-£y C Ir*'

NATIONAL BUREAU OF STANDARDS REPORT

6321

Pinal Report on Tests of Prestressed Cellular Slabs

(Series of Slabs Nos. 1 through 29)

by

Arthur P. Kirstein

Report to

Bureau of Yards and Docks

Department of the Navy

U. S. DEPARTMENT OF COMMERCE

NATIONAL BUREAU OF STANDARDS
THE NATIONAL BUREAU OF STANDARDS

Functions find Activities

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maintenance of the national standards of measurement and the provision of means and methods

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

MM PROJECT MBS REPORT

1001-12-4811 February 24, 1959 6321

Final Report on Tests of Prestressed Cellular Slabs

(Series of Slabs Nos. 1 through 29)

by

Arthur F. Kirstein

To

Bureau of Yards and Docks

Department of the Navy

IMPORTANT NOTICE

HATIOMAl BUREAU Of

Intended for me within '

to additional evaluation s listing of thk Report* eitl the Office of the Director however, by the Governs

to reproduce additional c ,

Approved for public release by the

Director of the National Institute of

Standards and Technology (NIST)

on October 9, 201 5.

or progress accounting document!

is formally published it Is subjected

ting, reproduction, or open-literature

irmisslon Is obtained In writing from

. C. Such permission is not needed,

call; prepared If that agency wishes <NBS>

U. $. DEPARTMENT OF COMMERCE

NATIONAL BUREAU OF STANDARDS

Final Report on Tests of Prestressed Cellular Slabs

(Series of Slabs Nos. 1 through 29)

Arthur F. Kirstein

This report presents a summary of the findings in

the study of the properties of twenty nine 5>- by 5-ft

prestressed cellular slabs tested under concentrated

loads. Deflections, strains, crack patterns, and loadcarrying capacities were recorded. The data reported

herein indicate that the primary mode of failure is

diagonal tension, that suitable jointing material between the units is necessary, that web reinforcement

of the units is required to increase the load-carrying

capacity of the slabs, and that the proper selection of

jointing material is important.

1. INTRODUCTION

At the request of the Bureau of Yards and Docks, the

Structural Engineering Section initiated a study of the proper

ties and behavior of prestressed cellular slabs subjected to

"punching” shear tests.

This is the final or summary report of this investigation

which includes the study of a series of prestressed cellular

slabs composed of six types of cellular units. Many variables

were introduced to cover a broad scope and to develop a slab

that could support a fairly large concentrated load at midspan

These variables were type and arrangement of units, jointing

materials, amount of prestress, and method of supporting the

slabs

.

2. DESCRIPTION OF TEST SPECIMENS

2.1 Cellular Blocks

Six types of cellular concrete blocks were examined in

this investigation. They were designated as Preload blocks,

unreinforced NBS blocks, stirrup reinforced NBS blocks, NBS

blocks reinforced with welded wire fabric, clay tile, and

pavement blocks. The principal dimension of these blocks

are shown in figure 1.

2 . The Preload blocks were 6-in. cubes having an opening

4.5- by 5-in. in cross section. There was a 1- by 2-in.

elliptical hole in each web through which the prestressing

unit could pass. The outside dimensions of those blocks

that were selected at random for measurement were found to

vary as much as l/8 in. from the specified dimensions. The

reinforcement in the blocks consisted of a single layer of

1- by 1-in. galvanized welded wire fabric of 15/15 gage.

These blocks were furnished to the National Bureau of

Standards by Preload Corporation which had procured them

from a commercial concrete products plant. Therefore, the

proportions of the concrete mix used in the blocks are not

known. However, a 3/4~ by 2- by 6-in. strip of concrete was

removed from one of the blocks aiqd was tested to determine

the modulus of elasticity, Poisson’s ratio* and the compressive strength of the concrete. Both static and sonic tests

were performed on this specimen which yielded an average

modulus of elasticity of 2.74 x 10° psi. The compressive

strength and Poisson's ratio were 4710 psi and 0.12 respectively, as determined by the static test.

The three types of NBS blocks were hollow 6-in. cubes

having an opening 4*5- by 4*5 iti. in cross section. There,

was a 1- by 2-in. elliptical access hole in each web to permit the passage of the prestressing units. These blocks

were cast in steel three-unit gang molds that were constructed to very close tolerances. The blocks made in these

forms were of superior quality and the exterior dimensions

of the blocks were within 0.01 in. of the nominal values.

The only difference between these types of blocks was in

the reinforcement of the webs. Details of the web reinforcement are shown in figure 1.

The pavement blocks were 6-by 15 5/8- by 7 5/8-in. concrete blocks with one oblong cell through the 6- by 15 5/8 in.

face. The cell, was bounded by two semi-circles of 2 l/4 in.

radii at the ends and straight lines between them. The shell

thickness was 3/4 in. One circular hole 1 in. in diameter

was made in each 6- by 7 5/8-in. face concentric with the

center line of the 7 5/8 in. sides and tangent to the center

line of the 6 in. sides. These holes accommodated the passage

of the prestressing tendons.

3.

The NBS type blocks and pavement blocks were made of a mix proportioned of one part type III cement and three parts

of sand, by weight, with a water-cement ratio of 0.57* This

mix had a 7-day compressive strength of approximately 6000 psi

as determined by tests of 2-in. cubes. However, the actual

units were moist-cured for a considerably longer period of

time and then some of them were put in dry storage before being assembled into slabs. Therefore, the compressive strength

of the concrete in the individual units should be expected to

be somewhat greater than 6000 psi.

