JPH092848A - Coal ash for mortar/concrete and mortar/concrete using the same - Google Patents

Abstract

PURPOSE: To obtain both coal ash for mortar/concrete having suitability of use as an admixture for cement/concrete, being judged by rapid and simple representative characteristics, capable of securing the use of a large amount of coal ash, fixed fluidity and air entraining properties, excellent in development of strength and mortar/concrete using the coal ash. CONSTITUTION: This coal ash for mortar/concrete has particle size constitution of any of the following (1) to (3). (1) One having <4m<2> /g BET specific surface area value and <=40wt.% remaining content value on >=45μm sieve. (2) One having >=4m<2> /g and <65m<2> /g BET specific surface area value and <=20wt.% remaining content value on 45μm sieve. (3) One has >=6m<2> /g and <10m<2> /g specific surface area value and <=10wt.% remaining content value on 45μm sieve.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to ash for mortar / concrete and mortar / concrete using the same.

[0002]

2. Description of the Related Art A large amount of coal ash (fly ash) produced as a by-product from a pulverized coal combustion boiler of a thermal power plant.
Is effectively used as a cement admixture, etc., but most of it is discarded as landfill. Fly ash used as a cement admixture has improved workability of concrete because the fly ash particles are smooth and spherical, and the concrete structure is densified to increase the long-term strength, watertightness, resistance to chemicals, etc. It is suitable for mass concrete structure where temperature crack due to self-heating is a problem because the heat of hydration of cement is mitigated by the mixture of fly ash, and it also has an inhibitory effect on alkali-aggregate reaction. It has many excellent properties as concrete, such as being present.

On the other hand, when fly ash is mixed with a large amount of concrete, there are problems such as delay of setting, reduction of initial strength, delay of strength development in a low temperature environment, and the like.
Naturally, there is a limit to the mixing amount. For example, the fly ash cement stipulated in JIS standard limits the replacement ratio of fly ash to cement to 30% at the maximum, and is not currently associated with the large use of fly ash.

Further, as one of the causes of hindering the large-scale use of coal ash, the variety of coal used in a thermal power plant, and the combustion conditions thereof are not the same, the state of the obtained coal ash greatly changes. You can come. Especially,
The unburned carbon remaining in the coal ash is used as a cement admixture, absorbs kneading water, and adsorbs various admixtures such as water reducing agents to ensure the desired fluidity and air entrainment. There is a difficulty in quality control in doing so, which is a factor to avoid using it.

The ignition loss of coal ash (JIS A6201 defines an ignition loss of 5% or less) or the amount of adsorbed methylene blue dye is used as a guide for understanding the properties of the unburned carbon.

[0006]

However, unburned carbon does not simply exist as coal particles, but is in a porous activated carbon state, and due to various coal and different combustion conditions, There are various adsorption performances,
The content of unburned carbon alone, such as the loss on ignition, does not necessarily correspond to the amount of adsorption. Also, the amount of methylene blue dye adsorbed is measured by measuring the blueness of the dye from the absorbance of the filtrate, which is operationally complicated and has little correlation with the amount of cement admixture adsorbed, which is related to the amount of admixture used. This cannot be effectively utilized.

For this reason, when coal ash is used as an admixture for cement concrete, it is necessary to frequently conduct a concrete mixing test and grasp the concrete properties before setting the type and addition amount of the air entraining agent or water reducing agent. The current situation is that it must be done. Therefore, the present invention eliminates the above-mentioned drawbacks and can judge the suitability for use as a cement and admixture for concrete with quick and simple representative characteristics, and secures a large amount of coal ash and a predetermined fluidity and air entrainment. It is an object of the present invention to provide a coal ash for mortar / concrete that can be produced and has good strength, and a mortar / concrete using the same.

