Civil engineering materials made from gypsum board waste and their manufacturing methods

Abstract

To provide a civil engineering material and its manufacturing method that suppresses the generation of hydrogen sulfide in a simple manner while utilizing gypsum board waste material.SOLUTION: The solidified material of the invention consists of 30-70 mass% of gypsum board waste material classified into 5 mm or less in particle size and 70-30 mass% of cementitious solidifying material.SELECTED DRAWING: Figure 4

Description

Technical Field

[0001] The present invention relates to a civil engineering material using waste gypsum board and a method for manufacturing the same.

[0002] Conventionally, new construction waste gypsum board generated during the construction of new houses is separated into gypsum and paper, and then, for example, as a raw material for gypsum board or gypsum for cement addition, or as a soil (ground) improvement material or solidifying material, most of it is recycled. However, the recycling rate of demolition waste gypsum board generated from the demolition of houses and the like is in a low state. <0000xxx><0000xxx><0000xxx>The reason for the low recycling rate of demolition waste gypsum board is that there is a risk of generating high-concentration hydrogen sulfide in an anaerobic environment when it is landfilled. Specifically, in an anaerobic environment, hydrogen sulfide generated from waste gypsum board is caused by glucose paste (organic matter) that bonds the gypsum board and paper, and calcium sulfate (CaSO4·2H2O) remaining in the paper, and is generated by the microbial activity of sulfate-reducing bacteria. Therefore, demolition waste gypsum board is landfilled in a managed landfill site, and the increased burden of disposal costs has become a problem.

[0004] Therefore, a method for manufacturing reusable granules from demolition waste gypsum board has been proposed. The manufacturing method mainly includes four steps: a crushing step of waste gypsum board, a paper component removal step of performing air vibration sorting or heat treatment, an additive mixing step, and a granulation step of the mixture. Among these, in the mixing step, by adding an alkali (such as calcium carbonate) to make the pH 8 or higher and performing mixing in an environment where the oxidation-reduction potential is a negative potential, the generation of hydrogen sulfide gas in the manufactured granules is suppressed (for example, see Patent Document 1).

Prior Art Documents

Patent Documents

Patent Document 1

[0006] However, the method for producing reusable granules from demolition-related gypsum board waste described in Patent Document 1 involves crushing the gypsum board waste to a size of approximately 10 mm or less during the crushing process. As a result, a large amount of paper component remains in the crushed gypsum board, requiring wind vibration sorting or heat treatment to remove the paper component, and further pH adjustment using additives under special conditions. This process involves many steps in addition to the main steps, making it complicated.

[0007] This invention was made in view of these problems, and aims to provide a civil engineering material that easily suppresses the generation of hydrogen sulfide while utilizing gypsum board waste, as well as a method for manufacturing the same. [Means for solving the problem]

[0008] To solve the aforementioned problems, the civil engineering material utilizing gypsum board waste of the present invention is It is characterized by being a solidified body composed of 30-70% by mass of gypsum board waste sorted to a particle size of 5 mm or less, and 70-30% by mass of cement-based solidifying agent. According to this characteristic, by classifying gypsum board waste into particle sizes of 5 mm or less, much of the paper attached to the gypsum board waste is removed. This significantly reduces the amount of organic matter that serves as a nutrient source for sulfate-reducing bacteria in an anaerobic environment, resulting in virtually no hydrogen sulfide generation from the solidified material. In addition, the solidified material, composed of gypsum board waste and a cement-based solidifying agent, exhibits excellent compressive strength. Therefore, it is possible to provide civil engineering materials that easily suppress the generation of hydrogen sulfide.

[0009] The aforementioned gypsum board waste is characterized by the fact that the generation of hydrogen sulfide is suppressed by classifying it into particle sizes of 2 mm or less. This feature means that more paper is removed from the gypsum board waste, further reducing the risk of hydrogen sulfide generation.

[0010] The aforementioned cement-based solidifying agent is characterized by being a mixture of Portland cement and glass. This characteristic increases the compressive strength of the solidified material while also reducing its weight.

