JP2005255425A - High toughness cement hardened body - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a high toughness cement hardened body having excellent dimensional stability and exhibiting a plurality of cracks in spite of a relatively low specific gravity. <P>SOLUTION: This high toughness cement hardened body is obtained by extruding cement paste containing at least hydraulic cement, a propylene fiber having 3-15 mm fiber length, 5-50 μm fiber diameter and aspect ratio of 150-1,000, a lightweight aggregate and water and curing the resultant formed body in an autoclave, and has specific gravity of 0.75-1.3 and 2.0-10% mixing ratio of the propylene fiber by volume. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a hardened toughened cement body, and more particularly to a hardened toughened cement body that exhibits a fracture mechanism that generates multiple cracks and breaks.

In recent years, a so-called high toughened cement hardened body that generates multiple cracks against a load and breaks is known (Patent Document 1). In the hardened tough cement body, even after the initial crack is generated when a load is applied, the fracture does not occur immediately, but the compounded fibers cause the bridge to bridge and share the stress, resulting in multiple cracks. However, it exhibits large deformation and breaking stress. The hardened tough cement body is generally obtained by extruding a cement composition paste and steam curing under normal pressure. However, since such a high toughness cement hardened body generally has a specific gravity of 1.4 to 2.0, its use has been limited.
JP 2002-338319 A

  In the past, development of low specific gravity products has been promoted for the purpose of improving workability, workability, workability, etc., and further expanding the use of various cement molded bodies, including hardened toughened cement bodies. . However, in cement-based extruded products, the lower the specific gravity (for example, the specific gravity is 1.3 or less), the dimensional stability upon water absorption and the freeze-thaw resistance tend to deteriorate. The value as a product does not occur just by the specific gravity. Furthermore, the low specific gravity product also has a problem that it takes a long time before it can be shipped.

  Therefore, autoclave curing is performed for the purpose of improving dimensional stability and freeze-thaw resistance and further stabilizing the quality of industrial products for cement-based extruded products. However, the polyvinyl alcohol fiber, which is a fiber used to develop a high toughness, that is, a fiber that causes multiple cracks to break with respect to a load, cannot be cured by autoclave due to its low melting temperature. Furthermore, even when polypropylene fibers are used, the strength of the cement matrix is excessively increased by the autoclave curing, and as a result, the multiple cracking performance is lost.

  The present invention provides a high toughness cement hardened body, particularly a high toughness cement-based extrudate, which has excellent dimensional stability and freeze-thaw resistance and exhibits multiple cracking performance while having a relatively low specific gravity. Objective.

  The present invention extrudes a cement paste comprising at least a hydraulic cement, a polypropylene fiber having a fiber length of 3 to 15 mm, a fiber diameter of 5 to 50 μm and an aspect ratio of 150 to 1000, a lightweight aggregate, and water, and the resulting molding A high toughness cement hardened body obtained by autoclaving the body, characterized by a specific gravity of 0.75 to 1.3 and a volumetric mixing rate of polypropylene fibers of 2.0 to 10% About the body.

  The high toughness cement cured body of the present invention has excellent dimensional stability and exhibits multiple cracks while having a relatively low specific gravity.

  In the present invention, “multiple crack” means the following. When bending stress is applied and the initial crack is formed in the hardened cement body, the stress concentrates on the cracked portion, and the normal hardened cement body breaks as it is. That is, fracture occurs at the stage of elastic deformation where the stress-strain curve becomes a straight line. Therefore, the energy absorption ability is low and brittle fracture is exhibited. On the other hand, even after the first crack is entered, there is a phenomenon in which the entire material does not immediately break, and a plurality of cracks are generated following the first crack. This is called multiple cracks. When multiple cracks occur, the stress is dispersed, so that even after the first crack is generated, it can withstand the increasing load and does not break until reaching a large strain, and exhibits high energy absorption and high toughness.

