JP2009286693A - Low hydration heat cement composition - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a cement composition which enables "all purpose cement" such as normal portland cement to have improved strength development of concrete and in a medium to long term age of 7 days and/or 28 days without increasing hydration heat. <P>SOLUTION: The cement composition contains 45-65 mass% C<SB>3</SB>S and 8-12 mass% C<SB>3</SB>A and has ≤1.0% free lime rate expressed by expression (1) and ≤10% water soluble Cr(VI) formation rate expressed by expression (2), wherein expression (1): (free lime rate (%))=(the quantity of free lime)÷[(the quantity of CaO in the cement)-0.7×(the quantity of SO<SB>3</SB>in the cement)-56×(the quantity of C in the cement)÷12]×100 (%) and expression (2): (the formation ratio (%) of water soluble Cr(VI))=(water-soluble Cr(VI))÷(total Cr)×100 (%). <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a low hydration heat cement composition having excellent strength development without increasing heat of hydration when used in concrete.

  The heat of hydration of Portland cement is generally 84 cal / g or less at 7 days of age and 96 cal / g or less at 28 days of age according to the guidance of the Ministry of Construction in 1990 from the aspect of durability of concrete structures. After that, the civil engineering specifications of the Ministry of Land, Infrastructure, Transport and Tourism stipulate that the age of 7 days is 350 J / g or less and that the age of 28 days is 400 J / g or less.

  In general, the heat of hydration of cement is the heat generated when cement reacts with water to form hydrates. The greater the amount of hydrates produced, the higher the strength of mortar or concrete and at the same time hydrates. Heat also increases. In other words, it is a general tendency that the heat of hydration of cement increases when the strength of concrete is improved.

  On the other hand, cement users desire low-hydration thermal cement to maintain high durability of concrete, but at the same time, further improvement of concrete strength development is also required.

As a method for reducing the heat of hydration of cement, a method of controlling the main mineral composition (for example, reduction of the amount of C ₃ S and C ₃ A) such as moderately hot Portland cement clinker or low heat Portland cement clinker, There is also a method of adding a mixed material (for example, blast furnace slag, fly ash or pozzolan) to each of them, but each method has a problem that strength development is reduced as heat of hydration is reduced (Patent Document 1 and non-patent document). Reference 1). In other words, it can be seen that the invention in Patent Document 1 has a significantly lower compressive strength, especially at 28 days and 91 days, than the conventional low-heat-mixed cement compositions that are commercially available.

On the contrary, in order to improve the strength development property, means such as “reducing the fineness (brane specific surface area)” or “increasing the amount of C ₃ S” are used. There was also a problem of increasing the number.

  As described above, in “general-purpose cement” such as ordinary Portland cement, the heat of hydration is increased without changing the basic characters (main chemical composition, mineral composition, fineness, gypsum form and added amount, etc.). However, although it is desired to design a material that improves the strength development of concrete, it has been difficult to obtain such a material with the prior art.

JP 61-097154 A

"Common sense of cement" 2004 edition, Cement Association, p.11-17

  The object of the present invention is to improve the medium-to-long term strength development of concrete at 7 days and / or 28 days without increasing heat of hydration in “general purpose cement” such as ordinary Portland cement. It is providing the cement composition which can be used.

  As a result of intensive studies to solve the above problems, the present inventors have found that the material age is 7 days and / or 28 days without increasing the heat of hydration of “general purpose cement” such as ordinary Portland cement. In order to improve the strength development of concrete in the medium to long term, it has been found that it is effective to set both the free lime ratio and the production ratio of the amount of water-soluble Cr (VI) to a predetermined value or less. The present invention has been completed.

