JP7399606B2 - cement composition - Google Patents

Description

The present invention relates to a cement composition containing fine fly ash powder whose particle size is adjusted in order to improve the performance of mortar and concrete.

Conventionally, mixed cement containing blast furnace slag, fly ash, and silica fume has been used, and high-strength mortar and concrete are manufactured using these.

As prior art related to fly ash to be mixed into a cement composition and concrete using fly ash, there are, for example, the inventions described in Patent Documents 1 to 6 below.

Patent Document 1 describes an ultra-high strength mortar composition comprising Portland cement, fly ash having a BET specific surface area of 2 m ² /g or more and less than 5 m ² /g, water, and a cement dispersant. , the mass ratio of Portland cement and fly ash is 90:10 to 70:30, the water/binder ratio is 0.1 to 0.2, and the cement dispersant contains a polycarboxylic acid dispersant. An ultra-high-strength mortar composition characterized by the following properties and an ultra-high-strength concrete composition in which coarse aggregate is blended with the mortar composition are disclosed.

Patent Document 2 describes fly ash that has been crushed into fine particles, has a mass average particle diameter (μm) in the range of 0.1 to 0.73 μm, and has a mass accumulation rate ( %) is 95% or more, and a Blaine specific surface area of 2.5 m ² /g (25000 cm ² /g) or more is disclosed. It is stated that it overcomes the problem of early strength decline of the cement and concrete hardened material used, increases the 28-day strength and long-term strength of the hardened material, and can be used for many purposes other than cement hardened material. There is.

Patent Document 3 discloses high-strength porous concrete with a water binder ratio of 10 to 20% using a mixture containing fly ash with a Blaine specific surface area of 2500 to 10000 cm ² /g as a binder.

Patent Document 4 describes cement, silica fume, and a filler having a particle size larger than silica fume (classified fly ash: Blaine specific surface area is preferably 4000 to 50000 cm ² /g, more preferably 6000 to 30000 cm ² /g, Particularly preferably ^, it is 7000 to 20000 cm ² /g. There is a disclosure.

Patent Document 5 describes a design for use in the construction of high-rise reinforced concrete structures, steel tube-filled concrete (CFT) structures, etc., which is characterized in that 2 to 25% by weight of fly ash with a particle size of 20 μm or less is blended in the patent claim. Regarding high-strength, high-fluidity concrete with a standard strength of 80N/mm2 or ^less , it shows high fluidity and low viscosity at a low water-cement ratio without silica fume, and shows high strength development even when subjected to thermal history. There is a disclosure of technology for providing cement for concrete with high strength and high fluidity.

Patent Document 6 discloses that one or more kinds of inorganic highly finely pulverized powders selected from the group consisting of Portland cement, limestone powder with a Blaine specific surface area of 7,000 to 30,000 cm ² /g, fly ash, and granulated blast furnace slag are used as powder components in Patent Document 6. A high-strength self-leveling cement composition is described, characterized in that the powder component contains 5 to 30% by weight of the highly finely pulverized inorganic powder.

Japanese Patent Application Publication No. 2008-189491 Patent No. 4034945 Japanese Patent Application Publication No. 2018-002510 JP2017-024933A Japanese Patent Application Publication No. 11-278908 Patent No. 3528301

When producing ultra-high strength mortar/concrete using blast furnace slag, fly ash, or silica fume, the amount of powder is large and the water-to-binder ratio is small, so it is necessary to use high-performance water reducing agents and good bonding with particle size and particle size. Without this material, it will be difficult to knead and ensure fluidity. Patent Document 1 uses a cement dispersant containing a polycarboxylic acid dispersant.

In addition, in addition to Portland cement, admixtures with fine spherical particles are used as binding materials for ultra-high-strength mortar and concrete, and a typical example is silica fume, but there are almost no substitutes for silica fume. do not have.

Under such circumstances, most silica fume is produced overseas, and if domestically produced industrial by-products can be used as a substitute for silica fume, it can contribute to reducing the environmental burden.

