JP2524583B2 - Carbonation curing method of γ-type dicalcium silicate - Google Patents

Description

TECHNICAL FIELD The present invention relates to the production of a hardened concrete having a low alkali concentration, which is useful as a building or civil engineering material. More specifically, it is a further improvement of γ-type dicalcium silicate. The present invention relates to the carbonation curing method.

(Prior Art) Cocrete products, which have been used in large quantities, are
Since it is a hydrate of Portland cement or mixed cement, the alkali concentration in the hardened body becomes extremely high, and in the case of glass fiber reinforced concrete, it is unavoidable that the glass fiber deteriorates during service, and therefore the strength of the concrete Has a drawback that it significantly decreases.

γ-type dicalcium silicate (hereinafter referred to as “γ-C ₂ S”) is γ-2
It is a mineral represented by the chemical formula CaO · SiO ₂ , and when it is carbonated in the presence of water, it reacts and hardens according to the following formula.

γ-2CaO ・ SiO ₂ ＋ 2CO ₂ ＋ 2H ₂ O → 2CaCO ₃ ＋ SiO ₂ ＋ 2H ₂ O …… (1) This γ-C ₂ S hardened material has a significantly lower alkali concentration than conventional concrete, so Portland cement hardening It had no drawbacks like the body, and it has been attracting attention as an industrial material for a long time, but since its mass production technology has not been established in the past, research on applied technology using this has not been done so far. there were.

However, the present applicant has previously developed a mass production technique for producing γ-C ₂ S powder from an inexpensive pigment at a low cost, which is disclosed in Japanese Patent Application No.
-153154 was proposed. Therefore, in the future, it will be required to develop various applied technologies using γ-C ₂ S that can be mass-produced in this way. The present applicant has already made some proposals related to this, but in the actual situation, further development of an application technique relating to γ-C ₂ S is desired.

(Problems to be Solved by the Invention) When a γ-C ₂ S powder is kneaded with water to obtain a molded product, which is carbonized and cured to produce a cured product, sufficient time is taken at a high water saturation. If it is carbonized and cured over time, it is possible to obtain a considerably homogeneous cured product in the case of a thin molded product, but there is a problem in economic efficiency. Particularly in a member having a certain thickness, an uncured portion remains inside and a uniform member cannot be obtained. Even if carbonation curing is carried out at an appropriate water saturation, the corners and ridges become too dry, resulting in insufficient curing, making it extremely difficult to obtain a uniform and high-strength cured product. The present inventor has solved such problems and made it possible to uniformly carbonate the inside of the molded body as well as the outer surface, and to shorten the time required for the carbonation. It is intended to obtain a cured product of.

(Means for Solving Problems) The present invention is to form a molded product by adding water to a mixture of γ-type dicalcium silicate powder and sand or a mixture of these and fibers as an admixture or a reinforcing material. Then, in producing a cured product by carbonizing the γ-type dicalcium silicate of this molded product, the water content of the molded product molded from the raw material mixture is adjusted to 0.4 to 0.8 by the water saturation defined by the following formula. After that, it is subjected to carbonation curing, and the surface of this cured body is subjected to moisture absorption treatment during curing,
Further, it is a method for carbonation curing of γ-type dicalcium silicate, which is characterized by performing carbonation curing. The present invention will be further described below.

The γ-C ₂ S used in the present invention reacts with CO ₂ and hardens according to the reaction shown by the following formula. In this case, water acts as a catalyst, and a certain amount of water must be present in order for the carbonation reaction to proceed smoothly.

CO ₂ + H ₂ O → H ₂ CO ₃ …… (2) 2CaO ・ SiO ₂ ＋ 2H ₂ CO ₃ → 2CaCO ₃ ＋ SiO ₂ ＋ 2H ₂ O …… (3) The present inventor has studied the carbonation reaction of γ-C ₂ S. As a result of various experiments, even if the amount of water present here is too large or too small, the carbonation reaction of the above formula (3) does not proceed smoothly, and a high strength cured product is obtained. I confirmed that I could not get it. When further experiments were carried out, the water content of the molded body was 0.25 to 0.95 at the water saturation shown by the above formula, preferably the carbonation reaction proceeded smoothly when it was 0.4 to 0.8, and high strength was achieved in a short time. It was found to be expressed.

