Pultrusion of Fabric Reinforced High Flyash Blended Cement Composites Barzin Mobasher1, Alva Peled 2, Jitendra Pahalijani1 1 Department of Civil and Environmental Engineering, Arizona State University, USA 2
Department of Structural Engineering Ben-Gurion University, Israel
The World of Coal Ash 2005 International Ash Utilization Symposium April 11-15, 2005 You created this PDF from an application that is not licensed to print to novaPDF printer (http://www.novapdf.com)
Scope of Presentation • Introduction • Pultrusion of Cement Composite Systems • Materials & Processing
• Experimental Observations • • • • •
Rheology Tension tests Crack Spacing Accelerated Aging Microstructure
• Conclusions You created this PDF from an application that is not licensed to print to novaPDF printer (http://www.novapdf.com)
Areas of Application for high performance fiber reinforced Materials • high tensile-toughness
•
• • •
AR Glass Fabric Vf =1.5%
16 Stress, MPa
•
characteristics superior impact, earthquake, and fatigue characteristics. prefabricated Structural elements, thin sheets, panels, cladding members. structural repair and retrofit. I-beams, structural members. Sound abatement walls.
20
12 8 GFRC, Vf =5%
4 0
0
0.01 0.02 Strain, mm/mm
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0.03
Fabric Reinforcing Methodology
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Environmental Effects of CO2 Emissions •7% of total green house gas produced can be related to CO2 generation due to cement production. •Every ton of cement produced generates a ton of CO2 lbs CO2 per Yd3 Percent of of concrete total CO2
CO2 Emissions
lbs CO2 per ton of cement
Energy use
1,410
381
60
Calcining of limestone
997
250
40
2,410
631
100
Total
•CO2 emissions from different fuels from ACEEE Consumer Guide to Home Energy Savings, 1991. •Estimates of emissions from calcining limestone from CO2 Release from Cement Production 1950-1985, by Richard Griffin, Institute for Energy Analysis, Oak Ridge Assoc. Universities, 8/87.
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Synergy Between AR-Glass Fabrics and Flyash • Rheology• Compaction and Anchorage of Fabrics
1-1x104 Seconds
• Bonding at the Interface zone Time
• Strength
• Calcium Hydroxide reduction
1-1x103 Hours
• Enhanced Bond
• Initial & Long Term Strength • Additional hydration products
• Durability and Aging • Long term durability
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1-1x104 Days
Flyash Chemical Composition Class F flyash supplied by Salt River Project was used. 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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Design Tertiary Mix with PC, Flyash, and silica Fume Mix Design 1 (Control)
Mix Design 2 (40% FA)
Mix Design 3 (60% FA)
Mix Design 4 (80% FA)
Water to solids Ratio
0.38
0.36
0.36
0.36
Water ,grams
3316
3316
3316
3316
Cement ,grams
8160
4896
3714
1857
Silica Fume, grams
676
676
676
676
Flyash, grams
0
3714
4896
6753
Superplasticizer
5.25 ml
5.25 ml
5.25 ml
-
% Flyash by weight
0
40%
52%
72%
% Flyash by Volume
0
40%
60%
80%
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AR Glass Fabrics Yarn Type
Yarn Nature
Strength (MPa)
Modulus of Elasticity (MPa)
ARglass
bonded
12762448
78600
Strain at Peak (mm/mm)
Filament size (mm)
Number of filaments in a bundle
Bundle dia. (mm)
0.0135
400
About 0.27
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Cement Paste Rheology • Parallel Plate Brookefield Rheometer • Hobart Mixer • Shear rate varied from a higher rpm value (20) at the start to a lower value (10). • Temperature was not controlled, 20-23 C. • Testing Protocol • Initial stabilizing time of 10 min. with a fixed torque. • Torque was measured continuously. The first set of readings at 20 rpm is taken for 2 minutes. Followed by readings at 15 rpm and 10 rpm for 2 minutes each. • Entire tests lasts for 16 minutes. • A plot of shear stress vs. strain rate was used to calculate the rheological properties.
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Torque
gap
Bingham model concept Stress
Stress
Yield stress
Plastic Viscosity
Shear strain rate Same Yield Stress BUT Different Plastic Viscosity
Shear strain rate Same Plastic Viscosity BUT Different Yield Stress
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Shear Strength, dyne/cm2
Effect of Flyash on Rheological Properties
Control 40% Fly ash 60% Fly ash 80% Fly ash
70
Mix
60
Control
48.24
2.98
40% FA
45.72
1.76
60% FA
38.66
2.84
80% FA
30.02
4.02
50
3
4
5
6
Yield Stress Viscosity (dyne/cm2) (centipoise)
7
Shear Rate, 1/sec
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50
5
40
4
30
3
20
2
10
1
0
0
20 40 60 Flyash Content , %
80
0 100
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Viscosity, centipoise
Yield Strength , dyne/cm2
Yield Strength and Viscosity
Glass Fabric-Flyash Composites • Composites with up to 8 layers of Fabric were • • • •
manufactured. Volume fraction about 1.5% Testing at two curing ages of 7 and 28 days. Accelerated testing after 28 days at 80°C. Microstructural evaluation using SEM and optical microscopy
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Mechanical Tests and Properties • Closed loop control direct tensile tests. • MTS testing machine with a capacity of 89KN. Metal plates with dimension of 25x30 mm were glued on the surface of the specimen at the grips to minimize damage. • The tensile load and elongation were recorded and converted to stress-strain response. • Tensile strength, stiffness, ductility, strain capacity, and cracking parameters were measured. • A procedure was developed to quantitatively measure the crack spacing parameters.
