JP2024039976A - Method of recovering cement raw material from waste concrete - Google Patents

Abstract

To provide a method of recovering a cement raw material less likely to be contaminated with aggregate, from waste concrete.SOLUTION: The method of recovering a cement raw material from waste concrete, includes a first step of crushing waste concrete, a second step of classifying the crushed waste concrete at a classification point where the cement paste content in fine granules is not less than 60 mass%, a third step of sorting the fine granules by dry-type gravity sorting into granules of a high specific gravity and granules of a low specific gravity, and a fourth step of recovering the granules of a low specific gravity.SELECTED DRAWING: None

Description

The present invention relates to a method for recovering cement raw materials from waste concrete.

Waste concrete generated from demolition work of reinforced concrete buildings, etc. is crushed to a particle size of about 40 mm after removing foreign substances other than concrete such as reinforcing bars, and used as roadbed material or backfill material. was. However, while waste concrete is increasing mainly in large cities, demand for roadbed materials, etc. is on the decline. Attempts have been made to separate the cement paste and aggregate adhering to the concrete and reuse this aggregate as recycled aggregate.

For example, waste concrete with a particle size of 1000 mm or less is crushed to a particle size of about 5 mm or less using a crusher and a fine crusher with a sieve interposed, and then the crushed material with a particle size of 0.5 to 5 mm is subjected to specific gravity sorting. A method of sorting crushed materials of 0.5 mm or less with a cyclone and recovering high specific gravity materials as recycled fine aggregate (Patent Document 1), a method in which crushed waste concrete of approximately 40 mm or less is further crushed to 5 mm or less, and this is polished. A method has been proposed (Patent Document 2) in which the mortar is removed, fine powder is removed from the treated material, and the recycled fine aggregate is recovered. In addition, after crushing the waste concrete and separating it into sand cement with a particle size of less than 5 mm and crushed gravel with a particle size of 5 mm or more using a vibrating sieve, the crushed gravel is ground to remove the mortar and separated into crushed gravel. This aggregate is separated by specific gravity and the high specific gravity is recovered as recycled aggregate, and the sand and cement are ground to separate the mortar and the sand and mortar are aggregated. A method (Patent Document 3) has also been proposed in which sand and cement are recovered by spirally classifying the aggregate.

Japanese Patent Application Publication No. 2001-220192 Japanese Patent Application Publication No. 08-245248 Japanese Patent Application Publication No. 11-314951

However, although the cement raw material recovered by the above-mentioned prior art has concentrated calcium, it contains a large amount of aggregate due to the fact that it is over-pulverized to improve the quality of the recycled aggregate. Therefore, since the recovered cement raw material has a high alkali equivalent content, there is a problem that its reuse is limited. Furthermore, since recycled aggregates are not widely used, there is a need for a method for recovering cement raw materials that does not rely solely on the recycled aggregate manufacturing process.
Therefore, an object of the present invention is to provide a method for recovering cement raw materials from waste concrete in which mixing of aggregate is suppressed.

As a result of studies to suppress the mixing of aggregate into cement raw materials, the present inventors crushed waste concrete and classified the crushed material at a classification point where the content of cement paste in fine particles was 60% by mass or more. By classifying the waste concrete and collecting fine particles rich in cement paste in advance, and then dry-type gravity sorting to recover the light specific gravity substances, cement raw materials with less aggregate mixed in can be efficiently converted from waste concrete. We found that it can be easily recovered.

That is, the present invention provides the following [1] to [4].
[1] A first step of crushing waste concrete,
A second step in which the crushed material obtained in the first step is classified at a classification point where the cement paste content in the fine particles is 60% by mass or more, and a dry specific gravity of the fine particles obtained in the second step. A method for recovering cement raw materials from waste concrete, comprising a third step of sorting into heavy specific gravity materials and light specific gravity materials, and a fourth step of recovering the light specific gravity materials obtained in the third step.
[2] After the second step and before the third step, after crushing the coarse particles obtained in the second step, the crushed product is made such that the cement paste content in the fine particles is 60% by mass or more. The cement raw material recovery method described in [1] above, which includes a step of classifying at a classification point.
[3] After the second step and before the third step, the coarse grains obtained in the second step are classified into two or more grain groups using at least a sieve with an opening of 5 mm, and the grain size is 5 mm or more. After dry specific gravity sorting of each grain group excluding coarse particles to obtain light specific gravity materials, and crushing the light specific gravity materials, the crushed materials are classified to a classification point where the cement paste content in the fine particles is 60% by mass or more. The method for recovering cement raw materials according to [1] or [2] above, which includes a step of classifying the raw materials.
[4] The cement raw material according to any one of [1] to [3] above, which is crushed in the first step until the cement paste content in the crushed material with a particle size of 5 mm or more is 15% by mass or less. Collection method.

