degradation of glass fiber reinforced concrete due to environmental effects.ppt

7/27/2019 Degradation of Glass Fiber Reinforced Concrete Due to Environmental effects.ppt

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Degradat ion o f Glass Fiber Reinforced Concrete Due to Environ mental Ef fects

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Overview.

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 constitutingof matrix and reinforcement.

Matrix :

It is the continuous phase and surrounds thereinforcements. It is made from polymer.

Bind the reinforcements (fibers/particulates) together

Transfer load to the reinforcements

Protect the reinforcements from surface damage due toabrasion or chemical attacks.

Reinforcement :

The term reinforcement implies some property

enhancement.Itis the dispersed phase, which normally bears themajority of stress. Different types of Fibers or Filamentsare continuous or discontinuous fibers .

Fiber Reinforced Polymer Composite


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Glass fiber-reinforced polymer composites (GFRPs)Most common fiber usedHigh strengthGood water resistanceGood electric insulating propertiesLow stiffness.

Carbon fiber-reinforced polymer composites (CFRPs)Good modulus at high temperaturesExcellent StiffnessMore Expensive than glassBrittleLow electric insulating properties

Aramid fiber-reinforced polymer composites (AFRPs)

Superior resistance to damage (energy absorber)Good in tension applications (cables, tendons)Moderate StiffnessMore Expensive than glass

Types ofFiber 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, whichoffers very good resistance to chemicals, but lower electrical

properties.

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

E-glass is electrical grade with low alkali content. It manifestsbetter electrical insulation and strongly resists attack by water. Morethan 50% of the glass fibers used for reinforcement is E-glass.

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

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


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Tensile Strength

GFRP bars have higher strength, than the specified yieldstrength fy of steel

reinforcing bars.

Modulus of ElasticityGlass Fiber reinforced polymer (GFRP) bars have lowermodulus of elasticity than steel bars . Hence limited tensilestrength is used to control width of cracks in tension zone atservice .

Creep and Shrinkage

Creep and shrinkage behavior in GFRP-reinforced members issimilar to that in steel-reinforced members.

GFRP vs. Steel Reinforced Concrete


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Shear Strength

The concrete contribution to shear strength is reduced inbeams with GFRP longitudinal reinforcement because of smallerconcrete compression zones and wider cracks

Chemical Attack

GFRP bars are non-corrosive and non-reactive to chlorides. Theyexperience a loss of strength with time, particularly in an alkalineenvironment

Stress-Strain Behavior

The stress-strain behavior of GFRP bars is linear elastic to failure,

with no yield plateau.

Thermal Conductivity

GFRP materials have relatively lower thermal conductivity thansteel

(Contd.)

GFRP vs. Steel Reinforced Concrete

ff f f


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Deleterious effects of several environments on fibers andmatrices

Water:

Polymeric fibers and matrices absorb moisture. Moistureabsorption softens the polymers

Weak acids:

Bridges in industrialized areas may be exposed to weak acidsfrom 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 contactwith bridge components. Strong acids can attack glass fibers,aramid fibers and polyester and epoxy matrices.

Weak alkali s:

Concrete containing pozzolanas can have pH values between 7and 10. Weak alkalis can attack glass fibers and polyestermatrices.

D l t i ff t f l i t


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Deleterious effects of several environments on

fibers and matrices

Strong alkalis:

Typical Portland cement concretes have pH values greater than10 and can cause degradation of glass fibers. Strong alkalis canattack glass fibers, aramid fibers, and polyester matrices.

H igh 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 andpolymeric 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 FRPreinforced concrete


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

Specifications of GFRPReinforcing Bars used:

GFRP bars provided by threedifferent manufacturers were usedin 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 at26 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 cancreep between 2 and 6 percent over six months, when stressed atabout 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 humidityconditions. for a period of 16 months

Results indicate that a continuously wet concrete environment maydegrade the bond properties of GFRP bars more than an outdoorexposure, by as much as 30 percent after 16 months of exposure.

Any bond strength degradation increases the required developmentlength of a reinforcing bar

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

Eff t f th l i ki f GFRP


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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 concretebridge deck reinforced with GFRP bars would not experiencecracking on the surface due to thermal expansion for concretecovers of 1, 2, and 3 in. and GFRP reinforcement with a diameter0.75 in. or smaller for conditions where a temperature rise < than 54F(13 C) from the concrete setting temperature takes place.


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Conclusion

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

But its degradation due to environmental conditions areneeded to be considered while designing of GFRPreinforced concrete elements.


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Thank You

degradation of glass fiber reinforced concrete due to environmental effects.ppt

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