JPS6251907B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention provides polyvinyl alcohol (hereinafter referred to as
PVA (abbreviated as PVA) relates to fiber-reinforced cement materials reinforced with fibers. Natural mineral fibers such as asbestos, inorganic fibers such as various types of glass fibers, glass fibers, other ceramic fibers, carbon fibers, and metal fibers such as steel have excellent weather resistance, heat resistance, high Young's modulus, and high strength. It has excellent mechanical properties in fibrous form. Conventionally, asbestos has been used for cement composite materials, but this poses resource depletion and hygiene problems. Furthermore, glass fibers and shirasu fibers have poor alkali resistance, and in particular, they can be called alkali-resistant glass fibers, causing problems in the durability of their alkali resistance. Metallic fibers made of steel or the like have problems in terms of adhesion and rust formation. Ceramic fibers, carbon fibers, etc. are expensive and difficult to use regularly in industry. When using an organic synthetic fiber instead, one that satisfies all mechanical and physical properties has not yet been obtained. Current polyolefin fibers such as polypropylene and polyethylene have good chemical resistance, but cannot provide heat resistance, high strength, or high Young's modulus.
The same applies to polyamide fibers. Furthermore, polyester fibers have disadvantages such as poor alkali resistance. The present invention provides a fiber-reinforced hydraulic material that has chemical resistance, particularly alkali resistance, which is a feature of inorganic fibers, and also contains PVA fibers that have a high Young's modulus, high strength, and low elongation. A hydraulic substance is a substance with an inorganic cement or an inorganic binder or adhesive that hardens by a hydration reaction. Examples of binders that harden through a hydration reaction include portland cement, silica cement, fly ash cement, alumina cement, blast furnace cement, and gypsum. The use of substances containing boric acid in cement materials has traditionally been prohibited as it has a very negative effect on cement coagulation. This is because "sugar, humic acid, boric acid, borax, etc., even in the presence of gypsum or lime, dissolve cement aluminates and immediately form aminosilicate gels, and in trace amounts the gels interfere with subsequent hydration. slow down coagulation,
If the amount exceeds a certain level, a large amount of gel will be formed, resulting in instant setting. Normal hydration is no longer possible and strength is severely impaired. '' is clearly stated in the Ceramics Handbook (edited by Gihodo, Ceramics Association, published in 1950, line 15), and it is a common belief that boric acid is synonymous with bad things. However, the present invention specifically applies to PVA containing boric acid or borax.
It has been found that by using fibers, boric acid or borax effectively affects the behavior of hydraulic substances such as cement in alkaline solutions. This fact indicates that boric acid or borax, which is said to have an adverse effect on cement coagulation, can best utilize the fact that boric acid gels PVA in an alkaline cement substance, and not only does it have no adverse effect on cement coagulation.
This shows that it works very effectively as a fiber for cement reinforcement. Yet another advantage of boric acid is that boric acid in PVA fibers improves the adhesion between the fibers and cement. Although the reason for this is not clear, the reaction between PVA and boric acid is well known, and it is known that intermolecular crosslinking occurs under alkaline conditions. It may be that boric acid present in the fibers in the cement molded product intervenes and causes some kind of reaction between PVA and the cement components.
Fibers containing 0.1 to 0.7% boric acid are strongly alkaline in cement molded products, so as mentioned above, naturally crosslinking occurs between PVA molecules in the molded product, restricting molecular movement and further increasing Young's modulus. It was discovered that it has the feature of increasing the reinforcing effect. PVA fibers are produced by adding boric acid to the PVA stock solution and spinning it wet through a nozzle in a caustic alkaline sodium sulfate bath.The PVA stock solution is crosslinked by the action of the boric acid, gelling and coagulating. A high draw ratio can be obtained by neutralizing this spun yarn with acid and washing away the sodium sulfate and excess boric acid. In other words, if the total stretching ratio is 900% or more, expressed as a percentage of the spinning speed and the speed of the final take-up roller, it has mechanical properties such as high strength, low elongation, and high Young's modulus, and is resistant to hot water. ,
Alkali-resistant PVA fibers are obtained. However, the greatest feature of this PVA fiber is that it contains 0.1 to 0.7% boric acid. If the boric acid content is 0.7% or more, intramolecular crosslinking is strong, and sufficient stretchability and workability are not obtained. Moreover, if it is less than 0.1%, it does not contribute to improving adhesion with cement and is difficult to wash industrially. The present inventors have developed various PVAs obtained in this way.