[0011] The present invention provides a method for manufacturing civil engineering materials using gypsum board waste, The crushing process involves crushing gypsum board waste, A classification process in which the crushed gypsum board waste is sorted to a particle size of 5 mm or less, A mixing step in which the gypsum board waste material with a particle size of 5 mm or less, which has been classified in the classification step, is mixed with a cement-based solidifying agent, The invention is characterized by including a solidification step of solidifying the mixed gypsum board waste and the cement-based solidifying agent. According to this feature, by classifying the crushed gypsum board waste into particles with a diameter of 5 mm or less in the classification process, much of the paper attached to the gypsum board waste is removed, thereby significantly reducing the amount of organic matter that serves as a nutrient source for sulfate-reducing bacteria in an anaerobic environment. Furthermore, by mixing it with a cement-based solidifying agent in the mixing process and then going through the solidification process, the compressive strength of the civil engineering material is improved. Therefore, it is possible to provide a method for manufacturing civil engineering materials that utilizes gypsum board waste while suppressing the generation of hydrogen sulfide in a simple manner.

[0012] The mixing process is characterized by mixing at a water content ratio of 0.31 or higher and less than 0.38. According to this characteristic, the compressive strength of the solidified body, which consists of gypsum board waste and cement-based solidifying agent, is further improved. [Brief explanation of the drawing]

[0013] [Figure 1] This graph shows the results of measuring the particle size distribution of crushed waste gypsum obtained by crushing gypsum board waste in an embodiment of the present invention. [Figure 2]In the examples, (a) to (e) are photographs showing the process of sieving crushed waste gypsum, obtained by crushing gypsum board waste, according to particle size using a metal mesh sieve. [Figure 3] This table shows the results of measuring the compressive strength of specimens prepared by varying the mixing ratio of waste gypsum and waste glass in the examples. [Figure 4] This table shows the results of measuring the hydrogen sulfide generation potential according to the particle size of the crushed waste gypsum in the examples. [Figure 5] This table shows the results of measuring the compressive strength of specimens prepared by varying the water content in the examples. [Modes for carrying out the invention]

[0014] The inventors discovered that a solidified material composed of gypsum board waste sorted to a particle size of 5 mm or less and a cement-based solidifying agent is superior as a civil engineering material that easily suppresses the generation of hydrogen sulfide while utilizing gypsum board waste.

[0015] The civil engineering material of the present invention will now be described. The civil engineering material is a solidified body obtained by mixing 30 to 70% by mass of gypsum board waste material classified to a particle size of 5 mm or less, preferably 3 mm or less, and more preferably 2 mm or less, with 70 to 30% by mass of cement-based solidifying agent, more preferably 30 to 40% by mass of gypsum board waste material and 70 to 60% by mass of cement-based solidifying agent, and then solidifying the mixture. It is preferable that the civil engineering material be solidified and formed into a plate-like or lump-like shape, but it may also be formed into granular shape.

[0016] Thus, by using gypsum board waste materials classified into a particle size of 5 mm or less for civil engineering materials, most of the paper adhering to the gypsum board waste materials, specifically, organic substances such as paper and glucose paste adhering to the paper (in this specification, unless otherwise specified, paper also includes organic substances adhering to the paper) can be removed. Further preferably, by using gypsum board waste materials classified into a particle size of 3 mm or less, more preferably 2 mm or less, the paper adhering to the gypsum board waste materials can be completely removed. Thereby, the amount of organic substances that become nutrients for sulfate-reducing bacteria in an anaerobic environment can be significantly reduced from the gypsum board waste materials, and the generation of hydrogen sulfide from civil engineering materials using gypsum board waste materials can be suppressed.

[0017] In addition, for civil engineering materials, as a cement-based solidifying material mixed with gypsum board waste materials, by using a mixture of Portland cement and glass, the compressive strength of the civil engineering materials can be improved and the weight can be reduced. More preferably, for civil engineering materials, based on 30 to 35% by mass of Portland cement, for the remaining 70 to 65% by mass in total of gypsum board waste materials and glass, by formulating so that the ratio of gypsum board waste materials: glass is 50:50, the compressive strength of the civil engineering materials can be improved and the weight can be reduced.

