Self-repairing, reinforced matrix materials

Self-repairing, fiber reinforced matrix materials include a matrix material including inorganic as well as organic matrices. Disposed within the matrix are hollow fibers having a selectively releasable modifying agent contained therein. The hollow fibers may be inorganic or organic and of any desired length, wall thickness or cross-sectional configuration. The modifying agent is selected from materials capable of beneficially modifying the matrix fiber composite after curing. The modifying agents are selectively released into the surrounding matrix in use in response to a predetermined stimulus be it internal or externally applied. The hollow fibers may be closed off or even coated to provide a way to keep the modifying agent in the fibers until the appropriate time for selective release occurs. Self-repair, smart fiber matrix composite materials capable of repairing microcracks, releasing corrosion inhibitors or permeability modifiers are described as preferred embodiments in concrete and polymer based shaped articles.

BACKGROUND OF THE INVENTION 
The present invention generally relates to matrix materials for use in a 
wide variety of end use fields and applications. More particularly, the 
invention relates to new and improved self-repairing, settable or curable 
matrix material systems containing so-called smart-release fiber 
reinforcements, alone or in combination with other reinforcement. My prior 
parent application, Ser. No. 540,191, filed Jun. 19, 1990, describes the 
new and improved inorganic and organic matrix composites employing 
concrete matrix systems and asphalt matrix systems as illustrative 
embodiments. That prior application describes smart-release hollow fiber a 
additives in settable construction materials and thermoplastic matrices, 
such as asphalt. This application is being filed to describe other 
embodiments of the smart-release matrix composite materials generally 
described in my earlier application and to provide additional examples of 
end use applications to which these new and improved compositions, 
articles and methods may be specially adapted and used. 
Cement is a fine, gray powder consisting of alumina, lime, silica and iron 
oxide which sets to a hard material after mixture with water. Cement, 
along with sand and stone aggregate, make up concrete, the most widely 
used building material in the world. Steel reinforcing bars (rebars) are 
commonly added to the interior of concrete for additional strength. 
There are many reasons for the popularity of concrete. It is relatively 
inexpensive, capable of taking on the shape of a mold, has exceptionally 
high compression strength and is very durable when not exposed to repeated 
freeze-thaw cycles. However, as a building or construction material, 
concrete, whether it is reinforced or not, is not without some 
shortcomings. One major drawback of concrete is that it is relatively low 
in tensile strength. In other words, it has little ability to bend. 
Concrete also has little impact resistance and is frequently brittle. A 
third major drawback is that its durability is significantly reduced when 
it is used in applications which require it to be exposed to repeated 
freeze-thaw cycles in the presence of water. Concrete is relatively porous 
and water is able to permeate the material. Freezing and thawing with the 
accompanying expansion and contraction of the water, forms cracks in the 
concrete. Furthermore, if salt is also present in the environment, it 
dissolves in the water and permeates into the concrete where it is capable 
of inducing corrosion in any of the rebars or other metallic 
reinforcements present. 
Various techniques have been suggested in the past for overcoming these 
drawbacks. The addition of fibers to concrete has improved its tensile 
strength but has decreased its compression strength. Providing exterior 
coatings on the outer surfaces of the concrete has reduced water 
permeation, but it is a time-consuming additional step and has little, if 
any, effect on the lasting strength of the concrete. The addition of 
modifying agents as freely-mixed additives into a concrete mixture before 
setting has also been tried. These efforts have met with generally 
unsatisfactory results. Attempts to add modifying agents in the form of 
micronodules or prills have also been tried. Frequently, the prills are 
designed to be heat melted to cause release of the modifying agent into 
the matrix after setting of the materials. These designs require the 
application of heat to release the beneficial additive into the matrix 
after cure. Moreover, the melted, permeated agents leave behind voids in 
the concrete which weakens the overall structure under load. Accordingly, 
a demand still exists for an improved concrete matrix material having 
greater tensile strength, greater durability and comparable or improved 
compression strength. 
In addition to cementitious building materials, the use of polymer 
composites as structural materials has grown tremendously in recent years. 
Polymer composite materials have advantages over steel or concrete 
including good durability, vibration damping, energy absorption, 
electromagnetic transparency, toughness, control of stiffness, high 
stiffness to weight ratios, lower overall weight and lower transportation 
cost. These polymer matrix materials comprise a continuous polymer phase 
with a fiber reinforcement therein. Some polymer composite materials are 
three times stronger than steel and five times lighter. They have 
heretofore been generally more expensive but their use may, in the long 
term, be economical because of their greatly reduced life cycle costs. 
Europeans have made bridges completely of specialty polymer matrix 
composite materials. The polymer composite materials may be used as 
rebars, tensioning cables, in bonded sheets, wraps, decks, supports, beams 
or as the primary structures for bridges, decks or buildings. Structures 
made from polymer matrix materials are specially effective in aggressive 
environments or are well adapted for building structures where 
electromagnetic transparency may be needed for highways, radar 
installations and hospitals. 
As used herein, matrix composite materials may refer to generally any 
continuous matrix phase whether it comprises a settable construction 
material such as cementitious materials or a thermoplastic material such 
as asphalt materials, as well as, other synthetic or natural high polymer 
materials ceramics, metals and other alloy materials. The matrix composite 
materials include various fiber reinforcements therein distributed 
throughout the matrix or placed at desired locations within the continuous 
phase. The matrix composite materials may be fabricated as large building 
structures and load bearing shaped articles, or they may be molded or 
machined as small parts for specialty uses. For example, the matrix 
material may comprise a thin sheet or web of material in the form of a 
foil, wrap, tape, patch or in strip form. As presently used in this 
specification, the term matrix composite material does not necessarily 
refer to large civil engineering structures such as highways and bridges. 
In connection with the polymer and/or metal or ceramic matrix composite 
materials, as well as, in the settable building materials such as concrete 
materials, special problems cause structures made from these materials to 
become aged or damaged in use. More particularly, special structural 
defects arise in use including microcracking, fiber debonding, matrix 
delamination, fiber breakage, and fiber corrosion, to name but a few. Any 
one of these microscopic and macroscopic phenomena may lead to failures 
which alter the strength, stiffness, dimensional stability and life span 
of the materials. Microcracks, for example, may lead to major structural 
damage and environmental degradation. The microcracks may grow into larger 
cracks with time and cause overall material fatigue so that the material 
deteriorates in long-term use. 