That is, the low hydration thermal cement composition of the present invention has a C ₃ S amount of 45 to 65% by mass and a C ₃ A amount of 8 to 12% by mass, and free lime represented by the formula (1). The cement composition has a rate of 1.0% or less and a water-soluble Cr (VI) production ratio represented by the formula (2) of 10% or less.
Free lime ratio (%) = Free lime amount ÷ (CaO amount in cement−0.7 × SO ₃ amount in cement−56 × C amount in cement ÷ 12) × 100% (1)
Water-soluble Cr (VI) generation ratio (%) = water-soluble Cr (VI) ÷ total Cr × 100% (2)

The amount of free lime in the above formula (1) contained in the cement composition of the present invention is the total amount of calcium hydroxide and quick lime (lime), and 60% or more of the free lime is calcium hydroxide (Ca Preferably present as (OH) ₂ ). Further, the water-soluble Cr (VI) production ratio represented by the formula (2) is more preferably 3 to 10%.

  Moreover, it is preferable that the cement composition of this invention contains Zr in the range of 120-240 mg / kg in a composition.

The cement composition of the present invention contains Portland cement clinker and gypsum, and the amount of mineral contained in the cement composition is 45 to 65% by mass for C ₃ S, preferably 50 to 60% by mass, and 8 for C ₃ A. -12 mass%, preferably 9-11 mass%.

Moreover, the concrete composition of the present invention uses 300 to 550 kg of the cement composition of the present invention per m ³ of concrete, and the water cement ratio is 25 to 60%, preferably 30 to 60%.

  In addition, the concrete composition of this invention can use sea sand, mountain sand, crushed sand, limestone crushed sand, slag crushed sand, etc. as a fine aggregate, and limestone etc. as a coarse aggregate. The admixture is not particularly limited, but it is possible to use a lignin sulfone salt type AE water reducing agent, a polycarboxylic acid type high performance AE water reducing agent or a high performance water reducing agent, a naphthalene sulfonic acid type water reducing agent, or the like. it can.

  The cement composition of the present invention has a free lime ratio of 1.0% or less and a water-soluble Cr (VI) generation ratio of 10% or less, so that the heat of hydration is 350 J / g or less at 7 days of age. When used as a concrete material with a material age of 28 days or less at 28 days of age, the strength development of the concrete can be improved, and it is possible to easily produce concrete having both high durability and high strength. And

Quantitative determination of calcium hydroxide content (CaO equivalent%) Relationship between Ca (OH) ₂ ratio and concrete compressive strength in ordinary concrete Relationship between Zr content and concrete compressive strength in ordinary concrete Relationship between Ca (OH) ₂ ratio and concrete compressive strength in high-strength concrete Relationship between Zr content and concrete compressive strength in high-strength concrete Relationship between Zr content and water-soluble Cr (VI) formation ratio

  Hereinafter, the present invention will be described in detail.

  The cement composition of the present invention is a cement composition containing Portland cement clinker and gypsum, wherein the residual rate of free lime is 1.0% or less, and the water-soluble Cr (VI) production ratio is 10% or less, preferably Is 3-10%.

Here, the free lime ratio is defined by the formula (1). From the total amount of CaO in the water cement, the amount of CaO derived from gypsum (= 0.7 × SO ₃ amount) and the amount of CaO derived from limestone (= 56 × the amount of C in the cement) / 12) is subtracted. The water-soluble Cr (VI) production ratio is defined by the formula (2).
Free lime ratio (%) = Free lime amount ÷ (CaO amount in cement−0.7 × SO ₃ amount in cement−56 × C amount in cement ÷ 12) × 100% (1)
Water-soluble Cr (VI) generation ratio (%) = water-soluble Cr (VI) ÷ total Cr × 100% (2)

  Here, the amount of free lime is the amount of free calcium oxide quantified by JCAS I-01: 1997 “Method for quantifying free calcium oxide in cement”, and the amount of water-soluble Cr (VI) is JCAS I-51: 1981. It is quantified by “quantification method of trace components in cement and cement raw material”.

  In the cement composition of the present invention, the water-soluble Cr (VI) generation ratio defined by the formula (2) is 10% or less, preferably 3 to 10%. Here, the total Cr amount of the formula (2) is 100 mg / kg or less, preferably 50 to 100 mg / kg, and the water-soluble Cr (VI) amount is 20 mg / kg or less, preferably 1 to 15 mg / kg. If the total Cr amount exceeds this range, strength development may be adversely affected. If the total Cr amount is less than this range, the strength enhancement effect may be reduced. Moreover, when the amount of water-soluble Cr (VI) exceeds this range, the amount of Cr (VI) eluted from the concrete increases, which may adversely affect the environment.