According to a conventional method, when the γ-C ₂ S powder is mixed with water and optionally a mixture containing other admixtures and / or reinforcing materials to form a molded body, the water saturation of the molded body is 0.4 to 0.8
Although it varies depending on the particle size distribution of the material used, it is usually obtained when 5 to 1% by weight of water is added at the time of molding. However, from the viewpoint of molding technology, when the amount of water added at the time of molding is as small as 5 to 10% by weight, the kneaded product has almost no fluidity and ordinary cast molding cannot be performed. There is a problem that you cannot do it. From the viewpoint of molding technology, in order to obtain a molded product having good moldability and a smooth surface, kneading water should be added in excess of the above-mentioned water saturation to increase the fluidity of the kneaded product, and to be cast. Is preferred. However, if the casting method is adopted, it is necessary to adjust the water content of the molded article by drying or the like so that the water saturation degree becomes 0.4 to 0.8, and then subject it to carbonation curing. Otherwise, a good cured product cannot be obtained as described above. However, in this case, it is not easy to uniformly dry the inside and the surface layer part of the molded body containing excess water to adjust the water content of the entire molded body to a water saturation of the above range, and often the surface layer part of the molded body is used. , Corners and edges were too dry. This tendency is unavoidable especially when the molded body is a thick plate. Therefore, if carbonation curing is carried out in this state, there is a problem that sufficient curing cannot be carried out in the surface layer portion of the molded body having a significantly reduced water saturation.

In order to avoid such a phenomenon, until now the water saturation of the molded body to be subjected to carbonation curing has been made slightly higher than an appropriate value in advance, and curing has been carried out for a long time, but with this, Productivity did not rise, and this resulted in higher costs. This will be further described with reference to experimental examples.

Example 60 ml of water was added to a mixture of 100 gr of γ-C ₂ S powder shown in Table 1, 100 gr of Toyoura standard sand and 4 gr of E glass fiber (13 mm chopped studland), and kneaded. Pour into the formwork and vacuum the bottom of the formwork to 10 x 10
It was molded into a plate shape of × 1 (cm). This molding is then placed at 20 ° C
It was put in the airtight type constant temperature box and was cured for various times while flowing carbon dioxide gas with a concentration of 99% or more. Thereafter, a 4 × 9 × 1 (cm) specimen was prepared for the cured body, and the three-point bending strength (7 cm span) and the bending strength were measured, and the carbonation rate of the sample was measured. Separately, when measured on a molded body immediately after molding which was molded in the same manner as above, the water saturation was 1.
It was 02.

The measurement results of the three-point bending strength and the carbonation rate of the cured product are shown in the attached figure. As is clear from this figure, long-term curing of 15 hours or more is required for the carbonation rate to exceed 50% and the bending strength to exceed 150 kg / cm ² . Moreover, it can be seen that the moisture content of the molded body is too large for almost 5 hours in the initial stage of curing so that curing is hardly performed.

In order to solve such a problem, in the present invention, the moisture saturation of the molded product is adjusted in advance so as to accelerate the start time of carbonation curing, and the surface of the molded product or the corner portion of the molded product is cured during curing. For example, water during the curing is sprayed on the part where the water easily dissipates at an early stage to absorb the moisture on the surface of the cured product,
It is intended to avoid insufficient carbonation and curing due to overdrying of this portion.

