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, Japan 1
Background & Objective 【 Fly ash (FA) cement concrete 】 Feature : improving workability, increasing long-term strength, reducing load to the environment, suppressing alkali silica reaction etc. Problem : difficult air content control, poor early strength However… 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 JCI-RILEM International Workshop, CONCRACK5, April 24-26, 2017, Japan 2
Materials Used Material Symbol Quality Density Note Ordinary Portland Cement/ SSA: 3320cm 2 /g Cement OPC 3.15 Made in Japan ig.loss: 3.41% Original Ashes/ Fly-ash FA 2.23 SSA: 3330cm 2 /g, Made in Japan Granulated Gypsum-added type/ SO 3 :2.03% BS 2.89 ground blast SSA: 4310cm 2 /g Made in Japan furnace slag Absorption: 1.18%, Dust/ S1 2.57 F .M.: 3.32 Made in Malaysia Fine Aggregate Absorption: 1.17 % , Natural Sand/ S2 2.55 F .M.: 1.82 Made in Malaysia Coarse Absorption: 0.71% G Crushed Granite/ 2.62 Aggregate F .M.: 6.98 Made in Indnesia Naphthalenesulfonate SP - - Chemical superplasticizer (Non AE) Admixture Retarding water reducing Ad - - agent SSA: specific surface area measured by Blaine’s method, FM: fineness modulus JCI-RILEM International Workshop, CONCRACK5, April 24-26, 2017, Japan 3
Mix proportions W/B = 40%, 50%, 60% （ W = 165 kg/m 3 ） FA OPC BS Slump: 12 ± 2.5 cm, Air content: below 2.0% Unit contents (kg/m 3 ) Binder W/B 【 Binder 】 types (%) W OPC FA BS S1 S2 G 40 289 124 0 398 286 1050 30% FA30 50 231 99 0 437 314 1062 70% 60 193 83 0 470 338 1052 40 144 0 268 403 290 1063 35% BS65 165 50 115 0 215 441 317 1070 65% 60 96 0 179 474 341 1060 14% 40 130 56 227 400 287 1053 FABS 50 102 46 182 438 315 1063 31% 55% 60 87 37 151 471 339 1054 Concrete mixing at 27 ℃ （ SS EN206-1 ） JCI-RILEM International Workshop, CONCRACK5, April 24-26, 2017, Japan 4
Test methods ① (Basic mechanical property) Compressive strength ： JIS A 1108 dia. 100 × 200 mm Young’s modulus ： JIS A 1149 Water curing at 27 ℃ 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 Embedded strain meter insulator (with thermocouple) JCI-RILEM International Workshop, CONCRACK5, April 24-26, 2017, Japan 5
Test methods ② (Thermal stress behavior) 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) 19 19 100 800 Strain gauge Threads partially removed 100 (mm) Thermocouple Invar bar (Elastic modulus ： 140,000N/mm 2 ) M26mm • Quasi-adiabatic curing (200 mm-thick expanded polystyrene) • The form was placed in the 27 ℃ room insulator JCI-RILEM International Workshop, CONCRACK5, April 24-26, 2017, Japan 6
Test methods ③ (DEF risk) Delayed Ettringite Formation(DEF) • Accelerate test(Ref. Duggan method) • dia. 100 × 200 mm contact ring gauge ① Temperature History ② Duggan process (1984, USA) 85 ℃ 90 80 Simulating the 70 condition inside Temperature ( ℃ ) 60 the mass concrete 50 40 continue 30 20 10 0 0 2 4 6 8 10 12 14 Age(days) ③ Change in length is measured using the contact ring gauge JCI-RILEM International Workshop, CONCRACK5, April 24-26, 2017, Japan 7
Results 1. Mechanical property (Strength, Shrinkage) JCI-RILEM International Workshop, CONCRACK5, April 24-26, 2017, Japan 8
Compressive strength 27 ℃ water curing 80 80 28 days 91 days Compressive strength (N/mm 2 ) 70 Compressive strength (N/mm 2 ) 70 BS65 FABS 60 60 FA30 50 50 40 40 FA30 FA30 BS65 BS65 30 30 FABS FABS 20 20 1.0 1.5 2.0 2.5 3.0 1.0 1.5 2.0 2.5 3.0 B/W B/W 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 JCI-RILEM International Workshop, CONCRACK5, April 24-26, 2017, Japan 9