Advanced matrix composites used in structural applications are susceptible 
to damage on both the macro- and microscopic levels. Typical macroscopic 
damage to composite laminates involves delaminations and destruction of 
the material due to impact. On the micrographic scale, damage usually 
involves matrix microcracking and/or debonding at the fiber/matrix 
interface. Internal damage such as matrix microcracking alters the 
mechanical properties of shaped articles made therefrom such as strength, 
stiffness and dimensional stability depending on the material type and the 
laminate structure. Thermal, electrical and acoustical properties such as 
conductance, resistance and attenuation have also been shown to change as 
matrix cracks initiate. Microcracks act as sites for environmental 
degradation as well as for nucleation of microcracks. Thus, microcracks 
can ultimately lead to overall material degradation and reduced 
performance. 
Moreover, prior studies have shown that microcracks cause both fiber and 
matrix dominated properties of the overall composite to be effected. Fiber 
dominated properties such as tensile strength and fatigue life may be 
reduced due to redistribution of loads caused by matrix damages. Matrix 
dominated properties on the other hand such as compressive residual 
strength may also be influenced by the amount of matrix damage. The impact 
responses of toughened polymer matrix composites have been studied and it 
has been shown that matrix cracking precedes delamination which, in turn, 
precedes fiber fracture. Tough matrices which can reduce or prevent matrix 
cracking tend to delay the onset of delamination which results in an 
improved strength composite and longer lasting composite material. 
Repair of damages is a major problem when these matrix composite materials 
are employed in large-scale construction or advanced structures. 
Macroscale damage due to delamination, microcracking or impacts may be 
visually detected and can be repaired in the field by hand. Microscale 
damage occurring within the matrix is likely to go undetected and the 
damage which results from this type of breakdown may be difficult to 
detect and very difficult to repair. 
In order to overcome the shortcomings of the prior art construction and 
polymer, ceramic or metal matrix composite materials, it is an object of 
the present invention to provide new and improved smart structural 
composite materials having a self-healing capability whenever and wherever 
cracks are generated. 
It is another object of the present invention to provide new and improved 
composite materials including self-repairing reinforcing fibers capable of 
releasing chemical agents into the local microscopic domains of the matrix 
to repair matrix microcracks and rebond damaged interfaces between fibers 
and matrices. 
It is a further object of the present invention to provide a new and 
improved structural material. 
It is another object of the present invention to provide a new and improved 
cementitious material. 
It is still a further object of the present invention to provide a new and 
improved cementitious or other construction composite material having 
greater durability and greater tensile strength. 
It is still another object of the present invention to provide a new and 
improved matrix composite materials containing smart self-repairing fiber 
reinforcement containing repair chemicals therein which may be released by 
the smart fibers as needed in response to an external stimulus, and 
optionally which may be refilled with additional repair chemicals as 
needed in the field. 
SUMMARY OF THE INVENTION 
In accordance with these and other objects, the present invention provides 
new and improved shaped articles comprising: 
a cured matrix material having a plurality of hollow fibers dispersed 
therein, said hollow fibers having a selectively releasable modifying 
agent contained therein, means for maintaining the modifying agent within 
the fibers until selectively released and means for permitting selective 
release of the modifying agent from the hollow fibers into the matrix 
material in response to at least one predetermined external stimulus. In 
accordance with this invention the shaped articles are matrix composite 
materials of varying size and end use applications. The cured matrix 
materials have within them smart fibers capable of delivering repair 
chemicals into the matrix wherever and whenever they are needed. 
The present invention also provides a new and improved method for providing 
shaped articles having long-term durability and environmental degradation 
resistance comprising the steps of providing a curable matrix composition, 
distributing a plurality of hollow fibers therein in desired manner so 
that the hollow fibers are disposed within the matrix material in a 
desired predetermined distribution. The hollow fibers are filled with a 
selectively releasable modifying agent therein which is not released 
during the mixing or distributing step. The fibers are structured so that 
the modifying agents stay within the interior spaces or cavities of the 
fibers within the matrix until the matrix is cured or set. After curing, 
the modifying agents are selectively released from the fibers by 
application or action of at least one predetermined external stimulus. 
In a preferred embodiment, the method of providing a improved durability 
shaped article comprises providing a cured matrix material containing 
smart self-repair fibers reinforcement therein. 
The principles of the present invention are applicable to space age 
polymer, metal and/or ceramic structural matrix composite materials as 
well as more conventional cementitious settable or curable building or 
construction materials. 
Other objects and advantages will become apparent from the following 
Detailed Description of the Preferred Embodiments, taken in conjunction 
with the Drawings in which:

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
In accordance with the present invention, new and improved shaped articles 
comprise curable, settable, cross-linkable and/or hardenable matrix 
materials. The matrix material comprises a continuous phase and is a 
material that may be shaped to form a three-dimensional shaped article 
adapted for a particular use. Matrix materials can include any curable, 
settable or hardenable materials used in construction, building, roofing, 
roadway, aircraft, automotive, marine, appliances, transportation and/or 
biomedical fields for making shaped articles. Typically these materials 
will be moldable or castable to form shaped objects or may be laminated or 
assembled into finished products. The matrix materials may be inorganic or 
organic in nature and may include by way of illustration: cement, 
concrete, sintered fly ash or bottom ash/phosphoric acid mixtures, ceramic 
including, for example, silicon oxide, titanium oxide, silicon nitride, 
and metals such as aluminum, steel or other metal alloys, carbon, 
graphite, asphalt, thermoplastic polymers, thermosetting polymers, 
thermoplastic elastomers, crosslinkable polymers, curable polymer resin 
systems and hydroxyapatite. Illustrative thermoplastic polymers include 
polyolefins, polyesters, polycarbonates, polyacrylates, polyarylates, 
polyamides, polyimides, polyaramides, polyurethanes, foaming polyurethane 
compositions and any other thermoplastic polymers used as engineering 
thermoplastics for making shaped articles. Thermosetting and crosslinkable 
polymers and curable resin systems may include, for example, one and two 
part epoxies, phenolformaldehyde resins and other thermosetting and 
crosslinkable polymers. Thermoplastic elastomers can include rubbery 
polymers and copolymers including, for example without limitation, 
styrene-butadiene, rubber, neoprene, SEBS, NBR, and EPDM rubbers and the 
like. Visco-elastic materials and various latex materials may also be 
used. The matrix materials may also comprise sinterable ceramic materials 
including hydroxyapatites, as well as, other ceramic materials such as 
silicas, titanium, carbides, oxides and alumina. The matrix materials may 
also comprise metal matrices including aluminum, iron, lead, copper, 
steel, bronze, phosphor bronze, brass and other alloys, as well as 
biomimetic systems like bone matrices formed of various calcium salts, as 
well as other organic and inorganic materials. 