Moreover, in this invention, the volume mixing rate of a fiber means the ratio for which the fiber accounts in a hardening body cross section, and the value measured in accordance with the following method is used. The hardened cement body is cut in a direction perpendicular to the extrusion direction at the time of molding, and a reflected electron image is observed at an acceleration voltage of 25 kV on the cut surface using a scanning electron microscope. The fiber mixing ratio _Vf in the hardened cement body is obtained as a value obtained by dividing the total cross-sectional area of the fibers on the observation surface in the field of view of the microscope by the area of the field of view of the electron microscope. As the fiber mixing rate V _f , an average value of values measured for three different visual fields in the cut surface of the test piece is adopted.

  In the present invention, by adopting a cement hardened body composition described in detail below and performing autoclave curing, it has a relatively low specific gravity and is excellent in dimensional stability and exhibits multiple cracks. Can provide. In the case of a high-toughness extruded product of the conventional compounding, the strength of the cement matrix is significantly increased by the autoclave curing, the balance between the strength of the reinforcing fiber and the adhesion between the fiber-cement matrix and the strength of the cement matrix deteriorates, and multiple cracks occur. There is a phenomenon that does not occur. . In the present invention, by adopting a specific hardened cement composition, even if autoclave curing is performed, the above balance can be maintained well, resulting in relatively low specific gravity, excellent dimensional stability, and fracture that exhibits multiple cracks. Realize the mechanism simultaneously.

  The hardened tough cement body of the present invention is formed by extruding a cement paste (composition) containing at least hydraulic cement, polypropylene fiber, lightweight aggregate and water, and curing the obtained molded body by autoclave, The specific gravity is 0.75 to 1.3, preferably 0.85 to 1.2. If the specific gravity is too large, the application is limited and the cured product cannot be used effectively. If the specific gravity is too small, it is extremely difficult to perform cement extrusion while maintaining the strength.

  The hydraulic cement used in the present invention is not particularly limited as long as it is a cement that can form a cured body by reaction with water. Specific examples of such hydraulic cements include various Portland cements, blast furnace cements, fly ash cements, alumina cements, silica cements, magnesia cements, sulfate cements, and the like.

  A polypropylene fiber (PP fiber) having a fiber length of 3 to 15 mm, preferably 5 to 12 mm, and a fiber diameter of 5 to 50 μm, preferably 10 to 40 μm is used. From the viewpoint of the balance between the adhesion between the fiber and the cement matrix and the strength of the cement matrix, it is more preferable that the PP fiber has an aspect ratio of 150 to 1000, particularly 200 to 500. When the fiber length is shorter or the fiber diameter is larger, the balance between the fiber-cement matrix adhesion and the cement matrix strength is deteriorated. That is, when a crack is first generated in a state in which bending stress is applied, the stress cannot be borne even if the fiber is cross-linked, and it is pulled out immediately. Will be destroyed. When the fiber length is longer or the fiber diameter is smaller, the balance between fiber strength and cement matrix strength is deteriorated. That is, in a state in which a bending stress is applied, the fiber itself is broken before the fiber is pulled out, so that multiple cracks do not occur. The material constituting the fiber is a material other than polypropylene, for example, when ordinary PVA fiber or high-strength polyethylene fiber is used as a fiber for developing high toughness, its melting temperature is low, so high toughness in autoclave curing The function as an industrial fiber is lost.

  The “aspect ratio” of the fiber is a value obtained by dividing the fiber length by the diameter of an equivalent circle having the same area as the area of the fiber cross-sectional area. When the aspect ratio is less than 150, when a crack is first generated in a state where a load is applied, stress cannot be borne even if the fiber crosslinks, and it is pulled out immediately and multiple cracks are generated. Destroy before you do. In addition, when the aspect ratio is larger than 1000, the fiber itself breaks before the fiber is pulled out under a load, so that multiple cracks do not occur.

  The PP fiber preferably has a tensile strength of 200 to 400 MPa and a tensile modulus of 2 to 5 GPa from the viewpoint of maintaining a better balance between fiber strength and cement matrix strength by improving the strength of the fiber. The tensile strength is a value measured based on JIS L1013. As the tensile modulus, a value measured based on JIS L1013 is used.