According to the present invention, it is possible to efficiently recover cement raw materials in which mixing of aggregate is suppressed from waste concrete. Therefore, the cement raw material recovered according to the present invention has a high cement paste content and a low alkali equivalent content, so it can be reused with a high raw material consumption rate. Furthermore, according to the present invention, materials that can be recycled as recycled aggregate can also be efficiently recovered from waste concrete. Therefore, the recovery method of the present invention is useful as a method for recycling waste concrete.

1 is a diagram showing an embodiment of a cement raw material recovery device applicable to a recovery method according to the present invention. It is a figure showing other embodiments of a cement raw material recovery device applicable to a recovery method concerning the present invention.

Hereinafter, preferred embodiments will be described in detail with reference to the accompanying drawings.
<First embodiment>
FIG. 1 shows an example of a cement raw material recovery device applicable to the recovery method according to the present embodiment. The cement raw material recovery equipment shown in Figure 1 consists of a waste concrete hopper for storing waste concrete, a dryer for stirring and adjusting the water content by blowing hot air through the waste concrete, and crushing the waste concrete after drying. It is equipped with a crushing device that separates the crushed waste concrete, a classification device that sorts the crushed waste concrete, and a dry gravity sorting device that dry-types the fine particles separated by the classification device.On the downstream side of the crushing device, there is a It is equipped with an intake fan that sucks in the dust, and a suction wind type specific gravity sorter (cyclone) that sorts the dust sucked in by the suction fan.

The recovery method according to this embodiment includes a first step, a second step, a third step, and a fourth step. Each step will be explained below.

(First step)
This process is a process of crushing waste concrete. This makes it easier to recover cement raw materials.
Examples of waste concrete include demolished concrete generated from civil engineering work, demolition of structures, etc., but it is preferable that the aggregate used does not contain limestone aggregate. As waste concrete, surplus concrete generated during construction of buildings etc. may be used. Furthermore, from the viewpoint of improving work efficiency and the quality of cement raw materials, concrete blocks that have been divided into small pieces, magnetically sorted, or manually sorted can also be used as waste concrete for the purpose of separating foreign substances such as reinforcing bars.
The size of waste concrete is usually 200 to 400 mm in maximum particle size. The "maximum particle size" here refers to the value obtained by collecting the largest waste concrete from waste concrete and measuring the point where the diameter of the waste concrete is the largest.

When the maximum particle size of waste concrete exceeds 40 mm, it is preferable to crush the waste concrete so that the maximum particle size of the crushed material is 40 mm or less. The lower limit of the particle size of the crushed material is not particularly limited, but from the viewpoint of work efficiency, it is preferably 0.01 mm or more, more preferably 0.05 mm or more, and even more preferably 0.1 mm or more.

A crusher can be used to crush waste concrete. As the crusher, known ones can be used, such as a jaw crusher that compresses and crushes with a fixed blade fixed to a frame and a moving blade, a striking plate rotated at high speed, and a repulsion plate fixed to the device. These include impact crushers that crush materials by impact, gyratory crushers and cone crushers that use a conical cone cape and eccentric mantle to compress and crush materials, and double roll crushers that rotate two rolls that compress and crush materials between them. Among these, from the viewpoint of suppressing cracking of the aggregate, it is preferable to use a compression type crusher such as a jaw crusher or a cone crusher in which the gap between the devices is set to about 40 to 80 mm. Note that the crusher may be equipped with a bag filter for collecting exhaust gas containing dust generated when waste concrete is crushed.

