プレストレスト鉄筋コンクリート曲げ部材内部のひびわれ状況に関する実験的研究(梗概) : その1.インク・樹脂ダブル注入実験方法について

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EXPERIMENTAL

STUDY

ON

INTERNAL

CRACKING

'

'

OFPARTIALLYPRESTRESSEDCONCRETE/

･

'

tt

tt tt t/

FLEXURAL

MEMBERS

'

･

c..

..

Part

1

:

Examination

of

double

injection

technique

by

KAZUO

SUZUKI*,

YOSHITERU

OHNO**

and

SOMCHAI

SRISOMPONG"'*,

Members

of

A.

!.

J,

1.

Introduction

Degree

of

corrosion

of

reinforcing steels

in

concrete structures must

be

related

to

the

severity of cracking

'and

loss

tt

.

t

of

the

composite

action

between

reinfercing steels and concrete or

the

separation of concrete

from

reinforcing steels

due

to

the

large

difference

'in

their

strain

capacities

[

1

].

Not

only surface crack widths

but

'aiso

the

internal

cracking characteristics

are,

thought

to

be

impprtant

for

the

corrosion controL

These

factors

also relate

to

the

bond

mechanism

between

reinfercing

steels

and concrete.

Until

today,

some studies on

internal

cracking

of reinforced concrete

(RC)

_prisms

with

deformed

bars

have

been

'

tt

t/t

tt

tt

reported,

In

ordinary

prestrqssed

conciete

(PC)

structures, crack control

is

not required

because

cracks are not allowed.

Therefore,

cracks

in

the

vicinity of sheath and

in

_grout

have

scarcely

been

investigated.

But

at

the

_present

time,

the

newly

developed

partially

prestressed

concrete

(PPC)

structures are

becoming

extensively used.

In

these

structures, cracks are allowed under

service

Ioad

but

the

available experimental

data

foT

areasonable crack control are-still very

limited.

The

study

in

this

field

is

in,urgent

need,

･･

･

'

In

this

_paper,

the

investigation

techniques

which employ

ink

andlor epoxy resin as

injecing

materials'are

discussed.

An

idea.was

conceived

that

in

orde[

to

investigate.internal

cracking more

_precisely

and

to

obtain not only

general

cracking

_pattern

but

also

sizes

of

c[acks

directly,

ink

and resin could

be

used

together

in

the

same specirnen.

The

technique

is

termed

herein

"double

_injection

_technique".

_In

_this

paper

the

examination on

double

,injection

technique

is

mainly

discussed

and

the

internal

cracking characteTistics will

be

discussed

in

Part2.

2.

Historical

Background

In

1965

Broms

[

2

].introduced

a

test

technique

for

investigating

internal

cracking

by

means of resin

injection･in

reinforqed concrete

_prism

for

which a small resin

injecting

hole

was

_providecl

in

_parallel

wjth

the

deformed

reinforcing

bar.

The

specimen

was

externally

coated

to

_prevent

outside air

from

entering

into

it.

Loading

was

dofie

by

_pulling

both

_protruding

ends of

the

bar.

Vacuum

pump

was applied,to remove

part

of

the

air

trapped

inside

the

specimen which rnight

_prevent

resin

from

_penetrating

into

the

very

fine

cracks.

With

the

co.rnbination of air

_pressure

and vacuum using

twe

pumps,

resin was

drawn

into

the

e{4cks.

The

injecting

_pr,efisure

was

approxiTn.ately

7.Q

kgflcmZ

for

which

Brorns

gave

a comment

later

that

it

was ratheT

high

because

the

axial

force

resulted

from

this

pressure

might cause some of

the

intemal

cracks

to

open up.

The

load

was maintained

till

the

hardening

of resin.

The

specimen was cut

to

reyeal

internal

cracks which

had

been

_preserved

by

the

hardened

resin.

Width

of

_primary

crack adjacent

to

the

reinforcing steel was

found

to

be

only

115

to

113

of

the

maximum width at concrete surface.

The

minimum crack width measured

in

the

test

was

O.

025

mm.

Since

ink

injection

was not

_performed,

other

details

of

internat

cracking,

for

instance,

_pattern

of

internal

cracks and separation of concrete

from

reinforcing steels were not

investigated.

'

PTofessor

of

Osaka

University,

Dr.

Eng.

#

_Research

_Associate

_of

Osaka

University

i"

_Graduate

_Student

_of

_Osaka

_University

Manuscript

received Septernber7,

19S4

-24-NII-Electronic Library Service

In

the

_sarne

_year,

_Goto

[

3

]

reported some

investigations

of

internal

cracks which

originated

from

lugs

of

deformed

bars,

based

on

the

test

using reinforced

concrete

_prisms.

Ink

was

first

filled

into

the

injecting

holes

_placed

in

_parallel

with

the

_reinforcing

bar.

L,oad

_{was appli6d}

by

_pulling

both

_protruding

_{ends of}

_the

bar.

_As

_cracks

_opened,

_ink

was automatically

drawn

into

them

_by

the

aid of

internal

vacuum suction.

In.1971

the

optimum results,

illustrations

and schematic

diagram

of

the

internal

cracks

_pattern

tested

_by

_this

_procedure

[4']

were

introduced.

Goto

et al

[s]

also studied shapes of

_primary

cracks

by

injectin'g

resin

into

reinforced concrete

_prisms.

They

stated

that

when

deformed

bars

were used

the

interior

opening of

_pJimary

crack was net regular.

Furthermore,

crack widths

adjacent

to

the

steel surfqce was much smaller

_than

_those

observed at

the

concrete surface.

Goto

did

not

state

the

relationships

between

the

_pattern

of

internal

cracks ancl sizes of

_pTimary

cracks

in

the

sarne specimen.

