FR2571360A1 - IMPROVEMENT OF COATINGS OF FIBERS OF GLASS OR RELATING TO THESE COATINGS - Google Patents

Abstract

A.PROCEDE FOR COATING GLASS FIBERS WITH AN ALKALINE RESISTANT COMPOSITE LAYER. B.PROCEDE CHARACTERIZED IN THAT IT INCLUDES STEPS OF: -APPLICATION ON FIBERS OF GLASS OF AN AQUEOUS POLYVINYL ALCOHOL SOLUTION; - DRYING OF THIS LAYER OF POLYVINYL ALCOHOL; AND HEAT TREATMENT OF THE DRIED LAYER AT A SUFFICIENT TEMPERATURE SO THAT THE POLYVINYL ALCOHOL CRYSTALLIZE SUITABLY WITH DEHYDRATION AND THERMAL DECOMPOSITION, THE POLYVINYL ALCOHOL CRYSTALLIZED, DEHYDRATE AND THERMALLY THERMALLY-DECOMISTICALLY-DECOMPOSED.

Description

Improvement of glass fiber coatings or related thereto

  The invention relates to glass fiber coatings and in particular to a process for coating glass fibers with a layer which protects them against an environment.

  alkaline, such as a matrix of Portland cement.

  Since glass fibers have excellent tensile strength and excellent modulus of elasticity, they have been used as reinforcing material in

resins of plastics material.

  Glass fibers or glass compositions in general such as a glass widely known as E-glass are rapidly fixed and weakened in an alkaline environment and subsequently in cement, when used as reinforcing materials in a matrix of Portland cement that is alkaline mainly in

  because of the presence of quicklime.

  In order to allow the use of glass fibers as reinforcing material in a cement matrix,

  it has been proposed in the prior art various composi-

  glass compositions comprising ZrO 2. Although the composition glass fibers comprising ZrO are resistant to alkaline attack when compared with E-glass, they do not

  not satisfactory for alkaline resistance.

  Another way to protect the glass fibers against deterioration by an alkaline environment is to provide a protective coating on the surface of the glass fibers. For example, British Patent No. 1,565,823 describes the application of an aqueous solution to glass fibers to form a protective coating therein. The aqueous solution consists essentially of (a) at least one water-soluble film-forming material having free hydroxyl groups, (b) at least one water-soluble ester

  formed by reaction of an aromatic carboxylic acid,

  hydroxy or di-hydroxy substituted with an alcohol having

  minus two hydroxyl groups, and (c) a crosslinking agent

  able to cross-link the hydroxyl groups of the film-forming material to make it thermosetting and if possible

  crosslinking agent for the ester of the film forming material. Toute-

  Once, the formation of the solution is complicated.

  In the production of glass fibers, when glass filaments are stretched from a mass of molten glass through a die, a solution is applied to them.

  continuous glass filaments so as to combine them into a

  CWater. Although water is sometimes used as a primer, it is also common to use an aqueous solution of polyvinyl alcohol. Although the alkali resistance of polyvinyl is good, it is water soluble and has low water resistance. As a result, glass fibers coated with polyvinyl alcohol as a primer can not be used as reinforcing material in a concrete matrix because

  that polyvinyl alcohol dissolves in water and

  adversely affects the hardening of the cement and that the

  cool polyvinyl gets wet with alkaline water from cement

  so that it attacks the glass fibers.

  When polyvinyl alcohol is used as a primer, after the aqueous solution of polyvinyl alcohol is applied to the glass fibers, it is necessary to dry it. In the prior art, drying was avoided

  at high temperatures because polyvinyl alcohol is

dials with heat.

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  According to the different tests of the applicants,

  we found with surprise that we get an excellent coat-

  glass fibers against deterioration in the cement matrix by heat treating at a high temperature, a polyvinyl alcohol which was common as

  primer for glass filaments.

  That is, if a layer of polyvinyl alcohol

  The coating is heated to a temperature of 1500 ° C or more, the coating layer is converted into a water-insoluble coating and the coated glass fibers are suitably coated.

  protected against deterioration in the cement matrix.

