Mechanical Properties of Concrete with Flyash Obtained from Blended Coal Mixtures

Barzin. Mobasher and Sandeep A. Mane Department of Civil and Environmental Engineering

Raphaël Tixier

ACerS, PAC RIM 4, November 7, 2001 You created this PDF from an application that is not licensed to print to novaPDF printer (http://www.novapdf.com)

ASTM Fly ash classification  Classification: ASTM

C 618 - 1998.

 Class

F flyash: Bituminous coal.  Class C flyash: Sub-bituminous coal

[SiO2+Al2O3+ Fe2O3], min, %

Class F 70

• Objectives of the present study: What are the properties of fly ash obtained from the combustion of blended coals (using subbituminous coal), but meeting the properties of class F flyash?

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Class C 50

Origin of coals for blended fuel Reference

Coal # 1

Coal # 2

A

50 % Lee Ranch

50 % PRB Eagle Butte

B

50 % Lee Ranch

50 % PRB North Antelope

C

40 % Lee Ranch

60 % PRB North Antelope

D

50 % Lee Ranch

50 % PRB Spring Creek

E

50 % McKinley

50 % PRB Spring Creek

F

75 % McKinley

25 % PRB Spring Creek

G and G2

Unit 1: 40 % Lee Ranch – 60 % Jacob Lake Unit 2: 30 % Spring Creek -30 % Jacob Lake-40 % Lee Ranch

H

50 % P & M

50 % PRB (Jacob’s Ranch)

I

Unit # 2 North and South Pipe

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Typical chemical composition Reference SiO2 Al2O3 Fe2O3 SiO2+ Al2O3+ Fe2O3 CaO MgO K2O Na2O SO3 LOI A

56

23

5

84

8.7

2.4

1.2

1.3

0.5 0.55

B

55

25

4

85

8.1

1.9

1.1

0.8

0.5 0.63

D

58

23

5

87

5.5

1.7

1.4

2.0

0.8 0.77

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Typical XRD pattern

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Mix Design of Concrete   





 

Characteristic compressive strength ( f’c)= 5000 psi Water/Binder ratio = 0.4 Materials: a. Cement b. Aggregates (Coarse and Fine) c. Water d. Flyash, (meeting F class) Type of mix: a. Control mix b. 15% flyash c. 20% flyash d. 25% flyash e. 30% flyash Activators: NaOH, KOH, Ca(OH)2 Dosage : 1%, 2.5% and 4% of total binder. Chemical Admixture: superplasticizer. Curing: normal and limited number of autoclave curing

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Mix designs developed in ASU laboratory Mix ID #

% FA

Cement content Lbs/cu.yd

High cement Content

Low cement content

Dry weight of materials, kg

W/B Cement

Fly ash

Water

Sand

CA

H_40_LS

0

1129.9

0.4

8.68

-

3.47

7.5

9.86

H20_40_LS

20

941.15

0.4

7.23

1.45

3.47

7.5

9.86

H25_40_LS

25

903.4

0.4

6.94

1.74

3.47

7.5

9.86

H30_40_LS

30

868.25

0.4

6.67

2

3.47

7.5

9.86

L30_42_LS

30

493

0.42

4.83

1.45

2.64

12.47

16.41

L30_42_HS

30

493

0.42

4.83

1.45

2.64

12.47

16.41

L30_45_LS

30

490

0.45

4.8

1.44

2.81

12.29

16.17

L30_45_HS

30

490

0.45

4.8

1.44

2.81

12.29

16.17

L35_42_LS

35

480

0.42

4.5

1.63

2.64

12.47

16.41

Note: HS and LS refers to high and low superplasticizers HS: 400ml/100 kg of cementious materials. LS: 200ml/100 kg of cementious materials

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Types of Test and Specimen 

Compression Test  



Conventional Flexure Test 



4 in. x 4 in. x 14 in. beam

Cyclic or Fracture Test  



Concrete: 3 in. diameter, 6 in. cylinder Mortar: 2 in. cubes

3 in. x 1 in. x 13.5 in. Type A beam 4 in. x 4 in. x 14 in. Type B beam

Restrained Shrinkage specimen

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Compression Test 

Closed-loop test to get the post peak response.



