EVALUATION OF THERMAL STRESS BEHAVIOR AND …concrack5/PPT-PDF/General Presentation by T... · EVALUATION OF THERMAL STRESS BEHAVIOR AND DEF RISK OF CONCRETE USING FLY ASH CEMENT

JCI-RILEM International Workshop, CONCRACK5, April 24-26, 2017, Japan 1

EVALUATION OF THERMAL STRESS BEHAVIOR AND DEF RISK

OF CONCRETE USING FLY ASH CEMENT

Yuji Mitani, Takuya Ohno, Katsuhiko Tada

Taiheiyo Cement Co. , Research & Development Center


Background & Objective

In the warm regions (ex. Southeast Asia) ・No need for precise air content control (absence of freeze thaw action) ・Enhanced early strength development (increased pozzolanic reaction)

Evaluate applicability of FA concrete to mass concrete structures in Southeast Asia experimentally. Compare with cement containing high GGBS content 1. Mechanical property(Strength, heat, shrinkage…) 2. Thermal cracking risk(Thermal stress behavior) 3. Delayed Ettringite Formation(DEF) risk

Feature: improving workability, increasing long-term strength, reducing load to the environment, suppressing alkali silica reaction etc.

【Fly ash (FA) cement concrete】

Problem: difficult air content control, poor early strength

However…


Materials Used Material Symbol Quality Density Note

Cement OPC Ordinary Portland Cement/ Made in Japan 3.15 SSA: 3320cm2/g

Fly-ash FA Original Ashes/ Made in Japan

2.23 ig.loss: 3.41% SSA: 3330cm2/g,

Granulated ground blast furnace slag

BS Gypsum-added type/ Made in Japan 2.89 SO3:2.03%

SSA: 4310cm2/g

Fine Aggregate

S1 Dust/ Made in Malaysia

2.57 Absorption: 1.18%, F.M.: 3.32

S2 Natural Sand/ Made in Malaysia

2.55 Absorption: 1.17 %, F.M.: 1.82

Coarse Aggregate G Crushed Granite/

Made in Indnesia 2.62 Absorption: 0.71%

F.M.: 6.98

Chemical Admixture

SP Naphthalenesulfonate superplasticizer (Non AE)

- -

Ad Retarding water reducing agent - -

SSA: specific surface area measured by Blaine’s method, FM: fineness modulus


BS

Mix proportions

Binder types

W/B (%)

Unit contents (kg/m3) W OPC FA BS S1 S2 G

FA30 40

165

289 124 0 398 286 1050 50 231 99 0 437 314 1062 60 193 83 0 470 338 1052

BS65 40 144 0 268 403 290 1063 50 115 0 215 441 317 1070 60 96 0 179 474 341 1060

FABS 40 130 56 227 400 287 1053 50 102 46 182 438 315 1063 60 87 37 151 471 339 1054

W/B = 40%, 50%, 60% （W = 165 kg/m3） Slump: 12±2.5 cm, Air content: below 2.0%

30%

70%

FA OPC

35%

65%

14%

31%55%

【Binder】

Concrete mixing at 27℃ （SS EN206-1）


Test methods① (Basic mechanical property) Compressive strength： JIS A 1108 Young’s modulus： JIS A 1149 Splitting tensile strength： JIS A 1113 Adiabatic temperature rise：

•Air circulation type equipment Autogenous shrinkage：

• Specimen: 400 x 400 x 400 mm • Quasi-adiabatic curing(200 mm-thick expanded

polystyrene) • Strain meter embedded in the center • The form was placed in the 27℃ room

dia. 100×200 mm Water curing at 27℃

insulator Embedded strain meter (with thermocouple)


Thermal Stress • Uniaxially restrained specimen(100 x 100 x 800 mm) • Invar bar(Linear expansion coefficient : 0.5×10-6/°C) • Possible to measure both thermal strain and autogenous shrinkage

strain at the same time (Unique evaluation method)

• Quasi-adiabatic curing (200 mm-thick expanded polystyrene)

• The form was placed in the 27℃ room

800 19

(mm)

100 19

100

Invar bar (Elastic modulus： 140,000N/mm2) M26mm

Threads partially removed Strain gauge

Thermocouple

Test methods② (Thermal stress behavior)

insulator


0102030405060708090

0 2 4 6 8 10 12 14

Tem

pera

ture

(℃)

Age(days)

Simulating the condition inside the mass concrete

85℃ ① Temperature History ② Duggan process(1984, USA)

Test methods③ (DEF risk)

Delayed Ettringite Formation(DEF) • Accelerate test(Ref. Duggan method) • dia. 100×200 mm contact ring gauge

③Change in length is measured using the contact ring gauge

continue


Results 1. Mechanical property

(Strength, Shrinkage)


Compressive strength

20

30

40

50

60

70

80

1.0 1.5 2.0 2.5 3.0

Com

pres

sive

stre

ngth

(N/m

m2 )

B/W

FA30BS65FABS

28 daysBS65

FA30FABS

20

30

40

50

60

70

80

1.0 1.5 2.0 2.5 3.0 Co

mpr

essiv

e st

reng

th (N

/mm

2 )B/W

FA30BS65FABS

91 days

Compressive strength at the same W/B : FA30 < FABS or BS65 28-day compressive strength: FA30 (W/B = 40%) ≈ BS65 (W/B = 50%) 56- and 91-day compressive strength: FABS = BS65

27℃ water curing


Young’s modulus & Tensile strength

0

1

2

3

4

5

6

0 20 40 60 80

Split

ting

tens

ile st

reng

th f t

(N/m

m2 )

Compressive strength fc （N/mm2）

FA30BS65FABS

ft=0.18fc0.77

0

10

20

30

40

0 20 40 60 80

Youn

g's m

odul

us E

C(k

N/m

m2 )

Compressive strength fc （N/mm2）

FA30BS65FABS

EC=5.9fc0.4

Young′s modulus and splitting tensile strength could be expressed individually by functions of compressive strength, regardless of the binder type.