  In the analysis by JCAS I-51, the timing of adding diphenylcarbazide is preferably within 15 seconds after the addition of sulfuric acid. When diphenylcarbazide is added 1 minute after the addition of sulfuric acid, a part of Cr (VI) is reduced to Cr (III) due to the influence of reducing substances (for example, sulfides) in the cement. This is because it is difficult to accurately quantify the content of Cr (VI) that is affected.

  When either one of the free lime content in the cement composition is 1.0% or less or the water-soluble Cr (VI) generation ratio is 10% or less is not satisfied, the compression is particularly 28 days when used as concrete. Strength decreases. This is thought to be because the presence of free lime or water-soluble Cr (VI) roughens the structure of cement hydrate, and in order to increase the medium- to long-term concrete strength, the ratio of free lime and water-soluble Cr ( VI) It is necessary to control the production ratio within the above range.

Moreover, it is preferable that the presence form of the free lime in the cement composition of this invention exists as Ca (OH) ₂ , and in order to improve intensity | strength expression more, Ca (OH) ₂ ( The ratio of (CaO equivalent amount) is preferably 60% or more, more preferably 70% or more, and still more preferably 80% or more.

Although it is not clear why the presence of free lime is Ca (OH) ₂ in order to improve the medium-to-long-term strength development, if free lime exists as CaO (quick lime), While this significantly accelerates the cement reaction, this makes the void structure of the hydrate coarse in the long term, whereas Ca (OH) ₂ is not as reactive as CaO, so the cement reaction is modest. This is considered to be because it tends to be a relatively dense structure that enhances the properties and does not adversely affect the void structure of the long-term hydrate.

Moreover, it is preferable that the cement composition of this invention contains Zr 120-240 mg / kg, More preferably 130-190 mg / kg, More preferably 140-180 mg / kg. By containing an appropriate amount of Zr, the production of water-soluble Cr (VI) can be effectively suppressed, and the strength development of the concrete can be improved. When Zr content is less than 120 mg / kg soluble Cr (VI) product ratio increases, Zr is dissolved in _{C 3} A exceeds the 240 mg / kg, the fluidity by increasing the _{C 3} A content It causes problems that cause a decrease and an increase in heat of hydration.

The cement composition of the present invention can be obtained by adding gypsum to a cement clinker and grinding it with a ball mill or the like. Containing ores of cement composition of the present invention, _{C 3} S content is 45 to 65 wt%, preferably 50 to 60 mass%, _{C 3} A quantity 8-12 wt%, preferably 9-11 wt% It is.

In the region where the amount of C ₃ S is 45% by mass and the amount of C ₃ A is less than 8% by mass, even if the free lime ratio and the water-soluble Cr (VI) generation ratio are within the scope of the present invention, The strength expression of 3 to 7 days) decreases with age.

On the other hand, if the amount of C ₃ S exceeds 65% by mass, the amount of C ₂ S that is easy to immobilize Cr becomes too small, so the amount of potassium chromate and the like increases, and the water-soluble Cr (VI) generation ratio is reduced. It becomes difficult to control to 10% or less.

Furthermore, if the amount of C ₃ A exceeds 12% by mass, the concrete fluidity is significantly lowered, which is not preferable.

Here, CaO, SiO ₂ , Al ₂ O ₃ , and Fe ₂ O ₃ content (mass%) in the cement are measured according to JIS R 5202: 1999 “Chemical analysis method of Portland cement”. Further, the C ₃ S amount, the C ₂ S amount, the C ₃ A amount, and the C ₄ AF amount are values calculated by the following Borg formulas (3), (4), (5), and (6).