Additional tests were conducted on the concrete to determine the Young’s modulus and Poisson’s ratio. Axial compression tests were made on columns of three blocks that were

grouted together in such a fashion as to make the direction

of the loading coincide with the axis of the cell. Sonic

modulus tests were also performed on 0.75- by 0.80- by 6-in.

strips that were cut from the cellular blocks. The results

obtained by both methods indicated an average Young's modulus

of 4 x 10 ° psi with a variation of - 10 percent. Poisson’s

ratio was found to be approximately 0.15.

The cellular clay tile blocks were made of a high grade

vitrified clay by the Federal Seaboard Terra Cotta Corporation.

The principal dimensions of the tile blocks were approximately

the same as those of the NBS blocks except that the tile had

circular Instead of elliptical holes in the webs. The tile

blocks had a good texture but the overall dimensions varied

as much as l/4 in.

Several of the clay tile were tested in axial compression

with the load applied in the direction of the cell. The average compressive strength was approximately 12,000 psi. The

typical st res s- st rain relationship for this was essentially

linear up to the failure load an yielded a Young’s modulus

of 4.4 x 106 psi and a Poisson’s ratio of 0,l5* Even though

the tile exhibited a compressive strength that was approximately twice that of the concrete, the tensile strength was

presumably not much greater than that of concrete.

4 . 2.2 Prestressing steel

Two types of steel bars were used as prestressing tendons

in this investigation. They were "Stressteel" and "Elastuff"

bars that were 5/8 in. in diameter. The anchorage for these

bars consisted of hexagonal nuts 1 l/l^-in. long which bore on

5 3/4“ by 5 3/4“ by 3/4“ in* anchor plates.

The tensile strength of unthreaded Stressteel bars was

found to be 163,000 psi, whereas threaded bars supported by

fully tightened nuts developed a tensile strength of 152,000

psi. The yield strength of this steel as determined by the

0.2 percent offset method was 142,000 psi. The stress-strain

characteristic was a straight line up to 65,000 psi, giving

a Young’s modulus of 30 x 10® psi; the secant modulus at

100,000 psi was 28.2 x 10^ psi. The reduction in area at

the point of fracture was 35 percent.

Tensile tests of the Elastuff steel indicated a stressstrain relationship that was essentially linear up to 95*000

psi, and exhibited a Young’s modulus of approximately 30 x 10®

psi. The yield strength of the bar was found to be 120,000

psi as determined by the 0.2 percent offset method and the

tensile strength was found to be 133*000 psi. Although

Elastuff bars are made of cold-worked high carbon steel, they

are fairly ductile and can be machined easily.

2.3 Description of prestressed slabs

The nominal dimensions of each slab containing 100 cellular blocks were 5 ft by 5 ft by 6-in. The arrangement of the

blocks in the slabs of this investigation are described as "crisscross”, and "aligned”. The crisscross assemblies contained blocks arranged so that the axis through the open ends

of one block was perpendicular to the axis of each adjacent

block, while the aligned assemblies were arranged so that the

axes through the open ends of all blocks were parallel. Both

assembly arrangements positioned the holes in the webs of

each block in such a fashion to permit the prestressing tendons to be staggered with respect to the mid plane of the slab.

Thus, the resultant prestressing force produced an axial compression in two directions through the slab.
°

-
5 . The principal variables in this test series were the

method of support, type of block, amount of prestress,

arrangement of blocks, and jointing material. A complete

summary of these variable factors is shown in Table 1 along

with the maximum load- carrying capacity and the deflection

sensitivity of each slab.

Most of the slabs were assembled by placing the blocks

in position on a large flat table. This method of fabrication produced slabs that were essentially flat while in the

unpres t res sed condition. Slabs Nos. 3 , 4, and 9 were assembled in two stages: First, the blocks were assembled into

5-ft beams with about l/8-in. grout joints. The beams were

then assembled together with l/8-in. grout joints between

them. These slabs became slightly warped upon prestressing

as did the slabs that were assembled without jointing material . Slab No. 25 was made of hollow pavement blocks which

were arranged as shown in figure 2 to produce a slab with

the nominal dimensions of 64- by 64“ by 6-in. Auxialiary

tests of prestressed beam assemblies of these blocks indicated that they required more rigid end anchorage than that

provided by the 6-in. blocks in order to obtain 1000 psi prestress in the concrete without causing distress in the individual units. To produce a more rigid end anchorage for this

slab the 12 blocks bordering the slab shown in figure 2 were

solid concrete. All of the bars in the transverse direction

were placed one-half bar diameter above the mid-plane, and

all of the bars in the longitudinal direction were placed

one-half bar diameter below the mid-plane.

2.4 Jointing material

There were six types of joints used in this investigation as indicated in Table 1. The grout was a 1:3 mixture

of type III cement and sand and the neat cement paste was

made of type III cement. The polyester resin (Selectron

5119)"”' contained Cab-o-s il’”' , a finely divided silica, as a filler and was activated by Lupersol DDM'”' which is 60 percent methyl ethyl ketone peroxide in dimethyl phthalate.

