JP5175165B2 - Manufacturing method of high strength building materials using hydraulic lime - Google Patents

Description

    The present invention relates to a method for manufacturing a building material having high strength using hydraulic lime.

    A member that supports a load (gravity, seismic force, wind load, etc.) in a building is called a structural member, and at present, any material of steel, reinforced concrete, or wood is used in most buildings. Other materials are not used for building structural members mainly because of their insufficient strength. Of the above three types of materials, reinforced concrete is a composite material composed of reinforcing steel and concrete. Reinforced concrete is a structure that exerts the tensile and compressive strength required for building members by reinforcing concrete having high compressive strength but low tensile strength with a rebar excellent in tensile strength. The reason why reinforced concrete is frequently used is that concrete can be provided in large quantities and at low cost.

    In addition to the above three types of materials, there is a material called natural hydraulic lime (NHL), and NHL does not dissolve in water after curing. Although it has characteristics, it is not used as a building structural member at present because of its inferior compressive strength compared to concrete. It has been known since ancient Roman times (BC 2nd century) that hydraulic lime is dissolved in water, left and dried. However, solidified hydraulic lime is also known to be brittle and insufficient in strength compared to concrete. After mixing siliceous natural limestone, natural hydraulic lime obtained by adding water and digesting it is a mixture of slaked lime and a material that exhibits a hydraulic property, a porazone substance, or artificial hydraulic lime (HL). Called.

Non-Patent Document 1 discloses that the compressive strength of natural hydraulic lime is approximately 1/23 to 1/10 at 13 weeks after placement compared to the compressive strength of cement.
Non-Patent Document 2 examines the influence of curing conditions (air curing, CO ₂ curing, or water curing) after placement on the strength characteristics of natural hydraulic lime. It is stated that the CO ₂ curing promotes the hardening of natural hydraulic lime, but the compressive strength finally obtained is not affected by the curing conditions.
Non-Patent Document 3 examines the influence of the aggregate mixed with natural hydraulic lime with water on the strength characteristics of natural hydraulic lime.

    A material similar to natural hydraulic lime is slaked lime. In the case of producing a molded body having high strength using slaked lime (calcium hydroxide), there is a method of pressing a mixture of calcium hydroxide and aggregate filled in a mold with a high-pressure press. Patent Document 1 describes a method for producing a solidified molded body for paving blocks including a vibration molding process and a carbon dioxide curing process. However, as shown in Example 2 of the present specification, a mixture of slaked lime and aggregate (standard sand) does not exhibit high strength in carbon dioxide curing. Patent Document 1 discloses that in the vibration forming process, the air in the kneaded product is expelled, and slaked lime, aggregate and water are homogenized and densely filled. It is described that it is a process of combining. Therefore, it is thought that the high intensity | strength which the solidification formation body using the slaked lime of patent document 1 shows originates in the kind of the magnesium chloride and sodium chloride added as an additive, or the used aggregate.

Non-Patent Document 4 describes that carbonic acid gas curing is performed in order to carbonate the cement surface, suppress neutralization, and increase the durability of the concrete. Cement has a lower calcium hydroxide content than natural hydraulic lime, while it contains more 2CaO.SiO ₂ hydrate (hereinafter C ₂ S), which is in the form of needle crystals. Exists (see SEM picture shown in FIG. 1). Hydrate C ₂ S is considered to act as an adhesive between calcium hydroxide crystals in the initial stage of NHL curing action, but it does not have such a function in cement that cures by bonding between hydrates. Further, in Non-Patent Document 4, it is known that hydrate C ₂ S is mainly γ-2CaO · SiO ₂ , but in NHL it is β-2CaO · SiO ₂ (hereinafter β-C ₂ S). .

As is clear from the above-mentioned documents, conventionally, it has not been considered that compressive strength that is comparable to concrete can be obtained using hydraulic lime. Furthermore, conventionally, the strength of slaked lime and concrete has been increased by a high-pressure press or additives, but a method of increasing the strength of hydraulic lime has not been known.
Yoshinori Katakura, et al., Research on material properties of natural hydraulic lime (NHL), Summary of Academic Lectures of Architectural Institute of Japan, pp. 171-172, September 2003 Akira Oda et al., Research on the strength and hardening of natural hydraulic lime (NHL), Summary of Academic Lectures of Architectural Institute of Japan, 925-926, September 2006 Ikeda, K. et al., Research on strength characteristics of natural hydraulic lime (NHL) -Examination on influence of aggregate characteristics-, Abstracts of Architectural Lectures of Architectural Institute of Japan, 685-686, August 2007 Ryoichi Serizawa et al., Technology for High Durability of Concrete Using γ-2CaO · SiO2 and Carbonation Curing, Kashima Technical Research Institute Annual Report, No. 52, pp. 107-112, September 30, 2004 JP 2006-240236 A

    An object of the present invention is to provide a method for producing a building material having high strength using hydraulic lime, and a building material and a composite material obtained by the method.