The present invention aims to solve the above-mentioned problems, and provides a cement composition that can obtain mortar concrete that exhibits high fluidity and low viscosity at a low water binder ratio without using silica fume. It is intended to.

The cement composition of the present invention has a particle size of 0.2 to 1.2 μm at a cumulative volume passing rate of 25%, a particle size of 0.3 to 2.3 μm at a cumulative volume passing rate of 50%, and a cumulative volume passing rate of 0.2 to 1.2 μm. It is characterized by containing fly ash fine powder having 90% particle size of 0.6 to 6.0 μm.

In producing ultra-high strength mortar/concrete, the particle size at a cumulative volumetric pass rate of 25% is 0.2 to 1.2 μm, and the particle size at a cumulative volume pass rate of 50% is 0.3 to 2.3 μm. By using fly ash fine powder with a particle size of 0.6 to 6.0 μm and a volumetric passage rate of 90%, fresh properties equivalent to or higher than ultra-high strength mortar/concrete using silica fume and similar strength properties can be achieved. is obtained.

More preferably, the particle size at a cumulative volume passing rate of 25% is 0.5 to 1.1 μm, the particle size at a cumulative volume passing rate of 50% is 0.8 to 1.8 μm, and the particle size is 90%. It is preferable to use fly ash fine powder with a diameter of 2.1 to 4.0 μm.

For example, in Patent Document 2 mentioned above, the mass average particle size (μm) is in the range of 0.1 to 0.73 μm, and the mass accumulation rate (%) at the particle size of 3.73 μm or less is 95% or more. In addition, ultrafine fly ash with a Blaine specific surface area of 2.5 m ² /g (25000 cm ² /g) or more has been disclosed, but it does not necessarily mean that the finer the fly ash, the better the performance such as mortaring time. do not have.

The fly ash fine powder used in the present invention has the above-mentioned particle size distribution, but the Blaine specific surface area is about 14,000 to 42,000 cm ² /g, more preferably about 16,000 to 34,000 cm ² /g. Within this range, compared to the case where silica fume is used, mortaring time can be shortened while suppressing the amount of high performance water reducing agent added.

Further, the BET specific surface area is about 4 to 14 m ² /g, more preferably about 5 to 12 m ² /g. Within this range, compared to the case where silica fume is used, mortaring time can be shortened while suppressing the amount of high performance water reducing agent added.

Regarding the blending of fly ash fine powder with cement, when Portland cement is used as the cement, it is preferable to substitute it in a range of 10 to 30% by weight relative to Portland cement.

More preferably, it is 18 to 30% by weight. At about 10% by weight, the reduction in mortaring time in ultra-high strength mortar/concrete is not necessarily sufficient compared to the case of silica fume, but when replacing 18 to 30% by weight, when replacing silica fume with 10% by weight The above effect of shortening mortaring time was observed.

In addition, regarding the fly ash fine powder used in the present invention, fly ash as a raw material is put into a crusher and finely powdered, and then classified, and the particle size at the cumulative volume passing rate of 25% is 0.2 ~ Use particles adjusted so that the particle size is 1.2 μm, the particle size at a cumulative volumetric passage rate of 50% is 0.3 to 2.3 μm, and the particle size at a cumulative volumetric passage rate of 90% is 0.6 to 6.0 μm. be able to.

For the grinding of fly ash to achieve the particle size distribution in the present invention, general grinders such as jet mills and media agitation mills can be used, and the fly ash is repeatedly ground by a dry grinding method using these grinders. By doing so, the fly ash can be made into an ultra-fine powder, and by classifying it after pulverization, the above-mentioned particle size distribution can be obtained.

When producing ultra-high strength mortar/concrete, the particle size at which the cumulative volumetric passage rate is 25% is 0.2 to 1.2 μm, the particle size at which the cumulative volumetric passage rate is 50% is 0.3 to 2.3 μm, By using fly ash fine powder with a cumulative volumetric passage rate of 90% and a particle size of 0.6 to 6.0 μm, fresh properties equivalent to or higher than ultra-high strength mortar/concrete using silica fume and similar strength can be achieved. characteristics are obtained.

