NATIONAL BUREAU OF STANDARDS REPORT

3317

REPORT ON CRACKING IN CONCRETE BLOCK MASONRY

CONSTRUCTION AT NAVAL SUPPLY DEPOT, MECHANICSBURG, PA.

by

J. ¥, McBurney

Report to

Bureau of Yards and Docks

Department of the Navy

<NBS>

U. S. DEPARTMENT OF COMMERCE.

NATIONAL BUREAU OF STANDARDS
U. S. DEPARTMENT OF COMMERCE

Sinclair Weeks, Secretary NATIONAL BUREAU OF STANDARDS

A. V. Aslin, Director

THE NATIONAL BUREAU OF STANDARDS

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^Office of Basic Instrumentation ^Office of Weights and Measures.
NATIONAL BUREAU OF STANDARDS REPORT

NBS PROJECT

IOOO-3O-I4.8OO May 21,

NBS REPORT

3317

REPORT ON CRACKING IN CONCRETE BLOCK MASONRY

CONSTRUCTION AT NAVAL SUPPLY DEPOT, MECHANICSBURG, PA.

by

J. W. McBurney

To

Bureau of Yards and Docks

Department of the Navy

U. S. DEPARTMENT OF COMMERCE

NATIONAL BUREAU OF STANDARDS

The publication, reprir Approvcd foT public relcasc by the prohibited

unless permission Is obi

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REPORT ON CRACKING IN CONCRETE BLOCK MASONRY

CONSTRUCTION AT NAVAL SUPPLY DEPOT, MECHANICSBURG, PA.

by

J. W. McBurney

1 . SUMMARY AND CONCLUSIONS

The Mechanicsburg Naval Supply Depot was investigated for

the purpose of determining, if possible, the cause of excessive

cracking of the concrete block masonry in certain of the storehouses at this site. The method finally followed was to select

the best and the worst structures frcm the standpoint of observed cracking and to compare them with respect to factors which

are common and which are unlike. Based upon inspections, study

of photographs, replies to a questionnaire answered by the Works

Officer, receipt of information from various other sources and

from the results of some laboratory tests on blocks and mortars,

some conclusions were reached and opinions formed.

( 1 ) The aggregate used in the manufacture of blocks used

in Building III4. (the poorest from the standpoint of cracking)

was largely limestone with some admixture of cinders. The blocks

used in Building 9 OI4., ( whi ch. was remarkably free from cracking)

were made with cinders as the aggregate,

(2) Both types of block were in essential compliance with

the American Society for Testing Materials and Federal Specifications for hollow load-bearing concrete masonry units with respect to strength and absorption.

( 3 ) Linear shrinkage at nine years for the II4 block (limestone and cinders) averaged 0,035 percent. The corresponding

shrinking of the 90li- blocks (cinder aggregate) was 0.05l percent

at age of six years,

(4) Reliable evidence was secured to the effoct that Building III4

. was built of block laid when about I4

. days old while the

block used in Building 90l|. has been stored at the site under

tarpaulins for from 30 to 60 days. This evidence would indicate

that the shrinkage of block used in Building 90I4. was much less

than had occurred in Building lliq.

1 .
(5) Examination and identification of the mortar gave no

evidence of unsoundness (expansion) as a cause of cracking.

(6) Straight vertical cracks spaced at regular intervals

and apparently not penetrating the concrete foundations of

Building lll\. and similar building, appeared to be associated

with steel columns or pilasters at these locations.

(7) Irregular cracking of various patterns and associated

with cracks in concrete foimdations may have resulted from

foundations settlement. There were more cracks in a 600 ft

length of foundation of Building lllj. than in the block masonry

supported by this foundation.

(8) Building 90li. had obviously good soil (rock) conditions.

No information on soil conditions could be obtained for Building

III4.. An unconfirmed rumor that its site was a former bog or pond was circulated,

(9) Building lli\. (6OO by 200 ft) had no expansion joints

in either masonry or foundations. Building 90I4. (I|.00 by 200 ft)

had four expansion joints,

(10) Building 111], departed widely from the recommendations

given in the NBS Report 3079, ^Requirements for concrete-masonry

construction.” Building 90L1. was in somewhat better agreement

with these requirements. The units of 90I1- may be considered as

having complied with the requirements for moisture content at

time of laying.

(11) No evidence was obtained on the effect of dehumidification. Building lllj. was dehumidified and was badly cracked,

whereas Building 90I4. was not dehumidified and was remarkably

free from cracking. There were, however, so many other differences between these two buildings that a conclusion with respect

to the effect of dehumidification appears unwarranted.

2. HISTORY OF INVESTIGATION

Early in the summer of 1952, the Bureau of Yards and Docks

had requested the National Bureau of Standards to investigate

certain cases of excessive cracking of concrete block masonry

construction used as storehouses at the Naval Supply Depot in

Mechanicsburg, Pennsylvania. The Depot was visited by J. W.

McBurney and C„ C, Plshburn of the National Bureau of Standards

on July 16, 1952, and a general inspection was made of the Depot

with particular reference to the structures that exhibited cracking, Specifications covering the materials, construction and

2 .
design of the masonry buildings were examined during this visit

and the problem was discussed with Lt, Commander W. E. Flynn

(Public Works Officer) and his aids. A set of photographs, made

on June 6, 19^2, and showing cracking patterns on certain of

these buildings was supplied. (See Appendix A). Commander

Flynn subsequently visited the National Bureau of Standards and

further discussions took place. Information was also sought

from various people who had contact with the Depot at the time

of construction (1944”45). As would be expected some rather

conflicting hearsay evidence was collected. It was decided to

confine the investigation to a comparison of two buildings (Nos.

llll and 9OI1.) , selected on the basis of showing the most and the

least cracking. A questionnaire relating to these two buildings

was prepared and submitted to Commander McRorey (Works Officer)

in June 1953. A reinspection of Buildings 90l|. and III4. was made

at that time. This questionnaire combined with Commander

McRorey’ s answer is reproduced as Appendix B of this report.

Arrangements were made for submittal of samples of block and

mortar from these two buildings for laboratory examination, and

they were received at the NBS in October 1953. The results are

presented under Laboratory Tests-,

3. GENERAL DESCRIPTION OF DEPOT

The Mechanicsburg Depot contains some 68 storehouse buildings which with four exceptions are 600 ft long by 200 ft wide.

One of these buildings, 9OI4., is located in the vicinity of the

Tank Farm and is a considerable distance from the main group.

This building is approximately IqOO ft long by 200 ft wide and

the soil conditions in the vicinity of this building appears to

be different from the corresponding conditions near the main

group. Of these 68 storehouses, 13 Q-ve of concrete block construction and the remainder are wood frame sheathed with asbestoscement board on both sides and with glass windows. Up to window

sill height (approximately I|. ft above floor level), the walls are

either l2-in. thick concrete or 12-in. thick clay brick masonry.

