Ground improvement body

Abstract

This product provides a ground improvement body that reduces CO2 emissions while maintaining fluidity before hardening. [Solution] The ground improvement body contains a binder containing recycled sludge dried fine powder and blast furnace slag fine powder, and a ground material, wherein the mass ratio MR1st of the blast furnace slag fine powder contained in the binder is 60% or more and 90% or less, and the mass ratio MR2nd of the recycled sludge dried fine powder contained in the binder is 10% or more and 40% or less.

Description

Technical Field

[0001] The present invention relates to a ground improvement body.

Background Art

[0002] Reducing CO2 emissions during construction is an important issue. Since cement, which is one of the main materials, has a large amount of CO2 emissions from the material, low-carbonization is being considered even in the construction of ground improvement bodies that use a large amount of cement.

[0003] As one method for low-carbonization, there is the utilization of recycled sludge dry fine powder obtained by recycling raw sludge (powdered sludge showing strong alkalinity, consisting of sludge from the mixer equipment of raw concrete plants and mixer trucks during cleaning, residual concrete and return concrete from the site, etc.). By recycling raw sludge in this way, not only can the environmental load associated with the final disposal of raw sludge be reduced, but also the recycled sludge dry fine powder, which is a recycled product of raw sludge, has a small amount of CO2 emissions from the material. Therefore, if the recycled sludge dry fine powder can be used in the ground improvement body, it can contribute to low-carbonization.

[0004] As a technique using recycled sludge dry fine powder, Patent Document 1 describes a cement composition containing raw sludge fine powder that can be used in a ground improvement body and can completely replace bentonite and partially replace cement. The raw sludge fine powder contained in the cement composition is obtained by heat-drying and pulverizing raw sludge within 5 days after the generation of raw sludge, and the ratio of cement and raw sludge fine powder in the cement composition is defined.

[0005] Ground improvement bodies are often used as retaining walls, and in such cases, stress members such as H-beams are inserted into the ground improvement body before it hardens, so it is necessary to give the ground improvement body a certain degree of fluidity before it hardens. However, when a portion of the cement is replaced with recycled sludge dried fine powder, the fluidity of the ground improvement body before hardening may decrease. Therefore, in practice, when high fluidity is required for the ground improvement body before hardening, the proportion of cement replaced with recycled sludge dried fine powder (replacement rate) must be limited to a small amount. As a result, the effect of reducing CO2 emissions becomes small. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] Japanese Patent Publication No. 2013-32233 [Overview of the project] [Problems that the invention aims to solve]

[0007] The objective of the present invention is to provide a ground improvement body that reduces CO2 emissions while ensuring fluidity before hardening. [Means for solving the problem]

[0008] [1] A ground improvement body comprising a binder containing recycled sludge dried fine powder and blast furnace slag fine powder, and a ground material, wherein the mass ratio MR1st of the blast furnace slag fine powder contained in the binder is 60% or more and 90% or less, and the mass ratio MR2nd of the recycled sludge dried fine powder contained in the binder is 10% or more and 40% or less. [2] The specific surface area of ​​the recycled sludge dried fine powder is 10,000 cm². 2 A ground improvement body as described in [1] above, which is greater than / g. [3] The ground improvement body according to [1] to [2] above, wherein the mass percentage of unhydrated cement contained in the recycled sludge dried fine powder is 40% or less. [Effects of the Invention]

[0009] According to the present invention, it is possible to provide a ground improvement body that reduces CO2 emissions while ensuring fluidity before hardening. [Brief explanation of the drawing]

[0010] [Figure 1] Figure 1 is a flowchart showing the method for producing the recycled sludge dried fine powder contained in the ground improvement body of the embodiment. [Figure 2] Figure 2 is a graph showing the table flow measurement results immediately after mixing in Examples 1-2 and Comparative Examples 1-10. [Figure 3] Figure 3 is a graph showing the table flow measurement results 60 minutes after mixing in Examples 1-2 and Comparative Examples 1-10. [Figure 4] Figure 4 is a graph showing the table flow measurement results immediately after mixing and after 60 minutes in Examples 3-4 and Comparative Examples 11-13. [Figure 5] Figure 5 is a graph showing the measurement results of the uniaxial compressive strength of the cured bodies obtained by curing for 7 days and 28 days in Examples 3-4 and Comparative Examples 11-13. [Modes for carrying out the invention]

[0011] The following will provide a detailed explanation based on the embodiments.