In

]972

IIIston

&

Stevens

[1

]

fOllowed

Broms'

technique

and

_performed

test

on

internal

cracking

in

reinforced

concrete

beams,

Internal

shapes of

_primary

cracks were

observed

to

be

irregular,

forked

and

discontinu6us.

Separation

of concTete'

from

reinfovcing steel was also observed,

but

the

separation clearance

ancl

its

area

in

relation with crack width or steel

stress

were not

discussed.

The

minimum width of crack whidh resin could

penetrate

was approximately

O.Ol

mm,

Since

ink

injection

was not

_performed,

the

formation

of

internal

cracks

was unobservable.

･

Previous

works on

internal

cracking mostly

dealt

with reinfoTced concrete

_prisms.

Those

on

beams

are still rare.

Particularly,

investigatiops

on

intemal

cracking of

partially

_prestressed

concrete

beams

have

not

been

clealt

with,

i,

e,

there

is

none

of

experimental

data

of cracking

in

the

vicinity of sheath'and

in

_grout.

Those

_previous

works _{employed either}

ink

_{or resin}

injections

_{which were}

independently

_performed

_to

_{obtain either cracking}

pattern

or crack widths only.

In

ordeT

to

investigate

directly

not only

_general

cTacking

_pattern

but

also sizes of

the

cracks as

they

are

in

the

same specimen,

those

conventional

injection

techniques-are

considered

to

be

impractical.

3.

PreliminaryTest(Exp.1)

3.1

TestProgram

Specimens

and materials

Objective

of

the

test

is

to

acquire a

better

injection

test

teehnique

using

ink

and epoxy resin as'injecting materials,

Ink

dyes

_{cracks and allows observation}

for

internal

_cracking

_pattern,

_{whereas epoxy resin retains} crack openings and allows measurement of craek widths.

Eight

beams

with

10

×

･20

cm rectangular

Table

1

Beam

specifications

(Exp.

1)

tion

and

the

-length

of

150

crn of reinforced or

･

partially

prestressed'concrete

were

fabricated

and arranged

in

'four

_pairs,

and each

_pair

sisted of

beams

of

the

same

descriptions.

One

of each

_pair

was

to

be

injected

with

ink

and

the

'

"9.

,29,.

.,

r

,J.,'

'

- RC:Retnferced conerete, 2o

,

io-c. prc<

Table2

Properties

of concrete and

grout

'

rc'M PPC-M

Fig.1

Sectionat

detai]s･of

test ,

beams

of

Exp.1

(in

cm) ,

Beammark-InjectedvithConcretetypePre-stressing

steelPrestressing

force(kgf)

RC.CInkConcrete

'

-'

RC-CResinConerete

.

,.

RC-MInkMortar

-t

-RC-MResinMortar

.L-

-ppc-cInkConerete"11bar

₈₀₀₀

ppc-cResinConerete11bar

₈₀₀₀

PPC-MInkMortar

_¢

11bar

8000

PPC-MResinMerter

_¢

ltber

sooo

Item

Cenclete-type

Ageattest(deys)Compressive

c:$:::sljModulusef

elesticlty

(kgf!em`)Tensile,{};::gs?

Concrete

20

₃₈₇

2.82xlo538･.2

E)cp.1Morter

22'

354

2.40xloS

./t

Grout

14

203

-

27.9

Exp.2Concrete41

₃₃₁

_2.71xlo531.4

'

X3Lr

Fig,2

Eifl},t/S,li

--Li3i

Detalls

ef reinforcing steeL

tin

mm)-25

--other with

resin.

Details

of

these

beams

areishown

in

Table

,1

and

Eig:1.

Concrete

was

prepared,,in,two

types,

one,was

'

of

･crushed

stone with a'maximum size of

10:mm,

the

other

･,

was

of/

saDd-cement mortar./･High:e,arly-str.ength

portland

ce-lment

and

riy,er sand were used.

Waterlcement

ratio was

O.55,.

For

_grb'u'

t,

Pozzlith,No.8

of

O,zs

%

and aluminum

powder,

of

O,

Q05

%

of

the

cement

by

weight were mixed with cement

_paste

with waterfcement ratio

of

O.45.

Th'e

propT

,i

erties

of

concrete

and

_grout

at, ages of

test

a;e shown

in

Table2.

''

''･

'./･//

'･'

'

''

i''''

'

,

Reinforcing

steel

bf

D

1･9

was-used

for

all

test

bearns.

The

details

of

this

steel are shown.in

Fig.2

The

prestressing

,

steel was

e11

mm

smooth

type

bar

_placed

in

a spiral･sheath

of

23

mm

inner'diameter;

Injecting

holes･were

provided

by

inlaying

¢

3

rnm steel wires

in

the

cleaTance of

6-7mm

be-tw.een

reinfercing steel and

the

outer surface of sheath

in

pa-railel

,with

them.

One

day

after concrete casting-the,

steel

wires

were

_pulled

ollt,

One

injecting

hole,for

investigating

gracks,in･,,grout

was

provided

inside

the

sheath

in･parallel

with

the

_prestressing

sleel,

The

diagram･of

construction,is shown

in

Fig`3.

The

specimens

,were

kept

moist

by

means

of ,

wet

cloth

and

_plastic

sheet

till

loading

test

Forms

were

re-moved after

2

dayg

to

allow

contact

type

strain

_gauges

to

be

attached

for

measuring

strain

changes

in

the

concrete.

Prestress

crete

beams

at

the

age of

7

days.

'

Shrinkage

of concrete,was observed･since removal･ of

forms

till

only

loss

of

prestressing･force

in

the

prestresSing

steel

but･'also

reinforcing steel

into

account.

