of time to lay the bed

jjfjibints in a 4-ft long course and 100 sec or more

j (jji]i|t)r an 8-ft long course. The time interval bejjjjj Ween the laying of any mortar bed to the

j,jjjiilacing of the blocks in the bed varied from a ^jJiiinimum of 20 sec for the first block to a maximum

ijfljljtf 5 min for the last block depending upon the

'ength of the course and the amount of alinement

ieeded.

Mortar for the head (vertical) joints was placed

only on the ends of the face shells. The first block in each course was laid at the end of the

course and without head joint mortar. The head

joints were then formed by buttering one end of

each block with mortar just before placing the

block in the wall. Laid in this way, the mortar

in the head joints was first placed in contact with

the units at the same side of each joint in the

course. With the exception of walls in one small

test group, there were no closure units in the concrete masonry walls. The first tooling of the mortar joints was done

when the wall was at midheight and before placing

the scaffolding. The joints in the upper half were

tooled after completion of the wall. The mortar

in the joints was still soft at the time of tooling

and it required about 30 sec to tool the joints in a

4-ft long course. The average thickness of the joints in the concrete masonry walls, calculated from the measured

dimensions of the walls and blocks, is listed below:

Calculated average joint thickness

Bed joints between

block courses Head joints between blocks

End Interior 2-joint 3-joint 5-joint 6-joint Special blocks block course course course course walls "

in. in. in. in. in. in. in.

0. 28 0. 35 0. 53 0. 36 0. 51 0. 41 0. 40

" The courses in these special flexure test walls were 8 ft long and contained 6 head joints. The walls were up- ended and the bed joints were in a vertical position when

the walls were tested.

The difference in bed joint thickness, noted for the end and interior blocks in a course, was due to the difference in the height of the blocks (see cols. 2 and 3 of table 10). When leveling a course, the mason was observed to tap the end blocks more

than he did the interior blocks.

5
Although no records were kept of the exact amount of mortar used during the construction

of each concrete masonry wall, it is estimated

that a 70-lb bag of masonry cement yielded enough

type N mortar to build approximately 60 ft^ of concrete masonry test wall. It required, therefore, the equivalent of approximately 113 full length stretcher units and from 5 to 5.4 ft^ of mortar to build 100 ft^ of test wall. The above mortar

requirements included that mortar needed for physical tests and the construction of bond-test

specimens made with the walls.

b. Special Details The recorded dimensions of the compressive,

racking and flexural strength walls are listed below:

Dimensions » of concrete masonry walls

Length Height

Kind of wall Aver- Maxi- Mini- Aver- Maxi- Miniage mum mum age mum mum

ft ft ft ft ft ft Compressive

4. 00 4. 00 3. 99 8. 01 8. 03 7. 99 Racking 8. 02 8. 03 8. 01 7. 98 8. 02 7. 94

Flexural 4. 00 4. 01 3. 99 8. 63 8. 69 8. 58

Flexural "= 3. 96 3. 97 3. 95 8. 67 8. 68 8. 65

» Measurement made on walls in position for test.

^ Bed joints horizontal, as constructed.

^ Bed joints vertical, after wall was up-ended.

Compressive strength walls contained 12 courses of

masonry. The first and odd-numbered courses, contained 2 stretcher units and 2 half units, one

at each end. The even-numbered courses and the

top course contained 3 stretcher units. The top

course of the wall was capped with a thin mortar

bed.

Racking test walls contained 12 courses of

masonry. The first and odd-numbered courses contained 5 stretcher units and 2 half units, one

at each end. The even-numbered courses and the

top course contained 6 stretcher units. Construction was started at the bottom right (east)

end of the walls. This lower right corner of the

wall was supported on and bedded solidly within

a 12 by 12 in. steel shoe which was alined and

connected by steel side plates to a 7-ft long channel which supported the remainder of the wall. After construction and before testing, these plates were removed leaving a }2-in. wide space between

the shoe and the channel. Cored spaces in the

blocks and other cavities in the masonry at the

lower right and upper left corners of the walls

which received a concentrated load during the

racking tests were filled solidly with mortar to prevent local failure of the masonry during the

tests. Flexural strength walls. Most of the flexural strength walls contained 13 courses of 4-ft nominal

length and were tested in the vertical position as

•wit built by applying horizontal loads to the quarte!

points of a 7 ft, 6 in. vertical span. When the wall»it \ were so tested the bed joints were normal to th^ span length and the loading conditions simulate^

top and bottom support. The bottom and th' odd-numbered courses contained 2 stretcher unit,

and 2 half units, as for the walls built for con^

pressive strength tests.

^ Flexural strength walls in two special group

contained six 8 ft, 8 in. long courses, each cours containing 6 stretchers with a half unit at one end,

Each wall was built and tightly contained withi| a steel frame. The first or bottom course was no, bedded in mortar. Each course was begun at th, right (east) end of the course by bedding the en^ of the unit in mortar against the vertical stet channel forming that end of the frame. Th

course was then laid from the left. The las stretcher block laid in each course was the secon(

block from the right end and was a carefully lai closure unit. Before laying the closure unit, th' end of the blocks adjacent to the closure and th,_,,

ends of the closure unit itself were heavily buttereij

ijjj with mortar.

After a wall was strong enough to be moved, th! steel frame was upended through a 90° angle an<, supported on the right end. The steel frame ex cept the channel section on which the wall wa

resting was then removed. The walls were testej

in this upended position, with the bed joints verti

cal, simulating end supports with complete absenc

of restraint at the other edges.

ills

iff

3.2. Composite Masonry Walls

The composite masonry walls consisted of

4-in. thick brick facing tier bonded to a 4-in. thicl' concrete masonry backing tier with brick heade

courses at every seventh brick course. The baci

of the brick facing was parged with mortar and th

wall construction was one having a high resistanc

to the leakage of wind-driven rain.

The bricks for the wall specimens were store( in an air dry condition and were adjusted in tem

perature with the air in the laboratory. Befor

use, the bricks were totally immersed in water fo 40 min or more. They were stacked after remova

from immersion and were considered ready foi laying as soon as water was no longer visible ot their surfaces. The bricks were laid in the wall

within 1 or 2 hr after removal from immersion

Several times daily, measurements were made o the rate of absorption (suction) of the brick. Thi

rate of absorption (absorption for 1 min durinj

partial immersion) at time of laying averaged 6 j and varied between 4 and 9 g.

! a. Typical Construction Details

The mortar for the bed joints was furrowed. A

brick header courses and at beds between blocl courses, the bed joint mortar bridged the coUa

joint and interconnected the parging.

The head joints in the brick stretcher course; were formed by buttering the exposed edges of thi

IS

1(1

6
bricks to a minimum face depth of 1 in. After

'lach 3 stretcher com-ses had been laid, the parge

;oat was apphed to the back of the brick facing

ier. The parging was keyed into the open head

loints between brick stretcher units and the mortar

''>vsls wet and plastic enough to be easily applied,

Without misalinement of the brick facing. Head

feints in the brick header courses were soUdly

aied with mortar. They were formed by butterng the bottom edges of each brick before shoving

Ihe header unit into its bed. If needed, additional

.^Vfcortar was slushed in from above.

TMw A course of backup block was laid after 3 brick

jtretcher courses had been laid and parged. Bed

"'""loint mortar under the block courses was laid and

'^^'Wrowed over the full thickness of the block.

^'Hortar for the head joints was placed only at the

^ ixiter shell of the blocks in the backing. No morar was placed on the inner shell. The construe-

.

ion of a compositee wall (built for flexural test)

3 illustrated in figure 2.

"tI Time studies were made during the construction

''^'^j.f a few of the composite walls. A single obserWtion indicated that an 8-ft long brick stretcher curse with cut units at each end was laid in 4 min,

i:0 sec. A series of observations made during the

'^"'kying of 8-ft long stretcher brick courses indicated

'f^hat the minimum time between the laying of a TM'^ortar bed and the placing of a stretcher brick

IVas 20 sec. The maximum time was 2 min, 25 sec. The back parging of three 4-ft long brick stretcher

' ourses required 1 min, 30 sec. The time required o parge three 8 ft long stretcher courses was 2 min,

15 sec.

j The laying and alinement of an 8-ft long block

|)acking course required 6 min, 30 sec, includmg

;»5 sec needed for laying of the bed joint rnortar. ai|rhe minimum observed time between laying of

baclhe mortar bed and placing of the block in an 8-ft Ibng course was 55 sec; the maximum time was

f, min, 20 sec.

: Tooling of the cut joints in brick stretcher

(iourses was done after 3 stretcher courses had been

Figure 2. Composite wait under construction.

604027 0—61 2

laid. At this time the mortar was still soft and

easily tooled. Mortar compacted easily under the

tooling iron and additional mortar was usually

added to the joints during the tooling operations.

It required about 1 min, 40 sec to tool the bed

and head joints in a single 4-ft long brick stretcher course and 2 min, 20 sec for the tooling of an 8-ft long course. Since the brick were not of modular dimension,

it was necessary to cut at least one brick in each

course. For this reason the thickness of head

joints in the brick courses was not estimated.

However, the average thicknesses of the other

joints in the composite walls were estimated from

the measured dimensions of the walls and of the

units. These dimensions are listed below

Calculated joint thickness in composite walls

Bed joints in: Head joints in block backing

Brick Block 2-joint 3-joint 5-joint 6-joint

facing backins; course course course course

in. in. in. in. in. in.

0. 40 0. 45 0. 72 0. 48 0. 54 0. 45

Measurements of joint thicknesses were made

on small random selected portions of mortar from

the brick facings of some of the walls after test. The average measured thicknesses of bed and head

joints in the brick facing tiers were % in. and %6

in., respectively. The average measured thick- ness of the parge coatings was Yie in. The amount of mortar yielded by a bag of

cementing material was sufficient to build about

18 ft^ of composite wall containing type N mortar

and about 16 ft^ of wall containing type S mortar.

The approximate amounts of building material

needed to construct 100 ft^ of composite wall were

830 bricks, 93 blocks, and 16 to 21 ft^ of mortar,

including the mortar used for making physical

tests and bond-test specimens.

b. Special Details

The dimensions of the compressive, racking and

flexural strength walls are listed below

Dimensions of composite masonry walls

Num- Length Height

Kind of ber of wall wall

speci- Aver- Maxi- Mini- Aver- Maxi- Mini- mens age mum mum age mum mum

.ft ft ft ft ft ft Compressive. 14 4. 02 4. 08 4. 00 8. 02 8. 06 8. 00 Racking 12 8. 02 8. 06 8. 00 8. 08 8. 13 8. 04

Flexural " 24 4. 02 4. 10 3. 99 8. 70 8. 82 8. 59

Flexural ^ 6 4. 02 4. 02 4. 01 8. 66 8. 73 8. 62

" Tested with brick facing tier in tension.

^ Tested with block backing tier in tension.
The lengths of 70 percent of the composite

walls were within in. of the average lengths

listed above. The heights of over 50 percent of

the walls were within ji in. of the average values.

A group of composite masonry walls ready for

test is shown in figure 3. Compressive strength walls contained 36 courses

of brick masonry in the facing tier, 6 of which

were header courses. Header courses were laid at the top and the bottom of the wall and between

every 6 stretcher courses. The backing tier contained 10 courses of concrete masonry laid in paired courses behind the

brick stretcher units. The lower of each pair of block courses contained 2 stretcher units and 2

half units; the upper course contained 3 stretcher

units.

Racking strength walls were constructed in a manner similar to that used for the compressive

strength walls. The right (east) ends of the lower

courses of masonry were solidly bedded in a steel shoe in the same manner as previously described

for the concrete masonry walls built for racking

strength tests. The lower right and the upper left corners were built of solid masonry to prevent

local failure at these points during the tests. Flexural strength walls were about 8 in. higher

than were the walls built for compressive strength

and racking strength. The additional height,

needed for test purposes, was obtained by adding

3 stretcher courses of brick and one of block at the bottom of the wall; see figure 2 and the wall

in right foregound of figure 3.

Figure 3. Composite masonry walls.

Most of the flexural-test composite walls wer

•built with the brick tier as the facing tier and wer

tested with the brick face in tension. One grou-ifeEe

of 6 composite walls was built with the bloc!

tier as the facing tier and was tested with tLj block face in tension.

5 3.3. Curing of Masonry Walls

The walls were constructed and stored in

heated laboratory equipped with humidifiers df signed to maintain a minimum relative humidit, _ of 50 percent. The laboratory temperatures anjjiete relative humidities were continuously recordej

with an instrument whose accuracy was satit, factorily checked from time to time by observf,

tions made with a sling psychrometer. The gerl eral range in laboratory temperature and relativ jetf humidity during the construction and curing i,. Jjt( laboratory air of the concrete and the composit

masonry walls is shown below

Range of laboratory temperature and relative humidity

Kind of masonry

Concrete__-

Composite.

Temperature

Extremes

Max

88

87

Min

°p

68

63

Daily mean

Max

°F

8284

Min

77

76

Relative humidit

Extremes

Max

%

82

69

Min

%

34

29

Daily mean

Max

%

6564

Mi' 5

The daily mean laboratory temperatures range

between 75 and 85 °F and the daily mean relativ

humidity in the laboratory ranged between 50 an

65 percent. Extremes in both temperature an

relative humidity occurred during periods of le^ than 1 hr while laboratory doors were opened t permit the passage of masonry materials and wa]

specimens. The temperatures and relative hu

midities recorded during the construction anj

curing of individual wall specimens are listed i| table 12 for the concrete masonry walls and ii table 13 for the composite masonry walls. The concrete masonry walls were tested at ag

of 15 days and the composite masonry walls at ag

of 14 davs.

ii

(Ctl

itim

itrt

is

iSM

1

4. Compressive Strength Tests

4.1. Test Equipment and Wall Preparation

After curing, each compressive strength test wall was plumbed in a vertical position on a bed of highstrength gypsum plaster poured on the platen of a 600,000-lb capacity hydraulic testing machine.

After the plaster bed had sufficiently hardened,

the wood wedges used for the plumbing operation were withdrawn from beneath the steel" channel

section supporting the wall. A 1-in. thick steel bearing plate was bedded in

plaster spread over the top of the wall. A 1-in.

square steel loading bar was positioned on th

bearing plate parallel with the wall axis at a dis

tance of }i of the wall thickness from the insidj

face of the wall. A steel loading beam hanginj,

beneath the head of the testing machine was low

ered and supported on the loading bar and on tenx porary leveling steel shims 1-in. thick. The l,100i lb combined weight of the top bearing plate, th

loading bar and the loading beam was uniforml;

distributed over the top of the wall. While th

upper plaster bed was still soft, an additional loac of about 3,900 lb was uniformly applied over th
J"

)lotK

I )p of the wall through the spherical bearing head

I the testing machine. After the plaster bed had

iffened, the spherical bearing head of the machine

as locked in position to prevent rotation of the

ead during the test. The compressometers and

sflectometers for measuring strain and deflec- on were fastened to the wall while the plaster

Ijeds hardened.

Vertical strains in the masonry were observed

ith 4 compressometers attached to the wall faces

'iear each corner. The supports for the compres-

)meters on the concrete masonry walls were at- ,ched to the concrete masonry units and were

cated approximately 4 in. from the top and

Dttom of each wall and 4 in. from the ends of the

all. The vertical gage length of these compres-

)meters was about 88 in. The deflectometers

Bed to measure the lateral deflection at midheight

each end of the concrete masonry walls Avere ee-hanging, straight edges, 90 in. long, supported

bout 3 in. from the top of the wall and restrained

gainst lateral motion at the bottom.

The supports for the vertical compressometers

cated in the brick facings of the composite walls

ere inserted by the mason about 5 in. from the

ids of the bed joints located 2 courses down from

le top and 2 courses up from the bottom of the

all. The gage length of these compressometers

as about 84.5 in. The compressometers on the

jncrete block backings of the composite walls

ere also about 84.5 in. long and were supported

om brackets attached to the concrete masonry

nits. The deflectometers used to measure the

teral deflection at midheight of the composite

alls were similar to those used on the concrete

lasonry walls. The measuring device attached

t» each compressometer and deflectometer was a

j.OOl-in. micrometer dial gage,

i"

, Compressive strength test walls in readiness for

'^'"^st are shown in figures 4 and 5.

alii

n i

SliQ

ediii

t if

it a

4.2. Loading Procedure

After the plaster beds had hardened sufficiently,

|ie steel shims beneath the leading beam were re- loved and the total load on the wall was adjusted

5,000 lb. Of this load, 215 lb was uniformly

istributed over the top of the wall and the remainer was applied on a line at the third point of the

all thickness. This 5,000-lb loading and the

bservations made under it were considered as the

ase to which all higher loadings and observations

ere related.

; Load was applied to the wall at a rate of 50,000

9/min in increasing increments, of 5,000, 10,000

jad 20,000 lb. Further increments of either 20,000

J

40,000 lb were then applied until it appeared

bssible that a further increment might cause failIre of the wall. After each increment the load

as reduced to the basic 5,000-lb load. Strain

ad deflection observations were made after applyiig and after releasing each load increment.

After the final load increment had been reduced

j|) the basic 5,000 lb, the measuring instruments

Figure 4. Concrete masonry wall ready for compressive

strength test.

Figure 5. Composite masonry wall ready for compressive

strength test.
were removed and the load on the wall was steadily

increased at the rate of 50,000 Ib/min until the

maximum load was reached.

4.3. Compressive Strength of Walls

a. Concrete Masonry

Cracking of the concrete masonry walls was first noted at 60 percent or more of maximum load.