[0008]

In order to achieve the above object, according to the ash for mortar / concrete of the present invention, it has a particle size constitution of any one of the following (1) to (3). And (1) BET specific surface area value of less than 4 m ² / g, residual value on 45 μm sieve of 40% by weight or less (2) BET specific surface area value of 4 m ² / g or more and less than 6 m ² / g, residual value on 45 μm sieve Is 20% by weight or less (3) BET specific surface area is 6 m ² / g or more and 10 m ² / g
Less than 45 μm, residual value on the sieve is 10% by weight or less

According to the mortar-concrete of the present invention, a mortar-concrete composition containing cement, aggregate, coal ash, and water, wherein the coal ash is any of the following (1) to (3) It is characterized by having one grain size configuration. (1) BET specific surface area value of less than 4 m ² / g, residual value on 45 μm sieve of 40% by weight or less (2) BET specific surface area value of 4 m ² / g or more and less than 6 m ² / g, residual value on 45 μm sieve Is 20% by weight or less (3) BET specific surface area is 6 m ² / g or more and 10 m ² / g
Less than 45 μm, residual value on the sieve is 10% by weight or less

Further, the mortar / concrete of the present invention has a cement / coal ash (weight ratio) of 0.5 to 3.0,
Preferably, it is 0.8 to 2.0 (claim 3), coal ash is used by substituting a part of the fine aggregate in the aggregate (claim 4), and coal ash is used as the fine aggregate. 30% by volume or more, preferably 45% by volume or more (Claim 5), at least one of an air entraining agent, a water reducing agent, and a high-performance water reducing agent (Claim 6); It is Portland cement or early strength Portland cement (Claim 7). Hereinafter, the present invention will be described in detail.

The coal ash used in the present invention has a particle size equivalent to or smaller than the fine aggregate mainly having a particle size of 5 mm or less obtained regardless of the combustion method of coal, and fly ash specified by JIS is of course, Fly ash and cinder ash, which are usually referred to as raw powder, or coal ash in a so-called broad sense, including fluidized bed fly ash, can be used.

As a result of various experiments, the present inventors have found that the particle size composition of these coal ash, especially the value of the specific surface area by the BET method is
It was found that the mortar-concrete fluidity correlates very well and is applied.
The specific surface area according to the BET method is one in which nitrogen gas is adsorbed and desorbed on the surface of coal ash particles, and the specific surface area is determined by the differential pressure thereof, which directly shows the amount of unburned carbon in the coal ash and the porosity, and It is simple and quick in terms of operation and device. That is, those with a low unburned carbon content and low unburned carbon porosity have a small BET specific surface area value, and conversely, those with a high unburned carbon content and high unburned carbon porosity. , BET specific surface area is large. The specific surface area of the inorganic part excluding unburned carbon in the coal ash is at most 0.5 to 0.8 m ² / g, and other values are comprehensively evaluated from the amount and porosity of the properties of unburned carbon. It can be said to show.

As a simple measurement method, the specific surface area value by the air permeation Blaine method is also often used in coal ash, and in the above-mentioned JIS A 6201, the Blaine specific surface area value is 24
It is specified to be 00 cm ² / g or more. However,
The Blaine method is originally intended to measure the fineness of cement, and as described above, the coal ash contains porous unburned carbon, and the Blaine method, the fineness of the coal ash,
It is difficult to say that the evaluation is always appropriate from both the properties of unburned carbon and unburned carbon. Incidentally, when the inventors analyzed 150 lots of coal ash generated from coal-fired power plants nationwide for two years from January 1993 to December 1994, the specific surface area value by the Blaine method was BET. A value of 0.5 to 0.05 relative to the specific surface area value, in other words, BE
The T specific surface area value is 2 to 20 times as large as the Blaine specific surface area value, and very effectively expresses the properties of unburned carbon, but a clear relationship cannot be obtained with the Blaine value.

As described above, the BET specific surface area value expresses the properties of unburned carbon. The larger the value, the more problematic the adsorption of cement admixtures such as water reducing agents and the more preferable as coal ash for cement and concrete. According to the present invention, the BET specific surface area value, as well as the particle size of coal ash, particularly the residue value on the sieve by AJS (air jet sieve), correlate very well with respect to the fluidity of mortar concrete, By specifying this range to make a suitable mortar and concrete coal ash,
(1) If the BET specific surface area value is less than 4 m ² / g, 4
Coal ash having a residual value on the 5 μm sieve of 40% by weight or less,
(2) If the BET specific surface area value is 4 m ² / g or more and less than 6 m ² / g, coal ash with a residue value on the 45 μm sieve of 20% by weight or less is obtained, and (3) BET specific surface area value is 6 m ² /
If it is g or more and less than 10 m ² / g, apply coal ash with a residual value on the 45 μm sieve of 10% by weight or less.

