JP2000143326A - Low-alkali hydraulic material - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a hydraulic material capable of maintaining alkalinity for a long period of time. SOLUTION: This hydraulic material is obtained by adding blast furnace water-granulated slag powder and silica fume to a low calcium type cement clinker comprising hauyne (3CaO.3Al2O3.CaSO4), belite (2CaO.SiO2) and ferrite (4CaO.Al2O3.Fe2O3) phase and calcium sulfate as main components. The amount of the total calcium sulfate is 10-50 wt.% calculated as anhydride (CaSO4) based on the total amount of the cement clinker and the blast furnace water- granulated slag. The calcium content based on silicate content is (CaO-2SO3)/ SiO2<1.0 (molar ratio). Water in which a hardened material is immersed has low alkalinity reducing pH with time.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a method for producing an aqueous solution which has a very low alkali elution and has a high pH even when immersed in water for a long time.
The present invention relates to a cementitious hydraulic material having low alkalinity and a low alkalinity. The hydraulic material of the present invention is used as a cement material that requires low alkalinity, such as a radioactive waste solidification treatment material or a material for a radioactive waste solidified buried disposal facility.

[0002]

[Technical Background] The amount of various radioactive wastes discharged from various nuclear facilities such as nuclear power plants is steadily increasing. Of these radioactive wastes, those of medium and low levels are placed in a radioactive waste treatment container such as a drum, solidified, sealed and made into a final form suitable for underground burial. The cement paste or cement mortar mainly used at present as the solidifying material is usually Portland cement.

[0003] However, the solidified radioactive waste material made of ordinary Portland cement has a problem in long-term safety. That is, since ordinary Portland cement is a highly alkaline material, it has become clear that metallic aluminum contained in radioactive waste reacts in a highly alkaline environment to generate hydrogen gas. Due to the generation of the hydrogen gas, there is a concern that the pressure in the processing container increases, the solidified structure is destroyed, and the performance of confining the radioactive material is impaired.

[0004] The problem caused by such high alkalinity is not limited to the solidified material. That is, while solidified low-level radioactive wastes are solidified in drums and the like, they are buried underground.In this burial disposal facility, fillers for filling voids between the solidified bodies or the facility itself are used. Cement concrete is used as a structural body. In addition, high-level radioactive waste is vitrified in a metal container called an overpack and disposed of in a deep underground facility.In this high-level waste disposal facility, cement concrete is used as a structure. I have. Even in such a disposal facility, when ordinary Portland cement is used, the following problems are feared due to its high alkalinity. One of them is the adverse effect on bentonite, which is used at the middle and low level outside the facility due to the water stopping function. That is, it has been pointed out that bentonite reacts with calcium ions and the like eluted from the cement, and its water stopping function is reduced. Bentonite is also located around the overpack in high-level waste disposal facilities, and there are concerns about similar problems. Corrosion of high-level solidified metal containers is also one of the problems expected in a highly alkaline environment caused by cement.

[0005]

2. Description of the Related Art Under the circumstances described above, there is a demand for the development of a low alkaline hydraulic material for disposal of radioactive waste. A great deal of research and development has been conducted on the development of hydraulic materials having low alkalinity.
Many of the reported low alkaline cement compositions are:
Calcium hydroxide Ca is one of the main causes of high alkalinity
Although it is intended to suppress the production of (OH) _2, the effect of reducing alkalinity is not sufficient even with these cement compositions. According to the experimental results of the present inventors, to further reduce the alkalinity of cement, it is not enough to suppress the production of calcium hydroxide, and it is necessary to design a material in consideration of other hydration products. is there.