The epoxy resin (Epon 828 )"”' was also filled with Cab-o-sil-”-

#A list of manufacturers and distributors from whom these

materials were obtained is given in the Appdndix along

with the mix proportions of the various jointing materials.

to give the consistency of petroleum jelly and was activated

with di ethylenetriamine . The epoxy/Thiokol adhesive contained

Epon 828'“, a polysulfide polymer, (Thiokol LP-3)", a resin

coated CaCO -3 (Surfex)“, Cab-o-sil-::- , and was activated with a mixture of DMP-30 and DMP-10-”- which are dimethyl aminomethyl

phenols

.

2.5 Prestressing procedure

Experience in prestressing operations indicates that it

is not necessary to apply prestress simultaneously to all

bars. Large amounts of prestress may be applied safely if

the prestressing force is applied in small equal increments

to all tendons. Approximately one-half of the prestress was

applied to the slab in small increments by tightening the

anchorage nuts with a wrench. The remaining prestressing

force was applied by means of a hydraulic jacking rig. This

final stage of the prestressing operation was accomplished

by using a suitable sequence of stressing the tendons so

that no unduly large differences in strain would be induced

in the blocks

.

The hydraulic jacking rig was equipped with a dynamometer

which had two electrical resistance wire strain gages bonded

longitudinally and two transversely on the calibrated section.

Each pair was connected in parallel and the two pair of gages

served as measuring and compensating gages, respectively. The

calibration curve for the dynamometer is shown in figure 3 .

3. TESTING PROCEDURE

3.1 Test setup

All of the slabs were tested to failure in a 600,000 lb

capacity hydraulic testing machine. They were simply supported

on a span along either two or four edges as indicated

in Table 1. A single concentrated load was applied to the

center of the slab through a 12- by 12- by 6-in, concrete loading block. Three different methods of supporting the slabs

on the testing machine platen were used. Slab No. 1 was

supported by pipe rollers that rested on 2- by 6-in.

timbers. This frame was found to be lacking in rigidity and

-”-A list of manufacturers and distributors from whom these

materials were obtained is given in the Appendix along

with the mix proportions of the various jointing materials

7.

accordingly was replaced by one consisting of 6-in. I-beams.

The frame consisting of 6-in. I-beams was used to support

all the rest of the specimens except for Slabs Nos. 5>r 7,

8, and 9. These slabs were tested on a frame made of 6- by

12-in. reinforced concrete beams supported by six 6-in. concrete cylindrical pillars as shown in figure Ip . This method

of support elevated the slabs about 5-ft above the testing

machine platen to facilitate the inspection of the crack

pattern during the load test. All of the bearing surfaces

in each method of support were set firmly with high strength

gypsum plaster to ensure intimate contact between individual

members

.

3.2 Instrumentation

The instrumentation used in this series of tests was

altered at times to make the tests more flexible and to obtain certain associated data that was peculiar to certain

specimens and types of supports. A complete description of

the instrumentation and gage location in this report is unwarranted as they have been discussed in detail In earlier

reports. Therefore, Table 2 is included to give direct

reference to the NBS Report and figure which describes the

instrumentation of each slab. However, instrumentation

diagrams for Slabs Nos. 28 and 29 are presented in this report in figures 5 and 6 respectively, since the results from

the tests of these slabs have not been reported previously.

All of the deflections of the specimens were measured

with micrometer dial gages. However, these gages were

supported in different ways to accommodate the measurement

of the deflection of slabs having two and four edge supports

The slabs having four edge supports indicated the characteristic ’’curl-up'1 of the corners and required a frame to

hold the dial gages that had a reference datum plane that

would not warp. Therefore, most of the slabs having four

edge supports were equipped with dial gage frames that used

the testing machine platen as the datum plane. A refinement

in the measurement of the deflection of slabs having four

edge supports was introduced later in the test series. In

this method of measurement the dial gages were attached to

two steel frames each of which was supported on three points

These points were located on the top surface of the slab

directly over the supports, and at the center of the support

where, theoretically, no deflection takes place. Figure 5

shows the location of the dial gages and the position of the

frame supports on Slab No. 28. The deflection measurements
'
8 . of slabs which were supported along two edges were made in a different manner. Since there is no characteristic curl-up

associated with the deflection of these slabs , the dial gages

were attached to steel angles which rested on the slab directly over the supports. Thus, the dial gages indicated

directly the deflections with respect to the supported edges

of the slab.

The variation of strain in eight prestressing tendons

in a number of slabs was measured by means of bonded wire

strain gages. Each of the eight bars was equipped with two

gages connected in series to eliminate the effects of any

bending that might take place. Pour of these bars ran through

the center portion of the slab in one direction, and the other

four were perpendicular to them. For the exact location of

these tendons see NBS Report 4951.

The strain in concrete blocks near the center loading

block was measured by eight bonded wire strain gages that

were mounted as shown in figures 5 and 6. These measurements

were made on all of the specimens except Slab No. 1.

Since it was of some interest to determine whether or

not the loading block was punched into the slab before diagonal cracks formed in the webs of blocks containing reinforcement, four dial gages were arranged around the loading block

on Slab No. 27 to determine the changes in depth of slab and

penetration of the loading block into the slab. See Table 2

for reference to a diagram and photograph of the instrumentation. Two of these gages had extensions that passed through

a hole in the top flange of the block and rested in a hole

in a steel plate cemented to the interior surface of the

lower flange of the block. These gages were expected to indicate when the diagonal cracks formed in the webs. The

other two gages were attached to the loading block and rested

on the top surface of the slab. These gages were expected to

indicate when the loading block was punched into the slab,

3.3 Test procedure

All of the slabs except Slab No. 25 were loaded at the

center of the top surface through a 12- by 12- by 6-in. concrete loading block. Since the units in Slab No. 25 were

16 -in. long, a concrete loading block 16- by 16- by 6-in. was

used to apply the load to this slab.
>
9.