Mortar-concrete with high fluidity and low viscosity can be obtained with low water binder ratio without using silica fume. If fly ash fine powder can be used as a substitute for silica fume, domestically produced industrial by-products can be used, contributing to reducing environmental impact.

Tests conducted to confirm the effects of the present invention will be described below.

1. Types of admixtures Table 1 shows the types of admixtures used in the test.

Fly ash fine powder FA is manufactured by repeatedly pulverizing using a pulverizer and then classifying it, and the particle size (D25) with a cumulative volumetric passing rate of 25% is 0.2 to 1.2 μm, 50%. Adjust the particle size so that the particle size (D50) is 0.3 to 2.3 μm and the 90% particle size (D90) is 0.6 to 6.0 μm. I created a variety.

N and SF are comparative examples, where N shows only ordinary Portland cement and SF shows only silica fume.
The particle size distribution of silica fume is coarse, but this is thought to be the result of fine particles agglomerating.

2. Mortar test Mortar was prepared and examined. As materials for the mortar, tap water, ordinary Portland cement, admixtures (see Table 1), standard sand, and a high performance water reducer (Master Glenium SP8HU from BASF Japan Co., Ltd.) were used. A commonly used Hobart mixer (capacity: 3 L, 0.125 kwh) was used as a kneading device.

Two water binder ratios were set, 17% and 33%, and the mixing method was changed depending on the water binder ratio.

When the water binder ratio was 17%, kneading was performed according to the following steps A) to D).
A) Stir ordinary Portland cement, admixture, and standard sand for 30 seconds with a Hobart mixer.
B) Add tap water and a high performance water reducer to the mixture of A), stir, and measure the mortarization time. After measuring the mortarization time, stir for 120 seconds.
C) Leave it still for 300 seconds.
D) Stir for 30 seconds.

When the water binder ratio was 33%, the mixture was mixed in accordance with JASS 5 M-702 (performance evaluation criteria for high-strength concrete admixtures).

After the materials were put into the mixer, the time required to reach a mixing state that allowed a flow test and was visually observed was measured as the mortarization time. The flow test was conducted in accordance with JIS R 5201 "Physical Test Methods for Cement." The compressive strength was measured at 7 and 28 days of age under standard curing.

Table 2 shows the mortar test results when the water binder ratio was 17%.
The substitution rate of silica fume was 15% with respect to ordinary Portland cement, which was set as level 1.
The case where the substitution rate of fly ash fine powder FA0.4 was 15% was set as level 2, and the case where the substitution rate was 30% was set as level 4.
Similarly, the case where the substitution rate of FA0.6 was 15% was set as level 3, and the case where the substitution rate was 30% was set as level 5.
In the case of FA1.0, FA1.5, and FA2.4, the substitution rate was set to 30% and level 6 to 8.
For level 8, it was impossible to measure flow, mortarization time, and compressive strength because the mixing was not done well.

Comparing Levels 2 and 3 with a replacement rate of 15% for fly ash fine powder with Level 1 for silica fume, it can be seen that the same level of flow can be obtained with a smaller amount of high performance water reducing agent than Level 1.
Furthermore, the 7-day and 28-day compressive strengths of Levels 2 and 3 were comparable to or higher than Level 1.

Similarly, when comparing Levels 4 to 7 with a replacement rate of 30% for fly ash fine powder and Level 1 of silica fume, Levels 4 to 7 also use a smaller amount of high performance water reducer than Level 1, and have the same flow rate. It turns out that you can get
Additionally, the mortaring time at 30% admixture replacement rate was significantly reduced compared to 15%, and the 7-day and 28-day compressive strengths for Levels 4 to 7 were comparable to or higher than Level 1. .

In particular, in Level 6 and Level 7, the mortaring time was 20 seconds and 40 seconds, respectively, and comparable 28-day compressive strength was obtained.