[0012] The inventors have conducted extensive research on ground improvement bodies and have found that by including a binder containing recycled sludge dried fine powder and blast furnace slag fine powder, and a ground material, and by setting the mass ratio of blast furnace slag fine powder in the binder (MR1st) and the mass ratio of recycled sludge dried fine powder in the binder (MR2nd) within predetermined ranges, it is possible to reduce CO2 emissions from the materials while ensuring the fluidity of the ground improvement body before hardening. Based on this finding, the inventors have completed the present invention.

[0013] The ground improvement body of the present invention contains a binder including recycled sludge dry fine powder and blast furnace slag fine powder, and a ground material. The mass ratio MR1st of the blast furnace slag fine powder contained in the binder is 60% or more and 90% or less, and the mass ratio MR2nd of the recycled sludge dry fine powder contained in the binder is 10% or more and 40% or less.

[0014] As described above, the ground improvement body of the present invention contains a binder and a ground material. The binder constituting the ground improvement body includes recycled sludge dry fine powder and blast furnace slag fine powder.

[0015] The recycled sludge dry fine powder contained in the binder will be described. Generally, concrete is manufactured by kneading Portland cement, aggregates such as gravel and sand, water, and admixtures in a forced kneading mixer. The concrete thus manufactured is transported to a construction site and placed, but there are cases where it remains partially unused or fails in the acceptance inspection. Such concrete is returned to a ready-mix concrete plant or sent to other treatment facilities as residual concrete or returned concrete. That is, such concrete is unused concrete that has not been used by the fresh concrete user. The recycled sludge dry fine powder contained in the ground improvement body of the present invention is manufactured by treating such unused concrete.

[0016] FIG. 1 is a flowchart showing a method for manufacturing the recycled sludge dry fine powder contained in the ground improvement body. In the method for manufacturing the recycled sludge dry fine powder, as shown in FIG. 1, first, a slurrying step S1 is carried out. In the slurrying step S1, water is added to the unused concrete to make it into a slurry. The slurry may contain washing wastewater obtained by washing the mixer of a truck agitator or washing wastewater in a ready-mix concrete plant.

[0017] After the slurrying step S1, an aggregate separation step S2 is carried out. In the aggregate separation step S2, solid components such as aggregates are removed from the slurry obtained in the slurrying step S1. The aggregate separation step S2 is performed by a plurality of vibrating sieves with different mesh sizes, and the slurry is sequentially processed to separate aggregates such as gravel and sand. The recovered aggregates can be reused. Also, the undersize remaining after separating the aggregates is sludge water rich in cement content.

[0018] After the aggregate separation step S2, a fine sand removal step S3 is carried out. In the fine sand removal step S3, a wet cyclone is used to remove fine sand, that is, fine sand components, from the sludge water to obtain concentrated sludge water. The obtained concentrated sludge water is processed in the next dehydration step S4. However, when the cement content contained in the concentrated sludge water is low, the concentrated sludge water may be sent back to the slurrying step S1 and reused as the water for slurrying other unused concrete. By doing so, the cement content can be further concentrated in the sludge water and the concentrated sludge water.

[0019] After the fine sand removal step S3, a dehydration step S4 is carried out on the concentrated sludge water. In the dehydration step S4, the concentrated sludge water is dehydrated by a filter press to obtain a sludge cake. The supernatant water obtained during dehydration can be reused as the mixing water for concrete.

