暑中環境下で打設されるモルタル試験体内部の温度分布に関する実験的研究

【論

　

文

1

UDC 　691

．

53　666

．

97 　　　

日本 建 築 学 会 構 造系 論 文 報 告集 第422号

・

1991年4_月

Jou

皿al 　of 　Struct

、

　Const【

．

　Engng

，

　AIJ

，

　No

．

4Z2t　ApT

．

，

1ggl

AN

　

EXPERIMENTAL

　

STUDY

　

ON

　

TEMPERATURE

DISTRIBUTION

　

INSIDE

　

MORTAR

　

SPECIMENS

PLACED

　

IN

　

HIGH

　

TEMPERATURE

　

AMBIENCE

　

　

暑 中環 境 下

で

_打設

さ れ る

モ ル タ ル

試験

体

内

部

の

_{温度 分 布}

に

関

す

る

_{実験 的}

_{研 究}

Yasunori

　

MA

　

TSUFUJI

＊

_，

　

Takaaki

　

OHKUBO

＊＊

，　

Tomoyuki

　

KOYAMA

＊ ＊ ＊

　　　　　　

松 藤 泰 典

，

大久 保

孝

昭

，

小 山 智 幸

　

In

　this　study _，　

the

　crack　occurrence 　

in

　the　early 　

time

　

in

　

the

　concrete 　

_placed

．

　

in

　_a　

hot

　_{weather 　en}

、

vironment 　was 　

discussed

　

from

　

the

　viewpoint 　of　the　temperature 　

distribution

　

in

　the

_、

specimens

．

　

Througll

　a　series　of　experiments 　

it

　was 　

brought

　

to

　

light

　

that

　the　relation 　

between

　the　ambient and ・ 皿

d・

・

f ・

mi ・

i

・

g

t・mp ・・atti_・es

，

　

h

・at 　

g

・

i

・

due’

t・

hyd

・ati・n 　and　

h6

・

t

　

l

・ ・s　

dti

・ t・

’

v・

p

・ ・

izati

_・n ・

ig−

nificantly 　affected　

the

　temperature 　

distribution

　

in

　

the

　specimens

．

　

KeVWOixls

：

high

　

temPerature

　ambience

，

　

initial

　crack _， 勿’Ztreather　concrete

_，

　

h

_）tiration

，　 uapariuation

，

　　　　　　

tempmature 　

diSt

_η

ibtttion

　　　　　　

暑 中 環 境，

初期

ひ び割れ

，

暑 中コ ン クリ

ー

ト， 水

和

，

脱水

，

温 度 分 布

1

．

　

lntroduction

　　　　　　　

’

．

　　　　　　　

．

　　　　　　

．

　

　

There

　

is

　a　

general

　view 　

that

　concrete 　mixed 　and

_／

or 　

_placed

　at　

’

a　

high

　ambient 　

temperature

，　namely 　

in

　a

hot

_甲

_『

ather environment _，　

be

　more 　

likely

　

to

　create 　se ヤeral 　

deficiencies

　

including

　

decreased

　workability

and 

long−

term

strength 　and 　

increased

　crack 　occurrence 　

than

　

the

　same 　

that

　was 　

_processed

　

likewise

　

but

　at

anormal 　

temperat

ロre1〕

．

　

In

　

this

　context

，

　many 　standards 　and 　specifications 　

including

　

JASS

　

5

　

have

provisions

　spec 主

fying

　a　mean 　

daytilne

　

temperature

　of　

25

℃ or　

higher

　

through

　

the

　apPlicable 　season

・

and

止eend

−

or

・

mixing 　

temperature

　

at

　

or

　

below

　

30

°

Cm

．

　

Howev6r

　neither 　reasoning 　

how

　

these

　values 　were 　set

nor 　sUggesting 　any 　

drawback

　expected 　wi 出

actual

　

temperatures

　

beyond

　

them

　were 　exactly 　cla

’

rified

_．

The

　relation 　

between

　many 　

problems

　associated 　wi 出

hot

　weather 　concrete 　and 　

the

　sources 　_of　

the

respective 

_problems

are　not 　

yet

　well 　explicated 　

by

　

quantitative

　approaches

，　so　such 　

provisions

　

for

　

the

hot

　weather 　concrete 　are　standardized 　

by

　only 　

qualitative

　countermeasuresz ，

・

3 ）

_．

　

　

In

　order 　

to

　establish 　an　acceptable 　

quality

　

Standard

　of　

the

　

hot

　weather 　concrete

，　

it

　

is

　essential 　

tha

ガ

the

problems

　Qf　

hot

　weather 　concreting 　

are

　at　

first

　analyzed

．

　

A

　recent 　report 　on 　

the

　

hot

　weather 　concrete4 ）

indicates

　

that

　as　

far

　as　

physical

　

_propqrties

　concern 　

there

　

is

　no　

drawback

　

to

　

the

　strength 　

dev610pment

　_of

the



body

　

because

　of　mix 　

plOPortion

　

for

　summer season 　except 　

the

　

degradati6n

　of　

the

　surface 　

layer

，

initial

　cracking 　

in

　

partichlar

，

　which

．

may 　create 　serious 　

problems．

　

　

Frbm

　

this

　

point

　

qf

　view 　and 　

particularly

　concerning 　

the

　

intemal

　

temperature

　condition 　of　specilnens

，

we 

have

conducted 　

the

　

present

　work 　

in

　order 　

to

　evaluate 　

the

　effect　of　ambient 　

temperature

　on 　

the

　

initial

cracking 

that



_grows

on　

thin

　concrete 　slabs　

for

　

floor

_，

　wall　ahd　

the

　

like

，　which 　are　

produced

　

in

上ot

weather 　_environments

．

本 研 究の

一

部 を， 平 成2年度建築学会大会で発表した

．

　　　　　　　