The matrix materials in accordance with this invention are processable to 
form shaped articles by molding, casting, sintering, laminating, 
machining, extruding, or other material fabrication method useful with the 
matrix material selected. The size and configuration of the finished 
shaped article produced is essentially unlimited including various small 
machined parts to very large engineering construction panels for use in 
building roadway and transportation applications. The matrix materials may 
be cured by means of catalysts, crosslinkers, radiation, heat, moisture, 
cooling or by any means used in this art for setting up, hardening, 
rigidifying, curing, setting or shaping these matrix materials to form 
shaped articles or objects. 
The new and improved shaped articles of this invention additionally 
comprise hollow fibers having interior spaces therein for containing 
selectively releasable modifying agents. The hollow fiber materials may 
include inorganic fibers or organic fibers. Illustrative inorganic fibers 
include, without limitation: fiberglass fibers, cement fibers, asphalt 
fibers, hydroxyapatite fibers, glass fibers, ceramic fibers, metal fibers, 
and the like. Illustrative organic fibers that may be used as the hollow 
fiber component may include, without limitation: polyolefin fibers, 
polyester fibers, polyamide fibers, polyaramide fibers, polyimide fibers, 
carbon fibers, graphite fibers, cellulose fibers, nitrocellulose fibers, 
hydrocarbon fibers Goretex.RTM. fibers, Kevlar.RTM. fibers, and the like, 
to name but a few. 
The fibers may be bundled, woven or loose. They may be held or engaged 
together with flexible web materials. They may comprise twisted pairs and 
additionally may include concentric structures of one or more fibers. The 
sidewalls of the fibers are typically rupturable or porous to permit the 
discharge or exiting of the modifying agent into the surrounding cured 
composite matrix material. The fibers may come in different shapes, 
volumes, and wall thicknesses. They may be generally notched, have 
periodic enlargements or bulges, V-shaped, double or multiple lumens, 
U-shaped, or they may comprise combinations of one or more different types 
of fibers. For example, double walled fibers are particularly useful for 
two-part modifying compositions such as epoxies. Doubled fibers including 
a metallic inside fiber and a glass outer sheath fiber are useful where 
bending of the metal fiber assists in breaking the glass carrier fiber. 
Additionally, assembled structures of polypropylene hollow porous fibers 
disposed inside a glass outer fiber might be used to permit a first break 
and release of modifying material to occur with the glass fiber and 
thereafter a secondary break and release of the polypropylene fiber at a 
later date to provide a specially long-term profile modification to the 
shaped matrix composites. The smart-release fibers may also be paired or 
include other specialty fibers such as piezoelectric fibers or optical 
sensor fibers for providing special monitoring, metering and diagnostic 
capabilities. Some of these specialty composites will be more particularly 
described hereinafter. The fibers may also be woven together into a web so 
that they may be wrapped as an organized bundle around rebars or the like. 
Although fiber materials are preferred, other container-like smart release 
structures or vessels may be provided for special end uses. For example, 
in relatively large structural parts it may be useful to add the repair 
chemicals in large flat balloons or bags layered or laid up within the 
matrix or layers of matrix. It should be apparent to those skilled in this 
art that for certain end uses, small release vessels having a shape 
somewhat different from hollow fibers for performing the same smart 
release functions may be employed. In addition, the fibers may be 
relatively small, chopped or comminuted fibers having lengths of less than 
about one inch and diameters of less than about 100 microns. The fibers 
and matrices may be readily used in usual shaping processes such as in an 
injection molding operations or the like. 
In accordance with this invention, the hollow fibers include certain 
internal modifying agents which are-selectively releasable from the fibers 
in response to the application of certain predetermined external stimuli. 
The modifying agents include agents which will modify the performance 
characteristics of the cured shaped article matrix materials in use. By 
way of illustration, the modifying agent may include polymerizable 
monomers such as methyl methacrylates, styrene or other polymerizable 
starting materials. They may additionally include two part epoxies wherein 
an epoxy precursor material is disposed in one fiber or in one lumen of a 
double lumen fiber and the amine or other cross-linking agent is disposed 
in an adjacent fiber or in the other lumen of the double lumen fiber. 
Other curable polymerizable monomers may also be employed. 
Another modifying agent which may be used herein includes a sealant used to 
prevent water permeability and ingress or egress of water or other liquid 
materials to and from the cured matrix composite. Illustrative examples 
for cement may include oily sealants to prevent ingress of water such as 
linseed oil or other known sealant materials. 
Another important modifying agent for both cementitious and polymer 
matrices include adhesives which cure in situ to repair microcracks within 
the matrix in use. Illustrative adhesives include one- and two-part 
adhesives, one- and two-part epoxy adhesives, cyanoacrylate adhesives, 
Elmer's glue and others known to those skilled in the art. The adhesives 
may bond matrix to matrix, fiber to fiber, as well as fiber to matrix. 
Certain Water barriers are particularly useful modifying agents for 
cementitious matrices. These may include special Zypex.RTM. brand sodium 
silicate additives as well as siloxane and silica additives known as Salt 
Guard.RTM. and the like. 
Another modifying agent useful in the shaped articles of this invention 
includes anticorrosion agents such as calcium nitrite. These are 
particularly useful in cementitious matrices employing rebar 
reinforcements or steel mesh reinforcements. 
Another example of a modifying agent which may be disposed in the interior 
of the hollow fibers for use herein includes antifreeze material such as 
polypropylene glycol. 
Fiber protectors may also be used as the modifying agents which can be 
materials which protect the fibers themselves within the matrix material. 
An example of this includes pH modifiers for protecting fiberglass in 
highly alkaline environments. 
Still another class of modifying agents particularly useful in polymer 
matrices are solvents which permits solvent action to actually repair 
microcracking damage locally at a cracking site or possibly to dissolve 
the matrix or fibers or both to permit them to re-form at a later time. 
In addition to solvents, other curable monomers and co-monomers may also 
serve this repair function. pH modification agents may also be used as the 
modifying agents, either alkali or acidic agents, which may be placed in 
the interior of the fibers only to be released by an appropriate pH 
changes in the matrix. Other additives may include flame retardant agents. 
Visco-elastic polymers may also be used as modifiers. 
In accordance with this invention, means are provided for maintaining the 
modifying agent within the hollow fibers. The modifying agents may be 
physically trapped by, for example, drawing liquid additives into the 
interior of the fibers and retaining them therein by capillary action or 
by closing off the ends of the fibers. For brittle fibers, sealing of the 
ends by heat or pressure may be one method for maintaining the modifying 
agents therein. Moreover, specialty coatings may be used, which will 
selectively degrade upon the occurrence of a particular external stimulus. 