The manufacturing method of the high intensity | strength hydraulic lime building material of this invention is a method which comprises the process which fills a formwork with the mixture containing (a) hydraulic lime and water, and uses for carbon dioxide curing. In this step (a), the volume expansion when the calcium hydroxide crystal and hydrate C ₂ S in hydraulic lime are combined with carbon dioxide and changed to calcium carbonate crystal is restrained by a mold. Bonds between crystals can be strengthened and high strength can be developed.
In a preferred embodiment of the present invention, after the step (a), the method may further comprise (b) a step of subjecting the mixture containing hydraulic lime and water to carbon dioxide curing after demolding. By the step (b), sufficient strength expression can be generated in the mixture of hydraulic lime and water.
In a further preferred embodiment of the present invention, the carbon dioxide curing can be carried out at a carbon dioxide concentration of 1% by volume or more. By curing at a carbon dioxide concentration higher than the carbon dioxide concentration in the atmosphere (approximately 0.03%), high strength can be expressed at an early stage.

In a further preferred embodiment of the present invention, a formwork characterized by having a release surface so that the surface of the hydraulic lime is in direct contact with the carbon dioxide atmosphere can be used. Although it is thought that the restraining effect by a formwork contributes to the strength expression of hydraulic lime, hardening and strength expression of the mixture of hydraulic lime can be accelerated | stimulated by increasing the contact surface to a carbon dioxide gas simultaneously.
In a further preferred embodiment of the present invention, hydraulic lime characterized by a cement coefficient of 0.55 to 0.75 can be used. This is because hydraulic lime having a cement coefficient of 0.55 to 0.75 is strong in strength development by carbon dioxide curing.

In a further preferred embodiment of the present invention, natural hydraulic lime can be used as hydraulic lime.
In a further preferred embodiment of the invention, the mixture of hydraulic lime and water can further comprise aggregate.
In a further preferred embodiment of the present invention, the water constituting the mixture may be one in which carbon dioxide gas is dissolved.
In a further preferred embodiment of the present invention, a step of injecting carbon dioxide gas into a mixture containing hydraulic lime and water can be included.
In another preferred embodiment of the present invention, a hydraulic lime building material having a compressive strength of 30 N / mm ² or more produced by the method described above is provided.
The hydraulic lime building material provided in a preferred embodiment of the present invention is a hydraulic lime composite building material further including a lattice-like, net-like or shaft-like reinforcing material inside.

    According to the method of the present invention, it is possible to produce a hydraulic lime building material having high strength. Furthermore, according to the method of the present invention, it is possible to quickly develop the strength of the hydraulic lime building material.

Natural hydraulic lime (NHL), according to the European standard EN4559-1 (2001) for building lime, is “of some clay or siliceous limestone powdered by digestion, regardless of grinding. Lime made by firing. All NHLs are hydraulic. Carbon dioxide in the atmosphere contributes to hardening. In the present specification, the term natural hydraulic lime is used in the same meaning as the European standard. In addition to natural hydraulic lime, there is what is called Roman cement or ancient cement, which is slaked lime (calcium hydroxide) and pozzolanic materials (silicic acid SiO ₂ , alumina Al ₂ O ₃ , iron oxide Fe ₂ O _3). It is a lime that has been added later. It is distinguished from natural hydraulic lime obtained by calcining clayey or siliceous limestone (also called marlstone, marl), and is referred to as artificial hydraulic lime in the present specification. Moreover, when using it by this-application specification, "hydraulic lime" contains natural hydraulic lime and artificial hydraulic lime. Even in the above European standards, natural hydraulic lime and artificial hydraulic lime are distinguished from each other. Artificial hydraulic lime is mainly composed of “Hydraulic Lime”: calcium hydroxide, calcium silicate and calcium aluminate. Lime made from a mixture of these components, hydraulic. Carbon dioxide in the atmosphere contributes to curing. ” In this specification, this point is also in accordance with the European standard.

There are the following three types of typical natural hydraulic lime, and the compressive strength is defined in the European standard EN459-1.
Type of NHL Compressive strength NHL2 2-7N / mm ²
NHL3.5 3.5-10N / mm ²
NHL5 5-15 N / mm ²