’

　

＊

Prof．

_，

　

Dept

．

　of　

Architect

ure

’

_，

　Faculty　of 　Engineering　

Kyushu

　　　

Univ

．

，

Dr

．

　

Eng

．

ts

　

Assoc

．

　

Prof

．

，

　

Dept

．

　of　Architecture，　

Faculty

　of　

Engineering

　　　Kyushu り

niv

．

，

Dr

．

Eng

．

＃ ＊ Research

　

Assoc

．

，

　

Dep

し



of　

Architecture

．

　Faculty　of　

Engineer

−

　　　

ing

　

Kyushu

　

Univ

．

，

M

．

　

Eng

．

九 州 大学 工学 部建築 学 科

　

教授

・

工博

九_{州 大 学工 学 部 建 築 学 科　助 教 授}

・

_{工 博}

九州大学工学 部 建築 学 科

　

助手

Study

on

the

relation

between

internal

temperature

distribution

of massive concrete

bodies

and crack

development

on

them

has

made noticeable

_{progress5)･fi).}

JASS5

defines

the

mass cencrete as

the

temperature

difference

of

25eC

or

higher

between

the

outermost and central

layers

as concerns as

concrete

body

of minimum size of

80

cm or

bigger.

In

other wards, crack occurrencg of concrete

body

is

evaluated on

the

basis

of spegific

physical

quantity,

namely

temperature.

Crack

occurrence'of

hot

weather concrete could

be

evaluated

by

the

same･way with mass concrete

except

for

the

minimum size

preyision

becquse

temperature

difference

inside

concrete

body

could

be

a

principal

cause as

it

enhances stress

by

accelerating

drying

shrinkage,

bleeding,

etc.

It

is

important

to

quantitatively

evaluate

the

relation

between

ambient

temperature

and crack occurrence, refLecting

the

fact

that

the

hot'weather

cohcrete

intrinsically

relates

to

high

ambient

temperatures.

In

this

study,

it

was

focused

to

evaluate

the

effect of arnbient

ternperatures

to

be

brought

onto

the

temperature

conditions of specimens as a

basic

study on

the

relation

between

high

temperature

ambience

and crack occurrence.

1'

-

'

For

the

experiments, mortar specimens were

_prepared

under various environmental conditions,

being

subjected

to

regular measurement of

their

internally

distributed

temperatures

for

24

hours

in

erder

to

exhibit

how

the

both

ambient air

temperature

over

the

_period

and

mortar

temperature

immediately

after

mixing, namely

end-of-mixing

temperature,

affect such

internal

temperature

distribution.

The

ambient

temperatures

were

kept

constant

through

the

_periods

of

_,placing

and curing.

2.

0utline

of

Experiment

2.1

Specimens

,

,. ,

The

materials of

the

specimens

for

the

_present

experiment and

the

mix

_proportion

and

_planned

end-of

-mixing

temperatures

are shown

in

Tables

1

and

2,

respectiyely.

Normal

_portland

cement and

beach

sand are used

for

all

the

specimens with a water cement ratio of

50

%.

_,

.,

･

,

For

the

_present

work we set

the

standard e,nd-of-mixing'temperature at

300C

as specified

in

JA$Ss

t

t

with

_'

two

additional

levels,

higher

and

lpwer

by

loeC

respectiyely,

thus

resuiting

in

20e,C,

3oeC

apd

'

4oeC

levels.

In

order

to

accomplish

these

planned

_,

,,

,,

temperatures,

the

respective materials were

_pre-

Tablel

Physical

properties

of materials

heate.d

up

to

the

teinperatures

shown

in

Table

2..

Placing

was rnade

immediately

after mixing.

2.2

.i

Conditions

of

･A.

mbient,Air

_,

.

For

the

present

woTk we selected

three

ambient

_,

teThperatures

of

15eC,

2seC

and

3seC

(2seC

±

_.

,

loec

as specified

in

JASS

5),

so

that

the

relatiOn

_Table2

Mix

_proportion

of mortar specimen

between

the,

ambient and specimen

teMPeratUreS

･

･

_and

_temperature

of materials

,

be

experimentally

found.

The

ambient

humidity

wqs

kept

constant at

,ZO

%

throughout

the

ex-penment.

,

,

'

These

ambient conditions

for

the

expenment

,

were accomplished

in

a curing room

3･OX3･5

×

tal･ga

i.:lem$

ss:;:l:i･ee

gpep,,',awa.,

i-

kt

℃_℃

2.

4

m

in

size under

the

_gontrol

of a warm and wet

_,

Seriesc:plamed end-crfmixing tempe:atune= 4oec

ambience simulation system').

Figure

1

shows the

'Matevia!sUsednaterialsSpecificGravi

ALserbedWater BatioX

OoumuitNerm1PortlanKl-OcaMlt.

'3.15

_-t

FineiggregateBeachSand' 2.ee(surfaoe-dry) 2.05 TetqperatureofMaberials,℃ Materials' WeightrfdebiesASeeiesBseriesC Watet ZB9,eoeo20 icemerit

579ac,co50:

FineAggregate1331･---･acsu40

schema of

this

simulation system which consists

of

detecting,

controlling and

final

controlling

elements.

The

detecting

element

detects

the

present

values of

temperature

and

humidity,

the

controlling element cqmpares

these

levels

with

reference

levels

and adjusts

the

output signals of

-2-tm3.0x3.5x2.4m

_{FinalControlling} Elenent Contoro11i Eldnent

un6.0x2.2x2.a"

DeteetingElerent Interfaoebetecting

Elecnmt

Cmpter

Figure1

The

s'cherna

･set

tenperetureand humidiby

･

get theP.I.P.Value

the

final

controlling element accordingly.