We investigated cement materials using fibers and found that cement materials that basically contain PVA fibers as shown below are extremely superior. That is, the Young's modulus of the fiber after being immersed in the cement mortar solution is 6.8×10 ² to 2.26×10 ³ Kg/mm ² , the strength is 80 to 160 Kg/mm ² , and the elongation at that time is 10% or less. , polyvinyl alcohol fibers with physical properties such that when broken after being kneaded into cement mortar and hardened, the fiber length exposed on the fractured surface is 500 micrometers (μm) or less, and has 0.1 to 0.7% boric acid in the fibers. It is a fiber-reinforced cement material containing 10% by weight of cement alone, cement and aggregate, or cement and aggregate and reinforcing bars or steel frames. According to the theory of reinforcing composite materials, a high Young's modulus is necessary, but I do not think that what is generally stated is sufficient regarding the reinforcing properties of composite materials. For example, there are factors such as the adhesion between the fibers and the cement matrix and the orientation of the fibers, and it is necessary to increase the so-called reinforcement efficiency. In the present invention
It is thought that boric acid in PVA fiber is a major factor in increasing its reinforcing efficiency. That is, the reaction between PVA and boric acid changes depending on the pH, and in an alkali with a pH of 5 to 6 or more, the hydroxyl group of PVA and boric acid crosslink. Therefore, it is presumed that in a highly alkaline bath such as a cement mortar solution, boric acid has a high binding strength due to the alkali and does not fall off, and is strongly crosslinked. Therefore, in the cement composite
PVA fibers have a strong structure due to the presence of boric acid, which overcomes the disadvantage of using boric acid or the like for cement coagulation, which was generally considered to be bad. Furthermore, the cutting strength of fibers is not fully utilized in the cement matrix. It can be seen that the breaking strength of the fiber-reinforced cement does not reach the resultant force of the breaking strength of the cement and the breaking strength of the fibers. That is, the elongation at break of plain cement mortar is within an extremely small elongation range of 0.02% or less. When the fiber strength is sufficiently exerted in such a small elongation range, if the adhesion between the fiber and cement is perfect, the fiber of minute length will be cut in an elongated form at the fracture surface. Therefore, the fiber length of the exposed portion must be an important factor regarding adhesiveness. The present inventors used the following as a measure of the affinity and adhesion of reinforcing fibers with the cement matrix:
The length of the cut fibers exposed on the fracture surface of the fiber-mixed cement solidified material influences the effectiveness of the cement material, with a limit of approximately 500 μm, and the smaller the cut length, the higher the bending strength of the cement material. I found out. In addition, the boric acid-containing PVA fibers having the above-mentioned physical properties with a cut length of 500 μm or less have a Young's modulus of 6.8×10 ² to 2.26×10 after immersed in cement mortar, probably due to the large binding effect of boric acid as described above. ³ Kg/mm ² and its strength is 80 to 160 Kg/mm ² , and its elongation is
We found that it was less than 10%. In the present invention, the cement mortar liquid is a slurry-like liquid prepared by adding 0.75 parts of ordinary Portland cement to 1 part of water and constantly stirring it with a stirrer. The fibers are immersed in it under tension or no tension,
This is after one week has passed. PVA fibers having the above characteristics are produced, for example, as follows. The PVA used has a polymerization degree of 800 to 3000.
and preferably 1400 to 2600. The degree of saponification used is 94 to 99.9 mol%. This PVA
A 10-20% aqueous solution is prepared, and 0.5-3% by weight of boric acid is added to PVA while keeping the pH below 4.5.