.Loading

and

injecti'ng

method

･.

,.

'

_Arrangement

_for

_loading

was aicantil'ever

tyPe.

Each

beam

end,as

slibwn

in

Fig,4,

The･,color

Df

ink

was

red,

and red

'

error resuLts-of

the

preparatofy,,teSts,･

injecting

pressure

of

tespectively.

Before

loadirig

ink･or

resin was

filled

into

the

'

loaded

while

the

_press,ure

was,maintained.

As

cracks

formed

the

cracks

by

injecting

_pressure

from

outside and

the

aid

of

Change

in

stgel stress

from

the

decompression

Aab

wfts

'

cantilever.

･

,

'

For

mk-injectedlbeams,

l,oad

was removed after

holdin

was maintained

fef

about

one week

for

resin

hardening.

After

the

plane

which

_passed'

through

the

reinforcing steel or

both

longitudinally

cut

into

two

,parts.

Then

yisual

inspec.tion

.

t

'

t

/

mlcroscope:

,/'･

'

,

,,,

'

During

the

test,

changes

is

surface crack widths were

c/

gauge

length

on

the.coricrete

surface

at

the

level

of rein was

done

in

yaf'i6us stages,

i.

e,

before

loading',

after''

/

Z:i:'X//:,gb,,,fi.;2ge,tlr`.e,L",a,i,.c,reck`,"g

can not

be

dt.I7f,tiy

,

3.

2

ResuLts

of

Injection

and

Consiclerations

'

-26-ii

･･

'

1..

r'･r

!i

i'

'

:

$:

Injeqt injeetinij

t ttt/Fig.

_3.･:

Fabrication

details/

bartote '

tt

.

boadcell'

tt'

Centactgagepaintg

f

.Oil 'te

tttttttttttttttttttt

_{ttttttttttttttttttt}

Spec ±men F･" Fixedendttt H-steElbearn 30 llOesn le

[ was

plgment

was

O.5

mjecbng

the

internal

controllgcl

g

fQr

a

few

unloading,'

{einforcing

was.

t/

measure

forcing

.and

prestressing

steels ln]ectlon

checked,

//t/

'

'/.

jaek

rnk.er tesin

Fig.

₄

Loading

&,

a[rangemgnt of

in]ection

<E,xp.

1)

was

transferred

to

the

_partially.

_prestressed

t tt

tt

loading

ancl

injection

test,

in

order

to

take'not

the

increment

of compression

force

in

the

/

/

t

/t

tt

loiaded

at a

_point.

_11o

cm

qpart

from

the

fixed

added

into

the

resin,

Basied

on

trial

and

and.5.okgflcm2

were useg

for

ink

and

resin,

'

i,

holes

as shown

in,Fig.3.

Beagis

were

then

filled

ink

oT [esin

_}vas

immediately-drawn

into

vacuum suctioh autgrnatically

produced.

at

_{3200kgflcm2at}

the

fited

end

of

the

'

minutes.

For

resin-i,njected ones,

cleflection

beams

were vertically splitted

through

,

a.nd

prestressing

steels..

The

grout

was

dond

with

the

aid of a

2o

magnification

'

/

ttt

t

tt

../

d

using

contact

type

strain

gauges

with

4

cm

in

(see

Fig.4).

Measurement

,

before

and after unloiding.

before

and,after

this

deyice

was

design,ated

to

simulate

the

'

:

..

NII-Electronic Library Service

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fi

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,i,,,

..,...,

...o..;.Meas"rse..p.o'l".t...li.

'f.,,

.-.re,-.,,I

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ti

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,o

B :InLtrv-1 checking

Fig.

5

Cracking

pattern

and

detail's

of

be'am

PPC-M

{Resin)

of

Exp.

1

(in

mm.

)

stages

(Ex,.1)

'

'

'

tt

Primary

crack stands

for

crack which

forms

and

_propagates

from

the

tension

face

of

beam

towatds

the

steels, whereas

internal

crack stands

for

crack which

originates･from'the

steel surface'and closes within,the

concrete.

In

ink-injected

beams,

the

staining of

ink

was retatively extensive especially around

the

fixed

erid

of

the

cantilever.

The

_pattern

of

_primary

and

internal

cracks could

be

distinguished

as red

lines

of cracks

from

the

staining

traces,

In

resin-injected

beams,

only

_primary

cracks

and some

branches

of approximately,O,Ol mm or

wider could

be

observed.

Staining

of resin on

the

splitted

faces

of

resin-injected

beams

was not extensive as

in

the

ink-injected

one.

Primary

cracks were widest at

the

concfete surface and

decreased

in

width upon･reaching

and

crossing

the

steel

bar.

The

minimum width of

crack

that

could

be

measured was approximately

o.

oos-O.Ol

mm,

.,'

.

.

/

Fig.5

shows-general

pattern

and

detaiis

of cracks

in

beam

PPC-M

which was

injebted

by

resin.

Primary

cracks were wider at

the

concrete surface

and

narrowed

towaras

the

reinforcing steel.,Internal

cracks

as appeared

in

the

ink-injected

beams

were not visible.

But

a

few

branches

of

_primary

cracks of approxirnately

O.

ol

mm wide

coti1cl

be

visible.

The

hatched

areas represent areas of separation of concrete

from

reinforcing steel.

These

aretis

were

coated

with

films

of

injected

resin.

Though

_the

ekact separation might

be

･more

extensive,

in

this

study,

only

the

territories

coated with

the

resin was

judged

as

the'significant

separation.