These wood frame structures were remarkably free from observable

cracking in their masonry. Cracking appeared to be confined to

the concrete block structures.

A number of these storehouses are dehumidified. Building

11L|. is known to be dehumidified and 90I4. is not dehumidified.

The concrete block masonry structures are supplied with heating

facilities according to available information.

3 .
[j-. LABORATORY TESTS

Eight concrete block from Building lli|. and eight from

feuilding 90l|. were received for test and examination. These

specimens had been removed from various points in the walls of

these buildings and were identified by numbers referring to

locations photographed at the time of removal. All of the

units were more or less damaged in that corners were missing

and parts of the shell and webs. A selection of the five most

perfect units from each sample was made and these were used

for compressive strength determinations and for measuring

shrinkage. The remaining specimens were broken into pieces

for determining absorption.

The -units selected for testing in compression were built

up to give plain bearing surfaces by use of a 1:3 Portland

cement-sand mortar. After curing of the mortar, the bearing

surfaces were shellacked and capped and tested according to

the method given in ASTM Standard CII4.O- 52 . Linear shrinkage was determined on three specimens of

each sample by the rapid method described in the Progress Report of the American Concrete Institute’s "Physical Properties

of High-Pressure Steam-Cured Concrete Block." (Journal of the

American Concrete Institute, April 1953)* In this method the

specimens were soaked in wa"ter for 2i|. hr at 73 ± 3 E and then

dried in an oven at a temperature of 220 to 235 F for [j.8 hr

and then cooled in a sealed drum for 2Lj. hr. Measurements of

length change were made after soaking and again after drying

and cooling using a 10-ln. Whittemore strain gage.

The absorption test was made by immersing pieces of

broken -units free from mortar in water for 2l\. hr according to

the method of ClL|.0-52.

The results of tests on the block from Building lli| are

presented in Table 1, and for Building 90[|., in Table 2.

Sample llLj. is in compliance with Grade A of ASTM Specifications C 9 O -52 (Hollow Load-Bearing Concrete Units) with respect to compressive strength and absorption. Sample 9011- rates Grade B in compressive strength since the average

strength is 985 psi instead of 1000 psi.

From inspection together with some qualitative chemical

examinations, it was established that the aggregate in block

from Building III4

. was predominantly limestone with some added

cinders. The aggregate for Building 90li- was cinders.

4.
Examinations of the mortar were confined to determining

the total content of magnesium oxide (MgO). Mortar from

Building III4. contained 2.0 percent and from 91I|., 2.8 percent

of magnesia calculated as magnesium oxide. The interpretation of these results is considered in the following section

of this report (Discfission) ,

5. DISCUSSION

In the section History of Investigation, it was stated

that Buildings lll^ and 90I4. were selected as the extremes in

degree of cracking. This section, for the most part, considers the application of available Information about these

two buildings with respect to factors which are common and

which are unlike, with the purpose of Identifying the factor

or factors which may explain the differences in performance.

In addition to the data presented under the section on labora

tory tests, this discussion is based upon Appendix A (Observation and comments on photographs of buildings of Naval

Supply Depot), Appendix B (Questions and Answers on design,

construction, materials and history of buildings lll\. and 90I4.)

and Ap;^endix C (Discussion of possible causes of cracking),

plus some unverified information from other sources. Appendix

C was prepared on the assumption that much of the observed

cracking could be ascribed to volume change of certain of the

materials of construction.

Masonry Units - That laboratory tests for shrinkage

showed 45 percent greater shrinkage for the units for Building 90l|. (slight cracking) compared with those from Building

III4. (excessive cracking) was unexpected. This result appears

reasonable in view of the constitution of the block (cinder

aggregate for 90L|. and predominantly limestone for Hi;) . A

possible explanation of this paradox appears in the answer

to Question 3D (Appendix B). The blocks used in 904 were

30 to 60 days old before laying and were protected at the

site by tarpaulins whereas, according to reliable information

the No. 114 blocks were laid within 4 days of forming. (See

discussion under ’’Shrinkage of units on drying” in Appendix

C), It may reasonably be considered that the use of wet

blocks contributed to the cracking behavior of Building II4

and that use of dried and aged block helped to minimize

cracking in Building 904 . Although no information is available, it is probable that values for shrinkage measured at

28 days or less after forming, would considerably exceed

shrinkages determined on similar units after ageing from 7

to 9 years.

5 ..
Mortar - Certain cracking patterns such as shown in

figure 17 TAppendix A) might be interpreted as resulting

from expansion. For this reason the soundness of the mortar

was questioned on the possibility that there might be ingredients which could cause an expansion. The values for magnesium oxide reported under laboratory tests are not considered

to be excessive and there is no evidence indicating that the

mortars initially contained ’significant amounts of free magnesium oxide. The mortar for Building llii was specified as a 1:1:6 cement-lime-sand mixture by volume and the lime was

specified to be a dolomitic hydrate made by autoclaving. See

Questions and Answers 7E in Appendix B. Assuming a 35 percent content of hydrated magnesia in ’’SuperLimoid" and

further assuming the dry weight proportions of a 1:1:6 mortar

to be the magnesia content would calculate as

2.17 percent. The 2.0 percent result from analysis is in

reasonable agreement wi-th the above value. The 2.8 percent

content of magnesia for the mortar from Building 90L|. would,

on the assumption of a 70:2[|.0 dry weight proportion of

masonry cement to sand, correspond to a 12 percent content of

magnesia in the masonry cement. This; is not unreasonable for

the masonry cement (Brixment) in question. It should be remarked that no reports of excessive expansion attributed to

either "Brixment" or the use of pressure hydrated lime have

been received.

On the basis of available information the difference in

behavior between Building lll| and 901). cannot reasonably be

ascribed to differences in the mortars.

Foundations - A continuous vertical crack from roof

through foundation is shown on the east wall of Building I). Item 3 of Appendix A) , The west wall center of Building 7

(item 6) shows more vertical cracking in the concrete than

in the masonry. The diagonal cracking in the masonry of the

east wall of Building 12 near the south end (Item 7) could

Indicate differential vertical movement of the foundation.

The vertical cracks in the foundation are compatible with

such an explanation. The southwest corner of Building 13

(Item 8) on the other hand is free from foundation cracks

and resembles more the cracking usually associated with

volume change, A conspicuous feature of Building III4. (See

Items 16, 17, and I8 of Appendix A) was the excessive vertical cracking of the concrete foundation of the east wall,

A co'unt of the number of cracks in the 600 ft length of the

east wall of IIJ4. showed a greater number of cracks in the

fo-undation than in the masonry superstructure. Some

of the foundation cracks were continuous with cracks in the

masonry and other cracks were unrelated.
Photograph No, 2 made September 21, 1953, shows a fine

crack in the foundation of Building 90i|. indicated as in the

west side at about the center approximately midway between

the two expansion joints ( 7A of Appendix B) . The crack extends upward into the block masonry for four courses. This

was either overlooked during the previous inspections or had

developed subsequently. It is the only foundation crack in

90l|. as far as known.