This stock solution is spun through a nozzle into a caustic salt bath and solidified. The boric acid mixed with PVA during spinning reacts with the rapid alkalinity, and the PVA coagulates. However, this alkalinity is neutralized and removed in order to color the PVA and remove boric acid later, and the boric acid content is removed by washing with water until the boric acid content falls within the range of 0.1 to 0.7%. Such fibers are completely dried, hot drawn, heat treated and wound. The stretching ratio is adjusted so that the final total stretching ratio is 900% or more, preferably 1100% or more. This fiber can be used by cutting it into lengths of 3 to 25 mm and mixing it into cement, etc., or by using it as an uncut filament. The content of PVA synthetic fibers in the cement material is preferably 0.5 to 10% by weight, preferably 1 to 5% by weight. If the content of PVA synthetic fibers is less than 0.5% by weight, the reinforcing effect is small and meaningless, and if it is more than 10% by weight, it does not contribute much to the reinforcing effect, and on the contrary, it may be used in cement slurry or mortar. Dispersibility and fluidity deteriorate, making handling difficult and meaningless. Next, the addition rate of asbestos is preferably 0 to 15% by weight. First of all, 0% by weight means that asbestos is not used, and adding asbestos up to 15% by weight means that it is used not only for its reinforcing properties but also as a dispersion aid and reinforcing material during molding. There are no restrictions on the use of asbestos. However, if the amount of asbestos added exceeds 15% by weight, it is meaningless from the viewpoint of moldability, dispersibility, and economy. Furthermore, it is also possible to add chopped strands of alkali-resistant glass fiber. Its addition rate is 0 to 10% by weight. When adding chopped strands of alkali-resistant glass fibers from 3 to 10% by weight, they have a synergistic reinforcing effect with PVA fibers, but if they exceed 10% by weight, the handling of concrete or mortar mixed with them may be affected. As this situation worsens, the economic efficiency of the reinforcing effect also deteriorates. Furthermore, pulp as a dispersion aid (material) may be used as the additive fiber. Types of pipes include groundwood pulp, kraft pulp, semi-chemical pulp, sulfite pulp, soda pulp, chemical ground pulp,
Furthermore, bamboo, straw, kozo, and mitsumata may be used, and recycled pulp such as used newspaper or cardboard may also be used. It is not particularly limited. It goes without saying that if each fibrous material is sufficiently dispersed due to the dispersibility of the fibrous mixture that has been added so far, it is better to avoid adding organic materials that have poor alkali resistance and are combustible as much as possible.
The pulp addition rate is preferably a low addition rate of 0.5~
2% by weight is good. For the above reasons, the addition rate of pulp is 0 to 5% by weight; if it is added in excess of 5% by weight, although it has a dispersion effect, the reinforcing properties and bending resistance deteriorate, and the flame retardancy as a civil engineering and construction material is lost. . A mixture of the thus obtained mixed fibers and cement alone, or a mixture of cement and fine aggregate such as sand, or a mixture in which coarse aggregate such as gravel or crushed stone is further added may be used. Furthermore, these cement mortar and concrete may be used in combination with reinforcing bars or steel frame structural materials to make cement molded products or structures, or as civil engineering materials such as paved roads. Synthetic fibers or synthetic pulp, natural fibers and metal fibers can then be used in place of the alkali-resistant glass fibers in some of the fiber compositions. The amount added is up to 10% by weight. To explain in more detail, the synthetic fibers used include strands such as slit yarns and split yarns made from filaments or films such as polyolefin-based polyethylene and polypropylene, polyamide-based nylon 6 and nylon 66, and other polyacrylonitrile and polyamide fibers. Chopped strands of vinyl chloride, polyvinylidene chloride, polyester, polyimide, polyamideimide, etc., such as Kevlar, can be used. As the synthetic pulp, polyethylene, polypropylene, or those obtained by flash spinning a polymer obtained by mixing these polymers with an inorganic filler can also be used. Addition of these organic synthetic fibers has the effect of improving not only bending strength but also impact resistance by adding those with high elongation and low Young's modulus. Next, the natural fibers may be cotton, manila hemp, jute, kozo, mitsumata, gampi, animal wool, or animal hair other than vegetable pulp. These aid in fiber dispersion and weight reduction in the mortar. The metal fibers may be fibers or strands of iron, steel, or various types of stainless steel.