The cracks started directly beneath the loading

bar and extended downward at a slight angle to- ward the tensile (outside) face of the wall. After

penetrating one or more courses the initial cracks

terminated in a bed joint at points near the inside

of the face shells in the tensile face. At this level and as loading increased a new crack formed near

the midthickness of the wall, the new cracks also tending to approach the tensile face of the wall

and again terminating in a bed joint. Maximum

load on the wall was usually reached before the

cracking had penetrated below the upper 2 or 3 courses. After maximum load was reached, the

formation of cracks continued at successively lower

elevations. In some walls, the crack formations

reached down to below midheight of the wall be

fore collapse of the wall. The 15-day compressive strengths for both the

gross and the net cross-sectional area of the concrete masonry walls and the properties of the mortars used in them are listed in table 14. The net cross-sectional area was 38 percent of

the gross area and was taken to equal the sum of

the minimum area of the face shells plus those portions of the end and cross web shells in good bearing contact with the mortar bed.

Significant data from table 14 and the compressive strength for both the net and gross areas of

the blocks are summarized below:

Compressive strength of concrete masonry walls

Mortar Compressive Compressive

properties strength of strength of block walls Mortar

designation

Air Com- Gross Net Gross Net

con- pressive area area * area area

tent strength

0/

/o psi psi psi psi psi

BN 18. 9 740 1, 100 2, 100 390 1, 030

CN 12. 1 940 1, 100 2, 100 430 1, 130 BS 16. 6 1, 730 1, 100 2, 100 440 1, 160 cs 10. 2 2, 140 1, 100 2, 100 470 1, 240

» Calculated for net area of face shells and crosswebs which was equal to about 52 percent of gross area.

^ Calculated for net area which was taken as the sum

of the portions of units in contact with mortar; this net area was about 38% of the gross area of the block. The compressive strength of the concrete masonry walls increased only slightly with increase

10

m the compressive strength of the mortar. Thes

strengths ranged from 390 psi on the gross are

for the BN mortar to 470 psi for the CS morta;

It is noted that the higher compressive strength c the type S mortars was not accompanied by a pre portionate increase in wall strength.

The compressive strength for the gross area ( the concrete masonry units used in the walls w£

about 1,100 psi. The compressive strength base on the net area of the blocks was 2,100 psi, appro:

imately equal to the compressive strength of tl CS mortar. For these tests and for strengths ( masonry and block based on gross areas, the con

pressive strength of the walls tended to be aboi

half or less of the compressive strengths of eith* the mortar or the block, which ever was tl weakest. On the net area basis, the wall strengtl were about half of the compressive strength of tt concrete in the blocks, again increasing bi

slightly with increase in mortar strength. It ma, be noted that the eccentric application of loa

affected the load distribution on the face shells ( the blocks in the top course of the wall, one she

carrying approximately double that of the other.

b. Composite Masonry

The composite masonry walls failed under con

pressive load by crushing of the face shells in tl concrete masonry units in one or both the to backing courses. Failure of some of the wal|

containing type S mortar was sudden, almost e? plosive in nature, and was accompanied by sheai,

ing at the collar joints of the header brick in on( or more of the upper bonding courses and witj

collapse of the wall toward the brick facing tiej jj Compressive load failures are illustrated in figurej

6 and 7. With the collapse and breaking up of tti wall, secondary bond failures occurred usually a) the bottom of the mortar beds between briC; courses as shown in figure 7. The 14-day com.pressive strengths of the con

posite masonry walls are listed in table 15 with th

properties of the mortars used in them. Signij

icant data from that table are summarized below

Compressive strength of composite masonry walls »

Mortar

designation

BN

CN

BSCS.

Mortar

properties

Air , content %

19. 3

12. 3

17. 6

10. 5

Compressive

strength

psi

680

820

1, 740

2, 200

Compressive

strength of block

Gross

area

psi

1, 240

1, 240

1, 240

1, 240

Net

area '

psi

1, 690

1, 690

1, 690

1, 690

Com-,

pressivr ''t' strengtt 4

of wall/

le

idf

uti

lid

Gross'

area

psi

ll(

It

itf

MS

72

77i 4

« Calculated for net area of face shells and cross wel which was equal to about 74% of gross area.
to I

fOl 1

hti i

FiGUEE 6. Compressive load failure of com'posite masonry wall

The data show that the compressive strength of

he composite masonry walls increased with the

lompressive strength of the mortar, ranging from

1111^20 psi on the gross area for the BN mortar to 950

!5si for the CS mortar. On the gross area basis

jind for type N mortar, the wall strength approxir^'Jinately equaled the compressive strength of the

^Inortar. For type S mortar, wall strength approximated half of this amount. As was the case for concrete masonry walls, the higher compresdve strength of the type S mortars was not

Accompanied by a proportionate increase in compressive strength of the walls. A considerable amount of compressive load was

'"transferred to the brick facing tier by the brick

[leaders in the bonding courses. It is likely, how-

=4j5ver, that the compressive strength of the conrete masonry units was the controlling factor

"^J ^iffecting the ultimate strength of the composite

kalis. The following may be noted from table 15. Fhe compressive strength of wall BN-1,

oaded axially over the top of the wall was approximately double that of walls BN-2 and BN-3

rhich were loaded on a line along the third point

ipf the wall thickness. At loads of about 300 psi

3n the gross area, vertical and horizontal cracks

w&CQ noted at the top of the brick facing tier in

Walls BN-4 and BS-1. The early weakness and

tracking of the brick courses may have resulted 'rom some irregularity in the construction of the

bop courses or from improper bedding of the loading equipment. The compressive strength of wall

lBS-4 loaded along the outer third point, measured

Prom the brick facing, was approximately equal to Figure 7. Compressive load failure of composite masonry

wall CS-3.

11
that of the similar walls BS-2 and BS-3 which were loaded at the inner third points measured

from the block backing. For like mortars, the

composite masonry walls were in general about

twice as strong in compression as were the concrete masonry walls.

4.4. Compressive Load Strain and Deflection

a. Shortening Strain and Set The shortening and the set strains were observed on all of the walls for each load increment up to about 70 percent of maximum load. The shortening and set strains averaged for all mortars and

for each wall type are shown in figure 8 for loads

up to and exceeding 250 psi for the concrete masonry walls and 500 psi for the composite

masonry walls. The range in strain and set for each wall type are also shown. The greatest

strains were observed for walls containing the BN

mortar; the least for walls containing the CS

mortar.

For the concrete masonry walls, the average

shortening strains at loads of 100 and 250 psi were 170X10"^ and 457X10''^ respectively. For the

composite masonry walls, average strains at loads

of 100, 250, and 500 psi were 89X10-^ 223X10-^

and 464X10"^ respectively. Thus for like loads

up to 250 psi, the composite masonry walls were

twice as stiff in compression as were the concrete masonry walls. Values of the ratios of set to shortening strains are listed below for one half of maximum load on

the gross wall area

Ratio of set to shortening strain at load of 50 percent of maximum

Kind of mortar Type of wall BN CN BS CS Average % % % % %

Concrete. 21 17 11 8 15 Composite . 10 10 9 8 9

For the concrete masonry walls, the ratio of set

to shortening strain decreased with increase in the

compressive strength of the mortar and was about

8 percent for walls containing the CS mortar.

The ratio was approximately a constant (9%)

for the composite masonry walls. As previously stated, walls BN-1, BN-4, BS-1,

and BS-4 behaved abnormally or else were loaded

in a manner different from their companion speci- mens. Even so, the shortening strains observed

in these walls were approximately the same in

amount as were those observed in their companion

specimens.

b. Modulus of Elasticity in Compression

The secant modulus of elasticity in compressio

of the various walls is listed in table 16 for loac

up to 250 psi for the concrete masonry walls an

for loads up to 500 psi for the composite masonr

walls. The secant modulus tended to increas

somewhat with the compressive strength of th mortar but the increase in moduli for the type

mortars over that for the type N mortars wa

considerably less than the corresponding increas

in the compressive strengths of the two types c mortars. The compressive strengths of the tw

type S mortars (BS and CS) approached that c the face shells of the block used in the concret masonry and there was httle difference in th

moduli of elasticity for walls containing thes

rnortars. The secant moduli in compression of the con: posite masonry walls were about twice those c concrete masonry walls containing similar moi

tars. This was probably due to the foUowin

facts: the ratio of net to gross area of the 4-ii^ thick block used in the composite walls was greate

than that for the 8-in. thick block in the concret

masonry walls. This, combined with some loa. transfer from the block backing tier to the brie

facing tier resulted in lower bearing stresses be

tween block and mortar in the composite wall

than for the concrete masonry walls. Also th

modulus of elasticity of the brick was greater tha

that for the blocks.

For both wall types the moduli for walls cor

taining the type N mortar decreased slightly witj

increase in load. For walls containing the type i; mortar, whose compressive strength approachef

or exceeded that of the concrete in the blocks; there was little or no decrease in modulus wit]

load increase.

c. Lateral Deflection and Deflection Set ^

The deflections observed at midheight of som

of the walls were affected by strain redistributioi

which occurred as the loading increased. Thes

changes did not appear to affect the average short

ening for the wall as a whole but they tended U

improve the resistance of the wall to compressive

loads and to reduce the deflection-load ratio. Ii'J a few of these walls the deflection-set (set iijj) deflection on release of load) was reduced belov' that found for the previous load increment,

should be noted that wall deflection may also hav

been slightly affected by minor variations in thi eccentricity of the applied loads.

No consistent relation was found between wal

deflection and the properties of the mortars usec^

in either the concrete or the composite masonrj'

walls. At one-half of maximum load, the deflection o the composite walls was considerably greate:

(about double) than that of the concrete masonrj'

walls. The deflections of both wall types wen'

about equal for loads up to the limit of the observations made on the concrete masonry walls.

i

12
eso)

toi

cretii itti

thesi

com

(Tel

l0M(

n The ratio of set to deflection at one-half of maxi-

|num load varied considerably but averaged about

percent for the concrete masonry walls and

ibout 13 percent for the composite walls,

jl The deflection of composite wall BS-4 loaded

thai

Figure 8. Compressive load strain.

/ Shortening Strom , Composite Mosonry Walls

Shortening Strain , Conaete

Masonry Walls A

• Average, All Mortars

c Mortor-CS

Mortar -BN

300 400

STRAIN

over the brick facing tier was about one-third of

that of its companion specimens which were loaded

over the block-backing tier and was opposite in

direction (concave on the brick face) to that of the

other walls.

5. Racking Strength Tests

5.1. Test Equipment and Method

a. Apparatus

The racking test apparatus was in the form of

rpflli yoke consisting of two steel side bars, one on

icbej^jBach side of the wall, connected at the ends to

ocbi&teel shoes placed at diagonally opposite corners of

mfihe wall. The upper end of the yoke was fitted

[iKith a hydraulic jack connected to a hand-operated pump which transferred load from the jack

Ithrough a load cell to the upper shoe. The load

;fjj][bell used for the tests on the concrete masonry

(Ift^alls was a 60,000-lb capacity Baldwin Type C

[1]j; j6R4 dynamometer. A 110,000-lb capacity load

yjpell was used for the tests on the composite

pj j, ijtnasonry walls. This load cell was made in the

s-jy^^jlaboratories of the Portland Cement Association

" yand was loaned to the Masonry Research Program

p( pXoT the wall tests. Strains in the load cells and in

jj](iJSR4 gages on the side bars were measured with a

] |Baldwin Type L strain indicator,

jjjyij The upper (west) end of the yoke with the ram

J I

(land load cell was supported on the table of a portliable hand-operated vertical lift stacker. The sup-

^jfporting table was fitted with a screw for making

-jJiBmall lateral adjustments and with a pivoted

^spring for flexibility of movement normal to the

jlong axis of the yoke.

Displacements in a direction parallel with the

[length of the wall were measured near the top and

ottom of the east end of the wall. The measureIments were made using 0.001-in. micrometer dial

.jjy.jgages supported on a rigid tripod resting on the

floor of the laboratory. The upper dial gage was

ijplaced about 6 in. below the top of the wall, the

lower gage was about 4 in. above the top of the

lower bearing shoe.

The racking load apparatus with the stacker

and strain indicator .equipment are shown in

figure 9.

b. Method of Test Each wall was tested where built and the loading

equipment was moved to and assembled at that

place. The lower shoe was disconnected from the

long channel section supporting most of the wall

permitting the shoe to function without restraint

from the supporting channel. The east ends of

the side bars (yoke) were pinned to the lower shoe

and the stacker was alined in position at the west

end of the wall. The west end of the yoke with

the ram and load cell in proper assembly were

fastened to the table of the stacker. The upper

shoe was then bedded in high-strength gypsum

plaster. While the plaster was still soft, the upper

end of the yoke was raised and moved into position

until the bearing face of the load cell was in proper

alinement with the shoe. A load of 5,000 lb was

immediately applied and maintained until the

plaster bed hardened.

This 5,000-lb load was the minimum load to which the wall was subjected during the test and

was considered as the base load to which all higher

loadings were related. The test was begun at the

5,000-lb load by making displacement observations

in the dial gages and strain observations on both

the load cell and the side bars of the yoke. These

observations were the base to which all other

observations were related.

13
Figure 9. Racking load test setup.

Load was increased by increments of 5,000 lb on

the concrete masonry walls and 10,000 lb on the

composite masonry walls. After each succeeding

increment the load was reduced to the basic 5,000

lb and observations of strain and displacement were made before and after each load increment.

The strain observations for the load cell were

taken as the true measure of load. The strain

observations on the diagonal side bars indicated an even load distribution between the two bars,

and the indicated loads from the side bar observations were usually in good agreement with those

indicated by the load cell, especially at the higher

loads. The sensitivity of the side bar strain

observations was considerably less than that

obtained with the load cell.

5.2. Racking Strength of Walls

a. Manner of Failure

Both the concrete masonry and the composite

masonry walls subjected to racking loads failed

in bond along zigzag paths passing through the

mortar joints and running parallel with the diagonal side bars. The initial cracking of the mortar

joints was observed in the concrete masonry walls

at about 60 percent or more of maximum load.

More often than not, these cracks were below the

loading bars but final failure was usually along a path above the bars.

14

At maximum load, the final failure in all of the

walls was sudden and was accompanied with a release of potential energy built up in the wall

and in the side bars of the loading mechanism. At

failure, the upper triangular portion of the test wall was moved some distance along the failure

plane, the amount of movement and the number of crushed and broken units tending to increase with

increase in the maximum load. It is unlikely that

many, if any, of the units in both the concrete and

the composite masonry walls were damaged before

the maximum load was reached. Such damage as was observed at failure was caused by the grinding

slide along the failure plane of the upper triangular

wall portion. It should be emphasized that bond

failure between the mortar and the units was the

primary cause of failure of the walls subjected to the racking tests. Typical failures under racking

load are shown in figures 10, 11, 12, 13a, 13b, 14a

and 14b.

It may be noted from these figures that the bond

failures in the bed joints of the concrete masonrywalls were about evenly divided between the top'^j

and the bottoms of the mortar beds. For the com-]

posite walls, bond failures in the bed joints of both

the brick facing and the block backing usually

occurred at the bottoms of the mortar bed.

Laboratory notes taken during the construction

of some walls and later examination of these wallsi after test indicated that bond failures in the head

joints usually occurred at that face of the mortar

Figure 10. Shear failure of concrete masonry wall BN-1.

Figure 14a. Shear failure in brick facing of composite masonry wall CS-1.

Figure 14b. Shear failure in block backing of composite masonry wall CS-1.

joint that was last placed in contact with a masonry

unit. For example, the bond of mortar applied to the ends of a block before the block was placed in

the wall was usually stronger than was the bond

at the opposite face of the joint.

The observations on the location of bond failure

planes in the head joints support the widely

accepted theory that suction of the masonry uni1 on the freshly applied mortar will tend to dry ourj

the mortar and lower the bond strength at th(

face of the joint last coming in contact with th(

unit. However, it may be observed from photo

graphs 13a, 13b, 14a, and 14b that this theory was not applicable to the bed joints in the compositt

walls. This matter will be discussed further ir that section of this paper which discusses the flex ural strength tests.

b. Racking Strength of Concrete Masonry Walls ' The 15-day racking strengths of the concretd

masonry walls are listed in table 17, together with,

the flexural bond strength observed on block assem

blies and other properties of the mortars used ir' the walls. Significant data from that table are summarized as follows:

Racking strength of concrete masonry walls *

Mortar properties

[ Racking strength

of walls '

Mortar

designa- Total Horition Air Com- diago- zontal con- pressive Bond nally force pei tent strength strength *> applied linear load foot of wall

BN

CN

BS

CS

%

18. 9

12. 0

16. 4

10. 3

psi740

890

1,750

2, 060

psi 9

11

20

23

lb 27, 000

41, 000

46, 000

52, 000

lb

2, 40C

3, 60C

4, OOC

4, 50C

ise

0

" Walls were aged in laboratory air and tested at age ol 15 days. Flexural bond strength of concrete block assemblies stored in laboratory air with the walls. jiij The racking strength of the concrete masonry

walls (in terms of the maximum horizontally' [ applied load) ranged from a minimum of 2,400 lb per linear foot for walls containing the BN mortar

to a maximum of 4,500 lb for walls containing the' CS mortar. The walls were observed to fail in, bond and there was a fair but not a precise rela-|||),^

tionship between racking strength and the flexural

bond strength of block assemblies built and aged

in laboratory air with the walls. This relationship is improved slightly by averaging the bond

strengths of all block assemblies, aged in laboratory

air, which were built with all of the concrete masonry walls including those subjected to racking,

compressive, and flexural loads.

Although the racking strength of the concrete

masonry walls was primarily a function of the

bond strength of the mortar, there was a secondary and less consistent relationship between

the strength of the walls and the compressive

strength of the mortars used in them. It should

be clearly understood that the relationship be16
isiti I ri|i| h

'elf I

fill I t

k

)Drjj

rek'

v^een the racking strength of the walls and the

ompressive strength of the mortars may hold

'nly for these tests which were made on walls

iiiilt with very wet consistency mortars. Had

]he mortars been of a drier consistency, their

ompressive strengths as measured would have

peen greater but both the racking strength of

'he walls and the bond strength of the mortars

0 the units might have been considerably less.