The

setting accuracy of

the

system

is

within ±

O.

sOC

for

temperature

and within about ±

2%

for

humidity.

'

2.3

Measurement

Item$

In

this

context,

the

mortar specirnens made of

those

mixes with

the

_proportions

shown

in

Table

₂

were

subjected

to

measurement

for

recording temperature change and

depth-wise

distribution

through

a

24hours

_period

from

the

_placing

time.

'

It

is

thought.that

the

temperature

change ofspecimes after

_placing

b6

affected

by

(

1

)

external causes such as ambient

temperature,

humidity

and wind speed and

internal

causes such as

(2)

cement

hydration

heat

_(gain)

and

(

3

)

vaporization

heat

due

to

water vaporizing

from

_the

surface

(loss).

From

this

_point

ofview;

in

addition

to

th'e

aforesaid

temperature

measurement,

the

heat

_generation

rate

in

the

specimens

due

_to

hydration

and

the

water vaporizing rate

from

_the

surface

(water

losing

rate) were

recorded so

that

the.time-based

_profiles

of

these

rates were

_plotted.

All

these

measurements constitute

the

_ground

foT

ultimate,ly evaluating

how

much effect such

internal

causes

have

brought

onto

the

temperature

conditions of

the

specimens.

All

the

measurement

items

are

Iisted

in

Table

_3,

of which

the

Tespective measurement methods are

outlined as

follews:

(a)

Temperature

measurement at

_points

distributed

inside

the

specimens

Each

specimen was a rectangular solid of

₄₀

cm

long,

₁₀

cpt wide and

10

cm

high,

with only

the

top

face

_(hereafter

"Open

_Face")

of a

40

cm ×

10

cm rectangular exposed

to

the

ambient air and

the

rest of

the

faces

isolated

from

the

air

by

means of a steel sheet

form

which conducted only

heat

tolfrom

the

ambient air.

In

other words,

drying

process

was allowed merely

through

Open

Face.

The

_{steel sheet}

form

was used

in

the

experiments

because

its

thermal

conductivity was

big

and

the

water of

fresh

mortar

specimen was not absorbed

into

it.

The

temperature

of such steel sheet

forms

had

been

brought

_into

equilibrium with

the

ambient air

before

_placing

was made

for

the

specimens.

The

temperatures

at

_points

distributed

inside

the

specimens and

their

changes with

time

were

measured

by

means of copper-constantan

thermocouples

atevery

five

minutes

for

24

hours

after

_placing.

The

thermocouples

were

_placed

at

_points

lining

along

the

vertical axis at

the

center ef

each

specimen with

distances

_specified

from

Open

Face

_{and rnortar}

_placing

_{was made carefully so as}

_to

_ensure

_the

mortar

in

full

contact with

the

thermocouples.

A

specimen

for

each series was subjected

to

this

measurement

because

it

had

been

_clarified

by

_preliminary

_experiments

_that

_temperature

_distribution

inside

specimens was

insensitive

value

to

the

organization of mortar specimen.

Such

measuring

_points

are shown

in

Fig.2.

The

heat

is

transferred

over

the

lateral

faces

of the specimen

throughout

as

the

lateral

faces

are net adiabati6

in

this

experiment.

However

on

the

assumption

that

this

rate of

heat

transfer

is

uniform,

from

the

measurements obtained

by

this

setting,

the

temperature

distribution

qualitatively

and

the

temperature

difference

in

the

section

_{quantitatively}

may represent

the

_general

state

in

wide slab of

_10cm

thick,

respectively.

(b)

Measurement

of

heat

_generation

rate

due

to

hydration

The

hydration

heat

was measured

for

24

hours

after

the

end-of-mixing

time

by

means of a micro calorimeteT.

The

specimens were

prepared

with

the

mortar

in

the

_proportion

as shown

in

Table

_2.

The

measurement was made at ambient

temperatures

of

150C,

250C

and

･350C,

the

sarne as

those

for

the

principal

experiment.

The

materials were

brought

inte

these

_temperatures

_befor

mixing

for

the

sake of

conditions

imposed

by

the

measuring system.

Three

specimens

for

each series were

_prepared

for

this

Table3

Measurment

Items

Heasurmer:tItens AmbientCmiittons

TratureHurnidiPlarmedhrrd-of-mixingTerperatuee Tenrperatu:eofspecirm

_{'Heightofvapo:izedWater15,25,ss.C70%R.H.}

_20,se,co℃

undertherespevtiveAmbientConditims

Heatduetokydratien _{equaltomspeetivembientTenpevattre}

-3---"t

..;.el,i･:..'/''r:,':1i.:1':'{li.;:'I,:

;'.i:.CInpftieL･:/-'.',rLt

tt

-!/.

ttttt

.,･Y'i;,':'l"li'';･";:'':'

-S..:.).v.,rt-/

±

=-

x

-::tt.-:t:tt.-1:,v--l･sJ

t

11

Stealseetform---J---Measuring_points

.

Syrrilpl

P,

iwa

]TIZs5

xB8

s

m

ll2

T,6,,O

xe

mo IEnwhber ofsrninl rm

tredistarx)efruuopen fa)e,mm

Figure2.

Measuring

_points

of temperature

in

the specimeB -: 6.0=･stu.

50vo.･

4Ds: 3.0g:

20::

ID",otidi

o

ii111:･iilii･ii･

,II AabientTevmp.

...150C

--･---25

℃

-

ss℃ :Ii.1//i!1Ill11!ltili'ti,,1..Li':!!