[0020] After the dehydration step S4, a crushing and drying step S5 is carried out on the sludge cake. The device used in the crushing and drying step S5 may be any device as long as it can dry while crushing the sludge cake. From the viewpoint of efficiently performing crushing and drying, a rotary drum is preferably used. The rotary drum is configured such that crushing and stirring blades that rotate at high speed are provided inside, and hot air can be supplied inside. The sludge cake is put into the inside of the rotary drum, and while rotating the crushing and stirring blades, hot air is supplied. Then, the sludge cake can be dried by the hot air while being crushed by the crushing and stirring blades to obtain regenerated sludge dry fine powder.

[0021] Furthermore, as mentioned above, recycled sludge dried fine powder is made from unused concrete that was not used by ready-mix concrete users. For unused concrete and concrete used by ready-mix concrete users, the ready-mix concrete users count their own CO2 emissions. Therefore, even if recycled sludge dried fine powder contains cement, the material-derived CO2 emissions from the recycled sludge dried fine powder are zero, meaning that the CO2 emissions related to the cement in the recycled sludge dried fine powder are zero. For example, the mass percentage of unhydrated cement contained in recycled sludge dried fine powder is 40% or less.

[0022] Furthermore, the blast furnace slag fine powder contained in the binder is the fine powder specified in JIS A 6206:2013 "Blast Furnace Slag Fine Powder for Concrete". Blast furnace granulated slag is produced by rapidly cooling molten blast furnace slag, which is generated simultaneously with ironmaking in the blast furnace, with water or air, and its basicity is 1.60 or higher. Blast furnace slag fine powder is obtained by drying and grinding this blast furnace granulated slag, or by adding gypsum to it.

[0023] By replacing some or all of the cement contained in conventional ground improvement materials (excluding the cement content in recycled sludge powder if the conventional ground improvement material contains recycled sludge powder) with recycled sludge powder or blast furnace slag powder, CO2 emissions from the materials can be further reduced. From the viewpoint of reducing CO2 emissions, it is preferable that the ground improvement material does not contain cement other than the cement content contained in recycled sludge powder.

[0024] Furthermore, the ground material that constitutes the ground improvement body is the material that makes up the ground, and is composed of rock, gravel, sand, fine-grained material, etc. For example, ground material can be obtained by excavating the ground.

[0025] In ground improvement bodies, the mass ratio MR1st (blast furnace slag fine powder × 100 / binder) of blast furnace slag fine powder contained in the binder is 60% or more and 90% or less. When the mass ratio MR1st of blast furnace slag fine powder is 60% or more, it is possible to reduce CO2 emissions compared to conventional ground improvement bodies while ensuring the fluidity of the ground improvement body before hardening. In other words, it is possible to suppress the decrease in fluidity of the ground improvement body before hardening caused by the use of recycled sludge dried fine powder, so the amount of recycled sludge dried fine powder used can be increased compared to conventional methods. As a result, CO2 emissions can be significantly reduced. From this viewpoint, the mass ratio MR1st of blast furnace slag fine powder is 60% or more, and preferably more than 70%. Furthermore, when the mass ratio MR1st of blast furnace slag fine powder is 90% or less, it is possible to suppress poor hardening of the ground improvement body even if the ground material is cohesive soil.

[0026] Furthermore, in the ground improvement body, the mass ratio MR2nd (recycled sludge dried fine powder × 100 / binder) of recycled sludge dried fine powder contained in the binder is 10% or more and 40% or less. When the mass ratio MR2nd is 10% or more, the effect of reducing CO2 emissions can be fully realized and the strength development of the ground improvement body can be stabilized. In addition, since the ground improvement body can have excellent fluidity before hardening, the mass ratio MR2nd is 40% or less, preferably less than 30%.