!t is erroneous and misleading to state that the

ompressive strength of a mortar and not its bond

trength is the important factor affecting the

jacking strength of concrete masonry. The comiiiressive strength of a mortar may be considered

s a possible measure of the racking strength of

lasonry only when the mortar is tempered to its ptimum bond strength consistency.

c. Racking Strength of Composite Masonry Walls

; The 14-day racking strengths of the composite

jioasonry walls are listed in table 18 with the bond

; trength and other properties of the mortars used

In the walls. Significant data from that table

j^re summarized as follows

Racking strength of composite masonry walls *

Mortar properties Racking strength

of walls

viortar Air ComBond

strength Total di- Horizontal

desig- »ation

content

pressive strength

Brick couplets

Composite

assemblies

agonally

applied load

force per lin- ear ft of wall

3N.-.

%

20. 1 13. 1

psi720 860

psi28

46

psi3354

lb 72, 000

« 104, 000

lb

6, 400

" 9, 200

17. 4

10. 8 1790 2270

4048

55

63

105, 000

=110, 000

9, 300

<= 9, 700

» Walls were aged in laboratory air and tested at age

af 14 days.

*> All bond-test specimens were cured under cover at

' aboratory temperature for 7 days. They were then stored

ivith the walls until tested at age of 14 days.

" Tensile bond strength of crossed-brick couplets.

^ Flexural bond strength of composite assemblies.

" Some walls in the group were not loaded to failure.

' The racking strength of the composite masonry

Walls (in terms of the maximum horizontally applied load) ranged from a minimum of 6,400 lb per linear ft for walls containing the BN mortar

'ito over 9,700 lb for walls containing the CS morItar. The composite masonry walls were observed

!to fail in bond as were the concrete masonry walls

Jteubjected to racking load. Although a maximum

load was not reached in the tests made on 3 composite masonry walls, the data indicate that

for similar mortars, the racking strength of the

composite masonry was nearly three times that

of the concrete masonry.

Since the ultimate resistance of all the composite walls representing two of the mortars was

not reached, a relationship between mortar properties and the racking strength of the composite

masonry could not be easily obtained. However,

it is very likely that the discussion given in the

previous section on the relationship between the

racking strength of concrete masonry and the

bond strength and other properties of the mortars

also fully applies to the composite masonry walls.

5.3. Racking Shear Strain

The racking shear strain was taken as the net

horizontal displacement of a point on the wall

relative to that of a point directly below, divided

by the vertical distance between the points. The

points in question were located near the top and

bottom of the east end of the wall. The shear strain and set were determined for loads up to 70 percent or more of maximum. A

considerable deviation existed between the dis- placements and strains noted for similar wall

specimens and no consistent relationship was

found between the shear strains and the properties

of the mortar used in either the concrete or the

composite masonry walls. The average racking load shear and set strains

for the concrete masonry walls and for the composite masonry walls are shown in figure 15 for racking loads up to 14 psi on the gross area for the concrete masonry walls and 46 psi on the

gross area for the composite masonry walls. Racking loads of 14 and 46 psi on the gross area of a

horizontal section are equal to about 1,300 and

4,400 lb per linear ft of wall, respectively.

The shear moduli for a racking load of 14 psi,

calculated for the gross wall area from the strains

shown in figure 15 are approximately 140,000 psi

and 220,000 psi for the concrete and composite

masonry walls, respectively.

m 40 ~

Figure 15. Racking load shear strain and set.

17
6. Flexural Strength Tests

All of the masonry walls subjected to flexural strength tests were tested by applying lateral line loads to the quarter points of a simply supported

7 ft, 6 in. vertical span. Twenty-eight concrete masonry walls were tested as built with the bed

joints horizontal and normal to the span length.

Six concrete masonry walls were tested with the

bed joints vertical and parallel with the span.

These six walls were built with the long dimension

horizontal and were turned through a 90° angle

and supported on one end when placed in the

testing apparatus.

All of the composite masonry walls were tested as built with the bed joints horizontal and normal

to the span length. Twenty-four composite walls were tested with the brick facing in tension by

applying line loads to the concrete masonry backing. Six composite walls were tested with the

concrete masonry backing in tension by applying

the load to the brick facing.

6.1. Test Equipment

The flexural load test apparatus consisted of a structural steel frame fitted with lateral load and

support devices and with a lever-actuated freely

revolving roller support for the test wall. The

lower lateral support for the walls was fixed parallel with the roller. The load lines and the upper

lateral support were hinged at the center, permitting movement in a horizontal plane. All of the

3-in. wide neoprene-faced aluminum loading and

support bars were free to rotate about their end

supports.

The lateral load and support devices were sus- pended on rollers at the top of the test frame and

could be moved to obtain the clearance needed

for placement of the wall in the test frame. The

apparatus is illustrated in figure 16. Load was applied to the wall with a 4-ton

capacity Hein Werner push and pull hydraulic

jack. The amount of load was measured with a Type L Baldwin strain indicator connected to either a 500-lb or a 5,000-lb capacity Baldwin

SR 4 load cell. A neoprene block was inserted

behind the jack to reduce the rate of load application from the hydraulic system.

Lateral deflection of the wall at midspan was

measured at each end of the wall with free hanging

deflectometers equipped with 0.001 -in. micrometer

dial gages. The deflectometers were suspended

from a point slightly above the upper wall support

and extended downward to a point slightly below

the lower wall support. The dial gage was at- tached to the deflectometer bar at midheight and

bore against a bracket mounted against the wall. A concrete masonry wall ready for test is shown

in figure 17.

6.2. Method of Test

Each wall was moved to the test frame and was

alined in position on the roller support with the

18

Figure 17. Concrete masonry wall in flexural load test frame.
ibwer lateral support in contact with tKc tensile

face of the wall. The loading mechanism was

ilien placed in position. When so placed, . the

Lpper load line was centered about 6 ft, 3 in. bove the bottom of the wall. For concrete

iiasonry, this load line was centered at the lower

'iortion of the 10th course of block. For comlosite masonry it was just above the center of

lie 28th brick course, about 7 in. above the 4th

leader course.

I Load was applied in increments of 100 lb for he concrete masonry walls and of 200 lb or more

or the composite walls. The load was released

fter each increment and deflection observations

/ere made after each load increment and release. )uring a test,, it was not considered desirable to lermit the wall to rock on the roller thereby

Dsing contact with the upper lateral support.

Therefore, the load at each load release was either

lero or the basic loading, depending on whether

Jie wall leaned away from or toward the loading

)ars. The time required for a load increment and

release was about 2 min. When the load exceeded

'boo lb, about 5 min was needed to substitute the

5,000 lb capacity load cell. A test was usually

Completed in 20 to 30 min.

i).3. Flexural Strength of Concrete Masonry

j Walls

h. Manner of Failure of Concrete Masonry Walls

' Tested With Bed Joints Normal to Span Length

I Walls with the bed joints normal to the span

ifailed in bond along one of the bed joints located

'between the load lines. The tensile strength of the

linortar at Joint intersections was greater then the

Ijoond strength of the mortar to the units. This

jresulted in a series of discontinuous bond failures

jbccurring alternately at the top and bottom of the

Icnortar bed. Each failure was symmetrical with

Imd opposite to a head joint as shown in figure 18. lA.bout half of the failures occurred in the first bed

1 joint below the upper load line and about 3 in. jbelow the center of this load line. No failures were

jnoted to occur between load and support lines.

The location of the principal failure planes in the concrete masonry walls tested witli bed joints

normal to the span is listed below.

Location of principal failure planes in concrete masonry

walls, tested with bed joints normal to the span

Number of joint

where failure oc- curred, numbered

below upper

load line

Total number

of walls Wall designations

1 13

3

6

3

1

1

BN-2, 3, 12; CN-1, 2; DN-2;EN-1, 3;BS-1,

2; CS-3; ES-1, 2 CS-2; BS-12; ES-3

BN-4, 11; DN-3; BS-3;

CS-1; DS-2

EN-2; BS-11; DS-1

DN-1

CN-3

2

3

4

5

6

b. Manner of Failure of Walls Tested With Bed Joints

Parallel With the Span

The concrete masonry walls tested with the bed

joints parallel with the span length failed in bond

between the mortar and the units. In five of the

walls, extensive vertical cracking along one or more of the bed joints between the courses was

noted at loads considerably below the maximum.

Maximimi load was reached with the development

of cracks in the head joints. One wall, wall BSP3, (strongest wall in its group) exhibited a crack

at maximum load having a zigzag pattern between

the load lines as shown in figure 19. No extensive

cracking along the bed joints was noted in this wall until after the test when a close examination

of the wall disclosed some hairline cracks of a pattern similar to that shown for the bed joints

in figure 18. During construction, the alinement in a vertical

plane of the 6 block courses was done by the mason

only at the ends of the wall. Some dishing or other misalinement of the courses may have been

unintentionally built into the masonry between

the wall ends at sections where the load and sup19
port lines were later placed in contact with the

masonry. Misalinement of this sort may have

caused an unequal load distribution between the

courses and may have been responsible for the

vertical cracking in the mortar beds between

courses which was noted in 5 of the 6 test walls. Reference to the notes kept during construction

of these walls indicated that any cracking at head

joints occurred on that side of a mortal- joint that was last placed in contact with a unit. This in- dicates that bond of mortar to the unit was greatest at the buttered side of the head joints. Large

cracks in the bed joints between the courses usuaUj,

occurred at the bottom of the bed, as laid, (se

fig. 19).

c. Flexural Strength of Concrete Masonry

The 15-day flexural strength of the concrete masonry walls is listed in table 19 with the physical

properties of the mortars used in them. In that

table, the modulus of rupture was calculated foi the gross cross-sectional area of the wall. Significant data from table 19 are averaged and summarized as follows:

Flexural strength of concrete masonary walls "

Mortar properties Flexural bond

strength •> Flexural strength

of walls Wall

Designation Water- cement

ratio

Initial flow Air content Compressive

strength

Air cured Sealed Maximum

uniform

load

Modulus

of rupture

Walls tested with bed joints normal to span length

% % % psi psi psi psi

BN 67. 2 135 19. 2 740 9 17 18. 3 13. 2 CN 73. 7 151 12. 2 890 11 14. 5 10. 5 DN 65. 6 140 17. 9 1, 420 18 25 22. 4 16. 1 EN 91. 4 140 0. 5 980 18 20 32. 6 23. 5 BS 58. 2 146 17. 6 1, 720 18 24 24. 1 17. 4 cs 61. 0 150 10. 4 2, 130 21 49 33. 3 24. 0 DS 57. 6 148 14. 8 2, 480 22 28. 2 20. 3 ES 71. 2 136 0. 8 2, 700 39 56 45. 6 32. 9

Walls tested with bed joints parallel with span length

BN-P 68. 4 140 19. 1 760 9 17 51. 5 37. 2 BS-P 59. 4 148 17. 1 1, 630 18 24 73. 7 53. 1

» Based on gross cross-sectional area of walls tested at age of 15 days. Flexural bond strength of bed joint mortar in two-block assemblies.

All of the concrete masonry walls subjected to

flexural loads were observed to have failed in bond.

The modulus of rupture of concrete masonry walls

tested with the bed joints normal to the span, cal- culated for the gross cross-sectional area of the

walls, ranged from a minimum of about 10 psi for walls containing the CN mortar to a maximum of

33 psi for walls containing the ES mortar. Similarly, the flexural bond strength of block assemblies made and aged in laboratory air with the

walls ranged from a minimum of 9 psi for assemblies containing the BN mortar to a maximum of

39 psi f-or assemblies containing the ES mortar.

In general, there was a fair agreement between

the flexural strength of the concrete masonry walls

and the bond strength of block assemblies made

and cured in laboratory air with the walls. This

agreement between wall strength and bond

strength is shown in figure 20 which also shows the

compressive strength of the mortars. Although the flexural strength of the concrete masonry walls was primarily a function of the bond

strength of the mortar, there was a secondary re- lationship between bond strength and compressive

strength; the flexural strength of the walls and of their companion block assemblies tended to in- crease with the compressive strength of the mortars. It should be clearly understood, as was

similarly noted in the discussion on the racking

strength of concrete masonry walls, that the rela- tionship between the flexural strength of the walls

and the compressive strength of the mortars may

hold only for these tests, made on walls built with

wet consistency mortars. It is misleading to state that the compressive strength of a mortar and not

its bond strength is the important factor affecting

the flexural strength of concrete masonry.

The effects of mortar properties, other than bond

and compressive strength on the flexural strength

of concrete masonry are difficult to evaluate.

Each mortar was tempered only to as wet a consistency as was practical for the mason. The effects of a range in consistency on mortar properties and

on wall strengths were not determined. The data

k

20
i Figure 19. Flexural bond failure of concrete masonry wall

1 BS-PS, tested with bed joints parallel to span.

do indicate that the high bond strength mortars

[ also had relatively high compressive strengths with

' relatively low air contents and water cement ratios.

' The bond strength of block assemblies cured in

* sealed containers for 7 days and then stored in air was, in general, considerably greater than that of

i similar assemblies aged continuously in air. As

I previously discussed, there was a fairly good agree- ment between the flexural strength of walls tested

with the bed joints normal to the span and the

bond strength of block assemblies which were aged

in laboratory air with the walls. If for like curing

conditions, the bond strength of block assemblies

^ 0 10 20 30 40 O BOND STRENGTH - BLOCK ASSEMBLIES- AIR CURED, psi * 500 1000 1500 2000 2500 3000

COMPRESSIVE STRENGTH OF MORTAR, psi

Figure 20. Relationship of bond and compressive strengths of mortar to the flexural strength of concrete masonry walls.

is representative of the flexural strength of walls,

the bond strength data indicate the great importance of proper curing on the flexural strength of concrete masonry.

The flexural strength of concrete masonry walls

tested with the bed joints parallel with the span was about 3 times that of comparable walls tested

with bed joints normal to the span. This ratio

might have been greater had not 5 of the 6 walls

tested with bed joints parallel with the span ex- hibited vertical cracking between the courses which may have reduced their flexural strength.

None of these walls had a continuous bed joint

running normal to the span and consequently the

failure section was constrained to follow a stepwise pattern, thereby considerably increasing the

length of joint resisting failure.

d. Deflection of Concrete Masonry Walls

The average values of deflection for each group

of concrete masonry walls are shown in figure 21

for walls tested with bed joints normal to span and

in figure 22 for bed joints parallel with span.,.. Since the deflections at low loads were small, the

deflections for the initial loadings were obtained by

extrapolating back to zero load. A wide range in

deflection was noted between similar walls in some

of the specimen groups and the deflection of only one wall was obtained for the CN mortar group.

For these reasons, the deflections shown in the curves are considered to be approximate only.

The following tabulation of deflections gives information on the stiffness of the concrete masonry

walls at a flexural stress of 10 psi and at on^-half

of maximum load. (See next page).

The data for walls tested with bed joints normal

to the span indicate that at a flexural stress of

10 psi, their stiffness tended to increase with the

bond strength of the mortar. No consistent rela- tionship was noted between mortar properties and

wall deflection at one-half of maximum load. The

21
Deflection of concrete masonry ivalls *

Wall designation

Number

of walls

Mortar properties Deflection at a flexural

stress of 10 psi on: Deflection

at one-half

in group Bond

strength

Compressive

strength Gross area Net area load

c

\lir

flte Walls tested with bed joints normal to span

psi psi in. in. BN 4 9 740 57X 10-'' 40 X 10-* 35 X 10-

CN 1 11 890 43 30 14 DN 3 18 1, 420 28 20 23 EN 3 18 980 28 20 33 BS 4 18 1, 720 25 17 22 cs 3 21 2, 130 31 22 38 DS 2 22 2, 480 27 19 28 ES 3 39 2, 700 18 13 32

Walls tested with bed joints parallel with span

BN-P 3

3

1

918

18

- 760

1, 630

1, 550

37X10-*

4332

77 X 10-* 126

114 BS-PBS-P3

» Measured at midspan for quarter point loading.

Average flexural bond strength of two-block assemblies stored in air with the walls

deflection at one-half of maximum load of walls

tested with the bed joints normal to the span

averaged approximately^ 0.003 in. That of walls

tested with the bed joints parallel with the span was considerably greater as would be expected

for walls supporting a load about 3 times as great.

No consistent relationship was noted between

the properties of the mortars used in the concrete masonry walls and the ratio of set in deflection to the total deflection. The dispersion of the set- deflection ratio was high. The average value of

the set-deflection ratio was 20 percent for walls

tested with bed joints normal to or parallel with

the span.

Figure 21. Deflection under flexural load of concrete masonry walls tested with bedjoints normal to span. Figure 22. Deflection under flexural load of concrete masonry walls tested with bed joints parallel to span.

22
6.4. Flexural Strength of Composite Masonry

Walls

a. Manner of Failure of Walls Tested With Brick Facing

in Tension

The composite masonry walls tested in flexure

{with the brick facing tier in tension failed rather

suddenly in bond at one or more of the bed joints

located 'between the load lines. The location of

[the principal failure planes is listed below. The

listing also indicates whether the bond failure was

;^t the top or bottom of the mortar bed.

Location of principal failure planes in composite masonry

walls, tested with brick facing tier in tension

L

icr*

Wall

designation

Number

of joint

where

failure occurred,

numbered

below

upper

loadline

Kind of brick courses adjacent to

failure plane and location of

failure on mortar bed »

Stretcher

to

stretcher ^

Stretcher

to header

b

Header

to stretcher *>

BN-1

BN-2

BN-3

CN-1

CN-2

CN-3

DN-1

DN-2

DN-3

EN-1

EN-2

EN-3^---

BS-1

4

12

11

510

11

134

5

8

5

7

1310

32

4

4

11

7

5

74

B

T

T

B

B

B

B

T

B

B

B

B

B

BS-2 B

B

B

BS-3

CS-1

CS-2

CS-3

B

B

T

T

DS-1

DS-2

DS-3

ES-1

B

B

ES-2 B

ES-3 B

Number « 24 12 " 8

'I » The letter "B

l! of the mortar bed. top of the bed.

b Proceeding downward.

