Note: Descriptions are shown in the official language in which they were submitted.
1 1582~2
This is a division of Application Serial No. 287,837,
filed September 30, 1977.
This invention relates to glass fibers coated with an alkali
impervious coating and more particularly to impregnated bundles of
ylass fibers for use in the reinforcementofcement and concrete
wherein the bundles are impregnated with alkali impervious
material.
It has long been known, asdescribed in Slayter U.S. Patent
Nos. 2,703,762 and 2,781,274, to employ glass fibersin the rein-
forcement of cementitious products, including hydrous calcium sili-
cate crystals, cement, concrete, mortar and like matrices having
a high alkali content. Glass fiber reinforcement contributes sig-
nificantly to the overall strength of such cementitious products by
reason of the high strength and flex:Lbility of the glass fibers.
One of the primary difficulties which has been incurred in the
use of glass fibers in the reinforcement of alkali cementitious
products items arises from the fact that such cementitious pro-
duct~ continuously age harden, giving off water of hydration.
This, in turn, results in the formation of calcium hydroxide with-
in the reinforced product which tends to slowly lessen the effec-
tiveness ofglass fibers. The net result is an overall loss of com-
posite strength and ductility accompanying the agingof the glass
fiber reinforced cementitious product. For that reason, ithas not
been advisable toemploy glass fiber-reinforced cementitious pro-
ducts for long terms, that is, five years or more, in load-
bearing applications.
It has been proposed, as described in U.S. Patent No.
3,839,270 as well as in the foregoing Slayter patents, to size
the glass fibers with an impervious, alkali resistant coating
material in an effort to protect the glass fibers from the dele-
terious effects of alkaline calcium hydroxide generated during
the hardening of the cementitious material.
1 ~ 582~2
There are two known methods of coating glass fibers. The
first method, referred to in the art as coating during forming,
involves the application of coating material to glass fibers as
they are being formed. Glass is melted in a glass melting
furnace equipped with a bushing on the bottom side, and the molten
glass flows through the openings in the bushing to form streams
of glass fibers which are rapidly attenuated into fine glass fila-
ments. The filaments are provided with a thin-film coating or
sizing as they are formed just before the glass fiber filaments
are gathered together to form a strand.
Another method of coating glass fibers involves impregnation
of strands, yarns, thxeads or cords, generally referred to in the
art as bundles~ In the impregnation of such bundles, the bundle
is immersed in a bath of impregnating composition and subjected to
a sharp bend while immersed therein to open the bundle and allow
the impregnating material to fully penetrate the bundle and fill
the interstices between the individual glass fiber filaments while
at the same time, forrning a coating around each of the glass
fiber filaments.
In recent years, alkali resistant glass fibers have achieved
wide-spread acceptance. Such alkali resistant glass fibers are
described in U. S. Patents Nos. 3,840,379; 3,861,927; and
3,861,926. It is now generally recognized that glass fibers
formed from glass as described in such patents have significantly
greater alkali resistance than other conventional glass fibers,
such as "E" glass fibers which have been in commercial use for
some time and are described in U. S. Patent No~ 2,334,961.
It has been further proposed, as described in U. S. Patent
No. 3,887,386, to employ in the reinforcement of cementi-tious
products alkali resistant glass fibers, the theory being that the
alkali resistant glass forming such glass fibers will not be
. ~15S2v~
:'
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deleteriously affected by the alkali generated during the
age hardening of the cementitious product in which the glass
.~ fi.bers are distributed as reinforcement. While the use of
alkali resi.stant glass fibers does improve the long term
.~ stability of ylass fiber reinforced cementitious products,
there is still a pronounced tendency for the glass fiber re-
. : inforced product to lose strength during aging.
It is, accordingly, an object of the present inven~
tion to provide an improved glass fiber reinforcing material
suitable for use in cementitious products which retain their
mechanical properties during age hardening.
According to one aspect of the present invention,
: there is provided a reinforcement material for a cementitious
product, the material comprising bundles formed of a plurality
of alkali resistant glass fibers, the bundles including an
alkali impervious impregnant which penetrates the bundles
to fill the interstices between the glass fibers, separating
each from the other.
8 2 v ~
The invention will be more fully understood from the
following description of a preferred embodiment given for
purposes of illustration but not of limitation, together with the
accompanying drawings wherein:
FIGURE 1 is a flow diagram, illustrating a treatment of
bundles of glass fibers to impregnate the bundles with alkali
impervious material;
FIGUR~ 2 is a simplified cross sectional view of a
bundle of glass fibers which has been impregnated in accordance
with the procedure diagrammatically illustrated in FIGURE 1.
FIGURE 3 is a cross sectional view of a bundle of glass
fibers in which the individual glass fiber filaments have a thin
size coating on the surfaces thereof, the bundle having been
subjected to impregnation by the procedure schematically
illustrated in FIGURE 1.
