2.2—Definitions and acronyms
The following definitions clarify terms pertaining to FRP
that are not commonly used in reinforced concrete practice.
These definitions are specific to this document, and are not
applicable to other ACI documents.
AFRP—aramid fiber-reinforced polymer.
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440.2R-8 ACI COMMITTEE REPORT
batch—quantity of material mixed at one time or in one
continuous process.
binder—chemical treatment applied to the random
arrangement of fibers to give integrity to mats, roving, and
fabric. Specific binders are used to promote chemical
compatibility with the various laminating resins used.
carbon fiber-reinforced polymer (CFRP)—a composite
material comprising a polymer matrix reinforced with
carbon fiber cloth, mat, or strands.
catalyst—a substance that accelerates a chemical reaction
and enables it to proceed under conditions more mild than
otherwise required and that is not, itself, permanently
changed by the reaction. See initiator or hardener.
coating, intumescent—a covering that blisters to form a
heat shield when exposed to fire.
composite—engineering materials (for example, concrete
and fiber-reinforced polymer) made from two or more
constituent materials that remain distinct, but combine to
form materials with properties not possessed by any of the
constituent materials individually; the constituent materials
are generally characterized as matrix and reinforcement or
matrix and aggregate.
contact-critical application—strengthening or repair
system that relies on load transfer from the substrate to the
system material achieved through bearing or horizontal
shear transfer at the interface.
content, fiber—the amount of fiber present in a composite,
usually expressed as a percentage volume fraction or weight
fraction of the composite.
content, resin—the amount of resin in a fiber-reinforced
polymer composite laminate, expressed as either a percentage
of total mass or total volume.
creep-rupture—breakage of a material under sustained
loading at stresses less than the tensile strength.
cross-linking—forming covalent bonds linking one
polymer molecule to another (also polymerization). Note:
an increased number of cross-links per polymer molecule
increases strength and modulus at the expense of ductility.
cure, A-stage—early period after mixing at which
components of a thermosetting resin remain soluble and
fusible.
cure, B-stage—an intermediate period at which the
components of a thermosetting resin have reacted sufficiently
to produce a material that can be handled and processed, yet
not sufficiently to produce specified final properties.
cure, full—period at which components of a thermosetting
resin have reacted sufficiently for the resin to produce
specified final properties (antonym: undercure).
cure, thermosetting resin—inducing a reaction leading
to cross-linking in a thermosetting resin using chemical
initiators, catalysts, radiation, heat, or pressure.
curing agent—a catalytic or reactive agent that induces
cross-linking in a thermosetting resin (also hardener or
initiator).
debonding—failure of cohesive or adhesive bond at the
interface between a substrate and a strengthening or repair
system.
delamination—a planar separation in a material that is
roughly parallel to the surface of the material.
durability—the ability of a material to resist weathering
action, chemical attack, abrasion, and other conditions of
service.
e-glass—a family of glass with a calcium alumina borosilicate
composition and a maximum alkali content of 2.0%. A
general-purpose fiber that is used in reinforced polymers.
epoxy—a thermosetting polymer that is the reaction
product of epoxy resin and an amino hardener (see also
resin, epoxy).
fabric—a two-dimensional network of woven, nonwoven,
knitted, or stitched fibers.
fiber—a slender and greatly elongated solid material,
generally with a length at least 100 times its diameter, that
has properties making it desirable for use as reinforcement.
fiber, aramid—fiber in which chains of aromatic polyamide
molecules are oriented along the fiber axis to exploit the
strength of the chemical bond.
fiber, carbon—fiber produced by heating organic
precursor materials containing a substantial amount of
carbon, such as rayon, polyacrylonitrile (PAN), or pitch in an
inert environment and at temperatures of 2700 °F (1500 °C)
or greater.
fiber, glass—filament drawn from an inorganic fusion
typically comprising silica-based material that has cooled
without crystallizing. Types of glass fibers include alkali
resistant (AR-glass), general purpose (E-glass), high
strength (S-glass), and boron free (ECR-glass).
fiber content—see content, fiber.
fiber fly—short filaments that break off dry fiber tows or
yarns during handling and become airborne; usually classified
as a nuisance dust.
fiber-reinforced polymer (FRP)—a general term for a
composite material comprising a polymer matrix reinforced
with fibers in the form of fabric, mat, strands, or any other
fiber form. See composite.
fiber volume fraction—the ratio of the volume of fibers
to the volume of the composite containing the fibers.
fiber weight fraction—the ratio of the weight of fibers to
the weight of the composite containing the fibers.
filament—see fiber.
filler—a finely divided, relatively inert material, such as
pulverized limestone, silica, or colloidal substances, added to
portland cement, paint, resin, or other materials to reduce
shrinkage, improve workability, reduce cost, or reduce density.
fire retardant—additive or coating used to reduce the
tendency of a resin to burn; these can be added to the resin or
coated on the surface of the FRP.
flow—movement of uncured resin under gravity loads or
differential pressure.
