Glass fibers resistant to basic media and their application to reinforcing of cement

The invention relates to glass fiber compositions and fibers having use as a reinforcement element of cement-base products. As such, the composition is able to resist attack of strongly basic media. The fibers of the invention comprise the following constituents, in proportions by weight: PA1 SiO.sub.2 --56 to 68%, PA1 ZrO.sub.2 --14 to 17%, PA1 Na.sub.2 O--12 to 20%, PA1 K.sub.2 O--0 to 8%, PA1 Al.sub.2 O.sub.3 --1 to 9%, and wherein the sum of Na.sub.2 O and K.sub.2 O is between 14 and 22%, and wherein the sum of SiO.sub.2 and Al.sub.2 O.sub.3 is less than 70%.

DESCRIPTION 
1. Technical Field 
This invention relates to glass fiber compositions. The compositions of the 
invention are able to resist the attack of strongly basic media and, as 
such, may find use as a reinforcement element of cement-base products. 
2. Background of the Invention 
Glass fibers comprise the material of choice in use in the improvement of 
mechanical properties of numerous composite products. This is because the 
glass fibers, when compared with other organic or inorganic fibers have 
particularly high characteristics of ultimate tensile strength and modulus 
of elasticity. The glass fibers that have been compared are those that are 
mechanically drawn from molten glass flowing through the orifices of a 
spinneret heated by Joule effect. 
The glass fibers, in addition to exhibiting the aforementioned mechanical 
properties, should also exhibit an excellent chemical resistance when used 
in the reinforcement of a cement-base product. It is, however, possible to 
minimize attack and corrosion of the glass fiber in the presence of a 
saturated Ca(OH).sub.2 solution impregnating the cement matrix by 
increasing the resistance of the same. 
According to the prior art, the resistance of glass fibers may be increased 
greatly by using glass compositions having a high content of zirconia 
(ZrO.sub.2). The use of zirconia in glass compositions is disclosed in 
British Pat. No. 1,243,972 and U.S. Pat. No. 3,861,926. 
While the use of zirconia in glass compositions has been found to increase 
resistance in regard to basic media, it has also been found that zirconia 
in glass composition gives rise to certain drawbacks. To this end, the 
presence of the oxide in glass fibers increases viscosity of the glass 
fibers and considerably raises the upper devitrification temperature 
(UDT). The temperature (T.sub.F) for drawing the glass fibers also 
increases as the glass fibers become more viscous. The change in the 
temperature for drawing glass fibers under circumstances that the 
viscosity of the glass fibers increases may not, however, be as sudden as 
the change in the upper devitrification temperature. Further, when the 
zirconia content increases, the difference between these temperatures may 
become increasingly small and the upper devitrification temperature can 
even become greater than the drawing temperature. With the latter 
condition, the risks of devitrification may be too great to consider 
production of glass fibers in an industrial installation. 
These risks may be reduced by adding one or more additional oxides to the 
base composition. The essential role of the additional oxides is to lower 
the upper devitrification temperature, and even to change the nature of 
the crystalline species that appears at the highest temperature. 
Experience has shown that industrial scale production of continuous glass 
fibers can be considered only if certain conditions are met by the glasses 
providing a source for the glass fibers. In particular, one condition to 
be met concerns the temperature difference between the temperature 
corresponding approximately to viscosity .eta., such as log .eta.=2.5 and 
the upper devitrification temperature which should be at least equal to 
80.degree. C., and preferably at least equal to 100.degree. C. Moreover, 
it is desirable that the drawing temperature corresponding approximately 
to viscosity .eta., such as log .eta.=2.8, be less than 1480.degree. C., 
and preferably less than or equal to 1400.degree. C. By adherence to this 
condition a rapid wear of the platinum alloy spinnerets, generally used to 
obtain continuous fibers, may be avoided.

SUMMARY AND BEST MODE FOR CARRYING OUT THE INVENTION 
An important aspect of the invention concerns the mechanical drawing of 
glass fibers that meet the conditions previously set out, at a cost that 
is as low as possible. 
Another aspect of the invention concerns the glass fiber composition which 
comprises a small number of constituents including zirconia and the glass 
fibers which exhibit an excellent resistance to basic media. The 
constituents, with the exception of zirconia are relatively inexpensive 
thereby to keep costs down, and the zirconia which is more expensive is 
introduced only in a moderate amount. 