  From the viewpoint of maintaining a better balance between the adhesion and the cement matrix strength by improving the adhesion between the fiber and the cement matrix, the PP fiber is subjected to a surface treatment that improves the affinity with the cement. It is preferable. By performing such surface treatment, the hydrophilicity of the PP fibers is improved and the adhesion with the cement matrix is improved, so that the balance with the cement matrix strength improved by the autoclave curing can be more effectively maintained.

  Examples of the surface treatment agent used for the surface treatment include those described in JP-A Nos. 64-33036 and 2000-34146. A more preferred surface treating agent is that described in JP-A No. 2000-34146, specifically a carboxyl group-modified polyolefin low molecular weight product.

  Specifically, the carboxyl-modified polyolefin-based low molecular weight material is one in which 1 to 10 carboxyl groups are introduced on average to a low molecular weight polyolefin having a number average molecular weight of 1000 to 6000 (for example, polypropylene or polyethylene). is there. In particular, the carboxyl terminal is preferably a potassium salt. In addition to potassium salt, sodium salt, calcium salt and the like may be used. When the number average molecular weight is too small, the affinity between the surface treatment agent and the fiber becomes weak, and the surface treatment agent is likely to fall off. If it is too large, it will be difficult to apply the surface treatment agent to the fibers. In addition, it is preferable to introduce more carboxyl groups because the hydrophilicity of the treated fibers increases and the dispersion of the fibers in the hydraulic cement composition is favorable, but it is technically difficult to introduce more than 10 carboxyl groups. . Further, when the carboxyl terminal is a potassium salt, it is replaced with calcium contained in the hydraulic cement composition, and the dispersion of the treated fiber in the hydraulic cement composition becomes better.

  From the viewpoint of easily performing surface treatment, that is, applying the treatment agent to fibers, it is preferable to use a surface treatment agent that is already in an emulsion form using a surfactant.

  The method for surface treatment of the PP fiber is not particularly limited as long as the surface treatment agent can be uniformly attached (coated) to the surface of the PP fiber, and for example, a dipping method, a spray method, or a coating method can be employed. In any case, the surface treatment may be performed at the stage after stretching in the fiber production process. Specifically, for example, after stretching in the fiber production process, a surface treatment agent (particularly in emulsion form) is dispersed in water, the PP fiber assembly is immersed in the obtained dispersion, and the fiber surface treatment agent is applied to the fiber surface. Cover uniformly. In order to uniformly adhere the surface treatment agent to the fibers, it is desirable that the fiber assembly is immersed in the surface treatment agent dispersion and then penetrated into the fiber assembly using a squeeze roll or the like. After coating, the cement-reinforced surface-treated PP fiber can be obtained by cutting to a predetermined length with a cutter.

The concentration of the surface treatment agent in the dispersion is not particularly limited as long as the high toughness cement cured body of the present invention is obtained, and is usually 0.6 to 20% by weight.
The adhesion amount of the surface treatment agent to the fiber is preferably 0.2 to 20% by weight with respect to the fiber weight. More preferably, it is 0.8 to 2 weight%. Moreover, it is preferable that 10 to 40% by weight of water is attached to the fiber weight.

  The PP fiber is blended in such an amount that the volume mixing ratio in the cured body is 2.0 to 10%, preferably 2.5 to 7%. When the volume mixing rate is less than 2.0%, the balance between fiber strength and cement matrix strength is deteriorated. That is, the stress concentrated on the crack can not be supported and the crosslinking action cannot be exhibited. Even if it is larger than 10%, the moldability deteriorates and it becomes uneconomical.