Adiabatic Temperature Rise

0

10

20

30

40

50

60

0 2 4 6 8 10 12 14

Adia

batic

tem

pera

ture

rise

(°C

)

Age (days)

W/B=40%

0

10

20

30

40

50

60

0 2 4 6 8 10 12 14 Ad

iaba

tic te

mpe

ratu

re ri

se (

°C)

Age (days)

W/B=60%

Temperature rise at 14 days: FA30 > BS65 > FABS Temperature continued to increase in BS65 and FABS after 14 days, more remarkably in BS65.

FA30 BS65 FABS FA30

BS65 FABS


Autogenous shrinkage

-400

-300

-200

-100

0

0 7 14 21 28

Stra

in (

x10-6

)

Age (days)

W/B=40%-400

-300

-200

-100

0

0 7 14 21 28 St

rain

(x1

0-6)

Age (days)

W/B=60%

FA30

BS65

FABS

FA30

BS65

FABS

Autogenous shrinkage: FA30 < FABS < BS65 (FA30 ≈ 1/2･FABS ≈ 1/3･BS65) Autogenous shrinkage increased with the increase in GGBS content.

Quasi-adiabatic curing Thermal expansion coefficient of concrete was assumed to be 10x10-6/℃


Results 2. Thermal Stress behavior


20

30

40

50

60

70

0 2 4 6 8 10 12 14 16 18 20 22

Tem

pera

ture

（℃

）

-500 -400 -300 -200 -100

0 100

0 2 4 6 8 10 12 14 16 18 20 22Age（days）

Inside Temperature & Strain of Invar bar

Temperature rise process ⇒Expansion strain

Temperature drop process ⇒Shrinkage strain

Maximum Temperature（℃）

W/B=40% FA30 59.3 BS65 59.3 FABS 57.5

W/B=50% BS65 53.5

FA30

BS65

BS65(W/B=50%) have equivalent compressive strength to FA30(W/B=40%)

FABS

FA30 = BS65 > FABS

Stra

in o

f Inv

ar b

ar(x

10-6

)

Expansion

Shrinkage

FA30 is smaller shrinkage than BS65 and FABS

Quasi-adiabatic curing


-1.0

0.0

1.0

2.0

3.0

4.0

5.0

0 2 4 6 8 10 12 14 16 18 20 22

Stre

ss （

N/m

m2 ）

Age（days）

Stress-Strength ratio(Tensile stress / Tensile strength): FA30 < FABS < BS65 FA30 has a higher resistance to thermal cracking as compared to

BS65 and FABS

Binder types σt （N/mm2）

ft （N/mm2）

σt / ft

FA30(W/B=40%) 2.05 4.27 0.48 BS65(W/B=40%) 3.39 4.77 0.71

FABS(W/B=40%) 2.93 4.51 0.65

BS65(W/B=50%) 2.54 3.74 0.68

Thermal stress

Tension

Compression

σt :Tensile restrained stress Calculated based on balance of forces

between concrete and invar bar ft :Tensile strength Calculated from the relationship with

compressive strength

FA30

BS65

BS65 (W/B=50%)

FABS

At the time of 20 days


Results 3. DEF risks


※ Duggan Assessment (1984). 0.05% (500με) is a higher limit could be used for construction

DEF risk

-1000

0

1000

2000

3000

4000

5000

6000

0 10 20 30 40 50 60 70 80 90 100

Expa

nsiv

e st

rain

(×10

-6)

Age (days)

Ettringite

Aggregate

OPC+K2SO4 (= 2% SO3)

FA30

BS65 FABS

Reflected electron image (SEM observation)

FA30, BS65, FABS showed no abnormal expansion strain at 91 days ⇒High resistance to DEF


Conclusions Concrete containing fly ash 30% were experimentally investigated in the 27℃ assuming use in warm regions(ex. Southeast Asia) to evaluate applicability of fly ash concrete to mass concrete structures and compare with cement containing high GGBS content 1. As Compared at the same water to binder ratio, compressive strength

of FA30 was lower than that of concrete with a high GGBS content.

2. Autogenous shrinkage in FA30 was significantly smaller than that in the high GGBS content concrete.

3. Tensile thermal stress occurring in FA30 subjected to a temperature history was significantly smaller than that in the high GGBS content concrete, suggesting an efficacy in controlling thermal cracking.

4. DEF risk evaluation by an accelerated test suggested that DEF risk would be low with FA30 which exhibited no abnormal expansion strain like the high GGBS content concrete.


Thank you for your attention

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EVALUATION OF THERMAL STRESS BEHAVIOR AND …concrack5/PPT-PDF/General Presentation by T... · EVALUATION OF THERMAL STRESS BEHAVIOR AND DEF RISK OF CONCRETE USING FLY ASH CEMENT