JPH11246283A - Cement formed body - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a cement formed body excellent in mechanical strength and durability and having low water absorption by carbonating a cement hardened body having a specific water absorption. SOLUTION: The cement hardened body having <=20% water absorption is obtained by forming and hardening a cement hardening composition prepared by blending cement admixtures such as a coagulation retardant, a water reducing agent and a fluidizing agent with a self-hardening composition consisting essentially of cement, an inorganic filler, an organic filler, reinforcing fiber, water and the like. An alkali portion, particularly calcium portion in the cement hardened body is carbonated by infiltrating and diffusing carbon dioxide in a gaseous state, a liquid state or a super critical state into the cement hardened body. As a result, fine pores inside of the cement hardened body are filled by the carbonate and made dense and therefore, the water absorption is decreased, the infiltration of water into the cement hardened body is restricted and water resistance and long term weathering resistance are improved.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a cement molded article having excellent durability and low water absorption.

[0002]

2. Description of the Related Art When a cement hardened material comes in contact with water, its alkali component is eluted, and if this is continued for a long period of time, its mechanical strength is lost. Therefore, the surface of the hardened cement is coated to prevent water from entering, or as disclosed in JP-A-5-270882, a water-repellent diorganopolysiloxane is added to the hardened cementitious composition. A method has been proposed in which a non-ionic surfactant is used to uniformly disperse and cure the cured cement to improve the water resistance of the resulting cured cement.

However, in the method of coating the surface of a hardened cement body, when the method is used, since the surface is constantly exposed to the outside, there is a chance that the surface is oxidatively deteriorated, damaged, or worn. It is large, and once breakage occurs, water enters from that portion, and it has been difficult to maintain the water resistance of the hardened cement body for a long time. Also, the method of adding a water-repellent component to the entire cement hardened body has problems that the material cost is increased and the long-term durability of the material is short with respect to the cement hardened body.

[0004]

DISCLOSURE OF THE INVENTION The present invention has been made to solve the above-mentioned problem, and the carbonized hardened body is subjected to a carbonation treatment to structurally densify the hardened cement body to improve the durability. It is an object of the present invention to provide a cement molded article having an excellent low water absorption.

[0005]

Means for Solving the Problems The cement molded article of the present invention is characterized by being obtained by subjecting a hardened cement having a water absorption of not more than 20% to a carbonation treatment.

In the present invention, the hardened cement means a hardened cement hardening composition, and is usually obtained by molding and curing the hardening cement composition. The cement hardening composition is a self-hardening composition mainly composed of cement, an inorganic filler, an organic filler, a reinforcing fiber, water and the like, and has a setting retarder, a water reducing agent, a fluidizing agent as an auxiliary component. Various cement admixtures, such as an agent, may be blended.

[0007] The cement hardening composition is prepared by mixing and kneading the above main components and subcomponents. The method of mixing and kneading is not particularly limited as long as they are uniformly dispersed. Mixers such as mixers, Erich mixers and kneaders are exemplified.

[0008] The method for molding the cement hardening composition is not particularly limited, and includes, for example, casting, pressing, and extrusion molding. The curing method is also not particularly limited. A method of aging in a heating / humidifying atmosphere may be used.

The cement is not particularly limited. For example, plain cement such as ordinary Portland cement, special Portland cement, alumina cement, Roman cement, etc .; special cement such as acid-resistant cement, fire-resistant cement, water glass cement; gypsum, lime And air-hardened cements such as magnesia cement. Of these, Portland cement and alumina cement are preferably used in terms of mechanical strength and water resistance.

The inorganic filler is not particularly limited as long as it does not dissolve in water and does not significantly impair the hardening reaction with cement and the function of other materials. Aggregate, fine aggregate and other commonly used inorganic fillers are used. Inorganic powder means, for example, aggregate for cement mortar such as silica sand, silica stone powder, river sand; mixed material for mixed cement such as blast furnace slag, fly ash, silica fume, bentonite; sepiolite, wollastonite, mica, talc , Calcium carbonate, etc., and at least one of them can be used.

The organic filler is not particularly limited as long as it does not dissolve in water and does not significantly inhibit the hardening reaction with cement and the function of other materials. For example, pulp, wood flour, wood chips, US pine wood chips (Rice pine chips), synthetic fiber powder and the like.

The reinforcing fiber is not particularly limited, and may be any of organic fibers and inorganic fibers, for example, organic synthetic fibers such as vinylon, polypropylene, acrylic, rayon, polyamide, polyethylene glycol terephthalate, and aramid; cotton, hemp, and wood. Natural organic fiber such as hair; carbon fiber,
Examples thereof include inorganic fibers such as glass fiber, potassium titanate fiber, tyrano fiber, and stainless steel fiber, and one or more of these may be used.

The carbonation treatment means a treatment in which an alkali component, particularly a calcium component, in the hardened cement is carbonated. The method of the carbonation treatment is not particularly limited.
Gas, liquid, supercritical state, etc., by infiltrating and diffusing carbon dioxide into the cement hardened body, carbonizing the alkali component or adding a component that generates carbon dioxide or carbonate ion in the cement hardenable composition in advance There is a way to put. Among these, gaseous carbon dioxide and carbon dioxide in a supercritical state are preferable because they have high diffusivity and can highly densify a cured cement body.

In the carbonation treatment of the cement molding of the present invention, the water absorption of the hardened cement before carbonation treatment must be 20% or less. The water absorption is described in the evaluation method described below. If this exceeds 20%, the voids and pores present in the hardened cement become too large in both size (size) and quantity, These exceed the limit of filling or densification with a water-insoluble carbonate by carbonation treatment, and it is difficult to reduce the water absorption.
The lower limit of the water absorption is not particularly limited,
% Is very difficult in practice.