[0018] Also, for glass, similar to gypsum board waste materials, it is preferable to use those crushed to a particle size of 2 mm or less. By mixing glass and gypsum board waste materials with the same particle size and cement, since the gypsum board waste material particles and glass particles are likely to be evenly arranged in the civil engineering materials, the glass functions as fine aggregate in the civil engineering materials, and the compressive strength of the civil engineering materials increases uniformly.

[0019] In addition, the civil engineering material contains nothing other than inevitable impurities except for gypsum board waste and cement-based solidifying materials. Although this will be described in the following examples, the present invention may contain materials other than these, preferably 20% by mass or less, and more preferably 10% by mass or less. As materials other than these, for example, admixtures such as surfactants and water-reducing agents, and admixtures such as polymers for cement admixture and expanding agents may be added.

[0020] In addition, the civil engineering material is a mixture of gypsum board waste and cement-based solidifying material in the above-mentioned mixing ratio, with a water content ratio of 0.30 or more and less than 0.70, preferably a water content ratio of 0.31 or more and less than 0.38, and more preferably a water content ratio of 0.32 or more and less than 0.34. By mixing, the compressive strength of the civil engineering material can be further improved.

[0021] Moreover, the method for manufacturing a civil engineering material using gypsum board waste of the present invention includes a crushing step of crushing the gypsum board waste, a classification step of classifying the crushed gypsum board waste to a particle size of 5 mm or less, preferably 3 mm or less, and more preferably 2 mm or less, and a mixing step of mixing the gypsum board waste classified in the classification step and a cement-based solidifying material (preferably a mixture of Portland cement and glass), and a solidifying step of solidifying the mixture.

[0022] Thus, the civil engineering material can easily suppress the generation of hydrogen sulfide by using gypsum board waste classified to a particle size of 5 mm or less, preferably 3 mm or less, and more preferably 2 mm or less. Furthermore, the civil engineering material is composed of a solidified body with a mixing ratio of 30 to 70% by mass of gypsum board waste classified to a particle size of 5 mm or less, preferably 3 mm or less, and more preferably 2 mm or less, and 70 to 30% by mass of a cement-based solidifying material, so that it can be a civil engineering material having sufficient compressive strength while suppressing the generation of hydrogen sulfide.

[0023] The embodiments for implementing the civil engineering material using gypsum board waste according to the present invention will be described below based on examples. Furthermore, regarding the civil engineering material, the conditions for obtaining sufficient solidified strength, the pretreatment method for gypsum board waste, and the hydrogen sulfide generation potential were measured, and the following experiments were conducted to clarify suitable mixing methods and pretreatment methods for effective utilization. [Examples]

[0024] The gypsum board waste and glass used in the civil engineering materials were demolition-related gypsum board waste and waste glass that were brought to a certain industrial waste treatment facility in 2019. The cement used was ordinary Portland cement (manufactured by Taiheiyo Cement Corporation).

[0025] First, as part of the crushing process, the gypsum board waste was roughly crushed using a jaw crusher, and then crushed using a rotary crusher to obtain crushed waste gypsum.

[0026] Next, as a classification step, the crushed waste gypsum was sorted into four categories using a metal mesh sieve (JIS test metal mesh sieve JIS Z 8801-1:2000): 5 mm or larger, 5-3 mm, 3-2 mm, 2-1 mm, and 1 mm or smaller.

[0027] The mass of each fraction of crushed waste gypsum was measured, and the cumulative particle size distribution was determined. As shown in the cumulative particle size distribution in Figure 1, it was found that approximately 80% of the waste gypsum had a particle size of 5 mm or less, and approximately 60% had a particle size of 2 mm or less.

[0028] Next, the mass percentage of paper contained in the crushed waste gypsum was measured. As shown in Figures 2(a) to (e), representative samples of about 100g each were taken, and fibrous paper and other materials were visually separated by hand sorting. The mass of each material was measured, and the percentage was determined. The results of the mass percentage of paper contained in the crushed waste gypsum are shown in Table 1.

