JPH10159340A - Concrete placing joint method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the formation of a laitance layer, and enhance adhesive strength of a construction joint by additionally placing a specific polymer emulsion concrete composite material before precedently placing concrete is hardened, and placing placing joint concrete after concrete and polymer emulsion concrete are hardened. SOLUTION: A polymer emulstion concrete composite materail on which a glass transition temperarture of a polymer or a copolymer in a polymer emulsion is (-) 35 to 50 deg.C, is prepared, and is added to a precedentry placing concrete layer and is compacted in a condition where the precedently placing concrete layer in a form is not hardened. Afterwards, curing in moist air is performed while the form is installed as it is. Next, placing joint concrete is fully added in the form on a hardened polymer emulsion concrete composite material layer in the form, and is compacted, and a specimen is formed, and curing in moist air is performed while the form is installed as it is.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improvement in a concrete joining method which solves problems such as insufficient strength of joints and water leakage in a concrete joining method.

[0002]

2. Description of the Related Art Concrete is desirably poured continuously so that structures are integrated. However, the limit of lateral pressure of a formwork, the amount of concrete that can be poured in a day, and mass concrete due to heat of hydration. Due to the problem of excessive temperature stress, etc., after dividing concrete into appropriate sections and hardening the previously poured concrete (hereinafter referred to as pre-cast concrete), the next concrete (hereinafter referred to as "cast-in-place concrete") ) Is usually typed. This construction method is called concrete transfer, and the interface that can be used for concrete transfer is called a joint. It is well known that if this joint construction is poor, problems such as insufficient strength of joints, water leakage, etc. occur, and these joint defects cause the durability of the entire concrete structure to be impaired. . The cause of the seam defect is the presence of a fragile layer having inferior properties called laittance formed on the surface of the pre-cast concrete due to breathing water.

[0003] As a method of treating the joint surface to cope with this problem, there is a method of shaving off the latence layer by spraying high-pressure water before hardening of the pre-cast concrete, and a method of spraying a setting retarder to cure only the surface layer. In general, a method of delaying the formation of the latency layer and suppressing the formation of the latency layer, or a method of shaving off the latency layer using a mechanical means such as wire brushing after hardening of the pre-cast concrete is generally used. Also, recently, after the pre-cast concrete has hardened, the latence layer is removed by mechanical means, and an epoxy resin, an unsaturated polyester resin or other synthetic resin adhesive is applied to the surface,
A method of passing concrete on top of this is also used.

[0004]

However, these processing methods have the following disadvantages. The high pressure water spraying method or the setting retarder spraying method cannot sufficiently remove the latency layer. Mechanical removal methods such as wire brushing are unsanitary for the respiratory system of workers due to the fine emission of dust during processing, and require washing after processing. In the resin-based adhesive application method, steps such as mechanical removal, washing with water, drying, and application of an adhesive are lengthened and processing costs are increased.

On the other hand, a polymer emulsion such as an ethylene-vinyl acetate copolymer emulsion, a polyvinyl acetate emulsion or a polyacrylate emulsion is sprayed on the concrete surface immediately after the casting, and the cast concrete is poured in before the polymer emulsion hardens. Although a method has been proposed, a method of pouring concrete at a time when the concrete is uncured or semi-cured is called "addition" and cannot be said to be a general jointing method. In view of the above situation, the present invention is to prevent the formation of a latence layer, increase the bonding strength of a joint, and eliminate the above-described joint defect in a so-called joining method performed after the pre-cast concrete is hardened. It was made for the purpose of.

[0006]

DISCLOSURE OF THE INVENTION The concrete transfer method of the present invention solves the above-mentioned problems, and the method comprises the steps of preparing a polymer emulsion-concrete composite material (where polymer The glass transition temperature of the polymer or copolymer in the emulsion is-
35 to 50 ° C.) to cure the concrete and the polymer emulsion-concrete composite material layer, and then pour in the cast concrete.