The

minimum

clearance

which resin could

_pen'etrate

was most

_probably

O,

O05-O,

_Ol

mm which

is

relatively

equal

to

the

minimum crack width

measurable

through

_the

resin

_penetration.

･

･

_.

The

observed [esults of cracks

in

grout

was also shown

in

Fig.5,

It

can

be

found

that

cracks

in

_grout

were

almest

in

_straight

lines

linking

_prestressing

_{steel surface and}

the

inner

surface of sheath and

_generally

_they

had

no

branches.

Most

of

the

cracks

in

grout

were so narrow and not easy

to

notice

by

naked eyes,

But

it

was rather

'

easy

to

observe

in

_the

ink-injected

beams

than･in

the

resin-injected ones,

because

ink

dyed

the

crack and'offered

good

contrast which was noticable

by

naked eyes.

In

such narrow cracks

_the

_pene{rated

resin was

_pale

and not

easy

to

be

noticed, without

the

aid

of

microscope.

,

'

Data

of changes

in

the

surface crack widths of

PPC-M

beams

measured at

tension

taces

using contact

type

strain

_gatiges

are shown

in

Fig.

ts.

Changes

in

crack

widths

in

the

PPC-M

beams

injected

with

ink

and resin separately were compared.

After

unloading stage

D

cracks

in

the

ink-injected

beam

closed

s"bstantially.

But

in

the

_{resin-injected} one, _{crack widths}

decfeased

_{only a}

little,

i.

_{e. approximately}

lo

%

from

_the

initial

_stage.

It

can

be

thought

that

the

resin

_penetrated

rather･well..

The

decrease

of crack width stilloccurred

_possibly

because

resin

has

srnailer modulus ef elasticity

than

that

of

concrete.

It

can

be

further

bbserved

_that

in

stage

E,

when

the

--

NII-Electronic Mbrary :===:le="=!== 1.e,i''os'tt'''-==:::=[=.g....ca

.e6=:.:==#=tas.ts====

beam

was splitted and

the

_prestressing

steel rerpoved,

the

c[acks reopened a

little

to

become

nearly compatible

to

'

the

initial

widths.

-,

'

/t

t

The

locatiDns,

sequence, widths and

profilesl

of

internal

and

primary

crack,s

never

repeat

themselves

even

in

a

pair

of

identical

bearns.

The

quantity

and measurements of cracks are unlikely

to

be

reproducible.

Therefore,

to

obtain

the

total

cracking

data,'

ink

or resin

injection

alone can not,fulfill

the

requirementsl

Widths

and

_profiles

of

primary

crack and seyerity of separation

from

the

resin-injected

beam

had

to

be

connected

with

_the

_pattern

of

internal

cracks observed

from

_.another

ink-injected..ane.

The

method

describecl

above

is

considered

to

be

impractical

and may

involve

kome

mistakes. _/

-

.,

'

'

4.

DoublelnjectionTest(Exp.2)

'

''.

,

'

'

4.I

TestProgram

'

_,

･,

Specimens

and materials

/

The

results obtained

from

'Exp.1

indicate

that

ink

and resin should

be

used

together

in

the

same

specimen

in

order

to

inv'estigate

iriternal

cracking rnore

precisely.

In

this

progrgm,

a

test

technique

was

developed

in

the

way

that

ink

and resin could

be

injected

one

by

one

into'the

same specimen.

Three

reinforced concrete

beapas

With

₁₂

'

×

2s

cm

recta'ngular section and

the

length

of

200

cm were used.

Fabrication

for

the

injection

system was

the

same as

that

of

Exp.1.

All

beams

were

identically

same

in

descriptions

as shown

in･Fig.7.

Aggrggates

for

concrete were

,crushed

st6ne with a maximum size of

10

mm and river sand.

Cement

and waterlcement ratio were

the

same

as

in

Eixp.1,

P{operties

of concrete at

diffeient

ages of

test

aFe shown

in

Table2,

Reinforcing

steel

of

D

lg

was used with

bottom

and side cover of

3

and

5

cm, respectively.

Loading

and

injecting

methods

･,

,

･

,i

The

three

beams

were

designated

to

undergo

three

different

injecting

test

methods

for

comparison.

Although

the

cantilever

beam-

offers wider range of steel

stress

along

its

span,

random nature

bf

crack

formation

makes

it

difficult.to,cQnfirm

only a single crack

_per

each'level of steel stress'as an accurate one.

In

this

test,

loading･was

arranged asia simply-support

type

with'third

_point

loading

of

60

cm

flexural

span

as shown

in

Fig.s.

Each

beam

was

Loaded

to

.the

level

of

2OOO

kgflcm!

of stress change

in

steel

from

the

･decompression

Aa.

in

the

constant

moment span.

･

･･

'

,

,'

･'i

Color

of

resin

was

green

in

contrast with･the red

ink:･

Since

ink

and resin

have

clifferent

_{physical'properties,}

in

order

to

fill

both

materials

into

the

cracks

injectien

has

to

be

_performed

twice

and

there

are

two

alternatives

in

practice,

that

is,･'whether･.unloading

should

be

done

or not after

the

first

injection

of

ink.

If'beam

is

once unloaded,

the

internal

vac'uu'm suction will

be,

utilized again at

the

･reloading

for

the

sUbsequent

injection･

of resin.

･On

the

other

hand,

if

the

beam

is

loaded

once only and

the

deflection･

is

maintained

for

both

injection

works,

there

will

nQt

be

any

interference･of

reloading effects

[

6]

_,'

but

the

aid･ of

internal

vacuum suction can not･

be,

bbtained

at

the

resin

injection

time.

'･･

.･･,''

,

.

･,

..1/･

'

･

For

these

reasons,,

the

following

injecting

methods wete

examined

and

discussed.