<Hardening mechanism of natural hydraulic lime>
Slaked lime (calcium hydroxide) Ca (OH) ₂ obtained by calcination / digestion of limestone (calcium carbonate) CaCO ₃ is combined with carbon dioxide CO ₂ in the air (hereinafter referred to as carbonation) to produce the original limestone CaCO. _It has the property of reducing to ₃ . Slaked lime is an air-hard material, and after hardening by mixing with aggregate and water, the calcium carbonate crystals that are produced do not bind and therefore do not develop strength.
Natural hydraulic lime is obtained by calcining and digesting limestone containing silicon dioxide SiO _{2 and the} like, and hydrates such as dicalcium silicate C ₂ S containing calcium hydroxide Ca (OH) ₂ as a main component. It is lime containing. The hydrate C ₂ S contained in NHL is mainly β-C ₂ S. In contact with water, hydrates such as C ₂ S bind between calcium hydroxide Ca (OH) ₂ crystals, and further, by calcium carbonate, calcium hydroxide Ca (OH) ₂ gradually becomes calcium carbonate CaCO from the surface. It changes to ₃ crystals. The calcium carbonate CaCO ₃ crystal is kept in a bound state by a hydrate such as C ₂ S, and the hydrate is converted into a calcium carbonate CaCO ₃ crystal by the same carbonation action.
When the surface layer is carbonated, the calcium carbonate CaCO ₃ crystal forms a granular structure including voids, and carbon dioxide gas in the air is supplied to the calcium hydroxide Ca (OH) ₂ at the back, so that the carbonation proceeds slowly. That is, natural hydraulic lime is a material having both hydraulic properties and air hardness, and exhibits strength after being cured by mixing with aggregate and water. In FIG. 2, the conceptual diagram of the hardening mechanism of a natural hydraulic lime is shown.

表１において、産地Ａとはフランス東部であり、産地Ｂとはフランス南西部である。表１から、セメント係数Ｃ.Ｉ.が高い天然水硬性石灰ほど規定強度が高くなり、二酸化ケイ素ＳｉＯ_２の割合も高くなっていることが分かる。天然水硬性石灰は歴史上、セメント発明の元となった石灰であり、セメントは水和成分を高めた材料である。セメントの化学成分はビーライトＣ_２Ｓのほか、ケイ酸三カルシウム（エーライト；３ＣａＯ・ＳｉＯ_２、以下Ｃ_３Ｓ）、カルシウムアルミネート（アルミネート；３ＣａＯ・Ａｌ_２Ｏ_３、以下Ｃ_３Ａ）、カルシウムアルミノフェライト（フェライト；４ＣａＯ・Ａｌ_２Ｏ_３・Ｆｅ_２Ｏ_３、以下Ｃ_４ＡＦ）および硫酸カルシウム（セッコウ；ＣａＳＯ_４・２Ｈ_２Ｏ）が含まれる。エーライト、ビーライト、アルミネートおよびフェライトは「クリンカー」と呼ばれる。
化学成分において、天然水硬性石灰とセメントはよく似ているが、天然水硬性石灰は、クリンカーの割合が小さく、さらにほとんどがビーライトＣ_２Ｓとして存在するのが化学的な特徴である。その割合はＮＨＬ２で約１０〜２５％、ＮＨＬ３．５で約２５〜４０％、ＮＨＬ５では約４０〜５０％である。ＮＨＬ５の場合はエーライトＣ_３Ｓも含まれる。一方で、セメントのクリンカーの割合は、通常９０％以上であり、すなわち含有される水酸化カルシウムの割合は１０％未満である。
消石灰は、天然水硬性石灰と比較して、ＳｉＯ_２、Ａｌ_２Ｏ_３、Ｆｅ_２Ｏ_３、ＭｇＯといったいわゆる不純分が極めて少ない石灰であり、したがって水和反応は起こらない。 <The main component of natural hydraulic lime>
The main components of natural hydraulic lime are calcium hydroxide Ca (OH) ₂ , calcium carbonate CaCO ₃ , dicalcium silicate (belite; C ₂ S; mainly β-C ₂ S), and silicon dioxide SiO ₂ .
As shown in Table 1, the chemical analysis results show that CaO is about 60% and silicon dioxide SiO ₂ that causes hydraulic properties is 10 to 20%. The cement coefficient CI (Cementation Index) in Table 1 is one of the indexes indicating the degree of hydraulic property, and is calculated by the following formula.

In Table 1, the production area A is eastern France, and the production area B is southwestern France. From Table 1, it can be seen that natural hydraulic lime having a higher cement coefficient C.I. has a higher specified strength and a higher proportion of silicon dioxide SiO ₂ . Natural hydraulic lime has historically been the basis of the invention of cement, and cement is a material with an increased hydration component. The chemical components of the cement are belite C ₂ S, tricalcium silicate (Alite; 3CaO · SiO ₂ , C ₃ S), calcium aluminate (aluminate; 3CaO · Al ₂ O ₃ , C ₃ A). ), Calcium aluminoferrite (ferrite; 4CaO.Al ₂ O ₃ .Fe ₂ O ₃ , hereinafter referred to as C ₄ AF) and calcium sulfate (gypsum; CaSO ₄ .2H ₂ O). Alite, belite, aluminate and ferrite are called “clinker”.
In terms of chemical components, natural hydraulic lime and cement are very similar, but natural hydraulic lime has a small proportion of clinker and is characterized by being mostly present as belite C ₂ S. The ratio is about 10-25% for NHL2, about 25-40% for NHL3.5, and about 40-50% for NHL5. In the case of NHL5, alite C ₃ S is also included. On the other hand, the proportion of clinker in cement is usually 90% or more, that is, the proportion of calcium hydroxide contained is less than 10%.
Slaked lime is so-called lime, such as SiO ₂ , Al ₂ O ₃ , Fe ₂ O ₃ , and MgO, which is extremely small compared to natural hydraulic lime, and therefore no hydration reaction occurs.