[0006] As a low alkalinity cement composition, many compositions containing calcium aluminate as a main component have been reported so far (Japanese Patent Application Laid-Open No. 1-208354). However, water containing calcium aluminate as a main component has been reported. It has become apparent that hard materials have insufficient low alkalinity for some applications. In addition, it has been pointed out that calcium aluminate shows a quick setting property by water injection and has a problem in practicality. In general, the performance required for a low-alkali hydraulic material requires that the workability during construction be good in addition to low alkalinity. In other words, it is necessary to secure a certain fluidity and a usable life with respect to a change in the working temperature and to adjust the curing time, and it is essential to develop an appropriate strength after curing.

[0007]

DISCLOSURE OF THE INVENTION The present invention solves the above-mentioned problems in the conventional low alkaline cement composition, has good workability and excellent strength, and has very little alkali elution over a long period of time. Therefore,
It is an object of the present invention to provide a low-alkali cementitious hydraulic material in which the pH of immersion water does not increase even if the cured body is immersed in water for a long time, but rather gradually decreases.

[0008]

That is, the present invention relates to the following low alkaline hydraulic material. (1) as mineral composition, Auin _{(3CaO · 3Al 2 O 3 ·} CaS
O ₄ ), belite (2CaO ・ SiO ₂ ), ferrite phase (4CaO ・ Al ₂ O
₃・ Fe ₂ O ₃ ), and a cementitious hydraulic material obtained by adding blast furnace slag powder and silica fume to a low calcium cement clinker containing calcium sulfate as a main component, and the total calcium sulfate amount is the same as that of the cement clinker. The total amount of the granulated blast furnace slag is 10 to 50% by weight in terms of anhydrous salt (CaSO ₄ ), and the calcium content with respect to the silicic acid content is (CaO-2SO ₃ ) / SiO ₂ <1.0 (molar ratio). A hydraulic material characterized by having a low alkalinity in which the pH of immersion water of a cured product decreases with time.

[0009] In the low alkaline hydraulic material of the present invention, the amounts of silica fume and blast furnace slag powder are specifically as follows. (2) The above (1), wherein the blending amount of the silica fume is 3 to 40% by weight based on the whole hydraulic material, and the blending amount of the granulated blast furnace slag is 10 to 300% by weight based on the cement clinker. Low alkaline hydraulic material.

The degree of alkali in the low alkaline hydraulic material of the present invention is specifically as follows. (3) The pH of the cured product immersion water is 10.
The low alkaline hydraulic material according to the above (1) or (2), which has a value of 5 or less.

Further, the low alkaline hydraulic material of the present invention includes the following aspects. (4) The low alkaline hydraulic material according to (1), (2) or (3), wherein gypsum is added together with the blast furnace slag powder and silica fume in a range of the molar ratio of calcium to silicic acid. (5) The low alkaline hydraulic material according to any one of (1) to (4), which is used as a solidification material, a filler, or a material for a treatment facility of radioactive waste.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described specifically with reference to embodiments. The low alkaline hydraulic material of the present invention,
As mineral composition, Auin _{(3CaO · 3Al 2 O 3 ·} CaSO 4), belite (2CaO · SiO _2), a ferrite phase _{(4CaO · Al 2 O 3 ·} Fe
₂ O ₃ ), and a cementitious hydraulic material obtained by adding a blast furnace slag powder and silica fume to a low-calcium cement clinker containing calcium sulfate as a main component, wherein the total calcium sulfate amount is controlled by the cement clinker. Salt and blast furnace granulated slag
O ₄ ) in terms of 10 to 50% by weight, and the calcium content relative to the silicic acid content is (CaO-2SO ₃ ) / SiO ₂ <1.0.
(Molar ratio), thereby realizing low alkalinity in which the pH of the immersion water of the cured product decreases with time.

In ordinary Portland cement, its main minerals alite (3CaO.SiO ₂ ) and belite (2CaO.SiO ₂ ) are used.
₂ ) When hydration hardens, a gel-like substance (amorphous calcium silicate hydrate: CaO-SiO _2-
Calcium hydroxide is generated together with H ₂ O and CSH gel), and the calcium hydroxide is one of the causes of high alkalinity. The CSH gel is usually CaO / Si
It has a high calcium type composition having an O ₂ ratio of 1.5 or more, and this CSH gel also causes high alkalinity.

