Cement composition and cementite

Abstract

To provide an admixture added to a cement composition containing coal ash that can improve the strength of a cement hardened body containing coal ash more than before, and a cement composition containing this admixture.SOLUTION: This invention relates to an admixture for addition to a cement composition containing coal ash, the admixture containing biomass ash as a major component. According to the present invention, by adding the admixture containing biomass ash as the major component to the cement composition containing coal ash, the resulting cement hardened body has improved compressive strength compared to that obtained from cement compositions containing no biomass ash but coal ash. Alternatively, the cost can be reduced by reducing the cement content while maintaining the same level of strength as before.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to admixtures, cement compositions, and cement hardened bodies, and particularly to admixtures for adding to cement compositions containing fly ash, cement compositions containing such admixtures, and cement hardened bodies.

Background Art

[0002] Conventionally, fly ash has been used as an admixture for cement compositions such as dam concrete, dikes, and mound materials (roadbeds, roadbase materials) under roads. Fly ash is discharged from electric power utilities such as thermal power plants, and using it as a raw material for cement compositions or an admixture for concrete leads to a reduction in waste.

[0003] Non-Patent Document 1 discloses manufacturing an artificial ground material from a cement composition obtained by mixing fly ash calculated from a coal-fired power plant with water (seawater), cement, etc., and Non-Patent Document 2 discloses manufacturing internal filling materials and revetment blocks in addition to the artificial ground material.

[0004] According to Non-Patent Documents 1 and 2, the cement hardened body obtained by including fly ash in the cement composition has the strength required for each application such as artificial ground material, and the amount of fly ash waste can be reduced by using it as an admixture for the cement composition.

Prior Art Documents

Non-Patent Documents

[0005]

Non-Patent Document 1

Non-Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0006] According to Non-Patent Documents 1 and 2, cementitious bodies with the necessary strength for various applications, such as artificial ground materials, can be obtained. However, there is also a need to further increase the strength of cementitious bodies containing coal ash. For example, there is a need to reduce costs by reducing the amount of cement used in the mixture while maintaining the same strength as conventional cementitious bodies.

[0007] In view of the above-mentioned problems, the object of the present invention is to provide an admixture to be added to a cement composition containing coal ash, and a cement composition containing this admixture, which can improve the strength of a hardened cement containing coal ash compared to conventional materials. [Means for solving the problem]

[0008] The inventors diligently conducted studies to achieve the above objective. As a result, they found that by including biomass ash as an admixture in a cement composition containing coal ash, the compressive strength of the resulting hardened cement was improved compared to a cement composition containing coal ash but without biomass ash.

[0009] In other words, the invention described in claim 1 for achieving the above objective is an admixture for addition to a cement composition containing coal ash, characterized in that it contains biomass ash as its main component.

[0010] According to this invention, by adding an admixture containing biomass ash as the main component to a cement composition containing coal ash, the resulting hardened cement does not contain biomass ash and has improved compressive strength compared to that obtained from a cement composition containing coal ash.

[0011] Furthermore, the admixture preferably contains 15% to 60% by mass of calcium oxide, 20% to 70% by mass of silicon dioxide, and 1% to 20% by mass of potassium oxide, based on the total mass of the admixture.

[0012] Furthermore, the above objectives can also be achieved by a cement composition characterized by containing the admixture of the present invention, coal ash, cement, and water.

[0013] The cement composition of the present invention preferably contains aggregate in an amount of 5% by mass or less relative to the total mass of the cement composition.

[0014] Furthermore, in the cement composition of the present invention, it is preferable that the volume percentage of the admixture relative to the total amount of the admixture and coal ash is 20% or more and 80% or less.

[0015] Furthermore, the above objective can also be achieved by a hardened cement body obtained by hardening the cement composition of the present invention. [Effects of the Invention]

[0016] According to the present invention, by adding an admixture mainly composed of biomass ash to a cement composition containing coal ash, the resulting hardened cement body does not contain biomass ash and exhibits improved compressive strength compared to a cement composition containing only coal ash. Alternatively, it is possible to reduce costs by decreasing the cement content while maintaining a strength comparable to conventional methods. [Brief explanation of the drawing]

[0017] [Figure 1] This is a bar graph showing the chemical composition of the admixture according to the present invention used in the examples. [Figure 2] This is a flowchart showing the method for preparing the cement composition according to the present invention in the examples. [Modes for carrying out the invention]

[0018] <Admixture> The admixture of the present invention is an admixture for addition to a cement composition containing coal ash, and mainly contains biomass ash.

[0019] To contain biomass ash as the main component means that the admixture contains 90% by mass or more of biomass ash based on its total mass. Further, it is preferable that the admixture contains 95% by mass or more of biomass ash based on its total mass, and it is particularly preferable that it contains 100% by mass.

[0020] Biomass ash is obtained by burning woody biomass, herbaceous biomass, and other food residues derived from plants.

