EVALUATION OF THERMAL STRESS BEHAVIOR AND DEF RISK OF CONCRETE USING FLY ASH CEMENT

Transcription

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

2 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

3 Materials Used Material Symbol Quality Density Note Cement OPC Ordinary Portland Cement/ Made in Japan Fly-ash FA Original Ashes/ Made in Japan Granulated ground blast furnace slag Fine Aggregate Coarse Aggregate BS S1 S2 G Gypsum-added type/ Made in Japan Dust/ Made in Malaysia Natural Sand/ Made in Malaysia Crushed Granite/ Made in Indnesia 3.15 SSA: 3320cm 2 /g ig.loss: 3.41% SSA: 3330cm 2 /g, SO 3 :2.03% SSA: 4310cm 2 /g Absorption: 1.18%, F.M.: 3.32 Absorption: 1.17 %, F.M.: 1.82 Absorption: 0.71% F.M.: 6.98 SP Naphthalenesulfonate - - Chemical superplasticizer (Non AE) Admixture Ad Retarding water reducing - - agent SSA: specific surface area measured by Blaine s method, FM: fineness modulus JCI-RILEM International Workshop, CONCRACK5, April 24-26, 2017, Japan 3

4 Mix proportions FA Binder 30% 70% 35% 65% 14% 55% 31% OPC Binder types W/B (%) 40 BS W/B = 40%, 50%, 60% (W = 165 kg/m 3 ) Slump: 12±2.5 cm, Air content: below 2.0% Unit contents (kg/m 3 ) W OPC FA BS S1 S2 G Concrete mixing at 27 (SS EN206-1) JCI-RILEM International Workshop, CONCRACK5, April 24-26, 2017, Japan 4

5 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 dia mm Water curing at 27 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 (with thermocouple) insulator JCI-RILEM International Workshop, CONCRACK5, April 24-26, 2017, Japan 5

6 Test methods2 (Thermal stress behavior) Thermal Stress Uniaxially restrained specimen(100 x 100 x 800 mm) Invar bar(linear expansion coefficient : / C) Possible to measure both thermal strain and autogenous shrinkage strain at the same time (Unique evaluation method) Strain gauge Thermocouple Threads partially removed 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 (mm) insulator JCI-RILEM International Workshop, CONCRACK5, April 24-26, 2017, Japan 6

7 Test methods3 (DEF risk) Delayed Ettringite Formation(DEF) Temperature ( ) Accelerate test(ref. Duggan method) dia mm contact ring gauge 1 Temperature History Simulating the condition inside the mass concrete Age(days) 2 Duggan process(1984, USA) 3Change in length is measured using the contact ring gauge continue JCI-RILEM International Workshop, CONCRACK5, April 24-26, 2017, Japan 7

8 Results 1. Mechanical property (Strength, Shrinkage) JCI-RILEM International Workshop, CONCRACK5, April 24-26, 2017, Japan 8

9 Compressive strength Compressive strength (N/mm 2 ) days 27 water curing B/W Compressive strength (N/mm 2 ) days B/W Compressive strength at the same W/B : < or 28-day compressive strength: (W/B = 40%) (W/B = 50%) 56- and 91-day compressive strength: = JCI-RILEM International Workshop, CONCRACK5, April 24-26, 2017, Japan 9

10 Young s modulus & Tensile strength Young's modulus E C (kn/mm 2 ) E C =5.9f c Compressive strength f c (N/mm 2 ) Splitting tensile strength f t (N/mm 2 ) f t =0.18f c 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

11 Adiabatic Temperature Rise Adiabatic temperature rise ( C) W/B=40% Adiabatic temperature rise ( C) W/B=60% Age (days) Age (days) Temperature rise at 14 days: > > Temperature continued to increase in and after 14 days, more remarkably in. JCI-RILEM International Workshop, CONCRACK5, April 24-26, 2017, Japan 11

12 Autogenous shrinkage Quasi-adiabatic curing Thermal expansion coefficient of concrete was assumed to be 10x10-6 / 0 0 Strain (x10-6 ) Strain (x10-6 ) W/B=40% Age (days) -400 W/B=60% Age (days) Autogenous shrinkage: < < ( 1/2 1/3 ) Autogenous shrinkage increased with the increase in GGBS content. JCI-RILEM International Workshop, CONCRACK5, April 24-26, 2017, Japan 12

13 Results 2. Thermal Stress behavior JCI-RILEM International Workshop, CONCRACK5, April 24-26, 2017, Japan 13

14 Inside Temperature & Strain of Invar bar Temperature( ) Strain of Invar bar(x10-6 ) (W/B=50%) have equivalent compressive strength to (W/B=40%) Quasi-adiabatic curing Expansion Shrinkage Age(days) Maximum Temperature( ) W/B=40% Temperature rise process Expansion strain Temperature drop process Shrinkage strain W/B=50% 53.5 = > is smaller shrinkage than and JCI-RILEM International Workshop, CONCRACK5, April 24-26, 2017, Japan 14

15 Thermal stress Stress (N/mm 2 ) Tension Compression (W/B=50%) Binder types At the time of 20 days σ t (N/mm 2 ) f t (N/mm 2 ) Age(days) Stress-Strength ratio(tensile stress / Tensile strength): < < has a higher resistance to thermal cracking as compared to and σ t / f t (W/B=40%) (W/B=40%) (W/B=40%) (W/B=50%) σ t :Tensile restrained stress Calculated based on balance of forces between concrete and invar bar f t :Tensile strength Calculated from the relationship with compressive strength JCI-RILEM International Workshop, CONCRACK5, April 24-26, 2017, Japan 15

16 Results 3. DEF risks JCI-RILEM International Workshop, CONCRACK5, April 24-26, 2017, Japan 16

17 DEF risk Duggan Assessment (1984). 0.05% (500με) is a higher limit could be used for construction Expansive strain ( 10-6 ) OPC+K 2 SO 4 (= 2% SO 3 ) Age (days) Ettringite Aggregate Reflected electron image (SEM observation),, showed no abnormal expansion strain at 91 days High resistance to DEF JCI-RILEM International Workshop, CONCRACK5, April 24-26, 2017, Japan 17

18 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 was lower than that of concrete with a high GGBS content. 2. Autogenous shrinkage in was significantly smaller than that in the high GGBS content concrete. 3. Tensile thermal stress occurring in 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 which exhibited no abnormal expansion strain like the high GGBS content concrete. JCI-RILEM International Workshop, CONCRACK5, April 24-26, 2017, Japan 18

19 Thank you for your attention JCI-RILEM International Workshop, CONCRACK5, April 24-26, 2017, Japan 19