That is, if the BET specific surface area value is small, a large residual value on the 45 μm sieve with a coarse particle size is allowed, and if the BET specific surface area value is large, the residual value on the 45 μm sieve is limited to a small value. By using the coal ash within the range, it is possible to secure the predetermined fluidity and air entrainment without increasing the water content ratio of the mortar and concrete. Also, the BET specific surface area value of coal ash and 45 μm
If any of the on-sieve residual values is out of the above range, a predetermined air entrainment amount cannot be secured, which is not preferable from the viewpoint of maintaining freeze-thaw resistance.

Next, the amount of coal ash used is such that the cement / coal ash (weight ratio) is in the range of 0.5 to 3.0. If this is less than 0.5, the amount of coal ash used becomes too large, the fluidity of the concrete is lost, and mixing is difficult, which is not preferable. On the other hand, when it exceeds 3.0, the purpose of the present invention is not suitable for the mass use of fly ash,
Moreover, the strength development is not sufficient, and the use of aggregates described later, particularly fine aggregates having a poor grain size balance, is limited, which is not preferable. Therefore, it is more preferable to set the cement / coal ash (weight ratio) to 0.8 to 2.0.

It is desirable that the coal ash be used by replacing a part of the fine aggregate in the aggregate described later. By replacing the coal ash with the fine aggregate in an amount of 30% by volume or more, preferably 45% by volume or more, it is possible to obtain concrete having excellent initial strength and long-term strength.

As the cement used in the present invention, various kinds of portland cements such as normal strength, early strength, super-early strength, moderate heat, sulfate resistance, and white can be used, but they are great for improving initial and long-term strength development. To be effective,
Preferably, normal Portland cement or early-strength Portland cement is used. The amount of cement used is, in particular for use as concrete, the unit amount of cement in the concrete is in the range of 200 to 500 kg / m ³ . If the unit cement content is less than 200 kg / m ³ , the strength development, especially the initial strength, is lowered, which is not preferable.
On the other hand, if it exceeds 500 kg / m ³ , it is not preferable because it is difficult to mix concrete in the case of using a large amount of coal ash for the purpose of the present invention.

Next, as the aggregate, it is possible to use ordinary aggregates such as sand, gravel, and crushed stone which are used for ordinary concrete, as well as artificial aggregates and the like, regardless of the type of aggregate. Among the aggregates, especially the fine grain aggregates have a poor particle size distribution balance and are considered to be unsuitable as ordinary concrete aggregates. The fluidity of the above can be secured and it can be suitably used as the aggregate of the present invention.

Further, according to the present invention, by using a high-performance water-reducing agent together, not only defects such as a decrease in initial strength and an increase in drying shrinkage due to an increase in the unit water amount can be eliminated, but also a large amount of fly ash to concrete can be eliminated. Mixing can be achieved, and moreover, even if a large amount of fly ash is mixed, it is possible to realize the production of concrete with good initial and long-term strength development.

As the high-performance water reducing agent, any one having a chemical composition conventionally used as an admixture for concrete, for example, an alkylylallyl type, a naphthalene type, a melamine type, or a triazine type can be used.
Desirably, a polycarboxylic acid salt-based admixture is preferable. Of course, it is possible to apply a high-performance AE water reducing agent having air entrainment performance. As this type of admixture, commercially available products include Reobuild SP-8S (manufactured by NMB, trade name), Mighty 2000 WHS (manufactured by Kao, trade name),
Chupol HP-8 (manufactured by Takemoto Yushi Co., Ltd., trade name) and the like can be mentioned. When the amount of coal ash is increased while maintaining the amount of unit cement per 1 m ^{3 of} concrete at a predetermined amount, the volume occupied by fine powder in the concrete increases and the fluidity of the concrete is impaired. It is possible to obtain a predetermined softness (slump value) in concrete by appropriately adjusting the amount of the agent added. The addition amount of the high-performance water reducing agent is adjusted in consideration of the Portland cement to be used, the aggregate, the coal ash, and the water reducing effect for the purpose, etc. Add 10% by weight. If it is less than 0.1% by weight, the water-reducing effect is substantially absent, and if it is added in excess of 10% by weight, the effects of improving the water-reducing property and the fluidity reach a ceiling.