C ₃ S amount (% by mass) = 4.07 × CaO amount (% by mass) −7.60 × SiO ₂ amount (% by mass) −6.72 × Al ₂ O ₃ amount (% by mass) −1.43 × Fe ₂ O ₃ amount (% by mass) -2.85 × SO ₃ amount (% by mass) (3)
C ₂ S amount (% by mass) = 2.87 × SiO ₂ amount (% by mass) −0.754 × C ₃ S amount (% by mass) (4)
C ₃ A amount (mass%) = 2.65 × Al ₂ O ₃ (mass%) − 1.69 × Fe ₂ O ₃ (mass%) (5)
C ₄ AF amount (mass%) = 3.04 × Fe ₂ O ₃ (mass%) (6)

≪Cement clinker manufacturing method≫
The cement composition of the present invention can be produced by the following method.

Cement clinker is used to adjust the amount of limestone used to adjust the amount of CaO, clay used to adjust the amount of SiO ₂ and Al ₂ O ₃ , coal ash, construction generated soil, blast furnace slag, sewage sludge, etc., and the amount of SiO ₂ used Keiseki, and _Fe 2 _{O 3} weight used for adjusting Tetsuseiko, copper Karami, using iron raw material such as converter slag, CaO _amount, the ratio of SiO 2, _Al 2 _{O 3} and _Fe 2 _{O 3} amount It is manufactured by changing the blending ratio of various raw materials so as to be appropriate and firing using a cement kiln.

  At that time, it is preferable to mainly use coal ash as the clayey raw material, and it is more preferable to use 100 to 250 kg / t-clinker of coal ash having a Zr content of 400 mg / kg or more. The Zr content in the cement clinker can be controlled by calculating the amount of Zr brought in from various raw materials and changing the use ratio of clay or construction generated soil and the coal ash.

  Free lime rate increases kiln burning point temperature by increasing coal dredging amount, and in some cases reduces raw material feed (reducing clinker burnout), and usage of waste with high water content such as sewage sludge This can be reduced by stabilizing the kiln operating state so that the kiln torque can be increased. In the firing of cement clinker, while measuring the free lime ratio, increase the dredging amount of coal to increase the kiln firing point temperature and kiln torque as much as possible, or in some cases the raw material feed amount (clinker firing amount) The free lime ratio is adjusted to 1.0% or less by combining the reduction and the reduction of the amount of water brought from waste such as sewage sludge.

The ratio of water-soluble Cr (VI) formation can be reduced by reducing the K ₂ O content in the clinker by using a raw material with low potassium content that easily forms chromate by combining with Cr. is there.

As a specific means for reducing the amount of potassium, it is preferable to use coal ash having a K ₂ O content of 1.2% by mass or less, preferably 1.0% by mass or less as a clay-based raw material. It is also effective to extract potassium together with chlorine using a chlorine bypass facility attached to the cement kiln to reduce the amount of K ₂ O in the clinker. At that time, it is preferable to use high chlorine-containing waste (waste plastic, municipal waste incineration ash, etc.) and increase the amount of chlorine brought to 200 to 2000 mg per kg of clinker.

≪Method for producing cement composition≫
The method for producing the cement composition is as follows.
Using the cement clinker produced by the above method, it is pulverized using a ball mill together with gypsum and the like to produce a cement composition. In that case, it is preferable to use ethylene glycol, diethylene glycol, ethanolamines, propanolamines, glycerin, etc. as a grinding aid about 0.02 to 0.1% with respect to cement.

  The cement composition of the present invention may contain one or more selected from blast furnace granulated slag, limestone, and fly ash as other components.

Examples of the gypsum to be added include natural gypsum, drainage gypsum, hydrofluoric acid gypsum, and phosphoric acid gypsum. The form of gypsum may be any form of dihydrate gypsum, hemihydrate gypsum, and anhydrous gypsum, but when water is not sprayed on the cement with a cement grinding mill, CaO (quick lime) is changed to Ca (OH) ₂ Therefore, it is necessary to use dihydrate gypsum.