Illustrative examples might include heat sensitive coatings, pH sensitive 
coatings, ion sensitive coatings, and the like. These coatings are 
effective to close off the pores of the hollow fiber walls or the ends of 
the fibers to prevent premature leakage of the modifying agent until the 
intended time. Illustrative coatings may include waxes, low molecular 
weight hydrocarbon oils and coating polymers to name but a few. 
In accordance with the present invention, means for permitting selective 
release of the modifying agent in response to the external stimulus may be 
provided. Illustrative examples include the selectively removable or 
dissolvable coatings which give way to permit leakage of the modifying 
agent in response to, for example, stimuli such as heating, cooling, 
loading, impacting, cracking, water infusion, chloride infusion, 
alkalinity changes, acidity changes, acoustlc excitation, low frequency 
wave excitations, hydrostatic pressure, rolling pressure, light 
sensitivity or laser excitation, or the like. Electrical currents, 
voltages, electrorheological excitation, radiation, or other energetic 
stimuli may also be employed or effective to permit or cause selective 
release of the modifying agent or agents from the fibers. 
In accordance with this invention, the selective release of the modifier 
occurs in the matrix when and where it is required and may lead to 
improved toughness, strength, ductility, brittleness, permeability, fire 
retardancy, stiffness, dimensional stability, modulus of elasticity, 
fatigue, impact resistance, and other improved properties. Specially 
important in accordance with this invention is the ability to repair small 
microcracks forming in the reinforced matrix composites. The selective 
release of the modifying agent may be chosen to be effective to rebond the 
fibers to the matrix, to repair the fibers themselves, to improve or 
restore the matrix to fiber interface, to repair delaminations, and to 
repair microcracks in the matrix itself which may repair or overcome 
cracking or corrosion induced dimensional weaknesses and ultimately 
reduced durability for the shaped articles. 
As has been mentioned above, the shaped articles in accordance with this 
invention may be used for a number of applications, both large and small. 
Large construction applications are particularly preferred, particularly 
those used in harsh environments or for outdoor use. Illustrative end use 
applications for the new and improved shaped articles in accordance with 
this invention include, for example without limitation, structural 
sandwich panels, exterior applied insulation panels, fire panels, 
construction building blocks, cements, concretes, fireproof doors, panels, 
walls, hazardous waste containment vessels, engines, concrete building 
blocks, roadways, bridges, dams, engines, road surfaces, roofing blocks, 
roofing shingles, decks for parking garages, and other building structures 
and columns. Other construction applications might include the use of 
these shaped, cured, smart-release composites in bridges, post-tensioning 
cables, road decks, road deck overlays, aircraft body components, 
including fuselages, wings and tip design, machined parts, helicopter 
blades as well as the aforementioned roofing structures. 
The shaped articles of this invention might also be useful in biomedical 
applications as bone replacements as prosthetic devices and as biomedical 
adhesives. More particularly, shaped articles of this invention may be 
used to form self-growing structures. In accordance with this aspect of 
the invention, the goal is to create a ceramic resembling bone which is an 
organic-inorganic composite created at low temperature due to the presence 
of organisms. Bone is made up of an oriented matrix which is secreted by 
bone forming cells referred to as osteoblasts. In natural bone, organic 
matrices are made up of structural molecules which serve as a scaffolding 
and which are laid down in very precise, oriented pattern of fibrils into 
and onto which inorganic crystalline phases form. The formation of the 
first crystals of inorganic salts of calcium phosphate are often referred 
to as initiation or nucleation which occurs along nucleation sites which 
appear at regular intervals along the organic scaffolding, usually 
collagen laid down by osteoblasts. Once nucleation has occurred, the next 
major process involves the continuation of crystalline growth from these 
nucleation sites outward along the fabric of the organic matrix and 
eventually between the molecules which serve as scaffolding. As crystal 
growth continues and forms against inorganic matrix, there is a loss of 
organic components which are designed to reserve space in the matrix 
forever expanding the inorganic phase. 
In accordance with this biological models, the present invention may be 
employed to provided a self-growing structure something like bone, wherein 
the hollow pores polymer fibers may release chemicals and act as an 
organic template on which to form a strong structural bone-like composite. 
This self-growing structure might be used for structural materials as well 
as for computer chips or for prosthetic devices. More particularly, just 
as ligaments or tendons have been used as natural matrices to form bone 
materials, these polymer tubes or fibers are used in accordance with the 
present invention to concentrate bone-like substances. The fibers are 
hollow and have porous walls. In accordance with this invention chemicals 
are released from the hollow fibers, particularly polymeric materials 
which are designed to cause targeted release of water in an inorganic 
matrix to form a structural network of calcium phosphate materials. 
Instead of using collagen gels to form a backbone network, in accordance 
with this invention, a matrix material including inorganic cementitious 
salts and a first polymer reactant may be provided which includes hollow 
fiber materials including a condensable or cross-linkable moiety reactive 
with polymer. Under appropriate conditions, release of the co-reactant 
from the fibers causes a condensation reaction of the matrix polymer in 
which water is produced. The water byproduct of the condensation reaction 
is used to hydrate cement to build up a structural backbone along the 
fiber regions. 
In accordance with another aspect of the invention, a hollow porous polymer 
fiber material may be placed in a calcium phosphate material matrix in 
which a polymer powder monomer is present. A cross-linking monomer is then 
released from the fibers into the matrix. The ensuing condensation 
polymerization reaction releases water, which then hydrates the calcium 
phosphate materials. Xypex or other cement crystallizing initiator 
materials may carry the hydration reaction away from the polymer fiber 
scaffolding within the inorganic matrix. The structural make-up of these 
materials may be designed to resist stresses by including piezoelectric 
fibers within the matrix. Lines of force may be generated by prestressing 
or stressing the piezoelectric polymer fibers along which charged 
cementitious ions will migrate. This will cause the polymer matrix to 
rearrange and the composite prestressing forces therefore will generate an 
appropriate microstructure within the material. 
Also in accordance with this aspect of the invention, self-healing may be 
accomplished by leaving some of the original fibers void or by adding 
additional fibers designed with specialty repair chemicals for repairing 
the system. Hollow porous fibers may be used to deliver repair chemicals 
at a later time if damage such as cracking occurs. Repair chemicals, 
either present as an adjuvant fiber additive or added to hollow fibers 
from the outside, may be used to improve the visco-elasticity of the 
entire component as desired. 