The differences in extent of foundations cracking between Building 9014. compared with Buildings Lj., 7, 12, and III4. (lll4 being the most conspicuous with respect to foundation

cracking) would indicate the possibility of foundation trouble

as one of the causes of the variation in extent of masonry

cracking. The rock near the surface shown in photograph

10980 (item 20 of Appendix A) would appear to provide a good

base for the footings of Building 904. A hearsay statement

was received to the effect that Building III4. was in part on

the site of a former pond or bog. Questions and Answers 70

(Appendix B) reports for Building 111].. "North half of east

wall shows additional excavation for depth of wall footings

on solid earth bearings. No record of any former bog or lake.” For Building 90I4. the record reports "solid earth and

rock foundations for footings." Rerunning of levels on finish

foundation walls were requested for bo'th buildings ( 6C ) . This

was done for Building 90l|. and no deviation of grade was found

but for III4. either levels were not run originally or no records

were available, hence deviations, if any, are unknown.

An argument against foundation settlement from soil conditions is the remarkable freedom from cracking of the claybrick masonry in the general vicinity of the concrete block

structures. The load on the foundations should, however, be

greater for the all block super-structures in comparison with

the wood frame super-structures.

Thought was given to the possibility of lateral flow of

soils under loading. See Questions and Answers 3A of

Appendix B. While not impossible, no evidence was provided

pointing to such an action. A 2000 psi concrete was specified for the footings and foundation of Building 111; and

2500 psi for 904. No admixtures were used in either concrete.

No information on source or grading of the aggregate for the

III4 concrete was available. Questions and Answers 1C gives

available information for 904

.

7 .
Differences in reinforcement of the foundations and footings of the two buildings (2c) do not appear to be significant.

Building 9014- had two expansion joints in each of the

I4.OO ft lengths. (120 ft each from the ends). Questions and

Answers ?A give the following information of Building 1114.

''’No expansion joints in any foundation or masonry block

walls,” and "Insufficient expansion joints in reinforced concrete foundation walls."

Freezing did not occur at early age on either concrete.

There does not appear to be any significant difference in exposures and early history.

In summary, the extent of cracking in the concrete

foundations of Building lllj. points to possible settlement of

the foundation. Absence of expansion joints in the building

might be the explanation considering volume change resulting

from changes in temperature and in moisture content. See

Appendix C for discussion of these factors. Movements in the

concrete foundation is one of the probable contributing causes

of cracking of the concrete masonry.

Design - The superior performance of Building 90I4- may

have been helped by the concrete block masonry being two

wythes in thickness, consisting of alternate reversed courses

of 8-in. widths. Building III4. was built of a single

thickness of 12-in. wide blocks. See Questions and Answers

2A of Appendix B.

The explanation of regularly spaced vertical cracks as

in the north end of Building 5 (Item 5 of Appendix A and

Questions and Answers Lj.A of Appendix B) also probably Building 9 and in the walls of Building llli. (Item lii and Questions

and Answers 2A) is that shrinkage of the blocks took place and

steel columns (Building 5 ) or pilasters (Building lli|) occur

at these locations. Note also the cracks associated with

anchorages on Building III4. (Items 10 to 13). It will be

noted as far as can be determined from the photographs, that

these straight vertical cracks do not extend down into the

concrete foundations. It is considered that the location of

such cracks result from design and could have been avoided by

suitable control joints and horizontal reenforcement. That

cracks resulting from shrinkage tend to occur when there is

a change in cross section is generally recognized. Reference

is made to Section 5 of the attached "Requirements for concrete-masonry construction,” NBS Report 3079 (January 30,

1954 )

.

8 .
It should be remarked that Building 111], departed widely

in many respects from the requirements referred to above.

Building 90li- has some expansion joints and also probably complied with 3e (storage of units) of these requirements.

Effect of Dehumidifying - One of the questions asked

NBS was whether dehumidifying contributed to the cracking of

these concrete block constructions. Building Il4 ^fas and

904 was not dehumidified but there were too many other

differences to permit selection of dehumidification as a factor in causing difference in amount and degree of cracking.

With a vapor barrier on the inner face of the masonry, it is

hard to see how moisture could be drawn in from the masonry.

On the other hand, there might be weather conditions in which

the moisture gradient was reversed. This would not seem a probable initial cause of cracking but might have something

to do with continuing cracking once it had started. This is

in line with the well known relation between degree of

saturation and effect of freezing and thawing, other things

being equal.

The conclusions from the data and observations considered in the foregoing discussion are presented at the beginning of this report.

10.1

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APPENDIX A

OBSERVATIONS AND COMMENTS ON PHOTOGRAPHS OF

BUILDINGS OP NAVAL SUPPLY DEPOT, MECHANICSBURG, PA,

PHOTOGRAPHS TAKEN JUNE 6, 1952,

(1) Building #3 N.E, corner, Photo 1085(G ) Cracks extending down from cantilever beams. Diagonal

at top and straight without regard to mortar joints below.

Diagonal and straight cracking around lintel of door,

(2) Building #4 end. Photo 1087(G)

Essentially straight cracks from roof to base. One

crack lined up with one end of lintel over door,

(3) Building #l|,East wall. Photo 1092(G)

Two cracks starting at roof. One continues through concrete. This one started as diagonal through mortar joints

for first four courses below roof and thereafter goes straight.

The other started straight at roof and not quite half way

down started to follow mortar joints to the right in a diagonal pattern. Below, the crack continued straight in line

with the straight crack above. According to the photo, the

crack disappeared before reaching the concrete.

(1-I-) Building #[(, East wall N. center. Photo 1095(G)

Picture apparently shows paint failures. If there is

any structural cracking it is not visible.

(5) Building #5? North end. Photo 1090(G)

Uniformly spaced straight cracks from roof to base.

Horizontal joints involved only at top and in connection

with openings. Resembles Bldg. #l\. N. end (2) but differs in

uniformity of distance between cracks. Suspect that has

columns or possibly abutting partitions behind these cracks.

(6) Building #7, West wall center, Photo 1080(G ) Except for cracking at ends of lintels and under sill of

left of two windows, the picture shows more cracking in concrete than in masonry. Is not this wall just across the

street from brickwork (600 ft) which shows no visible cracking?