According to the present invention, a low calcium cement clinker having the above-mentioned mineral composition is used, and the molar ratio of calcium to silicic acid is controlled within a certain range by adjusting the amounts of blast furnace slag powder and silica fume to be added thereto. In addition, while suppressing the formation of calcium hydroxide, which is a cause of high alkalinity, and a CSH gel having a high calcium type composition for a long period of time, a low calcium type hydrate is selectively generated. .

[0015] Here, the low-calcium Form hydrate ettringite, gehlenite hydrate _{(2CaO · Al 2 O 3 ·} SiO 2 · 8H
₂ O), C—S—H gel with a CaO / SiO ₂ molar ratio of 1.0 or less
Low calcium type CSH gel), alumina (Al ₂ O ₃ ) hydrated gel, ferrite (Fe ₂ O ₃ ) hydrated gel and the like. In the hydration reaction of cement, alumina hydrated gel and ferrite hydrated gel play an important role in the formation of low calcium type CSH gel, and such ultra-low solubility ettringite, ultra-low solubility and Due to the formation of low alkalinity gerenite hydrate and low calcium type CSH gel mainly, when the cured product is immersed in water for a long time, the pH of immersion water
Can be obtained with a low alkaline cementitious hydraulic property that gradually decreases with time.

As described above, the cement clinker used in the present invention is erwin (3CaO.3Al ₂ O ₃ .CaSO ₄ ),
Belite (2CaO ・ SiO ₂ ), ferrite phase (4CaO ・ Al ₂ O ₃・ Fe ₂
O ₃ ) and a low calcium cement clinker containing calcium sulfate as a main component. The alite (3CaO.SiO ₂ ) and aluminate phase (3CaO.Al ₂ O ₃ ) contained in ordinary Portland cement are not preferred because of their high calcium content, and are preferably kept as small as possible. It should be noted that instead of the low calcium cement clinker as described above, a boltland cement clinker such as ordinary Portland cement, moderate heat Portland cement or early-strength Portland cement is used, or if these are mixed with the low calcium cement clinker, the strength will be increased. Although expression is enhanced, a high calcium hydrate is formed, and the desired low alkalinity cannot be achieved.

The preferred mineral composition ratio of the low calcium cement clinker is as follows. Auin _{(3CaO · 3Al 2 O 3 ·} CaSO 4): 20~70 wt% belite (2CaO · SiO _2): 10~40 wt% ferrite phase _{(4CaO · Al 2 O 3 ·} Fe 2 O 3): 3~ 30% by weight of calcium sulfate (CaSO _4): 5~30 wt% aluminate phase _{(3CaO · Al 2 O 3)} : 5 wt% or less

Erwin (3CaO.3Al ₂ O ₃ .CaSO ₄ ) is necessary for producing an appropriate amount of ettringite, and its amount is suitably 20 to 70% by weight. Outside this range, it is not appropriate from the viewpoints of dimensional stability (expandability) of the molded body and ensuring workability during construction. Belite (2CaO.SiO ₂ ) is important for developing strength, and its amount is suitably from 10 to 40% by weight. If the amount is less than this, the strength developability is poor, and if it is more than this, the alkalinity cannot be reduced. Ferrite phase
(4CaO.Al ₂ O ₃ .Fe ₂ O ₃ ) has a function to promote the stable formation of clinker, especially the growth of belite grains, but if its amount ratio is less than 3% by weight, its effect is small, and 30% by weight. If the temperature exceeds the limit, melting occurs during clinker firing, and the temperature cannot be raised to a temperature at which sufficient crystal growth proceeds. Calcium sulfate (CaS
O ₄ ) suppresses the transition of belite from β phase to γ phase during clinker firing, preventing so-called dusting,
If the amount ratio is less than 5% by weight, the effect of stabilization is small,
Even if it exceeds 0% by weight, the effect does not increase. Since the aluminate phase (3CaO.Al ₂ O ₃ ) causes rapid setting, it is preferably as small as possible, and is suitably less than 5% by weight. The alite found in ordinary cement clinker is not substantially contained in the low calcium cement clinker of the present composition because it is chemically unstable.