" Number of walls involved.

indicates bond failure at the bottom

The letter "T" indicates failure at the

Failures were noted between stretcher courses

in 12 of the 24 walls. A typical failure section

between two stretcher courses is shown in figure

23. Since 11 of the 12 failures between stretcher course were at the bottom of the beds, the data

clearly show that for these tests the bond of mortar

to stretcher brick was stronger at the top of the

bed. This is contrary to the commonly accepted

opinion that the mortar bond between stretcher courses is greater at the bottom of the mortar bed.

It may be noted that the water retention of the

mortars was high and that the initial rate of

absorption of the brick was reduced to only 6 g

per 30 in.^ by prewetting the units. It may be

further noted that during the laying operation, the relative movement of mortar to brick

surface or of brick to mortar surface was greatest

at the top of the bed and occurred when the

bricks were laid in place with a slight shoving

motion. Some movement of this sort is essential

to the development of an intimate contact between

mortar and masonry unit and is common technique with most experienced masons. It is likely

the low "suction" of the brick and the high water

retention and water content of the mortar tended

to reduce the stiffening of the mortar that may

occur during the time interval between spreading

mortar on the bed and the placing of the upper

unit. Stiffening of this sort has been known to reduce the bond between the top of a mortar bed

and the brick placed upon it. However, for these

walls, the negative effects of the relatively slight

stiffening of the mortar was offset and overcome by the bond resulting from the mechanical key

developed between the mortar and the unit by

the shoving motion. Such a key is most easUy

obtained by using mortar of as wet a consistency

as is consistent with lack of segregation, proper

joint thickness and ease of handling by the mason.

One-half or 12 of the 24 composite walls tested

with the brick facing in tension failed at bed joints

that were adjacent to header courses. Four of the

failure planes were in mortar beds resting on header

courses and 8 were in mortar beds located below a header course. For any one wall, the number of

mortar beds which were adjacent to header courses was related to the number of beds lying between

stretcher courses as 2 is to 5. The incidence of

failure was, therefore, relatively higher for mortar

beds located at a header course than for beds lo- cated between stretcher courses.

All of the 4 failures in mortar beds placed directly

upon header courses were at the bottom of the

bed and at the plane between header brick and

mortar as shown in figure 24. Four of 8 failures in

beds located beneath header courses were at the

top of the bed and again in the plane between the

mortar and the header brick; see figure 25. For

these tests, it is indicated that the bond strength

at the top of mortar beds supporting a header

course was approximately equal to that at the

bottom of a bed resting upon a stretcher course.

It may be noted that the bond failures in onethird of all of the composite walls and in twothirds of those walls which failed near header

courses were in a plane lying between the mortar

bed and either the top or bottom surface of the

header brick.

23
Figure 23. Typical flexural bond failure between stretcher courses in brick facing of composite walls.

Figure 24. Flexural bond failure above header course in

brick facing of composite wall.

b. Manner of Failure of Walls Tested With the Block

Backing in Tension

The 6 composite masonry walls tested with the

block backing tier in tension failed in flexural

bond. Failure in 5 of the walls occurred at bed

Figure 25. Flexural bond failure below header course in

brick facing of composite wall.

joints between a brick header course and a i stretcher course. One wall, BN-E.2, failed at the 1 bottom of a bed joint between twoblock stretcher

courses. For this wall, the failure plane was less than 1 in. above the center of the upper load line. The location af the failure planes is given below.

24
\\ Location of failure planes in composite walls tested with the

I

" block hacking in tension

Number

of brick header

Kind of masonry courses adjacent

to failure plane and location of

failure on mortar bed » course Wall

designatioii

where

failure occurred,

numbered

below

upper

load line

Block to block b Block to header

brick

Header

brick to block b

BN-Rl—

BX-R2__.

BX-R3—

BS-Rl.--

BS-R2...

BS-R3--_

oo B

U

1 B

T

1 B

2 T

1 B

» The letter "B" indicates failure at the bottom of the mortar bed. The letter "T" indicates failure at the top of the bed.

b Proceeding: downward.

The data indicate that the bond of mortar to the concrete block stretcher units was greater

than the bond of mortar to the header brick.

Here again, the mortar bond tended in general to be stronger at the top of the bed than at the bottom, and the failure plane at header courses tended

to be in the plane between the mortar and the

header brick. A typical fiexural bond failure is shown in fig. 26.

-FiGUKE 26. Typical fiexural bond failure in block backing

of composite wall.

c. Fiexural Strength of Composite Masonry

The 14-day fiexural strengths of the composite

masonry walls are hsted in table 20 with the physical properties of the mortars used in them. In

that table the modulus of rupture was calculated

only for the gross cross-sectional area of the wall

assuming that the neutral axis was at the center

of a solid and homogeneous section. Significant

data from table 20 are averaged and are summerized as follows.

Fiexural strength of composite masonry walls *

WaU

Mortar properties Bond strength ^ Fiexural strength

of walls

designation

Water Initial Air Compres- Brick Com- Maximum Modulus

cement flow content sive couplets posite uniform of ratio strength assemblies load rupture

Walls tested with brick facing in tension

BN

% % % psi psi psi psf psi

69. 6 145 19. 4 670 31 38 34." 5 23. 1 ON 76. 3 154 12. 5 840 45 51 43. 0 28. 8 DN 65. 2 134 21. 3 1180 25 43 48. 1 32. 2 EN 97. 2 145 0. 2 1070 55 70 71. 4 47. 6 BS 59. 5 145 17. 4 1800 38 53 49. 8 33. 4 cs 63. 2 156 10. 6 2160 51 64 56. 0 37. 5 DS 56. 2 143 18. 8 2370 40 66 60. 2 40. 4 ES 73. 9 144 0. 4 3030 69 84 79. 3 52. 9

Walls tested with block backing in tension BX-R 69. 8 145 19. 1 700 31 40 46. 0 30. 8 BS-R 59. 9 146 17. 6 1820 38 74 54. 6 36. 8

" Based on gross cross-sectional area of walls tested at age of 14 days. Tensile bond strength of crossed-brick couplets and flexural bond strength of composite assemblies cured under cover

for 7 days and then stored in air with the walls.

25
All of the composite masonry walls subjected to

fiexural loads were observed to have failed in bond. The modulus of rupture of composite masonry walls, calculated for the gross cross-sectional area of the walls, ranged from a minimum of 23

psi for walls containing the BN mortar to a max- imum of 53 psi for walls containing the ES mortar.

Bond-test specimens were cured under cover for

7 days and then stored in air with the waUs. The

tensile bond strength of crossed-brick couplets was usually somewhat greater than the fiexural

strength of the walls and ranged from a minimum

of 25 psi for couplets containing the mortar DN

to 69 psi for couplets containing the mortar ES.

The fiexural bond strength of composite assemblies was generally considerably greater than that

of the walls and ranged from a minimum of 38

psi for assemblies containing the mortar BN to a maximum of 84 psi for assemblies containing the

mortar ES.

In general, there was a good relationship between the fiexural strength of composite masonry

walls tested with the brick facing in tension and

the bond strength of composite assemblies made

with the walls. This relationship between wall

strength and bond strength is shown in figure 27

which also shows the compressive strength of the

mortars.

Although the fiexural strength of the composite

masonry walls was primarily a function of the

bond strength of the mortar, there was a secondary relationship between the strength of the walls

and the compressive strength of the mortars used

in them. Similar relationships have been noted in

the discussion of the racking and fiexural strengths

of concrete masonry walls. All of these tests show

that the bond strength of a mortar and not its compressive strength is the most important factor

affecting wall strength.

The compressive strength of all mortars fell in

the same family of points when plotted against

the fiexural strength of the concrete masonry walls

(fig. 20). The compressive strengths of type N

and type S mortars fell into two separate families

BONO STRENGH OF COMPOSITE ASSEMBLIES, psi 500 1000 1500 2000 2500 3000

COMPRESSIVE STRENGTH OF MORTAR, psi Figure 27. Relationship of bond and compressive strengths

of mortar to the fiexural strength of composite masonry walls. 26

when plotted against the fiexural strengths of thf',_

composite masonry walls (fig. 27). The figuresindicate that the relationship between the com

pressive strength of the mortars and the flexura

strength of the walls may be affected by the typ(

of mortar as well as by the kind of masonry unit

There was no consistent relationship noted be

tween the water and air content of the mortarS: and the fiexural strength of the composite masonry walls. Any relationship which existed be- tween the fiexural strength of the walls and th(

air content of the moi tars may have been obscurec

by other variables such as the consistency, watei

content, and compressive strength of the mortar

Similar observations can also be made with re- spect to walls of concrete masonry. It may b(

noted that the water and air contents of thi

mortars used in the composite masonry averagec

slightly higher than for the mortars used in tht concrete masonry.

The fiexural strength of composite masonry

walls tested with the block backing tier in tension was slightly greater than that of comparable walk

tested with the brick facing in tension. A similar

relationship was noted for the fiexural bone

strength of composite assemblies tested with

either the brick facing or the block backing in tension and in orientation with the walls they

represented. Regardless of which tier was placed

in tension, the fiexural strength of the composite

walls was about twice that of concrete masonry

walls tested with bed joints normal to the span

d. Deflection of Composite Masonry Walls

The deflections of the composite masonry walls are shown in figure 28. Since a considerable!

range in defiection was noted between similar

walls in some of the specimen groups and since

the defiections for the initial loads were obtained

by extrapolating the data back to zero load, the

defiections shown in the curves are considered to be approximate only.

The deflection of the composite masonry walls was calculated for one-half of maximum load and

Figure 28. Deflection of composite walls subjected to-^ fiexural load.
tliLlfor flexiiral stresses, 10 and 17.5 psi, on both the

J'gTOSs and the net cross-sectional areas. In these .ETi - rfalculations, the net cross-sectional area of the

'iblock backing was taken to equal the minimum

cross-sectional area of the face shells of the block.

The thickness of the mortar parging was not included in the net area or in the calculations for

the positions of the neutral axis. The observed

deflections are listed below with the strengths of

bond-test specimens and the compressive strengths

of the mortars.

Deflection of composite masonry walls *

Wall designation

igeo

Compressive strenaith

of mortar

Bond strength of mortar

Brick

couplets

Composite assemblies

Wall deflection

At flexural stress of 10 psi

Gross area Net area

At flexural stress of 17.5 psi

Gross area Net area

At onehalf of maximum

load

Walls with brick facing in tension

'"^!bn.

CN-

-:,DN.

BSCS. iDStiienr'ESpsi psi psi in. in. in. in. 670 31 38 69X 10-* 61X10-' 189X10-* 169X10-* 82 X 10-* 840 45 51 58 51 113 101 87

1, 180 25 43 49 43 110 98 93

1, 070 55 70 18 16 32 29 45

1, 800 38 53 47 42 107 96 98

2, 160 51 64 31 27 63 56 69

2, 370 40 66 45 40 89 80 108

3, 030 69 84 25 22 44 39 78

Walls with block backinsj in tension BN-R 700 31 40 47X 10-* 30X 10-* 96X 10-* 61 X 10-* 79X 10-* BS-R 1, 820 38 74 29 18 56 36 58

jIjIT

A

* Average deflection measured at m.idspan for quarter point loading on groups containing 3 wall specimens.

incf 3i

isei

thf

tojc'

The deflection at a flexural stress of 17.5 psi on

'ithe gross area of composite masonry walls tested

Nvith the brick facing in tension ranged from a maximum of 0.019 in. for walls containing the

jimortar BN to 0.003 in. for walls containing the

jnortar EN. The wall deflections for a stress of 17.5 psi on the net area basis were slightly less than 90 percent of those figured for the solid wall

section. This ratio was 64 percent for walls

|tested with the block backing in tension.

I The deflections at a flexural stress of 10 psi on

Jithe gross area of walls tested with the brick facing

in tension and built with both types of mortars

pcontaining the masonry cements B, C, and D were

.40 to 50 percent of the deflections at a stress of

il7.5 psi. The deflections of walls similarly tested

and built with mortars containing the cement E

were reduced very nearly in proportion to the

stress ratio of 57 percent.

! In general, there was a good but not a precise

[relationship between wall deflection at a stress of

il7.5 psi and the strength of bond test specimens

containing similar mortars ; the rigidity of the walls

itended to increase with bond strength. The

deflection at one-half of maximum load of all liwalls tested with the biick facing in tension aversiged approximately about 0.008 in. This corre- jsponded to an average deflection of 0.003 in. at

one-half of maximum load for concrete masonry

walls. No consistent relationsliip was found between wall deflections at one-half of maximum

load and the bond strength and other properties

of the mortars.

The deflection at a stress of 17.5 psi of composite walls tested \\-ith the brick facing in tension was about double that of similar walls tested -with

the block backing in tension.

Other things being equal and for like flexural

stress, the deflections of composite walls tested

with the brick facing in tension were higher than

those of concrete masonry, walls tested ^vith bed

joints normal to the span. The average deflec- tion of concrete masonry walls at a flexural stress

of 10 psi on the gross area was 75 percent of that

noted for composite masonry walls. For a stress

of 5 psi, this ratio was 60 percent.

7. Discussion and Summary of the

Wall Test Results

The following tables summarize the data on the

compressive, racking, and flexm-al strength of the

walls along with the data on bond strength and

other properties of the mortars used in them.

This tabulation is followed by a brief discussion

and a summary of the test results. 27
Strength of concrete masonry walls

Mortar properties

Flexural bond

strength of block

assemblies

Strength of walls

Kind of mortar

Compressive " Modulus of rupture

Water

cement

ratio

Initial flow

Water

retention

Air

content

Compressive

strength

Air cured

Sealed

for 7 days Gross

area Net

area

Racking »

Bed joints

normal to span

Bed joints

parallel with span

Gross

area Net

area ' Gross

area Net

area '

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15

BN

%

67. 4 %

137 %83 %

19. 0

psi740psi9psi 17psi

390

psi

1, 030

lb

2, 400

3, 600

psi

13. 2

psi

18. 8

psi

37. 2

psi

53. 1 CN 73. 3 150 75 12. 1 870 11 430 1, 130 10. 5 15. 0 DN 65. 6 140 8288

17. 9 1, 420 98018 25 16. 1 23. 1 EN - - 91. 4 140 0. 5 18 20 23. 5 33. 5 BS 58. 6 145 83 17. 5 1, 730

2, 110

18 24 440 1, 160

1, 240

4, 000

4, 500

17. 4 24. 8 53. 1 75. 9

V^kJ 61. 1 151 77 10. 3 21 49 470 24. 0 34. 3 DS 57. 6 148 84 14. 8 2, 480

2, 700

22 20. 3 29. 0 ES 71. 2 136 89 0. 8 39 56 32. 9 46. 9

ij s

i!

» Walls were cured in laboratory air and tested at age of 15 days.

^ Average for mortars used in concrete masonry walls. Average compressive strength for line loading at third point of wall thickness.

"1 Net bearing area of face shells and cross webs in mortar bed.

^ Horizontal force per lineal foot of wall.

' Section modulus based on minimum cross-sectional area of face shells.

Strength of composite masonry walls » ati

ui

M Kind of mortar

Mortar properties

Water

cement

ratio Initial flow

Water

retention

Air

content

Compressive

strength

Bond

strength

Brick

couplets

Composite assemblies

Strength of walls

Compressive gross area

Racking d

Modulus of rupture

Brick facing tier in tension

Gross

area Netarea «

Block backing tier in tension

SIB

Gross

area Netarea «

10 11 12 13 14 J l!<

BN.

CN,

DN

EN.

BS.

cs. DS.

ES-

%

69. 4

76. 1 65. 2

97. 2

60. 0

63. 2

56. 2

73. 9

%

145

154 134

145

147

156

143 144

%

84

75

85

87

83

77

8387

%

19. 6

12. 6

21. 3

0. 2

17. 5

10. 6

18. 8

0. 4

psi

690

840

1, 180

1, 070

1, 780

2, 210

2, 370

3, 030

pst 3145

25

55

38

5140

69

psi 38

514370

5364

66

84

psi 720

770

lb

6, 400

< 9, 200

910

950

9, 300

< 9, 700

psi

23. 1 28. 8

32. 2

47. 6

33. 4

37. 5

40. 4

52. 9

psi

25. 9

32. 2

36. 1 53. 3

37. 4

42. 0

45. 2

59. 2

psi

30. 8

psi

48. 3

36. 6 57. 3

* Walls were cured in laboratory air and tested at age of 14 days.

Average for mortars used in composite masonry walls. Average compressive strength for line loading of third point of wall thickness from face of concrete masonry backing.

Horizontal force per lineal foot of wall.

« Section modulus based on area of brick facing tier and minimum cross-sectional area of face shells of block in the backing tier.

' Some walls in group were not loaded to failure. 28
7.1. Effects of Storage on Cement Properties

1. The Portland cement base masonry cements

i used in blends B and C were stored in sealed conI Itainers when shipped and received at the Bureau

n 1953. The physical properties of the two

blended cements were determined in 1954 and

-igain in 1959. Storage of the blends in sealed

containers for 5 years did not greatly affect their

Dhysical properties. The water requirement for 3ormal consistency was noted to have dropped 1 percentage point during the storage period.

2. Storage in sealed containers of the masonry

cement blends B and C for 3 years, from 1956 to 1959, appeared to have a relatively minor effect

,Dn the physical properties of the cements when

:ested in accordance with Federal Specification

"5S-C-I8IC as blended sand mortars. The tests Indicated a reduction in air content of the mortars

i)f 1 or 2 percentage points. The 28-day compressive strength was increased about 5 percent. The

jA^ater retention values were reduced about 2 percentage points.