The types of hydraulic lime used in the present invention include NHL2, NHL3.5, NHL5, HL2, HL3.5, HL5, etc., but are not limited to this, and are to be developed in the future. Also includes lime. Natural hydraulic lime varies slightly depending on the place of production, but calcium hydroxide Ca (OH) ₂ , calcium carbonate CaCO ₃ , dicalcium silicate (belite; C ₂ S), and silicon dioxide SiO ₂ are mainly used. Any component can be used. Natural hydraulic lime is famous from France, but may be from other origins such as Tunisia and Italy. A hydraulic lime having a cement coefficient of 0.55 to 0.75 is particularly preferable. When the cement coefficient is 0.5 or less, or 0.9 or more, the effect of strength development by carbon dioxide curing is not so high as compared to underwater curing. The mixing ratio of hydraulic lime and water may be a ratio in which a sufficiently kneaded hydraulic lime and water mixture has a desired fluidity. For example, the mixing ratio of hydraulic lime and water is adjusted so that the flow value according to the flow test method described in JIS R 5201 is 120 ± 10 mm. The water mixed with the hydraulic lime may be water in which carbon dioxide gas is dissolved.

    Natural aggregates, artificial aggregates, and recycled aggregates can be used as the aggregates used in the present invention, but are not limited thereto. Examples of natural aggregate include river sand, river gravel, mountain sand, mountain gravel and the like. Examples of the artificial aggregate include an artificial lightweight aggregate obtained by firing blast furnace slag aggregate, fly ash and the like at a high temperature. Examples of recycled aggregates include aggregates taken from concrete waste. Standard sand for cement strength test (JIS R 5201), No. 5 silica sand (for example, Kumamoto silica sand and Tohoku silica sand), and No. 7 silica sand (for example, manufactured by JFE Mineral Co., Ltd.) May be used. Depending on the type of aggregate and hydraulic lime to be used, the strength expression can be maximized by adjusting the blending ratio of the aggregate and hydraulic lime. When No. 5 silica sand is used, the mass blending ratio of NHL and aggregate is preferably 1: 2, and when No. 7 silica sand is used, it is preferably 1: 1. The mixing ratio of hydraulic lime, water and aggregate may be a ratio in which the sufficiently kneaded mixture has a desired fluidity. For example, the flow value (JIS R 5201) is 120 ± 10 mm. Adjusted.

    In the step of filling the mold with a mixture containing hydraulic lime and water and subjecting it to carbon dioxide curing, the mixture containing hydraulic lime and water is preferably subjected to carbon dioxide curing without removing the mold. . The period of carbon dioxide curing is a necessary and sufficient period for the mixture of hydraulic lime and water to harden so as not to lose shape after demolding. The period varies depending on the size of the mold, the ambient temperature, the humidity, and the like, but in general, it is preferably 2 to 10 days, and more preferably 5 to 8 days.

    Since the carbon dioxide concentration in the carbon dioxide curing is higher than the atmospheric concentration, the effect of developing the strength can be expected. High strength can be expressed at an early stage with carbon dioxide curing of 5% by volume or more, and high strength can be expressed at an earlier stage by using carbon dioxide curing at a higher concentration such as 10% or 20% by volume. be able to

Carbon dioxide curing can be adjusted according to the size of building materials to be manufactured and the surrounding environment. For example, when using a mold with an inner size of 40 x 40 x 160 mm, after placing the mold filled with a mixture containing hydraulic lime and water on the shelf of the carbon dioxide curing room, the door is closed and the interior is sealed Put it in a state. Thereafter, the air in the curing room is once degassed, and then carbon dioxide is injected to a desired concentration. In order to maintain a desired carbon dioxide concentration, carbon dioxide is appropriately injected automatically or manually. When using a carbon dioxide gas curing pot, it can also be performed in a pressurized environment. When placing at the construction site, a temporary carbon dioxide curing room can be installed around the formwork and carbon dioxide can be injected.
Carbon dioxide may be injected directly into a mixture of hydraulic lime and water. The injection can be performed using a suitable nozzle and can be before or after filling the mold.