,

i'

(

a,)

･

Method1'

(ordinary

method)'.

-This

method

is

the

one' applied.

in

Exp.1

where.ink o,r resin was

individually

injected

inte

a

_pair

of

identical

beams.

Inspection

could not

be

directly

done

in

only one specimen

'

t.

/.,

1

,//

,1

.t.

t,

t

/t

'

/tvi･

tt./

./tt

.t,

'

''

t 12H _'

I,

L...3

/t

//

-

･'

'

Fig.7

rc3-2(1)!

.1

nc3-2(2) ,

.v

lC3-2

{'])

-

･

;

l

Zaen.-::g:rkgficrn2

'

Cl); rnjectiQn

,Method

1

Sectional

details

of test

bearns.of

Exp.

2

Sin

crn)

,･i,/

'

'

,

''

toadcell Contactgagep6ihtseUjack

/･

･

, "-･v

-.

.,...x.-.-,,Specirnen･',

tt=Inkorresin

-H-steelbeam

'

'II'P-k--kr-Fig.B

60.

.i

.･60crn･

6D

.

Loading

&

arrangement

of

injection

(Exp.

2)

'

'

ttt

tt

t

t

-28

--NII-Electronic Library Service

to

_obtain

the

total

_pattern

and

sizes of cracks occurred

in

actual

situation.

Therefore,

a

_pair

of

specimens

of

the

'

same

descriptions

were necessary and

the

work

became

tedious.

Beam

RC3-2

(

1

}

was

tested

by

this

method

and

injected

with resin whlie

the

others were

designated

to

undergo

the

double

injection.

Through

these

arrangement, results on crack width,

_penetration

of

ink

andlor

resin and visibility

in'the

inspectien

could

be

extensively

compared.

(

b

)

Method2

(double

injection

I

).-Ink

was

first

injected

using air

_pressure

and

internal

vacuum suction

in

the

_{same way}

as

Method1.

After

btowing

the

injegted

ink

away,

the

beam

was unloaded and

the

surface cracks were sealed with a

type

of

flexible

bonding

material

to

_prevent

_pressure

loss

and

to

utilize

the

internal

vacuum _suction

for

the

_second

injection.

Reloading

_was

done

_to

_the

_same

revel

_of

_Aa.

_{and resin was}

_injected

with

the

same

technique

as

Method

1.

'

'

The

reloading may affect

the

initial

_{cracking condition}

to

_some

_extent

but

_resin

_penetration

is

highly

_expected

to

_perform

much

similarly

to

that

of

Method

1.

Beam

RC

3-2

(

2

)

was

tested

by

this

method.

(c

)

Method3

(double

injection

ll

>.-Ink

was

first

injected

with

the

same

technique

as

Method1.

After

blowing

the

injected

ink

away

the

surface

cracks

were

coated

with a

type

of rapid-hardening

_gum,

leavifig

narrow

parts

of cracks open as outlets

for

part

of

the''air

trapped

inside

the

specimen.

The

trapped

air may

_prevent

resin

from

entering

into

the

very

fine

cracks.

Then

resin was

injected

with a

_pressure

of

5.

0

kgflcm2

and

deflection

of

beam

was maintained

for

seven

days

for

resin

hardening.

By

this

method, resin

_penetration

depends

on

the

injecting

_pressure

only.

Hence

it

is

uncertain

_that

without

:a :

J

:

i

l

l

bl,b

"-

---6-"-4

: :

:

: :.a.

nc

Fig.9

Diagiam

ofcutting utilizing

_the

internal

vacuum suction, resin

_penetration

will

_perform

sufficient-ly.

Beam

RC

3-2

(-3

)

was

tested

by

this

method,

After

unloading,

all

tested

beams

were

splitted

and cut

by

diamond

cutteT

as shown

in

_the

diagram

in

Fig.9.

Inspection

and

crack measurement were

done

with

the

aid

of

a

40

magnefication microscope.

In

this

test

changes

in

surface crack widths were also measured using contact

type

strain

_gauges

at various stages on

the

concrete

surface at steel

levels,

4.2

Results

of

Inje,ction

and

Copsi-derations

Visibility

and

cracking

_pattern

Fig.10

shows

patterns

of

internal

craking of

the

three

beams,

In

beam

RC3-2

₍

1

₎

which was

injected

with

g

nn

e-s

iC3-2C3)

tAas!:200o

kgflcm2) "-ethod

3

===-nt Misit==== se-:::=:!:---,u:L:={rm)

I!,ot

aesin/liny/XtsL

::==/t=mt..t-ttt-t---m

-t'I.!----x-os,n-ttt-t--ny---t

li

@

la a. d ` ;:l/=:t2=i==' Slx'il1--thrNttlen.::!1 1

--'---i-"=t-''1'".os"::=#=====

o

@

@

tethodl

_hethod2

_Metbod3

'Fig.

₁₀

_CTacking

pattern

and typical

details

of

beams

of

Exp.

2

(in

mm.

)

Table3

Average

primary

crack,widths

{in

mm)

,

.

resin, only

_primary

cracks,originated

from

the

(Aq.=2000kgf!cm2)

'

,.,,,

tension

face

could

be

obseryed.

In

beams

'

,RC3-2

(2)'

and

RC3-2

(3),

the

dyeing

-traces

of

ink

showed

gener,al

cracking

_pattern

'

and

the

hardened

resin

pTeserved

and retained

,

.

crack widths

for

observation

and

measurement.

,/

'TaPie4

,

.,,

,

,

Do,tted

lines

in

,the

enlarged

details

represent

(AinVel?lgi;i(eAntLll-liS20ofo6Prkigrnf:[YmC,laflr..F

and'iengthS OfSeParatiOn.