I 7.2. Compressive Tests

j a. Manner of Failure

1H 3. A vertical crack developed at about 60 percent of maximum load in the webs of the blocks

jin the top course of concrete masonry walls subj jected to compressive load. This crack formed

idirectly beneath the eccentrically applied load line

lind angled slightly toward the opposite wall face,

jfcerminating near a bed joint after penetrating one

\pT two courses. A new crack then formed near

the center of the cross webs in the course beneath

•and followed the same general pattern as described

I jabove. Maximum load was noted when the cracks

jtiad penetrated 2 or 3 courses and the wall colLliapsed after the cracking had penetrated 4 or more

l||courses.

r,j The composite masonry walls subjected to the

Compressive load failed more suddenly than did

Lithe concrete masonry walls by crushing of the face

bhells of the block in the upper 1 or 2 courses.

'Tensile strains were observed in the brick facing

"l^f some of the composite masonry walls. No tenjsile strains were observed in the concrete masonry

Wis.

A redistribution of strain was noted during a Few tests of both kinds of masonry walls. This

• redistribution did not greatly affect the average

"Shortening of the wall specimen but did tend to

l^-educe wall deflection.

b. Compressive Strength

• 4. The average compressive strength on the net

jarea of the concrete masonry walls ranged from

'jil,030 to 1,240 psi and did not greatly exceed half

pf the compressive strength (2,100 psi) of the conI Crete in the blocks. In the upper courses of the

'wall, the eccentrically applied load carried by the

face shells in one wall face was about double that

carried by the face shells in the other wall face.

5. The average compressive strength on the

gross area of the concrete masonry walls ranged

from 390 to 470 psi. The strength calculated for the gross area was 38 percent of that calculated

for the net area.

6. The average compressive strength on ths

gross area of the composite masonry walls ranged

from 720 to 950 psi. The compressive strength

of composite walls built of type N mortar was

approximately equal to the compressive strength

of the mortars. That of walls built of type S

mortars was approximately half the compressive

strength of the mortar.

7. The average compressive strength on the

gross area basis of the composite masonry walls was about twice that of concrete masonry walls

built with similar mortars.

8. In general, the compressive strength of the

concrete and composite masonry walls increased

with the compressive strength of the mortar. The

type S mortars were considerably stronger than

were the type N mortars but the differences in

compressive strength between the two types of

mortars were not reflected in corresponding differ- ences in wall strengths. This may be due to the

fact that the strength of the walls containing the

type S mortars was somewhat limited by the compressive strength of the concrete in those face

shells which were subjected to the maximum

effects of load eccentricity.

c. Compressive Strain

9. The secant modulus of elasticity in compression at a compressive load on the gross wall area

of 100 psi ranged from a minimum of 530,000 psi

for concrete masonry walls containing the mjrtar

BN to a maximum of 1,180,000 psi for composite

masonry walls containing the mortar CS. For

both kinds of masonry, the compressive strength

of the type N mortars was less than that of the

concrete in the blocks and the moduli of elasticity

of the walls containing the type N mortars increased with the compressive strength of the mortars and decreased with increase in load. The

compressive strength of the type S mortars approached or exceeded that of the concrete in the

blocks. The moduli of elasticity of walls containing the type S mortars did not greatly change with

increase in mortar strength and with increase in

load up to the limit of the observations (about 70%

of maximum load).

10. For like loads on the gross wall area and

within the limits of the strain observations, the

average shortening under compressive load of the

composite masonry walls was about half that noted

for concrete masonry walls. Consequently, cal- culated for similar mortars of both type N and

type S and on the gross area basis, the secant modulus of elasticity in compression of the composite masonry walls was about double that of the concrete masonry walls.

11. At one-half of the maximum load on the

concrete masonry walls the ratio of set to shorten29
ing strain decreased with increase in the compressive strength of the mortar, ranging from 21

percent for the BN mortar to 8 percent for the CS

mortar and averaging 15 percent. At one-half

of the maximum load on the composite masonry

walls the ratio of set to shortening strain slightly

decreased with increase in the compressive

strength of the mortar, ranging from 10 to 8

percent.

Both the shortening strain and the ratio of set

to shortening strain were affected by the bearing

stresses between the mortar and the face shells of

the block, as well as by the relative compressive

strengths of the mortars and of the concrete in

the blocks.

d. Lateral Deflection

12. For like compressive loads on the gross wall area the lateral deflection at midheight of the

composite masonry walls was about equal to that

of the concrete masonry walls. The surface of

the brick facing tier in the composite masonry

walls was flexed convex by the eccentric loading.

The deflection of the composite walls was probably

affected by the incidence of tensile strain in the

brick facing and by the greater number of mortar

beds in this facing as compared to the number of

mortar beds in the block backing.

The ratio of set to deflection of the composite

masonry walls was about half of that noted for the concrete masonry walls. The dispersion of the

deflection values and of the set-deflection ratio

for replicate wall specimens of both kinds of masonry was high. For this reason, no consistent

relationship was found between the properties of

the mortars and the deflections of the walls.

7.3. Racking Tests

a. Manner of Failure

13. All of the walls subjected to racking loads

failed in bond. Because of the release of potential energy built up in the loading mechanism, the

failures were sudden and were accompanied with

the breakage of some of the masonry units lying

along the wall diagonal. Bond failure in the bed

joints of concrete masonry walls was about evenly

divided between the tops and bottoms of the mortar beds. Failures in the composite masonry walls

usually occured at the bottoms of the mortar beds.

For both wall types the bond failures in the head

joints were usually at that mortar face which was

last placed in contact with a masonry unit. Since

the strength of some of the composite masonry

walls exceeded the capacity of the loading equipment these walls were not loaded to failure.

b. Racking Strength

14. The racking strength of concrete masonry

walls in terms of the horizontal force per lineal foot of wall ranged from a minimum of 2,400 lb for the BN mortar to a maximum of 4,500 lb for the CS mortar.

15. The racking strength of composite masonry

walls in the terms of the horizontal force per lin- eal foot of waU ranged from a minimum of 6,400' lb for the BN mortar to over 9,700 lb for the CS

mortar. The strength of 3 of the 10 composite

inasonry walls exceeded the capacity of the loading equipment.

16. The average racking strength on the gross

cross-sectional area of the composite masonry walls was nearly 3 times that of concrete masonry walls

built with a similar mortar.

17. There was a fairly consistent relationship

between the racking strength of the concrete ma-" sonry wafls and the flexural bond strength of block

assemblies made with the walls. The racking^

strength of all of the composite masonry walls wa^'

not determined but the data obtained also indicate

fairly consistent relationship between the racking'

strength of the composite masonry and the' strength of bond-test specimens made with the' walls.

18. There was no consistent relationship be

tween the compressive strength of the mortars

and the racking strength of the walls. The data

obtained in these tests indicate that the bond'

strength of the mortar was the principal factor;' affecting the racking strength of the masonry and?

that the compressive strength was only a factor in so far as it affected the bond strength of the' mortars. |

c. Shear Strain

^

19. The shear moduli at a racking load of 14 ps|

(about 1,300 lb per linear foot of wall) averaged ap-i

proximately 140,000 and 220,000 psi for the

concrete and the composite masonry walls^

respectively.

. The ratio of set to shear strain of the compositd'

masonry walls was approximately two-thirds ofi that noted for the concrete masonry walls. As

may be expected from the lower ratio of voids to gross volume and the greater bonded area resist-' ing shear, the composite masonry walls were considerably stiffer under racking load than were the concrete masonry walls.

20. No consistent relationship was noted be-^ tween the shear moduli of the walls and the bond'

strength and other properties of the mortars. The

dispersion of the shear strains and of the ratio of

set to shear strain for replicate wall specimens was high as was also the case for the lateral deflection of walls subjected to compressive load.

7.4. Flexural Tests

a. Manner of Failure !

21. All of the concrete and composite walls

tested in flexure failed in bond.

22. Failures in concrete masonry walls tested,

with the bed joints normal to the span were located

alternately at the top and bottom of a mortar bed

and opposite to contiguous head joints. The fail- ures indicated that the tensile strength of the mor-

(ll

30
lin.

iadross

all

all

nia--]

ociiil

pin? as

att)

aii»

tait

ata

ond

ffor idi

ffia

tie

Ips'

ap- thq

ills;i

iist-l

'onthej

betar was greater than the bond strength of the

mortar to the face shells of the block.

The strongest of the 6 concrete masonry walls

that were tested with the bed joints parallel with

the span exhibited a stepwise crack passing alter- nately through head and bed joints from one side

of the wall to the other. The other five walls also

failed in bond at the head joints but they exhibited more or less continuous vertical cracks in the

mortar beds between the block courses.

23. Failures in composite masonry walls tested

with the brick facing in tension usually occurred

at the bottom of the mortar bed, contrary to the

widely accepted opinion that mortar bond is stronger at the bottom of the bed. The incidence

of failure was relatively greater in bed joints adjacent to header brick courses than in bed joints

lying between two stretcher brick courses. The

failures at the header courses were usually between

the mortar and either the upper or lower surfaces

of the brick headers.

P^ailure of 5 of the 6 composite masonry walls

tested with the block backing in tension also oc- curred at a header brick course and again usually

in the horizontal plane between the mortar bed

and the brick headers.

Once started, a bond failure at a header course

followed the most direct and uninterrupted horizontal section through the wall. Failures at other

sections had to pass through the mortar parging

and sometimes followed a stepwise path through

the masonry.

b. Flexural Strength of Concrete Masonry Walls

24. The modulus of rupture of concrete masonry

walls tested with bed joints normal to the span

ranged from a minimum of 10.5 psi for walls containing the CN mortar to a maximum of 32.9 psi

for walls containing the ES mortar.

25. The modulus of rupture of concrete masonry

walls containing the mortar BN and tested with

bed joints parallel with the span averaged 37.2 psi.

That of walls similarly tested and containing the

mortar BS averaged 53.1 psi. The modulus of

rupture of wall BS-P 3, the strongest in its group, was 66.8 psi.

c. Elfects of Orientation of Bed Joints on the Flexural Strength of Concrete Masonry Walls

26. The concrete masonry walls tested with bed

joints parallel with span were 3 or 4 times stronger

than were similar walls tested with bed joints

normal to the span. Walls tested with bed joints

parallel with the span did not have a continuous

I joint running normal to the direction of bending

and consequently the failure section was constrained to follow a stepwise pattern, thereby

considerably increasing the length of joint resisting

failure.

d. Flexural Strength of Composite Masonry Walls

27. All of the composite masonry walls were

tested with the bed joints normal to the span. The

modulus of rupture of composite masonry walls

tested with the brick facing tier in tension rangcul

from a minimum ot 23.1 psi for walls containing

the BN mortar to a maximum of 52.9 psi for walls

containing the ES mortar.

28. The modulus of rupture of composite

masonry walls containing the mortar BN and

tested with the block backing tier in tension was

30.8 psi. That of walls similarly tested and containing the mortar BS was 36.6 psi. 29. In general, the composite masonry walls

tested with the brick facing tier in tension and

with bed joints normal to the span were about

twice as strong as were concrete masonry walls

tested with bed joints normal to the span.

e. Effects of Orientation of the Direction of Bending

on the Flexural Strength of Composite Masonry Walls

30. The average flexural strength of composite

masonry walls tested with the block backing in tension was about 12 percent greater than that

of similar walls tested with the brick facing tier in tension. A similar relationship was found between the flexural bond strength of composite

assemblies tested with either the brick facing or the block backing in tension corresponding to the

orientation of the walls they represented.

f. Effects of Mortar Properties on the Flexural Strength

of Masonry

31. There was a fairly consistent relationship

between the flexural strength of concrete and composite masonry walls and the strength of bondtest specimens made with the walls. 32. There appeared to be some relationship

between the flexural strength of the walls and the

compressive strength of the mortar used in them.

For the composite masonry walls there was a dis- tinct relationship for each type of mortar. For

the concrete masonry walls, however, the mortars

of both types appeared to fall into a single family

of points. It is noted that these observations are applicable only to these tests which were made

with walls constructed with wet mortars. As dis- cussed in this paper, the mortars must be tempered

to as wet a consistency as is practical in order to develop high bond strength. Such a consistency

is not favorable to the development of maximum

compressive strength.

33. No consistent relationships were noted

between the air and water contents of the mortars

and the flexural strengths of the walls.

g. Effects of Curing Conditions on Flexural Strength

of Masonry

34. The modulus oT rupture of concrete masonry

walls was in fair agreement with the flexural bond

strength of block assemblies made and stored in

laboratory air with the walls. The daily mean

laboratory air temperatures ranged between 76

and 84 °F. The dail.y mean relative humidity in

the laborator}' ranged between 51 and 65 percent.

31
The flexural bond strength of block assemblies

cured in sealed containers for 1 week and then

stored in air with the walls was substantially

greater than the flexural strength of the walls and

of companion assemblies which were not cured in

sealed containers, but which were stored in air with the walls. Since the wet mortar in the bed

joints of the block assemblies contained a considerable amount of moisture, it is likely that the

relative humidity but not the temperature of the

air ambient to the sealed assemblies was higher

than the relative humidity of the air in the laboratory. The difference in the relative humidity to which the assemblies were exposed at an early age was probably responsible for the difference in their flexural bond strength. This difference in curing

conditions was also responsible for the difference

between the flexural strength of the walls and the

bond strength of those block assemblies which were

cured under cover.

35. All of the bond-test specimens made with

the composite masonry walls were cured in sealed

containers for 1 week and then stored in air with

the walls. The tensile bond strength of crossedbrick couplets made with the walls was usually

greater than the flexural strength of walls containing the same mortar and tested with the brick

facing in tension. The flexural bond strength of

composite assemblies was considerably greater

than that of the walls. It was evident from the

appearance of condensation moisture on the inside

of the cellophane sheet covering the composite

assemblies that the relative humidity of the air ambient to the specimens was considerably greater

than that of the air ambient to the walls. Here

again, it is highly probable that the difference

between the flexural strength of the assemblies

and that of the walls was due to the effects of dif- ferent curing conditions at early ages. The data

indicate the importance of proper curing on the

flexural strength of masonry.

h. Deflection and Stiffness of Walls Subjected to Bending

36. The rigidity of the walls at flexural loads

of less than one-half of maximum load tended to increase with the bond strength of the mortar.

37. At loads greater than one-half of maximum

load no consistent relationship was noted between

mortar properties and wall deflection. The aver- age deflection of the concrete masonry walls at onehalf of maximum load was about 0.003 in. The

average deflection of the composite masonry walls

tested with the brick facing in tension at one-half

of maximum load was about 0.008 in. 38. For like flexural stresses the concrete masonry walls were considerably stiffer than were

the composite masonry walls "tested with the brick

facing tier in tension. For a stress of 10 psi on

the gross wall area, the average deflection of concrete masonry walls was 75 percent of that noted

for composite masonry walls (tested with the brick

facing in tension). For a flexural stress of 5 psi on the gross area this ratio was 60 percent.

For a stress of 10 psi on the gross area, th^' deflection of composite masonry walls tested witfS the brick facing in tension was nearly double thai

of similar walls tested with the block-backing tier in tension. '« There were about half as many bed joints ir the block backing tier of the composite walls anc

likewise in the concrete masonry walls as were ir- the brick facing tier of the composite walls. Il follows that the number of bed joints in th(

tensile face of a wall and their extension in bone were the dominating factors affecting the stiffness, of wafls subjected to flexural load. The flexuraj

bond strength of these masonry walls was a smal)

fraction of the tensile strength of the masonrji

materials used in them and the elastic bending

deformations in the masonry materials themselves

did not appear to have an important effect on the- flexural rigidity of the walls. i'

i. Theoretical Flexural Stresses in Walls With Bed

Joints Normal to Span ,

39. The flexural stresses in the concrete and^

composite masonry walls, calculated in terms ol* an equivalent uniformly apphed load of "w" psf, are listed below for both the gross and the net

wall section.

Flexural stress in terms of a uniformly applied load "w" psfi

Flexural stress Ratio of

for: gross

section Kind of wall to net Gross Net section wall wall stresses section section

Concrete masonry

psi psi %

0. 72 w 1. 03 w 70 Composite masonry, brick

facing in tension 0. 67 w 0. 75 w 89 Composite masonry,

backing in tension block

0. 67 w 1. 05 w 64

The effects of reversing the direction of bending

in composite masonry walls are theoretically nil, when the stresses are calculated on the gross area

basis. On the net area basis the stresses with the

brick facing in tension are 71 percent of those,

calculated for the block backing in tension. For.

the actual tests of the walls and composite assem-

biies, these ratios were 84 and 81 percent, re- spectively. Regardless of the direction of bending, the composite masonry walls tended to fail at the header brick courses and it could be expected ' that their strengths would be equal when flexed

in either direction. ' In the flexural tests of walls there were no ^ tensile failures in the masonry units and none in the mortar except at vertical joints adjoining the I failure section. The modulus of rupture of the . concrete masonry walls, calculated on the gross

^ area basis, was in fair agreement with the similarly i calculated bond strength of block assemblies made

32
ntl

Bill

inn;

tin,

and stored in air with the walls. When estimating flexural strength by the usual flexural for- mulas, it is believed that the use of the gross area

section with its simpler calculations is preferable

to the use of the net area section. Whatever

method is used, the estimate of ultimate strength

(modulus of rupture) should not exceed the bond

strength of the mortar.

The assistance of all who helped in the preparation and testing of wall and bond-test specimens

is gratefully acknowledged. Special mention and

thanks is given as follows

To Ronald M. McPherson for his excellent work

while in responsible charge of the preparation of

the mortars and the measurement of their physical

properties.