[0027] Furthermore, the specific surface area of ​​the recycled sludge dried fine powder is 10,000 cm². 2 It is preferable that the specific surface area is greater than / g. If the specific surface area of ​​the recycled sludge dried fine powder is within the above range, excessive strength development of the ground improvement body can be suppressed. Therefore, the work of chipping away a part of the ground improvement body during excavation can be reduced. From this viewpoint, of the recycled sludge dried fine powder contained in the ground improvement body, more than half of it should have a specific surface area of ​​10,000 cm². 2 / g super 12000cm 2 It is preferable that the value be less than or equal to / g.

[0028] Furthermore, the ground improvement body may contain additives in addition to the binder and ground material described above, within the range that achieves the effects of the present invention. The additives can be appropriately selected depending on the application of the ground improvement body. Also, from the viewpoint of reducing CO2 emissions as described above, it is preferable that the additives do not contain cement.

[0029] Ground improvement materials can reduce CO2 emissions and have high fluidity before hardening, making them suitable for use as retaining walls.

[0030] Next, we will explain the manufacturing method for ground improvement structures.

[0031] As a method for manufacturing a ground improvement body, a ground improvement body can be obtained by kneading together a binder containing recycled sludge dried fine powder and blast furnace slag fine powder, a ground material, water, and additives as needed, and then curing the mixture to harden it.

[0032] Furthermore, in order to further increase the fluidity of the mixed material, which is the ground improvement body before hardening, it is preferable that the water-binder ratio of the mixed material ((amount of water) × 100 / (total amount of recycled sludge dried fine powder and blast furnace slag fine powder)) be between 200% and 300%.

[0033] According to the embodiments described above, the ground improvement material contains a binder containing recycled sludge dried fine powder and blast furnace slag fine powder, and a ground material. By setting the mass ratio MR1st of blast furnace slag fine powder and the mass ratio MR2nd of recycled sludge dried fine powder contained in the binder to predetermined ranges, it is possible to reduce CO2 emissions while ensuring the fluidity of the ground improvement body before hardening.

[0034] Although embodiments have been described above, the present invention is not limited to the embodiments described above, and includes all aspects included in the concepts and claims of this disclosure, and can be modified in various ways within the scope of this disclosure. [Examples]

[0035] Next, examples and comparative examples will be described, but the present invention is not limited to these examples.

[0036] (Examples 1-2, Comparative Examples 1-10) The raw materials in the amounts shown in Table 1 and 784 kg of water were mixed to obtain a mixture with the composition shown in Table 1. The water-binder ratio in the mixture was set to 280%, and the water-cement ratio to 230%. The raw materials used are as follows. The mass percentage of ordinary Portland cement contained in the binder was set to MR3rd.

[0037] OPC: Ordinary Portland Cement CemR 3 Recycled sludge dried fine powder BFS: Blast furnace slag fine powder

[0038] [Table 1]

[0039] Next, the table flow of the mixture was measured as follows. A frustoconical cone (70mm diameter at the top, 100mm diameter at the bottom, and 60mm in height) was placed on a flat plate, and after filling the cone with the mixture, the spread of the mixture when the cone was quickly lifted was measured as the table flow (immediately after mixing and after 60 minutes). The results are shown in Table 2.

[0040] Next, the uniaxial compressive strength of the hardened bodies obtained by curing the mixed material for 7, 28, and 56 days was measured in accordance with JIS A 1216. The results are shown in Table 2.

[0041] [Table 2]

[0042] Figure 2 is a graph showing the table flow measurement results immediately after mixing in Examples 1-2 and Comparative Examples 1-10. Figure 3 is a graph showing the table flow measurement results 60 minutes after mixing in Examples 1-2 and Comparative Examples 1-10.

[0043] As shown in Tables 1-2 and Figures 2-3, in the above examples, the table flow value of the compound containing recycled sludge dried fine powder and blast furnace slag fine powder, with the mass ratio of blast furnace slag fine powder MR1st and the mass ratio of recycled sludge dried fine powder MR2nd contained in the binder controlled within predetermined ranges, was high, reducing CO2 emissions and suppressing an excessive increase in the uniaxial compressive strength of the hardened compound. Therefore, it was found that the ground improvement body obtained by mixing the compound obtained in the examples with ground material and hardening it can reduce CO2 emissions while ensuring fluidity before hardening, and suppress an excessive increase in the uniaxial compressive strength of the hardened ground improvement body.