The slabs were first flexed by applying a load equivalent to one increment of the loading schedule. This load

was then removed and the slab was allowed to recover for

several minutes. All gages were read at this zero load condition,- and the readings were compared with the initial zero

load readings. After this flexing procedure the load was applied in increments, and gages were read for each increment

until the maximum load was reached. The load increments applied varied from 1000 to 5000 lb for the slabs depending on

the maximum load expected and the type of measurements that

were made.

4. TEST DATA

4.1 Deflection and load-carrying capacity of slabs

Figures 7r 8, and 9> show the observed relationship between the applied load and center deflection of the slabs.

The reciprocal of the slope of the linear or elastic portions

of these curves can be considered to be a measure of the deflection sensitivity of the slabs, and is expressed in terms

of micro inches of deflection per pound of applied load

{yl/. in. /lb) . Table 1 shows a comparison of the deflection

sensitivities and the load-carying capacities of the slabs.

Since the supports did not restrict the upward movement

of the slab, the twisting moments induced by the applied load

caused a ” curl-up” action to take place at the corners of the

slabs simply supported along four edges. The amount of curlup was measured by the upward movement of the corners with

respect to some fixed datum plane. Figure 10 shows the experimentally determined relationship between the applied load

and the vertical upward displacement caused by the twisting

moments

.

4.2 Variation of prestressing force

After the prestress is applied to the slab it may diminish slowly due to the following causes: (l) readjustment

of contact of cells, (2) relaxation of steel, (3) creep of

concrete, (4) shrinkage of concrete, and (5) movement in the

anchorage. In view of the fact that the Preload blocks used

to make Slabs Nos. 1, 2, 3, and 4» were about one year old,

the shrinkage of the concrete was negligible. Since Slabs

Nos. 3 and 4 Nad grout joints,' they were monolithic structures
_
10 .

and no readjustment of cells occurred. Therefore, the loss

indicated by the decrease in strain of bars in these slabs

must be attributed to causes (2), ( 3) y and (5). The loss of

prestress with time for Slab No. 3 is shown in Table 3 • However, in the case of Slabs Nos. 1 and 2 the loss of prestress

due to readjustment of the cells was observed from the time

when the anchorage nuts were tightened by wrench. When the

full prestress was applied to Slabs Nos. 1 and 2, most of the

readjustments of the cells had already taken place but the

process continued for a few days before it tapered off. Since

SR— ip gages were installed on some prestressing bars in Slab

No. 2 these losses were measurable. It was noted that the

loss of prestress in Slab No. 2 due to its being moved from

the working platform to' the test frame constituted 25 percent

of the total strain due to prestressing.

Figure 11 shows the loss of strain in the prestressing

tendons in Slabs Nos, 5y 7r 8, and 9. The Slab No. 9 made of

clay tile exhibited an average loss of strain in the tendons

of I), percent at three days and 8 percent at seven days, while

the tendons in the concrete slabs lost 8 percent of their

strain at three days and 13 percent at seven days. It is

evident from these data that the loss of strain' in the tendons is not only a function of time but also depends on the

material being prestressed. Since the concrete blocks used

to make Slabs Nos. 5* 7y and 8, were moist-cured until they

were assembled and prestressed, a portion of the loss in

strain in the tendons can be attributed to shrinkage of the

concrete. However, the shrinkage of the clay tile slab can

be considered to be negligible.

Since the prestressing tendons were either located at or

near the midplane of the slabs, no large changes in the strain

in the tendon were expected during the application of load on

the slabs. Measurements made during the tests indicated that

in general this was the case, as a maximum loss of about 2

percent of the initial prestress was observed for Slabs Nos,

5, 7 y and 9. However, Slab No. 2 lost about 8 percent of its

initial strain during the load test. The larger loss in

initial prestress was attributed to the readjustment of

blocks, as Slab No. 2 contained no jointing material.
.
11 . 4.3 Concrete strains

The loss of strain in the concrete due to shrinkage, creep,

and readjustment of the ungrouted block of Slab No. 5 is presented in figure 12. The average loss of strain for a six day

period was 37 percent of the original strain.

Previous NBS Reports Nos. 4396, 4951* 5212, and 5714* have

presented the observed relationship between applied load and

strain in the concrete for all of the slabs in this investigation except Slabs Nos. 28 and 29. Therefore, it will suffice

to present only typical results here and the unreported results

from Slabs Nos. 2o and 29. Figure 13 represents typical results

of slabs simply supported along two edges with the blocks arranged in a crisscross fashion and prestressed to 1000 psi in

both the longitudinal and transverse directions. The observed

relationships between applied load and concrete strain are presented for Slab Nos. 28 and 29 in figures 14 and 15* respectively. The legend in figure 13 also serves as a legend for

figures 14 and 15 except that Slab No. 28 was simply supported

along four edges and the strain in the concrete cannot be considered as longitudinal or transverse.

4<4 Crack patterns

The crack pattern observed in Slab No. 24* which was constructed of unreinforced NBS blocks, was typical of the diagonal tension failures reported in NBS Report No. 5212. The top

view of the crack pattern in Slab No. 24 is shown in figure 16.