[0007] As described above, the latence layer formed on the surface of the precast concrete in the concrete casting method is formed by fine particles inside the concrete floating with the breathing water after the precast concrete is poured. As a result of various studies by the present inventors, when the above-mentioned polymer emulsion-concrete composite material is used, the dense layer of the polymer emulsion having a small specific gravity moves to the surface side, and the surface of the composite material is reduced. By forming a polymer film on the surface of the concrete layer, it was confirmed that breathing water from the pre-cast concrete layer and the floating of fine particles accompanying the same were prevented from rising to the surface, and as a result, formation of the latency layer was prevented. Completed.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in more detail. The polymer emulsion-concrete composite material used in the present invention comprises cement, inorganic aggregate, polymer emulsion and water. Examples of the polymer emulsion used for this are NR latex, SBR latex, CR latex, MBR (methacrylic acid) (Methylbutadiene rubber) latex, rubber latex such as NBR latex, polypropylene emulsion, ethylene-vinyl acetate copolymer emulsion, polyvinyl acetate emulsion, polyvinyl propionate emulsion, polyacrylate emulsion, styrene-acrylate copolymer emulsion , Epoxy resin emulsion, vinyl chloride / acrylate copolymer emulsion, vinyl acetate / vinyl versatate re-emulsifying powder emulsion, etc. Fat emulsion or the like, the glass transition temperature of the polymer or copolymer contained in this -35
-50 ° C.

In these polymer emulsions,
(1) vinyl chloride: 40 to 85% by weight; (2) a compound selected from (meth) acrylic monomers having a solubility in water at 25 ° C. of less than 1 g / water of less than 100 g: 14.5 to 50% by weight; (3) Compounds selected from α or β-unsaturated carboxylic acids: including a copolymer having a glass transition temperature of −35 to 50 ° C. obtained by copolymerizing a raw material monomer of 0.5 to 10% by weight. Preferably, an emulsion is used.

Next, a copolymer comprising the above components (1) to (3) and an emulsion containing the copolymer will be described. (1) The vinyl chloride component is used to give the obtained copolymer mechanical strength, water resistance, acid resistance, alkali resistance, chemical resistance,
The (meth) acrylic monomer which gives aging resistance and the like and the solubility of the component (2) at 25 ° C. in water at 1 ° C./water is less than 100 g imparts flexibility to the copolymer, whereby Coalescence becomes excellent in film forming property, durability, bonding strength and adhesiveness,
(3) The component α or β-unsaturated carboxylic acid suppresses aggregation / separation of a copolymer emulsion due to a strong alkali component or a cationic component such as Ca ²⁺ , Al ³⁺ in concrete, and before film formation. Improve stability.

The vinyl chloride component (1) is used in an amount of 40 to 85% by weight, preferably 50 to 80% by weight, based on the total amount of the monomers (the same applies hereinafter). If the amount of the component (1) exceeds 85% by weight, the obtained copolymer becomes too hard and poor in film-forming properties, and a dense copolymer film is not formed, resulting in reduced water resistance. When the amount is less than 40% by weight, the mechanical properties and water / alkali resistance of the obtained copolymer film are reduced.

The solubility of the component (2) in water at 25 ° C. is 1 g /
Examples of the (meth) acrylic monomer having less than 100 g of water include an acrylate ester with an alcohol having an alkyl group having 3 to 18 carbon atoms and a methacrylate ester with an alcohol having an alkyl group having 2 to 18 carbon atoms. For example, two or more of these can be used as needed. A (meth) acrylic monomer having a solubility in water at 25 ° C. of 1 g / water of 100 g or more has a small number of carbon atoms in the alkyl group, so that the copolymer has a softening effect (a glass transition temperature lowering effect).
Is insufficient, and the film forming property, bonding strength and adhesive strength of the copolymer are inferior.
Further, the water resistance is also reduced. On the other hand, in the case of a (meth) acrylic acid ester with an alcohol having an alkyl group having 19 or more carbon atoms, although the solubility in water is satisfied, the copolymer film becomes too soft and the mechanical strength decreases. (2)
The amount of the components used is 14.5 to 50% by weight, preferably 20 to 45% by weight. If the amount used is less than 14.5% by weight, the obtained copolymer is too hard, resulting in insufficient film-forming performance, bonding strength, and adhesion. If it exceeds 50% by weight, the ratio of vinyl chloride decreases relatively, Strength and chemical resistance, particularly water resistance, are reduced.