In accordance with this invention, materials may be developed for 
application in self-repairing materials for use in facings, coatings and 
membranes. In accordance with this aspect of the invention, the new and 
improved fiber-containing matrix materials may be provided in the form of 
paints, membranes, roofing materials, or the like, including 
self-repairing liquids within the fibers. The materials may be provided in 
the form of wraps for buildings, bridges, roads, or the like, including 
webs or fabrics of smart fibers disposed within the matrix. Repair 
chemicals may repair cracks in the wrap itself or also seep into and 
repair adjacent structures to which the wrap is adhered to improve the 
overall structural performance over time. Specialty wraps including solar 
collecting fibers might also be added to the exterior of previously 
existing outdoor structures. 
Another biological or biomedical application for the new and improved 
shaped articles of this invention might include smart-release bandages, 
artificial skin materials, poultices, bandaids and the like which include 
smart fibers which release healing chemicals or healing promoting 
chemicals by upon movement of the patient or by application of another 
stimulus, such as for example, a heating pad, or the like. The smart 
fibers used in these bandage applications might include such release 
chemicals as oxygen releasing chemicals, moisturizers, aloe vera, 
antibiotics, anti-inflammatants, analgesics, non-stick agents or the like. 
Another illustrative use of the shaped articles of this invention might be 
polymer matrices including smart fibers therein which may be made to 
include dissolving chemicals which ultimately assist in de-naturing, 
degrading or destroying the polymeric structures by depolymerization or 
chemical reaction to improve recyclability of the polymer material. 
The shaped articles of this invention may also be used in various small 
shaped article applications including aerospace applications, pipe repair, 
engine pistons, rubber matrices, water-borne paints and coatings, rubber 
gasket materials and other seals and in woven fabrics. For example, in 
fabrics the fibers may contain a fabric glue to repair small tears or 
abrasions of the fabric. Hard self-repairing shaped articles, such as 
silicon nitride fibers in carbon-alumina matrices for pistons might be 
used. Metal matrices that may be employed include metals and alloys such 
as alumina as well as foamed metals. The fibers for these metallic 
composites may include adhesive materials or corrosion resistant materials 
to help repair the matrices or other desirable smart release additives. 
The new and improved smart fibers of the present may be disposed within 
large cross-sectional areas or sections of a matrix prior to cure which 
may thereafter be used to release curing agents from several positions 
disposed throughout the curable matrix simultaneously to speed up or 
assist in the curing of large cross-section polymer articles. Similarly, 
natural fibers such as wheat straws or the like may be added to concrete 
or adobe matrices to stabilize the composites so that they do not crumble 
or flow in use. 
In a related application, the new and improved smart matrix materials may 
be used to perform road repair and pothole repair. In connection with this 
aspect, smart release fiber-containing uncured material may be added to a 
pothole. An agitation or pressure may be used to release curative agents 
from the interior of fibers provided in the matrix material to promote 
adhesion and curing of the pothole repair mass to the substrate road 
surface. Additional fibers may be provided,,containing repair adhesives 
which release in response to tire pressure, to further strengthen and 
reinforce the pothole patch in use. 
Another highway application of the present invention includes the use of 
smart release fibers to add phosphorescent chemicals to concrete or 
asphalt matrices. Phosphorescent roads may clearly demarcate the road or 
highway surface from non-road driving surfaces at night without the need 
for street lights or other markers or reflectors. The smart matrix 
materials would permit renewed release of phosphorescent agents into the 
road surface, as the layers of the road surface are worn away by highway 
traffic. A continually replenishing supply of chemicals that could absorb 
sunlight during the day and re-emit it as phosphorescent light in the 
evening hours would be provided. 
In accordance with another aspect of this invention, the shaped articles 
may include hollow and continuous matrix formed into a shaped article and 
having hollow fibers therein which permit visual inspection of the 
structural part in use. The use of hollow, air-filled fibers permits 
persons to actually look into and see inside the matrix to see cracks near 
the fibers. These hollow fibers also permit exterior introduction of 
chemicals to be performed to add chemicals to a previously cured matrix. 
Hollow or filled fibers may be provided with dyes or other sensing or 
sensible materials to identify the presence of structural stresses or 
weaknesses and also the locations of these stresses in large structural 
articles. For example, release of dyed materials from fibers may permit 
the dye to migrate to the surface to indicate a structural compromise or 
repair need in a highway, bridge, or the like. Specialty dyes such as 
X-ray sensitive dyes may be added to help diagnose a small 
micro-structural repair problem. More particularly, if the dye is leaked 
into the matrix in use due to structural damage, periodic diagnostic teams 
may test with high energy beams shined into the matrix. The interactive 
dye would signal back after excitation in a detectable manner so that the 
need for attention or repair would be revealed. Piezoelectric fibers may 
also be used to evaluate the state of the matrix. Remote sensing of eddy 
currents or electrical or magnetic fields generated about the fibers in 
response to pressures or stress may be detected in a matrix in these ways. 
Still another application for the shaped articles of this invention can 
include non-biological but biomimetic materials wherein a polymer matrix 
containing crystallizable mineral elements such as alumina alkoxide may be 
provided. A condensation reactive element or ingredient provided inside 
the smart fibers may be released on application of appropriate external 
stimulus from the smart fibers within the matrix containing the alumina 
crystals. The by-product water of the condensation reaction in this case 
may be used to cause alumina crystals to grow at specified locations 
within the shaped article. 
Another special useful application of the shaped articles in accordance 
with this invention is as a containment structures for radioactive or 
chemical waste materials. In accordance with this aspect, fibers provided 
with chemically sensitive coatings or radiation sensitive coatings may be 
provided which are adapted to release scavenger compounds when radiation 
or chemical waste is detected. The compounds will then migrate from the 
fibers into the matrix to scavenge and render harmless radioactive or 
chemical materials leaking into the containment vessels to prevent them 
from being discharged from the containment area into the environment. 
Alternatively, permeability modifying agents may be released from the 
coated fibers to boost the impermeability of the containment vessel to 
water-borne contaminants. 
The new and improved shaped articles of this invention may be employed to 
form self-repairing impact resistance layers in laminated materials and 
structures. For example, a clear, transparent polymer matrix containing 
adhesive filled glass fibers may be used as an interlayer between two 
safety glass or polymer sheets. Impact fracture of a base sheet will cause 
local release of repair adhesive from the interlayer to control 
fragmentation and rebond cracked or fractured sections of a laminate. 