[0044] On the other hand, the above comparative examples did not satisfy at least one of the following conditions: containing recycled dried sludge fine powder and blast furnace slag fine powder; the mass ratio MR1st of blast furnace slag fine powder contained in the binder being within a predetermined range; and the mass ratio MR2nd of recycled dried sludge fine powder contained in the binder being within a predetermined range. Therefore, the above comparative examples could not reduce CO2 emissions while ensuring the table flow of the mixture. Furthermore, there were also comparative examples that could not suppress an excessive increase in the unconfined compressive strength of the hardened mixture. From the above, it was found that the ground improvement bodies obtained by mixing the mixture obtained in the comparative examples with ground material and hardening them could not reduce CO2 emissions while ensuring fluidity before hardening. Furthermore, it was found that there were ground improvement bodies that could not suppress an excessive increase in the unconfined compressive strength.

[0045] (Examples 3-4, Comparative Examples 11-13) The composition shown in Table 3 (binding agent amount 280 kg / m 3A mixture containing ground material was prepared using the following: The water-binder ratio in the mixture was set to 280%, and the water-cement ratio to 230%. As ground material, sandy soil (a sample with little disturbance, wet density 1.823 g / cm³) was collected by all-core boring at a construction site in Tokyo. 3 A water content of 31.5% was used. The table flow was measured in the same manner as in Example 1. Furthermore, the hardened bodies obtained by curing the mixture for 7 and 28 days were measured for unconfined compressive strength in accordance with JIS A 1216. The BB used in Comparative Example 13 was blast furnace cement type B.

[0046] [Table 3]

[0047] Figure 4 is a graph showing the table flow measurement results immediately after mixing and after 60 minutes in Examples 3-4 and Comparative Examples 11-13. Figure 5 is a graph showing the uniaxial compressive strength measurement results of the cured bodies obtained by curing for 7 days and 28 days in Examples 3-4 and Comparative Examples 11-13.

[0048] As shown in Table 3 and Figures 4-5, in Examples 3-4, recycled sludge dried fine powder, blast furnace slag fine powder, and ground material were included, and the mass ratio of blast furnace slag fine powder MR1st and the mass ratio of recycled sludge dried fine powder MR2nd in the binder were kept within predetermined ranges, thus ensuring the fluidity of the mixture while reducing CO2 emissions. Furthermore, Examples 3-4 achieved uniaxial compressive strength equivalent to Comparative Examples 11-13. On the other hand, Comparative Examples 11-13 did not satisfy at least one of the following conditions: including recycled sludge dried fine powder, blast furnace slag fine powder, and ground material; the mass ratio of blast furnace slag fine powder MR1st being within predetermined ranges; and the mass ratio of recycled sludge dried fine powder MR2nd being within predetermined ranges. Therefore, they were unable to ensure the fluidity of the mixture while reducing CO2 emissions.

Claims

1. It contains a binder containing recycled sludge dried fine powder and blast furnace slag fine powder, and a ground material. The aforementioned recycled sludge dried fine powder is a processed product of unused concrete. The mass ratio MR1st of the blast furnace slag fine powder contained in the binder is 60% or more and 90% or less. A ground improvement body wherein the mass ratio MR2nd of the recycled sludge dried fine powder contained in the binder is 10% or more and 40% or less.

2. The specific surface area of ​​the aforementioned recycled sludge dried fine powder is 10,000 cm². ２ The ground improvement body according to claim 1, which is greater than / g.

3. The ground improvement body according to claim 1, wherein the mass percentage of unhydrated cement contained in the recycled sludge dried fine powder is 40% or less.

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