According to the invention the composition comprises the oxides set out 
below, in the indicated proportions by weight of 
SiO.sub.2 --56 to 68%, 
ZrO.sub.2 --14 to 17%, 
Na.sub.2 O--12 to 20%, 
K.sub.2 O--0 to 8%, 
Al.sub.2 O.sub.3 --1 to 9%, 
and wherein the sum of Na.sub.2 O+K.sub.2 O is between 14 and 22%, and the 
sum of SiO.sub.2 +Al.sub.2 O.sub.3 is less than 70%. 
An excessive increase in the viscosity of the glass may be avoided by 
maintaining the summations of constituents within the limits set out. If, 
under the circumstances of the composition, both the SiO.sub.2 and 
Al.sub.2 O.sub.3 are to play a traditional role of forming the vitreous 
network, it should be observed that the Al.sub.2 O.sub.3 should be 
introduced in only a moderate amount. To this end and within the context 
of the invention, the oxide of aluminum may increase the risks of 
devitrification. The oxide of aluminum is advantageously introduced by a 
complex vitrifiable raw material which contributes other oxides, such as 
SiO.sub.2, Na.sub.2 O, K.sub.2 O. The use of such a raw material, which by 
itself forms a combination of oxides, exhibits the advantage of 
facilitating the melting of the vitrifiable material. The advantage may be 
considerable in the case of glasses that are viscous by nature. In 
addition, the raw material is not expensive. 
It has been found that fiber glasses belonging to the field heretofore 
defined may be produced on an industrial scale under circumstances that 
the silica content is between 58 and 66%, the alumina content is between 1 
and 7.5%, and the sum of the two contents is no greater, and preferably 
less than 68%. This make up of the composition has been found to exhibit a 
temperature difference between the temperature corresponding to log 
.eta.=2.5 and the upper devitrification temperature greater than 
100.degree. C. 
The chemical resistance of glass fibers buried in a cement-base matrix 
generally may be improved by the joint action of ZrO.sub.2 and one or more 
additional oxides. A widely used combination of oxides, and a combination 
considered to be economical, includes ZrO.sub.2 and one or more 
alkaline-earth oxides. These latter oxides, however, may be the genesis of 
increased risk of devitrification. 
According to the invention glass fibers exhibiting an excellent resistance 
to basic media may be drawn from a composition despite the fact that the 
composition contains only a single oxide, namely zirconia active with 
regard to the increase of resistance. This is the case even though the 
oxide is introduced in a moderate amount. However, by keeping the zirconia 
within the limits set out, the invention advantageously avoids excessively 
increasing the viscosity of the glasses and the risks of devitrification. 
These advantages of the invention render it possible to use only Na.sub.2 O 
and K.sub.2 O in the adjustment of the viscosity of the glass so that the 
drawing temperature for the glass fibers will remain less than or no more 
than equal to 1480.degree. C. As such, there will be a sufficient 
temperature difference between the drawing temperature and the upper 
devitrification temperature. 
While it has been found that the established aims may be met by the use of 
Na.sub.2 O, only, it is nevertheless considered advantageous to introduce 
K.sub.2 O into the glasses of the invention. The oxide will be introduced 
in a rather slight amount and it has been found that the introduction of 
K.sub.2 O is especially advantageous under conditions that the sum of the 
alkaline oxides exceeds 19%. Introduction of K.sub.2 O into the 
composition has certain advantages, particularly that of using complex 
vitrifiable raw materials containing, in particular, Na.sub.2 O and 
K.sub.2 O. 
The glasses of the invention exhibit excellent characteristics particularly 
when the percentage by weight of Na.sub.2 O is maintained between 13 and 
19%, and when the percentage by weight of K.sub.2 O does not exceed 6%. It 
is particularly desirable to maintain the sum of Na.sub.2 O and K.sub.2 O 
between 15 and 20%. 
A most advantageous composition within this field may comprise the oxides 
set out below, in the indicated proportions by weight of 
SiO.sub.2 --58 to 66%, 
ZrO.sub.2 --15 to 16%, 
Na.sub.2 O--13 to 19%, 
K.sub.2 O--1 to 6%, 
Al.sub.2 O.sub.3 --1 to 7%. 