[0021] Examples of woody biomass include chips such as unused thinned wood, sawmill residues, recycled wood, sawdust, and bark. Examples of herbaceous biomass include bamboo, rice husks, sugarcane, rice straw, and tea dregs. Examples of food residues derived from plants include fruit peels and coffee extraction residues.

[0022] From the viewpoint of stable supply of biomass ash, it is preferable that the biomass ash is combustion ash obtained by burning woody biomass such as unused thinned wood, sawmill residues, and recycled wood in a woody biomass power plant.

[0023] Preferably, the admixture contains 15% by mass or more and 60% by mass or less of calcium oxide (CaO), 20% by mass or more and 70% by mass or less of silicon dioxide (SiO2), and 1% by mass or more and 20% by mass or less of potassium oxide (K2O) based on the total mass of the admixture.

[0024] When the admixture containing biomass ash as the main component of the present invention is blended into a cement composition containing coal ash, the compressive strength of the hardened body is improved. Although the reason for this compressive strength improvement effect is not clear, the inventors推测 that it is due to the fact that calcium oxide, silicon dioxide, and potassium oxide are contained in the admixture in the above ratios.

[0025] Furthermore, it is even more preferable that the admixture contains, based on the total mass of the admixture, 25% to 50% by mass of calcium oxide (CaO), 25% to 55% by mass of silicon dioxide (SiO2), and 2% to 10% by mass of potassium oxide (K2O).

[0026] The chemical composition of the admixture can be determined, for example, by X-ray fluorescence analysis.

[0027] <Cement composition> The cement composition of the present invention comprises the above-mentioned admixture of the present invention, coal ash, cement, and water.

[0028] The admixtures are as described above, and their explanation will be omitted here.

[0029] Coal ash consists of ash particles generated by the combustion of coal, and is mainly produced at coal-fired power plants. Coal ash is broadly classified into clinker, which is a porous, lumpy ash that falls to the bottom of a boiler after coal is burned and the ash particles melt and solidify, and fly ash, which is fine, spherical particles collected by an electrostatic precipitator from ash floating with the combustion gases. In this invention, fly ash is mainly used as coal ash.

[0030] The amount of coal ash and admixture added to the cement composition is 400 parts by mass or more and 700 parts by mass or less, preferably 500 parts by mass or more and 650 parts by mass or less, per 100 parts by mass of cement.

[0031] Furthermore, the volume percentage of the admixture relative to the total amount of admixture and coal ash in the cement composition is preferably 20% to 80%, and particularly preferably 20% to 60%. Note that if this volume percentage of the admixture exceeds 50%, the fluidity of the fresh cement composition decreases; therefore, from the viewpoint of the fresh cement composition, it is preferable that it be 50% or less.

[0032] When the volume percentage of admixtures relative to the total amount of admixtures and coal ash in the cement composition is between 20% and 80%, the compressive strength of the hardened cement body after 91 days of age increases significantly compared to hardened cement body without admixtures.

[0033] Cement is an inorganic bonding material that hardens when mixed with water, and in this invention, hydraulic cement is used. As hydraulic cement, single-component cements such as Portland cement (JIS R5210), hydraulic lime, Roman cement, and natural cement may be used, or blended cements such as lime-blended cement and blended Portland cement (JIS R5211, R5212, R5213) may be used.

[0034] Water is added to the cement composition to harden the cement. The water used is not limited to pure water; tap water, river water, lake water, and seawater can also be used.

[0035] Furthermore, the cement composition may also contain optional components such as gypsum, copper slag, and aggregate.

[0036] Gypsum is added to induce the formation of ettringite, thereby suppressing the leaching of harmful elements from coal ash.

[0037] Aggregates are generally used in the manufacture of concrete and are added to suppress the heat generated by the hydration reaction of the cement composition, suppress shrinkage, and reduce the amount of cement used to lower costs. Aggregates are divided into coarse aggregate and fine aggregate. Coarse aggregate is retained by 85% or more by mass through a 5 mm mesh sieve, while fine aggregate passes through a 5 mm mesh sieve and passes through a 10 mm mesh sieve by 100% by mass.

[0038] Examples of aggregate materials include river sand, mountain sand, sea sand, blast furnace slag, and copper slag. In this invention, coal ash and admixtures are not included in the aggregate.

[0039] Since the cement composition containing the admixture and coal ash of the present invention tends to have a low specific gravity, for example, when a cement hardened body having a weight capable of withstanding tsunamis or waves is required, it is preferable to add fine aggregate (such as copper slag, sand, or gravel) with a high specific gravity in order to secure a predetermined unit volume weight.

[0040] On the other hand, for applications other than such, it is preferable to include aggregate in an amount of 5% by mass or less relative to the total mass of the cement composition, more preferably 1% by mass or less, and particularly preferable not to add any aggregate, in order to reduce weight and improve workability and transportability.

[0041] Next, we will describe the method for preparing the cement composition.