In this step, the crushed material having a maximum particle size of 40 mm or less may be further crushed for a second time using a crusher. As the crusher, for example, a dry crusher such as a vibration mill, a cone crusher, a jaw crusher, etc. can be used. In this case, it is preferable to crush so that the cement paste content in the crushed material having a particle size of 5 mm or more is preferably 15% by mass or less, more preferably 10% by mass or less, and still more preferably 5% by mass or less. The crushed material may be crushed by circulating it multiple times. Note that the cement paste content is measured according to the method described below.
When performing secondary crushing using a compression crusher, it is preferable that the set (close) be set within a range of ±25% with respect to the maximum particle size of the original aggregate contained in the waste concrete. It is also possible to provide a retention mechanism in the discharge section so that the sample is always filled in the crushing chamber of the crusher.

Further, in this step, as shown in FIG. 1, the dust of −0.15 mm particles generated during crushing can be collected using a suction fan. Then, the sucked dust can be sorted into heavy specific gravity and light specific gravity by a suction wind type specific gravity sorter (cyclone), and the light specific gravity can be recovered as a raw material for cement.

(drying process)
In this embodiment, drying may be performed for the purpose of adjusting the moisture content of waste concrete before the first step or after the first step but before the second step. Drying can be carried out at a temperature of preferably 20 to 300°C, more preferably 75 to 110°C, preferably 30 minutes to 3 hours, and even more preferably 1 to 2 hours. Thereby, the water content in waste concrete can be reduced to less than 5%. Note that drying can be performed by extracting exhaust gas discharged from the cement manufacturing process.

(Second process)
This step is a step in which the crushed waste concrete obtained in the first step is classified at a classification point where the cement paste content in the fine particles is 60% by mass or more. Thereby, mixing of aggregate into cement raw materials can be suppressed.
This step can use a classifier. As the classifier, any known classifier can be used, and examples thereof include a sieve classifier, an air classifier, and an inertial classifier. For example, the sieve classifier may be a vibrating type, an in-plane motion type, a rotating type, or a fixed type, and the type is not particularly limited. Regarding the opening shape, a punch metal screen, a grizzly feeder, a wedge wire screen, a louver screen, or a comb blade screen can be used. Further, examples of the air classifier include a dry cyclone, a rotor classifier, an elbow jet classifier, and the like.

In this process, the waste concrete crushed material is separated into coarse particles and fine particles, and the classification point is determined using the cement paste content of the fine particles as an index. Here, in this specification, "cement paste content" refers to a value measured by the following method.

After pulverizing the sample, the mass of the residue is measured by dissolving it in hydrochloric acid (1+100) in accordance with the Cement Association of Japan method F-18. Next, the mass proportion of the insoluble residue (in.sol) is calculated using the following formula (i), and is taken as the aggregate content.

Aggregate content (in.sol) (%)=w/s×100 (i)

[In the formula, w represents the residual mass (g), and s represents the sample mass (g). ]

Next, assuming that the sample contains only two components, cement paste and aggregate, the cement paste content is determined from the following formula (ii).

Cement paste content (%) = 100 - Aggregate content (%) (ii)

Then, the cement paste content of the fine particles separated by classification is analyzed by the method described above, and the classification point at which the cement paste content becomes 60% by mass or more is determined. From the viewpoint of suppressing the mixing of aggregate, the classification point should preferably be able to separate fine particles with a cement paste content of 63% by mass or more, and more preferably be able to separate fine particles with a cement paste content of 65% by mass or more. preferable.
In addition, in the cement raw material recovery device shown in Figure 1, a sieve type classifier is used, and a mesh opening of 0.15 mm is adopted as the classification point at which the cement paste content in the fine particles is 60% by mass or more. There is.

(Third step)
This step is a step in which the fine grains obtained in the second step are subjected to dry specific gravity sorting to classify them into heavy specific gravity materials and light specific gravity materials. This allows the cement paste to be concentrated into a light specific gravity material while suppressing the mixing of aggregate.
Any known dry type gravity sorter can be used, but zigzag wind type gravity sorters, air table type gravity sorters, suction A wind-powered specific gravity sorter is preferred.
In addition, in the cement raw material recovery apparatus shown in FIG. 1, a suction wind type specific gravity sorter (cyclone) is used.