1 .
C7) Building #12, East wall near S, end, Photo 109l4-(Cj)

Diagonal cracking of masonry combined with related and

unrelated cracks in concrete might result from settlement

with resulting vertical shear.

(8) Building #13i S.W. comer. Photo 108l4.(G)

The right hand crack appears to line up with the inner

face of the other wall. This is a common location of cracking on masonry where volume change is occurring. The diagonal cracking to the right of the down spout and the

horizontal cracking between masonry and concrete might indicate a horizontal shear. The concrete does not appear to be

cracked according’ to this’ photograph.

(9) Building #ll4.. South end, Photo 1093(G)

Cracking pattern consists for the most part of vertical

lines from roof to base usually not including horizontal

joints. The cracks resemble those shown in Items (2) and (5).

Item (9) differs from Item 2 in being more frequent and in

having vertical cracks on both sides of openings. The difference from (5) is lack of uniformity in distance between cracks

and also in having more relation to openings.

(10) Building #lllt-, West wall, Photo 1096(G)

Association of vertical cracks at roof line with anchorages of supports for permanent awning will be noted. Below

the awning these cracks displace diagonally to the right and

then continue down vertically with some tendency to show

parallel doubling. Note the increasing displacement of the

vertical cracks below the awning in relation to the cracks

above from left to right. Whether the platform shows cracking associated with the masonry cracking is not distinguishable in the photograph. Compare (10) with (fl) . Also (11).

(11) Building #1114., West wall, center, Photo 1082(G-)

Another portion of the wall shown in (10), The same

origin of cracks above awning is evident as in (lO). The

cracks differ in being more diffuse (tending to branch and

give parallel cracks) and in the location of short cracks

between the principal cracks at anchorages. The displacement

of cracks below the awning does not appear in photograph (11).

Appendix A

2 .
(12) Building West wall, Photo 1097(G)

Another portion of wall shown in (10) and (11). Cracking above awning corresponds in location and appearance to

(11). The three types of cracking (diagonal following joints,

straight vertical and diffuse) are shown in this view. The

unusual feature of figure 12 is that none of the cracks

above the awning extends below. The only cracks appearing

below the awning are two short (6 courses) straight cracks

on both sides of the large door.

(13) Building #lll|-, West wall. Photo 1086(G)

Still another portion of the wall sh'own in Nos, (lO),

(11), and (12), The peculiarity of the pattern is (a) that

two out of five cracks visible above the awning do not extend

down to the awning and (b) there are only two continuous

cracks below the awning. In one case a crack extends half

way down from the awning and in another the cracks start

half way down. In the third case, the picture does not show

any continuation of the crack below the awning. This absence -of cracking is along the door on the right.

(1L|.) Building #lll4-, S, E, corner. Photo 1099 (<j)

Essentially straight vertical cracks from roof to

foundation. Regularity of spacing might indicate some design feature (columns). Note short cracks around ends of

lintels and a few short cracks extending up from concrete

foundati;on„ If the concrete is cracked, it is not evident

in the photograph.

(15) Building #llLt-, North end, Photo 1091(G)

The origin of all vertical cracks extending from roof

to foundation is with one exception the vertical offsets of

the parapet. This exception is the crack midway between the

two center parapet offsets. Several short cr.acks extend

upward from the foundation. The usual vertical cracking is

associated with openings,

(16) Building #lll|-. East wall. Photo 1083(G)

Thjis, with the exception of some cracking seen in

No, (8) and above the awning in Nos. (11) and (12) shows a

different type of cracking. Note (a) the parallel cracking

in the two roof-t o-f oundation cracks; (b) the reversal of

diagonal cracking to the right of the lower opening; (c) the

pattern above and around the upper opening (lintel); and

( d) the vertical cracking in the concrete foundation.

Appendix A

3 .
(17)

Building East wall^ Photo 108l(G)

The straight vertical cracks are short (6 to 8 courses)

and are confined to locations immediately below the roof and

below window sills, and along the ends of lintels. Cracks

otherwise follow joints. Diagonal cracking above lintels

and extending down right and left (inverted V) to both ends

of lintels is conspicuous. Caulking (remedy for cracking)

has been applied over the entire length of the bed joint between the first and second courses of block above the lintels

A conspicuous feature of this photograph is the number of

vertical cracks in the concrete foundation. A count was made

of the cracks in the 600 ft length of the east wall of Building #1114.. The cracks in the concrete exceeded in number thos

in the masonry. This is the only photograph showing horizontal cracks through blocks.

(18) Building #llli. East wall. Photo 107Q(G)

The greater number of vertical cracks in the concrete

foundation compared with the number in the block masonry will

be noted. The cracking in the masonry follows a "delta"

pattern (single cracks going straight and then branching into

a number of parallel or diverging cracks.

(19) Building N. E. corner. Photo 1088(G)

According to this photograph, the brick masonry is entirely free from cracks. This is in agreement with observation of another building having a 6'00 ft length of brick

mas onry

.

(20) Excavation for Tank Farm Addition, Photo 1098(0-)

This shows soil conditions in the vicinity of Building

#904 which is characterized by minimum cracking.

Appendix A
APPENDIX B

Questions and Answers on Design, Construction, History

and Materials of Buildings II4 and 904

Subsequent to the inspection made on July 16, 1952, by

Messrs. McBurney and Fishburn, information was secured from

various sources and study had been given to the photographs.

The following questions are intended to provide further information and to check the correctness of information from

unofficial sources. Most of these questions deal with Buildings lli| and 9OI4. since these two buildings represented the extremes of condition when inspected in July 1952.

For convenience. Commander C, E. McCrorey*s reply of

July 6, 1953, is combined with the questionnaire.

A. Questions on Design

lA . Quest! on

What are the dimensions,, length, breadth, height,

and thickness of masonry in llii compared with 90I4.?

Answer

Building ll4

Length - 602’ 8”

Width - 202' 6"

Height - 26’ 8 l/2" - eaves

Wall Thickness 1’

gable

Building 904

Length - 4^2’ 8”

Width - 202’ 6"

to bottom Height - 21’ 2”

Wall ) Height at Thick-) - 1’ l/2”

ness ) 2A . Que s t i on

Are there any differences in design (pilasters,

columns, roof, partitions, etc.) between these two buildings?

Answer

Building ll4

The walls are of masonry block construction - block

size - 12” wide I6” long 8” thick with 3 hollow cells in

each. Pilasters of masonry block 32" long and 1’ wide

1 ,
Appendix B

spaced on 20’ centers for side walls and 2 pilasters on

end walls and fire walls - spaced 66’ centers or l/3

points of wall and backed up by exterior wall. These

masonry block pilasters were reinforced by 8 - 3/il" reinforcing steel rods and cells filled with concrete - then

topped off with 6 courses of brick to receive steel

trusses, with the exception of the 2 pilasters in end

and fire walls where the other structural steel is bearing on 12” exterior end walls and on fire walls. All interior and Intermediate columns are H beam steel columns.