This widespread cracking of the flanges of the blocks was

accompanied by extensive crack formations in the webs of the

blocks. In contrast to this widespread cracking of unreinforced

blocks a typical top view of the crack pattern in the NBS blocks

reinforced with welded wire fabric of Slab No. 27 is shown in

figure 17. This localized punching failure around the loading

block was accompanied by only minor cracks in the webs of a few blocks immediately surrounding the loaded area of the slab.

As mentioned previously in the text, measurements were

made on Slab No. 27 to determine the punching action of the

loading block and the vertical movement of the lower flange

with respect to the upper flange in the blocks around the

loaded area. The results of these observations are shown in

figure 18. Attention is directed to the fact that the dial

gages measuring the extension of the block webs did not indicate a sudden extension in the web associated with the formation of large cracks until the ultimate load was reached and
,

*
12 . the loading block punched into the top surface of the slab.

It is realized that the measurements made with the dial

gages mounted on the loading block contain minor errors due

to the local deformation around the loaded area. However,

no attempt was made to correct these errors as they were

considered to be quite small.

5. DISCUSSION

The slope of the load-deflection curves in figures 7»

8, and 9, and the deflection sensitivities given in Table 1

indicate that a much larger deflection is exhibited by slabs

containing no jointing material. This large deflection with

load is especially pronounced in those slabs composed of the

blocks having poorer dimensional tolerances. However, when

jointing material is used in slabs composed of either the

NBS type blocks or the blocks with poorer dimensional tolerances the slabs deflect less and carry a greater load as indicated in Table 1.

In general, the data presented herein indicate that the

load-carrying capacity of slabs containing reinforced NBS

blocks can be increased by using stronger jointing materials

,

but no increased capacity was exhibited by slabs containing

unreinforced NBS blocks. This is probably due to the premature failure of the weaker webs of the unreinforced blocks.

Upon evaluation of the testing method and considering

that the manner of failure was punching or diagonal tension

failure, it is evident that assemblies of this type that are

subjected to such severe shear conditions require reinforcement of the block webs to increase the load- carrying capacity.

Figure 10 shows the observed relationship between the

applied load and the vertical upward displacement of the

corners of the slabs which were supported along four edges.

Since the upward displacement of the corners was not restricted in these tests, no measurements were made of the force

necessary to arrest this movement. If slabs of this type

are used in structures that do not permit this displacement

of the corners, the theory given In NBS Report No. 1|396

should be adequate to predict strains and deflections.

13.

As previously stated slabs of this type lose prestress due

to four major causes: (l) readjustment of contact of units,

(2) relaxation of steel, ( 3 ) creep of concrete, and (I4 ) shrinkage of concrete. The first cause is eliminated when jointing

materials are used in construction. Thus, the primary causes

of stress loss are the same for this type of construction as

for conventional post tensioned prestressed concrete.

The typical crack patterns shown in figures 16 and 17 indicate that the use of reinforcement in the block webs is very

beneficial in reducing the widespread cracking exhibited by

Slab No. 2 I4

. shown in figure 16 to the localized cracking of

Slab No. 27 shown in figure 17.

Comparison of the two curves in figure 18 indicates that

an increase in the rate of penetration of the loading block in

the slab is associated with the first measurable change in the

depth of the web of the cells adjoining the loaded area. Although these displacements appeared to develop simultaneously,

it is worth noting that the large values of penetration by

the loading block of loads approaching the maximum cannot be

accounted for by the much smaller value of extension of the

block web. It is probable, therefore, that punching shear was

the primary cause of failure in slabs of the type exemplified

by Slab No. 27.

6. CONCLUSIONS

The results of this investigation can be summarized in

the following conclusions:

1. A suitable joint material must be provided between

the blocks to ensure intimate contact.

2. To improve the load- carrying capacity of these slabs

it is necessary to provide suitable reinforcement in

the blocks to increase their resistance to diagonal

tension failures. An increase in the compressive

strength of the material cannot be utilized as long

as there is no commensurate increase in the tensile

strength.

3. All of the slabs reported herein failed in diagonal

tension or punching shear.

14 .

4. The theory presented In NBS Report No. 4396 should

he adequate to predict strains and deflections in

slabs of the type tested in this investigation when

they are supported along four edges.

5. When unreinforced NBS blocks are used to fabricate

a slab, no strength advantage is derived from the

use of the stronger and more expensive epoxy resin

over the polyester resin or neat cement paste as a jointing material.

6. The load- carrying capacity of slabs containing reinforced NBS blocks can be increased by using stronger

jointing materials

„

7. Slabs containing reinforced NBS blocks fail in a pure punching action as the four units directly under

the loading block are punched into the slab.

8. Since the pavement blocks are prone to fail by diagonal tension at low loads and since they require ^special end anchorages to withstand the prestressing

force, they were found to be unsuitable for use in

prestressed slabs of this type.

USC OMM- NBS- DC
-

.

.
APPENDIX

The following is a list of materials used in preparing

the adhesives used in these tests and their sources:

Epon 828 - epoxy resin

Shell Chemical Corporation

380 Madison Avenue

New York 17, N, Y.

Cab-o-sil - finely divided silica

Godfrey L. Cabot, Inc.

Mineral and Chemical Division

77 Franklin Street

Boston 10 , Mas s

.