_,the

penetration

,of

ink

in

,very

fine

parts

of

.

･･

.,.

..,cracks

while

th.e

solid

lines

represent

_parts

of

cracks

whieh

were

_penetrated

either･

by

,resip

,

,., only or

bp,tb

ink

and resi,n.

It

can

be

noted

that

,

internal

cracks.formed su;rounding

each

pri,m:

ary

crack,･

In

bea.m

RC

3-2

(

l

),

separation of

-

_Specimen

_was

_inje'cted

_{with oniy resin'}

qOnCrete

frOM

reinforcing

steel cogld

be

'

obseryed

as

staining

o{ resin along

the

steel

recess.

-In

beams

RC

3-2

(

2

)

and

RC

372

(

i

)

the

staining of resin was,seen

tb

overcoat

on

that

of

ink

and

,was

less

extensive,

suggesting

that

ink

_penetrated

much

better.

The

hatched

areas repreSent

the

separation areas

judged

through

resin.penetration which

has

minimum

clearance of most

_probably

O,O05-O.Ol

mm.

Primary

cracks

Table

3

shows average widths of

_primary

crhcks measured

through

the

resin

_penetration.

The

data

indicate

that

the

average crack widths were

in

the

range

of

O.

120-O.

134

mm and

o.

o98-O.

113

mm at

tension

faces

and side

faces

of

the

'

three

beams,

respectively,

The

average

crack

width adjacent

to

the

steel surface was approximarely

O.

04s

mm.

It

can

be

thought

that

measurements of

primary

clacks

obtained

from

these

beams

of

different

injection

methods conformed

vrith

each other welL,

_,.

.

.

,

'

'

_'Table4shows

the

average

lengths

of

_primary

cracks and,lengths'of separation of concfete

fiom

reinforcing

/

'

steel.

Crack

lerigth'stands

for

the

Iength'bf

_prim'ary

crack

ineasured

through

ink

of resin

_penetration

from

tension

fac'e

o{

the

beam

to

apex

of

the

crack.

'

"'

_'

'

tt

1

It

was

_previously

anticipated

that

crack

length

and

length

of

separation

would

be

longesC

in

b'earn

RC

3-2

(

2

)

due

to

the

reloading effect, and shortest

in

beam

RC

3-2

(

3

>

due

'to

the

absence _of

internal

_{vacuurn suetion.}

But

Table

4

indicates

that

there

wtis only a

little

difference

in

crack

lerigths

between

the

two,

and

the

average

length

'

of

separation was

tinexpectedly

longest

in

beam

RC

3-2

(

3

>.

The

latter

was

possibly.

due

to

random

fQrmation

of

/

1

cracksi

It

can

be

thought

that

reloading

had

less

effects and

the.penetrability

of resin of

Method3

(double

injection

">

wag

comparable

to

the

others

in

kpite

ef

the

'ab'sence

of

internal

vacuum suption.

････'

,

//t/

/.

ma-2{1}

Locatien

ec±mensRC3-2(1)HC3-2{2)RC3-2(3)

Sectiona-aTensienfaceO;120Oi134O.124

Nearsteele.o4oO.035O.034

Sidefaeee.

. .

Sectienb.bNearsteelO.035O.043O.055

Item

SpecimenRC3-2(1)-RC3.2(2)RC3-2(3)

CrackiengthByink

.

122.0 117.9'

Bres

±n93.7

88.1

,86.5

Lengthof

separationByresin48.5

･61.3'.,63.,5

.2D

Ev

.ISfiP.3".

.10:U

'

.05

.20

E-;

.tse.;s.

.lo:U.05

`Zo

s-.issPA)-ti

.10:v.05

'

E'

ABC D･,E

O,ABCDE

eABC

_,

t.t

Various stages

.

･

Varieus steges. Varieus,

t.

tt

'

Varieus stages- A:After ink injection, B:After resin injeet ±on

e:eefore unleading

.

DtAfter unloaaing

E:After splitting

Fig.

₁₁

Changes

in

crack width at side

faggs/in,various

stages

(Exp.2>

DE stages

/

t//

t

tt

_ttt/t

1

'

'

'.t

''tt

-30-NII-Electronic Library Service

Injecting

pressure

and retainability of resin

'

'

Fig,11

shows changes

in

_primary

crack widths

at

side

faces

of

three

beams

at'varieus stages of

test

The

changes

of

data

from

stage

A

to

B

of

beams

RC

3-2

(

2

)

and

RC

3-2

(

3

}

were slightly

different,

In

beam

RC

3-2

(2)

crack

widths

in

stage

B

were

increased

a

little

from

stage

A,

whereas

in

beam

RC3-2

(3)

such

phenomenon

could

not

be

observed.

This

difference

arised

_possibly

due

to

some reloading effects.

Although

the

injecting

_pressure

foT

resin was

5,O

kgflcmZ

which was much

higher

than

that

of

ink

injection,

the

magnitude

did

not affect

to

increase

crack widths.

The

data

in

Fig.

11

also

indicate

that

there

was some

decrease

in

crack widths

in

ttnloading

stage

D

which was relatively small and

had

similar

tendency

among

the

three

beams.

As

a matter of

fact,

Methods2

and

3

were

both

applicable.

Although

the

_{penetrability}

of resin was relatively

same

among

the

three

methods,

Method

3

was more

practical

than

Method

1

_{and much simpler}

thgn

Method

2.

Therefore,

Method

3

is

proposed

for

the

investigation

of

this

subject,

'

5.

Conclusions

This

paper

describes

a new

injection

test

technique

for

investigation

of

internal

cracking

of

concrete

members such as

_partially

_prestressed

concrete

and

reinforced concrete.