Examples of lightweight aggregates in the present invention include ultralight aggregates such as perlite and permiculite, natural lightweight aggregates such as volcanic rubble, artificial lightweight aggregates such as calcined fly ash, and by-product lightweight aggregates such as expanded slag. It is done. By using such a lightweight aggregate, the strength of the cement matrix can be moderately lowered to maintain a good balance between the strength of the reinforcing fibers and the strength of the cement matrix, and further, the low specific gravity of the cement cured body can be maintained. And excellent moldability of cement paste. If a lightweight aggregate is not used, the low specific gravity and moldability cannot be ensured while maintaining the above balance. For example, by increasing the blending amount of water, a low specific gravity can be ensured while maintaining the above balance, but the moldability of the cement paste is remarkably lowered, making it difficult to produce a molded body. In addition, for example, it is possible to reduce the weight based on the water retention of the additive by increasing the amount of the additive having water retention performance such as pulp and extender material more than usual, but the strength of the cement matrix is increased. Since it rises too much, the balance cannot be maintained.
Among the lightweight aggregates, ultralight aggregates, particularly pearlite, are preferable from the viewpoint of more effectively maintaining the balance and easily achieving the low specific gravity and excellent formability.

  The blending amount of the lightweight aggregate is not particularly limited as long as the above balance can be maintained and the low specific gravity of the hardened cement body and the excellent moldability of the cement paste can be secured. Usually, 10 parts by weight or more, particularly 10 to 80 parts by weight is appropriate for 100 parts by weight of hydraulic cement. Preferably it is 30-70 weight part, More preferably, it is 40-60 weight part.

  In addition to the above components, the cured product of the present invention preferably contains pulp, siliceous raw materials, water-soluble cellulose and the like.

  The pulp is preferably natural pulp such as cotton pulp or wood pulp. If it is a natural pulp, it will not specifically limit, The recycled pulp from not only a virgin pulp but used paper can also be used. In the case of wood pulp, either chemical pulp obtained by chemically removing lignin from the wood structure or mechanical pulp obtained by mechanically treating wood can be used. The pulp preferably has a fiber length of 0.05 to 10 mm. The blending amount of the pulp is not particularly limited, and is usually 0.1 to 40 parts by weight, preferably 0.1 to 10 parts by weight with respect to 100 parts by weight of the hydraulic cement. From the viewpoint of effectively reducing the strength of the cement matrix to more effectively maintain a good balance between fiber strength and fiber-cement matrix adhesion and cement matrix strength, 0.5 to 3 parts by weight is more preferable. . When the amount of the pulp is small, the shape retention property is lowered and the molding becomes difficult. When the amount of pulp is too large, the matrix strength is excessively increased and multiple cracks are not generated.

As the siliceous raw material, for example, silica powder, blast furnace slag, silica sand, fly ash, diatomaceous earth, silica fume, amorphous silica and the like can be used. Silica powder and silica sand are preferred because they contribute to improving the strength and dimensional stability of the cured body. As these siliceous raw materials, those having a specific surface area (according to the method described in JIS R 5201) of 3000 to 15000 cm ² / g are preferably used. The amount of the siliceous raw material is not particularly limited, and is usually 40 to 100 parts by weight, preferably 50 to 80 parts by weight with respect to 100 parts by weight of the hydraulic cement.

  Examples of the water-soluble cellulose include alkyl celluloses such as methyl cellulose and ethyl cellulose, hydroxyalkyl celluloses such as hydroxyethyl cellulose, hydroxyethyl methyl cellulose, hydroxypropyl methyl cellulose, and hydroxyethyl cellulose, hydroxyalkyl alkyl celluloses, and carboxymethyl cellulose. The water-soluble cellulose imparts viscosity to the composition and improves the moldability when the paste-like cement composition is extruded. The blending amount of the water-soluble cellulose is not particularly limited, and is usually 0.1 to 10 parts by weight, preferably 0.5 to 7 parts by weight with respect to 100 parts by weight of the hydraulic cement.