Other materials such as carbon fiber and mica can also be used. As mentioned above, the addition rate of alternative fibers such as alkali-resistant glass fibers to mortar or concrete is limited to 10% by weight in terms of handling and workability, and exceeding this limit is economically disadvantageous. Regarding metal fibers, the reinforcing effect decreases due to cracks in the cement, the occurrence of rust due to weathering, and the volume effect on the added weight is small due to the high specific gravity. The PVA fiber of the present invention compensates for these drawbacks. Furthermore, carbon fibers, mica, etc. cannot sufficiently exhibit their reinforcing properties because of their poor adhesion to cement mortar. By dispersing them with PVA fibers, we were able to create a durable composite material. There are various methods for forming these fiber-reinforced cement mortar or concrete, but there are no particular limitations. For example, pressure molding method, vibration molding method,
It can be used in vibration and pressure molding methods, centrifugal force molding methods, paper molding methods, winding molding methods, vacuum molding methods, and extrusion molding methods. Filament-shaped fibers are used for filament winding, plate-shaped molded products, thick plate-shaped molded products, reinforcing bar-filled molded products, etc., which are used for products that are subjected to stress in the direction of the fiber axis. It can also be used as a woven fabric, net, or nonwoven fabric for plate-shaped molded products, cylindrical molded products, etc. The scope of use of this PVA fiber is cement tiles,
Thick slate, corrugated asbestos slate, asbestos cement board and its secondary products, asbestos perlite board, asbestos cement pipe for water supply, pulp cement board, pulp cement pipe, asbestos cement cylinder, wood wool and wood chip cement board, concrete board, concrete Artificial stone blocks, mortar boards, terrazzo blocks, terrazzo tiles, reinforced concrete assembly walls, prefabricated concrete members, structural materials such as prestressed concrete double T slag, sheet piles or reinforced concrete sheet piles, prestressed concrete sheet piles, centrifugal reinforced concrete foundation piles, reinforced concrete pipes, centrifugal reinforced concrete It can be fully used as a brittle matrix reinforcing material when solidifying cement, plaster, etc. for pipes, centrifugal reinforced concrete poles, etc. It can be applied not only to the above-mentioned cement products but also to structures other than these, building interior and exterior parts, and civil engineering materials, and the following various uses are shown as specific usage methods. First of all, it is used in civil engineering as a road paving material, such as for paving general roads, expressways, runways, overlays, paving pedestrian bridges, paving bridge decks, repair materials for these, or sidewalk boards, etc. can. It can also be used for formwork used as molding formwork and waste formwork. Pipes include sewer pipes, electric lamp pipes, cable ducts, etc. Further, as road materials, it can be used for soundproofing materials, road signs, pavement reinforcement materials, side gutters, tunnel interior materials, piles, etc. Second, building-related members include exterior materials, which can be used for shell structures, curtain wall exterior wall panels, roofing materials such as slate, parapets, spandrels, and exterior reliefs. Furthermore, it can be used as interior material for wall materials, reliefs, floor materials, and ceiling materials. Other materials include formwork, disposable formwork, floorboards, beams, machine platform foundations, nuclear reactor pressure vessels, liquefied petroleum gas containers, partitions in buildings, and staircase materials. Thirdly, marine or fishery components include those used in thin shell structure compositions for use as cement materials for ferrocement such as marine equipment, boats, etc., floats, floating bridges, fishing reefs, wave-dissipating blocks such as tetrapods, seawall blocks, etc. available for use. Fourthly, as agricultural and stock-producing related parts, it can be used for tanks, silos, seedbeds, fence pots, pots, flower pots, sheet piles for side ditches, etc. It can also be used for materials such as containers for processing waste such as radioactive materials. There are no limitations on the use of other materials. Next, the present invention will be further explained with reference to Examples. Example 1, Comparative Example 1 Polymerization degree 1750 with addition of 4% boric acid, saponification degree
A PVA aqueous solution with a concentration of 16% (99.9 mol%) was spun using a 1000-hole gold plate in a caustic salt bath. The adhering caustic soda is completely neutralized in a sulfuric acid bath, and the boric acid content in the spun PVA fiber is 0.1 to 0.7.
It was washed with water so that it was within %. The filament was dried in a dry air dryer, hot-stretched to 300%, further heat-treated, and wound. At this time, the total stretching ratio was 1300%, the amount of boric acid remaining in the fiber was 0.4%, and a filament of 3025 dr was obtained. For comparison, we prepared fibers with a residual boric acid content of 0.05% and a fiber with a high boric acid content of around 1.2%, and hot-drawn and heat-treated the fibers to examine their physical properties. -1. The fibers thus obtained were cut into lengths of 3 mm, the water-cement ratio was set to 0.5, the cut fibers were added and mixed to the cement in an amount of 2% by weight, and the mixture was placed in a mold and press-molded. Curing was carried out in water for 28 days. The bending strength of this molded product and the average length of the PVA fibers exposed on the fractured surface were 414 μm, and the fluff was short. It is shown in Table-1. The bending strength of the molded plate was also measured.