The strength of the hydraulic lime building material produced by the method of the present invention can be evaluated by the compressive strength generally used when evaluating the strength of concrete or the like. The compressive strength is a value obtained by dividing the maximum load by the original cross-sectional area of the test piece subjected to the compression test. In addition, 28-day strength, which is a general standard for concrete, was adopted as a standard in this specification.
The hydraulic lime building material produced by the method of the present invention has a compressive strength of 30 N / mm ² or more. In the method of the present invention, it is possible to produce a hydraulic lime building material having a compressive strength of 37 N / mm ² or more, further 41 N / mm ² or more by adjusting the blending ratio with the aggregate. Portland cement used as a material for concrete and mortar for civil engineering and construction is stipulated in JIS R 5210 to have a 28-day strength of 42.5 N / mm ² or more. Since the hydraulic lime building material of the present invention has a strength of at least about 70% of the prescribed strength of Portland cement, it can be expected that it can also be used as a structural member. For example, it can be used for a structural frame / cement secondary member (interior / exterior panel, car stopper, concrete block, U-shaped groove, floor slab, etc.).
Moreover, the hydraulic lime building material manufactured with the method of this invention can contain a grid | lattice-like, net-like, or axial reinforcement material inside. The lattice-like, mesh-like or shaft-like reinforcing material may be made of metal such as iron, resin, glass fiber, carbon fiber, or vegetable fiber, but is not limited thereto.

強度発現は、万能試験機（１００トン万能試験機、島津製作所）による一方向単調加力法で行い一軸圧縮強度（Ｎ／ｍｍ^２）を測定し、荷重制御は、欧州規格ＥＮ４５９−２に規定される条件である圧縮試験：４００Ｎ／ｓで行った。圧縮強度は、試験体３体の平均値を求めた。 (Example 1)
<Experiment method>
The natural hydraulic lime used in the test is NHL2 from the A region (eastern France), NHL2, NHL3.5, NHL5 from the B region (southwest of France), and their chemical components are as shown in Table 1.
The strength test was carried out by adopting a method defined in European standard EN4592-2 (2001) for building lime and preparing a 40 × 40 × 160 mm specimen. The test method of European standard EN459-2 is compliant with Japanese Industrial Standard “Physical Test Method for Cement” (JIS R 5201). A 40 × 40 × 160 mm specimen was prepared by installing a mixture of natural hydraulic lime, aggregate and water (hereinafter referred to as NHL mixture) in a mold having an inner dimension of 40 × 40 × 160 mm. As shown in FIG. 3, the mold has a free side of 40 × 160 mm.
As the aggregate, standard sand for cement strength test (Japanese Industrial Standards JIS R 5201, Japan Cement Association) was used. In Example 3, in addition to the standard sand, No. 7 silica sand (Kumamoto silica sand) and No. 5 silica sand (JFE mineral) having different particle size distributions were used.
Curing conditions are underwater curing (temperature 20 ± 1 ° C., relative humidity 60 ± 5%), as well as underwater curing (temperature 20 ± 1 ° C.) specified in European standard EN459-2 and Japanese Industrial Standard JIS R 5201. Three conditions of carbon dioxide curing (temperature 20 ± 1 ° C., relative humidity 60 ± 5%, carbon dioxide concentration 5 volume% to 20 volume%) were adopted.
The installation period of the test specimen in the form differs depending on the curing conditions. For underwater curing, after placing the NHL mixture on the mold, cover the release surface of the mold with a glass plate, seal the NHL mixture, demold after standing for 7 days, and remove the demolded NHL mixture in water. It was used for curing. In the case of air curing, the NHL mixture was placed in a mold, left standing for 7 days without sealing the mold with a glass plate, and then demolded, and subjected to air curing. In the case of carbon dioxide curing, three different conditions were tested (carbon dioxide curing AC). The test piece of carbon dioxide gas curing A was prepared by placing the NHL mixture on the mold, leaving it in the carbon dioxide gas without sealing the mold with a glass plate for 7 days, then demolding, and removing the demolded NHL mixture with carbon dioxide. It was used for curing. The specimens for carbon dioxide curing B and C are placed in the mold, the NHL mixture is placed on the mold, the release surface of the mold is covered with a glass plate, the NHL mixture is sealed, and the mold is left to stand in water for 2 days or 7 days. Then, the demolded NHL mixture was subjected to carbon dioxide curing.

Strength development is performed by a unidirectional monotonic force method using a universal testing machine (100-ton universal testing machine, Shimadzu Corporation), and uniaxial compressive strength (N / mm ² ) is measured. Load control is specified in European standard EN459-2. Compression test which is a condition to be performed: It was performed at 400 N / s. For the compressive strength, the average value of three specimens was determined.