  In the cured body of the present invention, if necessary, mineral fibers such as sepiolite, wollastonite, talc, attapulgite, rock wool, inorganic materials other than silica such as mica, alumina, calcium carbonate, vinylon fibers, polyethylene fibers, Reinforcing fibers other than PP fibers such as carbon fibers, water reducing agents, surfactants, thickeners and the like can also be blended.

  The hardened tough cement body of the present invention can be obtained by extruding a cement paste formed by blending water into the cement mixture composed of the above components, and curing the obtained molded body by autoclave curing. The blending amount of water is not particularly limited as long as good moldability of the cement paste can be ensured, and is usually 30 to 80 parts by weight, particularly 40 to 60 parts by weight with respect to 100 parts by weight of the hydraulic cement.

  A denser hardened body can be obtained by extrusion molding. Further, since the PP fibers are predominantly oriented in the extrusion direction, the reinforcing effect by the cross-linking action of the fibers can be effectively exhibited against the tensile stress in the extrusion direction or the bending stress from the direction perpendicular to the extrusion direction.

Autoclave curing is steam curing under high temperature and pressure. Although the conditions are not particularly limited, specifically, the molded body is held in an autoclave at a pressure of 4 to 10 kg / cm ² , preferably 5 to 7 kg / cm ² for about 5 hours or more. Since the tobermorite crystals or quasicrystals are formed by the autoclave curing, it is considered that the dimensional stability, matrix strength and freeze-thaw resistance of the cured product are improved.
In the present invention, after extrusion, it is more preferable to perform steam curing under normal pressure prior to autoclave curing.

(Example 1)
100 parts by weight of ordinary Portland cement, 60.0 parts by weight of quartzite powder (specific surface area 4000 cm ² / g), 50.0 parts by weight of pearlite, 1.0 part by weight of pulp, 5.0 parts by weight of sepiolite, polypropylene fiber A7.2 Part by weight and 6.0 parts by weight of methylcellulose (manufactured by Shin-Etsu Chemical Co., Ltd.) were added, and the mixture was powder mixed for 3 minutes with a mixer. While continuing the powder mixing, 51.0 parts by weight of water was added little by little and mixed for 2 minutes, then transferred to a kneader and kneaded for 3 minutes to knead the cement paste. The obtained cement paste was extruded from a cylinder type vacuum extruder through a mold. As the discharge port size of the mold, a rectangular shape having a width of 80 mm and a height of 15 mm was used. The molded body discharged from the mold was received in the tray. The molded body was wrapped with a plastic film along with the tray, and steam cured in a thermo-hygrostat. In the steam curing, the temperature was maintained for 5 hours under the conditions of 98% humidity, normal pressure and 70 ° C. After that, autoclaving was performed to obtain a hardened tough cement body. In the autoclave curing, the pressure was maintained at 5 kg / cm ² for 5 hours.

(Examples 2-6 and Comparative Examples 1-5)
A hardened toughened cement was obtained in the same manner as in Example 1 except that the blended fiber, blending ratio and autoclave curing conditions were changed as shown in Table 1.

(Evaluation)
Bending strength A test body for a simple bending test with a two-point load of 80 mm in width, 15 mm in thickness and 250 mm in length (extrusion direction length) was cut out from the obtained molded body.
The distance between the loading points was 60 mm, the distance between the fulcrums was 180 mm, and the crosshead speed was 0.5 mm / min. Based on the measured load P, the bending stress σ _b was evaluated by the following formula:
σ _b = PL / bt ²
In the formula, b represents the width of the test piece, t represents the thickness of the test piece, and L represents the distance between the fulcrums. Fig. 1 shows the situation of a simple bending test with two points. 11 is a test body, 12 is a fulcrum, and 13 is a loading point. The bending strength indicates the maximum stress of a bending stress-displacement (deflection) curve.

Peak deflection The maximum specimen displacement when the above bending strength was achieved was evaluated as peak deflection.
Number of cracks The test specimen that was broken after the above-described bending strength evaluation was visually observed, and the number of cracks was measured. The number of cracks was expressed as an average value of three specimens.
The specific gravity of the specific gravity cured body was measured by the Archimedes method.

