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

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

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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

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

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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…

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

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BS

Mix proportions

Binder types W/B (%) Unit contents (kg/m3) W OPC FA BS S1 S2 G

FA30 40 165 289 124 398 286 1050 50 231 99 437 314 1062 60 193 83 470 338 1052 BS65 40 144 268 403 290 1063 50 115 215 441 317 1070 60 96 179 474 341 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）

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

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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)

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  • 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

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10 20 30 40 50 60 70 80 90 2 4 6 8 10 12 14

Temperature (℃)

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

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Results

  • 1. Mechanical property

(Strength, Shrinkage)

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Compressive strength

20 30 40 50 60 70 80 1.0 1.5 2.0 2.5 3.0 Compressive strength (N/mm2) B/W FA30 BS65 FABS

28 days

BS65 FA30 FABS

20 30 40 50 60 70 80 1.0 1.5 2.0 2.5 3.0 Compressive strength (N/mm2) B/W FA30 BS65 FABS

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

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Young’s modulus & Tensile strength

1 2 3 4 5 6 20 40 60 80

Splitting tensile strength ft (N/mm2) Compressive strength fc （N/mm2）

FA30 BS65 FABS

ft=0.18fc

0.77

10 20 30 40 20 40 60 80

Young's modulus EC (kN/mm2) Compressive strength fc （N/mm2）

FA30 BS65 FABS

EC=5.9fc

0.4

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

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Adiabatic Temperature Rise

10 20 30 40 50 60 2 4 6 8 10 12 14

Adiabatic temperature rise (°C) Age (days)

W/B=40%

10 20 30 40 50 60 2 4 6 8 10 12 14 Adiabatic temperature rise (°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

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Autogenous shrinkage

  • 400
  • 300
  • 200
  • 100

7 14 21 28

Strain (x10-6) Age (days)

W/B=40%

  • 400
  • 300
  • 200
  • 100

7 14 21 28

Strain (x10-6) 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/℃
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Results

  • 2. Thermal Stress behavior
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20 30 40 50 60 70 2 4 6 8 10 12 14 16 18 20 22

Temperature（℃）

  • 500
  • 400
  • 300
  • 200
  • 100

100 2 4 6 8 10 12 14 16 18 20 22

Age（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

Strain of Invar bar(x10-6)

Expansion Shrinkage

  • FA30 is smaller shrinkage

than BS65 and FABS

Quasi-adiabatic curing

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  • 1.0

0.0 1.0 2.0 3.0 4.0 5.0 2 4 6 8 10 12 14 16 18 20 22

Stress （N/mm2） 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

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Results

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

DEF risk

  • 1000

1000 2000 3000 4000 5000 6000 10 20 30 40 50 60 70 80 90 100

Expansive strain (×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

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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

  • f 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.

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Thank you for your attention