Results

from

the

conventional

injection

test

indicated

that

if

ink

or

resin

alone

is

injected

into

cracks ofa specimen

the

crack

_pattern,

sizes and shapes of

the

cracks

can not

be

obtained

directly

and

together

as

they

are.

An

idea

was conceived

in

trying

to

inject

both

ink

and

resin one

by

one

into

the

same specimen, and

the

method

is

called

"double

injection

technique".

The

test

may

be

conducted

in

two

ways;one

is

te

untoad

the

beam

after

ink

injection

and reload

it

to

utilize

the

internal

vacuum suction and

the

other

is

to

inject

resin after

ink

without unloading

the

beam

in

order

to

ayoid any reloading

effects,

The

examination was consequently

done

and

the

results may

be

summarized as

follows

:

(

a

)

Checking

changes

in

surface crack widths confirmed

that

reloading effects may enlarge

_primary

crack widths

to.some

extent

(b)

The

absence of

internal

vacuum suction

in

the

double

injection

(double

injection

E)

does

not affect

the

penetrability

of resin.

(c)

Injecting

_pressure

of

5.

0kgffcm2

for

resin

injection

in

this

study

does

not affect

the

cracking conditions,

(

d

)

The

double

injecting

method

proposed

in

this

paper

which

does

not Tequire unloading work seems

to

be

one

of

the

most

_practical

and reliable

technique

for

the

investigation

of

internal

6racking

of concrete members.

References

l)

Iilston,

J.

M.

and

Stevens,

R.F.

:Internal

Cracking,

J.

Concrete,

_Jul.

_1972,

_pp.

_28-31.

2}

BToms,

B.B.

:

Technlque

for

Investigation

of

Inteinal

Cracks

in

Reinfercedi

Concrete

Members.

J.

ACI62,

Jan.

1965,

pp.35-43.

.

3}

Goto,

Y.

,

Ueda,

S.

and

Maki,

Y.

:

Investigation

of

Tension

Cracks

in

Reinforced

Concrete

Members,

2nd

Syrnposium

on

Defermed

BaTs,

Conefete

Library

No.14,

Dec,

1965

(in

Japanese).

4}

Goto,

Y,

:

Cracks

Formed

in

Concrete

aiound

Deformed

Tension

Bars,

J.

ACI,

Apr.

1971,

pp244-251.

s>

Goto,

Y,

and

Otsvka,

K.

:

Experimental

Studies

on

Cracks

Formed

in

Conprete

around

Deformed

Tension

Bars,

Proc.

JSCE

No.

294,

Feb.

1980

(in

Japanese).

,

t

/

6)

'Suzuki,

K.,

Ohno,

Y

and

Miyarnaru,

T,

:

FlexuTal

Behaviour

of

Partially

Prestressed

Concrete

Beams

under

Repeated

'

Loading,

Review

of

the

38th

Gengral

Meeting,

The

Cement

Association

of

Japan,

1984.

'

-31-【

研 究 論 文

1

UDC ：

624

．

012

．

46

：

624

．

012

．

45

：693

．

554 日本 建 築学 会構 造 系 論 文 報告 集 第 356 号

・

昭 和

60

年

10

月

プ

_レ．

ス

ト

レ

ス

ト

．

鉄筋

コ

ン

ク

1

丿

一

ト

曲

げ

部材

内

部

の

　　

ひ

び

わ れ

状況

に

関 す

る

実験

的 研

究

、

_（

_{梗 概 ）}

そ の

1

_{． イ}

ン

ク

・樹脂 ダブ

ル

注 入

実 験方 法

に

つ い

て

正

会

員 正 会 員 正 会 員

鈴

　　

木

．

’

計

　

夫

＊

大

　 　

野

　

義　 　

照

＊ ＊

ソ

ム

チ

ャ

イ ・

琴 リ

ー

ソ ン

ポ

ン＊ ＊ ＊

　

1．序

　

鋼 材

の

腐 食

の

観 点

か ら

，

コ ンク リ

ー

ト

構

造

物

の ひびわ れ は_， その

表

面で の

幅

だ けで な く

，

部 材 内 部

での ひび わ

．

れ

形

状

な ら

び

に

鋼 材

周

辺 での

_状

態

が

問 題

に な る。

特

に

鋼

材 周

辺の ひ

び

わ れ はコ ン ク リ

ー

トと

鋼 材

の

付

_{着 機 構}

に

も

重 要

な

影

響 を

与

え る

。

鉄 筋 コ ン ク リ

ー

ト

（

以

下

RC

と

略

記 ）部材

に お け る

異 形 鉄

筋

周

辺 でのひび わ れ

状 況

にっ いて

_内外

で い くつ _かの

研

究

が

報告

さ れて は い るが

，

次

の

2

節

で述べ _{る よ う な}い くつ かの

_課

題 が

残

さ れて いる。 ま た，

近

年 普

通

鉄

筋

よ り は

腐 食

に

敏 感

であ る と

言

わ れて い る

PC

鋼 材

を

用

い

，

常 時 荷 重 下

で ひ びわ れ の

発 生

を

許

す

m

種

PC

あ るい は

プ

レ ス トレ ス ト

鉄 筋

コ ン ク リ

ー

ト

似

下

PRC

と

略 記 ）構 造

が

利 用

さ れ

始 め

て いる が

，

従

来

プ

レス トレス トコ ン ク リ

ー

ト

構 造

は ひびわ れが

許 容

さ れてい な かっ たこと も あり

，

シ

ー

ス の

周 辺

，

グラ ウ ト

内

部 等

の

PC

鋼 材

周 辺

で の ひび わ れ

状 況

は まっ た

く 明

ら かに さ れて いない

。

　