DMP-10) - Dimethylaminomethyl phenols

DMP-30)

Rohm and Haas Company

Washington Square

Philadelphia 5, Penna.

Diethylenetriamine

Chemical Rubber Company

8616 Georgia Avenue

Silver Spring, Md

.

Selectron 5119 - polyester resin

Pittsburgh Plate Glass Company

One Gateway Center

Pittsburgh, Penna.

Lupersol-DDM - 60^ Methyl ethyl Ketone peroxide

in dimethyl phthalate

Novadel-Agene Corporation

Lucidol Division

1740 Military Road

Buffalo, N. Y.

Thiokol LP-3 - polysulfide polymer

Thiokol Chemical Corporation

Trenton 7, New Jersey
- •
APPENDIX (continued)

Surfex - resin coated calcium carbonate

Diamond Alkali Company

12 S, 12th Street

Philadelphia 7> Penna.

The following are the proportions used to mix the jointing materials used in this investigation:

Grout - 1 part type III cement to 3 parts of sand,

by weight.

Neat cement - type III cement.

Polyester resin - batch proportions:

200 grams Selectron 5>119

12 grams Cab-o-sil

2 grams Lupersol DDM

Epoxy resin - batch proportions:

200 grams Epon 828

12 grams Cab-o-sil

16 grams Diethylenetri amine

Epoxy/Thiokol - batch proportions:

Component A

100 grams Thiokol LP-3

100 grams Surfex

10 grams Cab-o-sil

2.5 grams DMP-30

2; 5 grams DMP-10

Component B

250 grams Epon 828

250 grams Surfex

7.5 grams Cab-o-sil

Components A and B were proportioned in the ratio of 1:1.
.
Table 1. Comparison of Test Results

Slab

t——

r

* Method •

* of '

' support '

Arrangement

of

blocks

• Amount

' of

1 prestress

“1

' Type

' of

• steel

t

9

9

, Jointing

t material

9

9

' Type

' of

' block

,

9

9 Deflection , Maximum

sensitivity, load

9

9 9

9 9

* psl 9

9

9

9

9

9 /A In. /lb ' kips

9 1 ’ 4 edge ’Crisscross

9 9

'1000

'1000

long. trans ’Stressteel

9

9

1 None

9

9

’ Preload

9

9

... 1 11.80

9

2

1 4 edge ’

9 9

do '1000

'1000

long. trans

1 do

9

9

1 do ' do

• 3 00 ’ 16.25

9

5 » 4 edge

i t do • 1000

•1000

long. trans »Elastuff

9

* do

9

f NBS

9 0.97 t 18.009

3 , 4 edge ,

9 r do ,1000

,1000

long. trans

9,3tressteel

)

9 Grout

9

» Preload

9 0.90 ! 35.009 4 , 4 edge ,

! 9 do ',1000 ,1000

long. trans

9

t do

9

9

f do

9

9

, do

9 1.10 ! 34.259 7

f

f b edge

J

9 9

do 1 1000

Jiooo

long. trans

j Elastuff

9

; do

9

J NBS

9

0.70 j 27.28

9 8

1 4 edge 1 do '1000 '1000

long. trans

1 do

9

’ do

9

• NBS”

9 0.70 ’ 39.85

9

9 i 4 edge i

i t do ,1000

,1000

long. trans

t do

9

9 do

9

9 Clay tile

9 0.80 1 26.809 28 , 4 edge t

1 9

do J iooo

,1000

long. trans

J do

9

f Neat cement

9

J NBS

+

9

0.67

J 49.60

c 16

j 4 edge •

( f

do '1000 '1000long. trans ’Stressteel

9 'Polyester resin ’ NBS

9

9

0.68 ' 31.50

9

20 9 4 edge ’

9 9 do •1000

•1000

long. trans ’Elastuff

9 lEpoxy resin

9

' . NBS

+

9 0.80 9 50.009

10 2 edge 'Crisscross

9 9 JlOOO long. 1000 trans

' Stress heel

9

None

9

J NBS

9

1-57 J 17.00

9 11 1 2 edge ' do '1000

'1000

long. trans

1 do

9 ’Neat cement

9

* do

9 1.27 f 26.25

9

26 2 edge 9

9 9 do •1000 long..

,1000 trans »Elastuf

f

9

’ do

9

• NBS

+

9 1.21 t 41-209 19

9 9

, 2 edge ,

i 1 do ,1000

,1000

long. trans jStressteel

9 tPolyester resin9

, NBS

9 1.39 J 28.009 24 t 2 edge J

9 9

do JlOOO ,1000

long. trans

J El as tuff

9

f Epoxy resin

9

9 1.41 \ 28.00

9 21 ' 2 edge ' do '1000

•1000 long.

trans

f do

9

* do

9

’ NBS

9 1.23 1 45.909 29 9 2 edge ,

9 9 do ,1000

,1000

long. trans

9

, do

9

t Epoxy/Thiokol

9

, do

9 1.34 ! 42.20

9

17 2 edge Crisscross

9 9

'iooo

J ^00

long. trans

'Stress teel

9

9

None

9

t

' NBS

9

9

2.54 1 11.00

9

9 18 ’ 2 edge »

9 9 do •1000

, 500

long. trans

1 do

9 *Neat cement

9

i do

9 1.40 • 24.309 27 2 edge f

1 9 do JlOOO

, 5oo long.

trans

f Elastuff

9

9

, do

9

J NBS4

9 1.24 ; 40.20

9 15 1 2 edge ' do '1000

' 5oo

long. trans ’3tressteel

9 'Polyester resin 1 NBS9 1.58 1 17.60

9

22 9 2 edge i

9 9 do • 1000

, 5oo

long. trans 9Elastuff

9 tEpoxy resin9

i NBS4

9 1.30 9 42.009

12

J 2 edge 'Aligned

9 9

'iooo

J 5oo

long. trans 'Stressteel

9

None

9

9

' NBS

:

9

2.32

; 13 10

9 13 1 2 edge *

t 9 do •1000

• 500

long. trans

* do

9 ’Neat cement

9

* do

9 1.17 • 18.10

9

14 9 2 edge f

9 9 do ,1000 long.