FIGURE 4 is a cross sectional view of a cementitious
; product reinforced with bundl~s of glass fibers~
FIGUR~ S is a cross sectional view of a cementitious
product reinforced with bundles of glass fibers. The individual
glass fiber filaments have a thin size coating on their surface
such as in FIGURE 3.
FIGURE 6 is a graph, illustrating the variation of
total elongation of glass fiber reinforced cementitious products
with aging, and
FIGURE 7 is a graph of the variation of Charpy impact
strength with aging of glass fiber reinforced cementitious
products.
In a broad sense, the present invention resides in a
fiber reinforcement suitable for reinforcement of a cementitious
product and in the reinforced product itself. In another sense,
the invention resides in a reinforcement for cementitious
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'i
articles including a bundle of fibers, such as alkali resistant
glass fibers, thoroughly impregnated with alkali impervious
material, such as wax~ and in the reinforced cementitious product.
Concepts of the present invention reside in the dis-
covery that significant improvements in the mechanical properties
of glass fiber reinforced cementitious products can be achieved
through the use of bundles of alkali resistant glass fiber which
have been thoroughly impregnated with an alkali impervious wax
material whereby the wax material serves to permeate the bundle
of glass fibers and hence saturate bundle interstices. It has
been found that when alkali resistant glass fibers treated in
this manner and then combined with cementitious materials in
the manufacture of glass fiber reinforced cementitious products
in accordance with known procedures, the glass fiber reinforced
cementitious products produced have unexpectedly high mechanical
properties, including elongation and Charpy impact strength.
What is even more surprising with respect to glass fiber
reinforced cementitious products in accordance with this inven-
tion is the fact that those mechanical properties, while
initially higher, remain at unexpectedly high levels even though
the glass fiber reinforced cemPntitious products are subjected
to extensive aginy.
In a broad sense, this invention can use any of the
well known glass fibers or alkali resistant glass fibers
although a preferred form of the invention uses alkali resistant
glass fibers. Alkali resistant glass fibers are now well known
to those skilled in the art and are commercially available. In
general, the glass from which such alkali resistant glass fibers
are formed contains relatively high levels of zirconia, usually
in amounts of the order of 5 ~ 25o~ Most alkali resistant glass
fibers are formulated of glasses having the following major
components:
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~ 1 58252
Parts by Weight
SiO2 55 - 80%
Alkaline earth metal oxide(s) 4 - 20%
(CaO, MgO, BaO, etc.)
Alkali metal oxide(s) 1 - 20%
(Na2O, K2O, etc.)
Zr2 5 - 25%
TiO2 0 - 10%
In addition, such alkali resistant glasses may also contain
small amounts of alumina, chromium oxide, tin oxide and the like.
There are many other well known glass fibers that are
commercially available. The most widely known of these are
"E" glass fibers, which are described in U. S. Patent No. 2,334,961
issued on November 23, 1943. The impregnant must be impervious
to alkali materials so that the impregnant does not break down
when subjected to alkali materials, such as calcium hydroxide,
generated during age hardening of the cementitious products
with which the glass fibers are combined as reinforc~ment. It is
preferred to employ wax coating materials, and preferably waxes
containing functional groups capable of reaction with the free
hydroxyl ~roups contained on the glass fiber surfaces. For this
purpose, it is frequently preferred to employ saponifiable waxes,
oxidized waxes and sulfonated waxes.
In r.lany applications, impregnated glass fiber bundles are
combined with cementitious materials in accordance with known
techniques such as the use of a spray gun in which the glass fiber
bundles are chopped, combined with cement and sprayed onto a
surface to form the glass fiber reinforced cementitious product.
For that purpose, it is generally desired to employ a wax of the
sort described above having a relatively high melting point to
avoid tackiness and to provide some degree o~ brittleness to insure
1 1~82~2
that the chopping equipment completely chops the impregnated glass
fiber bundles prior to ejection from the chopping gun. Polymeric
wax blends have been found to be highly suitable for this purpose;
such polymeric wax blends are microcrystalline waxes blended with
the product formed by copolymeri2ation of an olefin, such as
ethylene or propylene, with vinyl esters, such as vinyl acetate.
~ owever, it is believed a wide variety of alkali impervious
impregnants may be used in the practice of this invention. These
might include polyester resins, phenolic novolak resins such as
those formed by condensation with a phenolic compound such as
phenol with a lower aliphatic aldehyde such as formaldehyde, epoxy
novolak resins, furan resins, polyamides, polyepoxides, rubber
(natural and synthetic latices such as SBR rubber) and like
materials as well as blends of these materials.