  When producing the cement composition, the grinding temperature (mill exit cement temperature) is controlled to 80 to 140 ° C., and 30 to 90% by mass of the first added dihydrate gypsum is dehydrated to form hemihydrate gypsum. The water vapor pressure in the mill is increased as much as possible by dehydrating dihydrate gypsum. Further, the water vapor pressure may be increased by spraying water into the mill and increasing the pulverization temperature to 100 to 140 ° C.

  Furthermore, the pulverized cement composition is maintained at a temperature at which the temperature of the cement composition is sufficiently high and dihydrate gypsum gradually becomes hemihydrate gypsum in the cement silo, and the ratio of hemihydrate gypsum stays at 37 to 95% by mass or less. Within 30 minutes, specifically within 60 minutes after pulverization at 60 to 120 ° C. After that, about 10 to 40% of the dihydrate gypsum remaining at the time of silo insertion in the silo is dehydrated to become semi-hydrate gypsum, that is, (dihydrate gypsum ratio at the time of mill outlet sampling-silo removal Dihydrate gypsum ratio at the time of exit) ÷ dihydrate gypsum ratio at the time of mill outlet collection × 100% is cured for a period of time of 10 to 40%. Specifically, the curing time is about 2 hours to 2 days.

  When manufacturing the cement composition, the amount of calcium hydroxide contained in the cement at the cement silo outlet is measured, and the ratio of calcium hydroxide to the amount of free lime is 60% or more, preferably 70% or more, more preferably 80%. As described above, adjustments are made by combining actions such as an increase in the amount of water spray in mill grinding and an increase in grinding temperature, or extension of the cement silo storage period.

By the above operation, CaO (quick lime) can be more reliably changed to Ca (OH) ₂ . Moreover, since the amount of hemihydrate gypsum does not exist excessively, false condensation (stiffness) does not occur. In order to confirm whether Ca (OH) ₂ is within a predetermined range, the obtained cement composition is taken out at a proper time, measured with a thermogravimetric analyzer, milling temperature, watering amount, and silo from the mill. Adjust and control the charging time and the curing time in the silo.

  When this cement composition is used as concrete, the water-cement ratio is 25 to 60%, and the amount of cement used per unit concrete is 300 to 550 kg. This is due to the temperature rise inside the concrete structure due to cement hydration. While being able to suppress expansion cracks, high strength can be achieved, and concrete having excellent durability can be obtained.

(1) Production of cement clinker and cement composition Limestone, clay, coal ash, meteorite, and iron concentrate are used as the main raw materials for cement clinker, and the C ₃ S amount in the clinker is 55 to 63 mass %, C ₂ S amount is 15 to 20% by mass, C ₃ A amount is 8.5 to 11.5% by mass, and C ₄ AF amount is 8.5 to 11.0% by mass. Using the mixture, the clinker was test-fired in an actual NSP kiln.

Further, the Zr content was adjusted by changing the use ratio of coal ash, and the Zr content in the clinker was changed in the range of 100 to 250 mg / kg. Coal ash, _{K 2} O content of 0.7 to 1.0 wt%, Zr content using those 430~780mg / kg, the amount was adjusted in the range of 60~180kg / t- clinker . In addition, the usage-amount of coal ash is No. of the cement composition shown in Table 1. 1 to 10 are 60 to 90 kg / t-clinker, No. 1 11 and 13-19 are 115-180 kg / t-clinker.

Add gypsum to the resulting cement clinker, add blast furnace slag and / or limestone in a total amount of 5.0% by mass or less, add 0.03% diethylene glycol as a grinding aid, and mix and pulverize with a ball mill. Thus, a cement composition having a brain specific surface area of 3050 to 3400 cm ² / g and an amount of SO ₃ of 1.89 to 2.07% by mass was produced.

  The produced cement composition is shown in Table 1. Table 2 shows the physical test results of the cement compositions in Table 1.

  No. The cement compositions 1 to 18 are selected from the cement clinker fired as described above, and those having different free lime ratios, Zr contents, and water-soluble Cr (VI) formation ratios are selected and mixed. The free lime ratio is 0.5 to 1.8%, the Zr content is 106 to 245 mg / kg, and the water-soluble Cr (VI) production ratio is a trial product so as to be different within a range of 7 to 17%.