炭酸ガス養生Ａは、炭酸ガス濃度５容積％で行った。使用した骨材は標準砂である。各養生により作成した試験体の一軸圧縮強度（Ｎ／ｍｍ^２）を測定した。
図４に実験結果を示す。炭酸ガス養生Ａを行った消石灰及びＮＨＬ試験体は、水中養生及び気中養生を行ったものより高い強度を有することがわかる。炭酸ガス養生Ａを行ったＢ産地のＮＨＬ２およびＮＨＬ３．５（白色）の強度が、水中養生のものと比較して、約３倍の上昇を見せた。炭酸ガス養生Ａを行ったＡ産地のＮＨＬ２は、水中養生の６．８９倍の強度を有している。
Ａ産地のＮＨＬ２およびＮＨＬ３．５（白色）の気中養生と炭酸ガス養生を比較から、空気中に存在する微量の炭酸ガス（濃度０．０３％以下）では強度が十分に発現されないことがわかる。すなわち、炭酸ガス濃度を上昇させることで９〜１４倍の強度上昇を行うことができる。
消石灰は炭酸ガス養生では高い強度を発現しない。消石灰、すなわち水酸化カルシウム結晶から炭酸カルシウム結晶へ炭酸化により強度を高めるには、結晶間を結合するための高い圧力が必要となる。しかし、天然水硬性石灰は、図２で示したとおり、水和物Ｃ_２Ｓにより炭酸カルシウム結晶間が一時的に結合されることで、高い圧力をかけなくても型枠内に充填し炭酸ガス養生することで強度が上昇する。 (Example 2)
<Effect of curing conditions on NHL strength development>
About slaked lime, NHL2 of A production area, NHL2, NHL3.5, and NHL5 of B production area, the expression of the intensity | strength for 28 days by a curing condition (underwater curing, air curing, and carbon dioxide curing A) was compared.
Test specimens of slaked lime and NHL were prepared as in Example 1 and subjected to a strength test. The blending ratio is as shown in Table 3.

Carbon dioxide curing A was performed at a carbon dioxide concentration of 5% by volume. The aggregate used is standard sand. The uniaxial compressive strength (N / mm ² ) of the specimen prepared by each curing was measured.
FIG. 4 shows the experimental results. It can be seen that the slaked lime and the NHL specimen subjected to the carbon dioxide curing A have higher strength than those subjected to the water curing and the air curing. The intensity of NHL2 and NHL3.5 (white) in the B production area where the carbon dioxide curing A was performed showed an approximately three-fold increase compared to that of the underwater curing. NHL2 in the A production area where the carbon dioxide curing A is performed has a strength 6.89 times that of the underwater curing.
A comparison of air-curing and carbon dioxide curing of NHL2 and NHL3.5 (white) in the region A shows that a small amount of carbon dioxide (concentration of 0.03% or less) present in the air does not provide sufficient strength. . That is, the strength can be increased 9 to 14 times by increasing the carbon dioxide concentration.
Slaked lime does not develop high strength with carbon dioxide curing. In order to increase the strength of slaked lime, that is, from calcium hydroxide crystals to calcium carbonate crystals, by carbonation, a high pressure is required to bond the crystals. However, as shown in FIG. 2, natural hydraulic lime is filled in the mold without applying high pressure because the calcium carbonate crystals are temporarily bonded by the hydrate C ₂ S. Strength is increased by gas curing.

<Relationship between silicon dioxide content and strength>
As shown in Table 1, it seems that natural hydraulic lime has a higher content of silicon dioxide SiO _{2 and} a higher cement coefficient C.I. as the upper limit of the prescribed strength of European standard EN459-1 is higher. From the results shown in FIG. 4, there was a high strength increase due to carbonation when CI was in the range of about 0.55 to 0.75. The specified strength of European standard EN459-1 is an upper limit of 7 N / mm ² for NHL2 and an upper limit of 10 N / mm ² for NHL3.5, and the strength can be increased by 2.5 times or more by carbon dioxide curing. Further, in FIG. 4, but shows the result of the slaked lime in which the aggregate with the same standard sand, strength development from very small, can understand the role of hydrates, such as dicalcium silicate C _{2 S} to the strength.

Example 3
<Relationship between aggregate mixed with NHL and strength development by carbon dioxide curing>
In order to examine suitable aggregates and mixing ratios, using No. 7 silica sand and No. 5 silica sand, the mass mixing ratio of natural hydraulic lime: aggregate: water is 1: 1: 0.55, : 2: 0.55, and 1: 3: 0.55, the strength expression by carbon dioxide curing was compared. As shown in the sieve permeability of the aggregate in FIG. 5, No. 7 silica sand contains more fine particles than others. Standard sand contains particles that are rougher than No. 7 silica sand and No. 5 silica sand. The experiment was performed under the conditions of carbon dioxide curing A using NHL2 and NHL3.5 (white) of the A production area, and the intensity was measured for 28 days. The water NHL ratio was adjusted so that the flow value was 120 ± 10 mm.
As shown in the experimental results in FIG. 6, the strength varies depending on the blending ratio of natural hydraulic lime and aggregate. By adjusting the mixing ratio as appropriate, almost the same strength as that obtained with the standard sand could be obtained in any aggregate. That is, when the type of aggregate is different, high strength can be expressed by adjusting the blending ratio.