(Fourth step)
In this step, the light specific gravity materials sorted in the third step are recovered. The recovered light specific gravity materials are prevented from being mixed with aggregate, and the cement paste content is increased to 65% or more. Therefore, through this step, it is possible to recover a cement raw material with a high cement paste content and a low alkali equivalent content.

In addition, in this embodiment, after the second step and before the third step, the coarse particles obtained in the second step are crushed, and the crushed material is crushed so that the cement paste content in the fine particles is 60 mass. % or more may be used for classification.
For crushing the coarse particles, the secondary crushing described in the first step can be employed. Moreover, the classification of the crushed material can be performed by the same operation as in the second step, and the preferable aspect of the cement paste content in the fine particles is as explained in the second step.
In addition, in the cement raw material recovery device shown in Fig. 1, coarse particles of +0.15 mm are secondarily crushed, and the crushed materials are classified using a sieve classifier with an opening of 0.15 mm to separate fine particles. The fine particles are mixed with the fine particles obtained in the second step, and the mixture is subjected to a third step to be separated into heavy specific gravity materials and light specific gravity materials, and the light specific gravity materials are recovered.

<Second embodiment>
FIG. 2 is an example of a cement raw material recovery device that can be applied to the cement raw material recovery method according to the present embodiment. The cement raw material recovery device shown in FIG. 2 has the same configuration as the cement raw material recovery device according to the first embodiment, but includes a crushing device for crushing light specific gravity materials downstream of the dry specific gravity sorting device, The difference is that the present invention further includes a classifier for classifying crushed materials of light specific gravity and a dry gravity sorter for dry gravity sorting the fine particles separated by the classifier. In addition, the crushing device, classifier, and dry specific gravity sorting device installed downstream of the dry specific gravity sorting device can be used without installing these devices. You may use it.

The recovery method according to this embodiment is similar to the recovery method according to the first embodiment in that it includes the first, second, third, and fourth steps, but differs in the following respect. That is, after the second step and before the third step, in the recovery method according to the first embodiment, the coarse particles obtained in the second step are crushed, and the crushed material is classified at a classification point where the cement paste content in the fine particles is 60 mass% or more. However, in the recovery method according to this embodiment, the coarse particles are subjected to the following steps a, b, c, and d. The first and second steps of the recovery method according to this embodiment are as described in the first embodiment.

Step a: The coarse particles obtained in the second step are classified into two or more particle groups using at least a sieve with an opening of 5 mm.
Step b: Dry gravity sorting is performed for each grain group excluding coarse grains with a grain size of 5 mm or more, and the grains are separated into heavy grains and light grains.
Step c: The light specific gravity material obtained from each grain group is crushed.
Step d: The crushed material is classified at a classification point where the cement paste content in the fine particles is 60% by mass or more.

First, step a will be explained.
Step a is a step of classifying the coarse grains obtained in the second step into two or more grain groups using at least a sieve with an opening of 5 mm.
In this step, a sieve classifier can be used. A known sieve classifier can be used, and specific examples are as described in the second step of the first embodiment.

In this step, from the viewpoint of suppressing the mixing of aggregate, the waste concrete crushed material is separated into preferably 5 or more grain groups, more preferably 6 or more grain groups, and still more preferably 7 or more grain groups. Note that the upper limit of the number of grain groups is not particularly limited, but from the viewpoint of work efficiency, it is preferably 9 or less, and more preferably 8 or less. In this case, the opening of each sieve can be selected as appropriate to obtain the classified material with the desired particle size, but from the viewpoint of suppressing the mixing of aggregate and recovering recycled aggregate, a sieve with an opening of 5 mm may be used. It is preferable to use at least a sieve having a mesh size within the range of 0.1 to 0.2 mm. In this step, the particles may be sorted in order from the one with the largest opening, or may be sorted in the order from the one with the smallest opening.