Control: Load and Circumferential displacement



Measurement: Load, Actuator reading, Circumferential and Axial displacement

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Effect of amount of flyash at 28 daysstress vs. circumferential strain 8000 7000

Stress, psi

6000 5000

y

Control 10% Flyash

x

25% Flyash 30% Flyash Weight of flyash

4000 3000 2000 1000 0 0.000

0.002 0.004 0.006 0.008 0.010 Circumferential strain, in/in

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0.012

Effect of amount of flyash at 28 daysstress vs. axial strain 8000 Control 20% Flyash 25% Flyash

6000 Stress, psi

30% Flyash Weight of flyash

4000

y y

2000

0 0.000

0.001

0.002 0.003 Axial strain, in/in

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0.004

Effect of activators on 30% flyash concrete at 7 days 6000 2.5% NaOH 2.5% KOH

5000

2.5% Lime

Dosage of activators

Stress, psi

4000 3000

y

2000 1000 0 0.000

x

0.004 0.008 0.012 Circumferential strain, in/in

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0.016

Effect of activators on 25% flyash concrete at 28 days 7000 No activators 1% NaOH

6000

2.5% NaOH

5000

2.5% KOH

Stress, psi

Dosage of activators

4000 3000

y

2000

x 1000 0 0.000

0.004 0.008 0.012 Circumferential strain, in/in

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0.016

Effect of Superplasticizers on 30% flyash concrete at 28 Days 5000 Age = 28 Days

Stress, Psi

4000

L30_42_LS L30_42_HS L30_45_LS L30_45_HS L35_42_LS

3000

2000

1000

0

0

0.002 0.004 0.006 0.008 Circumferential Strain, in/in

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0.01

Comparison of compressive test result for different volume of flyash and superplasticizer 20 28 Days 7 Days

18 16

H30_40_LS

Mix ID

14

H30_40_LS

12

TRM_SRP_30FA

10

L35_42_LS

8

L30_45_LS

6

L30_45_HS

4

L30_42_LS

2 0

L30_42_HS

0

1000 2000 3000 4000 5000 6000 7000 8000 Compressive Strength, Psi

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Effect of flyash levels and NaOH, KOH levels at 28 days 8000 No activators 1% NaOH

Compressive strength, psi

7000

2.5% NaOH 2.5% KOH Dosage of activators

6000

5000

4000

3000

0

5

10

15 20 % of flyash

25

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30

Comparison of flyash levels, curing conditions, and NaOH, and KOH levels for mortar cubes 7000 Average compressive strength, psi

6500

Autoclave curing

6000 28 Days

5500 5000 4500

Activators

4000

NaOH

3500

7 Days

3000

KOH NaOH

2500 2000

0

5

10 15 20 25 30 35 40 45 50 Weight of flyash, %

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Flexure Test • Closed-loop test to get the post peak response. • Measurement: Load, Actuator reading, CMOD and Displacement

• Control: Load and CMOD

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Effect of different flyash content on flexural strength 2000 Control 15% Flyash

1600

20% Flyash

Load, lbs.

25% Flyash

1200

30% Flyash

800 P

400

0 0.000 0.005 0.010 0.015 0.020 Crack Mouth Opening Displacement, inches

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Effect of activators on 30% flyash concrete No activators

2000

2.5% NaOH 2.5% KOH

Load, lbs.

1500

2.5% Lime

Dosage of activators

P

1000

500

0 0.000 0.004 0.008 0.012 0.016 Crack Mouth Opening Displacement, inches You created this PDF from an application that is not licensed to print to novaPDF printer (http://www.novapdf.com)

Effect of Superplasticizers on flexural strength of concrete at 28 days. 1500

Age = 28 Days

Load, Lbs

1200

L30_42_LS L30_42_HS L30_45_LS L30_45_HS L35_42_LS

900

600

300

0

0

0.01

0.02 0.03 0.04 Deflection, in

0.05

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0.06

Effect of age and cement content on flexural strength of concrete 2100 H30_40_LS_28 Days H30_40_LS_7 Days L30_42_LS_28 Days L30_42_LS_7 Days

1800

Load, Lbs

1500 1200 900 600 300 0

0

0.01 0.02 0.03 0.04 0.05 Crack Mouth Openig Displacement,in

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0.06

Comparison with respect to weight of flyash and activator dose 2400 No activators 1% NaOH 2.5% NaOH

Flexural load, lbs.

2000

2.5% KOH

Dosage of activators

1600 P

1200

800

0

10

20 % of flyash

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30

Comparison of flexural strength for different volume of flyash and superplasticizer 20 28 Days 7 Days

18 16

H30_40_LS

14 Mix ID

H25_40_LS

12

TRM_SRP_30FA

10

L35_42_LS

8

L30_45_LS

6

L30_45_HS

4

L30_42_LS

2

L30_42_HS

0

0

500

1000 1500 Flexure Load, Lbs

2000

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Comparison of flexural toughness for different volume of flyash and superplasticizer 20 28 Days 7 Days

18 16

H30_40_LS

14 Mix ID

H25_40_LS

12

TRM_SRP_30FA

10

L35_42_LS

8

L30_45_LS

6

L30_45_HS

4

L30_42_LS

2 0

L30_42_HS

0

5

10 15 Toughness, Lbs.in

20

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25

Fracture toughness using Cyclic loadingunloading Tests 300 20% Flyash 30% Fly ash

LOAD, lbs.