, 500 trans

9 do

9 9Polyester resin

9

9 do

9 1.16 , 19.60

23

1 9

, 2 edge ,

9 9 do J 1000

, 5oo

long. trans

, Elastuff

9

9

, Epoxy resin

9

J NBS4

9 1.15 J 45.00

9

2? ' 2 edge ’Special t ,'1000 long. 'Elastuff 'Grout ' Pavement 1.41 ' 20.75

1000 trans,

Vt Blooks relnforoed with l/4-ln. stirrups.

+ Blocks reinforced with 1- by 1-ln. - l5/l5 weld wire fabric,

£ See arrangement lr. figure 2.
...

* >
1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

16

17

18

19

20

21

22

23

24

25

26

27

Index to instrumentation diagrams for

slabs in this investigation.

Report Figure

1+396

4396

4396

4396

4951

disassembled

495i

495i

4951

5212

5212

5212

5212

5212

5212

5212

5212

5212

5212

5714

5714

5714

5714

5714

5714

5714

5714

6321

6321

3

3

3

3

3

3

3

3 and 4

3

3

3

3

3

3

4

3

3

3

5

4

4

4

4

6

4 o 7 and 8

5

6
.*

'
Table 3.

Loss

of

strain

in

steel

and

concrete

with

time

in

Slab

No.

3.

O

00

O LA CA

CA + 1 1 1 LA O • CO 1 1 O'

CO S'-— C\J + 1 0 1—1 s

O'

00 0 (A CO £ ft CO + 1 0 1—1 ms£ 1A (A

CD CD- LA 1 1 Eh "LA CO + 1 1—1 50£ ft± CO

•H ft ftt 1—1

CO CO + 1 CO 1—1

CD£ 1—1

rH

-P (A

O rH

00 CA <A 1 CD 1 1 £

ft 1 1 CA

O'

A 1 1 CO CO + 1 1—1

*-

W

— CA

ft

O CO 1 1 CO 1 l—1 £0 ft ft £ £

ft f 1 rH £ CO CO rH *—

CO' • • £ £

ft • •H •H £ £ \ \ I—1 H • CO £ £ 00 • •H •H r"3 ft £ £ £ 0 •H ft m ft m £ <0 O rH Oft O 1 1 1 1 1 •H 0 s m m

-p 1—1 » CD - 0

•H 0 -p -p -p -p m -ft £ £ £ £ £ £ ft CD 0 0 O 0 •H £ s a E ft 0 £ 1—1 0 ft 0 ft £ ft £ £ £ £

-P 0 00 0 co

co 50 £ £ £ •H •H i—1 *H rH 1—1 £ X £ ft £ ft •H £ •rH £ •h £

P>

Q

•H £» £ co £ co £ -P P> M ca ca

—

—' —

—1

-£

O

co c

O CO

CO 1 1 1—1 + +

CA IA la

LA ft 1—1

c— co + +

"LA 1—1 p CO ft O'

-p ft fA CO 1—1 p + + £O IA LA £ -ft CO [

O "LA co 1 1 1—1 O + + £ OJ O CA ft 0

-£ CA 1 co0

50 -ft £ CA ft- fA

£3 CA CA + +

LAO

C

ft CO

CO CA + +

CO o- ArH 1—1 1 1 1 1 CA + + £O ft ft £ £

ft 1 1 1 1 £ CO CO 1 1 •—

co s - • • £ £

ft • •H •H 1 £ £ \ \ 1 •H • co \ £ £ co • •rH •rH ft £ £ £ <3 •H ft m ft m

-H ft

O rH 0 ft

O rH 1—1

•H 0 s m

m

-p 1—1 £h - 0 - 0

•r

H 0 -p -p -p -p m -ft £ £ £ £ H £ -P P O 0 0 0 •H £ E ft E ft 0 Cj [—1 P ft 0 ft £ ft £ £ £ £

-P 0 CO 0 to

co 50 £ £ £ •H i» •rl >3 i—1 *H rH 1 1 £ ft £ ft £ ft

•rH £-1 •rl E •h E

p> 0 Cti «rH £ ft

•H 5 £ co £ to £ ft ft H ca ca

—‘ *- 1 «~.

indicates

an

increase

in

strain

indicates a

decrease

in

strain.

»

1 1

1 rV^i" >

2

y

_l_

1 CHAMFER

1 -H *1" 3" C

4

L 1

l"x l"- 15/15

WELDED

WIRE

FABRIC

WELDED WIRE FABRIC

6

" -<

n

V

1 " K

T

i

1

1

1

UNREINFORCED

NO. 4 GAGE

STEEL WIRE

REINFORCED

TILE

-— SOME BLOCKS

HAD HOLES IN THIS POSITION

TO PERMIT THE

STAGGERING OF

TENDONS.