In a preferred embodiment, the waste concrete crushed material is separated into seven grain groups using a first sieve, a second sieve, a third sieve, a fourth sieve, a fifth sieve, and a sixth sieve. This can be mentioned. In this case, the opening of the first sieve is 5 mm, the opening of the second sieve is preferably more than 2.0 mm and no more than 2.5 mm, and the opening of the third sieve is 1.0 mm or more and 2.5 mm. The opening of the fourth sieve is preferably at least 0.5 mm and less than 1.0 mm, the opening of the fifth sieve is preferably at least 0.3 mm and less than 0.5 mm, and the opening of the sixth sieve is preferably at least 0.3 mm and less than 0.5 mm. It is preferably 0.1 mm or more and less than 0.3 mm. In the cement raw material recovery apparatus shown in FIG. 2, a sieve classifier is used, the first sieve has a mesh opening of 5 mm, the second sieve has a mesh opening of 2.5 mm, and the third sieve has a mesh opening of 5 mm. The sieve has an opening of 1.2 mm, the fourth sieve has an opening of 0.6 mm, the fifth sieve has an opening of 0.3 mm, and the sixth sieve has an opening of 0.6 mm. It is 15mm.

Suitable particle groups include classified products with a particle size of 5 mm or more, classified products with a particle size of 2 mm or more and less than 2.5 mm, classified products with a particle size of 1.0 mm or more and less than 2.5 mm, and particles with a particle size of 0.5 mm or more. Examples include a combination with a classified product having a particle size of less than 1.0 mm, a classified product having a particle size of 0.3 mm or more and less than 0.5 mm, and a classified product having a particle size of 0.1 mm or more and less than 0.3 mm.

Step b is a step in which each particle group, excluding coarse particles with a particle size of 5 mm or more, is subjected to dry specific gravity sorting to classify them into heavy specific gravity materials and light specific gravity materials. Incidentally, coarse particles having a particle size of 5 mm or more can be reused as recycled aggregate.
Dry specific gravity sorting may be performed individually on all grain groups except coarse grains with a particle size of 5 mm or more, or may be performed on all grain groups together.
For dry specific gravity sorting, a known dry specific gravity sorter can be used, and a specific example is as described in the third step of the first embodiment. In addition, in the cement raw material recovery apparatus shown in FIG. 2, an air table type specific gravity sorter is used.

In this step, light specific gravity materials are recovered, but heavy specific gravity materials can be reused as recycled aggregate.

Step c is a step of crushing the light specific gravity material obtained from each grain group. The light specific gravity materials may be crushed for each grain group, or the light specific gravity materials of each grain group may be crushed into one. Note that the secondary crushing described in the second step of the first embodiment can be used for crushing the light specific gravity material.

Step d is a step of classifying the crushed material obtained in step c at a classification point where the cement paste content in the fine particles is 60% by mass or more. The crushed materials may be classified for each grain group, or the crushed materials of each grain group may be classified as one. Note that this step can be performed by the same operation as the second step according to the first embodiment. A preferred aspect of the cement paste content in the fine particles is as explained in the second step of the first embodiment. Further, the coarse particles obtained in this step can be reused as recycled aggregate.
In addition, in the cement raw material recovery device shown in Figure 2, a sieve type classifier is used, and a mesh opening of 0.15 mm is adopted as the classification point at which the cement paste content in the fine particles is 60% by mass or more. There is.

(Third step)
This step is a step in which the fine grains obtained in the second step are subjected to dry specific gravity sorting to classify them into heavy specific gravity materials and light specific gravity materials. The dry specific gravity sorting may be performed on the fine grains obtained in the second step and the fine grains obtained in step d separately, or may be performed on the fine grains obtained in the second step and the fine grains obtained in the step d.
For dry specific gravity sorting, a known dry specific gravity sorter can be used, and a specific example is as described in the third step of the first embodiment.
Note that the cement raw material recovery apparatus shown in FIG. 2 uses a suction wind type specific gravity sorter (cyclone).

(Fourth step)
In this step, the light specific gravity materials sorted in the third step are recovered. In the third step, when the fine particles obtained in the second step and the fine particles obtained in step d are separately subjected to dry specific gravity sorting, each light specific gravity material is collected and mixed. This suppresses the mixing of aggregate and increases the content of cement paste to 65% or more. Therefore, through this step, it is possible to recover a cement raw material with a high cement paste content and a low alkali equivalent content. In addition, the specific gravity material obtained in this step can be reused as recycled aggregate.

