Degradation of Glass Fiber Reinforced Concrete Due to Environment

Degradation of Glass Fiber Reinforced Concrete Due to Environmental Effects

Smita Singh


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Table of Contents

• Introduction

• Fiber Reinforced Polymer Composite

• Glass Fiber Reinforcement

• GFRP Composite vs. Steel Reinforced Concrete

• Deleterious effects of several environments on fibers and matrices

• Environmental Deformations of GREP bars- Degradation of tensile strength- Direct shear capacity

- Predicted deflections due to creep- Bond behavior and development length- Effects of thermal expansion on cracking of FRP

reinforced concrete


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The use of glass fiber-reinforced polymer (GFRP) composites is becoming

increasingly common in construction, both in new construction and in the

repair of deteriorated structures.

Benefits of GFRPs are well-recognized: high strength-weight ratio, corrosion

and fatigue resistance; ease of handling, and ease of fabrication.

The mechanical properties of a hybrid material system may deteriorate much

faster than that suggested by the property degradation rates of the individual

components making up the hybrid system.

There is a need to make analysis on the mechanical properties of GFRP when

exposed to environmental conditions

Introduction


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A composite is a mixture of two or more phases (materials). FRP is a two phase composite constituting of matrix and reinforcement.

Matrix : It is the continuous phase and surrounds the reinforcements. It is made from polymer. Bind the reinforcements (fibers/particulates) togetherTransfer load to the reinforcementsProtect the reinforcements from surface damage due to abrasion or chemical attacks.

Reinforcement : The term ‘reinforcement’ implies some property enhancement. It is the dispersed phase, which normally bears the majority of stress. Different types of Fibres or Filaments are continuous or discontinuous fibres .

Fiber Reinforced Polymer Composite


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• Glass fiber-reinforced polymer composites (GFRPs)– Most common fiber used– High strength– Good water resistance– Good electric insulating properties– Low stiffness.

• Carbon fiber-reinforced polymer composites (CFRPs)– Good modulus at high temperatures– Excellent Siffness– More Expensive than glass– Brittle– Low electric insulating properties

• Aramid fiber-reinforced polymer composites (AFRPs)– Superior resistance to damage (energy absorber)– Good in tension applications (cables, tendons)– Moderate Stiffness– More Expensive than glass

Types of Fiber Reinforced Polymer Composite


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Properties Of Continuous and Aligned GFRP, CFRP, AFRP

1 psi = 6.895kPa


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Glass Fiber Reinforcements

• Glass fiber reinforcements are classified according to their properties.

• A-glass is a high-alkali glass containing 25% soda and lime, which offers very good resistance to chemicals, but lower electrical properties.

• C-glass is chemical glass, a special mixture with extremely high chemical resistance.

• E-glass is electrical grade with low alkali content. It manifests better electrical insulation and strongly resists attack by water. More than 50% of the glass fibers used for reinforcement is E-glass.

• S-glass is a high-strength glass with a 33% higher tensile strength than E-glass.

• D-glass has a low dielectric constant with superior electrical properties. However, its mechanical properties are not so good as E-or S-glass. It is available in limited quantities.


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Tensile StrengthGFRP bars have higher strength, than the specified yield strength fy of steel reinforcing bars.

Modulus of ElasticityGlass Fiber reinforced polymer (GFRP) bars have lower modulus of elasticity than steel bars . Hence limited tensile strength is used to control width of cracks in tension zone at service .

Creep and ShrinkageCreep and shrinkage behavior in GFRP-reinforced members is similar to that in steel-reinforced members.

GFRP vs. Steel Reinforced Concrete


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Shear StrengthThe concrete contribution to shear strength is reduced inbeams with GFRP longitudinal reinforcement because of smaller concrete compression zones and wider cracks

Chemical AttackGFRP bars are non-corrosive and non-reactive to chlorides. They experience a loss of strength with time, particularly in an alkaline environment

Stress-Strain BehaviorThe stress-strain behavior of GFRP bars is linear elastic to failure, with no yield plateau.