実験結果は表４に示すとおり、炭酸ガス養生の前に水中養生したもの（炭酸ガス養生Ｂ及びＣ）に比べ、ＮＨＬ混合物を型枠に設置直後に炭酸ガス養生（炭酸ガス養生Ａ）に供したものは、高い強度を発現する。炭酸ガス養生Ｂ及びＣでは、水和反応後、脱型したＮＨＬ混合物を炭酸養生に供したが、炭酸ガス養生ＡではＮＨＬ混合物を型枠設置した状態で炭酸ガス養生に７日間供し、脱型したＮＨＬ混合物を更に炭酸養生に供した。炭酸ガス環境下での型枠養生が高強度発現に寄与することがわかった。これは、天然水硬性石灰中の水酸化カルシウム結晶が二酸化炭素と結合し、炭酸カルシウム結晶へと変化する過程で、体積膨張に伴う型枠による拘束が結晶の結合を強固なものとしていると考えられる。
また、炭酸ガス養生Ｂ及びＣの試験体は、図４の水中養生の試験体よりも２倍以上高い強度を発現していることから、水和反応による硬化には型枠内に設置したときのような拘束効果があり、炭酸化による高強度発現に寄与していることの証拠ともなる。 Example 4
<Examination of carbon dioxide curing conditions>
About the test body created by the three conditions carbon dioxide curing (carbon dioxide curing AC of Example 1) from which the installation conditions of a mold differ, the expression on the 28th was compared.
As the test body, NHL3.5 (white) was used for natural hydraulic lime, and standard sand was used for the aggregate. The mass blending ratio of NHL3.5: standard sand: water was 1: 3: 0.55. In the carbon dioxide curing B and C, before the carbon dioxide curing, after the NHL mixture is placed in the mold, the mold is sealed and left in water for 2 days or 7 days. Went to make. Carbon dioxide gas curing A is used for carbonic acid curing immediately after installation in a state where the release surface of the mold is not blocked after the NHL mixture is installed in the mold. The uniaxial compressive strength (N / mm < ² >) of the test body created by carbon dioxide curing AC was measured.

As shown in Table 4, the experimental results are provided for carbon dioxide curing (carbon dioxide curing A) immediately after installation of the NHL mixture in the mold, compared to those cured under water (carbon dioxide curing B and C) before carbon dioxide curing. The developed one exhibits high strength. In carbon dioxide curing B and C, the dehydrated NHL mixture was subjected to carbonation curing after the hydration reaction, but in carbon dioxide curing A, the NHL mixture was subjected to carbon dioxide curing for 7 days with the form installed, and demolded. The NHL mixture thus obtained was further subjected to carbonate curing. It was found that the formwork curing under carbon dioxide environment contributes to high strength. This is because the calcium hydroxide crystals in natural hydraulic lime are combined with carbon dioxide and transformed into calcium carbonate crystals, and the restraint by the mold associated with volume expansion makes the crystal bonds strong. It is done.
In addition, the carbon dioxide gas curing test specimens B and C exhibit strength that is more than twice as high as that of the underwater curing test specimen of FIG. There is a restraining effect like this, and it is also evidence that it contributes to high strength expression by carbonation.

<Examination of carbon dioxide concentration>
The effect of carbon dioxide concentration on the strength development of NHL was tested. The 28-day strengths of NHL specimens prepared with carbon dioxide curing A with 5% by volume, 10% by volume, and 20% by volume carbon dioxide gas concentration were compared. Natural hydraulic lime used NHL2 and NHL3.5 (white) from A, and aggregate used standard sand. The mass mixing ratio of NHL: standard sand: water was 1: 3: 0.55.
The test results are shown in FIG. By increasing the carbon dioxide gas concentration, a high strength can be achieved somewhat early, but the strength increase is small even when compared with the case where the carbon dioxide gas concentration is 5% by volume.
Considering the hardening mechanism of natural hydraulic lime, strength development is performed by supplying a necessary amount of carbon dioxide for changing calcium hydroxide to calcium carbonate. In order to obtain high strength in a short period of time, the carbon dioxide concentration needs to be 5% by volume or more.

  The SEM photograph of FIG. 8 shows the crystal structure of natural hydraulic lime subjected to carbon dioxide curing. It can be seen that the calcium carbonate crystals are bound. On the other hand, the cement has a needle-like crystal structure as shown in the SEM photograph of FIG. 1, and it can be seen that there is almost no bonding between calcium carbonate crystals.