-,,IT4i'Iili.1il'tt,=

tL/./.

t[/Ii111l/1111/lIllillllII

i

･Tn,ll1'l.l.･iLi1!L'l

Mlilill-[F-ll;Ii

11Ll1.1

N-[l{i･:.l,II.tii-E-rs.i.MI

T-.i''lItii1I･lliiil･

2

4

6

8

P

12 va 16 18

20

22

pt

Time aftier pleE'ing .hours

Figurq3

T,he

curves of

heat

generation

rate

due

to

hydration

measurement. ,

･

,

(c)

Measurement

of

the

amount of vaporized water

<lossed

water)

･

.

,

For

measurement of

the

amount of vaporized water, specimens of

10

cm

high,

the

same,height as

that

of

the

specimens

for

the

_principal

experiment

but

with asquare

top

face

(Open

Face>

of

5

cm ×

s

cm were

used

for

single

face

drying.

The

amount of water of vaporized

from

Open

Face

was measured at a

precision

of

O.

ol

g

every

15

minutes

for

24

hours

and

the

change with

time

was

plotted

to

evaluate

how

much

the

temperature

distribution

in

the

specimens

be

affected,

by

the

heat

loss

due

to

water

･vaporization.

_Three

specimens

for

each series were subjected

to

this

measurement

for

_producing

a mean

value.

Heat

loss

per

specimen was obtained

by

converting

the

measured amount of water vaporized

from

Open

Face

of

the

special specimen

in

the

_preliminary

experiment.

In

p.onnection

with

this,

heat

loss

of

,580

cal

_per

_gram

of water

loss

was assumedS}.

3.

Test

Results

and

Discussion

3.1

Curves

of

Heat

Generation

Rate

due

to

Hydration

.

The

curves of

heat

_generation

rates

due

to

hydration

in

the

_present

specimens at ambient

temperatures

of

150C,

2sOC.,and,3seC,

respectively were shown

in

Fig.3.

These

curves represent

the

amount of

generated

heat,per

cerpent weight

(g)

in

specimen

for

temperature

measurement

(10

×

10

×

40

cm).

The

higher

the

ambient

temperature

was,

the

_greater

the

maximum value of

the

heat

generation

rate

due

to

hydration

was and

the

more

_quickly

this

value was reached.

The

_profile,

of

the

hydration

heat

gene.ration

afteT

the

_period

of accelerated

hydration

took

a shape similar

in

general

to

those

of

the

time-depend.ent

temperature

changes

in

the

specimens as showp

Fig.

5

in

Subsection

3,

3,

indicating

that

the

heat

_gain

due

to

hydration

significantly affected

the

,thermal

behavior

of

the

specimens.

3.2

Curves

of,Rate of

Heat

Loss

due

to

Vaporization

･

'

.,

,

ACI

prepared

nomographs

for

predicting

an amount of water vaporized

from

a

fresh

concrete ma'ss on

the

basis

of relation

between

the

temperature

of

the

concrete and

its

ambience

(temperature

and

humidity

of the ambient air and wind speed9).

Disctissing

only

the

temperature

aspect

based

on

these

nomograph,

the

higher

the

concrete

temperature

is

ata consistent ambient

temperature

or

the

lower

the

ambient

temperature

is

with a concrete mass

having

a consis'tent

temperature,

the

gieater

amount of

water evaporates.

This

behavior

agrees well with,tbe result

_{gf'vapQrizatiQn}

measurement

in

the

_present

'

experiment. /

'

2.0H.

1.8kpt

1.6vd3 1,4v: 1,2-ts 1,Oag o.B"o'

O,6X

O.4i'

O.2

tt

o

l･ kmblent/terO..ut, lF,-M)d-ef-mixingTenp.

---･----20

_℃

-.,.,..."30

_℃

-

urc ::/i/mtt1

k.･-1

lirrl al

Itt;llijil

''' _l,::

･i･il

EF

.ttvlH,,

--

_i

(a)

The

24

68

10

12

l4

16 le

₂₀

₂₂

_pt

Tine after plating .heurs

curves of amount of vaporizea water

k 1.5zexooxU.

'1.0g:fi

O.5sxfi

o

'im･:-,2sc-t-t-t-t-tind-orf-ntixingTerp,

_{"""'.2oec'3cr.C400c}

.--...

---24

<b)

The

curves

68

O

12

va

16

18

ap

22 2L T±me sfter pleeing ."eurs

of rate of

heat

loss

due

tovaporizatien

Figure4

Test

results of vaporized water

As

examples

of

test

results,

the

amount of vaporized water and

the

rate of

heat

loss

_per

mortar weight

(g)

due

to vaporization

from

the

specimens, measurements･of

these

w'ith

the

specimens

having

_the

end-of-mixing

temperatures

of

20eC,

300C

_4nd

400C

at

the

ambient

temperature

of

250C

are shown

in

Fig.4(a)

and

Fig.4(b),

resPectively.

The

rate of

heat

loss

exhibited a maximum value

immediately

after

placing

and

theri

decreased

quickly

foT

1

to

2hours

before

taking

a

_gentle

downhill

slope.

The

higher

the

end-of-mixing

temperature

of specirnen was,

the

_greater

the

heat

loss

was where

_the

ambient

temperature

was

･consistent,

within a

_period

of

1

to

2

hours

after

_placing.

Although

it

does

not appear on

the

figures,

the

lower

the

ambient

temperature

was,

the

_greater

the

amount of

heat

loss

was.

After

this

period;

the

difference

in

the

rates of

heat

loss

due

to

different

ambient

temperatures

diminished

to

mil as

'

the

time

elapsed.

In

other words, with specimens

having

a consistent end-of-mixing

temperature,

the

lower

the

ambient

temperature

was,

the

_greater

effect

the

heat

loss

due

to vaporization

_gave

to

the

speclmen

temperatures.