[0029] [Table 1]

[0030] As shown in Table 1, crushed waste gypsum with a particle size of 5 mm or larger contained a large amount of paper. Crushed waste gypsum with a particle size of 3 to 5 mm contained a very small amount of paper. Crushed waste gypsum with a particle size of 3 mm or smaller contained no paper. These experimental results confirmed that paper attached to gypsum board waste does not easily become smaller than the waste gypsum through crushing, and therefore, especially when sieving with a particle size of 5 mm or smaller, the paper tends to remain on the sieve mesh, and a large portion of it can be removed.

[0031] Next, test specimens were prepared using waste gypsum with a particle size of 2 mm or less and waste glass with a particle size of 2 mm or less, crushed using the same crushing procedure as described above for waste gypsum board. The materials used were ordinary Portland cement (C), waste gypsum (P), and waste glass (G), and three types were prepared by varying the mixing ratio (mass%) of waste gypsum and waste glass. The water content (w) in the mixing process of these materials was set to 0.38. The mixing conditions are shown in Table 2 below.

[0032] [Table 2]

[0033] The test specimens were prepared as cylindrical solidified bodies with a diameter of 50 mm and a height of 100 mm for compressive strength testing. Three solidified bodies were prepared for each type of specimen by vibration compaction, and the solidification process involved air curing at 20±2°C. The curing conditions were 7, 14, 28, 63, 91, and 183 days. Three specimens of each type were subjected to uniaxial compression testing (in accordance with JIS A1216), and the compressive strength was measured.

[0034] Figure 3 shows the uniaxial compressive strength of specimens when the mixing ratio of waste gypsum A and waste glass is varied, at a water content of 0.38. The compressive strength was highest for waste gypsum:glass = 50:50 (specimen Y3) over all curing periods, reaching 15.5 N / mm² after 183 days of curing. 2The results were as follows. It was also confirmed that the compressive strength increased when the amount of waste gypsum was less than the amount of waste glass. The reason for the increase in compressive strength is presumed to be the effect of waste glass as fine aggregate. Furthermore, it is presumed that when the amount of waste gypsum was large, ettringite was formed in the solidified body, and the compressive strength decreased due to the expansion of its crystals. In addition, for all specimens Y1 to Y3, after a curing period of 183 days, the compressive strength was 8 N / mm, which is the JIS standard value (JIS A 5406) ​​for hollow blocks (concrete block type A). 2 Since it exceeds [a certain value], it is considered that it can be used for retaining walls and the like.

[0035] Next, the hydrogen sulfide generation potential of crushed waste gypsum, sieved according to particle size, was measured. Specifically, 200g of crushed waste gypsum was placed in a 1000mL Erlenmeyer flask, 400mL of degassed water (degassed with nitrogen gas) was added, and the mixture was stirred by hand for about 10 seconds. Then, the gas phase in the flask was replaced with nitrogen gas for 2 minutes, and the flask was sealed with a rubber stopper and incubated in a 40°C constant temperature room for 1 week. After 1 week, the hydrogen sulfide gas concentration in the gas phase of the flask was measured using a portable gas chromatograph GA5000. In addition, only the paper used in the gypsum board waste was peeled off by hand, 20g of the paper was placed in a 1000mL Erlenmeyer flask, and a hydrogen sulfide gas generation experiment was conducted using the same method as above. The experimental results are shown in Table 3 and Figure 4 below.

[0036] [Table 3]

[0037] As shown in Table 3 and Figure 4, hydrogen sulfide was generated (50 ppm or more) from the fraction with a particle size of 5 mm or larger. This is presumed to be because, as shown in Table 1, the proportion of paper in this fraction is high, resulting in a large amount of organic matter such as glucose glue adhering to the paper, which causes the generation of hydrogen sulfide. Furthermore, no hydrogen sulfide was generated from crushed waste gypsum with a particle size of 5 mm or less. Although a small amount of paper was attached to the crushed waste gypsum with a particle size of 3 to 5 mm, it is presumed that hydrogen sulfide was not generated because the amount of attached paper was extremely small. In addition, as shown in Table 3, in the experiment using only paper, 18.5 ppm of hydrogen sulfide was detected, which was a lower concentration than in the waste gypsum with a particle size of 5 mm or larger. This is thought to be because a large amount of glucose glue remained in the waste gypsum even after the paper was removed.