The low alkaline hydraulic material of the present invention contains a certain amount of silica fume. Silica fume has an action of further fixing calcium content due to its high pozzolanic reactivity and further suppressing alkalinity. The amount of silica fume to be blended is suitably from 3 to 40% by weight based on the entire low alkaline hydraulic material. If it is less than 3% by weight, the effect of reducing alkalinity by the pozzolanic reaction is insufficient. On the other hand, if the content exceeds 40% by weight, the fluidity is reduced due to the fine particle size of the silica fume, and the workability is greatly reduced, which is not preferable.

The low alkaline hydraulic material of the present invention contains a predetermined amount of blast furnace slag powder together with silica fume. By containing an appropriate amount of blast furnace slag powder, it is possible to promote and enhance medium- to long-term strength development while maintaining low alkalinity. The blast furnace slag powder reacts with calcium hydroxide generated from cement to promote its disappearance by hydration reaction based on its latent hydraulic property, and reacts with ettringite to form a low calcium type CSH gel. In addition to not only contributing to the development of medium- to long-term strength, it also exerts the effect of lowering salt elution.

The amount of the blast furnace slag powder is suitably from 10 to 300% by weight based on the low calcium cement clinker. If the amount is less than 10% by weight, the desired effect is not sufficiently exerted. If the amount is more than 300% by weight, the strength development becomes slow, and the short-term strength is not sufficiently developed, which is not preferable in practical use.

Depending on the composition of the low calcium cement clinker, it is advisable to add gypsum to supplement the SO ₃ amount. The gypsum may be any of dihydrate, hemihydrate and anhydrous, but anhydrous gypsum is desirable for controlling the hydration rate. In the hydration reaction, the calcium sulfate component reacts with the alumina component or the calcium component supplied from the clinker and the blast furnace slag powder to form ettringite, thereby reducing the amount of calcium hydroxide and achieving short-term strength development. Contributes and further suppresses drying shrinkage.

The low alkaline hydraulic material of the present invention has a total calcium sulfate content of 10 to 50 in terms of anhydrous salt (CaSO ₄ ) based on the total amount of the cement clinker and the granulated blast furnace slag.
% By weight, and the calcium content relative to the silica content is (C
a _{aO-2SO 3) / SiO 2} <1.0 ( molar ratio). The silica fume, the blast furnace slag powder and the gypsum are used in the ranges of the above-mentioned amounts, respectively, and are used in the range of the total calcium sulfate and the molar ratio of calcium to silicic acid.

The total amount of calcium sulfate is based on the total amount of the cement clinker and the granulated blast furnace slag, and anhydrous salt (CaSO ₄ )
If it is less than 10% by weight, the desired effect cannot be sufficiently exhibited. If calcium sulfate alone in the clinker is not sufficient, it is necessary to add gypsum to make up the shortage. On the other hand, if the amount exceeds 50% by weight, depending on the curing conditions, ettringite may be undesirably formed to cause expansion cracks or the like due to abnormal generation of ettringite.

In the above low calcium cement clinker, the molar ratio of calcium to silicic acid (CaO-2SO ₃ )
When / SiO ₂ is larger than 1.0, the above molar ratio is adjusted to less than 1.0 by adding silica fume or the like. The above molar ratio of ordinary Portland cement is approximately 2.
9, and the molar ratio of the hydraulic material of the present invention is about 1
/ 3, which is much smaller.