'

,

_,

From

these,

it

is

apparent

that

the

water vaporization significantly affects

the

-specimen

temperature

during

a

_period

of about

₂

hours

after

_placing

and

the

degree

of

the

effect changes

depending

on

this

temperature

as well as

the

ambient

temperature.

-･

,

3.3

Time-dependent

Temperature

Change

of

Specimens

3.3,1

Effect

of

Ambient

Temperature

The

time-dependent

tempe'rature

changes of

the

specimens under

the

respective ambient conditions

shown

in'Table3

were

plotted'in

Figs,5(a),

5(b>

and

5(c)

which. correspond

_to

_the

_planned

end-of-mixing

temperatures

of

20eC,

300C,and

400C,.respectively.

Each

set of curves

in

these'figures

consists of

the

six measuring

_points

of

T2,

5,

T10,

T20,

T30,

T40

and

T50

as shown

ih

Fig.

2.

The

number of symbol means･

the

distance

_(mm)

frorn

Open

Face.

'

These

curves of

the

lnternal

temperatures

of specimens

in

those

figures

represented a

_general

_tTend

that

they

came close

to

the

ambient

t.emperature

_quickly

during

the

_period

of about

3

hollrs

afteT

_placing

and

_then

went up significantly

higher

than

this.

The

_profiles

of

temperature

change

dbserved

at

Point

T2.

5

that

is

closest

to

Open

Face

are schematically'shown

in

Fig.

5

which suggest

that

the

_principal

three

factors

listed

in

tfie

_pTevious

section

be

contributory

to

this

_general

trend.

During

a

_period

of about

3

hours

afte.r

_placing,

the

specimen

temperature

rises with an end-of-mixing

temperature

that

is

lower

than

the

arnbient

temperature

and

falls

with

the

reversed relation of

the

two

temperatures.

The

differehce

in

the

shape of

the

_pro'files

is

more

d･istinct

with a

larger

difference

between

the

two

temperatures.

This

time

section represents

the

dormant

_period'for

hydration

_and

it

is

thus

deduced

that

the

steep

temperature

changes

be

dominated

by

those

due

to

heat

conduction

_to!from

-5-the

ambience.

IF

addition,

the

heat

loss

due

to

Vaporization

affects such

temperature

changes

during

this

_period

so much so

that

it

can not

be

ignored.

As

shown

in

Fig.

6

for

instance,

with an

end-of-mixing

temperature

higher

than

that

of

the

ambience,

the

temperature

of specimens changes

taking

a course

below

the

level

of

the

latter

for

a while when a

_period

of

2

to

5

hours

has

elapsed

after

_placing.

This

can not

be

rgasoned

by

heat

conduction andlor

hydration

but

only

heat

loss

due

to

vaporization at

Open

Face

and

the

signifi-cance

of

the

third

effect

in

the

specimen

tempera-ture

change

is

so

indicated,

When

the

_period

of accelerated

hydration

had

come,

the

specimen

temperature

started

to

_go

up,

resulting

in

the

profile

having

a swelling above

the

ambient

ternperature.

As

typified

by

the

curves

in

Fig.5,

the

temperatures

inside

speci-mens reached

their

_peaks

in

a range

from

7

to'

16

houTs

after

_placing,

though

their

heights

signi-ficantly

varied

depending

on

the

ambient

temper-ature,

It

was

found

that

the

higher

the

ambient

ternperature

was,

the

higher

these

heights

were

and

the･more

_quickly

the

peaks

came.

As

discus-sed

later,

the

_gradient

of the

distribttted

tempera-･

ture

field

inside

the

specimens

became

maximum.

As

the

time

further

elapsed,

the

specimen

temperatures

came closer

_gradually

to

that

of

the

ambience and

they

were almost

in

line

with

it

after

about

24hours

from

_placing

time.

As

seen

in

Figs.

s,

the

higher

the

ambient

temperature

was,

the

more

_quickly

the

specimen

temperatures

be-came

in

line

with

it.

Summarizing

these

findings,

the

effect of

the

ambient

temperature

on

the

temperature

change of

specimens was significant, and

the

higher

the

former

was,

the

more striking

temperatu're

profile

was shaped

in

a shorter

time

afteT

_placing.

3.3.2

Effect

of

End-of-mixing

Temperature･

With

the

end-of-mixing

temperatures

of

20eC,

30eC

and

400C,

the

specimen

temperatures

changed with

time

as.shown

in

Figs.7fa),

7(b)

and

7(c),

respectively under

the

ambient

condi-tions

specified

in

Table2.

The

curves

in

these

figures

represent

the

temperature

profiles

at

Point

T2.5

that

was closest

to

Open

Face

and

Point

T50

that

located

in

the.middle

of

the

specimen

height.

The

rest of

the

'measuring

points

-6

--ve .' ut a -e

,H

u e a op -e u k = -di -,e a e etv ue

.

mse:xx-,

:s:x:

-ve -th g di ti-ri v e ; -･-o -p u rd " -_" H ¢ p

co353025ro15

,493S3025oo

15 40353025

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Figure

5

e246

Ti.e

B

10sfter

12

14plating16

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10,heuTs22'

pa

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tt

,l,1"1eentfal,la,ge

'

/t

mbioric:.;3st{]ttesi,i,ri,it.

laei'I'rritlpt

tuedtlcdibZ-2sFt

/1fab

{Imtrgltayqr'ld) 1

imaicteibilrstc

epehfate

024.