As the α- or β-unsaturated carboxylic acid of the component (3), acrylic acid, methacrylic acid, maleic acid,
Examples thereof include fumaric acid, crotonic acid, itaconic acid and their acid anhydrides, and two or more of these can be used as needed. (3) The amount of components used is 0.5 to 10
% By weight, preferably 1 to 8% by weight. Consumption
If the amount is less than 0.5% by weight, the dispersion stability of the obtained copolymer emulsion will be poor, and if it exceeds 10% by weight, the water resistance will be reduced and the obtained copolymer will be hard.

In the above copolymer, an ethylenically unsaturated monomer other than the components (1) to (3) is used in an amount of not more than 10% by weight of the total amount of the monomer so as not to impair the object of the present invention. It can be used as needed. Such monomers include:
Styrene, styrene derivatives, acrylonitrile, vinyl acetate, vinyl propionate, ethylene, methyl acrylate, ethyl acrylate, methyl methacrylate, etc.,
Hydroxyl-containing monomers such as 2-hydroxyethyl (meth) acrylate and 2-hydroxypropyl (meth) acrylate, (meth) acrylamide, N-methylol (meth) acrylamide, N-methoxymethyl (meth) acrylamide, N- Amide group-containing monomers such as butoxymethyl (meth) acrylamide and diacetone (meth) acrylamide; amino group-containing monomers such as dimethylaminoethyl (meth) acrylate and diethylaminoethyl (meth) acrylate; methoxyethyl (meth) Alkoxy group-containing monomers such as acrylate and butoxyethyl (meth) acrylate, glycidyl group-containing monomers such as glycidyl (meth) acrylate and glycidyl allyl ether, divinylbenzene, allyl (meth) acrylate, ethylene glycol And monomers having two or more radically polymerizable unsaturated groups in one molecule such as di (meth) acrylate, diethylene glycol di (meth) acrylate, and trimethylolpropane tri (meth) acrylate. It can be used in combination of two or more.

The copolymer can be produced by a known emulsion polymerization method using each of the above monomers. That is, the above-mentioned monomers are mixed, and an emulsifier, a polymerization initiator, etc. may be added thereto, and emulsion polymerization may be performed in an aqueous system, such as a method of collectively charging polymerization, a method of performing polymerization while continuously supplying each component, and the like. Various methods can be applied. The copolymer emulsion obtained by emulsion polymerization can be used as it is as a raw material for a polymer emulsion / concrete composite material.

Examples of the emulsifier for emulsion polymerization include anionic emulsifiers such as alkyl or alkyl allyl sulfate, alkyl or alkyl allyl sulfonate, and dialkyl sulfosuccinate; and cationic emulsifiers such as alkyltrimethylammonium chloride and alkylbenzylammonium chloride. And nonionic emulsifiers such as polyoxyethylene alkyl phenyl ether, polyoxyethylene alkyl ether, and polyoxyethylene carboxylate. The copolymer used in the present invention is provided with excellent water resistance by the above components (1) and (2), particularly the component (1), and is not softened by water or alkali. If a large amount of a low molecular weight emulsifier is contained, this will be absorbed into water or eluted into water, weakening the mechanical strength of the copolymer film and impairing the abrasion resistance. Therefore, instead of using the above emulsifier, a reactive interface having copolymerizability is used. Preferably, an activator is used. Examples of the reactive surfactant include those described in JP-A-6-166156, which is an application of Nissin Chemical Industry Co., Ltd., one of the applicants of the present invention. It is preferable to use at least 80% by weight. The amount of the emulsifier used generally varies depending on the properties required for the copolymer, and is preferably large, for example, to improve polymerization stability or to improve the mechanical and chemical stability of the emulsion. On the contrary, in order to improve the water resistance of the dried film, the smaller the amount, the better. Usually, from about 1 to 10 parts by weight per 100 parts by weight of the total amount of the monomers, depending on the respective purpose. I can decide.

Examples of the polymerization initiator include water-soluble types such as persulfates such as potassium persulfate and ammonium persulfate, aqueous hydrogen peroxide, t-butyl hydroperoxide, hydrochloride of azobisamidinopropane, benzoyl peroxide, and cumene. Hydroperoxide, dibutyl peroxide, diisopropyl peroxydicarbonate,
Examples thereof include oil-soluble types such as cumyl peroxy neodecanoate, cumyl peroxy octoate, and azobisisobutyronitrile. Further, if necessary, a redox system using a reducing agent such as sodium acid sulfite, Rongalit, L-ascorbic acid, saccharide, amine or the like can be used. The amount of the polymerization initiator used may be about 0.01 to 3 parts by weight based on 100 parts by weight of the total amount of the monomers. The polymerization reaction may be carried out usually at about 35 to 90 ° C., and the reaction time may be usually about 3 to 40 hours.