Many alkali impervious wax materials are commercially
available. Preferred commercially available microcrystalline
waxes include: Eluax from DuPont; Candelilla wax from Frank B.
Ross Co., Inc.,; and Bakelite Co-Mer resin EVA 301 from Union
Carbide. Waxes pliable at room temperature are normally preferred.
Bundles of the glass fibers, in the practice of this
invention, can be impregnated with the alkali impervious resinous
coating material in accordance with known technique.
In a preferred form of the invention, it is important to
thoroughly impregnate the glass fiber bundle to saturate or to
p~rmeate th~ interstices of the bundle and thereby reduce voids
in the bundle to a minimum. From a practical stand point, the
bundle should be at least 60~ permeated with the alkali impervious
material, and preferably at least 80% permeated.
An impregnation technique is illustrated in FIGURE 1 of the
drawing. As shown in this figure, a bundle 10 which is formed of
a plurality of alkali resistant glass fibers, is passed over a
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roller 12 and is immersed to travel through a bath 14 containing
the alkali resistant material dispersed in aqueous medium or in
the form of a hot melt. As the bundle 10 is passed over the
roller 12 and into the bath 14 of the impregnant material, it is
passed over a pair 16 of rollers i~mersed in the impregnant
whereby the bundle 10 is subjected to a sharp bend to open the
bundle and permit the solids of the impregnating material to
penetrate the glass fiber bundle and fill the interstices between
the individual glass fibers of the bundle.
After passage through the impregnant bath 14, the bundle 10
is moved from the bath and passed over a roller 18 and through
a roller or die 20 which serves to remove excess impregnating
composition from the bundle and to work the solids of the
impregnant composition into the bundle. The impregnated bundle
is then dried, either by air drying or passage through an oven
in accordance with known techniques to remove the aqueous diluent
from the impregnant or cooled in a water bath in the case of
hot-melt treatment.
The resulting bundle is shown in cross section in FIGURE 2
of the drawing. As can be seen from this figure, individual
glass fibers 22 forming the bundle are each coated by the solids
of the impregnant 24. The impregnant 24 thus serves to coat the
individual glass fibers and to fill the space between them to form
a unitary bundle structure. This configuration not only serves
to protect the glass fibers from the effects of alkali generated
during the aging of cementitious produc-ts, but also serves to keep
matrix material from the interior of the bundle. This keeps the
bundle flexible in cementitious products and, therefore, the
unitary bundle structure is kept at a different modulus from the
matrix. This relationship between the unitary bundle structure
and matrix discourages crack propagation.
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Normally/ glass fibers are sized in the fiber forming
operation. As is now well known, size compositions frequently
used in the coating of glass fibers can be formulated to include
an organo silicon compound, usually in the form of an organo
silane or its hydrolysis product, whereby the organo silicon
compound serves to promote a more secure bonding relationship
between the individual glass fiber filaments and the alkali
impervious coating material forming the bundle in which the sized
glass fibers are distributed.
As illustrated in FIGURE 3, the individual glass fibers 22
have a thin film coating 26 on the individual surfaces thereof.
The primary advantage in the use of sized glass fibers stems from
the fact that size compositions impart to the glass fiber
surfaces lubricity, and thereby prevent or substantially minimize
destruction through mutual abrasion of the individual glass fiber
filaments during processing.
The amount of the impregnant material applied to the glass
fiber bundles should be an amount sufficient to protect the glass
fibers from alkaline materials by thoroughly penetrating the
- 20 bundle to fill the interstices between the individual glass fiber
filaments and to form a coating about each of the individual
glass fiber filaments. Various amounts of impregnant can be used
for this purpose; good results are obtained when the amount of a
wax impregnant varies from 10-60% by weight as determined by loss
on ignition, and preferably 20-50% by weight.
The impregnated bundles of glass fibers can be combined
with cementitious materials in accordance with well known
procedures. Various cementitious materials can be used for this
purpose, including cement, Portland cement, concrete, mortar,
gypsum and hydrous calcium silicate.
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Impregnated bundles of glass fibers can be combined
with the cementitious material in a variety of ways, e.gO by
spraying or molding composites of the cementitious materials
and the glass fiber bundles.
If desired, it is believed possible to use other
fibrous materials, in addition to the impregnated bundles of
glass fibers. These include asbestos fibers, mineral wool or
organic fibers or materials (e.g. wood fibers, pulp fibers,
cotton, straw~ bagasse, wood flour, hemp, rayon and the like).