6Time

S

10after

12

14placing16

IS

20

n

pa

,hevrs

/tt/

(t)IEtxYtr."erp.iApt

lcatfaX.th.ytr

l1/

Aabiait/tut).-stcctucate. eerndtspt ltmwhLdrij':"2geC C)enfabe [tht!allaYtr'

imittidi,LIStcCfpehfde

,O

2

4

6

8,

P

12.va

T6

18

ro

22

pa

rime

after _placipg .hours

Time-dependent

temperature changes of the

specimens

(Effect

of ambient

temperature)

'/E

3o

g

v

2s

t

g2o

a

5

'

O

-2

4

₆

8'O 12 va 16 IB Z) 22 M

Time efter plecinR

.hours

Figure6

Typical

figure

of time-dependent temperature

ve . 40mS35"vX30mX

25:e

ro:v?15e

oo .40mS35avX

30e-o

25:g

totsg

i5ts

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4035

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02468D

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ro

22

pa

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o

.2

46eV12

_va

₁₆

Ttme eiter placiaa

ls

ronz

,hours

O246Bn12

va

16

IB

ronZ

Time efter pleeina .hours

Figure7

Time-dependent

temperature changes of

the specimens

(Effect

of end-of-mixing

temperature)

bited

temperatures

between

those

at

these

two

As

Figs,7

tell,

the

effect of end-of-mixing

ve

.esaxtrx:Bexsts

32.530.027,52502Z520.017.515D12.5

o

32.5e

bopg

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27.5geetsX

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ve .tud-1"geaca-oek'"eliUae"ts 42,5co.o3Z535.032.5,30.0275

Figure

8

(a)

keienttttp.a 1sc,End-ofdw teep.-

3[f

℃

o

1,o

_ee

_so

_4o

_so

6D

no

eo

gD

lao

The distenee from open face

.c-o

ID

2o

3o

a,o

so

oo

lo

ao

go

toD

The d±stanse fTom open tace

,c-(c}

inbienttenp.

=

st,

Ehdi-ef-mhdrR tap. . Xf℃

o

ID zo

_3s)

4o

_so

_6o

_7o

_aD

_go

_nD

The dtstanse from open feee .cm

Temperature

distributions

inside

specimen

polnts.

temperature

was observed only

for

about

5

hours

after

placing

as

far

as

this

temperature

was confined

in

the

range of

the

present

experiment.

After

such

_points

of

time

the

specimen

temperatures

changed

in

similar

_profiles

under

different

ambient cenditions

regardless of

the

end-of-mixing

temperature.

This

brought

it

to

light

that

the

end-of-mixing

_temperature

hardly

affected

hydration

heat

_generation

during

the

_peTiod

of accelerated

hydration,

while

the

ambient

temperature

dictated

the

height

of

the

peak

of

the

specimen

temperature

_profile

as well as

length

of

time

required

by

the

_peak

to

appear after mortar

_placing.

Before

discussing

the

importance

of control on end-of-mixing

temperature

under

the

hot

weather

environment,

it

has

to

be

determined

what effects of

the

temperature

conditions

inside

specimens

for

about

5

hours

after

placing

be

given

to

their

_physical

_properties.

3.4

Temperature

Distribution

inside

Specimens

3.4.1

Effect

of

Ambient

Temperature

The

temperature

distributions

inside

specimens are exemplified

by

Figs.

8(a),

8(b)

and

8(c)

which

-7-represent

the

results of experirnent under ambient

temperatuTes'

of

15eC,

25eC

and

35eC

respectively.

All

these

curves w.ere obtained with an end-of-mixing

temperature

of

30"C,'!o

each of which a number

indicating/the

length

of time after mortar

_placing

was attached.

With

an end-of-mixing

temperqture

higher

than

the

ambient

temperature

as

in

the

cases of

Figs.

_8(a)

and

8(b),

the

temperature

distribution

inside

specimens were represented

by

the

convex curves with

their

top

located

nearly

in

the

middle of

the

specimen

height

(5

cm

distant

from

Open

Face)

after

the

time

of

placing.

On

the

other

hand,

with an end-of-mixing

temperature

lower

than

the

ambient

tempe;ature

as

in

the

case of

Fig.8(c),

the

temperature

distribution

curve

immediately

after

_placing

took

a concave shape with

its

bettom

nearly

in

the

middle and

it

_gradually

flattened

and

then

took

a

convex shape.

Comparing

the

temperatures

of

the

both

outermost

layers

(top

and

bottom)

with

each other of

the

respective curves,

the

top

layer

having

Open

Face

exhibited a

lower

temperature

than

that

of

the

bottom

one

isolated

from

the

ambienqe

by

the

steel

form.

This

may

_probably

be

attributed

to

the

heat

loss

due

to

vaporization at

Open

Face.

On

the

assumption

that

the

both

temperatures

of

the

steel

form

and

the

ambient air were equal,

it

may

be

deduced

that

the

temperature

difference

between

the

two

layers.be

virtually caused

by

the

heat

loss

due

to

yaporizat'ion.

_.

'

As

is

apparent

in

Figs.

8,

t,he

closer

to

an outermost one a

_given

layer

was,

the

lower

temperature

and

the

_greatei

_gradient

of the

distribution

curves it exhibited.

'

The

time-dependent

changes of

the

temperature

difference

between

the

outermost and central

layers

were

plotted

for

the

respective ambient

temperatures

as shown

in

Fig.9(a)

to

9(c).

The

_greater

the

temperature

difference

between

the

two

layers

is,

the

_greater

_gradient

thermal

strain may

be

_produced

in

a specimen, resulting

in

a

_greateT

_possibility

of crack occurrence.

_.

With

aconsistent end-of-mixing

temperature

as

in

Figs.

9(a),

9(b)

and

9(c)

at

that

of

2oOC,

3oOC

and

'

4oeC,

respectively, such a

tendancy

was

found

that

the

higher

the

difference

between

ambient and

end-of-mixing

temperatuTe

was,

the

greater

the

initial

temperature

differece

between

the

outermost and

central

layers.