At the start or at the end of the emulsion polymerization, a basic substance is added to adjust the pH, so that the stability of the copolymer emulsion upon standing, freezing, mechanical stability, chemical stability and the like can be improved. Can be improved. In this case, the obtained copolymer emulsion is preferably adjusted to have a pH of 5 to 11, and for that purpose, ammonia, ethylamine, diethylamine, triethylamine, ethanolamine, triethanolamine, dimethylethanolamine, caustic soda, caustic potash, etc. Can be used.

The copolymer has a glass transition temperature of -35 to
It is necessary to be 50 ℃, if less than -35 ℃, the copolymer film becomes too soft, the mechanical strength is reduced,
On the other hand, when the temperature is higher than 50 ° C., a continuous film is not formed when the concrete is transferred, and good mechanical strength and water resistance cannot be obtained. The glass transition temperature of the copolymer is determined by the following equation. 1 / Tg = Σ (Wi / Tgi) Tg: glass transition temperature of the copolymer (absolute temperature display) Tgi: glass transition temperature of the homopolymer of the monomer component (i) (absolute temperature display) Wi: copolymer weight Weight fraction of component (i) in the coalescence (Bull. Am. Phys. Soc., Vol. 1, p. 123
TGFox method)

The cement used for the polymer emulsion / concrete composite material in the present invention includes ordinary portland cement, white portland cement, blast furnace cement, silica cement, fly ash cement, alumina cement and the like. As inorganic aggregate,
River gravel, river sand, crushed sand, silica sand may be mentioned, and these may be the same as those used for pre-cast concrete and cast-in concrete, preferably fine aggregate such as river sand, crushed sand and silica sand. (Φ5 mm or less) is preferably used.

If the amount of the polymer emulsion used in the polymer emulsion-concrete composite material used in the present invention is too small, the copolymer film does not sufficiently cover the cement and the inorganic aggregate on the concrete surface. The floating of the fine particles accompanying the surface cannot be suppressed, and the formation of the laitance layer is allowed.If the amount is too large, a large amount of expensive polymer emulsion will be used, and the joining cost is extremely high. Therefore, the solid content of the polymer emulsion is preferably 5 to 45 parts by weight, more preferably 15 to 20 parts by weight, based on 100 parts by weight of cement. In addition, the amount of inorganic aggregate used is 200 to 3 parts per 100 parts by weight of cement, as in the case of pre-cast concrete and cast-in concrete.
It is good to be 00 parts by weight. The water added for the hydration of the cement is preferably selected from the range of 20 to 60 parts by weight per 100 parts by weight of the cement, and should be 40 parts by weight or more in order to obtain high fluidity of the composite material. However, the amount of water in the polymer emulsion must be taken into account. As a mixing method for obtaining this composite material, a method of uniformly mixing cement and inorganic aggregate, then adding and mixing water, and further kneading by adding a polymer emulsion is preferable. It should be noted that if the order of addition of water and the polymer emulsion is reversed, the water in the polymer emulsion may be used rapidly for cement hydration and destroy the polymer emulsion.

In the concrete transfer method of the present invention, the above-mentioned polymer emulsion / concrete composite material is poured over the uncured pre-cast concrete, and both layers are cured by natural curing, and then the connection is performed. Concrete is poured in, whereby a highly reliable concrete transfer can be easily achieved. The thickness of the polymer emulsion-concrete composite material to be added in the present invention is extremely small according to the common sense of concrete that if the thickness is too small, the aggregate diameter is reduced to 1/3 or less of the concrete thickness. Need to be used after being sieved, which causes an increase in aggregate cost.If the thickness is too large, the polymer emulsion / concrete composite is expensive, which causes an increase in joint cost. , Preferably in the range of 5 to 20 mm.

[0023]

Next, the present invention will be specifically described based on examples and comparative examples, but the present invention is not limited to the description of the examples. In the examples, parts and% represent parts by weight and% by weight, respectively.