The characteristics of the composition of glasses of the invention may be 
appreciated by reference to the table, below, including the several 
examples. These experimental results make evident an advantageous use of 
the glass fibers of the invention in the reinforcement of cement-base 
products. 
TABLE 
__________________________________________________________________________ 
n.degree.1 
n.degree.2 
n.degree.3 
n.degree.4 
n.degree.5 
n.degree.6 
n.degree.7 
n.degree.8 
__________________________________________________________________________ 
SiO.sub.2 
58,5% 
61,0% 
61,8% 
61,8% 
65,0% 
63,0% 
67,0% 
59,0% 
ZrO.sub.2 
15,0% 
15,0% 
14,6% 
14,6% 
14,0% 
17,0% 
16,0% 
16,0% 
Na.sub.2 O 
16,5% 
16,9% 
16,6% 
13,3% 
12,0% 
19,0% 
14,0% 
16,0% 
K.sub.2 O 
2,8% 
2,1% 
-- 3,1% 
8,0% 
-- 1,0% 
6,0% 
Al.sub.2 O.sub.3 
7,2% 
5,0% 
7,3% 
7,2% 
1,0% 
1,0% 
2,0% 
3,0% 
t.degree.(.degree.C.) 
pour 
log .eta. 
= 3 1343 
1324 1399 
1421 
1435 1327 
1411 1311 
= 2,8 1378 
1360 1438 
1460 
1475 1360 
1450 1345 
= 2,5 1434 
1421 1504 
1522 
1521 1417 
1512 1403 
UTD(.degree.C.) 
1330 
-- 1260 
1400 
-- 1250 
-- 1340 
.DELTA.(.degree.C.) 
104.degree. C. 
&gt;100.degree. C. 
244.degree. C. 
122.degree. C. 
&gt;100.degree. C. 
157.degree. C. 
&gt;100.degree. C. 
63.degree. C. 
__________________________________________________________________________ 
UDT = Upper devitrification temperature 
.DELTA. = temperature (log .eta. = 2.5 UDT 
The aptitude of glass fibers drawn from a composition may be evaluated by 
measuring the development of the ultimate tensile strength of the glass 
fibers within the medium that is reinforced. In the environment of a 
cement, the ultimate tensile strength of the glass fibers may be evaluated 
after a more or less long stay in a suspension of Portland cement in 
water. The ratio of the amounts of water and Portland cement is chosen so 
that the pH of the suspension is equal to 12.6. Testing of the glass 
fibers, immersed in the suspension maintained at a temperature of 
80.degree. was carried out during aging times spread between 1 and 17 
days. The graph (FIG. 1) shows a development of ultimate tensile strength 
of glass fibers having a composition which corresponds to the composition 
of the Table, see column 1 (No. 1). The graph also shows, for purposes of 
illustration, a development of ultimate tensile strength of glass fibers 
of a known glass. The data relating to the known glass and the glass (No. 
1) was obtained under the same conditions, and was subjected to 
substantially the same agings. The known glass, having a demonstrated 
aptitude in the reinforcement of cement, is described in French Pat. No. 
2,053,211 and marketed under the trademark "CEMFIL." 
The aging of the two glasses was practically identical. Further, as 
illustrated by the graph, the ultimate tensile strengths of glass (No. 1) 
and the known glass may substantially be represented by a single curve. To 
the extent that the method used reveals the behavior of the glass as a 
reinforcement in cement, the aptitude of the glass fiber corresponding to 
glass (composition No. 1) is certainly comparable to that of the "CEMFIL" 
fiber. 
According to the invention, glass fibers having the above composition may 
be used either alone or in association with other organic or inorganic 
fibers, such as cellulose fibers or asbestos fibers, and may be used to 
reinforce cement-base products. The glass fibers, according to the 
invention, may be incorporated in the form of continuous yarns or cut 
yarns, such as, for example, rovings, ribbons, mats, fabrics, and so 
forth, in the cement matrix. In this application, the term "cement" should 
be understood to designate ordinary hydraulic cements, such as Portland 
cement. The term "cement-base product" should be understood to designate 
all products formed from mixture of cement and aggregates or other 
materials, such as sands, mica, ultrafine silica, ashes, and so forth.