本

研

究

は以 上の よ う な 諸 点 をふ ま えて

，

PRC

曲

げ

部

材 内部

の

鉄

筋

や

PC

鋼

材

周 辺

に お け るひ び わ れ

状 況

，

コ ン ク リ

ー

ト

断 面

を

横

断

す る 主 ひび わ れの

形 状 等

を

明

ら か に し よ う と す る もの で あ る

。

　 本報告

のその

1

では

，

観察手

段

と して

従 来

か ら

用

い ら れてい る

イ

ン ク あ るいは

樹 脂

をひ

び

わ れ

内

に注 入す る

方

　

i

　　　　　　

　

tt

法

につ い て

PRC

は り

材

へ の適

用 性

を

検 討

し

，

1

次

い でそ の

結

果 に

基

づ き インク と

樹

脂 を 同 じ 試 験

体

に 注 入 す る

「

double

　

injection

　

technique

_」

の

方 法 を 試

み て

良

い

結

果

が

得

られた の で これら の

注

入

方 法

につ い て の

検 討結

果 を

報 告

す る。 な お

，

こ れ ら

注

入

法

に

よ

っ て

得

ら れ た

PRC

曲 げ部 材 内

部

の ひ び わ れ

状

況 に

関

す る

結

果

は

次 回

に

報 告

する

。

　1 _{大 阪 大 学 　 教 授}

・

工博 ＃ _{大 阪 大 学 　 助 手}

・

_T

．

_修 ＊＊ ＊ _{大阪 大 学 　 大 学 院 生} 　 〔昭 和 59 年 9月7日 原稿受 理 口

，

昭 和

60

年

5

月

7

日改 訂 原 稿 受 理 　 日

，

討 論 期 限 昭和 61 年 1月末日 ｝

　 　

2．

歴 史 的 背 景 　 　 　

’

　 　

・

　 　

コ ン ク

リ

ー

ト

内部

の ひ び わ れ

状 況

に

関 す

る

既 往

の

研 究

　

の

主

な

も

の に は_，

樹 脂

を

RC

両 引 試 験 体

の ひ び わ れ

内

　

に

注

入 してコ ンク

リ

ー

ト

内 部

の ひ

び

わ れ

状

況 を

初

め て

観

　

察

し た

Broms

の

研 究

2 ｝，　

RC

両 引

試 験 体

や はり

試 験 体

に

　

イ

ンク を

注 入

して

異 形 鉄 筋

の ふ し か ら

発 生

しコ ンク リ

ー

　

ト

内部

で

閉

じ る

“

内部

ひび われ

”

の

存

在

を

明

ら かに し

，

　

また は り

内 部

の ひびわ れ パ タ

ー

ンを

調

べ た

後 藤 等

の

研

　

究

3L4 ）

，

5 ）

，

お

よ

び

Broms

と 同

じ

方 法

で

樹

脂

を

注

入 し

RC

　

はり

内 部

にお

け

る

主

ひび わ れの

形

状

やコンク リ

ー

ト と

鉄

　

筋

の

間

の は だ

離

れ に

_{言 及}

し た

Illston

と

Stevens

の

研 究

．

・

　］］_{な ど が}

あ

るが_， い

ず

れ も

RC

部材

に

関

す る

も

の で あり

，

ま たひび わ れ

制 御 設 計

の

対 象 と

なっ て いるコ ン ク リ

ー

ト

表 面

ひび わ れ

幅

ある い は

鉄 筋 応 力

とコ ンク リ

ー

ト内 部

で の

_幅

や は だ

離

れの

状 態 と

の

関 係

等

につ い ては

十 分

には

明

ら かに さ れていない

。

　

3．

予 備 実 験 （

実 験

1

）

　

己

　

3，1

実 験

概

要

　 試 験 体

は

表

1

お よ び

図

ユ に

示

す よ う な

RC

お よ

び

PRC

の

4

種 類

の は り で

，

そ れぞれ

イ

ンク お よ び

樹

脂 注

入

用

に

2

_体

つつ

_{作 成}

_{し た} 。 モ ル

タ

ル

お

よ

び

コ ン ク リ

ー

ト に は

早 強

ボル トラン ドセ メン

トを用

い _，

水

セメ ン ト

比

は いず れ も

55

％で ある。 グラ ウ トに は

ポ

ゾ リス

No ．

8

と アル ミ

粉

を そ れ ぞ れ

_セ

メ ン

ト重 量

の

0．

25

’

％ お よ

び

O．

005

％ を 混 人 し た

水

セメ ン ト

比

45

％

の

早 強 ボ

ル

ト

ラ ン ド セ メン トペ

ー

ス トを 用いた

。

これ らの試 験

時

の 力

学

的 性 質

を

表

2

に

示

す

。

鉄 筋

に は

_φ

11mm

の 丸

鋼

，

シ

ー

ス には

内径

23mm

の ス パ

イ

ラル シ

ー

ス

を用

い た

。

　

載 荷

は 図

4

に

示

す よ う な

片 持

ばり

形 式

で

行

い

，

荷 重

の

大

き さ は 固

定

端 に おいて鉄 筋

位 置

の コ ン クリ

ー

ト

応 力

が

零

の

状 態 （

以

下

本 報

では

Decompression

と 呼ぶ ） か ら の鉄 筋 応 力

変 化

量 △σ。が

3200kgf

〆

cm2 に な る よ うに

定

め た

。

注

人 は

載 荷 前

に

鋼 材

と

平 行

に

設

け た

径

3mm

の

注

入 孔 （図

3

参 照

）

にイン クまた は

樹 脂

を

満

た し

，

載 荷 中

一 32 一