Example 1 After sufficiently replacing the inside of a polymerization vessel equipped with a stirrer, a condenser, a thermometer and a nitrogen gas inlet with nitrogen, 1150 of deionized water was used.
Parts, vinyl chloride 600 parts, 2-ethylhexyl acrylate (solubility to water 0.01 g / water 100 g) 370 parts, maleic anhydride 30 parts, emal O (sodium lauryl sulfate, manufactured by Kao Corporation, trade name) 10 parts, Neugen EA-170 (polyoxyethylene nonyl phenyl ether, manufactured by Daiichi Kogyo Seiyaku Co., Ltd.
(Trade name) 30 parts were charged, and after the temperature in the polymerization vessel was raised to 60 ° C, 100 parts of a 1% aqueous solution of ammonium persulfate was injected to start the reaction, and the reaction was carried out for 16 hours while maintaining the internal temperature at 60 ° C. To complete the polymerization. Next, cool the inside of the vessel to 30 ° C,
40 parts of Nonion HS-240 (polyoxyethylene octyl phenyl ether, manufactured by NOF Corporation, trade name) and KM-
681FA (Silicone-based defoamer, manufactured by Shin-Etsu Chemical Co., Ltd.
10 parts of trade name) was added, the pH was adjusted to 8.5 with sodium hydroxide, and the mixture was aged at room temperature for 24 hours. The obtained copolymer emulsion had a solid content of 45.3% and a viscosity of 170 cP, and the glass transition temperature of the copolymer in the emulsion was -6.2 ° C.

On the other hand, 100 parts of ordinary Portland cement,
Standard sand made from Australian natural sand [Prepared by the Japan Cement Association, particle size 0.08 to 2 mm] 300 parts and 50 parts of water are kneaded with a mortar mixer to prepare a pre-cast concrete, and this is mixed with a bottom surface of 40 parts.
Into a mold frame of mm × 40mm and height of 160mm, put an amount of 75mm in height, and fix this mold to the table vibrator CF-1033 for cement strength test [Maruto Seisakusho Co., Ltd.] Then, it was compacted for 5 minutes at a frequency of 2800 times / minute and a total amplitude of 0.8 mm. Next, 100 parts of ordinary Portland cement, 300 parts of standard sand of Australian natural sand (described above) and 25.6 parts of water are kneaded with a mortar mixer, and 44.4 parts of the above copolymer emulsion is added and kneaded. Polymer / cement ratio = 20
%, Water / cement ratio = 50%, aggregate / cement ratio = 300%
A polymer emulsion-concrete composite material is prepared, and the pre-cast concrete layer in the above-mentioned formwork is in an uncured state, and a quantity having a thickness of 10 mm is poured thereon. The compact was compacted under the conditions, and after that, the wet-air curing was performed for 3 days under the condition of 20 ° C. × 90% RH with the mold attached. Next, the cast-in-place concrete having the same composition as the pre-cast concrete is poured into the form over the hardened polymer emulsion / concrete composite material layer in the form,
Compacted under the same conditions as pre-cast concrete, 40mm x 40mm
Form a test specimen of × 160mm and leave the mold attached at 20 ℃ × 90
The wet-air curing was performed for 3 days under the condition of% RH. After this, the specimen without the mold was cured in water at 20 ° C for 2 days, taken out of the water 15 minutes before the bending strength test, and used a Michaelis type double lever type bending tester (JISR 5201). When a bending strength test was performed at a loading speed of 50 N / sec, 3 to 5 N
/ Mm ² , and although the fractured surface was at the boundary of the cast-in concrete, a fractured surface that could break through the cast-in concrete was observed.

Examples 2 to 6 In the same manner as in Example 1, a copolymer emulsion was prepared using monomers and emulsifiers of the kind and amount (expressed in%) shown in Table 1, and a polymer emulsion-concrete composite was prepared. Materials were prepared and test specimens were prepared. When a bending strength test was performed in the same manner as in Example 1, all were 3 to 5 N / mm ^2.
Met. The solubility of the (meth) acrylic monomer (2) used at 25 ° C. in water is as follows. -N-butyl acrylate: 0.2 g / 100 g of water-2-ethylhexyl methacrylate: 0.01 g / 100 g or less of water (2-ethylhexyl acrylate is mentioned above) The details of the emulsifier used are as follows. is there. (Reactive surfactant) ・ Eleminol-JS-2 (trade name, manufactured by Sanyo Kasei Co., Ltd.) ・ Aqualon RN-20 (trade name, manufactured by Daiichi Kogyo Seiyaku Co., Ltd.) See JP-A-6-166156. (The non-reactive surfactants Emal O and Neugen EA-170 are described above.)