As has been mentioned above, various means may be provided to force the 
repair chemicals out of the fibers. Chemicals may be pumped into hollow 
fibers from the outside or propellant gases may be injected into 
previously filled fibers to which external access has been provided to 
force the chemicals out. Other methods to promote repair chemical release 
may include electrical, magnetic, and chemical means which alter the 
shape, permeability or coating integrity of the fibers. Shaped memory 
alloy materials may be used as the fiber or these materials may be used in 
the fiber to squeeze the fiber and thereby pump the chemicals out. Fibers 
which change their shape in response to applied light or magnetic forces 
or fields may also be used to discharge the chemicals as desired. 
The smart release shaped articles and materials in accordance with the 
present invention may be used throughout building structures to provide 
earthquake proof buildings which can withstand seismic activity with 
reduced hazard and damage. This is accomplished by preventing flying 
debris from being created and by supporting building structures in 
matrices adapted to visco-elastically respond to seismic vibration. 
Because the beneficial improvements provided by the new composition, 
articles and methods of this invention may be useful for broad range of 
applications, it is difficult to specifically enumerate each of them. The 
present invention will be further illustrated by several specific end use 
applications provided to further illustrate the improvements provided by 
the present invention. 
Referring now to FIGS. 1a-1f, the new and improved self-repairing fiber 
reinforced matrix composite and its operation in the field is shown. As 
depicted in FIG. 1, a hollow fiber containing an adhesive modifying agent 
and coated with a thin coating material is dispersed within a settable or 
curable matrix material which may be either a polymer or cementitious 
material. As shown in FIG. 1b, a loading applied to a shaped article 
causes strains within the matrix, which in turn cause the fiber to break 
and the matrix to crack. This causes the modifying chemical agent disposed 
within the hollow fiber to be released into the vicinity of the crack in 
the matrix as shown in FIG. 1b. The modifying agent flows and fills the 
void as shown in FIG. 1e and eventually cures to rebond the fiber to the 
matrix and to repair the fiber to itself as shown in FIG. 1f. This 
schematically illustrates the modified fiber concept of the present 
invention. 
Referring now to FIGS. 2a-2e , a similar smart fiber repair embodiment is 
depicted wherein the smart hollow fibers contain anticorrosive modifying 
agent and are coated with fibers which are pH sensitive. These smart 
fibers are disposed within the matrix adjacent the rebar reinforcement by 
selectively positioning them adjacent the rebar as the matrix is poured 
into the concrete mold or the rebar can actually be wrapped with the 
hollow fibers which have been previously banded together as a web or tape. 
In accordance with this matrix composite construction, the anticorrosion 
filled smart fibers are disposed immediately adjacent the rebars. The 
anticorrosive chemical compounds are not released to protect the rebars 
unless or until the exchange has occurred in the vicinity of the rebar, 
either due to chloride iron infiltration or carbon dioxide intrusion. The 
advance of corrosive chemicals breaks down the pH versus sensitive coating 
on the smart fiber, releasing the protective anticorrosive agent to 
protect the rebar from corrosion by the environmental chemicals found in 
FIGS. 2c-2e. 
Referring now to FIGS. 3a-3c, the smart fiber matrix is shown in operation 
in plain and in antifreeze modifying agent disposed within the hollow 
fibers. A water-based antifreeze expands as it cools to force its way out 
of the pores in the hollow fiber, thereby dislodging the coating, if 
present, and permitting the antifreeze to exit into the local environment 
of the matrix. As shown in FIGS. 3b-3c, the release of the antifreeze into 
the matrix lowers the freezing temperature of moisture in the materials 
within the matrix preventing freeze/thaw damage from occurring to the 
matrix. 
Referring now to FIG. 4, a debonding of a coated fiber is shown as a 
mechanism for releasing the modifying agent contained within the smart 
fiber into adjacent areas of the matrix. This can occur, for example, 
where there is coating applied to the smart fiber to retain the modifying 
agent within the fiber interior as a higher affinity for the surrounding 
matrix in a cured state than to the fiber. Accordingly, debonding of the 
fiber from its coating allows the pores to become open to permit chemical 
release. 
Referring now to FIG. 5, there is illustrated in the embodiment wherein 
modifying agent release is caused by torting, twisting or other load 
changes which cause a dimensional change in the shape of the hollow fiber, 
which in turn forces the modifying agent out into the surrounding matrix. 
These torting, twisting or other loads placed on the fiber may cause local 
debonding of the fiber from its coating, permitting release as shown in 
FIG. 4 or a mechanical forcing of the contents of the fiber through the 
pores, which in turn causes dislodgment of the coating may also occur. 
Referring now to FIGS. 6a and 6b, the application of the compressive load 
on a twisted fiber bundle can cause debonding of the coating from the 
twisted fibers forcing fluid contained within the hollow spaces of the 
fiber through the fiber pores and into the surrounding matrix. 
Referring now to FIG. 7, a preferred embodiment of the present invention 
includes providing the smart hollow fiber reinforcement within a matrix so 
that end portions of the fiber are accessible from the exterior of the 
matrix to permit additional modifying agents to be supplied into the 
fibers of the matrix. As depicted therein, a reservoir of modifying agent 
may be placed in the fiber and a vacuum pump may be attached to the 
opposed ends to draw the modifying agent into the fibers to replenish any 
leaked materials therein. 
FIG. 8 is an extension of the concept described and schematically 
illustrated in FIG. 7 wherein a series of hollow smart fiber 
reinforcements are arranged in a continuous network to permit the 
additional chemicals to be added from the outside throughout the entire 
matrix. 
Referring now to FIG. 9, other mechanisms may be employed for dislodging or 
releasing the modifying agent into the surrounding matrix at a selected 
time after curing, such as, by example, using laser energy to cause an 
aneurysm to form in the fiber which permits leakage. 
Referring to FIG. 10, hydrostatic pressures may also cause the fiber 
diameter to be locally reduced, causing an exiting of the modifying agent 
into the surrounding matrix. 
FIG. 11 shows an embodiment wherein acoustic excitation is employed as the 
means for releasing the modifying agent from the fiber. 
FIG. 12 is an alternate embodiment wherein waves of low frequency such as 
seismic waves may pass through the matrix in such a manner as to cause 
debonding of the fiber from a coating or uncoated fibers may cause the 
modifying agent to exit from pores disposed within the fiber matrix 
disposed within the hollow fiber. 
FIGS. 13a through 13h demonstrate in a side-by-side comparison the ability 
of the smart fiber reinforced matrix composite materials prepared in 
accordance with this invention to prevent environmental distress and aging 
frequently encountered by prior art composite materials. A comparison of 
FIGS. 13a and 13e shows that the modifying agent in FIG. 13a is an entire 
corrosion agent to prevent corrosion of the rebars and in that case 
calcium nitrite is preferred. 