The γ-C ₂ S molded body that is carbonized and cured in the present invention is prepared by adding water to a mixture with γ-type dicalcium silicate powder or a mixture of these and fibers as an admixture or a reinforcing material, and adding water by a conventional method. Molded. The fiber as the reinforcing material used here may be carbon fiber, glass fiber, synthetic inorganic fiber, or organic fiber. As the molding method, any of a premix method, a spray suction method, and a direct spray method can be adopted. Next, the formed body is adjusted by a known means such as drying or vacuum suction so that the water content becomes 0.4 to 0.8 in terms of water saturation. If the water saturation is less than 0.4, the strength of the cured product after carbonization curing is insufficient, and if it exceeds 0.8, the carbonation curing time becomes long, which is not preferable.
The molded body whose water content has been adjusted as described above is then subjected to carbonation curing in a carbon dioxide gas atmosphere. At this time, C in the gas containing CO ₂
The O ₂ concentration is preferably 30 vol% or more. If this carbon dioxide curing is continued, the surface layer of the molded body, such as the surface and corners of the molded body, will dry faster than the inside of the molded body. Is subjected to a moistening treatment. The amount of water sprayed here is generally 0.25
~ 3.0 wt% is preferred. If it is less than 0.25% by weight, the moisture absorption effect is small, and if it exceeds 3.0%, it absorbs too much moisture and the time for the next carbonation and curing is prolonged, which is not preferable. The molded body that has been subjected to the moisture absorption treatment is subsequently carbonized and cured to obtain a final cured body.

By doing so, it is possible to carry out curing while maintaining the surface layer portion inside the molded body at a substantially uniform water saturation throughout the entire period of carbonation curing.

 The present invention will be further described with reference to examples.

Example 1. 30 ml of water was added to a mixture of 50 gr of γ-C ₂ S powder shown in Table 1, 50 gr of Toyoura standard sand and ₂ gr of E glass fiber (13 mm chop strand), and then the molding pressure was 100 kg / cm ^2. In 1
It was molded into a plate shape of 0 × 5 × 1 (cm). The molded body was then left in a room at 20 ° C. and a relative humidity of 50% for various times to adjust the water content. As a result, molded articles having various water contents were obtained.

Separately, the water content, the apparent porosity and the apparent specific gravity of the molded product molded in the same manner as above were measured, and thereby the water saturation of the molded product was measured. Also, the water saturation was calculated from the dry raw materials of various molded products having different water contents.

The various molded bodies whose water contents were adjusted as described above were placed in an airtight thermostat box at 20 ° C., and carbonation was carried out for various times while flowing carbon dioxide gas having a concentration of 99% or more into the box. After such curing for 2 hours and 4 hours, 1% by weight of water is sprayed on the surface of the molded body to absorb moisture, and then carbon dioxide is cured for 2 hours.
I went on time. Each cured body after curing was cut into a size of 10 × 1 × 0.3 (cm) from the edge of the cured body. Analyze the carbon content of this cut piece,
Thereby, the carbonation rate of the ridge portion of the γ-C ₂ S powder compact was measured. The three-point bending strength (7 cm span) of each cured product was measured. These are shown in Table 2. In the table, those without moisture absorption treatment and those with moisture saturation outside the range specified in the present invention are also shown as comparative examples.

As is clear from the results shown in Table 2, it is preferable that the water content of the molded product is adjusted to 0.4 to 0.8 in terms of water saturation. When the water saturation is less than 0.4, the strength of the cured product after carbonation curing is low, and even if moisture absorption treatment is performed during curing, the effect of improving strength is small. Further, if the water saturation exceeds 0.8, the curing time becomes long, which is not preferable. Table No.6, 7,
On the surface, corners and ridges of the effect bodies of Nos. 9 and 11 (comparative examples), brittle portions thought to have an insufficient carbonation reaction were observed. However, according to the present invention (No. 4, 5, 8 and 1
No such brittle portion was observed in the cured product of (0).

Example 2 In the same manner as in Example 1, a molded body having a moisture saturation of 0.45 and the same shape as in Example 1 was obtained. This was carbonized and aged for 4 hours in the same manner as in Example 1, and then the surface of the cured body was treated with water for a third time.
Various amounts were sprayed as described in the table. Continue to 2 more
Carbonated for an hour. A three-point bending strength test was carried out on the obtained material in the same manner as in Example 1, and the carbonation rate of the ridge was measured. The results are shown in Table 3.