When pulverizing the cement clinker, the amount of water added to the cement clinker and the pulverization temperature (mill exit cement temperature) are adjusted, and the ratio of Ca (OH) ₂ is changed to 68 to 100 (CaO equivalent)%. (Examples 1 to 7).

No. 19 (Example 8) is a cement composition in which an extraction clinker containing a large amount of CaO (lime) is added to a cement composition having a small amount of free lime, and the ratio of Ca (OH) ₂ is lowered to 53%.

The test method for cement is as follows.
(1) Measurement of free lime and calcium hydroxide and measurement of limestone amount The free lime content in the present invention is the total amount of calcium hydroxide and quick lime (lime). JCAS I-01: 1981 “Analysis of Free Calcium It was assumed that it was equal to the amount of free calcium oxide measured according to “Method”. The calcium hydroxide content was measured using a thermogravimetric analyzer (EXSTRAR6000 series TG / DTA6200, manufactured by Seiko Instruments Inc.), measuring 30 mg of cement sample in an aluminum container and heating rate under N ₂ atmosphere. The weight loss was measured at 10 ° C./min, and the weight loss near 350 to 450 ° C. was considered to be due to calcium hydroxide dehydration (Ca (OH) ₂ → CaO + H ₂ O). As (mass% CaO conversion), it calculated with the following formula (refer FIG. 1).
Calcium hydroxide content (mass% CaO equivalent) =
400-500 ° C. weight loss (mass%) ÷ 18 (water molecular weight) × 56 (CaO molecular weight)

  In addition, the amount of CaO derived from limestone is derived from limestone from the amount of C in the cement measured using a carbon / sulfur analyzer CS-400 (manufactured by Leco), assuming that fly ash is not included in the cement. Of CaO = 56 × (C amount in cement) ÷ 12.

(2) Measurement of total Cr amount and water-soluble Cr (VI) amount The total Cr amount and water-soluble Cr (VI) amount are in accordance with JCAS I-51: 1981 “Method for quantifying trace components in cement and cement raw materials”. Measured. Diphenylcarbazide was added about 10 seconds after the addition of sulfuric acid.

(3) Zr determination method Zr in cement and coal ash was determined by the following procedure.
<1> Zr content in cement The test solution was prepared according to JCAS I-52: 2000 “Method for quantifying trace components in cement by ICP emission spectroscopic analysis and electric heating atomic absorption spectrometry”. The Zr content in the test solution was quantified using an analyzer (SPS 3000 manufactured by SII Nanotechnology) and converted to the content in cement.
<2> Zr content in coal ash The preparation of the test solution is the same method as the determination of lead by atomic absorption spectrometry in Section 3.18 of JCAS I-51: 1981 “Method for quantifying trace components in cement and cement raw materials” The Zr content in the test solution was quantified using an ICP emission spectroscopic analyzer (SPS3000 manufactured by SII Nanotechnology) and converted to the Zr content in coal ash.
In the ICP analysis, the internal standard selected from Be (10 mg / kg), Y (5 mg / kg) or Sr (10 mg / kg) having the smallest content in the test solution was used.

(4) Method of measuring heat of hydration of cement composition The heat of hydration of Portland cement was measured according to JIS R 5203: 1995 “Method of measuring heat of hydration of cement (heat of solution method)”.

(5) Method for measuring mortar compressive strength of cement composition The mortar compressive strength of Portland cement was measured according to JIS R 5201: 1998 “Physical Test Method for Cement”.

(6) Concrete Performance Evaluation Method (6-1) Concrete Mixing Concrete performance evaluation was performed based on two blends of ordinary concrete and high-strength concrete shown in Table 3.