In FIGS. 13b and 13f the permeability of the matrix may be controlled by 
setting up a polymerized polymer within the matrix as shown in FIG. 13f to 
prevent permeability. This may be effected in several ways, and in one 
preferred embodiment, polymerizable components are freely mixed within the 
concrete which require only the exposure to a liquid catalyst to cause 
them to set up into an impermeable barrier. FIGS. 13c and 13g illustrate 
the release of antifreeze materials in FIG. 13g to prevent freeze/thaw and 
to brittleness and cracking due to ice crystals formation within the 
matrix from occurring. Finally, FIGS. 13d and 13h illustrate the 
development of local microcracks due to local loading which may be locally 
repaired by release of repairing adhesives as in FIG. 13h to fill cracks 
or voids and rebond fibers and matrices adjacent microcracks to prevent 
major microscopic failures from occurring. 
In accordance with this invention, the smart fiber hollow fibers used to 
make the smart fiber reinforcements in accordance with this invention may 
have any desired configuration. As illustrated in FIGS. 14 through 20, a 
wide variety of cross-sectional configurations may be employed, as well as 
multi-lumen tubes and multiple concentric tube assemblies may be employed. 
Referring now to FIG. 21, the new and improved smart fiber matrix composite 
materials in accordance with this invention may be used in connection with 
other matrix protecting practices to provide redundant protection against 
environmental damage. As depicted in FIG. 21, a cementitious matrix 
including rebars may include surface coatings and sealants to prevent the 
ingress of harmful environmental liquids. Calcium nitrite anticorrosion 
chemicals may be freely mixed within the cement and the smart fiber 
reinforcements may be disposed immediately adjacent the rebar containing 
additional anticorrosive modifying agents in accordance with this 
invention for release as needed when the concentration of corrosion 
chemicals get sufficiently high to stimulate their release. 
Referring now to FIGS. 22a through 22d, there is depicted a special 
embodiment of the present invention wherein the notion of smart fiber 
release and repair is coupled with specialty fibers. As depicted in FIG. 
22a through 22d, the smart fiber itself comprises a piezoelectric fiber 
into which a liquid chemical is first applied or deposited by providing an 
electric current to the piezoelectric components of the fiber. The 
modifying chemicals accretes within and on the surfaces of the web of 
fibers making up the solid piezoelectric cylinders, which in turn hollow 
fibers which may be placed and disposed within the matrix. In accordance 
with these embodiments the modifying agents are released from the 
piezoelectric fibers by the application of service load stresses on the 
matrix. These generate electrical charges in the piezoelectric fibers due 
to their piezoelectric character. The electrical charges cause positive 
ions to move from inside the porous fibers into the surrounding matrix. 
Negative ionic materials located in the matrix may also be drawn into or 
attracted to the piezoelectric hollow fiber. In this way repair can be 
done by dispersing charged ions into the matrix or may through by 
selectively drawing undesired materials into the fibers to remove them and 
causing damage to the matrix. 
Referring now to FIGS. 23a through 23d, another specialty application for 
the smart fiber reinforced matrix materials in accordance with this 
invention is shown, which include an impermeable barrier equipped with 
smart sensors in addition to a hollow fiber wrapped rebar composite in 
accordance with this invention. The impermeable barrier may be connected 
to sensor equipment shown as a feedback loop capable of detecting ingress 
of moisture, changes in voltage or changes in chloride iron concentration, 
As shown in FIG. 23b, once the ingress of moisture is sensed at the 
impermeable barrier layer, an electrical signal may be sent through the 
inner barrier layer, causing discharge or migration of cat ions from the 
middle layer towards the rebar, which causes a coating on the smart fiber 
to be broken down to permit release of the modifying agent contained 
therein of anticorrosion chemicals into the immediate vicinity of 
the-rebar to prevent corrosion. 
As depicted in FIGS. 23c, the hollow smart fibers in accordance with this 
invention are disposed in a region bounded by the barrier layer on one 
side and the rebar on the other to provide redundant backup protection to 
the rebar to prevent corrosion. More particularly, the hollow fibers 
contain water binding chemicals which effectively remove the damaging 
water from reaching the rebar in that intermediate region, thereby 
preventing corrosion. 
In FIG. 23d, an alternate aspect is provided wherein the barrier is 
electrified to provide a galvanic cell in the immediate region between the 
barrier layer and the rebar. A counter galvanic cell is created about the 
hollow middle fibers which contain a modifying chemical inside the buffer 
zone, which in turn can release moisture binding hydroscopic chemicals in 
response to application of electrical charges or may release anticorrosive 
chemicals. In accordance with FIG. 23e, the hollow fibers disposed within 
the barrier buffer zone may include zinc ions which will migrate and coat 
the rebar in a galvanizing or electric lading action by application of the 
voltage between the barrier and rebar. 
Referring now to FIGS. 24 and 24b, another specialty embodiment of the 
invention includes the use of optical fibers as the self-repairing fiber 
which in turn contains a modifying chemical which may be positioned within 
the matrix. Twisted pair fibers, for example, may be used as shown in 
FIGS. 24a and 24b. In response to the application of applied loads, the 
optical fibers may be changed in their transmission properties indicating 
a break or leak in the matrix and may in turn be caused to discharge their 
internal modifying agent into the surrounding matrix to, for example, 
repair a microcrack as shown in FIG. 24d. 
FIGS. 25a and 25b depict a similar embodiment involving the use of glass 
hollow fibers as surrounding hollow fibers for containing adhesive repair 
modifying agents and for housing an optical fiber therein. As shown in 
FIG. 25b, microcracking of the matrix causes release of the repair 
adhesive locally within the matrix to prevent further cracking and 
breaking which might damage the optical fiber and its transmission 
capability. 
Referring now to FIGS. 26a and 26b, a different use of optical fibers as 
the smart fibers in a matrix composite in accordance with this invention 
is shown. More particularly, a cladded optical fiber having an interior 
cavity filled with an adhesive repair chemical is provided in a 
surrounding polymer or cement matrix. The light transmission of the intact 
fiber is of a given value. Once applied, loads are caused cracking and 
bending of the matrix as shown in FIG. 26b which will cause bending of the 
fibers decreasing the amount of light transmitted therethrough. 
Referring now to FIGS. 27a and 27b, another glass fiber embodiment is shown 
wherein an assembly including an outer hollow glass tube filled with 
adhesive modifying agent and including an optical fiber therein and a 
middle fiber therein provide a special matrix composite. As shown in FIG. 