In this embodiment as well, the dust generated during crushing may be subjected to a suction air type gravity sorter (cyclone) to separate it into heavy and light specific gravity materials, and the light specific gravity materials may be recovered as cement raw materials. Further, a drying step of drying the waste concrete may be provided before the first step, or after the first step and before the second step.

The cement raw material recovered according to the present invention can have the following characteristics (1) and (2).
(1) The cement paste content is usually 65% by mass or more, preferably 67% by mass or more, and more preferably 70% by mass or more. The upper limit of the cement paste content is not particularly limited and may be 100% by mass, but is usually 95% by mass or less, preferably 93% by mass or less, and more preferably 90% by mass or less.

(2) The alkali equivalent is usually 2% or less, preferably 1.8% or less, more preferably 1.5% or less, still more preferably 1.3% or less. In addition, it can be judged that the lower the alkali equivalent content, the less the amount of aggregate mixed in. The lower limit of the alkali equivalent is not particularly limited and may be 0%, but is usually 0.1% or more, preferably 0.3% or more, and more preferably 0.5% or more. Here, in this specification, the "alkali equivalent" refers to the amount calculated by the following formula (ii) from the results of chemical analysis of the sample.

Alkali equivalent (Na ₂ Oeq) = Na ₂ O + 0.658K ₂ O (ii)

[In the formula, Na ₂ O is the content (%) of sodium oxide in the sample, and K ₂ O is the content (%) of potassium oxide in the sample. ]

In this way, the recovered cement raw materials are of high quality and contain no aggregates, so they can be reused without restriction.

Hereinafter, embodiments of the present invention will be described in more detail with reference to Examples. However, the present invention is not limited to the following examples.

1. Analysis of Cement Paste Content After pulverizing the sample, the residual mass was measured by dissolving it in hydrochloric acid (1+100) in accordance with the Cement Association of Japan method F-18. Next, the mass ratio of the insoluble residue (in.sol) was calculated using the following formula (i), and was defined as the aggregate content.

Aggregate content (in.sol) (%)=w/s×100 (i)

[In the formula, w represents the residual mass (g), and s represents the sample mass (g). ]

Next, assuming that the sample contained only two components, cement paste and aggregate, the cement paste content was determined from the following formula (ii).

Cement paste content (%) = 100 - Aggregate content (%) (ii)

2. Chemical analysis (CaO, Na ₂ O, K ₂ O)
Measured by X-ray fluorescence analysis (XRF). ZSX Primus II (manufactured by Rigaku Corporation) was used as a fluorescent X-ray analyzer.

3. Analysis of Alkali Equivalent Alkali equivalent (Na ₂ Oeq: total alkali content in the sample) was calculated using the following formula (ii) from the results of chemical analysis.

Alkali equivalent (Na ₂ Oeq) = Na ₂ O + 0.658K ₂ O (ii)
[In the formula, Na ₂ O is the content (%) of sodium oxide in the sample, and K ₂ O is the content (%) of potassium oxide in the sample. ]

In this example, the waste concrete used was a dismantled concrete mass having a maximum particle size of about 300 mm and containing no limestone aggregate as the original aggregate.

Example 1
(First step)
The waste concrete mass was firstly crushed using a jaw crusher to a particle size of 40 mm or less, and the crushed material was dried at 110° C. for 1 hour, and then further crushed secondarily using a cone crusher. The cone crusher was set (closed) to 15 mm, and the secondary crushing was carried out twice.
(Second process)
The waste concrete crushed material was classified using a sieve with an opening of 0.15 mm.
Next, the coarse particles (screened material) were subjected to secondary crushing using a jaw crusher, and classified again using a sieve with an opening of 0.15 mm. In addition, it was confirmed that when the opening was 0.15 mm, the cement paste content of fine particles (under-sieve material) was 60% or more.
(Third step)
The fine grains (under-sieve material) obtained in the second step were subjected to dry specific gravity separation using a dry specific gravity sorting device (cyclone), and were separated into heavy specific gravity products and light specific gravity products.
(Fourth step)
Light specific gravity materials were recovered as raw materials for cement. The collected cement raw materials were analyzed for cement paste content, CaO content, and alkali equivalent. The results are shown in Table 1.