  If heated to 150 C or more, polyalcohol

  vinyl is sufficiently crystallized and affected by

  thermal decomposition. It can be considered that the decomposi-

  thermal reaction can be expressed by the chemical

(I), (II)

  (CH 2 -CH) n CH 2 -CH - (CH = CH) -CH 2 -CH- + nH O 0) 2) n 2 n 2

OH H OH

(CH = CH) n-CH2-CH-CH2-CH-

n 2 2

OH OH

  p (CH = CH) CH-CH + CH-CH- (n 2 3

0 OH

  That is, the heat treatment causes dehydration as represented by formula (I) and an additional chemical decomposition as shown

formula (II).

  When the polyvinyl alcohol is subjected to such thermal decomposition, the tensile strength of the polyvinyl alcohol is reduced. Accordingly, it was avoided that polyvinyl alcohol be decomposed by heat in the prior art. However, reducing the tensile strength of polyvinyl alcohol is not essential for the coating of glass fibers because

  fiberglass, by itself, has a resistance to trac-

  sufficient. The change in properties of alcohol

  lyvinyl which becomes insoluble in water is more important for the protection of glass fibers against deterioration

in the cement matrix.

  The invention is based on new knowledge

acquired by the applicants.

  According to the invention, a method is

  for the coating of glass fibers with a layer of

  alkali-resistant site which comprises the steps of: - application on the glass fibers of an aqueous solution of a polyvinyl alcohol, drying of the applied polyvinyl alcohol layer, and - thermal treatment of the dried layer at a temperature

  sufficient for the polyvinyl alcohol to crystallize sufficiently

  with dehydration and thermal decomposition,

  this crystallized polyvinyl alcohol, dehydrated and

  decomposed making the layer of resistant compounds

alkaline.

  The aqueous polyvinyl alcohol solution can be applied to the glass fibers at different times of their production and drying and heat treatment

are then carried out.

  The heat treatment is carried out at a temperature of 150 to 500 ° C., or better still at 170 to 450 ° C., in order to

  cause dehydration and thermal decomposition.

  Glass fibers are adversely affected by a

  heat treatment at a temperature above 500 C.

  A saponification rate and a

  polymerization rate of the vinyl alcohol which will be

  90 per cent or more and from 300 to 2,600 respectively.

  is lying. It is also possible to use a polyvinyl alcohol

  modified water-soluble agent such as a polyvinyl alcohol derivative

  nyl, a saponified copolymer of vinyl acetate or a derivative of the saponified copolymer. For example, polyvinyl formai and polyvinyl butyral are examples of polyvinyl alcohol derivatives, polyvinyl ethylene alcohol and silanol-modified polyvinyl alcohol are examples of saponified copolymers of vynyl acetate, and ethylene polyvinyl form is an example of-derived

  of saponified copolymer of vinyl acetate.

  In order to compensate for the weakening or reduc-

  In view of the tensile strength of the polyvinyl alcohol caused by the heat treatment, the aqueous solution may additionally contain a coupling agent to assist the bonding of the layer of alkali-resistant compounds to the surface of the glass. lubricant to reduce friction between coated surfaces of adjacent filaments, and a

  softening agent to soften the coated layer, a plasticizer

  to increase the plasticity property of the coated layer and / or a polymer to prevent the coating of

  the surface is damaged by abrasion during handling.

  subsequent pumping such as winding.

  The concentration of polyvinyl alcohol in

  the aqueous solution will preferably be from 1 to 20% by weight.

  The glass fibers subjected to the treatment of the invention may be of glass composition such as E-glass but are preferably alkaline-resistant glass compositions containing ZrO 2 at 5% by weight.

  weight or more to be used as reinforcing material

in the cement matrix.

  Specific examples of the invention are described below:

EXAMPLE 1

  Glass filaments all 13.5μ in diameter are drawn from each of three masses of molten glass having different glass compositions as shown in Table 1 through a multi-orifice die. 200 filaments are combined into a bundle and wound on a spool to give a cake. Two test pieces are prepared

of each of the melted glasses.

  On one of them, a conventional polyvinyl acetate primer is applied to the continuously drawn filaments and cut to give a test tube, a dried bundle (without heat treatment) of a length of 5 cm. The deposit

  Primer on the beam is about 2% by weight.