[0038] From the above results, it was confirmed that by using waste gypsum crushed to a particle size of 5 mm or less, preferably 3 mm or less, and more preferably 2 mm or less, it is possible to produce a solidified body in which paper is sufficiently removed and hydrogen sulfide is not generated.

[0039] Next, the compressive strength of the specimens was measured when the water content was changed during the mixing process. Figure 5 shows the results of the compressive strength test of specimens when 30% by mass of cement and the remaining 70% by mass of waste gypsum and glass were mixed in a ratio of waste gypsum:glass = 50:50, and the water content was changed from 0.3 to 0.37.

[0040] As shown in Figure 5, the highest compressive strength was obtained with a moisture content of 0.33 after a curing period of 91 days. Furthermore, with a moisture content of 0.37, the amount of mixed water increased, resulting in greater fluidity, but the compressive strength decreased.

[0041] Although embodiments and modifications of the present invention have been described above with reference to the drawings, the specific configuration is not limited to these embodiments, and any changes or additions that do not depart from the spirit of the present invention are also included.

[0042] In the above embodiment, Portland cement was used as the cement-based solidifying agent as an example, but the present invention is not limited thereto, and for example, blended cement, special cement, or eco-cement may be used. Furthermore, Portland cement may be mixed with coal ash such as fly ash or clinker ash, sand or gravel, sodium silicate, blast furnace slag or steelmaking slag, incineration ash or sludge, etc. When mixing in fly ash, compressive strength can be maintained by keeping the ratio of fly ash replacement from Portland cement to 25% or less.

[0043] Furthermore, although the above embodiment illustrates a configuration using glass with a particle size of 2 mm or less, the present invention is not limited thereto, and for example, the particle size of the glass may be changed as appropriate.

[0044] Furthermore, while the above embodiment illustrates the use of gypsum board waste from demolition projects brought to an industrial waste treatment facility, the present invention is not limited thereto. For example, gypsum board waste from new construction projects or gypsum board waste containing both new construction and demolition projects may also be used.

[0045] Furthermore, while the above-described embodiment illustrates a solidification process involving air curing at 20±2℃ for 7, 14, 28, 63, 91, and 183 days, the present invention is not limited thereto. For example, the temperature and curing period may be changed, or equipment that promotes dewatering of the solidified material may be used. Industrial application fields

[0046] It can be used as civil engineering material such as roadbed material and concrete block products.

Claims

1. This solidified body is composed of 30-70% by mass of gypsum board waste sorted to a particle size of 5 mm or less, and 70-30% by mass of cement-based solidifying agent. The aforementioned cement-based solidification material is characterized in that at least one of Portland cement, blended cement, special cement, or eco-cement is mixed with glass of a particle size similar to that of the aforementioned gypsum board waste, making it a civil engineering material utilizing gypsum board waste.

2. The civil engineering material utilizing gypsum board waste according to claim 1, characterized in that the generation of hydrogen sulfide is suppressed by classifying the gypsum board waste to a particle size of 2 mm or less.

3. The civil engineering material utilizing gypsum board waste according to claim 1 or 2, characterized in that the cement-based solidifying agent is a mixture of Portland cement and the glass.

4. The civil engineering material utilizing gypsum board waste according to claim 3, characterized in that, with respect to 30 to 35% by mass of the Portland cement, the remaining 70 to 65% by mass of the gypsum board waste and the glass combined is blended in such a ratio of gypsum board waste:glass = 50:

50.

5. The crushing process involves crushing gypsum board waste, A classification process is performed to classify the crushed gypsum board waste material to a particle size of 5 mm or less. A mixing step in which the gypsum board waste material with a particle size of 5 mm or less, which has been classified in the classification step, is mixed with a cement-based solidifying agent which is a mixture of at least one of Portland cement, blended cement, special cement, or eco-cement, and glass with a particle size similar to that of the gypsum board waste material. A method for manufacturing civil engineering materials using gypsum board waste, comprising a solidification step of solidifying the mixed gypsum board waste and the cement-based solidifying agent.

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