Although the amount of boric acid remaining in the PVA fiber was set to 1.2% in the washing process described in the comparative example, the hot stretchability was poor and was as low as 650%. Therefore, fibers exhibiting sufficient fiber physical properties could not be obtained, and satisfactory product characteristics could not be obtained.

[Table] Example 2 A 16.5% aqueous solution with a degree of polymerization of 1730 and a degree of saponification of 99.9 mol% was used as an acidic stock solution with a pH of 3.5, and 1.5% of boric acid was added to PVA, followed by spinning in a caustic alkaline sodium sulfate bath.
The alkali was completely neutralized in an acidic bath, and the adhering sulfuric acid, sodium sulfur, and boric acid were washed with water to a concentration of 0.2%. After drying, this was hot stretched to a total stretching ratio of 1350% and wound up. I got one with a single fiber denier of 1.8 dr. The fibers thus obtained were cut into 6 mm pieces, and an aqueous dispersion containing 2% by weight of the fibers, 5 parts by weight of grade 5R chrysotile asbestos, some pulp, and the remainder 93% by weight of ordinary Portland cement, A slate board was made using a small laboratory slate machine, and its bending strength was measured two weeks after pressing in air. The fractured surface of this molded product was observed with an optical microscope, and the fiber length exposed from the fractured surface was measured and found to be as short as 358 μm on average. For comparison, the boric acid content of 0.9% is 1350% under the same conditions.
could not be drawn and no yarn could be obtained. for that
It was set as 800% and evaluated in the same manner as in Example 2. The results are shown in Table-2.

[Table] When the fibers of Example 2 were put into cement mortar heated to 75°C, the shrinkage stress was 1 g and the shrinkage rate was 1.8%. The bending strength was also significantly higher than that of the comparative example. Example 3 and Comparative Example 3 The PVA fiber obtained in Example 2 was cut to a length of 4 mm, and chrysotile asbestos 5R was added and not added, and alkali-resistant glass fiber was cut to a length of 10 mm. Dostrand or other fibers were added to the above mixture, standard sand from Toyoura was added as a fine aggregate, ordinary Portland cement was added and dry mixed, and finally water was added to form a mortar. The water/cement ratio of this mortar was all constant at 0.5, and the fine aggregate/cement ratio was 3. Table 3 shows the main values of the fibers used.

[Table] As Comparative Example 3, a product without PVA fiber was shown and compared. 4cm x 4cm of these cement mortar mixture
The material was poured into a 4 cm x 16 cm mold and cured in water at 20°C for 28 days, then its physical properties were compared. Its composition and physical property values are shown in Table 4.

[Table] The bending strength of those with PVA fibers is 1.4 to 1.7 times higher than those without PVA fibers, and the tensile strength is also 1.3 times higher.
Improved by ~1.5 times.

Claims (1)

[Claims] 1. The Young's modulus of the fiber after immersed in cement mortar solution is 6.8×10 2 to 2.26×10 3 Kg/mm ² , the strength is 80 to 160 Kg/mm 2 , and the elongation at that time is 6.8×10 ² to 2.26×10 ³ Kg/mm ² . 10% or less, the fiber length exposed at the fracture surface when broken after being kneaded into cement mortar after hardening is 500 micrometers or less, and the fiber contains 0.1 to 0.7
Polyvinyl alcohol fiber with % boric acid
Fiber-reinforced cement materials containing 0.5 to 10% by weight of cement alone, cement and aggregate, cement and aggregate and reinforcing bars or steel frames. 2. The fiber-reinforced cement material according to claim 1, which contains 0 to 15% by weight of asbestos, 0 to 5% by weight of pulp, and 0 to 10% by weight of alkali-resistant glass fiber. 3. Claim 1, which contains 0 to 15% by weight of asbestos, 0 to 5% by weight of pulp, and 0 to 10% by weight of synthetic fibers other than alkali-resistant glass fibers, synthetic pulp, natural fibers, or metal fibers. Fiber-reinforced cement material as described in Section.