It should be noted that in the combination of the above components, ettringite is formed at an early stage, hydration proceeds while alumina hydrated gel coexists, and monosulfate hydrate is formed.
(3CaO.Al ₂ O ₃ .CaSO ₄ .12H ₂ O) is to be largely suppressed, and then hydration by calcium silicate is to occur. As a result, the hydration reaction proceeds while maintaining low alkalinity immediately after water injection, and calcium hydroxide generated by hydration of calcium silicate is also consumed. As a result, the resulting C—S—H gel is also of a low calcium type, and the cured product is maintained at a low alkalinity and has sufficient strength.

The alkalinity of the hydraulic material of the present invention is characterized in that as a result of the above component adjustment, when the cured product is immersed in water, the pH of the immersion water gradually decreases over time. Specifically, p
H is 10.5 or less on a 300 day immersion basis. By the way,
The pH of immersion water of ordinary Portland cement is about 12.5.
Before and after, this pH hardly changes during the soaking period of several years. In addition, although the gypsum and the blast furnace slag powder are added to the low alkaline cement, the pH of the immersion water is about 11 to 12 even though it has already been proposed, the pH hardly changes during the immersion period, and the pH gradually decreases. What you do is not known. On the other hand, in the hydraulic material of the present invention, as shown in Examples described below, the pH gradually decreases during the lapse of 300 days after immersion, and as an example, the pH after immersion for 300 days drops significantly to 10.5 or less. I do.

The setting and hardening time of the hydraulic material of the present invention is governed mainly by the formation of ettringite by the hydration reaction of Irwin (3CaO.3Al ₂ O ₃ .CaSO ₄ ). The curing time can be adjusted by adding an appropriate setting retarder or setting regulator accordingly. As setting retarders or regulators, organic acids such as citric acid and gluconic acid and salts thereof, and inorganic compounds such as zinc oxide and magnesium silicofluoride are known, and these can be used in the present invention. . The addition amount of these is suitably 0.1 to 10% by weight based on the hydraulic material,
Adjustment for about 20 to 300 minutes is possible depending on the amount of addition. If the addition amount is larger than this, it is not preferable because curing failure may occur. It should be noted that the lower the construction temperature, the smaller the amount of use.

The low alkaline hydraulic material of the present invention can be used as ordinary mortar or concrete by kneading with an aggregate such as sand or gravel if necessary. In addition, various admixtures such as a water reducing agent, an AE agent, a high-performance AE water reducing agent, and a thickener can be used. The cement clinker may have the same particle size as ordinary cement powder, and silica fume, blast furnace slag powder and gypsum may have the particle size generally used.

[0030]

EXAMPLES The present invention will be specifically described below with reference to examples. Note that these examples do not limit the scope of the present invention. Examples and Comparative Examples A hydraulic material was prepared by using a cement clinker having a mineral composition shown in Table 1 and adding silica fume, blast furnace slag powder and gypsum in the amounts shown in Table 1. The particle size of the cement clinker is 3200 to 3750 cm ² / g of Blaine specific surface area, and the particle size of the granulated blast furnace slag is about 4300
cm ² / g (commercially available from Nippon Steel Kimitsu Works) and gypsum are type II anhydrous gypsum, and the particle size is about 7000 cm ² / g of Blaine specific surface area. The mortar flow value, the compressive strength of 7 to 91 days and the pH of immersion water were measured for the hydraulic material. The results are shown in Tables 2 and 3.

(A) The flow value is based on Japanese Industrial Standards (JIS R
5 hitting flow was measured according to 5201-1992). (B) The pot life was measured using a JIS coagulation tester. (C) In the pH test of the immersion water, the pH value from 7 days to 91 days after the paste kneaded at a water / powder ratio of 40% was sealed at 20 ° C. for 9 hours, and the cured product was pulverized to 125 to 250
μm part is immersed in 10 times the volume of ion-exchanged water,
The value was measured. The number of days was counted from the day of immersion. The value of “Ball Mill” in Table 3 indicates the cement composition powder and its 10
This is the pΗ value after forced hydration while rotating a year with double volume ion-exchanged water in a ball mill. In addition, unhydrated clinker minerals and granulated blast furnace slag were not detected in the sample after ball mill hydration, and the sample was in a state close to fully hydrated.