27b, in response to an applied load, the middle fiber bending assist in 
breaking the outer glass tube to thereby release the repairing adhesive to 
the matrix. The optical fiber polymer may be bent or stretched and light 
lost to cladding coating on the fiber may be detected outside the matrix 
to determine bending of the fibers and possible microcracking therein. 
Referring now to FIGS. 28a through 28c, another use-of an optical fiber for 
forming the smart repair fibers in accordance with this invention 
illustrates reliance on release of the repair chemicals within the optical 
fiber to change the optical characteristics to indicate that microcracking 
has occurred wherein the change in volume of the repair material can 
indicate the volume cracks that needed to be filled and the change in 
refracturing index of light transmitted through the fiber may also give an 
indication of the volume of the cracks that have been filled in accordance 
with this invention. 
Referring now to FIGS. 29a and 29b, a plurality of septums or brag optical 
gradings may be positioned along the modifying agent filled optical fiber 
in accordance with this invention to permit the diagnostic detection of 
the location of cracks by noticing changes in the refracturing index 
located between gradings. FIGS. 29a and 29b illustrate a further preferred 
embodiment employing optical fibers as the hollow fiber component of the 
smart matrix materials in accordance with this invention. The elongate 
optical fiber is subdivided into longitudinal segments by dividers or 
septums over brag optical gradings which maintain the optical transmission 
characteristics along the fiber when filled with the chemical modifying 
agents. As depicted in FIG. 29b, in the event of a breakage and leaking of 
the repair chemical into the adjacent matrix, the dividers or septums 
limit the quantity of fluid loss to a local segment only. The change in 
optical characteristics in that local segment will still serve to identify 
the location of the crack, while preventing an overall loss in all of the 
fiber fluid contents. 
Referring to FIGS. 30a-30d, still another optical fiber hollow fiber 
embodiment of this invention is depicted employing fibers of predetermined 
longitudinal length or dimension having a mirror end well at one end 
thereof and having repair chemical disposed therein. Checks on the 
integrity of the optical fiber segment can be made by intermittently 
sending an optical pulse along the short length of the fiber and bouncing 
it off the mirror and comparing the reflected intensity to the transmitted 
intensity to determine whether or not there has been a change along the 
length of the fiber. By placing a mirror intermediate the length of a row 
of fiber, the fiber sensing the optical sensing test could be performed 
from either end and in that manner the location of the break on one side 
of the mirror or the other could be determined. 
Referring now to FIG. 30c, the new and improved smart matrix material is 
shown in a rebonded condition wherein the interior modifying agent, in 
this case an adhesive, has leached into the surrounding matrix to repair 
crack, to bond the matrix to itself, and to bond the coating to the matrix 
and the coating to the fiber. This restores the overall integrity of the 
composite, and in some cases, may lead to actual increases in overall 
strength and performance for the rebond material. 
FIG. 30d illustrates the exterior refilling design in accordance with the 
preferred embodiment for vacuum pump refilling of a broken optical fiber 
to repair or restore optical transmission service therealong. 
In accordance with the present invention, other embodiments for using the 
self-repairing fiber reinforcement smart matrix composite matrix materials 
described herein will be readily apparent to those skilled in this art. 
For example, employing ceramic matrices such as a hydroxyapatite ceramic 
minerals and reinforcing hollow fibers containing bio-compatible crack 
repairing adhesives may be used in joint replacements or as shaped 
articles for prosthetic devices. In this manner, biomedical embodiments 
for the smart matrix composite materials possessing the self-repair 
properties may be used to provide improved or extended fuselage to 
prosthetic devices and bone replacements. Stress load fractures occurring 
within the artificial bone or joint segment will self-repair in accordance 
with the principles of this invention. 
In still another embodiment of the present invention, the overall matrices 
may be used in building applications to provide some seismic resistance or 
earthquake-proof properties to the structures. More particularly, the 
response of a solid matrix material containing rigid-filled fibers or 
liquid-filled fibers may vary in response to seismic waves. Rheological 
fluids and electrorheological fluids are known which are stiff in one 
condition, and thereafter upon application of electrical current, may 
become fluid or liquid. These fillings within reinforcing fibers may be 
intentionally changed periods of seismic activity in response to, for 
example, a sensor switch to liquefy or fluidize building structures to 
better withstand seismic vibration activity without causing brittleness. 
In the liquefied electrorheological state, the overall matrix composite 
may be better able to withstand energy vibration than might be encountered 
in the solid rigid composite structure. 
In still another aspect of the invention, it is known that alkali reactions 
are sometimes caused within cementitious matrix materials when aggregate 
reacts with matrix causes an expansion of the aggregate against the 
matrix. This causes internal stresses to develop within the matrix 
composite or shaped article, which usually appears as cracks within the 
matrix. The use of the smart fibers in accordance with the present 
invention containing adhesives will repair some of these cracks. In 
addition, instead of adhesives these smart fibers may be filled with pH 
modification agents such as acidic agents to neutralize the alkali 
reaction. In addition, fibers filled with the alkali reaction inhibiting 
acidic modifying agent may be used in combination with the matrix repair 
adhesive filled smart fibers in accordance with this invention. 
In accordance with this invention, the matrix selected may vary, for 
example, Ribtec.RTM. mats of stainless steel fibers may be slurry 
infiltrated with cement, hollow fibers for repair may be included. Under 
loading, the mat causes the cement to form microcracks, which in 
accordance with this invention releases the repair adhesives into the 
matrix to provide a repaired high toughness composite material. Depending 
on the matrix selected, different fiber properties may be desired, for 
example, in rigid matrix materials such as cementitious set materials or 
Sintrex ceramic materials more flexible fibers may be desirable, whereas 
in polymer matrices having inherent elasticity or flexibility, more rigid 
fibers such as glass or metal fibers may be desired. In addition, it may 
be desired to use fibers which become brittle over time. Fibers may be 
connected to each other with flexible parts to ensure that they do not 
break prematurely during mixing or compounding. Furthermore, chemicals 
which survive the long periods of time and which survive repeated 
temperature variations may also be used as the modifying agents. Although 
several different matrix materials have been disclosed or suggested 
herein, others may still be used by those skilled in this art. Although a 
number of different kinds of fibers have also been described, still other 
fibers might also be used by those skilled in this art in accordance with 
the principles of this invention. Different modifying agents and different 
mechanisms for selective release of the modifying agent in response to an 
external stimuli or internal stresses caused by other external occurrences 
might also be developed and designed by those skilled in the art given the 
principles provided herein. Accordingly, all such obvious modifications 
may be made herein without departing from the scope and spirit of the 
present invention as defined by the appended claims.