Furthermore,

this

difference

exhibited a maximum value at

the

same

time

when

the

temperature

change

_profile

had

reached'its'peak as

described

in

Subsection

3,

1,

,and

the

higher

the

'

ambient

temperature

was,

the

greater

the

maximum value was.

Sirnilar

tendencies

were observed with

'

other end-of-mixipg

temperatures.

3.4.2

Effect

Qf

End-of-mixing

Ternperature

The

effects of end-of-mixing

temperatures

(200C,

300C

and

40eC)

on

,the

tirne-dependent

change

of

temperature

difference

between

the

outermost and central

layers

were shown

in

Figs,

10(a),

10(b)

and

10(C)

at an ambient

temperature

of

15eC,

25eC

and

35"C,

respectiVely.

'

In

these

figures,

such a

tendency

is

shown

that

with aconsistent ambient

tempeTature,

the

higher

the

end-of-mixing

temperature

was,

the

_greater

the

temperature

difference

between

'the･butermest

and

central

layers

became

in

the

early

time

(Domain

I

in

the

figures)

after

placing.

However,

the

difference

becarne

almost equal regardless of

the

end-of-mixing

temperatures

in

the

later

period

(Domain

ll

).

Here,

the

juncture

of

Domai･n

I

arid

Domain

ll

was

defined

as the time when the temperature

difference

between

the

specimens at each ambierit

temperature

becarne

O.

2eC

after

_placing.

As

Figs.

Io

tell,

the

junctures

of

the

domains

I

and

ll

were about

6.

5,

4.

5

and

4

hours,

･respectively

after

_placing,

at ambient

temperature

of

150C,

250C

and

350C,

exhibiting a

tendency

that

higher.

the

ambient

temperature

was,

the

shorter

became

the

_period

during

which

the

end-of-mixing

temperature

affected

such

temperature

difference

inside

specimen.

It

is

thottgh

that

the

magnitude of

temperature

difference

affects

the

_po$sibility

of crack occurrence, so

these

relation

is

disscussed

from

the

viewpoint of

the

tensile

strain capacity of concrete as

follows.

According

to

the

work

by

Kasai

et al.iO', the

tensile

strain capacity of concrete

is'about

several

thousands

_u

up

to

acumulative

temperature

of

60

to

80

TeT(ff.

"C

)

and

then

rapidly

_goes

down

te

exhibit

a minimum value of several

tens

_pt

at

_2oo

TOT

followedi

by

a very

_gentle

uphill slope extending with

the

.age.

Based

on

this

experimental results, the

length

of

time

required

for

th'e

tensil

strain capacity of the

-8-present

specimen

to

reach such a minimum yalue after

_placing

was estimated

to

be

_12.

₅

hours,

_7.

₃

_hours

and

4.

7

hours

at ambient

temperatures

of

150C,

25eC

and

350C,

respectively, all which

fell

in

Domain

ll

of

F,igs.

10.

It

seems

that

the

temperature

difference

between

the outermost apd central

layers

at

the

time

when

the

tensile

strain capacity

takes

as a small value as several

tens

_p

may significantly affect crack occdrrencg.

Furthermore

in

Domain

[

_of

Figs.

9

_and

10,

_the

_temperature

difference

_inside

_specimen

was not _affected

by

end-of-mixing

temperature

and

became

greater

when

the

ambient

temperature

bec4me

higher.

'

On

the

other

hand

in

Domain

I

of

Figs,

_10,

since

the

specimen

has

as much

tensile

strain capacity as

several

thousands

_pt,

it

seems

that

the

inter-layer

temperature

difference

between

the

outermost and

centTal

layers

may

little

affects crack occurrence.

Nevertheless

m

Domain

I,

the

higher

the

end-of-mixing

_teinPerature

was,

the

_greater

the

inter-layer

temperature

difference

was, and

the

_greater

the

difference

between

the

encl-of-mixing and ambient

temperatures

was,

the

more

_quickly

_the

i3.0

."'.4o e

I;

o

/k

_,,

e"iO "o

e

O2468P12 va 16 18

ro

22U

eU

O

24

68

n

12

va

16 18 ro 22 pa

Titue after plecing .ho"rS Tine after _plficivg

.hours

oe

.euau-U-igtrivekn"esk-a

-eu Ue ve.

.vucte"e-g-vvkw"a-vzaem-ee

4,O

3.02,O

1.0

o-1.0

Figure

9

(b}lem:of-orrfthgEerrp.=3crOc

Ftl/lill

't/

/tTt-.,.t..

Ii1

mbientTemp.

'

11l

t-t-'-tt'-tttttttt.15

25℃℃ 350C

Il-sstt-'i','--i･-.jjJ"bLLIIII!i1

s-

'-J

'

.

/ Jtt i

-P":L=i,-ll-L:-1/

l

ll/--Il111

,

tt..

Il['

O

･2

4

6

8

n

12

va 16 IB

20

22 pa

Time after placing .ho"rs

5.04.0

30mo1.0

o

O246Bn12

va

16

18

ro

22Z

Time after _plecing ,hours

Time-dependent

changes of

the

tempgrature

difference

between

open

face

and central

layer

of the specimens

{Effect

of a.mbient

ture)

d(e)EfuI-itdntienfp.tl4[ficIUU1

_tT:.'tt

-

r

i

f/l'tIf AmbientTenp, ' t

-t-t-t-ttt-ttt-ttt'15.C25

℃ ss'c

NI

h

l;

sJiitli-tt11

ll]

-'j'1'..i-;1.tl-!･'Fi-INIMI

llillll

a)AnhientlterP.=l,End-ofmixingTenp. LLtt',

t-t-t-t-t-t2e'c30ec40bC

'ttttttt

,ILll･tuI rl:'

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,

,imllL'

N'N1

''i

.