To Earnest P. Moran, the mason who built

the walls, for his cheerful cooperation and for the

caretully uniform workmanship he used in the

construction of wall specimens.

Valuable assistance in the interpretation of test data and in the preparation ot this Monograph

was furnished by the Industry Committee on Masonry Research, representing those producers

of masonry cement who sponsored and furnished some financial aid to the investigation. The

members of the Industry Committee were: Chairman C. E. Wuerpel, Vice President, Marquette Cement Manufacturing Company; C. L. Davis, Director, Quality and Technical Services

Division, Manufactiiring Department, Universal

Atlas Cement Company; W. J. McCoy, Director

of Research, Lehigh Portland Cement Company;

M. A. Swayze, formerly Director of Research,

Lone Star Cement Corporation. In addition, particular mention and sincere

thanks are given to: R. E. Copeland, Director of Engineering, National Concrete Masonry Association.

Harry C. Plummer, Director oi Engineering and

Technology, Structural Clay Products Institute.

J. J. Shideler, Manager, Products and Applications Development Section, Portland Cement

Association.

8. Appendix I. Tabular Information

ling i

'

area

the ]m

For

reTable 1. Properties of the masonry cements used in blends B and C. Table 2. Properties of blended Ottawa sand mortars

tested in accordance with Federal Specification SSC-lSlc.

Table 3. Physical properties of portland cement used in ASTM C270 type S mortars. Table 4. Properties of the cements used in the wall

constructions. Table 5. Properties of blended Ottawa sand mortars containing cementing materials used in the wall constructions. Table 6. Grading and other properties of masonry sand. Table 7. Unit weight of cementing material and weights of dry materials in mortar batches. Table 8. Sieve analysis of expanded slate (Solite) aggregate used in concrete masonry units. Table 9. Batch weights and other data pertaining to concrete masonry units. Table 10. Shape, size, and physical properties of concrete masonry units. Table 11. Physical properties of brick. Table 12. Laboratory temperature and relative humidity

during construction and curing of concrete masonry

walls. Table 13. Laboratory temperature and relative humidity

during construction and curing of composite masonry

walls. Table 14. Compressive strength of concrete masonry walls and properties of mortars, including bond strength.

Table 15. Compressive strength of composite masonry

walls and properties of mortars, including bond strength.

Table 16. Secant modulus of elasticity of masonry walls

in compression.

Table 17. Racking strength of concrete masonry walls and

properties of mortars, including bond strength.

Table 18. Racking strength of composite masonry walls and properties of mortars, including bond strength. Table 19. Flexural strength of concrete masonry walls and

properties of mortars, including bond strength.

Table 20. Flexural strength of composite masonry walls and properties of mortars, including bond strength.

Table 1. Properties of the masonry cements used in Blends B and C »

Cement

desig- nation

Weight

per bag

Specific gravity b

Resi- due on

No. 325 sieve

Blaine

fineness, porosity

0.530

Normal

consist- ency HjO content by

weight

Time of

initial set

Autoclave expansion

48 hr.

1 2 3 4 5 6 7 8

Masonry cements ased in blend B

4.. 8

22

3536Averagelb70

70

70

7070

2.89

2. 93 2.90

2.90 2.90

%

1.2

4.

1

4.3

1.5 1.0

6300

6500 6400

7400 7700

%

28.0

25.4

27.0

27.0

28.2

hr: min

9:30

5:30

4:45 4:00

3:45

%

0. 127 .079

.071

.081 .007

70 2.90 2.4 6900 27.1 5:30 0.073

Masonry cements used in blend C

2 70 2.91 6.6 6300 25.6 3:30 0. 058

18 70 2.92 3.1 6600 28.4 5:30 .034 24 70 2. 89 1.0 5900 29.2 5:00 .042 27 70 2.92 2.6 5700 28.6 3:45 .090 32 70 2.86 1.2 8100 27.4 4:15 .073 Average. 70 2.90 2.9 6500 27.8 4:30 0. 059

» Determined in accordance with requirements of Federal Specification SS-C-181C on samples received in 1953.

>» Determined in accordance with the requirements of ASTM C188:-44.

33
Table 2. Properties of blended Ottawa sand mortars

tested in accordance with Federal Specification SS-C-181c

Table 3. Physical properties of portland cement used 17, ASTM C270 Type S mortars «

Mortar

designation Water- cement

ratio

Initial flow Water

tion

Air con- volume

Compressive

strength at age of

7 days 28 days

1 2 3 4 5 6 7

Masonry cements used in blend B

% % % % psi psi

4 46.2 109 87 19.8 1080 1410

8 45.2 110 91 24.8 1040 1290 22. _ - 47.0 109 87 21.8 1190 1390

35 46.2 108 86 23.1 1150 1390 36 47.6 108 89 21.6 1060 1360

Average 46.4 109 88 22.2 1100 1370

Masonry cements used in blend C

2 51.7 108 81 13.4 1440 1860

18 50.0 108 77 11.5 1490 1980 24 48.6 111 78 15.5 1350 1670 27 48.6 109 78 15.0 1630 2030

32 48.6 111 85 14.5 1230 1570

Average 49.5 109 80 14.0 1430 1820

Table 4. Properties of the cements used in wall

constructions *

Resi- Blaine Water Auto- Cement Year Weight Specific due on fineness content clave designa- of per gravity No. 325 porosity for nor- expantion test bag sieve of 0.530 mal con- sion at sistency 2 days

1 2 3 4 5 6 7 8

Cements used in type N mortars

lb % % %

B 1954 70 2. 90 2.4 6900 27.

0. 073 B 1959 70 2.9 6960 26.0 .06 C 1954 70 2. 90 2.9 6500 27.8 .059 G 1959 70 3.0 6570 27.0 .06 D 1954 75 2. 96 10.6 5300 24.8 .015 D 1959 75 12.4 5580 24.0 0 E 1959 72 2. 81 33.0

Cements used in type S mortars «

Bs 1959 78 2.98 4.4 5030 24.0

C. 1959 78 2.98 5.0 4900 25.0 D, 1959 81.3 3. 02 8.9 4930 24.0

E, 1959 79.3 2. 92 29.0

» Values for the blended cements B and C, listed for the year 1954 were

talcen as the average for the individual cements used in the Wends; deter- mined in accordance with requirements of Federal Specification SS-C-181c.

i" Determined in accordance with requirements of ASTM C 188-44.

« The cements used in the type S mortars were the same as those used in the type N mortars, except for the addition of 50 percent by volume of portland cement.

Compressive strength

Air en- Autoclave

Specific surface Initial set

3 day 7 day

trainment expansion Blaine

fineness

1 2 3 4 5 6

psi 2080

psi 3370 %

6.9 %0. 07 3250

hr: min

3:30

Determined in accordance with Fed. Spec. SS-C-192(b)

Table 5. Properties of blended Ottawa sand mortars

containing cementing materials used in wall constructions '

Air Compressive strength Cement Date Water- Initial Water content at age of designa- of cement flow reten- by

tion test ratio tion volume

7 days 14 days 28 days

1 2 3 4 5 6 7 8 9

Cements used in type N mortars % % % % psi psi psi B 1956 45.9 110 84 21.4 1180 1550 B 1959 45.0 112 82 19.4 1440 1540 1670 C 1956 48. 5 110 79 15.4 1510 1950 C 1S59 49.0 111 76 14.6 1570 1780 1980 D 1953 46.2 113 89 23.3 1680 2070 D 1959 44.0 112 88 22.2 1720 2650 2890 E 1959 64.0 108 86 5.1 1710 1940 2340

Cements used in type S mortars

B, 1956 42.3 108 84 19.3 2090 2650 B, 1959 43.0 113 80 18.5 2120 2360 2810 C, 1956 44.0 109 78 14.6 2470 3240 C, 1959 45.0 110 74 13.3 2670 3110 3330 D. 1959 42.0 112 83 17.7 2900 3180 3610

E, 1959 53.5 107 80 5.4 2950 3580 4080

» Determined in accordance with requirements of Federal Specification SS-C-181C.

•> The cements used in the type S mortars were the same as those used in the type N mortars, except for the addition of 50 percent by volume of port - land cement.

Table 6. Grading and other properties of masonry sand

Sieve size

Sand grading, weight

passing

Eeceived June 1957 Received Nov. 1957

4 %

100

10095

74

26

5.4

/o 100

100

96

71

181.6

8

16 - 30

50100

Fineness modulus..

Specific gravity . _ Absorption percent by weight2. 002. 61 1.4

2. 14

2. 61 1.4

llisi

34
Table 7. Unit weight of cementing material and weights

of dry materials in mortar hatches

Nominal

weight of cementing

material

Batch weights (dry)

Mortar Cementing

material Sand

BN, CN

Ib/fP

70" lb 14.6

20.

1

lb5070 DN 75 15. 6 50 21.9 70 EN 72 15. 0 50 21.0 70 BS CS 78 18.2 25.0

5070 DS.- 81. 3 19.0 50 26.7 70 ES —

79.3 18.6 50 26.1 70

Table 8. Sieve analysis of expanded slate (Solite) aggregate used in concrete masonry units

Sieve size

Bloclis used in:

Concrete masonry

walls

Composite masonry

walls % passing % passing H 100 100

4 84 85

8 - 60 52

16 39 30 30.- 25 17 50- _ 16 10 100 9.6 4.0

Table 10. Shape, size, and physical properties of concrete masonry units »

Item

Dimension (as used in wall)

in_. Thickness Height

Length

Thickness of shells and wobs

in.- Face shell. --{Sfn:: Web shell at plain end.jTM? j[ -

-

Web shell at open end.{TM?^- -

Inner web shell {mfn"

Dry weight lb.. Weight per ft ^ of concrete

lb.. Absorption per ft ' of concrete lb-. Compressive strength, gross area psi-. Compressive strength, net

area ' psi.-

Kind of masonry wall

Concrete

Stretchers i>

Both

ends open 0

7. 63

7. 63

15. 63

1.75

1.25

1.59

1.08 2.00

1.13

23.6

84.6

13.6

1140

2150

One

end

open

7.70

7.70

15. 67

1.75 1.25

1.75

1.27

1.59 1.08

1.95

1.09

23.0

80.6

13.5

1070

2020

Halves

Double

unit

7.70

7.70

15.69

1.75

1.25

1.94 1.75

2.90

2. 18

24.7

79.6

13.6

1430

Sash

unit <>

7.62

7.62

7. 59

1. 50 1.25

1.94

1.75

Composite

Stretchers both

ends

plain '

3. 64

7. 57 15.59

1.75 0.96

1.25 1.08

1.38

1.00

15.0

86.3

13.6

1240

1690

» Determined in accordance with ASTM method C140-56. Two-cell units.

« Dimensions as shown on Besser drawing No. 46602, mold assembly 46697

or 46733. Dimensions as shown on Besser drawing No. 46663.

» Three-cell units, Besser drawing No. 20514, mold assembly 17747.

' Based on average net area as indicated on Besser drawings.

I Table 9. Batch weights and other data pertaining to concrete masonry units

Item, per batch

Portland cement lb.

Silica flour. lb.

Solite aggregate lb. Yield—8X8X16-in. stretchers.. 4X8X16-in. stretchers. Mixing time min.

Pre-set time, minimum hr.

Autoclave curing. cycle.. "Buildup" period -hr-- "Hold" period. hr.. "Blow down" period hr..

Total time hr. Steam pressure during "hold" psi.

Blocks used in:

Concrete masonry

312.5

187.5

2550

120

Composite masonry

312.5

187.5

2250

168

6

2

Table 11. Physical properties of brick

Dimensions Absorption ModWidth Length Thickness

Initial rate 24 hr

cold

5 hr

boil

Saturation

coeffi- cient

ulus

of rupture

Compres- sive strength

1 2 3 4 5 6 7 8 9

in.

3. 61

in. 7.96in.

2. 28

g16 %

6.4 %

9.4 0. 68

psi 1390psi 16100

» Determined in accordance with ASTM Designation C 67-57.

35
Table 12. Laboratory temperature and relative humidity during construction and curing of concrete masonry walls'

Date of construction

July 1. July 3__ July 8. _ July 10. July 15.

July 17. July 22. July 24. July 31. Aug. 5.. Aug. 5... Aug. 7... Aug. 12.. Aug. 14.. Aug. 19.. Aug. 21.. Aug. 26.. Aug. 26.. Aug. 28.. Aug. 28..

Sept. 3.. Sept. 4.. Sept. 9.. Sept. 11. Sept. 11.

1957

Sept. 13. Sept. 18. Sept. 20.

Jan. 15. Jan. 15. Jan. 16. Jan. 16.

1958

Wall designation •>

Compressive

BN-1.

CN-1.

BS-1.. CS-1.

BN-2. CN-2.

BS-2..

CS-2.

BN-3_

CN-3.

BS-3.

CS-3.

Flexural

BN-1.

CN-1.

BS-1..

CS-1.... BN-2...

CN-2.., BN-Pl.

BS-2_.- CS-2. BS-Pl.

BN-3..

DN-l... BN-P2.

DS-1.... DN-2._.

DS-2._.. BS-P2..

CN-3...

BS-3.... BN-P3.

CS-3.... DN-3..

BN-3..

BS-P3.

BN-11.

BS-11.- BN-12_

BS-12._

Racking

BN-1.

CN-1.

BS-1..

CS-1.. BN-2.

CN-2-

BS-2.

CS-2. BN-3.

CN-3.

BS-3.

CS-3.

Temperature and rela- tive humidity on day

of construction »

Of

82

8183

82

7888

77

84

82

80

84

80

7779

74

76

8584

78

75

78

82

76

75

79

78

7978

RH

%

52

52

5553

57

5560

56

62

52

56

5462

6265

5563

64

52

52

67

65

58

75

70

72

6169

52

5153

51

Curing temperatures Relative humidity during curing

Mean Maximum Minimum Mean M!aximum ATIVi. inIll im1 lUTim LI 111

7 8 9 10 11 12 op "F "F % % %

82 87 76 57 74 45

82 87 76 57 74 42 82 88 75 56 73 42 82 88 75 58 73 42

82 88 75 60 73 42 82 88 75 60 73 42

81 88 74 59 73 45

81 88 74 59 73 45

81 86 74 58 72 44 80 86 70 58 72 44

80 86 70 58 72 44 80 86 70 58 72 44

78 86 70 58 72 43 78 86 70 58 72 43

79 87 70 59 73 43

78 87 70 59 73 43 80 87 72 62 82 43

80 87 72 62 82 43 80 87 72 63 82 43

80 87 72 63 82 43

80 87 72 65 82 45

80 87 72 65 82 45

79 85 70 65 82 36

79 85 70 64 82 36

79 85 70 64 82 36

79 85 70 64 82 36

78 86 68 59 74 34

78 86 68 57 74 34

77 81 68 54 62 40

77 81 68 54 62 40

77 81 68 54 62 40

77 81 68 54 62 40

» Walls were cured in laboratory air and were generally tested at age of 15 days. Temperature and relative humidity values were taken from a cali- brated wall recorder and are approximations for the indicated periods.

b The first two letters designate the mortar. The numeral indicates the

wall sequence in chronological order. Walls whose designations include a P

were built with the long dimension horizontal. These walls were stood on

one end and tested with the bed joints vertical.

° Observed at time wall construction was started. Table 13. Laboratory temperature and relative humidity during construction and curing of composite masonry walls ^

Date of construction

Wall designation i"

Compressive Flexural Racking

Temperature and rela- tive humidity on day

of construction "

RII

Curing temperatures

Mean Maximum Minimum

Relative humidity during curing

Mean Maximum Minimum

Sept. 24. Sept. 27. Sept. 30. Oct. 1, 2- Oct. 4...

1957 BN-1.

BN-1...

BN-Rl."

CN-l.'l! BN-1.

Oct. 7...

Oct. 8, 9. Oct. 10-.

Oct. 11..

Oct. 14-.

CN-1.

BS-1.

BS-l... BS-Rl"

CN-1.

Oct. 16, 18. Oct. 21 Oct. 22

Oct. 23 Oct. 24

CS-1.

CS-1. BS-1.

BN-R2.

BN-2-..

Oct. 25 Oct. 29 Oct. 30, 31. Nov. 1---.. Nov. 4

BN-2.

CN-2.'

CN-2- BN-2.

BS-2. Nov. 5 Nov. 6 BS-2. BS-R2.

See footnotes at end of table.

"F

73

68

75

8180

83

84

83

83

80

82

8180

8182

8182

83

81 - 80

82

79

%

50

37

5352

51

52

51

5149

5052

52

52

55

54

50

52

5152

50

Of

79

82

84

83

83

83

84

81

7979

79

79

79

79

79

79

7979

op

87

86

86

86

84

84

84

84

84

85

85

op

74

75

75

75

75

75

75

63

63

63

6363

63

6366

66

66

66

66

66

%

5452

52

5352

53

54

5452

54

53

53

52

52

53

5352

5152

52

52

52

61

61

61

61

6464

64

6363

63

63

63

63

63

63

63

63

63

61

36
Table 13. Laboratory temperature and relative humidity during construction and curing of composite mashnary walls—Con.

Date of construction

1957

•Jov. 7, 8 <ov. 12, 13-.

>}ov. 14

<ov. 15

'Jov. 18, 19.

"Jov 20

STov. 21.--.-

>Jov. 22-—-

>Jov. 25 Vov. 26, 27- Vov. 29--.

Dec. 2

Dec. 3, 4 —

Dec. 5, 6--

Dec. 9 Dec. 10 Dec. 11, 12- Dec. 13

,Dec. 16 Dec. 18, 19—

Dec. 20

iJDec. 26 1958 &an. 2

Ilan. 3

ilan. 6 — Ijan. 7- -- Tan. 8

Wall designation ^

Compressive

CS-2-

BN-3.

CN-3.

BS-a'-

CS-3

BN-4.

BS-4..