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Various stages of cracking
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Crack Spacing Evolution
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Crack Spacing Measurement
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Stiffness Degradation with Crack formation 25
60
400
300
Tangent Modulus, MPa
Stress, MPa
20 15
200
10 100
5 0
0
0.01 0.02 Strain, mm/mm
0
0.03
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40
20
0
Crack spacing, mm
TGSFA40-5
Stress Strain and Crack Spacing Interaction 60
40% Flyash
Stress, MPa
20
40 15
10 20 5 - (7 day curing) (7 day curing)
0 0
0.02
0.04
0.06
0 0.08
Strain, mm/mm You created this PDF from an application that is not licensed to print to novaPDF printer (http://www.novapdf.com)
Mean Crack Spacing, , mm
25
Effect of Curing on Composite Response 60
40% Flyash
Stress, MPa
20
40 15
10 20 - (7 day curing) - (28 day curing) (28 day curing) (7 day curing)
5
0 0
0.02
0.04
0.06
Strain, mm/mm You created this PDF from an application that is not licensed to print to novaPDF printer (http://www.novapdf.com)
0 0.08
crack spacing (), mm
25
Effect of Curing Duration 30
Control 40% Flyash 60% Flyash 80% Flyash
Stress, MPa
Stress, MPa
30
20
Control 40% Flyash 60% Flyash 80% Flyash
20
10
10
28 day curing
7 day curing 0
0 0
0.02
0.04
Strain, mm/mm
0.06
0.08
0
0.02
0.04
Strain, mm/mm
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0.06
0.08
Mechanical Properties as a function of Age for 7 and 28 day curing periods Mix ID 0
40%
60%
80%
Maximum Load (KN)
Ultimate Strength (MPa)
Ultimate Strain (mm/mm)
Stiffness (MPa)
Toughness (MPa)
Average (Std. Dev)
7
5.92 (0.87)
19.40 (3.74)
0.030 (0.003)
3520.7 (177.5)
0.367 (0.072)
Average (Std. Dev)
28
6.71 (0.58)
21.45 (2.39)
0.0254 (0.002)
4981.2 (211.1)
0.358 (0.053)
Average (Std. Dev)
7
4.16 (0.50)
18.73 (3.04)
0.080 (0.030)
1651.3 (112.1)
1.062 (0.315)
Average (Std. Dev)
28
5.28 (0.76)
23.79 (2.49)
0.0258 (0.003)
4753.2 (151.3)
0.394 (0.074)
Average (Std. Dev)
7
4.53 (0.49)
24.27 (2.09)
0.024 (0.003)
2360.4 (125.1)
0.384 (0.069)
Average (Std. Dev)
28
5.27 (0.43)
28.69 (3.71)
0.0255 (0.001)
5015.2 (178.2)
0.482 (0.075)
Average (Std. Dev)
7
3.64 (1.40)
19.09 (7.35)
0.0283 (0.0108)
2575.3 (201.3)
0.417 (0.206)
Average (Std. Dev)
28
4.25 (0.94)
23.45 (3.94)
0.0170 (0.003)
4051.1 (215.5)
0.288 (0.107)
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Effect of Accelerated Aging 30
30
-
-
Aging at T = 80 C
Stress, MPa
Stress, MPa
Aging at T = 80 C 20
10
0
10
28 days curing- 40% 28 days aging- 40%
0
0.01
0.02
Strain, mm/mm
20
0.03
0
28 days curing- 40% 28 days aging- 40% 28 days curing - 60% 28 days aging - 60% 0
0.01
0.02
Strain, mm/mm
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0.03
Evaluation of Microstructure • Mixtures containing flyash result in lower viscosity and better flow of the matrix around the surface of the fabric. • Interstitial fabric filling by flyash particles. • Reduction in capillary voids and the transition zone in the vicinity of the inter yarn spacing • Strong bonding in mixtures with high levels of flyash.
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Flyash at the yarn junction
60% flyash mixture You created this PDF from an application that is not licensed to print to novaPDF printer (http://www.novapdf.com)
Matrix penetration in between two adjacent fabric layers (60% Flyash mixture)
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Transverse and longitudinal Yarns After Tension Testing
Loading Direction You created this PDF from an application that is not licensed to print to novaPDF printer (http://www.novapdf.com)
Failure of Bonded Junctions
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Load Transfer Mechanism Attributed to the Failure of Yarn Junctions
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Optical Microscopy of Crack Deflection Mechanisms Loading direction
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Fiber Buckling Due to Pullout and Subsequent Unloading
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Conclusions • The synergy between the use of flyash cement based composites and • • • • • •
AR Glass Fabrics can be used at various time scales. Improved mechanical behavior of composites with flyash compared to similar composites without flyash was observed. Composites with Tensile strength of the order of 20-28 MPa at strain capacities of 2-4% can be obtained. The aging of the glass fabrics in the presence of flyash is insignificant. The role of the fabric reinforcement in development of distributed cracking was documented using image analysis techniques. A good correlation between the rheology properties of the fresh mixture and the mechanical performance of the composite. Various modes of toughening are present due to the reinforcing effect of fabrics.
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