The method for adjusting the water absorption of the hardened cement body is not particularly limited, and can be achieved by changing the water-cement ratio of the hardenable cement composition, the forming method, and the like. In order to harden the cement, only water necessary for hydration of the cement is required, and by reducing other excess water, the water absorption of the hardened cement can be reduced. Therefore, depending on the amount of the filler added, by setting the water-cement ratio to about 20 to 40%, a hardened cement body having a relatively low water absorption can be obtained. However, in practice, if the water-cement ratio is too small, the fluidity of the cement-curable composition decreases, and not only molding becomes difficult, but also hydration of the cement becomes insufficient and the cement In some cases, it becomes difficult to develop the mechanical strength of

[0016]

The cement molded article of the present invention is obtained by subjecting a hardened cement body having a specific water absorption or lower to a carbonation treatment, so that pores and voids existing therein are densely filled with a carbonate to make the cement insoluble. As a result, it becomes a cement molded body with excellent durability and low water absorption, and as a result, alkali does not elute,
The mechanical strength is not easily reduced.

[0017]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in more detail by way of examples, but the present invention is not limited to only the examples listed here.

Examples 1 to 3 and Comparative Example 1 (1) Preparation of hardened cement Normal Portland cement (made by Chichibu Onoda Cement Co.)
100 parts by weight, 50 parts by weight of silica sand, 1 part by weight of hydroxypropylmethylcellulose (having a viscosity of 30,000 cps of a 2% by weight aqueous solution at 20 ° C.) and 5 parts by weight of a polypropylene fiber having a fiber length of 6 mm were mixed. After further mixing with water in a proportion, the mixture was put into a mixer and kneaded uniformly to obtain various cement curable compositions. Thereafter, the above-mentioned cement-curable composition was pressed at 100 kg /
The mixture was pressurized at a pressure of ² cm ² and subjected to steam curing at 60 ° C. and 90% RH for 12 hours to obtain a hardened cement body having a thickness of 5 mm.

(2) Carbonation treatment of hardened cement body The hardened cement body obtained in the above (1) is placed in an autoclave, and is heated at a temperature of 70 ° C. and a pressure of 80 in a carbon dioxide atmosphere.
The mixture was left at kg / cm ² for 1 hour to carry out a carbonation treatment to obtain a cement molded body having a low water absorption.

(3) Evaluation The physical properties of the cement molded article having a low water absorption obtained in the above (2) were evaluated based on the evaluation methods described later, and are summarized in Table 1.

Comparative Examples 2 and 3 Cement molded bodies were prepared in the same manner as in Examples 1 to 3 except that the carbonation treatment was not performed at the water addition amounts shown in Table 1 and the physical properties thereof were evaluated. Table 1 summarizes the results.

[0022]

[Table 1]

The present invention will be described below with reference to the results shown in Table 1. In Example 1 and Comparative Example 2, the composition of the cement molding was the same, but the former was subjected to carbonation treatment, and the latter was not. The results of measuring the pore size distribution of both are shown in FIG. 1 and FIG. 2, and by performing carbonation treatment, the intrusion volume (unit weight of the cement molded body) was obtained over a wide range of the pore size. The volume of pores and voids contained per unit; cc / g) is significantly reduced, and the water absorption is also reduced from 16% to 9%.

In the comparison between Example 2 and Example 3, the amounts of water added to the cement hardening composition were 35% and 30%, respectively.
%, The water absorption can be lowered by reducing the amount of water to 10% and 8%, respectively. But,
In Comparative Example 3 in which the water-cement ratio was further reduced, the fluidity of the cement-curable composition was lost, and molding was impossible.
When the hardened cement of Examples 2 and 3 was further subjected to a carbonation treatment, the water absorption was extremely reduced to 6% and 5%, respectively. In addition, cement molded bodies with reduced water absorption are
The retention of bending strength before and after the water resistance test increased.

In Comparative Example 1, it was found that even if the hardened cement having a high water absorption exceeding the limit was subjected to carbonation, the improvement in water absorption was extremely small.

Evaluation method (a) Water absorption rate A hardened cement body before carbonation treatment and a hardened water-resistant cement body after the treatment were cut to prepare a measurement sample, and JIS A
Each water absorption was measured in accordance with 5209.

(B) Strength Retention A test sample was prepared by cutting a cured cement body, immersed in water for 24 hours, and then dried at 50 ° C. for 24 hours. A water resistance test was repeated 20 times. The bending strength was measured before and after the water resistance test in accordance with JIS A 1408, and the ratio of the retention of the bending strength after the water resistance test to the initial bending strength before the water resistance test was calculated.

(C) Pore size distribution The pore size distribution of the cement molded product of Example 1 and the cured cement of Comparative Example 2 was measured using a porosimeter.
The results are shown in FIGS.

[0029]

According to the present invention, since the pores inside the molded body are filled with carbonate and densified by the carbonation treatment, the cement molded body of the present invention has a reduced water absorption, and the cement cured body has The penetration of water into water is restricted, and the water resistance is improved. Therefore, various cement secondary products such as roofing materials, exterior wall materials, and bathroom materials according to the present invention are excellent in long-term weather resistance and durability, and have stable mechanical strength, so that their utility value is extremely high. large.

[Brief description of the drawings]

FIG. 1 is measurement data of pore size distribution of a cement molded body of Example 1.

FIG. 2 is measurement data of pore size distribution of a cured cement body of Comparative Example 2.

Claims (1)

[Claims] 1. A cement molding obtained by subjecting a hardened cement having a water absorption of 20% or less to a carbonation treatment.