As shown in Table 2, the samples of the present invention (Example N
In any of O.1 to 6), the pH of the water in which the cured product was immersed was 11.5 or less, the pH gradually decreased after immersion, and the pH after 300 days was 10.5 or less. On the other hand, Comparative Example 1 shows relatively low alkalinity, but has a pΗ value of 11.5 or more, and does not realize sufficiently low alkalinity. Further, Comparative Example 3 exhibited high alkalinity which greatly exceeded pH 12. In Comparative Example 2, although the pH was low, the pot life was short, the fluidity was insufficient, and the compressive strength was significantly low, which was not suitable for practical use.

Further, as shown in Table 3, the hydraulic material of the present invention was compared with Comparative Example 2 of ordinary Portland cement in all evaluation items of fluidity, pot life and mortar compressive strength. The values showed little difference, and it was confirmed that the material was suitable for practical use in terms of workability and strength.

[0034]

[Table 1]

[0035]

[Table 2]

[0036]

[Table 3]

[0037]

The hydraulic material of the present invention differs from ordinary Portland cement and the like in the hydration reaction of cement.
Since the low calcium hydrate is selectively produced, the alkalinity is low, and the alkalinity is kept low for a long period of time. In addition, it has the same workability as ordinary Portland cement and is excellent in developing strength. Therefore, it is most suitable as a solidification material or a filler for the treatment of radioactive waste or a structural material of a treatment facility.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) // (C04B 28/14 B09B 3/00 301R 7: 345 18:14 22:06) (72) Inventor Hideki Fujita 2-1-1, Tsukimi-cho, Kumagaya-shi, Saitama Pref. Inside OTEC Co., Ltd. (72) Inventor Satoshi 2-1-1, Tsukimi-cho, Kumagaya-shi, Saitama Pref. Otec Co., Ltd. (72) Michihiko Hironaga, inventor 1646 Abiko, Abiko-shi, Chiba F-term in the Central Research Institute of Electric Power Industry (reference) 4D004 AA50 AB09 BA01 BA02 BB03 CA45 CC13 4G012 PA29 PB04 PC13 PD03

Claims (5)

[Claims] The mineral composition is erwin (3CaO.3Al ₂
O ₃ · CaSO _4), belite (2CaO · SiO _2), the ferrite phase (4Ca
O.Al ₂ O ₃ .Fe ₂ O ₃ ), and a cementitious hydraulic material obtained by adding blast furnace slag powder and silica fume to a low-calcium type cement clinker containing calcium sulfate as a main component. Is anhydrous salt (CaSO ₄ ) based on the total amount of the above cement clinker and granulated blast furnace slag
10 to 50 wt% in terms of and a calcium content for silicate content _{(CaO-2SO 3) / SiO} 2 <1.0 ( mole ratio), pH of the cured body soaking water decreases over time A hydraulic material having low alkalinity. 2. The composition according to claim 1, wherein the amount of silica fume is 3 to 40% by weight based on the whole hydraulic material, and the amount of granulated blast furnace slag is 10 to 300% by weight based on the cement clinker. The low alkaline hydraulic material according to the above. 3. The low alkaline hydraulic material according to claim 1, wherein the pH of the hardened body immersion water is 10.5 or less on the basis of 300 days of immersion. 4. The low alkaline hydraulic material according to claim 1, wherein the gypsum is added together with the blast furnace slag powder and the silica fume in a molar ratio of calcium to silicic acid. 5. The low alkaline hydraulic material according to claim 1, which is used as a solidifying material, a filler or a material for a treatment facility of radioactive waste.