Thermal Conductivity GFRP materials have relatively lower thermal conductivity than steel

(Contd.)GFRP vs. Steel Reinforced Concrete


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Deleterious effects of several environments on fibers and matrices

• Water: Polymeric fibers and matrices absorb moisture. Moisture

absorption softens the polymers • Weak acids: Bridges in industrialized areas may be exposed to weak acids

from acid rain and carbonization, with pH values between 4 and 7. Weak acids can attack glass fiber sand polyester matrices.

• Strong acids: Accidental spillage may cause strong acids to come in contact

with bridge components. Strong acids can attack glass fibers, aramid fibers and polyester and epoxy matrices.

• Weak alkalis: • Concrete containing pozzolanas can have pH values between

7 and 10. Weak alkalis can attack glass fibers and polyester matrices.


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Deleterious effects of several environments on fibers and matrices

• Strong alkalis: Typical portland cement concretes have pH values greater than

10 and can cause degradation of glass fibers. Strong alkalis

can attack glass fibers, aramid fibers, and polyester matrices.• High temperatures: Carbon and glass fibers are resistant to high temperatures.

However, high temperatures adversely affect aramid fibers and polymeric matrices.

• Ultraviolet radiation: Carbon and glass fibers are resistant to ultraviolet radiation.

However, ultraviolet radiation adversely affects aramid fibers and polymeric matrices.


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Time Dependent Deformations of GREP bars

• Degradation of tensile strength• Direct shear capacity• Predicted deflections due to creep• Bond behavior and development length• Effects of thermal expansion on cracking of

FRP reinforced concrete


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For determining time dependent deformations of GREP bars, experimental analysis was done.

Specifications of GFRP Reinforcing Bars used:

GFRP bars provided by three

different manufacturers were used in the experiments The bars are identified as bar P, V1, and V2.

Environmental Deformations of GREP bars


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Degradation of tensile strength

•The tensile strength of GFRP bars degrades with time while in contact with simulated concrete pore solution (alkaline) .

•The overall average tensile strength reductions were 1 percent at 26 weeks and 7 percent at 50 weeks


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• Larger shear strength degradations are expected to occur in GFRP bars exposed to high pH solutions

• Bar types P, V1, and V2 were exposed to different alkaline and chloride for 51, 71, and 71 weeks respectively.

• GFRP bars were tested at a constant load rate in direct shear.

Direct shear capacity


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Predicted deflections due to creep

Creep can be defined as the increase in length of a bar loaded with a constant force over time, beyond the initial (elastic) deformation.

From experimental results it was observed that GFRP bars can creep between 2 and 6 percent over six months, when stressed at about 23 percent of the ultimate strength of the bar.


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Bond behavior and development length

A set of specimens was exposed outdoors and another set was exposed indoors under high temperature and high humidity conditions. for a period of 16 months Results indicate that a continuously wet concrete environment may degrade the bond properties of GFRP bars more than an outdoor exposure, by as much as 30 percent after 16 months of exposure. Any bond strength degradation increases the required development length of a reinforcing bar

Average slip at loaded end of 0.5 in. diameter bars at failure


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Effects of thermal expansion on cracking of GFRP reinforced concrete

• The setting temperature of the specimens was assumed to occur at 95 °F (32 °C).

• The experimental results indicated that a typical 8 in. thick concrete bridge deck reinforced with GFRP bars would not experience cracking on the surface due to thermal expansion for concrete covers of 1, 2, and 3 in. and GFRP reinforcement with a diameter 0.75 in. or smaller for conditions where a temperature rise < than 54 °F(13 °C) from the concrete setting temperature takes place.


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Conclusion

GFRP composites have many excellent structural qualities and some examples are high strength to weight ratio, material toughness, and fatigue endurance. Other highly desirable qualities are high resistance to elevated temperature, abrasion, corrosion, and chemical attack.

But its degradation due to environmental conditions are needed to be considered while designing of GFRP reinforced concrete elements.


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Thank You

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Degradation of Glass Fiber Reinforced Concrete Due to Environment