There is no expansion provided in concrete foundation wall,

masonry or roof steel.

Building 901;

The walls are of masonry block construction. These

masonry blocks came in two sizes, one 8” x 8” x 16” and

one 8" X 4" ^ 16”, 3 cell block and laid in alternate

courses 8” x then I4." 8”. The steel columns are

built-in masonry side, end and fire walls. Brick masonry

is used around all columns on all exterior walls and

keyed in masonry block construction. Expansion joints are

provided in the exterior side walls, where the 2 - fire

walls join same and extend from top of concrete footing

to roof. There is no expansion in ends or fire walls.

3A. Questl on

Describe the floors in 114 socid 904 with respect to

material, support and base, and relation to foundations.

Could there be floor loading such that flow of soil under

the floor might take place?

Answer

The floor in Building Il4 is concrete throughout,

laid on graded earth. The concrete was type C-1 2,000

psi 6" thick, with no reinforcing *«*other than over the

under-floor heating ducts, which run along the entire

perimeter of exterior walls. One-half inch expansion

joint is provided betweeen all walls and floor slabs.

-^-Addendum to Spec, deleted 6x6x10 reinforcing steel

in lieu of substituting 6" concrete thickness for 5"

thickness with reinforcements. Suggestion made by A & E

contractor and approved by ROinCC

.

2 .
Appendix B

The floor of Building 90i| is 6x6x10 mesh concrete

throughout, laid on 6" compacted sand and gravel fill.

The concrete is type P-1, 3,500 psi reinforced with 6x6

wire mesh. Expansion joint is provided betwepn all walls

and floor slabs.

l\.A . Quest! on

Are the regularly-spaced cracks on the north end of

Building 5 related to the presence of pilasters, columns,

etc. at the location of these cracks?

Answer

The regularly spaced cracks in North wall appear 20

feet on centers where steel columns are built in masonry

block walls.

5A. Questl on

Is there any horizontal reinforcement in the masonry?

Answer

Pencil rods only where steel columns are blocked in

masonry walls.

6A . Questl on

What is the design of the lintels?

Answer

Building nil has 6 12’ wide x 12’ high overhead door

openings in each side-wall, total of 12. The end walls

each have 2 overhead door openings size 12’ wide and 13’

high, total of 1| doors. The lintels over overhead doors

on street side are 2 ’9” x 1’ x ll| ’ reinforced with 6 3/i|"

0 rods, hooked ends, 3 top and 3 bottom and tied with

l/i|” (/ rod ties 12" O.C.

The window lintels above overhead doors on street

side are 1’ 9" x 1’ x ll| ' reinforced with 6 3/4" rods,

hooked ends, 3 top and 3 bottom and tied with l/l|" /

rod ties 12" O.C.

The end wall door lintels are 2’ 6" x 1’ x 13’

reinforced with 6 3/i|" / rods, hooked ends, 3 top and

3 bottom and tied with l/i|" / rod ties 12" O.C.

3 .
Appendix B

The lintels over overhead doors on railroad platform side are 3 ’ 6 " x 9

" x li|> reinforced with i|

0 rods, hooked ends, 2 top and 2 bottom and tied with

lA\-" 0 "tie rods 0,G.

The window lintels over these doors are 1 » I4

. l/2"

X 1» X li|* reinforced with 6 3/k" 0 rods, hooked ends

and tied with l/ii" 0 tie rods 12" O.C.

Type C-1 2,000 psi concrete used (Y’D Spec. 13YC)

.

Building 90I4

. has 3 12' x 12' overhead doors on each

side of building, total of 6 , and one 12 ' wide x 13 ' l|- 3/l+" high overhead door in each end wall, total of 2

doors

.

All overhead door lintels are 2'l/2" x 1' x IJ4

.

reinforced with 6 5/8 "/^ rods, hooked ends, 3 top and 3

bottom and tied with I/4 " 0 rod ties 12" O.C.

The window lintels over these doors are 1 ' I|.-l/L|."

X 1' X llj. ' reinforced with L|.-5/8" (/ rods, hooked ends,

2 top and 2 bottom and tied with 1/L|." 0 tie rods 12" O.C.

Type D-1 2,^00 psi concrete used.

?A. Quest! on

What is there with respect to expansion joints in

the masonry?

Answer

Building Ilk.

No expansion joints in any foundation or masonry

block walls. Insufficient expansion joints in reinforced

concrete foundation walls. Lack of horizontal reinforcing and expansion joints in masonry block walls.

Building 904

Expanslon joints in foundation walls and masonry

block walls from footing to roof in exterior side walls,

2 on each side 120 ' from end walls, (where fire walls

join exterior walls). Total 4 expansion joints in entire

building walls. No expansion joints in end walls or fire

walls

.
Appendix B

B. Questions on Construction

IB . Ques tl on

What were the dates of beginning and completing construction of III4. and 90[i-?

Answer

Building lll^. - Date started - approximately 1st week

August I9I4-I4-; date finished 3rd Peb . 19k ^

All foundation walls and block walls completed before

6th Nov. 194-^ as shown on Progress Photograph No. ^9-14-95.

No other records available.

Building 904 - Date started - May 28, 1947? date

completed 11 Jan, 1949. Concrete foundation started 24

July 1947; concrete foundation completed l5 Oct. 1947.

Masonry block started 12 Nov. 1947; masonry block completed 10 Apr. 1948.

All concrete foundation walls were 2-1/2 to 3 months

old before any masonry block walls were laid on same.

2B . Question

Is a log of weather conditions available for these

construction periods? If so, can an abstract be furnished or made available?

Answer

Buildings 114 and 904 - Log available - can be furnished. Weather records requested from Weather Bureau.

C. Questions on Foundations, Footings, and Soil Conditions

1C . Question

What was the concrete mix used for footings and

foundations for II4 compared with 904 (proportions,

nature and source of aggregates, admixture If any)?

5.
Appendix B

Answer

Concrete mix and proportions.

Building III4

. - Concrete mix Y&D Spec, 13 Y.C. T 3rpe

C-1 2,000 psi. Mix of aggregates - No record. No admixtures used.

Building 90lj. - Concrete mix Y&D Spec. 13 Y.C. Type

D-1 2,^00 psi, 489 lb cement - 1302 sand - 1952 - wash

gravel

.

Fine Aggregate

Total Passing

Square Openings

Course Aggregate

Total Passing

Square Openings

3/8 in 100^

#4 93^

#20 56^ #50 15^^

#100 5 . 3^

1 l/k in 100^

1 in 96^

1/2 in 41^ #4 3fo

No admixtures used.