TABLE 1

  1 2 3 4 5 t 6 SiO 2 (% by weight) 55 68 60

A1203 (% by weight) 14 - -

2 3 a> 1

> B203 (% by weight) 8 -

c RO * 1 (% by weight) 23 12 -

o R20 * 2 (wt%) 15 20

0 2

  o E ZrO2 (wt%) 5 20 Proportion of primer, Proportion of primer.2.0 3.1 2.1 3.3 1.8 3.2 on beam (% by weight) Heat treatment without with without without with without Resistance to O 133 120 130 119 The tensile strength of the beams after residence was observed in the cement matrix at 800 ° C (kgf / mm). 1: RO = alkaline earth metal oxide

* 2: R20 = alkali metal oxide.

  To obtain the other test pieces according to the invention, an aqueous solution was prepared which contained% by weight of polyvinyl alcohol and 0.5% by weight of agent.

  silane coupling. The polyvinyl alcohol that was used

  It has a saponification rate of 98.5 mol% and is commercially available as * NL-05 in THE NIPPON SYNTHETIC CHEMICAL INDUSTRY CO., LTD, while A-1100100 is produced and sold by UNION CARBIDE ( Corporation US) was used as silane coupling agent. The aqueous solution was heated to 70 ° C. and applied to the drawn filaments

continuously.

  A beam of 1 m length was cut from an undried cake and dried. The ratio of primer to beam was about 3% by weight. Then the beam was heat-treated at 200 ° C for 5 minutes and

  took a specimen with a length of 5 cm.

  As was shown in Table 1,

specimens Nos. 1 to 6.

  The central section about 1 cm from each

  test tube was inserted into a Portland cement paste

  dinary and maintained in the water vapor at about 80 C and 100% relative humidity for several days. The tensile strength of the specimen was measured after remaining in the cement paste each day. Numbers

  are given in Table 1.

  If we compare test tubes n 1, 3 and 5

  with specimens 2, 4 and 6 according to the invention,

  It will be appreciated that alkali resistance

  the beam is improved considerably according to the invention.

tion.

EXAMPLE 2

  filaments each having a 13.5 bridge dimmer were drawn from a multi-orifice die of a molten glass mass whose composition was SiO 2 60% by weight, R 20 20% by weight and ZrO 2 20% by weight , and were combined into a bundle which was wound on a bobbin to give a cake. Water was applied to the continuously drawn filament in place of the primer as

  polyvinyl acetate, polyvinyl alcohol or others.

  Twelve pieces of bundle, each about 1 m long, were cut on the cake. These beam pieces were immersed in an aqueous solution as

as shown in Table 2.

TABLE 2

  Polyvinyl alcohol saponified at a rate of 90 mol% (N-300 of NIPPON SYNTHETIC 3% by weight

CHEMICAL INDUSTRY CO., LTD)

Silane coupling agent (A-100

CARBIDE UNION) 0.15

  Cationic surfactant (SO x softener from ONYX CO. (US Corporation) 0, 10 Water- 96.75 The beam pieces were taken from the

  aqueous solution and dried. Then these pieces were

  rounded into rings about 10 cm in diameter and have been

  heat treated in an electric oven at temperatures below

  between 130 and 6000C for different durations

  from 1/20 to 600 nm as shown in chart 3 for

vets 7 to 18 respectively.

  The ratio of the amount of primer for each

  test piece is also indicated in the talbeau 3.

  The water resistance such as the solution in the water and the degree of swelling in the water of each test piece were measured and are also indicated in FIG.

table 3.

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  The tensile strength of each specimen was measured, after being held in the cement paste for several days as in Example 1. The results

are given in Table 3.

TABLE 3

  Test tube no. 7 8 9 10 11 12 13 14 15 16 17 18.

  Temperature (C) 130 150 170 190 210 230 270 310 350 450 500 600 Heating time (min) 600 600 600 30 5 1 1/4 1/6 1/12 1/20 1/20 1/20 Proportion of primer on 4.4 4.3 3.8 4.0 4.8 2.9 3.5 3.0 3.8 3.3 3.4 3.0 the beam (% by weight) Rate of | Rate of 0.17 0.01 0 0 0 0 0 0 0 0 0 0 Resistance Water solutionGreatness degree 1.35 0.65 0.53 0.51 0.45 0.41 0.42 0, 39 0.40 0.34 0.32 0.29 _ _ _ 0 Resistance to 0 123 125 115 110 112 103 95 91 86 84 75 60 Traction of the beam after f aisceau after 3 80 92 97 98 100 99 90 89 85 82 74 56 cement matrix at 80C 6 49 75 91 93 96 95 88 85 83> 80 72 57 cement at 80 C, (Kgf / mm2) o