（Ｗ／Ｃ：水セメント比（質量比）、
ｓ／ａ：細骨材率（＝細骨材÷全骨材（細骨材＋粗骨材））（体積比））

(W / C: water cement ratio (mass ratio),
s / a: fine aggregate ratio (= fine aggregate ÷ total aggregate (fine aggregate + coarse aggregate)) (volume ratio))

(6-2) Aggregate, admixture and water used Fine aggregate: Mixed sand ・ Sea sand / Hakata 50% + Crushed sand / Sumitomo Coal Mining 50%.
Coarse aggregate: 2015/50% + 1505/50% from Miyano, Yamaguchi Prefecture.
Admixture: High-performance AE water reducing agent Leo build SP8SBs (manufactured by NM)
AE water reducing agent Pozzolith No. 70 (made by Pozoris)
Water: tap water

(6-3) Mixing of concrete The mixer, mixing amount and procedure used for mixing of concrete are as follows.
Mixer: Forced biaxial mixer (nominal volume 55L)
Mixing amount: 30 L / batch Mixing time and procedure a) After adding fine aggregate and cement to the mixer, knead for 10 seconds.
b) Add water (including admixture) and mix for 60 seconds.
c) Add coarse aggregate, knead for 60 seconds, let stand for 5 minutes, and then mix and discharge for 15 seconds.

(6-4) Evaluation Items and Test Methods for Concrete Performance Table 4 shows the evaluation items and test methods for concrete performance.

(7) Measurement result of heat of hydration of cement composition As shown in Table 2, the heat of hydration of any cement composition was 350 J / g or less at 7 days of age and 400 J / g or less at 28 days of age, water. There was no increase in Japanese heat.

(8) Concrete performance evaluation results The concrete performance evaluation results of the cement composition of Table 2 are shown in Table 5 for ordinary concrete and Table 6 for high strength concrete.

(8-1) Ordinary concrete As can be seen from Table 5, a cement composition (No. 11) in which the free lime ratio in the cement satisfies 1.0% or less and the water-soluble Cr (VI) generation ratio satisfies 10% or less. 13-19 and Examples 1-8 are compared with cement compositions (No. 1-10, 12, Comparative Examples 1-11) in which either of the above two conditions or one of them is out of range. The compressive strength of concrete was high.

Moreover, although the data of Examples 1-8 (No. 11, 14-19) were plotted about the relationship between Ca (OH) ₂ ratio and concrete compressive strength in FIG. 2, Ca (OH) ₂ ratio is 53. It can be seen that the compressive strength of the cement composition of Example 8 (No. 19), which is as low as%, is slightly lower than that of Examples 1 to 7 in which the Ca (OH) ₂ ratio is 60% or more. That is, it can be seen that the Ca (OH) ₂ ratio is preferably 60% or more as in Examples 1 to 7 in order to make the strength at 28 days of age at 43.5 N / mm ² or more.

  Furthermore, in FIG. 3, the relationship between Zr in a cement composition and concrete compressive strength was shown. It has been shown that the Zr content should be 120 mg / kg or more.

(8-2) High-strength concrete As can be seen from Table 6, a cement composition satisfying a free lime ratio of 1.0% or less in the cement and a water-soluble Cr (VI) generation ratio of 10% or less (Examples) 2, 4 and 8), the compressive strength of the concrete was higher than that of the cement composition (Comparative Examples 2, 4, 8, 10) in which either one of the above two conditions or one of the two conditions was out of the range.

FIG. 4 shows the relationship between the Ca (OH) ₂ ratio and the concrete compressive strength in the high-strength concrete. As in the case of the ordinary concrete shown in (8-1), the Ca (OH) ₂ ratio The cement composition of Example 8 (No. 19) with a small 53% was slightly lower in compressive strength than Examples 2 and 4. That is, in high-strength blended concrete, in order to more reliably improve the 28-day strength to 84 N / mm ² or more, the Ca (OH) ₂ ratio is 60% or more as in Examples 1-7. I understand that it is good.

  Further, FIG. 5 shows the relationship between the Zr in the cement composition and the concrete compressive strength. In order to reliably improve the concrete compressive strength, the Zr content is set to 120 mg / kg as in the case of ordinary concrete. It turns out that it is good to be above.