Jan. 9 DS-3

Flexural

CS-2-.

BN-3... BN-R3.

CN-3...

BS-3-.. BS-R3.

CS-3.

DN-1.

DN-2. DN-3.

DS-1..

DS-2..

Racking

CS-lCN-2.

BS-2-

CS-2.

BN-3.

CN-3.

BS-3

CN-4.

Temperature and rela- tive humidity on day

of construction v

79

85

78

83

80

82

79

78

77

7578

75

73

7982

78

80

76

8179

76

75

707576

75

RH

5050

54

54

515149

53

4948

5448

54

55

5050

5148

49

51

51

5150

5048

Curing temperatures

Mean Maximum Minimum

79

78

78

79

78

77

77

77

78

78

79

7980

80

80

79

78

7876

76

76

77

7777

78

8585

85

85

81

81

81

81

86

8686

86

86

86

85

85

85

8585

79

80

80

80

8181

81

66

66

68

68

7373

73

73

64

64

64

64

64

64

6464

71

71

71

71

7168

68

68

68

68

71

71

Relative humidity during curing

Mean Maximum Minimum

10

52

51

51

51

51

51

51

51

52

52

53

63

53

53

53

52

52

62

52

52

52

62

5151

51

51

51

51

11

61

61

61

6160

60

60

60

61

61

6161

61

61

616160

60

60

58

68

57

67

5762

62

62

62

29

29

31

3138

38

3838

36

35

35

35

35

35

35

35

3838

38

38

38

38

3838

4040

40

40

Walls were cured in laboratory air and were generally tested at age of 14 days. Temperature and relative humidity values were taken from a cali- brated wall recorder and are approximations for the indicated periods.

i> The first two letters designate the mortar. The numeral indicates the

wall sequence in chronological order. Flexure test walls were normally

tested with the brick facing in tension. Walls whose designation includes an R were tested with the block backing in tension.

" Observed at time wall construction was started. Table 14. Compressive strergth of concrete masonry walls and properties of mortars including bond strength »

Wall designation b

Mortar properties Flexural bond strength

of block assemblies e Maximum compressive load

Water

cement

ratio w/c

Initial flow c Water

retention <• Yield e Air

content by

volume

Compressive strength of cubes '

Air cured ! Sealed ' Per linear

foot On gross area On netarea

1 2 3 4 6 6 7 8 9 10 11 12

BN-1... %

66.2

67.2

68.6

or

/o133

139

143

%

84

8183

fp/bag

3. 18

3. 22 3.28

%

18.2

18.7

19. 7

psi 780

760 700

psi

k 89

10

psi lb 36.6X103

36.4

37.6

psi 390 380

410

psi 1030

1000

1080 BN-2-.... BN-3

Average 67.3

74.0

73.0 72.3

138

140 152

152

83

75

74

77

3.23

3. 05

3. 06

3. 05

18.9

11. 6 12.3

12.4

740

940

920

950

9

k 9

1010

36.2

42.2

41.2

3.5.5

390

460

450

390

1030

1210

1180

1030

CN-1.... GN-2-. CN-3

Average 72.8

58.4

58.7

59.4

146

145

144

147

75

8182

84

3. 05

2. 94

2.95

2. 98

12.1

16.3

16.4 17.0

940

1770 1770

j 1660

10

15

k 817

39.6

40.3 40.9

41.2

430

440

440

450

1130

1160 1160

1180

BS-1 BS-2

BS-3... Average 68.8

60.2

62.0

62.1

145

154

141 154

82

79

77

76

2. 96

2. 77

2. 78 2.80

16.6

10.4 9.8

10.5

1730

2030

2260

2140

13

17

k 15

k 30

40.8

43.1 42.6

43.5

440

470

460

470

1160

1240

1210

1240

CS-1 CS-2

CS-3

Average .

37

61.4 150 77 2. 79 10. 2 2140 21 37 43.1 470 1240

« Walls were cured in laboratory air. Nominal wall dimensions were

0'-8" thick, 4'-0" long, and 8'-0" high. Joints in the front face of the wall were

tooled concave. Walls were loaded on a line at the third point of the wall

thickness from the back face.

•> The first two letters designate the mortar. The numeral indicates the

wall sequence in chronological order for each specimen group.

" When the number of drops of the flow table was less than 25, the initial flow was calculated by adding two percentage points to the observed flow for each drop less thaii 26. Ratio for 25 drops of the flow table for either the observed or extrapolated

flows. The number of drops of the flow table was the same for the flows measured before and after suction.

s Yield in cubic feet of mortar per bag of cementing material.

' Mortar cubes were cured in accordance with the requirements of ASTM

C270. The cubes, bond-test specimens and the walls were tested at the same

age and at 15 days unless otherwise noted.

e Modulus of rupture for gross cress-sectional area of the section. Unless

otherwise noted, failure was at the plane between the upper unit in the assembly and the top of the mortar bed.

h Cured in laboratory air with the walls.

' Cured in sealed containers for 7 days and then stored in laboratory air.

' Tested at age of 14 days.

k Failure was at the plane between the bottom of the mortar bed and

the lower unit in the assembly. 37
Table 1 5. Compressive strength of composite masonry walls and properties of mortars including bond strength »

Wall designation >>

BN-1 BN-2

BN-3

BN-4

Average CN-1 CN-2

CN-3

Average BS-1 BS-2

BS-3

BS-4

Average CS-1 CS-2

CS-3

Average

Mortar properties

Water- cement

ratio w/c

%

69.4

69.9

76.0 76.0

76.0

76.0

62.1 60.5

61.0

59.3

60.7

62.

63.7

63.7

63.2

Initial flow c

%

139

144

147

151

145

156

159

1.54

142

144

1.53 146

156

156

155

156

Water

retention

%

83

83

85

87

85

76

75

74

75

8184

83

7778

75

Yield

ffi/hag 3.25 3.29

3. 34

3. 24

3. 28

3. 10

3. 08

3.13

3.10

2.98

3. 00

3. 06

3. 05

3. 02

2. 79 2.84

2. 82

2. 82

Air

content by

volume

%

18.7

19. 5 20.8

18. 2

19.3

12.1 11.6

13.2

12.3

15.8

16.9

18.5

19.0

17.6

10.0

11.1 10.3

10.5

Compressive strength of cubes '

psi

720

710

630

670

830

820

820

820

1820

1650

1740

j 1730

1740

2160

t 2290 2160

2200

Bond strength e

Brick

couplets "

33

27

30

48

40

45

29

3632

36

52

52

55

Composite

assemblies i

psi 52

37

32

32

38

48

53

57

50

55

40

65

7174

70

Maximum compressive

load

Per linear

foot

lb 141.9X103

66.6

56.5

168.1

71.3

76.4 72.5

73.4

53.

87. 2 87.2

80.9

»87. 2

97.8 92.6

81.3

90.6

On gross area

psi •1490

730

700 590

1 720

750 800

760

770

560

910

910

' 850

.151

i a-

! H.a.

"910

1020 970

850 -§-

r 950

f Walls were cured in laboratory air. Nominal wall dimensions were 0'-8" thick, 4'-0" long and 8'-0" high. Joints in the brick facing of the wall were

tooled concave. With two exceptions, walls BN-1 and BS-4, the walls were

loaded on aline at the third point of the wall thickness from the back face. Load on wall BN-1 was applied uniformly over the top area. Wall BS-4

was loaded on brick facing tier at third point of wall thickness from front face

of waU. The first two letters designate the mortar. The numeral indicates the

wall sequence in chronological order for each specimen group.

c When the number of drops of the flow table was less than 25, the initial flow was calculated by adding two percentage points to the observed flow

for each drop less than 25.

<> Ratio for 25 drops of the flow table for either the observed or extrapolated

flows. The number of drops of the flow table was the same for the flows measured before and after suction.

e Yield in cubic feet of mortar per bag of cementing material.

' Mortar cubes were cured in accordance with the requirements of ASTM

C270. The cubes, bond-test specimens and the walls were tested at the same

age and at 14 days, unless otherwise noted.

e All bond-test specimens were cured in sealed containers for 7 days, and

then stored in laboratory air with the walls.

i> Average tensile strength of crossed-brick couplets. Usually, 4 couplets were made with each wall specimen.

i Modulus of rupture for gross cross-sectional area of a composite assembly made with the wall specimen.

j Tested at age of 13 days.

^ Tested at age of 15 days.

I Average for walls BN-2 and BN-3. » Average for walls BS-2 and BS-3.

Table 16. Secant moduli of elasticity of masonry walls m compression'-

Secant modulus of elasticity

Load i> Concrete masonry walls Composite masonry walls BN CN BS CS Average BN CN BS CS Average

1 2 3 4 5 6 7 8 9 10 11

psi 25

50

75100 __ 150_ 200 250

300.

psi 58X10 * 58

55

53

514845

psi 62X10 4 6058

58

5756

55

psi 62X10 * 64

64

63

6262

61

psi 64X10 4 62

6263

63

62

61

psi 62X10 4 6160

5958

57

55

psi 125X10 ' 104

103

103

101

101 100

10099

95

psi 119X10 <

• 122

115

112 115

112

111

111 110

106

psi 119X10 * 122

117

118

117 118

117

116 113

112

psi 114X10 * 119

117 118

122

123

122

122

122

122

psi 119X10 * 117 113 113

114

113

112

112

110

109 400 500

n

1)1,

San

a Walls were loaded on a line at the third point from the back, unevposed, face, increment. Walls were built and tested in groups of three.

>> Average load on gross wall area.

38

Load was reduced to a basic minimum (5 kips) after each successive load
Table 17. Racking strength of concrete masonry walls and properties of mortars including bond strength"

Wall designation t

Mortar properties

Water- cement

ratio w/c

Initial flow " Water

retention <i Yield Air

content by volume

Compressive strength

of cubes '

Flexural bond strength

of block assemblies «

Air cured ^ Sealed '

Racking strength of walls

Total

diagonally applied

load

10

Horizontal

force per linear

ft of wall

N-1 N-2

PN-S

Average

%

66.4 67.6

69.

1

%

132

140

141

%

85

8187

fP/bag

3. 21 3.20 3.28

%

19.0

18.1 19.5

psi 750

760

i'710

psi

i 5

7

i 15

psi lb 28X10 3 28

25

lb 2400

2400

2200

iN-1 lN-2

IN-3 Average67.7

74.0 73.6

73.0

138

155

155

147

84

76

76

73

3.23

3. 06

3. 05

3. 06

18.9

11.8

11.9

12.4

740

860

810

990

1112

i 10

27

414438

2400

3600

3900

3300

S-1 S-2

S-3 Average73.5

58.0

59.4 59.4

152

148 146

140

75

8282

81

3. 06

2. 96

2. 96

2. 95

12.0

16.8

16.3 16.0

1630

1770

1860

192022 j 27

46

48

44

3600

4000

4200

3900

!S-1 IS-2

I S-3 Average58.9

60.2

60.2

62.1

151

151 154

82

7778

74

2. 95

2. 77

2. 77

2. 79

16.4

10.3

10.4

10. 2

1750

2100 2080

1 1990

20

16

1537 48

46

5546

54

4000

4800

4000

4800

60. 152 76 10.3 2060 23 48 52 4500

-j » Walls were cured in laboratory air. Nominal wall dimensions were 0'-8"

kiick, 8'-0" long, and 8'-0" high. Joints in the brick facing of the walls were

fooled concave.

•jl t. The first two letters designate the mortar. The numeral mdicates the

1/all sequence in chronological order for each specimen group.

.,' = When the number of drops of the flow table was less than 25, the initial

)jlow was calculated by adding two percentage points to the observed flow for |ach drop less than 25.

r| Ratio for 25 drops of the flow table for either the observed or the extrapolated flows. The number of drops of the flow table was the same for the flows

.jneasured before and after suction.

J ' Yield in cubic feet of mortar per bag of cementing material.

' Mortar cubes were cured in accordance with the requirerrents of ASTM

C270. The cubes, bond-test specimens and the walls were tested at the same

age and at 15 days unless otherwise noted.

« Modulus of rupture for gross cross-sectional area of the section. "Unless otherwise noted, failure was at the plane between the upper unit in the as- sembly and the top of the mortar bed.

I" Cured in laboratory air with the walls.

' Cured in sealed containers for 7 days and then stored in laboratory air.

' Failure was at the plane between the bottom of the mortar bed and the lower unit in the assembly. Tested at age of 16 days.

I Tested at age of 13 days.

il Table 18. Racking strength of composite masonry walls and properties of mortars including bond strength"

1 Mortar properties Bond strength e Racking strength

of walls Wall designation >> Water- Air con- Compres- Composite Total Hoizontal cement Initial Water Yield ' tent by sive Brick assem- diagonally force per

ratio w/c flow c retention <i volume strength couplets h blies ' applied linear ft of cubes ' load of wall

1 2 3 4 5 6 7 8 9 10 11 % % % fPlbag % psi psi psi lb lb bN-1 68.0 146 84 3.25 19.0 ' 800 34 77X103 6800 PN-2 68.5 147 84 3. 26 19.2 740 29 42 73 6500 BN-3 69.9 145 86 3. 40 22.2 620 26 22 66 5800

i Average - --- 68.8 146 85 3. 30 20.1 720 28 33 72 6400 lDN-1 76.0 155 76 3. 08 11.9 t870 54 47 1 94 I 8300 CN-2 --. 76.0 151 77 3.13 13.1 880 41 49 101 8900 CN-3 76.0 158 75 3. 15 13.7 820 49 65 1 110 '9700 CN-4 76.0 148 77 3.15 13.7 850 38 54 110 9700 Average 76.0 153 76 3. 13 13.1 860 46 54 ' 104 ' 9200 BS-1 59.2 154 82 2. 95 16.1 n> 1870 43 109 9600 BS-2 61.0 148 85 3. 05 18.3 1680 39 55 - 85 ' 7500 PS-3 59.3 144 83 3.02 17.9 1830 37 100 8900 Average- 59.8 149 83 3.01 17.4 1790 40 55 105 9300 bs-1 62.6 154 77 2. 81 10.3 2340 48 65 110 9700 1CS-2 63.7 156 75 2. 85 11.2 2190 48 61 ' 110 1 9700 Average .-. . 63.2 155 76 2.83 10.8 2270 48 63 ' 110 '9700

» Walls were cured in laboratory air. Nominal wall dimensions were

P'-8" thick, 8'-0" long and 8'-0" high. Joints in the brick facing of the walls

iwere tooled concave.

•> The first two letters designate the mortar. The numeral indicates the

^valI sequence in chronological order for each specimen group,

i = When the number of drops of the flow table was less than 25, the initial

Iflow was calculated by adding two percentage points to the observed flow

'"or each drop less than 25.

<i Ratio for 25 drops of the flow table for either the observed or extrapolated

.ows. The number of drops of the flow table was the same for the flows easured before or after suction.

e Yield In cubic feet of mortar per bag of cementing material.

' Mortar cubes were cured in accordance with the requirements of ASTM

j|C270. The cubes, bond-test specimens and the walls were tested at the same

jlage and at 14 days, unless otherwise noted.

8 All bond-test specimens were cured in sealed containers for 7 days, and

then stored in laboratory air.

t Average tensile strength of crossed-brick couplets. Usually, 4 couplets were made with each wall specimen.

' Modulus of rupture for gross cross-sectional area of a composite assembly made with the wall specimen.

i Tested at age of 22 days.

k Tested at age of 16 days.

I Not loaded to failure. " Tested at age of 13 days.

" Failed in an unusual manner and not included in the average for the

group.

39
Table 19. Flexural strength of concrete masonry walls and properties of mortars including bond strength »

Mortar properties Flexural bond strength

of blooli assemblies e Flexural strength of walls Wall designation ^ Water

cement

ratio

Initial flow " Water

retention Yield = Air content by volume

Compressive strength

of cubes '

Air cured ^ Sealed Maximum

uniform

load j

Modulus

of rupture

1 2 3 4 5 6 7 8 9 10 11

Walls tested with bed joints normal to span length

BN-1 BN-2

BN-3

BN-4

BN-U.^..

BN-12.--.

Average. CN-1 CN-2

CN-3

Average. DN-1 DN-2

DN-3

Average. EN-1 EN-2 EN-3

Average. BS-1

BS-2. BS-3

BS-11 BS-12

Average CS-1 CS-2

CS-3

Average DS-1

DS-2

Average, ES-1 ES-2

ES-3

Average

%

65.7

67.2

69.1 70.0

65.5 65.7

67.2

74.0

74.0

73.0

73.7

67.

66.2 63.5

65.6

90.0

91.5 92.8

91.4

58.0 59.4

59.4

57.0

57.0

58.2

60.2 60.6

62.

58.6

56.6

57.6

70.0

71.3

72.2

71.2

%

131 140

130

131 132

144

135

154 158

142

131 142 148

140

140

144

140

140

151

144

144

146

146

146

150

150

151

148

147

148

138

134

137

136

%

83

84

82

82

8683

83

78

76

72

75

85

86

76

82

87

82

83

85

84

79

7776

85

83

84

/( Vbag

3. 19 3.22

3. 22

3. 19

3. 34 3.27

3. 24

3. 06

3. 06

3. 06

3. 06

3. 24

3. 28

3. 22

3. 25

3.02

3.01

3.01

3. 01

2. 94

2. 96 2.95

3.02

3. 05

2.99

2.78

2. 78

2. 79

2. 78

2.93

2.92

2.92

2. 69 2.70

2.70

2.70

%

18.5

18.8 18.0

17.

22.2 20.5

19.2

12. 12.1 12.4

12.2

16.8

19.0 18.0

17.9

0.8

0.4

0.4

0.5

16.6

16.5

16.1

19.0 19.8

17.6

10. 7 10.3

10.

14.5

15.1

14.8

1.