BLOCK

PRELOAD BLOCK

7-5 ±8 h

PAVEMENT BLOCK

FIGURE I DRAWING OF ALL BLOCKS USED IN TEST SERIES

Ls

FIGURE 2. ARRANGEMENT OF PAVEMENT BLOCKS IN SLAB NO. 25

Io

x

o

a>

o

Sdl* ‘30d0d

FIGURE 3

STRAIN

FIGURE 4 TEST SET-UP OF SLAB NO. 9 ON CONCRETE FRAME

K

4

'- 6

m

0

1 To

=C

<

<

1C ii O c

1 1 D

1 6 12 c-m

C -7^

6 5

>

«> Yoading /

A BLOCK A

A////////

C-(2)

C * 6

_ >

&

CD C-(4)

C - 8

i t

DIAL GAGE / J

SUPPORTS

j L

1 7 13 1C 0rc-d)

C - 5

7

Z

•

SLAB

SUPPORT.

i 3

‘

IID i LA O \ £ D j*t * - I

o

>

>

Y

ui

CL

l> <

>

>

cn

QC

<

CD

CO

I

BARS STAGGERED

5

'- 0

"

-> N

legen d:

GAGES I THROUGH 18 INDICATE DIAL GAGES

CI-C4 INDICATE SR-4 GAGES ON BOTTOM SURFACE OF SLAB

C5 - C8 " " " " TOP " " "

FIGURE 5. LOCATION OF DIAL GAGES AND STRAIN GAGES

ON SLAB NO. 28 (SIMPLY SUPPORTED ON FOUR EDGES).

N

legend:

GAGES I THROUGH 12 INDICATE DIAL GAGES

CI-C4 INDICATE SR-4 GAGES ON BOTTOM SURFACE OF SLAB

C5 - C8 " " " " TOP " " "

FIGURE 6. LOCATION OF DIAL GAGES AND STRAIN GAGES ON

SLAB NO. 29 (SIMPLY SUPPORTED ON TWO EDGES).

APPLIED

LOAD

,

KIPS

APPLIED

LOAD,

KIPS

FIGURE 7. OBSERVED RELATIONSHIP BETWEEN APPLIED LOAD

AND CENTER DEFLECTION OF SLABS.

I~o

Ui

UIQ

OCUJ

o

o

UJ

UIQ

OCUJ

UJo

oc

UI

hUJo

Q

z

<

Q

<

O

o

UI

a.CL<

UJ

UI

UI

CQ

a.x (0 CO 00 Z <

2 -J I- w

UI h- > CJ oc u

UJ _J CO u

CD u

o c

00

UJ

oc

z>2

u_

o

ro

sdi>i ‘avoi aaiiddv

sdM ‘avoi a3Hddv

APPLIED

LOAD,

KIPS

APPLIED

LOAD,

KIPS

FIGURE 9. OBSERVED RELATIONSHIP BETWEEN APPLIED LOAD

AND CENTER DEFLECTION OF SLABS.

FIGURE 10. EXPERIMENTAL RELATIONSHIP BETWEEN APPLIED

LOAD AND VERTICAL MOVEMENT OF CORNERS.

SLAB

NO.

FIGURES II 8 12

NUMBER

OF

DAYS

AFTER

PRESTRESSING

FIGURE

12.

LOSS

OF

PRESTRESS

IN

CONCRETE

OF

SLAB

NO.

5

PRIOR

TO

TEST.

SLAB

NO.

19

SLAB

NO.

24

Sdia ‘OVOl Q3nddV

FIGURE

13.

OBSERVED

RELATIONSHIP

BETWEEN

APPLIED

LOAD

AND

CONCRETE

STRAIN

CD

io

xO

o

''fr

o

o

to

LlJ

if) o

2

o w

OJ ho

o

<

ccH

co

LJ

l~

Lu

Ct

O

2

O

o

o

o

LJ>

C/5 CO

LJ

CC

CL

CJ o

o

00

sdia ‘avcn adnddv

FIGURE

14.

OBSERVED

RELATIONSHIP

BETWEEN

APPLIED

LOAD

AND

CONCRETE

STRAIN

(SLAB

NO.

28

-

NEAT

CEMENT

JOINTS)

.

FIGURE

15.

OBSERVED

RELATIONSHIP

BETWEEN

APPLIED

LOAD

AND

CONCRETE

STRAIN

(SLAB

NO.

29

-

EPOXY/

THIOKOL

JOINTS)

.

SUPPORT SUPPORT

N

FIGURE 16. TOP VIEW OF CRACK PATTERNS IN SLAB NO. 24.

^ N

FIGURE 17. TOP VIEW OF CRACK PATTERNS IN SLAB NO. 27.

VERTICAL

EXTENSION

OF

BLOCK

WEBS

sdi)H

l avoi 03l“lddV

PENETRATION

OF

LOADING

BLOCK

INTO

SLAB

AND

VERTICAL

EXTENSION

OF

BLOCK

WEBS,

SLAB

*

NO.

27.

U. S. DEPARTMENT OE COMMERCE

Lbwla Ij, Strauss, Secretory

NATtONAL mmfcAU OP STANDARDS

A. V, Astiit, director THE .NATIONAL BUREAU OE STANDARDS

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