2C . Que s t i on

What was the nature and degree of reinforcement in

the footings and foundations of Il4 compared with 904?

Answer

Building II4 - Footing and foundation reinforcing.

Horizontal l/2" c 12" o.c.

Verticals 1/2" jZ) c 12" o.c.

Footing is 1» 8" Walls are 1’ 0" 2" x 4" key

Building 904 - Horizontal 3/8" / longitudinal, 5/8"

Vertical°V8" 0 at I 8 " o.c.

3/8 " / at 12"c,c. both faces of

foundation wall running horizontally.

3C . Que 3 1 i on

Were the footings and foundations subject to freezing at early ages? At what age of the foundation was

the masonry superstructure started and at what age

fini shed?

6 .
Appendix B

Answer

Building lll|- - The footing and foundations were not

subject to freezing. Masonry block walls started last

week of August and completed about 6th Nov. 1944 • Building 904 - The footings and foundations were not

subject to freezing. Masonry block walls started 12 Nov

1947 and completed 10 Apr 1948 • Concrete footings and concrete foundation walls

started 24 Jul 194?> completed l4 Oct 194?

4C . Question

At what age was cracking of the concrete foundations

of 114 first noted?

Answer

Building 114 - No record available but some time in

March after north wall building Oil collapsed, 23 Peb

1945.

5C . Que s t i on

Is there any evidence of vertical shear along any of

the vertical cracks in the foundations of Building 12

(see photo 1094 ^ January 6, 1952)?

Answer

No vertical shear apparent.

6C . Questl on

Were reasonably accurate levels run on any of these

foundations (particularly 114 ) before masonry was started?

If so, could levels be rerun?

Answer

Building II4 - Unknown - Levels could not be rerun.

Building 904 - Finish foundation wall levels run and

no deviation of grade found.

7 .
Appendix B

7C . Quest! on

According to report, Building III4. is located on the

site of a former bog or lake and 90l|. is on bed rock close

to the surface. Are these statements true?

Answer

Building III4. - Prom data of field books the North

half of East wall shows additional excavation for depth

of wall footings on solid earth bearing. No record of

any form bog or lake.

Building 90I4. - Solid earth and rock foundations for

f ootings

,

8C . Ques ti on

Along side Building 7 (?) is a glass- transite board building with brick up to the window sills. The mortar in the

brick work is reported to be Lehigh or Brixment masonry

cement, and the 600-foot length of masonry is quite free

from cracking. Are there any site or foundation differences between building 7 and the one described?

Answer

The type building mentioned has for exterior walls a

brick curtain wall sill high with a concrete sill doweled

to same. Above brick curtain wall is wood studs exterior

for window framing and cement asbestos covering to eave

of roof. The building is wood frame construction, with

wood columns spaced 20’ centers both ways, wood girders

and purlins built up to receive wood deck roof. No site

or foundation differences in buildings.

D, Questions on Concrete Masonry Units

ID. Que s t i on

According to report Building lli| uses either an

(expanded) slag block or a ^0-^0 mixture of slag and limestone. What are the facts? What block is used in 90l|.?

If the record is uncertain, a laboratory examination would

probably supply this information.

Answer

Unknown.

8 .
Appendix B

2D. Quest i on

According to report the source of the block was York

and Harrisburg and, according to one rumor, some blocks

were made at the site. Is this true? Can the different

sources of block be assigned to specific buildings, particularly lli| and 904.? Answer

Building llLj. - Source of Block 12" x 8" x I 6 " hollow

masonry units, York Building Products Company, York, Pa.

Building 904 - Source of Block, Harrisburg Building

Units Co., Harrisburg, Pa. 8" x 8" x I 6 " and 4

." ^ 8" x 16".

To our knowledge no blocks were made on Building site.

3U . Questl on

It has been stated that the block used in 114- was less

than 4- days old at the time of laying. Is this true? What

was the corresponding age at laying of the block in 904-?

Answer

Building 114- ” Unknown.

Building 904- - One to two months and protected at site

with tarpaulins.

E. Questions, on Mortar

IE . Quest! on

The 194-4-“45 specifications \mder which 114- was built

call for a 1;1:6 cement-lime-sand mortar by volume with

the lime to be the Warner Company's "Super-Liraoid" . Was

this lime actually used or was "normal" (Llmoid brand)

used? The date 194-5 seems rather early for the commercial

production of pressure hydrated lime such as "Super-Limold".

On the answer to this questl.'on would depend whether expansion of mortar is a possible factor to be considered.

Answer

Building 114. - Letter from Jamus Steward & Company and

John B. Kelly, Inc., sub -contract or - Philadelphia, Pa.

Mortar mlxl-l-6for .masonry construction.

9 .
Appendix B

Cement - Lehigh Portland Cement Co., Lehigh Valley

Mills or Unionbridge, Md.

Lime - Super Limoid as manufactured by Warner Company

from Morrisville, Pa.

Sand - Bar Sand as furnished by Warner Company from

Morrisville, Pa. approved OICC letter 29th Aug 19i|l|.

2E . Question

What mortar was specified (and used) in 90l|.?

Answer

Building 90li. - Brixment type 2 masonry cement, Louisville Cement Company of New York, Akron, N. Y.

F. Questions on Maintenance and Repair

IP o Que s t i on

What are the painting histories of 11[|. and 90I4.?

(Types and brands of paint and frequency of repainting.)

Answer

Building 111]. - 1 of 7 Buildings

Work started 1^ May 19l]-7, completed Aug 1947

Type of cement water paint Medusa, prepared dry

paint mixed at job site with water - 2 coats.

Building 90l| - Work started 12 Oct 1949j completed

21 Oct I9I4-9

Type of cement water paint. Sears Roebuck & Company

prepared dry paint mixed at job site with water - 2 coats.

2P . Quest! on

Describe materials and methods for filling cracks.

Does caulking material extrude from cra:oks? If so, at

what seasons of the year (temperature and rainfall conditions)? The answer to these questions may provide information as to cyclic volume changes in the masonry.

10 .
Appendix B

Answer

Before paint was applied all cracks up to 3/l6" were

cleaned and filled with masonry caulking compound. Where

loose mortar appeared and larger cracks than 3/l6” were

found same was raked out and new mortar replaced. Seems

to push out in winter months.

3F . Question

If the caulking is renewed from time to time ( time

intervals), is the renewal required by failure of the material or change in the cracks?

Answer

Regular caulking compound was used at first but dried

out and shrunk leaving openings. Approximately 2 years

ago this was replaced with a pitch type caulking which has

given no trouble up to the present time.

IpP . Question

What is the nature and thickness of the vapor barrier

on the inside of ll4? Does this require renewal or repair? Does 90I4. have a vapor barrier and DH?