As is clear from Table 3, the amount of water absorbed by the cured product in the present invention is preferably 0.25 to 3.0%. When the water content absorbed is less than 0.25% by weight, the effect of improving the properties of the cured product due to moisture absorption is small, and when it exceeds 3% by weight, curing cannot be completed in a short time to form a good cured product.

Example 3 Water was added to and mixed with a mixture of 1 part by weight of the γ-C ₂ S powder used in Example 1 and 1 part by weight of river sand having a diameter of 2 mm or less to prepare a mortar. A roving of E glass separately prepared together with this mortar was cut into 25 mm chopped strands and molded into a thin plate of 900 × 450 × 10 mm by a spray suction method. The amount of fiber added was 5%. Thereafter, this molded body was dried in a dryer at 60 ° C. until the water saturation of the molded body reached 0.50. Next, this was placed in an airtight constant temperature box and carbonized at a room temperature for 4 hours while flowing carbon dioxide gas having a concentration of 99% or more. After that, water was sprayed on the surface and edges of the molded body, and thereafter, carbon dioxide gas curing was performed for another 2 hours. The amount of water sprayed is 1.5
It was set to% by weight. About the cured product obtained after curing 250 x 50
3-point bending strength (200 mm span) by making a specimen of × 10 mm
Was measured. Its value was 275 kg / cm ² .

The sample measured above is crushed to 1 mm or less.
When 0 kg was placed in 70 ml of distilled water and stirred, and the pH value of the supernatant after 24 hours was measured, it was 10.3.

Example 4. To a mixture of 100 gr of γ-C ₂ S powder shown in Table 1, 100 gr of Toyoura standard sand and 4 gr of E glass fiber (13 mm chopped strand) was added 60 ml of water and kneaded, and then a mold equipped with a suction device. Pour this into the frame and vacuum suction the bottom of the formwork to 10 x
Plate-shaped moldings having various thicknesses were molded at 10 (cm). The molded product was dried in a dryer at 50 ° C. until the water saturation of the molded product reached 0.55. Then, this was placed in an airtight constant temperature box at 30 ° C. and aged for 5 hours while flowing carbon dioxide gas with a concentration of 99% or more. After that, remove this from the constant temperature box, and water on the surface 1.
5 wt% was sprayed and moistened, and carbon dioxide was aged for 2 hours. A 4 × 9 × 3 (cm) specimen was prepared from the cured cured body, and a three-point bending test (7 cm span) and a carbonation rate were measured. As a result, the bending strength was 143 kg / cm and the carbonation rate was 54%. Moreover, there was no uncured portion in the center of this cured product.

As a comparative example, a molded body similar to that described above was molded, placed in a similar airtight box, and subjected to similar carbon dioxide gas curing for 20 hours, and then a test piece of a similar size was prepared.
The point bending test and the carbonation rate were measured. The results are shown in Table 4.

(Effect of the invention) As described above, according to the present invention, it is possible to obtain a concrete having a high strength and a low alkali, which can be uniformly aged in all parts of a hardened body, and is widely used. It will be of interest to those skilled in the art.

[Brief description of drawings]

The figure shows the curing time, carbonation rate and bending strength (kg / c)
is a graph showing the relationship between m ^2).

Claims (1)

(57) [Claims] 1. A molded product is molded by adding water to a mixture of γ-type dicalcium silicate powder and sand or a mixture of these and fibers as an admixture or a reinforcing material, to mold the molded product.
In producing a cured product by carbonating type dilime silicate, the water content of the molded product molded from the raw material mixture is adjusted to 0.4 to 0.8 by the water saturation defined by the following formula, and then carbonized and cured, A method for γ-type dicalcium silicate carbonization and curing, characterized in that the surface of the molded article is subjected to moisture absorption treatment during the course of curing and further carbonation and curing.