FRP—fiber-reinforced polymer.
glass fiber-reinforced polymer (GFRP)—a composite
material comprising a polymer matrix reinforced with glass
fiber cloth, mat, or strands.
grid, FRP—a rigid array of interconnected FRP elements
that can be used to reinforce concrete.
DESIGN AND CONSTRUCTION OF EXTERNALLY BONDED FRP SYSTEMS 440.2R-9
hardener—in a two-component adhesive or coating, the
chemical component that causes the resin component to cure.
impregnate—to saturate fibers with resin or binder.
initiator—a chemical (most commonly organic peroxides)
used to start the curing process for unsaturated polyester and
vinyl ester resins. See also catalyst.
lamina—a single layer of fabric or mat reinforcing bound
together in a cured resin matrix.
laminate—multiple plies or lamina molded together.
layup—the process of placing reinforcing material and
resin system in position for molding.
layup, wet—the process of placing the reinforcing material
in the mold or its final position and applying the resin as a
liquid.
length, development—the bonded length required to
achieve the design strength of a reinforcement at a critical
section.
load, sustained—a constant load that in structures is due
to dead load and long-term live load.
mat—a thin layer of randomly oriented chopped filaments,
short fibers (with or without a carrier fabric), or long random
filaments loosely held together with a binder and used as
reinforcement for a FRP composite material.
matrix—the resin or binders that hold the fibers in FRP
together, transfer load to the fibers, and protect them against
environmental attack and damage due to handling.
modulus of elasticity—the ratio of normal stress to
corresponding strain for tensile or compressive stress below
the proportional limit of the material; also referred to as
elastic modulus, Young’s modulus, and Young’s modulus of
elasticity; denoted by the symbol E.
monomer—an organic molecule of relatively low molecular
weight that creates a solid polymer by reacting with itself or
other compounds of low molecular weight.
NSM—near-surface-mounted.
pitch—viscid substance obtained as a residue of petroleum
or coal tar and used as a precursor in the manufacture of
some carbon fibers.
ply—see lamina.
polyacrylonitrile (PAN)—a polymer-based material that
is spun into a fiber form and used as a precursor in the
manufacturer of some carbon fibers.
polyester—one of a large group of synthetic resins,
mainly produced by reaction of dibasic acids with dihydroxy
alcohols; commonly prepared for application by mixing with
a vinyl-group monomer and free-radical catalysts at ambient
temperatures and used as binders for resin mortars and
concretes, fiber laminates (mainly glass), adhesives, and the
like. Commonly referred to as “unsaturated polyester.”
polymer—the product of polymerization; more commonly a
rubber or resin consisting of large molecules formed by
polymerization.
polymerization—the reaction in which two or more
molecules of the same substance combine to form a
compound containing the same elements and in the same
proportions but of higher molecular weight.
polyurethane—reaction product of an isocyanate with
any of a wide variety of other compounds containing an
active hydrogen group; used to formulate tough, abrasionresistant
coatings.
postcuring—application of elevated temperature to material
containing thermosetting resin to increase the level of polymer
cross-linking and enhance the final material properties. See
cure, thermosetting resin.
pot life—time interval, after mixing of thermosetting resin
and initiators, during which the mixture can be applied
without degrading the final performance of the resulting
polymer composite beyond specified limits.
prepreg—a sheet of fabric or mat containing resin or
binder usually advanced to the B-stage and ready for final
forming and cure.
pultrusion—a continuous process for manufacturing fiberreinforced
polymer composites in which resin is impregnated
on fiber reinforcements (roving or mats) and are pulled
through a shaping and curing die, typically to produce
composites with uniform cross sections.
resin—generally a thermosetting polymer used as the
matrix and binder in FRP composites.
resin content—see content