Answer

Building llLj. - Thickness of vapor barrier ranges between 1/32” and 1/16". Primer is cutback asphalt - Plintkote #267. Sealer is Plintkote C-13-HPC stable non- flowing

asphalt emulsion (non-fibrated)

.

Building 90I1. - None - No dehumldlfi cati on.

G-, Questions on History of Cracking

IGr . Question

Can a log be furnished on the cracking history of

llJL|.? If available, give age for first appearance of

cracking and subsequent changes with time, noting also

any changes such as installation of DH, changes in occupancy, etc. Does there appear to be any relation between

weather (seasonal or otherwise) and formation of new

cracks or changes in width or extension of old cracks?

11 .
Appendix B

Answer

There is no log available but cracking is apparently

a progressive process. However it seems as though new

cracks are more noticeable in the spring which would indicate some frost action as far as the widening of the cracks

is concerned. The pattern does not seem to change, regardless of changes in occupancy or Installation of D/H,

2G , Qnestl on

At what age did cracking first appear on 90l|? Have

these cracks changed with age?

Answer

Building 90L|. - Cracks appeared only .on 1 side of concrete overhead donr lintels and extend upwards. On side

walls and 1 side of concrete overhead door lintels on end

walls. These end wall doors are offset 2* from center

line of wall and crack is in center of wall extending to

top of wall and about l/2 way down in door opening. There

are no cracks in concrete foundation walls at these locations. These cracks appeared three to six months after

walls were erected. The cracks are small and there is no

noticeable change in same.

These solid concrete reinforced lintels weigh approximately 3,000 to 3,800 pounds each, and do not carry any

appreciable superimposed loads - therefore, could be hollow

thus lightening same.

12 .
APPENDIX C

DISCUSSION OF POSSIBLE CAUSES OF CRACKING

Concrete Masonry Units

Since the concrete blocks used in Building III4. and 90l|.

are reported to include limestone and cinders as aggregates,

the following discussion emphasizes the properties of these

ingredients

,

Shrinkage of Units on Drying

That concrete masonry units will shrink during drying is

well known. The amount of shrinkage depends upon a number of

factors such as (1) age of the unit (time elapsed between

forming the unit and the initial measurement), (2) method of

curing, (3) the degree of saturation (amount of contained

water) or conversely the degree of drying, (I4.) the nature of

the aggregate, and (5) the ratio of binder (portland cement)

to the aggregate. Certain other factors such as water-cement

ratio,’ grading of aggregate, and method of forming may have

an effect on shrinkage.

Considering the above factors in order, "green” blocks

(those delivered at an early age limited only by development

of sufficient strength to permit handling and transportation)

would be expected to give maximum shrinkage. Such blocks

would not yet have developed much strength, and the portland

cement would not have completely reacted with the mixing

water, and the excess water would have had little opportunity

to evaporate. According to Mr. Paul Woodworth, Director of

Research and Development of the Waylite Company, the

construction at Mechanicsburg (Building lll|.) was done with

blocks not over i; days old at the time of laying.

The purpose of steam curing is to speed up the reaction

between water and portland cement and thus harden the blocks.

The usual treatment (steam at atmospheric pressure) has little

effect in drying the blocks. Pressure steam curing both accelerates strength gain and drives off moisture. There is experimental evidence that pressure steam curing reduces

shrinkage by roughly one-half compared with non-pressure steam

curing. The effectiveness of pressure steam curing in reducing

shrinkage of concrete masonry units is strikingly shown by some

data published by the Housing and Home Finance Agency (Housing

Research Paper No. 2^, "Relation of Shrinkage to Mortar Content in Concrete "Masonry. Units"). Table 6 in this paper

(copy enclosed) presents values for shrinkage of cinder block

1 .
Appendiz C

cured with high pressure steam in comparison with cinder

block cured by high temperature steam, high temperature steam

plus l50° P drying, low temperature steam, and moist air.

Drying to moisture and volume equilibrium took place at 70

and at 2^ percent relative humidity on resaturated blocks.

Curing with high pressure steams gave shrinkage (linear) of

from 0.016 (70^ RH) to 0.026 percent ( 2^^ RH) compared with

O.OJ4.2 and 0,065 percent for low pressure steam cure and

0.038 and 0.062 percent for cure in moist air. The reduction

in time to reach equilibrium for high pressure steamcuring

compared with the other types of curing was very noticeable.

The degree of saturation is what the lj.0 percent limit

given in specifications (ASTM C90-[|.[j. and Federal Specification

SS-C-621) is intended to control. Obviously, a i\.0 percent

limit on degree of saturation at time of delivery (or sampling)

has no relation to condition at time of laying the blocks in

the wall if the blocks are exposed to weather subsequent to

sampling. A more pertinent test would appear to be setting

limits on the total shrinkage resulting from drying previously

saturated specimens. British Standard BS8314--194-4 gives maximum permissible drying shrinkage of O.OI4. and 0.06 percent, for

dense and lightweight aggregate blocks respectively. The

corresponding limits, for partition blocks (BSL|.92 and 728-1944)

are 0.06 and O.O 8 percent, respectively. It is assumed that

the units after laying in masonry will not resaturate to the

degree resulting from total Immersion for several days in

water. Such subsequent saturation would occur only where very

defective workmanships or design had been used in the masonry.

Data are not available for determination of the relation of

saturation by immersion to saturation at very early ages

(shortly after "final set" of the cement, for example) in establishing volume change. Also uncertain is the choice and

comparison of drying methods in these tests. Oven drying at

various temperatures has been used. Preferred is drying by

exposure to air of controlled low relative humidities. As an

example of this type of drying, see data from Kluge, Sparks

and Tuma presented as part of the discussion of effect of

aggregate. Copy of this paper ‘’Tjightweight-Aggregate Concrete" is enclosed. The data in HHFA Housing Report No. 25

give comparisons of initial moisture content and shrinkage

compared with moisture contents and shrinkage determined on

resaturated block.

The differences in permissible shrinkage of concrete

block classified as made with dense and lightweight aggregates

by British Standards were given above. The data reported by

Kluge, Sparks, and Tuma were obtained on cast concrete which

differed from concrete used in block making principally in

2 .
Appendix C

its higher water-cement ratio. The exposure consisted of 7

days in a fog room followed by drying in air at 70° F and

relative humidity of 55 percent. Zero time was removal from

the fog room. Drying continued up to l80 days. The data on

a number of concretes differing with respect to aggregate are

presented graphically in figure 8, and the shrinkage at 100

days in inches per foot are given in Table L(. . Sand-gravel

concrete had shrunk in length from approximately 0.03 to 0.06

percent at 100 days, at which time equilibrium appeared to

have been reached.