  FIG. 6 shows the relationship between the Zr content and the water-soluble Cr (VI) formation ratio. However, there is an optimum range of the Zr content for reliably reducing the water-soluble Cr (VI). It can be seen that the Zr content should be 120 to 240 mg / kg in order to control the amount of water-soluble Cr (VI) to 10% or less and improve the strength development by only controlling the amount.

Although the mechanism of action relating to the reduction of water-soluble Cr (VI) and the increase of concrete compressive strength by optimizing the Zr content is not clear, the following may be considered.
As shown in FIG. 6, the relationship between the Zr content and the water-soluble Cr (VI) amount is represented by a downwardly convex curve with the Zr content at the top of 140 to 160 mg / kg, and the Zr content is 120 A reduction effect of water-soluble Cr (VI) is observed in the region of ~ 240 mg / kg. This is because when Zr is present in an appropriate amount, Cr is easily dissolved in a calcium silicate phase having a low dissolution rate in water, and it is difficult to become a water-soluble compound such as potassium chromate that dissolves immediately after water contact. Seem.
Moreover, when Zr and Cr are combined and dissolved in the calcium silicate phase, the hydration activity of C ₃ S or C ₂ S is improved, and it is considered that the medium-to-long-term strength development is improved.

As described above, it can be seen that the concrete composition using 300 to 550 kg / m ³ of the cement composition of the present invention and having a water / cement ratio of 25 to 60% is excellent in strength development on the age of 28 days.

Claims (7)

The amount of C ₃ S is 45 to 65% by mass, the amount of C ₃ A is 8 to 12% by mass, the free lime ratio represented by the formula (1) is 1.0% or less, and the water-soluble Cr represented by the formula (2) (VI) Cement composition having a production ratio of 10% or less:
Free lime ratio (%) = Free lime amount ÷ (CaO amount in cement−0.7 × SO ₃ amount in cement−56 × C amount in cement ÷ 12) × 100% (1)
Water-soluble Cr (VI) production ratio (%) = water-soluble Cr (VI) ÷ total Cr × 100% (2).   The amount of free lime in Formula (1) is the total amount of calcium hydroxide and quicklime (lime), and the amount of calcium hydroxide (CaO equivalent) is 60% or more of the amount of free lime. Cement composition.   The cement composition according to claim 1 or 2, wherein the cement composition contains Zr in a range of 120 to 240 mg / kg. The cement composition according to claim 1, water, coarse aggregate, fine aggregate, and a water reducing agent, the cement composition is 300 to 550 kg / m ³ , and the water / cement ratio is 25 to 60. % Concrete composition. The concrete composition according to claim 4, wherein water is 130 to 200 kg / m ³ , coarse aggregate 700 to 1200 kg / m ³ , and fine aggregate 600 to 900 kg / m ³ . Cement so that the amount of C ₃ S in the cement is 45 to 65% by mass, the amount of C ₃ A is 8 to 12% by mass, and the water-soluble Cr (VI) generation ratio represented by the formula (2) is 10% or less. Adjusting the clinker raw material,
Firing the adjusted cement clinker raw material so that the free lime ratio represented by the formula (1) is 1.0% or less, and obtaining a cement clinker;
A method for producing a cement composition comprising a step of mixing and pulverizing the obtained cement clinker and gypsum and curing with a silo,
Including a step of adjusting the watering amount at the time of pulverization, the pulverization temperature, and / or the curing period in the silo so that 60% or more of the amount of free lime in the formula (1) is calcium hydroxide (CaO equivalent). Process for producing a characterized cement composition:
Free lime ratio (%) = Free lime amount ÷ (CaO amount in cement−0.7 × SO ₃ amount in cement−56 × C amount in cement ÷ 12) × 100% (1)
Water-soluble Cr (VI) production ratio (%) = water-soluble Cr (VI) ÷ total Cr × 100% (2).   The manufacturing method of the cement composition of Claim 6 which grind | pulverizes a cement clinker and dihydrate gypsum, sprinkling water.

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