Young’s modulus & Tensile strength 40 6 0.4 E C =5.9f c Splitting tensile strength f t (N/mm 2 ) 0.77 f t =0.18f c Young's modulus E C (kN/mm 2 ) 5 30 4 20 3 2 FA30 FA30 10 BS65 BS65 1 FABS FABS 0 0 0 20 40 60 80 0 20 40 60 80 Compressive strength f c （ N/mm 2 ） Compressive strength f c （ N/mm 2 ） Young′s modulus and splitting tensile strength could be expressed individually by functions of compressive strength, regardless of the binder type. JCI-RILEM International Workshop, CONCRACK5, April 24-26, 2017, Japan 10
Adiabatic Temperature Rise 60 60 W/B=40% W/B=60% FA30 Adiabatic temperature rise (°C) Adiabatic temperature rise (°C) 50 50 BS65 FABS FA30 40 40 BS65 FABS 30 30 20 20 10 10 0 0 0 2 4 6 8 10 12 14 0 2 4 6 8 10 12 14 Age (days) Age (days) Temperature rise at 14 days: FA30 > BS65 > FABS Temperature continued to increase in BS65 and FABS after 14 days, more remarkably in BS65. JCI-RILEM International Workshop, CONCRACK5, April 24-26, 2017, Japan 11
Autogenous shrinkage Quasi-adiabatic curing Thermal expansion coefficient of concrete was assumed to be 10x10 -6 / ℃ 0 0 FA30 -100 -100 FABS Strain (x10 -6 ) Strain (x10 -6 ) FA30 BS65 -200 -200 FABS -300 -300 W/B=40% W/B=60% BS65 -400 -400 0 7 14 21 28 0 7 14 21 28 Age (days) Age (days) Autogenous shrinkage: FA30 < FABS < BS65 (FA30 ≈ 1/2 ･ FABS ≈ 1/3 ･ BS65) Autogenous shrinkage increased with the increase in GGBS content. JCI-RILEM International Workshop, CONCRACK5, April 24-26, 2017, Japan 12
Results 2. Thermal Stress behavior JCI-RILEM International Workshop, CONCRACK5, April 24-26, 2017, Japan 13
Inside Temperature & Strain of Invar bar 70 Maximum Temperature （ ℃ ） BS65 (W/B=50%) have Temperature （ ℃ ） 60 equivalent compressive FA30 59.3 strength to FA30 (W/B=40%) 50 W/B=40% BS65 59.3 40 FABS 57.5 W/B=50% BS65 53.5 30 Quasi-adiabatic curing 20 FA30 = BS65 > FABS 0 2 4 6 8 10 12 14 16 18 20 22 Strain of Invar bar(x10 -6 ) 100 Temperature rise process Expansion 0 ⇒ Expansion strain Shrinkage FA30 -100 Temperature drop process -200 -300 FABS ⇒ Shrinkage strain -400 BS65 FA30 is smaller shrinkage -500 0 2 4 6 8 10 12 14 16 18 20 22 than BS65 and FABS Age （ days ） JCI-RILEM International Workshop, CONCRACK5, April 24-26, 2017, Japan 14
Thermal stress At the time of 20 days 5.0 σ t f t Binder types （ N/mm 2 ） σ t / f t （ N/mm 2 ） BS65 4.0 FABS FA30 (W/B=40%) 2.05 4.27 0.48 Stress （ N/mm 2 ） 3.0 BS65 (W/B=40%) 3.39 4.77 0.71 FABS (W/B=40%) 2.93 4.51 0.65 2.0 BS65 (W/B=50%) 2.54 3.74 0.68 FA30 1.0 σ t :Tensile restrained stress Tension BS65 Calculated based on balance of forces (W/B=50%) 0.0 between concrete and invar bar Compression f t :Tensile strength -1.0 Calculated from the relationship with 0 2 4 6 8 10 12 14 16 18 20 22 compressive strength 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 JCI-RILEM International Workshop, CONCRACK5, April 24-26, 2017, Japan 15
Results 3. DEF risks JCI-RILEM International Workshop, CONCRACK5, April 24-26, 2017, Japan 16
DEF risk ※ Duggan Assessment (1984). 0.05% (500με) is a higher limit could be used for construction 6000 Ettringite 5000 Expansive strain ( × 10 -6 ) OPC+K 2 SO 4 4000 (= 2% SO 3 ) 3000 2000 BS65 1000 FABS Aggregate 0 FA30 -1000 0 10 20 30 40 50 60 70 80 90 100 Reflected electron image Age (days) (SEM observation) FA30, BS65, FABS showed no abnormal expansion strain at 91 days ⇒ High resistance to DEF JCI-RILEM International Workshop, CONCRACK5, April 24-26, 2017, Japan 17
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