[0027]

[Table 1]

Example 7 Ethylene vinyl acetate emulsion having a solid content of 55% and a viscosity of 1500 cP (glass transition temperature of copolymer: 0 ° C.) as a copolymer emulsion, 36.3 parts of Sumikaflex 400 (trade name, manufactured by Sumitomo Chemical Co., Ltd.) A polymer emulsion / concrete composite material was prepared in the same manner as in Example 1 except for the addition of, and a specimen was prepared using this in the same manner as in Example 1. When the hardness test was performed, it was ² to 4 N / mm ² .

COMPARATIVE EXAMPLE 1 Concrete having a height of 82 mm was driven in using the above-mentioned formwork with the same concrete mix as the pre-cast concrete of Example 1, and compacted under the same conditions.
Moisture and air curing was performed for 3 days under the condition of 90% RH, the mold was removed, the joint surface was scraped off by 2 mm by sandblasting, washed with water, and air-dried for 1 day. Next, this concrete test piece was mounted on a formwork, and concrete of the same composition was poured into the formwork to form a 40 mm × 40 mm × 160 mm test piece. The wet and dry curing was performed for 3 days under the condition of × 90% RH. After that, the underwater curing was carried out under the same conditions as in Example 1, and the specimen was taken out of the water 15 minutes before the bending strength test and subjected to the bending strength test under the same conditions. Yes, bending strength is 0.5N /
mm ² or less.

For reference, concrete was poured into the above-mentioned formwork with the same concrete composition as the pre-cast concrete of Example 1 and compacted under the same conditions.
mm × 40 mm × 160 mm specimen is molded,
Perform moisture curing under the same conditions for 3 days, remove the mold, perform underwater curing under the same conditions, remove from the water 15 minutes before the bending strength test, and perform the bending strength test under the same conditions. As a result, the fracture surface was substantially at the center of the concrete specimen, and the bending strength was 3 to 5 N / mm ² .

[0031]

According to the method for transferring concrete of the present invention, only the polymer emulsion-concrete composite material is applied to the uncured surface of the previously poured concrete, and the rising of the breathing water and the accompanying fine particles is reduced. The formation of the resulting surface fragile layer can be suppressed. Therefore, problems such as insufficient joint strength and water leakage caused by the surface fragile layer of the previously poured concrete are solved, and the concrete joining method of the present invention is extremely effective in practical use.

 ──────────────────────────────────────────────────続 き Continuing from the front page (72) Inventor Tsutomu Saga 1-406-1, Yoshino-cho, Omiya-shi, Saitama Shin-Etsu Polymer Co., Ltd. (72) Inventor Ichiro Yai 2--17-33 Kitafu, Takefu-shi, Fukui Prefecture No. Nisshin Kagaku Kogyo Co., Ltd. (72) Inventor Shuichiro Shinohara 2-17-33 Kitafu, Takefu City, Fukui Prefecture

Claims (2)

[Claims] 1. A polymer emulsion-concrete composite material (where the glass transition temperature of the polymer or copolymer in the polymer emulsion is -35 to 50 ° C.) before the previously poured concrete hardens. A concrete casting method, which comprises: casting the concrete and the polymer emulsion-concrete composite material layer, and then pouring in the cast concrete. 2. The polymer emulsion-concrete composite material comprises: (1) 40 to 85% by weight of vinyl chloride;
The solubility in water at 1 ° C is less than 1 g / water 100 g (meth)
Compounds selected from acrylic monomers 14.5-50% by weight
And (3) an emulsion, a cement, and an inorganic aggregate containing a copolymer obtained by copolymerizing a raw material monomer comprising 0.5 to 10% by weight of a compound selected from α or β-unsaturated carboxylic acids. The method according to claim 1, wherein: