JP4843271B2 - Cement composition for inhibiting alkali silica reaction and cement-containing composition - Google Patents

Description

  The present invention relates to a cement composition for suppressing alkali silica reaction and a cement-containing composition containing the same.

  Cement-containing compositions such as mortar and concrete generally include a cement composition and an aggregate. Depending on the aggregate used, such concrete structures, etc., penetrated from the outside, such as reactive silica in the aggregate, alkali contained in cement, aggregate, other admixtures, etc. It is known that abnormal expansion may occur due to a reaction with alkali, resulting in destruction. This reaction is called an alkali silica reaction or an alkali aggregate reaction. In order to suppress this, the following measures have been taken by the Ministry of Land, Infrastructure, Transport and Tourism in 2002 (see Non-Patent Document 1).

  That is, in this measure, the concrete used for the structure must be checked for any one of the following three measures in order to suppress the alkali silica reaction. These three measures include (a) the suppression of the total amount of alkali in the concrete, (b) the use of mixed cement and the like having an inhibitory effect, and (c) the use of aggregate that is recognized as safe.

  Among them, the measure (c) has become difficult to adopt since the acquisition of aggregate resources has become difficult in recent years. For this reason, the importance of the measure (a) or (b) is increasing. However, for example, in an environment where alkali penetrates into the structure from the outside, the measure (a) may be insufficient depending on the conditions. In such a case, it is necessary to take the countermeasure (b).

Usually, in the countermeasure of (a), a mixed cement obtained by mixing a predetermined amount of a mixed material such as blast furnace slag fine powder with cement is mainly used. In addition, lithium compounds are known as other materials that suppress the alkaline silica reaction. Examples of using these lithium compounds include a method of injecting lithium compounds into concrete (see Patent Document 1), concrete. A method using a lithium compound that has a small influence on the fluidity of the liquid (see Patent Document 2) and the like are disclosed.
"Measures for suppressing alkali-aggregate reaction", [online], August 1, 2002, Ministry of Land, Infrastructure, Transport and Tourism, [Search June 1, 2005], Internet <URL: http: //www.mlit.go .jp / kisha / kisha02 / 13 / 130801_.html> JP 2002-173380 A JP 2004-196666 A

  However, when the above-mentioned blast furnace slag fine powder is used, problems such as a decrease in initial strength of the resulting structure, cracks due to temperature changes, and cracks due to drying shrinkage may occur. Moreover, since the above lithium compound is very expensive, the cost for suppressing alkali-silica reaction has become too large. Thus, when using a mixed material, instead of being able to suppress the alkali silica reaction, new inconveniences tend to occur.

  Then, this invention is made | formed in view of such a situation, and it aims at providing the cement composition which can suppress an alkali silica reaction, without adding a mixing material. Moreover, it aims at providing the cement containing composition containing this cement composition.

  In order to achieve the above object, the present inventors have intensively studied the influence of various cement compositions on the alkali silica reaction, and found that the chemical composition of the cement is related to the expansion rate due to the alkali silica reaction. The present invention has been completed.

That is, the cement composition for suppressing alkali silica reaction of the present invention is a cement composition containing cement clinker and gypsum, and has a composition containing SiO ₂ , Al ₂ O ₃ and Fe ₂ O ₃ , SiO ₂ / (Al ₂ O ₃ + Fe ₂ O ₃ ) is 2.5 or less in terms of mass ratio.

The Portland cement generally used as a conventional cement composition is produced by adding gypsum to a Portland cement clinker and grinding. Portland cement _{clinker, 3CaO · SiO 2 (C 3} S), 2CaO · SiO 2 (C 2 S), 3CaO · Al 2 O 3 (C 3 A) and _{4CaO · Al 2 O 3 · Fe} 2 O 3 (C ₄ AF) is a fired product having a main mineral, and the firing properties of clinker and the properties of cement are easily affected by the mineral composition. However, regarding the alkali-silica reaction, the relationship with these mineral compositions has never been known so far.

In contrast, in the alkali silica reaction inhibitor for cement composition of the present invention, as described _above, it is SiO 2, _Al 2 _{O 3} and _Fe 2 _{O 3} satisfies a specific mass ratio. According to the study by the present inventors, such a cement composition can greatly suppress the alkali silica reaction as described above when it is mixed with aggregate to form a concrete composition. There was found. Therefore, when such a cement composition is used, a mortar, a concrete composition, or the like that can suppress the alkali-silica reaction without adding a mixture or the like can be obtained.

  It is preferable that the cement composition for suppressing alkali silica reaction of the present invention further contains at least one inorganic powder selected from the group consisting of blast furnace slag, fly ash, limestone, silica fume and silica. By appropriately selecting and containing these inorganic powders, it is possible to improve various properties of the cement composition and the cement-containing composition containing the cement composition.

  The present invention also provides a cement-containing composition comprising the alkali silica reaction-suppressing cement composition of the present invention and an aggregate. Since this cement-containing composition contains the above-described cement composition for suppressing alkali silica reaction of the present invention, the alkali silica reaction can be significantly suppressed regardless of the type of aggregate without adding a mixture. .

  In the cement-containing composition of the present invention, it is preferable that the aggregate is determined not to be harmless by the alkali silica reactivity test method. Since the cement composition contained in the cement-containing composition of the present invention is excellent in the effect of suppressing the alkali silica reaction as described above, the configuration of the present invention is determined not to be harmless by the alkali silica reactivity test method described above. This is particularly effective when using an aggregate that easily causes an alkali silica reaction.

  The aggregate is at least one aggregate selected from the group consisting of vitreous silica, tridymite, cristobalite, opal, volcanic glass, chalcedony, latent quartz, and quartz having a distorted crystal lattice structure. Is also suitable. These aggregates are also usually susceptible to alkali silica reaction in concrete and the like. Therefore, the configuration of the present invention is extremely effective when these aggregates are used.

  The cement-containing composition of the present invention is particularly suitable for use in a structure that is exposed to an environment in which salt penetration from the outside occurs. Since the cement-containing composition for suppressing alkali silica reaction of the present invention has an excellent alkali silica reaction suppressing effect, the structure is exposed to an environment where an alkali silica reaction is likely to occur due to the influence of salt penetration from the outside. This is particularly effective when applied.

  According to this invention, it becomes possible to provide the cement composition for alkali silica reaction suppression which is excellent in the effect which suppresses an alkali silica reaction by setting it as a specific chemical composition. Thereby, there are many kinds of aggregates that can be used, and a cement-containing composition such as a mortar or a concrete composition that can effectively use various aggregates can be provided. A structure using such a cement-containing composition has improved durability, and can be used for a long time without repairing. As a result, maintenance costs can be reduced. It will be a thing.

  Hereinafter, preferred embodiments of the present invention will be described in detail.

  First, the cement composition will be described.

A cement composition according to a preferred embodiment includes at least clinker and gypsum, such as silicon dioxide (SiO ₂ ), aluminum oxide (Al ₂ O ₃ ), ferric oxide (Fe ₂ O ₃ ), and It has a composition containing sulfur trioxide (SO ₃ ).

Suitable _clinker, those containing SiO 2 20 to 23 _{wt%, Al} 2 O 3 _{5.5~7.7 wt%, Fe} 2 O 3 _2.9~4.9 wt%, the CaO64~67 mass% Is mentioned. The cement composition preferably contains gypsum in an amount of 1.5 to 3.5% by mass in terms of the amount of SO ₃ in the cement.

The cement composition has a mass ratio of SiO ₂ / (Al ₂ O ₃ + Fe ₂ O ₃ ) of 2.5 or less. That is, it was calculated by dividing the SiO ₂ content (mass%) contained in the cement composition by the sum of the Al ₂ O ₃ content (mass%) and the Fe ₂ O ₃ content (mass%). The value is 2.5 or less. This value is called the silicic acid rate (SM). _{Incidentally, SiO 2, Al 2 O 3} , Fe 2 O 3 , etc. The content of the cement composition (mass%) can be determined by a method in accordance with JISR 5202-1999 "Methods for chemical analysis of Portland cement" .

  In the cement composition of the present embodiment, the silicic acid ratio is 2.5 or less, and preferably 1.7 to 2.4. When the silicic acid ratio is greater than 2.5, when this cement composition is combined with aggregate to make a cement-containing composition such as mortar and concrete composition, it is determined that it is not harmless particularly in an alkali silica reactivity test. When the aggregate is used, the amount of expansion in such a cement-containing composition tends to be undesirably large.

Is not necessarily clear details of the causes, the silicate ratio is high, in a clinker, (abbreviated as _{"C 3} S") 3CaO · SiO ₂ which is formed from the chemical components and 2CaO · _SiO 2 ( The ratio of 3CaO.Al ₂ O ₃ (abbreviated as “C ₃ A”) or 4CaO.Al ₂ O ₃ .Fe ₂ O ₃ (abbreviated as “C ₄ AF”) to the amount of “C ₂ S”) This is probably due to the relative decrease. Then, than the hydrate produced from the C 3 _S and C _{2 S,} C 3 _A and C ₄ towards the hydrate produced from the AF, gel formed during the alkali-silica reactivity is a cause of the expansion There is a tendency that the effect of suppressing expansion by changing the amount of substance produced and its characteristics (swellability, viscosity, etc.) is large. For this reason, it is considered that the amount of expansion when the cement-containing composition is used becomes excessive as a result of the decrease in the ratio of the amounts of C ₃ A and C ₄ AF as described above.

Incidentally, the silicate ratio is reduced in the cement composition, C _{3 A} and C ₄ AF in the composition (these are referred to as "gap phase") so that the amount increases. However, since this interstitial phase has a low melting point, if the silicic acid ratio is too small, specifically smaller than 1.7, the amount of the melt produced during clinker firing increases, and the clinker is fused. It tends to be easy to do. For this reason, it is preferable from a viewpoint on a manufacturing process that a silicic acid rate shall be 1.7 or more.

  The cement composition of the present embodiment may further include a mixed material that can improve desired properties in addition to the clinker and gypsum described above. Such a mixture is preferably contained in the cement composition in an amount of about 0 to 5% by mass. Examples of such a mixed material include inorganic powders such as blast furnace slag fine powder, fly ash, limestone powder, silica fume and silica stone powder.

  For example, by adding blast furnace slag fine powder, fly ash, or the like, the effect of suppressing the alkaline silica reaction by the cement composition can be enhanced. Usually, in order to obtain a sufficient suppression effect of the alkali silica reaction, it is necessary to add a certain amount or more to the cement composition. As a result, characteristics such as initial strength of the resulting structure are lowered. There was a case. On the other hand, in the cement composition of the present embodiment, since the alkali silica reaction can be sufficiently suppressed without adding a mixed material, the amount of these mixed materials added is reduced or not added. Even in such a case, an excellent effect can be obtained.

In addition, the silicic acid rate mentioned above is a value in the whole composition including the clinker, gypsum and other mixed materials when the cement composition contains the above-mentioned mixed material. That is, when SiO ₂ , Al ₂ O ₃ or Fe ₂ O ₃ is contained in the mixed material, the silicate ratio is adjusted in consideration of these components contained in the mixed material. Since gypsum contains almost no of the above components, the clinker in the cement composition is used when the cement composition does not contain a mixed material, or when it contains a mixed material but does not contain the above components. The silicic acid ratio may be approximated to be the silicic acid ratio in the entire cement composition.

  The cement composition of the present embodiment can be obtained by mixing and pulverizing cement clinker and gypsum, or by mixing after pulverizing cement clinker and gypsum. As gypsum, dihydrate gypsum, hemihydrate gypsum, anhydrous gypsum and the like can be used alone or in combination.

  As the cement clinker for obtaining the cement composition, limestone, clay, or the like, which are mixed and fired can be applied. As a raw material of cement clinker, steel slag, non-ferrous slag, coal ash, sewage sludge and the like, which are industrial wastes and industrial byproducts, may be used in addition to natural raw materials.

As the cement clinker, for example, one having a silicic acid ratio within the above-described preferred range is preferable. In addition, when a mixed material containing SiO ₂ , Al ₂ O ₃ or Fe ₂ O ₃ is added to the cement composition, the cement clinker is considered in consideration of the content of these components contained in the mixed material. It is preferable to set the acid ratio. Here, the silicic acid ratio of the cement clinker can be adjusted by changing the blending ratio of raw materials and chemical components during the production.

  Next, the cement-containing composition will be described.

  The cement-containing composition is a composition containing aggregate in addition to the above-described cement composition, and includes a mortar and a concrete composition. The mortar is a composition obtained by adding fine aggregate to a cement composition, and the concrete composition is a composition obtained by further adding coarse aggregate to mortar.

  The aggregate contained in the cement-containing composition is not particularly limited as long as it is usually used as an aggregate such as mortar and concrete, but is preferably an aggregate determined to be harmless by a predetermined alkali silica reactivity test method. . Since the cement composition of the present embodiment is excellent in the effect of reducing the alkali silica reaction with the aggregate, the cement-containing composition obtained in combination with the aggregate that easily causes such an alkali silica reaction, Even when a structure is formed, abnormal expansion hardly occurs.

  Here, the predetermined alkali silica reactivity test is not particularly limited as long as it is a test for evaluating the alkali silica reactivity of an aggregate generally used in a concrete composition or the like. Specifically, “Aggregate Alkali Silica Reactivity Test Method (Chemical Method)” defined in JIS A 1145, and “Aggregate Alkali Silica” defined in Appendix 7 of JIS A 5308 “Ready Mixed Concrete”. “Reactivity Test Method (Chemical Method)”, “Aggregate Alkali Silica Reactivity Test Method (Mortar Bar Method)” defined in JIS A 1146, or JIS A 5308 “Ready Mixed Concrete” Annex 8 "Aggregate alkali-silica reactivity test method (mortar bar method)".

  The cement-containing composition of the present embodiment is effective when combining the cement composition of the above-described embodiment with an aggregate determined to be harmless in at least one of the above tests. This is particularly effective when combined with aggregates that are determined to be non-hazardous.

  Examples of such aggregates include glassy silica, tridymite, cristobalite, opal, volcanic glass, chalcedony, latent quartz, or quartz having a distorted crystal lattice structure. Examples of vitreous silica include Pyrex (registered trademark) glass and glass waste materials. Note that quartz having a distorted crystal lattice structure exhibits wave quenching in, for example, observation with a polarizing microscope. These are often determined to be non-hazardous in the alkali silica reactivity test, but even when these aggregates are used, when combined with the above cement composition, it is a structure or the like. A cement-containing composition that hardly causes abnormal expansion can be obtained.

  The cement-containing composition of the present embodiment can be produced by a normal method. For example, the mortar composition can be produced by mixing a predetermined amount of cement composition, water, and fine aggregate. Moreover, you may add a predetermined amount of chemical admixture, fiber, etc. to a mortar composition as needed. As this chemical admixture, various water reducing agents such as an AE water reducing agent, a high performance water reducing agent, a high performance AE water reducing agent, a coagulation adjusting agent, a thickening agent, a water retention agent and the like can be used. Furthermore, the concrete composition can be produced by further blending coarse aggregate with the mortar composition as described above.

  The above cement-containing composition is applied as various structures by molding and solidifying it. Such a structure exhibits good durability even when used in an environment where salt penetration from the outside occurs. Here, the environment in which the permeation of salt from the outside means an environment in which an alkali salt acts from the outside. Examples of such an environment include environments affected by seawater and sea breeze. Such an environment can also be formed in a chemical factory or the like that manufactures or uses alkali salts.

  In an environment where salt penetration from the outside occurs as described above, the amount of alkali in the cement-containing composition such as a mortar or a concrete composition is small, and it is normally considered that abnormal expansion is extremely unlikely to occur. Even so, the permeation of the alkali salt from the outside produces a part with a high alkali concentration, which causes abnormal expansion. However, the structure composed of the cement-containing composition of the present embodiment is excellent in the alkaline silica reaction suppressing effect because the cement composition itself contained in the structure contains the alkali salt from the outside as described above. Even if there is, it is extremely difficult to cause abnormal expansion.

  As described above, the cement-containing composition of the present embodiment can exhibit excellent durability when applied as a structural material. Therefore, such a cement-containing composition can be used for breakwaters, breakwater blocks, fish reefs, revetments, coastal bridge piers, etc. It can be suitably used as a material for a concrete structure that receives sea breeze. Also, concrete floors in cold districts or bridge slabs, or anti-freezing materials composed of alkali salts, etc., such as girders or piers, and concrete structures that are easily in contact with dissolved water. It can also be suitably used as a material.

  EXAMPLES Hereinafter, although an Example demonstrates this invention still in detail, this invention is not limited to these Examples.

(Preparation of cement composition)
Portland cement clinker was fired, gypsum was added thereto and pulverized to a Blaine specific surface area of 3300 ± 100 cm ² / g, and the Portland cements of Preparation Example 1 and Comparative Preparation Example 1 having the compositions shown in Table 1 were respectively obtained. Obtained. The composition of Portland cement was measured according to JIS R 5202-1999 “Chemical analysis method of Portland cement”. Moreover, “Na ₂ Oeq.” In Table 1 represents the total alkali amount and is a value calculated by Na ₂ O (mass%) + 0.658 × K ₂ O (mass%).

(Preparation of aggregate)
Pyrex glass # 7740 (manufactured by Corning) was used as an aggregate, and this was adjusted to the particle size shown in Table 2 to prepare an aggregate.

(Preparation of mortar composition)
Using the Portland cement of Preparation Example 1 and Comparative Preparation Example 1, respectively, the mortar compositions of Example 1 and Comparative Example 1 were prepared according to the method shown below. The case of using Portland cement of Preparation Example 1 corresponds to Example 1, and the case of using Portland cement of Comparative Preparation Example corresponds to the Comparative Example.

  That is, first, 200 g of water was added to 400 g of Portland cement and mixed for 30 seconds with a Hobart mixer. Next, the aggregate prepared above was added to this mixture and kneaded at a low speed for 1 minute, and then rested for 1 minute and 30 seconds. Meanwhile, the mixture adhering to the container was scraped off. Next, the mixture was further kneaded at a high speed for 1 minute, paused for 1 minute and 30 seconds, scraped off in the same manner, and finally kneaded at a high speed for 15 seconds to prepare a mortar composition.

(Measurement of expansion coefficient)
As shown below, after the specimens were formed using the mortar compositions of Example 1 and Comparative Example 1, the coefficients of expansion were measured.

  That is, first, the mortar composition was poured into a 25 mm × 25 mm × 285 mm mold, cured for 24 hours after moisture curing, and then demolded to obtain a specimen. The specimens were prepared and cured at 23 ° C. ± 2 ° C.

  Then, the length (base length) of the obtained specimen was measured. Next, the obtained specimen was placed vertically so as not to touch water in a sealed container with water in the lower part. This specimen was stored in an environment of 38 ° C. ± 2 ° C. for 12 days together with the container, and the container was moved to a room of 23 ° C. ± 2 ° C. and stored for 16 hours or more. The length of the specimen after such storage was measured, and the length at the age of 14 days was obtained.

Then, based on the obtained base length and the value of the length at the age of 14 days, the expansion rate at the age of 14 days of each specimen was determined according to ASTM C 490-00a “Standard Practice for Use of the Deformation of Length Change”. of Hardened Cement Paste, Mortar and Concrete ”.
L = (Lx−Li) / G × 100

  Here, L: Expansion rate at 14 days of age, Lx: Difference in readings of dial gauge between reference rod and specimen at 14 days of age, Li: Dial between reference rod and specimen at base length measurement Gauge reading difference, G: nominal gauge length of 254 mm, respectively.

  Table 3 summarizes the coefficient of expansion (%) of the specimens obtained from the mortar compositions of Example 1 and Comparative Example 1. In Table 3, “Expansion coefficient ratio” indicates the value of the coefficient of expansion of the specimen of Example 1 which is converted based on the coefficient of expansion of the specimen of Comparative Example 1 as 100.

  From Table 3, it can be seen that the specimen obtained using the mortar composition of Example 1 is significantly suppressed in expansion as compared with the specimen obtained using the mortar composition of Comparative Example 1. confirmed.

Claims (1)

A method for suppressing an alkali silica reaction of a structure to which a cement-containing composition is applied,
The cement-containing composition contains cement clinker and gypsum, and has a composition containing SiO ₂ , Al ₂ O ₃ and Fe ₂ O ₃ , and has a mass ratio of SiO ₂ / (Al ₂ O ₃ + Fe ₂ A cement composition for suppressing alkali silica reaction having an O ₃ ) of 2.36 to 2.4, and an aggregate determined to be harmless by an alkali silica reactivity test method, comprising vitreous silica, tridymite, cristobalite, opal, applied volcanic glass, and at least one kind of aggregate selected from chalcedony and SenAkiraTadashi stone English or Ranaru group, a cement-containing composition containing,
A method for suppressing an alkali silica reaction, wherein the structure is exposed to an environment in which salt penetration from the outside occurs .