200

100

0 0.000

0.002

0.004 0.006 0.008 Crack Mouth Opening Displacement, in

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0.010

0.012

Average toughness values, Type A specimen 2.50 2.5% Lime 2.5% KOH

2.00 Toughness, lbs/in

2.5% NaOH 1.50

1.00

0.50

0.00 0

5

10

15 20 25 Weight of flyash, %

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30

35

Average toughness values, Type B specimen 16

2.5% KOH 4% NaOH 2.5% NaOH

Toughness, lbs/in

12

2.5% Lime 2.5% KOH 2.5% NaOH

8

Control

4

0 0

5

10 15 20 25 Weight of flyash, %

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30

35

Field trial conducted in collaboration with ADOT to demonstrate performance of newly developed mix design of concrete with higher percentage of flyash by ASU

Test section of pavement along which samples were collected

Concrete pouring in test section of pavement

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Sample collection from pavement sections

-Tucson ready mix concrete with SRP 30% fly ash. (TRM_SRP_30FA) - Tucson ready mix concrete with 30% fly ash. (TRM_30FA) -Tucson Ready mix concrete with 20% fly ash. (TRM_20FA)

collection of test samples from pavement sections

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Effect of age on 30% flyash concrete for samples collected from field trial 4000 TRM_SRP_30FA

3500

7 Days 28 Days

Stress, psi

3000 2500

W/C = 0.4 FA = 30%

2000 1500 1000 500 0

0.002 0.0045 0.007 0.0095 Circumferential Strain, in/in

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0.012

Comparison of flexural strength for different volume of flyash in concrete samples collected from field trial 1200 TRM_20FA TRM_SRP_30FA

1000

Load, Lbs

800 Age = 28 Days W/C = 0.42

600 400 200 0

0

0.01

0.02 0.03 0.04 Deflection, in

0.05

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0.06

Compressive Strength as a function of age for Field Samples 6000 TRM_20FA TRM_SRP_30FA

Compressive Strength, Psi

TRM_30FA

5000

4000

3000

0

10

20

30 40 Age, Days

50

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60

Comparison of experimental and theoretical curve generated using R-curve program for 30% flyash concrete 1200 E = 14000 0.25 a0 = 12.75 mm b = 101.6mm t = 101.6 mm S = 406.4 mm KIC = 48.00 MPa*mm.5 CTODc = .05

Load, Lbs

900

% FA = 30

LSPC30_42_1 LSPC30_42_2 Model Fit

Age = 28 Days W/C = 0.42

600

300

0

0

0.005 0.01 0.015 0.02 0.025 Crack Mouth Opening Displacement,in

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0.03

Comparison of fracture resistance R for different superplasticizer content and w/c ratio generated using R-curve program 0.2 Age = 28 Days

Fracture Resistance, R

0.16 L30_42_LS

0.12

L30_45_LS

L35_42_LS L30_42_HS L30_45_HS TRM_SRP_30FA TRM_20FA

0.08

0.04

0

0

20

40 60 Crack Length, in

80

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100

Comparison of Stress Intensity factor obtained from Theoretical R-curve analysis for different mixes 8 KIC

28 Days

7

Mix ID

( FIELD )

6

TRM_SRP_30FA

5

L35_42_LS

4

L30_45_LS

3

L30_45_HS

2

L30_42_LS

1 0

L30_42_HS

0

10

20 30 40 50 Stress Intensity Factor, K

60

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70

Experimental setup of shrinkage test and recording of strain gage readings Concrete

Steel Tube

Strain gages

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Inspection of cracks using digital camera and microscope

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Comparison of experimental and theoretical curve of shrinkage test 300

Strain gage readings, microstrains

Control 25% Flyash Theoretical

200

Es = 2.9E7 psi C u = 0.235 sh = 540 microstrains

First crack

100

0

-100 0

3

5

8 10 Time, days

13

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15

18

Experimental result obtained from restrained shrinkage test of samples collected from the field 100 TRM_20FA TRM_SRP_30FA TRM_30FA

Micro Strains

80 60 40 20 0 -20

0

10

20 Age, Days

30

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40

Crack formation in shrinkage specimens collected from field during restrained shrinkage test

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Average crack width measured during restrained shrinkage test for samples collected from field 1.4 TRM_20FA TRM_30FA TRM_SRP_30FA

Avg. Crack width, mm

1.2 1 0.8 0.6 0.4 0.2 0

5

10

15

20 25 Age, Days

30

35

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40

Conclusions 







Up to 30% of cement in cement based mixtures was replaced by blended coal flyash resulting in high strength and ductility. Even though addition of flyash with various chemical activators results in low early strength, it has higher strength than control concrete after the 28-days period Use of Sodium Hydroxide as an activator plays an important role in the hydration process and improves the compressive strength. Similar results were obtained in Autoclaved specimens. Concrete containing flyash also shows a significant increase in the flexural stiffness and ductility

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Conclusions (contd.) 



The flexural properties of the Potassium hydroxide activated concrete are superior to the Sodium and Calcium hydroxide activators. Cyclic load-unload tests can be used to compute fracture properties of cement based materials.

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