  9 41 71 86 90 91 92 88 86 83 81 71 55

_

  12 37 71 84 88 92 91 87 83 81 80 72 54

o 'CD

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  The results show that specimens 8 to 17, treated at temperatures of 150 to 500 ° C, have excellent alkali resistance when compared with another specimen No. 7 treated at a temperature below 150 ° C. another specimen No. 18 which has been treated at

  temperature of 600 C higher than 500 C, has a good resistance

  but does not have a high tensile strength if held in the cement paste. This is understandable because fiberglass itself is weakened by heat treatment at a temperature as high as

600 C.

  Table 3 also teaches us that resistance

  water is excellent if the heat treatment

  is at 150 C or more, preferably 170 C or more.

  Regarding the color of the specimens, specimen No. 7 is white but nos. 8 to 18 are yellow

or brown.

  Then, using infrared spectrometry or a spectrophotometer, we analyzed different

  spectra of all specimens 7 to 18 and one specimen

  beam before heat treatment. This analysis

  lysis shows us that a carbonyl group and a methyl group were formed in the coating of each of the specimens 9 to 18. This means that the thermal decomposition which has the chemical formula (II) was caused by a treatment.

with heat of 170 C or more.

EXAMPLE 3

  On the cake of Example 2, 6 pieces of length of approximately 1 m of beam were taken. These specimens were put in an aqueous solution containing different polyvinyl alcohols by their degree of saponification and / or polymerization as shown in Table 4 and were then heat treated at 200 ° C. for 5 minutes to give

specimens 19 to 24.

  Each aqueous solution contains a surfactant

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  Cationic active (Cation Softener x Con) at the rate of 1/20 in

weight of polyvinyl alcohol.

TABLE 4

  Test tube 19 20 21 22 23 24 Saponification (mol%) 90 95 97 98 99 99 m Polymerase ratio 1700 500 2600 1800 300 1100 polymerisation: Concentration> (wt%) 4 5 4 4 5 4 oo Ratio (%) o O Ratio (% _ 5.7 5.9 5.0 5.3 6.4 6.4 6.7 -.4

= 0 110 119 118 113 116 115

  Tensile strength 0 - 1 0 9

3 90 101 105 103 97 98

  of the fascine after residence in the matrix in X 6 83 93 93 96 94 93 cement to 800C i 9 78 84 88 92 90 91

2 9

(Kgf / mm2)

12 76 80 84 91 87 92

-

  All specimens were subjected to tensile strength tests in the same manner as

  example 1.The results are shown in Table 4.

  Specimens 19 to 24 show excellent

  slow resistance to alkaline products.

  s ITABLE N 5 Test specimen No. 25 26 27 28 29 30 31 32 33 34 35 36 Poly alcohol Alecolpoly-saponifi- pymic degree Degree of vinyl cation cation modification modified (mol%) (m.ol% Polyvinyl Formal Content 97 500 Formal 2 l Polyvinyl 96 300 70 mol% 3 Butyral 96 300 Btr, 70 mol% Butyral ________________________ Butyral

M Ethylene Copoly-

  o Polyvinyl merification 3 ethylene alcohol 5 mol%

Ethylene Copoly-

97,500

  Polyvinyl 97 500 merification 3 Ethylenic alcohol 30 mol% Polyol alcohol Percent l vinolic 98 500 0.5 mol% vinyl Si.lanol 3 modified by O silanol _

Ethylene Copoly-

  Polyvinyl 98 500 ethylation merit

  Formaldehyde 20 Mol% 3 Degree of formaldehyde 20 mol% Water 97 97 97

Water + isopropyl

  pyl alcohol Dioxane 97 97% primer on the beam (by weight) 3,3 3,4 4, 0 3,7 2.9 3.1 2.8 2.5 3. (3.33.5 3.2 Respectancre ad ltracioemnt dtemque (C) ______ _______ _ _ Heat Treatment Temperature (OC) 130 200 130 200 130 200 130 200 130200 130 200 Tensile Strength of the Resistance at the tracing u 0 130 101 125 102 127 108 122 105 132 113 131 110 beam after stay in the cement matrix 3 75 95 67 81 78 99 72 84 71105 68 82 a

0 0

  800C (Kgf / mm2) D C (Kgf / mm) c6 43 86 39 73 51 94 48 75 47 94 36 71

  9 36 84 33 68 42 90 35 72 4092 29 64 -

  12 32 83 27 64 38 89 30 69 3590 25 61

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EXAMPLE 4

  Twelve pieces of about one-half length were cut on the cake of Example 2. These specimens were immersed in aqueous solutions containing various modified polyvinyl alcohols as shown in Table 5. Next, the specimens were dried and then dried. heat treated at different temperatures as shown in Table 5 for specimens No. 25 to 36. These specimens were subjected to a tensile strength test in the same manner as in Example 1. The result of the measurements

is shown in Table 5.

