Composite Materials in Civil Infrastructure (Structural Composites)

I. Introduction

Pizhong Qiao (Chiao), Ph.D., P.E., SECBDepartment of Civil and Environmental Engineering

Washington State UniversityPullman, WA 99164-2910

Phone: (509) 335-5183; Fax: (509) 335-7632Email: Qiao@wsu.edu

1.1 COMPOSITES (1)• COMPOSITES

• Combination of two or more constituent materials on a macroscopic examination to produce a new material with enhanced properties: Concrete = aggregate + cementHuman Bone = fiberlike osteons

+ interstitial bone matrix

• Key: can be identified by the naked eye. ConcreteAlloy metals combined on a microscopic scale, which is macroscopically homogeneous, cannot be distinguished by naked eyes and does not belong to composite.

• Outcome: Through well design, exhibit the best qualities of their components or constituents and often some qualities that neither constituent possesses.

1.1 COMPOSITES (2)• Natural Composites:

– Wood: Cellulose fibers + lignin matrix– Bone and Bamboo etc.

• Synthetic Composites:– Tire: steel or polymer fiber + rubber matrix– Fiberglass (e.g., boats): Chopped fibers + polyester– Fiber-reinforced Plastic (FRP) composites: panels, beams,

columns• Hybrid Composites:

– Wood or concrete wrapped with polymer composites– Wood beams reinforced with FRP plates on the tension side– Sandwich structure (face sheets with wood core)

Fibrous composite Particulate composite

1.1 COMPOSITES (3)• Main Factors for Using Composites:

• Weight Reduction (See Fig. 1.1, p. 3 in the book)• Corrosion Resistance• Design Flexibility

Note: Specific modulus (strength) = modulus (strength)-to-density ratio

1.1 COMPOSITES (4)• Stiffness and Strength of materials

1.1 COMPOSITES (5)• Characteristics of Composites: Fiber + MatrixTo carry loads effectively in various directions, laminates are designed and produced (See Fig. 1.2):

• In a given direction, the laminate of Fig. 1.2 is less strong than a unidirectional laminate aligned in the direction of the load

• In the transverse direction to the reinforcement, the matrix must carry the load

• Strength and stiffness are proportional to the amount of fibers in the matrix (Fiber volume fraction)

• The reinforcing fibers provide the useful engineering properties (e.g., strength and stiffness); whereas the matrix serves to protect and stabilize the fibers while transferring loads among the fibers predominantly through shear.

1.1 COMPOSITES (6)• Fig. 1.2 Assembly of three layers into a laminate

1.1 COMPOSITES (7)• The unidirectional composite is much stronger than the cross-plied quasi-isotropic one in the θo direction.

1.2 ADVANTAGES OF COMPOSITES

• High strength-to-weight ratio (specific strength)• High stiffness-to-weight ratio (specific stiffness)• Noncorrosive, nonmagnetic, nonconductive• High energy absorption properties: acoustic and seismic

responses• High fatigue-life• Ability to incorporate sensors in the material to monitor

and/or correct its performance Smart composites• Ability to tailor the material (both fiber architecture and

shape) for specific applications, and to design the material with other inherent properties (UV light, flammability, smoke toxicity)

• Ease of fabrication of large complex structural shapes or modules Modular construction

1.3 DISADVANTAGES OF COMPOSITES

• Cost of raw materials and fabrication• Possible weakness of transverse properties• Weak matrix and low toughness• Environmental degradation of matrix• Difficulty in attaching• Difficulty with analysis

1.4 TYPICAL PROPERTIES OF COMPOSITES (1)• Typical properties of unidirectional composites:

*** See Table 1.1, p. 8 in the book ***

1.4 TYPICAL PROPERTIES OF COMPOSITES (2)• Typical values for a laminate with stitched E-Glass fabric and

Polyester resin (*** See Table 1.2, p. 10 in the book ***)

1.5 COMPOSITES IN CIVIL ENGINEERING (1)General Applications:• Fiber-Reinforced Plastic (FRP) shapes: panels, rods, tubes,

beams, columns, cellular panels (highway bridge decks), etc.:• Cables and Tendons as tension elements (pre- and post-

tensioning of structures)• Beams, girders and cellular panels to support large loads

(vehicular and pedestrian bridges)• Trusses in a wide variety of structures (bridges,

transmission towers, and industrial plants)• Columns, posts and pilings to carry vertical loads (bridge

columns, marine pilings, and utility poles)

1.5 COMPOSITES IN CIVIL ENGINEERING (2)

FRP shapes

Cellular panel bridge deck

Marine pilings

1.5 COMPOSITES IN CIVIL ENGINEERING (3)General Applications (cont.):• Laminates and wraps to strengthen structures:

• Fabrics for external reinforcement (wrapping) of concrete, wood, and even steel (strengthening, rehabilitation, and retrofit (impact: retrofit-hardening))

• Laminates (or plates) bonded to beams on the tension side (reinforcement and strengthening and repair)

• Filament winding of concrete and wood cores (railroad crossties and utility poles)

• Composite rebars and grids to reinforce concrete in bridge decks and highway barriers

• Composite cables and tendons to prestress/post-tension concrete structures (bridges and building)

1.5 COMPOSITES IN CIVIL ENGINEERING (4)Common names used in industry:• RP: Reinforced Plastics• FRP: Fiber-reinforced plastics (Polymer) – the most popular one• GFRP / CFRP: Glass FRP/Carbon FRP• ACM: Advanced composite materials (aerospace/automotive

industry)Motivation for using composites in civil infrastructure:• There is an enormous interest on research, development and

implementation of new and advanced engineered materials needed to alleviate major problems adversely contributing to infrastructure deterioration worldwide, such as corrosion of steel, high labor costs, energy consumption, environmental pollution, and devastating effects of earthquakes. The U.S. Infrastructurereceived the "grade" of D by the American Society of Civil Engineers, who estimated rehabilitation costs of 1.3 trillion dollars over the next five years.

1.5 COMPOSITES IN CIVIL ENGINEERING (5)Some visible examples are:• Over 40% of the approximately 600,000 highway bridges are in

need of repair or replacement;

• About 12 to 16 million railroad timber ties are replaced annually at a cost of over $600 million;

• The California Dept. of Transportation (CalTRANS) is investing several billion dollars to retrofit bridge piers with composites(generally carbon fabrics bonded externally);

• The Dept. of Defense is investigating composite reinforcements to protect buildings and military facilities against terrorist attacks.

• Several highway decks have been constructed using composites in West Virginia, Ohio, Kansas, New York, and Missouri etc.

1.6 COMPOSITE MATERIALS IN CIVIL INFRASTRUCTURETwo most popular applications of FRP in Civil Infrastructure: • High-performance FRP highway bridge decks (replacement of

deteriorated concrete or wood decks and new deck construction)

• Retrofitting and rehabilitation of concrete structures with FRP composite (externally wrapping of concrete with FRPs)

Design Application

Composites

Pedestrian composite bridge