Example 2
(First step)
The waste concrete mass was firstly crushed using a jaw crusher to a particle size of 40 mm or less, and the crushed material was dried at 110° C. for 1 hour, and then further crushed secondarily using a cone crusher. The cone crusher was set (closed) to 15 mm, and the secondary crushing was carried out twice.
(Second step, step a)
The waste concrete crushed material was classified using sieves with openings of 0.15 mm, 0.3 mm, 0.6 mm, 1.2 mm, 2.4 mm, and 5 mm. In addition, it was confirmed that when the opening was 0.15 mm, the cement paste content of fine particles (under-sieve material) was 60% or more. In addition, coarse particles of 5 mm or more were recovered as recycled coarse aggregate.
(Step b)
For each particle group of 0.15-0.3 mm, 0.3-0.6 mm, 0.6-1.2 mm, 1.2-2.5 mm, and 2.5-5 mm obtained by classification, Dry specific gravity sorting was performed using an air table type dry specific gravity sorting machine.
(Step c)
After sorting, the light specific gravity materials were combined into one and subjected to secondary crushing using a jaw crusher.
(Step d)
The crushed material obtained in step c was classified again using a sieve with an opening of 0.15 mm. In addition, it was confirmed that when the opening was 0.15 mm, the cement paste content of fine particles (under-sieve material) was 60% or more.
(Third step)
The fine grains obtained in the second step (under sieve) and the fine grains (under sieve) obtained in step d are mixed and subjected to dry specific gravity separation using a dry specific gravity separator (cyclone), and the and light specific gravity materials.
(Fourth step)
Light specific gravity materials were recovered as raw materials for cement. The collected cement raw materials were analyzed for cement paste content, CaO content, and alkali equivalent. The results are shown in Table 1.

Comparative example 1
The waste concrete mass was firstly crushed using a jaw crusher to a particle size of 40 mm or less, and the crushed material was dried at 110° C. for 1 hour, and then further crushed secondarily using a cone crusher. The cone crusher was set (closed) to 15 mm, and the secondary crushing was carried out twice.
The waste concrete crushed material was pulverized to a total size of 0.15 mm or less using a ball mill. The resulting pulverized product was analyzed for cement paste content, CaO content, and alkali equivalent. The results are shown in Table 1.

Comparative example 2
The waste concrete mass was firstly crushed using a jaw crusher to a particle size of 40 mm or less, and the crushed material was dried at 110° C. for 1 hour, and then further crushed secondarily using a cone crusher. The cone crusher was set (closed) to 15 mm, and the secondary crushing was carried out twice.
The waste concrete crushed material was classified using a sieve with an opening of 0.15 mm. The fine particles (under sieve) were analyzed for cement paste content, CaO content, and alkali equivalent. The results are shown in Table 1.

From Table 1, in both Examples 1 and 2, the cement paste content is 70% or more and the alkali equivalent is 1.3% or less, so the cement paste content is high and aggregate is mixed. It was confirmed that it is possible to recover cement raw materials with suppressed

Claims (4)

A first step of crushing waste concrete;
A second step in which the crushed material obtained in the first step is classified at a classification point where the cement paste content in the fine particles is 60% by mass or more, and a dry specific gravity of the fine particles obtained in the second step. A method for recovering cement raw materials from waste concrete, comprising a third step of sorting into heavy specific gravity materials and light specific gravity materials, and a fourth step of recovering the light specific gravity materials obtained in the third step. After the second step and before the third step, after crushing the coarse particles obtained in the second step, the crushed materials are classified at a classification point where the cement paste content in the fine particles is 60% by mass or more. The cement raw material recovery method according to claim 1, comprising a step of classifying. After the second step and before the third step, the coarse particles obtained in the second step are classified into two or more particle groups using at least a sieve with an opening of 5 mm, and coarse particles with a particle size of 5 mm or more are separated. After dry specific gravity sorting of each grain group except for fine grains to obtain light specific gravity materials, after crushing the light specific gravity materials, the crushed materials are classified at a classification point where the cement paste content in the fine grains is 60% by mass or more. The cement raw material recovery method according to claim 1, comprising the step of: The cement raw material recovery method according to any one of claims 1 to 3, wherein in the first step, crushing is performed until the cement paste content in the crushed material having a particle size of 5 mm or more is 15% by mass or less.