  The results teach us that it is possible to use a modified polyvinyl alcohol such as a polyvinyl alcohol derivative, a saponified copolymer of polyvinyl acetate, or a derivative of a saponified copolymer in place of polyvinyl alcohol so that alkali resistance

  glass fiber is significantly improved.

EXAMPLE 5

  From the cake of Example 2, 10 pieces of beam of about 1 m were cut and immersed in

  different aqueous solutions containing polyvinyl alcohol

  and other additives as shown in Table 6.

  Then, these specimens were dried and then heat-treated at 200 ° C. for 5 minutes to give specimens No. 37

at 46.

TABLE 6 '

  Specimen n 37 38 39 40 41 42 43 44 45 46 Polyvinyl alcohol 3.0 3.0 3.0 3.0 3.0 3.0 3.0 3.0 3.0 3.0 Silane 0.03 0.2 Cationic softener X Con 0.003 Dibutyl phthalate 0.15 Glycerine 0.15 Acrylic ester emulsion 0.3 3.0 3.5 SBR Latex 0.3 3.0 % of primer on the process 3.9 3.6 4. 3 4.0 3.7 3.5 5.3 5.5 4.2 5.9 weight (% by weight) Beam flexibility * _ O c)

  0 O 82 101 103 119 118 124 135 131 130 139

Tensile strength -

  after-residence beam 3 81 97 100 106 108 101 95 90 108 91 in the matrix of cement (Kgf / mm2) 9 79 93 98 90 94 88 75 62 93 68

12 80 93 97 88 91 86 73 60 89 65

  LM ul * tL bad 0 good, excellent o

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  In Table 6, silane is the co-agent of

  cationic softener x Con being the lubricating agent

  and softening agent, di-butyl phthalate and glycerine are the plasticizers, an emulsion of acrylic ester and styrene-butadiene rubber (SBR) in the form of latex being the polymers to prevent the coating surface from being abraded during subsequent manipulations such

than the winding.

  The tensile strength test, similar to that of Example 1, was carried out on each test specimen

  37 to 46. The results are shown in Table 6.

  According to the results, all the test pieces show a

  excellent resistance to alkalis. The flexibility of the

  ceaux was observed by sight and by hand. The results

  observed are also shown in Table 6.

  The flexibility of the bows is improved by the presence of the additives described above. However, the total amount of additives is advantageously from 0.001 to 1 part by weight per part of polyvinyl alcohol if

  consider the effect on alkali resistance. Test-cases

  Nos. 44 and 46 have a slightly degraded alkali resistance.

EXAMPLE 6

  From 16 undried cakes from the test

  No. 6, in Example 1, continuous beams were taken

  at a speed of 10 m / min and wound them on a reel after passing them through a 2.50 m long drying oven and heated to 130 C. The roll was introduced into an electric oven and heated at 190 C for 2 hours. Then the roller was combined in concrete

  by the spraying technique to form a reinforcing concrete

  fiberglass (GRC). The length of the chopped fibers was adjusted to 25 mm and the proportion of mixed fibers was adjusted to 5% by weight. The mortar used was composed, in weight ratio, of 1 Portland cement, 0.6 of No. 5 silica sand, 0.06 cement expansion agents (DENKA CSA No. 20 manufactured by DENKI KAGAKU KOGYO KABUSHIKI KAISHA, Japanese corporation), 0.007 water reducing agent (Mighty 150, manufactured by KAO CORPORATION, Japanese) and 0.38 water.

  The cut fibers and mortar were pulverized

  on the surface of a mold so that the GRC has a thickness of 10 mm. The glass fibers have behaved excellently in cutting, molding and adaptability to the mold. Especially, mold adaptability was superior to common glass fibers, using

  a polyvinyl acetate primer of the prior type.