In the present invention, the air entraining agent has a chemical composition conventionally used as an air entraining agent for concrete, for example, nonionic type, anionic type, oxyethylene type, higher fatty acid salt type, natural resin acid salt type chemical composition. Any thing can be used. For example, AE-775S (manufactured by NMB, Inc., product name) containing an alkylcarboxylic acid compound as a main component, Vinsol (manufactured by Yamamune Chemical, product name) of natural resin acid, Seeker AER (Nippon Seeker of the Alkylphenol system). , Product name) and the like. In the present invention, it is desirable to adjust the addition ratio of the air entraining agent to adjust the air entraining amount of concrete to 4.5 to 5.5%.

As described above, according to the present invention, the amount of unburned carbon that adsorbs a cement admixture such as a water reducing agent and an air entraining agent, and the BET specific surface area value that directly expresses the porosity, and the residual value on the sieve are calculated. Since it is regulated, the type and amount of the water reducing agent to be used can be set very easily, a predetermined fluidity and air entrainment can be secured, and desired concrete performance can be obtained.

[0024] In addition to the above-described compounding ingredients, the present invention is a rapid-hardening material which is usually used in concrete.
Various concrete admixture materials such as quick-setting admixtures, high-strength admixtures, hydration accelerators, setting regulators, and various fibers as reinforcing materials,
Steel or the like can also be used.

There is no limitation on the method of mixing and kneading the above-mentioned components, as long as they can be uniformly mixed and kneaded. Moreover, usually, the order of addition of the components is not particularly limited. Furthermore, various curing methods can be applied for curing after placing concrete, and any of room temperature curing, high temperature curing, normal pressure steam curing, and high temperature and high pressure curing can be adopted. Can be carried out to obtain a higher strength concrete hardened body.

[0026]

As described above, the particle size of the coal ash particles, particularly AJS (air jet. Since the residual value on the sieve by sieve is set, the type and amount of cement admixture such as water reducing agent and air entraining agent that are easily adsorbed by unburned carbon can be set very easily, and the predetermined flow rate can be set. And concrete entrainment, and the desired concrete performance can be obtained. In addition, by appropriately adjusting the concrete mix, even if a large amount of coal ash is used, it does not impair the excellent properties of coal ash described above as concrete, but rather exerts these properties synergistically. It is possible to obtain concrete having good initial strength and long-term strength development.

[0027]

EXAMPLES Example 1 With respect to various types of coal ash generated from a coal-fired power plant, the mortar unit water content ratio according to JIS A 6201 was measured. The results are shown in Table 1. still. The unit water ratio is mortar blended without adding coal ash (ordinary Portland cement 520 g, Toyoura standard sand 1040 g and water 33
8g) shows the ratio of the amount of water and the amount of water in the same flow value of the mortar formulation (normal Portland cement 390g, coal ash 130g and Toyoura standard sand 1040g) with the addition of coal ash (see JIS A 6201).

[0028]

[Table 1]

As is clear from Table 1, the unit water amount ratio is
There is little correlation between the amount of methylene blue adsorbed and the loss on ignition value, and in the combination of the BET specific surface area value of the present invention and the residual value on the 45 μm sieve, the unit water content ratio specified in JIS A 6201 is 102% or less. Is obtained.

(Example 2) NO8 to 1 used in Example 1
The mortar test was conducted by changing the mixing ratio of coal ash of 2, 15 and 16. The mortar composition is a composition in which the amount of unit cement and the amount of water are constant, and part of the sand is replaced with coal ash, and the test is conducted so that the mortar air content is 8.0% (equivalent to 4.5% concrete air entrainment). A commercially available anionic AE agent (AE-775S manufactured by NMB Corporation) was prepared,
In addition, a carboxylic acid type high-performance water reducing agent (Rheobird SP-8S manufactured by NMB Co., Ltd.) was added so that the flow was the same (210 mm), and the required amount of AE agent and water reducing agent were added together with the setting end time. I asked. The mortar composition is shown in Table 2 and the test results are shown in Table 3.

[0031]

[Table 2]

[0032]

[Table 3]

In Table 3, the required amount of the AE agent and the amount of the water-reducing agent increase as the BET specific surface area increases, but in the present invention, the setting end time delayed by this is also within the allowable range. On the other hand, the comparative example requires a larger amount of AE agent and water reducing agent,
The setting delay due to this is remarkable.