Natural hydraulic lime can be applied to the production of various forms of materials by utilizing the high strength expression technology by carbonation of natural hydraulic lime. Alternative applications can be made to various materials such as ceramic products, wooden products, cement-based secondary members, and steel-based secondary members.
Furthermore, by absorbing carbon dioxide gas, an effect of recovering carbon dioxide originating from decarburization discharged from the raw stone during the production of natural hydraulic lime can be obtained. Carbon dioxide originating from decarburization accounts for 60 to 70% of the production of natural hydraulic lime, and carbon dioxide is circulated as shown in FIG.
Assuming that all the calcium carbonate is converted to calcium oxide at the time of firing, the carbon dioxide CO ₂ recovery rate of natural hydraulic lime is expressed as It can be calculated as follows.

CO ₂ molecular weight 44.0095C / CaO molecular weight 56.0074C × content of CaO in NHL 0.60 = 0.47

That is, by utilizing this carbonation technique, about 470 (kg) of carbon dioxide can be recovered per 1 (t) of natural hydraulic lime.
A structure using cement as a raw material is difficult to recover carbon dioxide from the point that carbonation does not proceed easily and the reinforcing bar corrodes due to the problem of neutralization due to carbonation.
From the amount of cement sold (H17) in 2005 by the Japan Cement Association, carbon dioxide CO ₂ emissions from “cement products” (cement-based secondary members) among the sales items can be calculated as follows.

Cement sales 7,526,094 (t) x decarburization-derived CO ₂ emission rate per cement (t) 0.44 = 3,311,481 (t CO2)

Here, the emission rate of carbon dioxide CO _{2 from} decarburization per cement (t) is 0.44, which is the measure against global warming in the cement industry (Ministry of Economy, Trade and Industry, Industrial Structure Council, General Resource Energy Study Group, FY2005) Voluntary Action Plan Follow-up Joint Subcommittee materials: Materials 8-14, p. 173, January 2006) Cement production 71,682000 (t) in 2004 and limestone-derived CO _{2 as the} raw material Calculated from the amount of emissions 31,70400 (t).

Limestone-derived CO ₂ emissions 31,70400 (t) / Cement production 71,682000 (t) = 0.44

That is, by using natural hydraulic lime as an alternative to “cement products”, about 3.3 million (t) of carbon dioxide CO ₂ can be reduced per year.
On the other hand, 429.1 million (t), which is about 70% of the cement sales volume, is “green concrete” made in the field. The amount of carbon dioxide released by this calculation is 18.88 million (t) per year, which is too much to compare with the amount of carbon dioxide released by “cement products”.
By using carbon dioxide gas injected into a mixed liquid of natural hydraulic lime to increase the strength, carbon dioxide gas recovered from factory exhaust in the manufacturing industry, energy industry, etc. was introduced to the construction site, and a formwork was used. Usage such as on-site work becomes possible. This method is thought to lead to significant suppression of carbon dioxide emissions.

Hydration of cement by SEM (2000 to 3000 times) (Teaching material for building materials, quoted from Architectural Institute of Japan, 1995) Conceptual diagram of the hardening mechanism of natural hydraulic lime The formwork is filled with a mixture of NHL, aggregate and water Relationship between NHL type, curing conditions and compressive strength Aggregate particle size distribution (sieving transmittance) Relationship between aggregate type and compressive strength Relationship between carbon dioxide concentration and compressive strength during carbonic acid curing SEM photograph showing the crystal structure of natural hydraulic lime cured with carbon dioxide Manufacturing process of natural hydraulic lime components with carbon dioxide circulation

Claims (11)

(A) A method for producing a high-strength hydraulic lime building material, comprising a step of filling a formwork with a mixture containing hydraulic lime and water and subjecting the mixture to carbon dioxide curing. After the step (a)
(B) The method according to claim 1, further comprising a step of subjecting the mixture containing hydraulic lime and water to carbon dioxide curing after demolding.   The method according to claim 1 or 2, wherein a carbon dioxide gas concentration of the carbon dioxide gas curing is 1% by volume or more.   The method according to any one of claims 1 to 3, wherein the mold has a release surface so that a surface of the hydraulic lime is in direct contact with a carbon dioxide atmosphere.   The method according to any one of claims 1 to 4, wherein the cement coefficient of hydraulic lime is 0.55 to 0.75.   The method according to any one of claims 1 to 5, wherein the hydraulic lime is natural hydraulic lime.   The method according to any one of claims 1 to 6, wherein the mixture of hydraulic lime and water further comprises aggregate.   The method according to any one of claims 1 to 7, wherein the water constituting the mixture is obtained by dissolving carbon dioxide gas.   The method according to any one of claims 1 to 8, comprising a step of injecting carbon dioxide gas into a mixture containing hydraulic lime and water. The hydraulic lime building material which has the compressive strength of 30 N / mm < ² > or more manufactured by the method as described in any one of Claim 1 to 9.   The hydraulic lime composite building material according to claim 10, comprising a lattice-like, mesh-like or shaft-like reinforcing material inside.

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