[0042] The cement composition is prepared using a method similar to that used for preparing general mortar. Specifically, the powder components, such as cement, coal ash, and admixtures, are first mixed together. For powder mixing, a well-known hand mixer or pan mixer used in mortar production can be used, but is not limited to these.

[0043] After mixing the powders, water is added and the mixture is kneaded. After kneading, it is preferable to scrape off any remaining unmixed material from the corners of the mixer and around the stirring blades. Finally, the mixture is kneaded again to obtain the cement composition. An example of the cement composition preparation flow is shown in Figure 2.

[0044] <Hardened cement> The cement hardened body of the present invention is a cement hardened body obtained by hardening the cement composition of the present invention. Specifically, it is obtained by pouring the above-prepared cement composition into a formwork that is appropriately provided and curing it. No reinforcing bars are incorporated into the formwork, and therefore, the obtained cement hardened body does not contain reinforcing bars.

[0045] The cement composition poured into the formwork is compacted to remove air bubbles. Compaction is carried out by vibration compaction using a vibrator.

[0046] After compaction, the material is cured until the required compressive strength is achieved, resulting in a hardened cement body.

[0047] Therefore, according to the admixture, cement composition, and hardened cement of the present invention, by adding an admixture mainly composed of biomass ash to a cement composition containing coal ash, the resulting hardened cement does not contain biomass ash and has improved compressive strength compared to that obtained from a cement composition containing coal ash. Alternatively, it is possible to reduce costs by reducing the cement content while maintaining a strength comparable to conventional methods.

[0048] Furthermore, coal ash contains harmful elements (arsenic, selenium, fluorine, and boron), and depending on the amount of coal ash used, the amount of these harmful elements leached from the cement hardened body may exceed the soil environmental standards. However, since the compressive strength of the cement hardened body has been improved compared to conventional methods, the leaching of harmful components from coal ash in the cement hardened body can be suppressed more effectively than before.

[0049] Furthermore, by replacing coal ash with an admixture that primarily contains biomass ash, the amount of harmful elements contained in the hardened cement body is simply reduced, and the amount of harmful elements leached out can be decreased compared to conventional methods. [Examples]

[0050] The present invention will be described in detail below with reference to examples, but the present invention is not limited to these examples. 1. Preparation of cement composition In this invention, biomass ash was used as the admixture. The chemical composition of the biomass ash (admixture) is shown in Figure 1.

[0051] This admixture was mixed in a Hobart-type mortar mixer with a nominal capacity of 10 L with cement, coal ash, and gypsum in the proportions shown in Table 1, as shown in Figure 2, at a mixing volume of 3 L for 15 seconds. Then water was added and mixed for another 30 seconds, after which the mixer was stopped.

[0052] The mixture was scraped off any insufficiently mixed residue from the corners of the mixer and around the stirring blades, then mixed for another 90 seconds before being discharged from the mixer to obtain the cement composition.

[0053] [Table 1]

[0054] 2. Manufacturing of cement hardened bodies (test specimens) The obtained cement compositions for the Comparative Example, Examples 1-3, and Reference Example were each poured into cylindrical formwork measuring 5 cm in diameter and 10 cm in height, and compacted using a table vibrator (vibration frequency: 60 Hz).

[0055] After casting, the molds were removed one day later, and curing was performed underwater. Curing was carried out in a 20°C test chamber to obtain test specimens. For each cement composition, three specimens were prepared at 7 days (age 7), 28 days (age 28), and 91 days (age 91), for a total of nine specimens.

[0056] 3. Evaluation Nine test specimens were obtained for each cement composition and subjected to compressive strength testing. The compressive strength testing was conducted in accordance with JIS A 1108:2018 "Test Method for Compressive Strength of Concrete".

[0057] Three compressive strength tests were conducted on each cement composition at each age, and the average value was taken as the compressive strength for that age. The results are shown in Table 2.

[0058] [Table 2]

[0059] A comparison of the comparative examples in Table 2 with Examples 1-3 shows that replacing the coal ash in the cement composition with a biomass ash admixture increases the compressive strength of the hardened cement.

[0060] It should be noted that a system in which coal ash is 100% replaced with biomass ash does not contain coal ash and is therefore a reference example outside the scope of this invention. [Industrial applicability]

[0061] The admixture of the present invention is for addition to cement compositions containing coal ash. The cementized body without reinforcing bars after the cement composition has hardened can be used as embankment, seawall, roadbed material, etc.

Claims

1. A cement composition comprising an admixture for addition to a cement composition containing coal ash, coal ash, cement, and water, The aforementioned admixture contains biomass ash as its main component, The amount of coal ash and admixture added is 400 parts by mass or more and 700 parts by mass or less per 100 parts by mass of cement, and The volume percentage of the admixture relative to the total amount of the admixture and coal ash is 20% or more and 80% or less. A cement composition characterized by the following features.

2. The cement composition according to claim 1, characterized in that it contains aggregate in an amount of 5% by mass or less relative to the total mass of the cement composition.

3. A cementite-hardened body obtained by hardening the cement composition according to any one of claims 1 to 2.

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