(Embodiment 3) NOs 1 to 16 shown in Embodiment 1
Using the coal ash of No. 1, concrete was prepared with the following composition. The high-performance water reducing agent is adjusted with a slump of 18 cm as a target, the AE agent is kept constant, the air entrainment amount is determined, and a freeze-thaw test of concrete according to JIS A 6204 is performed, and the relative dynamic elastic modulus is 60% or less. The number of repeated freeze-thaw cycles was determined. The results are shown in Table 4 together with the measured values of compressive strength.

[0035] (concrete mix) cement coal ash fine aggregate Coarse aggregate AE agent superplasticizer ^{300kg / m 3 173kg / m 3} 563kg / m 3 1021kg / m 3 5.0kg / m 3 0.5 ~1.4 kg / m 3 Cement: Ordinary Portland cement manufactured by Chichibu Onoda Cement Co., Ltd. Fine aggregate: Land sand (Shizuoka) specific gravity 2.59, FM 2.75 Coarse aggregate: Crushed stone (Ibaraki) maximum size 20 mm, specific gravity 2.64, FM 6.66 high Performance water reducing agent: NMB product Rheobuild SP-8S Air entraining agent: NMB product AE-775S

[0036]

[Table 4]

In Table 4, the present invention exhibits a performance of excellent freeze / thaw property by ensuring a predetermined air entrainment amount, but in each of the comparative examples, the air entrainment amount cannot be ensured and the freeze / thaw property is poor. It is a thing.

[0038]

EFFECTS OF THE INVENTION According to the present invention, it is possible to judge the suitability for use as coal ash for mortar concrete without considering various coal types, combustion conditions of generating power plants, etc. In addition to ensuring fluidity and air entrainment, it is possible to obtain concrete with good strength development in the initial and long periods, and it is possible to effectively use a large amount of fly ash, which is an industrial by-product.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification number Reference number within the agency FI technical display location C04B 14:06 24:04) 103: 30 111: 20 (72) Inventor Koichi Tanigawa Sakura Chiba Prefecture 2-4-2 Daisaku City, Chichibu Onoda Central Research Institute (72) Inventor Noriaki Sone 2-4-2 Daisaku Sakura City, Chiba Prefecture Chichibu Small Noda Research Center (72) Inventor Masahito Matsuhisa Chiba Chichibu Onoda Co., Ltd. Central Research Laboratory, 2-4-2 Daisaku, Sakura-shi, Japan (72) Inventor Satoshi Ashiyahara 2-4-2 Daisaku Sakura, Chiba, Chiba, Japan (72) Inventor Koichi Soeda 2-4-2 Daisaku, Sakura-shi, Chiba Chichibu Onoda Central Research Institute

Claims (7)

[Claims] 1. A coal ash for mortar / concrete having a particle size constitution according to any one of the following (1) to (3). (1) BET specific surface area value of less than 4 m ² / g, residual value on 45 μm sieve of 40% by weight or less (2) BET specific surface area value of 4 m ² / g or more and less than 6 m ² / g, residual value on 45 μm sieve Is 20% by weight or less (3) BET specific surface area is 6 m ² / g or more and 10 m ² / g
Less than 45 μm, residual value on the sieve is 10% by weight or less 2. A mortar-concrete composition containing cement, aggregate, coal ash, and water, wherein the coal ash has a particle size constitution according to any one of the following (1) to (3). Mortar and concrete. (1) BET specific surface area value of less than 4 m ² / g, residual value on 45 μm sieve of 40% by weight or less (2) BET specific surface area value of 4 m ² / g or more and less than 6 m ² / g, residual value on 45 μm sieve Is 20% by weight or less (3) BET specific surface area is 6 m ² / g or more and 10 m ² / g
Less than 45 μm, residual value on the sieve is 10% by weight or less 3. Cement / coal ash (weight ratio) is 0.5 to.
Mortar concrete according to claim 2, characterized in that it is 3.0, preferably 0.8 to 2.0. 4. The mortar concrete according to claim 2 or 3, wherein coal ash is used by replacing a part of the fine aggregate in the aggregate. 5. The mortar concrete according to claim 4, wherein the coal ash content is 30% by volume or more, preferably 45% by volume or more, based on the fine aggregate. 6. The mortar concrete according to claim 2, further comprising at least one of an air entraining agent, a water reducing agent, and a high-performance water reducing agent. 7. The mortar concrete according to claim 2, wherein the cement is a normal Portland cement or an early-strength Portland cement.