1' 1 u o. 4.0

s

g

3.o

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g.

2.o

:

1,O

3

:

e.

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:

"

-ID

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g

O2468n12

va 16 18

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22

Z

Ti-e after placing ,bou:s

ee ･ 4.o w

.

3.0

ts

U

2.0 -"

:

10

s

t

ts

o

e

e

-lo

o

fi

O2468D

12 va 16 le 20 22

pa

Ti-e efter plaeing .heurs

FigurelO

Ti!ne-dependent

changes of

the

temperature

difference

between

open

face

and central

layer

of the specimens

(Effect

of end-of-mixing

temperature}

--

9-(b}thibietitlterp.1ei2f{;

ltdaninI1,t dnninll Midsfmiiing

t-t-t-t-ttttt-ttttt

Tenp.20 ℃ sc℃ coeCii.1 tsl.S s.

fne

-L-I･

-FTTI-1 F t

<c)mbimetenp-43scEnd-eflmixingTonp.

idanninI ₂₀ ℃

t-t-t-t-t-tco'c

t

dmll-t---40bCL ,

'

i

_!

s

x

.

. L-.

d

'-'

M.:･1

'inter-layer'

_temperature

_differen

¢e changed. o".

3.0

Figure

11

shows

the

relation

between

:'such

inter-:.

_zs

layer

temperature

differehces

one'h6u'r after

_pla-'

'

g

zo

ci

'

?:･.,w,hs

'

gh,;;,2,tg.kg.",a:g,y.pi:a.'J,2'2e.Zlg,P.O,:l:g

･

,\.

Ibs

:IS:,[llP,i?",bl:Y,e,Zttr;S6.EkilS,ff,i#t,i?,2,`S,2::r,3I

'ao･s

less

ef

the

ainbient

tempe'rature

within

the

limits

:.

O

of

this

experirnent, which

is

characterized

by

the

fi

-O'5

inter-layer

temperature

difference

which

becomes

bigger

as

the

difference

between

end-of-mixing

temperature

and ambient

temperature

becomes

bigger･

This

relatien may

be

illustrated

in

such a

FigUre

11

way

that

there

is

no

difference

between

the

inter-layer

ternperature

differences

of

two

con-crete masses

during

a

_period

of several

hours

after

placing,

one

having

an end-of-mixing

tempeirature

of

20eC

and

placed

at

an

ambient

temperature

of

15eC

and

the

other

having

an end-of-mixing

temperature

of

40

35"C.

' AmbientTenp. i･ o15 ℃

-lt

A2s"c ''' oss.C "j'''''

'

''

''''

'''-ttt

'''j

'

/t)

t/t

-IS

-10

-5

O

5

10

15 20

_as

Ttieteptperature difference betveen

'end-･ef-mixing

tepperatu[e and azabient

teNperature ,OC

Time-dependent

changes of

the

temperature

difference

between

open

face

and central

layer

of

the

specimens

(Effect

of the temperature

difference

between

end-of-mixing temperature

and ambient

temperature)

eC

and

_placed

atailambient'

temperature

of

This

analysis of

the

measurements

in

connection with

the

respective

domains

led

to

aview

that

in

the

aspect of

temperature

difference

inside

specimen,

it

be

not necessary

fot

the

end-of-mixing

temperature

to

be

much

lowered

in

a

hot-weather

environment.

On

the

basiis

of

this

view combined with

the

finding

that

the

smaller-the

difference

between

the

end-of-mixing and ambient

temperature

was,

the

more slowly

the

inter-layer

temperature

difference

changed,

it'

may

be

deduced

that

bringing

the

end-of-mixing

temperature

close

to

the

ambient

temperature

be

effective

for

lowering

the

temperature

difference

inside

'

specimen.

However,･

the

loss

'of

workability

due

to

a

high

end-of-mixing

temperature

should

be

'

recovered

by

some operation41 means.

4.

Conclusion

In

this

study,

the

crack occurrence

in

the

early

time

in

the

concrete

_placed

in

hot

weather

environment

was

discussed

from

the

viewpoint of･the.

temperature

distribution

in

the

specimens.

Through

a series of

experiments

it

was

brought

to

light

that

the

relation

between

the

ambient and end-of-mixing

temperatures,

heat

_gain

due

to

hydration

and

heat

loss

d,ue

to

vaporization significantly affected

the

temperature

distribution

in

the

specimens.

The

_principal

results obtained

from

this

study aTe sumrnarized as

follows:

,

1.

The'ambient

temperatu.re

significantly affects

the

time-dependent

temperature

change of

the

specimens, and

the

higher

the

ambient

temperature

is,

the

more striking

_profile

the

tempeTature

of

the

specimens exhibits

in

the

early

time

after

_placing.

2.

Inside

the

specimens,

the

closer a m.easuring

point

comes

to

the

outermost

layer,

the

more steeply

the

temperature

falls

and

the

_greater

the

temperature

gradient

becomes.

In

the

cross sectiop

therefore

the

tensile

strains

due

to

the

temperature

difference

appear

in

the

outermost

layer

or

its

_proximity

rather

_than

the

central

layers.

3.

The

relation

between

the ambient and end-of-mixing

temperatures,

the

heat

gain

due

to

hydration

and

the

heat

loss

due

to

vaporization

from

the

specimens

be

the

_princiPal

factors

for

characterizing

the

thermal

conditions of

the

specimens

in

the

early

time

after

_placing.

4.

It

was

found

that

the

end-of-mixing

temperature

hardly

affected

the

temperature

diStribution

in

the

specirnens

during

the

period

in

which

the

tensile

strain capacity of concrete went

down

to

several

tens

_"