0.8

0.6

0.8

I 760

720 850

810

> 700

' 610

740

850 970

I 1340

1370

' 1540

1420

900

1060

1590

1730

1830

> 1760

' 1700

1720

2010

2240

2150

2130

2320

2630

2480

2650 2780

2670

2700

pst m6

10 m 7 m 10 » 1316

'24

' 13

' 18

1624

' 18 '26

' 12

1533

25

19

22

5227

39

39

psi

' 17

' 16

21

'25

25

'20

20

21

' 17

1736

62

56

56

psf

23.7

16.7 21.3

15.4

14.4

18.3

14.6

14.8

14.1

14.5

20.9

20.4

25.8

22.4

32.3 29.8

35.6

32.6

20.0

20.7 26.7

25.2

28.0

24.1

22.9

29.0 47.9

33.3

27.9

28.4

28.2

33.2

37.9

65.7

45.6

Walls tested with bed joints parallel with span length

BN-Pl 68.9

68.

68.

141 138

141

83

8386

3. 24

3. 25

3. 27

18.7

19.

19.5

750

780 760

m 4 » 10 m 11

56.2 37.6

60.6

40.4

27.1 44.0 BN-P2... BN-P3

Average. BN-Pl. __

n 13

68.4

59.4

59.4 59.4

140

150 146

148

84

85

8284

3. 25

2.98

2.99

2. 99

19. 1

16.9

17. 1 17.4

760

1650

1700

1550

-9

13

1029

" 17 51.5

69.6

68.9

92.7

37.2

43.0

49.6

66.8 BN-P2BN-P3-

Average _

23

59.4 148 84 2. 99 17. 1 1630 > 18 -24 73.7 53.1

» Walls were cured in laboratory air. Nominal wall dirrensions were 0'-8" thick, 4'-0" long and 8'-8" high. Joints in the front, tensile face of the wall were tooled concave. Walls were supported in a vertical position and loaded on lines at the quarter points of a 7'-6" span.

>> The first two letters designate the mortar, the numeral indicates the wall sequence in chronological order for each specimen group. Walls whose

designation includes a P were built with the long dimension horizontal. Those walls were stood on one end and tested with the bed joints vertical.

" When the number of drops of the flow table was less than 25. the initial flow given above was calculated by adding two percentage points to the observed flow for each drop less than 25. Ratio for 25 drops of the flow table for either the observed or extrapolated

flows. The number of drops of the flow table was the same for the flows measured before and after suction.

' Yield in cubic feet of mortar per bag of cementing material.

' Mortar cubes were cured in accordance with requirements of ASTM

C270. The cubes, bond-test specimens and the walls were tested at the sam

age and at 15 days unless otherwise noted.

« Modulus of rupture for gross cross-sectional area of the section. Unless' otherwise noted, failure was at the plane between the upper unit in the assembly and the top of the mortar bed.

h Cured in laboratory air with the walls.

' Cured in sealed containers for 7 days and then stored in laboratory air.

I Equivalent uniformly distributed maximum load on a span length of

7.5 ft.Based on gross cross-sectional area of wall.

' Tested at age of 14 days. n Failure was at the plane between the bottom of the mortar bed and the lower unit in the assembly.

n Grand average for all similar bond-test specimens including those made

with walls tested in compression and racking.

40
Table 20. Flexural strength of composite masonry walls and properties of mortars including bond strength

Mortar properties Bond strength s Flexural strength

of walls

J Wall designation Water Water Air con- Compres- Composite Maximum Modulus

J cement Initial reten- Yield ' tent by sive Brick assem- uniform of rupratio flow » tion <i volume strength couplets ii blies i load i ture '' of cubes '

1 2 3 4 5 6 7 8 9 10 11

Walls tested with brick facing in tension % % % fP/bag % psi psi psi psf psi

69.

1

69.9

139 80 3. 23 18.3 700 31.4 21.0

. ^-2 149 85 3.26 18.8 700 37 39 33.0 22.

1

69.9 146 85 3. 36 21.2 600 35 44 39.0 26.

1

69. 6 145 83 3. 28 19. 4 670 ' 31 '38 34. 5 23.

1

76.8 152 75 3. 09 11.9 840 44 40 33.0 22. 1

- N-2 76.0 155 74 3.09 12.

1

860 43 60 43.5 29.

1

N-3 76.0 154 74 3.14 13.4 830 41 39 52.6 35.2

76.

3

154 74 3. 11 12. 5 840 ' 45 '51 43. 0 28. 8

|iN-l 65.6 135 84 3. 38 21.0 1210 27 51 45.0 30.2

H|)Jsf_2 _ 65.2 131 84 3. 37 20.8 1240 26 35 52.5 35.2 tN-3 - 64.7 137 87 3.43 22.4 1080 23 44 46.8 31.4

65. 2 134 85 3. 40 21. 3 1180 25 43 48.

1

32. 2 W-l 97.0 143 86 3.02 0.4 1130 53 63 67.7 45.

1

J;N-2 --- 97.3 146 88 3. 01 0 1040 53 66 71.7 47.8 ;n-3 97.3 147 88 3. 01 0.1 1040 59 81 74.9 49.9

I Average 97. 2 145 87 3. 01 0.

2

1070 55 70 71. 4 47. 6

)IS-1 60.3 143 81 2. 97 16.2 1820 41 53 51.8 34.7

58.8 146 84 2. 97 17.1 1780 36 55 46.5 31.2

59 5 146 82 3. 05 18.

9

1800 36 51 5 34 2

i Average - 59.5 145 82 3.00 17.4 1800 '38 '53 49.8 33.4

:s-i 62.

1

157 76 2. 78 9.9 2090 53 56 55.0 36.8 pS-2 63.7 158 77 2.84 11.0 2080 54 70 58.

1

38.9 pS-3 — 63.7 154 78 2. 84 10.8 2300 48 50 54.8 36.7

i Average 63.2 156 77 2.82 10.6 2160 1 51 '64 56.0 37.5

.pS-1 —

55.9 143 85 3. 05 19.0 2320 41 61 60.7 40.7 DS-2 56.3 143 82 3. 06 18.9 2320 37 63 65.6 44.0 pS-3 56.3 142 83 3.04 18.5 2480 42 74 54.2 36.3

'; Average 56.2 143 83 3.05 18.8 2370 40 66 60.2 40.4

\iS-l - 72.8 142 88 2.69 0.6 3120 67 94 91.5 61.0 SS-2 -- 74.1 144 86 2.70 0.4 3080 69 73 72.

1

48.1 -ES-3 — 74.7 146 86 2.70 0.

1

2880 70 74.3 49.5

Average 73.9 144 87 2.70 0.4 3030 69 84 79.3 52.9

1 Walls tested with block backing Ln tension

iBN-Rl 69.6 141 83 3.25 18.6 760 41 41.2 27.6 i8N-R2 - 69.9 149 84 3. 23 18.1 730 27 44 53.1 35.6 IBN-R3 - 69.9 145 87 3. 34 20.6 620 31 35 43.8 29.3 Average

.

- 69.8 145 85 3. 27 19.

1

700 31 40 46.0 30.8 ©S-Rl 59.5 147 82 2. 99 17.

1

1860 37 77 50.1 33.6 JBS-R2 - 61.0 147 83 2. 99 16.6 1840 41 87 63.3 42.6 'BS-R3 -- 59.3 144 83 3. 05 19.

1

1760 33 58 50.4 33.8 Average— - 59.9 146 83 3.01 17.6 1820 138 74 54.6 36.6

« Walls were cured in laboratory air. Nominal wall dimensions were V 8" thick, 4' 0" long and 8' 8" high. Joints in the front, tensile face of the

ivall were tooled concave. Walls were supported in a vertical position and

4oaded on lines at the quarter points of a T 6" span.

>> The first two letters designate the mortar. The numeral indicates the Vail sequence in chronological order for each specimen group. Flexure test

I .jwalls were normally tested with the brick facing in tension, walls whose

j"-* llesignation includes an R were tested with the block backing in tension, as* c When the number of drops of the flow table was less than 25, the initial flow given above was calculated by adding two percentage points to the Dbserved flow for each drop less than 25.

^ Ratio for 25 drops of the flow table for either the observed or extrapolated

flows. The number of drops of the flow table was the same for the flows measured before and after suction.

« Yield in cubic feet of mortar per bag of cementing material.

' Mortar cubes were cured in accordance with requirements of ASTM

C270. The cubes, bond-test specimens and the walls were tested at the same age and at 14 days, unless otherwise noted.

e All bond-test specimens were cured in sealed containers for 7 days and

then stored in laboratory air.

h Average tensile strength of crossed-brick couplets. Usually, 4 couplets were made with each wall specimen.

' Modulus of rupture for gross cross-sectional area of the section of a composite assemblage made with the wall specimen.

' Equivalent uniformly distributed maximum load on a span length of

7.5 ft.

I" Based on gross cross-sectional area of wall.

' Grand average for all similar bond-test specimens including those made

with walls tested in compression and racking.

41
9. Appendix II. Construction, Curing, and Testing of Bond-Test Specimens

The materials used in the bond-test specimens were representative of those used in the walls. Block assemblies were made with the concrete masonry walls. Brick couplets and a composite

assembly were made with each composite masonry

wall.

9.1. Equipment

The equipment used to make bond-test speci- mens is listed below.

Mortar board, one, brass covered, about 18 in. square.

Trowels included the mason's trowel and a small

straight-edged laboratory trowel.

Molds, two, for the mortar bed joints in crossedbrick couplets. The molds were of brass with

square openings with sides beveled outward from

top to bottom at a slope of 0.08. Two metal

positioning pins were inserted at one side of the

bottom of each mold.

Spoon, short-handled scoop or table spoon.

Straight-edge, steel, about 10 in. long.

Drop hammer for cross-brick couplets. Weight

of frame 2.3 lb. Nominal weight of hammer 2

lb; height of drop VA in. Drop hammer for block assemblies. Weight of

frame 4.0 lb. Weight of hammer 3.5 lb; height

of drop 4 in. The drop hammers are illustrated in figure 29.

9.2. Concrete Block Assemblies

a. Construction and Curing

One, and sometimes two, concrete block assemblies were made with each concrete masonry wall. The assemblies were made by the same mason who constructed the walls, when the walls were

Ijroi

few

of

iltila

near midheight and while scaffolding was beinf

erected preparatory to completion of the wall. The lower block of the assembly was p\a,ce(

with the wide portion of the face shells uppermost

Mortar for the bed joint between the two blockr

of the assembly was placed over the face shells ii a manner similar to that used in the wall construe

tion. One minute after the mortar was applied

the upper unit was placed in its bed. A drop ham

mer was then centered on the upper unit and thi 3.5-lb hammer was dropped a distance of 4 in Extruded mortar was cut away from the sides o the assembly and the bed joints were tooled witlltJ a rounded iron. The degree of compaction of th

mortar was affected by its air content and th(

thickness at the bed joints in the block assembliesi jjini was not necessarily representative of the thickness

of the bed joints in the wall. One block assembly was made with most of th(

52 concrete masonry walls. In those cases where more than one assembly was made, the seconc

(duplicate) . assembly was placed in a sealed con

tainer immediately after its completion and was

cured at laboratory temperature for 7 days. Afte;

7 days the seal was removed and curing of the: assembly continued in laboratory air. The con-' Crete block assemblies were tested with the walls! they represented, usually at the age of 15 days.

b. Testing

Test frames, illustrated in figure 30, were fas- tened at the top and bottom of the concrete block

assemblies. The %-m. diameter clamping screws;

in each frame were located in vertical planes:

passing through the end and center cross webs!

of the block. The clamping screws were tightened

by means of a torque wrench using a torque of|

30 to 40 in./lb.

A vertical load was applied to the assembly

through a ball bearing placed at a distance of 10

Figure 29. Drop hammers. Figure 30. Test frames for masonry assemblies.

42
n.

c. Data

from the longitudinal vertical axis of the

pecimen. The uniform rate of load apphcation

roduced a flexural failure in the tensile face of

e assembly within 1 or 2 min.

A block assembly in position for test is shown

figure 31. Failure of the block assemblies occurred at the

; 1 »lane between the upper unit and the mortar bed

pj[;^|n over half of the specimens.

lllD

til' I The flexural bond strengths of the block assem4illies were calculated for the gross cross-sectional rea of the section and are listed in tables 14, 17

!^,t|!nd 19 of appendix I. The data are also briefly

i[iscussed in the main body of this paper. Some

,4 ijalculations made on the net area basis using the

Me'iiinimum cross-sectional area of the face shells

s4'-ielded values about 15 percent greater than those

Ibtained for the gross area.

i' m.m

m

Four crossed-brick couplets were made by a

jfcboratory assistant, with each composite wall;

(jwo couplets were representative of the materials

ai jjised in the lower half of the wall, and the other two

m

9.3. Crossed-Brick Couplets

a. Construction and Curing

Figure.31. Concrete block assembly ready for test.

were representative of those used in the upper

half of the wall. The lower brick of each crossed-brick couplet was mounted on a pedestal to provide room for cutting away extruded mortar from the two joint

faces beneath the upper brick of the couplet.

The mold for the bed joint mortar was positioned on the lower brick.

The mold was partially filled by sharply dashing

5 half-spoonfuls of mortar to the surface of the

brick enclosed by the mold perimeter. In this operation, a half-spoonful of mortar was applied

to each corner and one to the center of the bond

area. The time was then noted and the mold was

loosely filled to heaping with mortar, using the

small laboratory trowel. Excess mortar was

struck off from the mold with a straight-edge start- ing on a diagonal across the mold and working

first to one corner and then to the opposite corner

of the mold. The straight-edge was slightly in- clined in the direction of the pass. To reduce the

possibility of drawing water and fines to the top of

the bed, a slightly sawing motion was used and

only one pass was made over each half of the bed.

The mold was removed after striking off the excess mortar.

At one minute from the time of noting the first applications of mortar, the upper brick was carefully placed on the bed in a position crosswise to that of the lower brick. The hammer frame was

promptly and gently positioned on the upper brick

using one hand and while holding the weight of

the hammer in the other hand. The hammer was

immediately dropped a distance of I/2 in. The

drop hammer was then removed from the specimen

and the maximum extrusion of mortar over the

top surface of the lower brick was measured. The

extruded mortar was cut away with a laboratory

trowel. The compaction of the mortar, the

amount of extrusion and the thickness of the

mortar bed was dependent upon the air content

(density) of the mortar.

The crossed-brick couplets were placed in sealed

containers and were cured at laboratory temperatures for 7 days. After 7 days, the seals were removed and the couplets were then cured in

laboratory air. When the couplets were removed,

condensation moisture was usually present on the

inside of the metal containers, indicating the

existence of a high relative humidity in the air ambient to the couplets during the 7-day initial curing period. The crossed-brick couplets were

tested with the walls they represented usually at the age of 14 days.

b. Testing

The upper brick of each couplet was supported on a 3-pronged jig resting on the platen of the

testing machine. A second tripod was supported on the lower brick of the couplet and load was

applied to the couplet through a ball bearing rest- ing on this tripod, as shown in figure 32. The

43
Figure 32. Crossed-brick couplet ready for test.

uniform rate of load application produced a tensile bond failure in 1 or 2 min. Failure occurred

at the plane between the upper unit and the mortar bed in about 90 percent of the specimens.

The extent of bond at this failure plane was excel- lent as may be noted from examination of figure

33. As indicated in the figure, tensile failure of

the mortar occurred over small areas in some

specimens.

c. Data

The tensile bond strength of the crossed-bricl

couplets was taken to equal the maximum appliec

load divided by the square of the average widtl

of the brick. The average strengths for each 4 specimen group of couplets are listed in tables 15. 18, and 20, of appendix I. They are also briefl] discussed in the main body of this paper.

9.4. Composite Assemblies

a. Construction and Curing

t

One composite assembly was made by the maso!

with each composite wall. They were built o the materials used in the wall construction whei

the wall was near midheight and while scaffolding was being assembled for completion of the wall

The physical properties of the mortar used in th

wall were measured from samples taken at th(! time the assemblies were made. i To facilitate gripping of the specimen in the tesi

| frames, the top and bottom courses of the assem 1 blies were of brick, laid in rowlock bond. Th(^

facings and backings of the assemblies, betweei

the rowlock courses, were built in a manner similai to that used in the walls. A typical composit<

assembly, tested with the brick facing in tension was about 15.8 in. long, 16 in. high, and 7.96 in

thick. The brick facing of such assemblies con

tained 3 brick stretcher courses laid in running

bond. The backing contained a single 4X8X16-

in. concrete masonry unit.

Assemblies tested with the concrete backing tiei in tension contained two block courses and six brid

stretcher courses between the upper and lowei

rowlock courses. Two similar assemblies were

also built with a brick header coiu-se at midheight

of the specimen. Composite assemblies are illus- trated in figure 34. The composite assemblies were placed in sealed

containers after their completion and were cured

at laboratory temperatures for 7 days. After

7 days, the seals were removed and the assemblies were then cured in laboratory air. Cellophane

44

Figure 33. Tensile bond failures in crossed-brick couplets.
34. Composite assemblies and crossed-brick couplets in first and second curing stages.

was used to seal the large assemblies as shown at the extreme left of figure 34. Condensation moisture was noted on the inside of the cellophane cover opposite the brick portions of the assembly.

No moisture could be seen on the cellophane adja- cent to the concrete masonry units in the assembly.

The composite assemblies were tested with the

walls they represented, usually at the age of 14

days.

b. Testing and Test Data

The composite assemblies were tested in flexure

using the same test equipment and in the same

general manner of test as that previously described

for the block assemblies. Initial cracking noted

in the brick facing of some assemblies was similar

to the isolated bond failures described in the tests on concrete masonry walls subjected to flexural loads with the bed joints normal to the space. Data obtained from the tests on the assemblies

are listed in tables 15, 18, and 20 of appendix I and are also briefly discussed in the main body of

this paper.

o

45

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