The glass fibers, whether employed as reinforcement in
the form of continuous impregnated bundles or chopped strands
formed from impregnated bundles, are distributed throughout the
cementitious material whereby the cementitious material Eorms
a continuous phase. By way of illustration, a cross section of
a glass fiber bundle reinforced cementitious material 34 is
shown schematically in FIGURE 4~ In this figure, the cemen~
titious material 28 represents the cementitious material forming
the continuous phase whereas the impregnated bundles of glass
fibers distributed throughout the cementitious material are
represented as 30, randomly dispe~sed in the cementitious
material matrix. The individual glass fiber filaments can have a
thin size coating on their surfaces and be formed into bundles
31 such as in FIGURE 5.
The amount of glass fibers employed can be varied within
relatively wide ranges. Usually good reinforcement is obtained
where wax impregnated glass fiber bundles are employed in an
amount sufficient to constitute between l and 40~ by welght of
the cementitious material.
Reference is now made to the following example which is
provided by way of illustration, and not by way of limitation, of
the manufacture of wax impregnated alkali resistant glass fiber
bundles and reinforced cementitious products made therefrom.
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1 15~2~2
EXAMPLE
An alkali resistant glass having the following composition
Ingredient Weight Percent
SiO2 61.1
CaO 5.1
Na2O 14.4
K2O 2.6
Zr2 10.4
Tio2 6.0
23 0.3
Fe23 0.2
is formed into glass fibers using conventional techniques. The
glass fibers, in the form of a bundle of closely grouped glass
fibers, are then subjected to impregnation with a hot-melt
impregnating composition at a temperature of 130-140C.
formulated as follows:
Microcrystalline wax 80%
(Paxwax 6413 from
National Wax Co., Skokie, Ill.)
Ethylene-vinyl acetate 20%
copolymer (EVA 301)
Impregnation is carried out in accordance as illustrated in
FIGU~E 1 of the drawing, after which the impregnated bundles of
glas~ fibers are quenched in a water bath to set the impregnant.
Using conventional techniques, chopped bundles of the
impregnated alkali resistant glass fibers are then combined with
cement to form a glass fiber bundle reinforced cementitious
product.
The cementitious product is then tested to determine its
mechanical properties, including percent elongation and Charpy
impact strength.
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For purposes of comparison, alkali resistant glass fibers
prepared from the composition described above are sized in forming
with a size composition containing polyvinyl acetate, and then
combined with cement using the same procedures as described above.
The cementitious products thus formed are also subjected to testing.
For further comparison, glass fibers formed from "E" glass
are subjected to impregnation in the sar.~e way and combined with
cement, and untreated "~" fibers are also combined with cement.
In each of the comparative tests, the same techniques for
combining the glass fiber bundles with the cement was used, and
with the same proportions.
The results of these tests are shown in FIGURES 6 and 7 of
the drawing. These figures plot total elongation versus weeks
of immersion in water maintained at 50C. and Charpy impact verus
~eeks of immersion in water maintained at 50C., the water
providing an artificial aging condition.
Referring initially to FIGURE 6 of the drawing, lt will be
seen that the glass fiber reinforced cementitious product prepared
from glass fibers as described above (identified as AR glass
bundle - wax impregnant) maintains a substantially constant
elongation after aging for 8 weeks in hot water; whereas the "E"
glass fiber bundles ("E" glass bundle - wax impregnan-t) otherwise
processed in the same manner, have a significantly lower
elongation. All glass strand diameters shown in the drawings
corresponded to 7500 yds./lb.
The bundle of alkali resistant glass fibers containing only
a thin size coating (identified as alkali resistant glass bundle-
sized) shows a drastic loss in elongation after accelerated
aging for several weeks in hot water. It has been determined
experimentally that the size coating on the glass fibers is
removed within about two weeks of the time that the cementitious
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product is immersed in the water, and thus that test approximately
corresponds to the use of untreated alkali resistant glass fibers
in the reinforcement of cement. The "E" glass bundle, untreated
in any fashion, also shows a drastic decrease in elongation.
Even more dramatic improvements can be seen by reference
to FIGURE 7, a plot of Charpy impact strength versus time of
immersion in 50C. waterO There it is shown that the reinforced
product formed from the alkali resistant glass fiber bundle
~reated with an alkali impervious material has a significantly
higher Charpy impact strength which is maintained over 8 weeks of
artificial aging. In contrast, the "E" glass treated in the same
manner provides a cementitious product in which the Charpy impact
strength decreases much more rapidly, from a lower initial value.
Even lower Charpy impact strengths are obtained for cementitious
products reinforced with alkali resistant glass fiber bundles
which have simply been sized or with cementitious products
reinforced with untreated "E" glass fiber bundles.
While an embodiment of the invention has been described with
reference to the use of a blend of a microcrystalline wax and
an ethylene-vinyl acetate copolymer, it will be understood that
various other alkali resistant materials can likewise be used as
the impregnating material to provide equivalent results.
It will be understood that various changes and modifications
can be made in the details of procedure, formulation and use
without departing from the spirit of the invention, especially
as defined in the following claims.
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