Dimensional change rate A test body having a width of 80 mm, a thickness of 15 mm, and a length (length in the extrusion direction) of 250 mm was cut out from the obtained molded body. The specimen was placed in a dryer and dried at 60 ° C. ± 3 ° C. for 24 hours. Two test marks (chips) were attached to the test piece with an epoxy resin at intervals of 100 mm. Thereafter, the distance (A) between the gauge points was measured with a strain gauge. The upper end of the test body was held at 3 cm below the water surface and immersed in water at 20 ± 3 ° C. for 24 hours. After 24 hours, the sample was taken out of the water, excess moisture was wiped off with a cloth, and the distance between the gauge points (B) was measured. The dimensional change rate at the time of water absorption was calculated using the following formula.
Dimensional change rate (%) = (B−A) / A × 100

Freezing and thawing resistance The molded body obtained was cut into a length of 100 mm in the extrusion direction as a test body and evaluated according to ASTM-C666 (Method B). Specifically, in-air freezing and thawing in water were defined as one cycle, and the state of the test specimens after performing 300 cycles was visually evaluated and ranked. In the air freezing condition, the test specimen was left in the air for 1.5 hours under the condition of ambient temperature −17.8 ° C. As for the melting conditions in water, the specimen was left in water for 1.5 hours under the condition of water temperature + 4.4 ° C.
○: No cracks or cracks occurred, no abnormality;
Δ: There are some cracks and cracks, but there is no practical problem;
X: There are cracks and cracks on the entire surface, and there are practical problems.

“PP fiber A” uses potassium lauryl phosphate as a surface treatment agent, and indicates a polypropylene fiber having a fiber diameter of 18 μm, a fiber length of 6 mm, and an aspect ratio of 333. The tensile strength is 360 MPa and the tensile modulus is 4.8 GPa.
“PP fiber B” uses a carboxyl-modified polyolefin-based low molecular weight material (an aqueous dispersion of “Yumex EM-100” manufactured by Sanyo Chemical Industries) as a fiber surface treatment agent, and has a fiber diameter of 18 μm and a fiber length of 6 mm. And polypropylene fibers having an aspect ratio of 333. The tensile strength is 360 MPa and the tensile modulus is 4.8 GPa.
“PVA fiber” refers to a PVA short fiber having a fiber diameter of 40 μm, a fiber length of 6 mm, and an aspect ratio of 150.

It is a schematic explanatory drawing which shows the 2-point loading simple bending test condition of a cement molding.

Explanation of symbols

  11: specimen, 12: fulcrum, 13: loading point.

Claims (6)

  Cement paste containing at least hydraulic cement, polypropylene fiber having a fiber length of 3 to 15 mm, a fiber diameter of 5 to 50 μm and an aspect ratio of 150 to 1000, a lightweight aggregate and water is extruded, and the resulting molded body is cured by autoclave. A hardened toughened cemented body having a specific gravity of 0.75 to 1.3 and a volume mixing ratio of polypropylene fibers of 2.0 to 10%.   2. The hardened toughened cement according to claim 1, wherein the lightweight aggregate is blended in an amount of 10 to 80 parts by weight with respect to 100 parts by weight of the hydraulic cement.   3. The hardened toughened cement according to claim 1, wherein the lightweight aggregate is blended in an amount of 30 to 70 parts by weight with respect to 100 parts by weight of the hydraulic cement.   4. The hardened tough cement material according to claim 1, wherein the lightweight aggregate is pearlite.   The hardened toughened cement body according to any one of claims 1 to 4, wherein the pulp is blended in an amount of 0.5 to 3 parts by weight based on 100 parts by weight of the hydraulic cement. The polypropylene fiber is surface-treated with a carboxyl group-modified polyolefin low molecular weight product in which an average of 1 to 10 carboxyl groups are introduced into a low molecular weight polyolefin having a number average molecular weight of 1000 to 6000. The tough cement hardened body according to any one of the above.

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