The ranges reported above were on concretes differing in

cement factor (sacks of cement per cubic yard of concrete).

It will be noted from the data in Kluge's paper that differences in shrinkage of considerable magnitude result from

differences in cement factor but there is no observable correlation between them.

A higher water-cement ratio would obviously provide more

evaporable water and hence be associated with a greater total

shrinkage Resulting from removal of water. This is in accord

with the well recognized effect of additional water on the

shrinkage of mortars and concretes cast in non-absorbent

molds. The method of forming of concrete block is in their

favor compared with poured concretes since a relatively low

water-cement ratio is used in block making. Note that the

shrinkages reported in HHPA Housing Research Paper No. 25 on

commercial block are very small in comparison with the shrinkage on concretes made with similar aggregates as reported by

Kluge, Sparks, and Tuma.

The large initial shrinkage of concrete units is usually

associated with the large initial loss of water Introduced

during mixing. In general, submersion for a considerable

time would be necessary to recover by expansion the original

volume (length) measured before drying. Reversible volume

changes, small in magnitude compared with the shrinkage resulting from initial drying, take place with changes in relative humidity of the ambient air. Changes in moisture content

and resultant volume changes resulting from wetting by rain

are also considered to be small in magnitude unless design or workmanship are such as to permit ready entry of water into

the masonry.

In summary, shrinkage of concrete masonry units (linear)

may range from 0.02 to 0.l5 percent or greater during the loss

of water contained in units before laying in the wall. The

magnitude of the shrinkage depends upon the previous history

of the block and its composition.

3 .
Appendix C

For such reasons as (1) the wide range in amount of

cracking (Building #llJi compared with Building #904 for example), (2) variations in cracking patterns from building to

building and in the same building, and (3) the reported history of continued cracking (formation of new cracks and

widening of existing cracks) there is the probability that

other factors may be operating in addition to the shrinkage

of units heretofore discussed. The following possible factors are considered. The order of this consideration is

without respect to the degree of probability of these factors

Thermal Expansion of Concrete Masonry Units

R. E. Copeland ("The Problem of Shrinkage Cracking")

reported that the coefficient of thermal expansion of typical concrete block ranged from 2.5 to 5.5 millionths inch

per inch per degree P in the range 0 to 100° P. This would

correspond to a length change of from 0,025 to 0.055 percent

for a 100° change in temperature. Corresponding data on

comparable plain concrete (expanded clay and shale or slag

aggregates in 7”Sack mixes) from Price and Cordon gave from

I4..4 to 5.3 millionths inch per inch per degree P. (In;terms

of cracking, 833 millionths inch per inch equals 1 inch in

100 ft)

.

Expansion of Concrete Block Other Than

Reversible Volume Changes Resulting From

Change in /Temperature and in Moisture Content

The probability of "alkali-aggregate" reactions occurlng

such as are assocated with certain opaline, rhyolitic, or

chert concrete aggregates in the western part of the United

States is low if the aggregates in the blocks are what they

are reported to be. Limestone and cinders have never been

reported as suspect in the alkali aggregate reaction in any

of the very considerable literature on this phenomenon. On

the basis of available data, alkali-aggregate expansion does

not appear to be a factor in the performance of the concrete

block under consideration.

Volume Changes of Mortar

Various investigators have reported values for the

shrinkage of mortar. These data have, with few exceptions,

been determined on specimens cast in non-absorbent molds and,

in general, the earlier the age of the initial reading, the

greater the shrinkage subsequently measured. The few volume

change measurements which have been made on masonry (brick)

indicate, however, that slight expansions (linear) take place

4.
Appendix C

rather than shrinkage. See enclosed paper by McBumey on

^Cracking in Masonry Caused by Expansion of Mortar" for a summary of the findings of Davis and Troxell together with

a discussion of mortar shrinkage as a factor in cracking.

The explanations of the discrepancy between the volume

change of mortar cast in non-absorbent molds and the volume

change of masonry is considered to be that mixing water is

removed from mortar by contact with absorbent units while

the mortar is still plastic. Since shrinkage of mortar, as

with concrete block, results from removal of water, there

is, under these conditions, a very low water-cement ratio

at the time when the reactions of setting and hardening beginj and this small amount of water for the most part reacts

with the constituents of portland cement rather than being

lost through evaporation or other means for removal from the

mortar

.

McBurney's paper considers in detail the abnormal expansion of mortar and its consequences resulting from the

presence of free magnesium oxide (MgO) in mortar. The specifications (1944”^) covering concrete block construction at

Mechanlcsburg call for 1:1:6 cement-lime-sand mortar by

volume and require "Limoid" or "Super Limoid" made by the

Warner C omp any' 6f Philadelphia to be the lime. This brand of

lime is understood to be a dolomitic hydrate, but the Super

Limoid refers to that company’s autoclaved lime. If Super

Limoid were used, cracking from the use of unsound mortar

ingredients can be dismissed as highly improbable. Neither

does there appear to be grounds for assuming the presence of

soluble sulfates which might react with mortar to cause expan

si on.

Foundati ons

One of the unverified reports dealing with the Mechanics

burg Depot was that Building Il4 occupied the site of a pond

or bog, and the excessive cracking of the foundation and

superstructure of this building could therefore be ascribed

to foundation settlement. The lack of cracking in Building

904 is correspondingly ascribed to bed rock outcropping on

and near the site. See photograph No. IO 98G showing excavations near Tank Farm.

Weathering

The effect of such factors in weather as temperature

change fmd precipitation has been previously discussed in

part. Freezing and thawing remains to be considered from

the standpoint of this action' s

• effect on cracking. From

5 .
Appendix C

observations of units during laboratory freezing and thawing

and of masonry exposed to natural weathering, it is concluded

that one effect of repeated freezings and thawings is to open

up and extend previously formed cracks. The accepted explanation of this action is that water expands about 9 percent

in freezing and therefore exerts pressure, if the body during--

freezing is saturated with water. There is the further possibility that dehuraidifi cation may, under certain climatic conditions, reverse the saturation gradient in masonry and build

up saturation beyond what would normally occur without dehumldification. In any case, the reported continuation of cracking could result either from continued action of the factors

causing the original cracking or from the frost action discussed in this paragraph.

Enclosures

Housing Research Paper No. 2^, "Relation of Shrinkage to

Moisture Content in Concrete Masonry Units," Housing and Home

Finance Agency.

R, W. Kluge, M. M, Sparks and E. C, Tuma "LightweightAggregate Concrete,” Reprint Title No. i|-5”37 of the American

Concrete Institute.

J, W. McBurney "Cracking in Masonry Caused by Expansion

of Mortar," 19^2, Reprint American Society for Testing

Materials

.

NBS Report 3079, "Requirements for Concrete-Masonry Construction," (January 30 , 195^).
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