* After molding, the sample concrete slabs were covered with a polythene sheet and stored in the store for 1 day. Then, the concrete slabs were taken out of the mold and deposited in water at 20 C until aging of 28 days. Then, the flexural strength of the concrete samples was measured at 288 Kgf / cm. After the plates were kept for another 12 days in hot water at 80 C, the resistance to

bending was 230 Kgf / cm2.

RE V E N D I C A T I 0 N S

  1) Process for coating glass fibers

  with an alkali-resistant composite layer

  in that it comprises steps of: - application on the glass fibers of an aqueous solution of polyvinyl alcohol,

  drying of this layer of polyvinyl alcohol

  and - heat treatment of the dried layer at a temperature sufficient for the polyvinyl alcohol to crystallize properly with dehydration and thermal decomposition, the crystallized, dehydrated and thermally decomposed polyvinyl alcohol producing the composite layer

alkali resistant.

  2) The process according to claim 1, wherein

  characterized in that the aqueous solution is applied to continuous glass filaments which are drawn from a mass of molten glass by a die, the drying and the heat treatment being carried out after the glass filaments have been grouped into one plurality of bundles and coiled

  in a coil to form a cake.

  3) Process according to claim 2, characterized

  characterized in that the drying is carried out on the continuous bundles which are taken on a plurality of cakes and the heat treatment is carried out after the bundles

  were rewound together on a reel.

  4) Process according to claim 1, characterized

  characterized in that after the glass filaments have been drawn from a mass of molten glass through a die, grouped into a plurality of bundles and wound into a coil, an aqueous solution is applied to the bundle and the the drying and the treatment are then carried out

the heat.

   Process according to any one of claims 1 to 4, characterized in that the treatment at the

  heat is carried out at a temperature of 150 to 5001C.

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  6) Process according to any one of the claims

  cations 1 to 5, characterized in that the heat treatment

  is carried out at a temperature of 170 to 450 C.

  Process according to any one of the

  cations 1 to 6, characterized in that the heat treatment

is done in the air.

  8) Process according to any of the claims

  cations 1 to 7, characterized in that the heat treatment

  is carried out in a heating oven.

  9) A method according to any of the claims

  cations 1 to 8, characterized in that the polyvinyl alcohol

  has a degree of saponification of 90 mol% or more.

   Process according to any one of the

  cations 1 to 9, characterized in that the polyvinyl alcohol

  has a degree of polymerization of 300 to 2600.

  11) A method according to any of the claims

  1 to 10, characterized in that the polyvinyl alcohol is a water-soluble modified polyvinyl alcohol such as a polyvinyl alcohol derivative, a saponified copolymer

  vinyl acetate or a derivative of the saponified copolymer.

  12) Process according to claim 11, characterized

  in that the derivative of the polyvinyl alcohol is

  polyvinyl formal or polyvinyl butyral. 13. Process according to claim 11, characterized

  in that the saponified vinyl acetate copolymer is an ethylene polyvinyl alcohol or a polyvinyl alcohol

modified by a silanol.

  14) The process according to claim 11, wherein

  in that the derivative of the saponified acetate copolymer

  of vinyl is the formaldehyde of ethylenepolyvinyl.

   Process according to any one of the

  Claims 1 to 10, characterized in that the aqueous solution has a concentration of polyvinyl alcohol of 1 to 20% by weight.

  16) Process according to any one of the

  Claims 1 to 15, characterized in that the aqueous solution contains at least one coupling agent to assist the binding of the alkali-resistant composite layer to the glass surface, a lubricating agent to reduce friction between the coated surfaces of the adjacent filaments , a softening agent to soften the coating surface, a plasticizer to increase the plastic properties of the applied layer and a polymer to avoid abrasion

  coating during subsequent treatment.

  170. The method of claim 16, wherein

  in that the coupling agent is a silane, the lubricant and the softening agent consist of a cationic surfactant, the plasticizer being selected from dibutyl phthalate and glycerol and the polymer being a emulsions of acrylic esters and latex of

butadiene rubber (SBR).

  18) Process according to any one of

  Claims 1 to 17, characterized in that the fibers are

  made of an alkaline resistant glass containing ZrO2

at a rate of 5% by weight or more.

  19) Glass fibers characterized in that they are coated by the process according to any one

of the preceding claims.

  ) Material from concrete, characterized in that it is formed by incorporating coated glass fibers according to claim 19 into

a concrete matrix.