Table 3 shows the mortar test results when the water binder ratio was 33%.
The substitution rate of silica fume was 10% with respect to ordinary Portland cement, and was set at level 9.
The case where the substitution rate of fly ash fine powder FA1.8 was 10% was set as level 10, the case where the substitution rate was 20% was set as level 11, and the case where the substitution rate was 30% was set as level 12.
Similarly, the replacement rate of FA1.9 was set to 20%, and the level was set to 13.

Comparing Level 9 and Levels 10 to 13, the flow and mortaring time are comparable, the 7-day compressive strength is higher than SF using silica fume, and the 28-day compressive strength is about the same. strength was obtained.

From the above, in the mortar test, by using the fly ash fine powder of the present invention, fresh properties equivalent to or higher than ultra-high strength mortar using silica fume and similar strength characteristics were obtained.

3. Concrete test results Next, concrete was prepared and examined. The materials used were tap water, ordinary Portland cement, admixtures (see Table 1), crushed andesite sand, crushed andesite, and a high-performance water reducing agent (Master Glenium SP8HU from BASF Japan Co., Ltd.). A forced twin-screw mixer (capacity: 60 L, 52 revolutions/min) was used as the kneading device.

Kneading was performed according to the following steps A) to D).
A) Ordinary Portland cement, admixture, and andesite crushed sand are stirred for 30 seconds using a forced twin-screw mixer.
B) Add tap water and a high-performance water reducer to the mixture of A), stir, and measure the mortarization time (the time when the mortar material is in a mixed state that allows a flow test and can be visually observed after putting the mortar material into the mixer). did. After measuring the mortarization time, the mixture was stirred for 90 seconds.
C) Let stand for 300 seconds.
D) Stirred for 30 seconds.

After kneading, a slump flow test was conducted in accordance with JIS A 1150. In addition, compressive strength tests were conducted in accordance with JIS A 1108 at material ages of 7, 28, and 91 days under standard curing.

Table 4 shows the experimental results when the water binder ratio was 15%.

Level 14 using silica fume had a silica fume substitution rate of 15%.
In levels 15 to 18 using fine fly ash powder, level 15 had a FA1.6 replacement rate of 30%.
Levels 16 to 18 use FA0.8, and the replacement rates of FA0.8 are set at 30%, 18%, and 13%, respectively.

In Levels 15 to 17, the time to reach 50 cm flow and mortaring time were reduced compared to Level 14, and an improvement in fresh properties was observed. Furthermore, the compressive strength is comparable to that obtained using silica fume.

Although the mortaring time of Level 18 is longer than that of Level 14, comparable results are obtained in terms of time to reach 50 cm flow and compressive strength.

From the above, in the concrete test, by using the fly ash fine powder of the present invention, fresh properties equivalent to or higher than ultra-high strength concrete using silica fume and similar strength characteristics were obtained.

Claims (3)

A method for producing a cement composition containing fine fly ash powder, wherein the fine fly ash powder is produced by charging fly ash into a crusher and repeatedly crushing it using a dry crushing method to classify the fine powder. , the particle size at a cumulative volume passing rate of 25% is 0.2 to 1.2 μm, the particle size at a cumulative volume passing rate of 50% is 0.3 to 2.3 μm, and the particle size at a cumulative volume passing rate of 90% is 0. .6 to 6.0 μm and a Blaine specific surface area of 14,000 to 42,000 cm ² /g. A method for producing a cement composition containing fine fly ash powder, wherein the fine fly ash powder is produced by charging fly ash into a crusher and repeatedly crushing it using a dry crushing method to classify the fine powder. , the particle size at a cumulative volume passing rate of 25% is 0.5 to 1.1 μm, the particle size at a cumulative volume passing rate of 50% is 0.8 to 1.8 μm, and the particle size at a cumulative volume passing rate of 90% is 2 .1 to 4.0 μm and a Blaine specific surface area of 16,000 to 34,000 cm ² /g. The method for producing a cement composition according to claim 1 or 2, wherein the cement composition is characterized in that the fine fly ash powder is substituted with Portland cement in an amount of 10 to 30% by weight. Method for producing cement compositions.