Method for determining soil improvement materials and mixes

Abstract

To propose a ground improvement material that can reduce CO2 emission while ensuring solidification performance necessary for ground improvement, and a method to determine the composition of a ground improvement body using this ground improvement material.SOLUTION: A ground improvement material containing water, a binder and an admixture and a method to determine the composition of a ground improvement body mixed with soil include a process of measuring standard temperature indoor test strength, which is the strength of the specimen cured indoors at the standard temperature, a process of measuring on-site temperature indoor test strength, which is the strength of a specimen cured at a temperature taking into account the environment temperature where ground improvement is to be carried out, and a process of calculating the strength ratio between the on-site temperature indoor test strength and the standard temperature indoor test strength. When the intensity ratio is less than 1, the composition of the ground improvement body is determined so that the strength obtained by multiplying the on-site temperature room test strength by the correction coefficient is greater than the designed strength.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a soil improvement material and a method for determining a mix ratio. [Background technology]

[0002] Ground improvement involves adding and mixing solidifying materials such as lime and ordinary Portland cement into soft ground to stabilize it. For special soils that cannot be sufficiently improved with lime and ordinary Portland cement alone, cement-based solidifying materials made by mixing ordinary Portland cement with blast furnace slag or other admixtures may be used. Meanwhile, in the field of concrete, there are cases where the amount of ordinary Portland cement used is reduced in order to reduce the environmental impact (see, for example, Patent Document 1). Because blast furnace slag has properties similar to cement, such as latent hydraulic properties, if the amount of Portland cement used is reduced by using blast furnace slag, the amount of CO2 emitted during the production of Portland cement can be reduced. Therefore, in the field of ground improvement, there is a desire to reduce the environmental impact by reducing the amount of Portland cement used or by replacing Portland cement with other materials. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent No. 6137850 Summary of the Invention [Problem to be solved by the invention]

[0004] The objective of the present invention is to propose a ground improvement material that ensures the solidification performance required for ground improvement while reducing CO2 emissions, and a method for determining the mix of ground improvement bodies using this ground improvement material. [Means for solving the problem]

[0005] The soil improvement material of the present invention for solving the above problems contains water, a binder, and an admixture, and the binder is mainly composed of ground granulated blast furnace slag. The ground granulated blast furnace slag is limestone fine powder , Blast furnace cement type B and calcium carbonate One or more selected ingredients are added. The admixture may be slaked lime, quicklime, or a lime-based expanding material. and Calcium sulfoaluminate-based expander Material The admixture is preferably added in an amount of 3 to 40 parts by weight based on 100 parts by weight of the binder. This ground improvement material uses a binder mainly made of ground granulated blast furnace slag instead of Portland cement (for example, ordinary Portland cement or blast furnace cement type B), which makes it possible to reduce CO2 emissions during concrete production. , Blast furnace cement type B and calcium carbonate One or more ingredients selected from the above are added. Furthermore, slaked lime, quicklime, lime-based expanding materials, calcium sulfoaluminate-based expanding materials, and Blast-furnace cement type B Since it contains an admixture made of one or more materials selected from Portland cement, the necessary solidification performance is ensured even if the main component is ground granulated blast furnace slag instead of Portland cement.

[0006] The method for determining the mix proportion of a soil improvement body formed by mixing the soil improvement material with soil includes the steps of measuring the standard temperature laboratory test strength, which is the strength of a test specimen cured indoors at a standard temperature; measuring the in-situ laboratory test strength, which is the strength of a test specimen cured at a temperature that takes into account the temperature environment at the site where the soil improvement is performed; and calculating the strength ratio between the in-situ laboratory test strength and the standard temperature laboratory test strength. If the strength ratio is less than 1, the mix proportion of the soil improvement body is determined so that the strength obtained by multiplying the in-situ laboratory test strength by a correction factor is equal to or greater than the design strength. If the strength ratio is equal to or greater than 1, it is preferable to determine the mix proportion of the soil improvement body so that the strength obtained by multiplying the standard temperature laboratory test strength by a correction factor is equal to or greater than the design strength. Furthermore, it is preferable to mix the soil improvement body so that the calcium hydroxide content in the hardened soil of the soil improvement body is within the range of 4.9 to 12 parts by weight, calculated on anhydrous basis. When determining the mix proportions, it is common to check the unconsolidated and consolidated properties through indoor tests under temperature environments specified in guidelines, etc., but in actual on-site construction, the temperature environment varies depending on the construction location and time, and there is a concern that the required strength may not be achieved at the specified material age, especially in low-temperature environments. According to the mix proportion determination method of the present invention, the various differences in conditions that occur between the on-site and indoor environments are organized as strength ratios, and a mix that satisfies the required strength is selected, thereby ensuring the necessary solidification performance. [Effects of the Invention]

[0007] The soil improvement material and method for determining the mix proportion of the present invention make it possible to reduce CO2 emissions while ensuring the solidification performance required for soil improvement. [Brief explanation of the drawings]

[0008] [Figure 1] 1 is a flowchart showing the steps of a method for determining the mix of ground improvement bodies according to this embodiment. [Figure 2] This is an explanatory diagram of a method for determining the mix of ground improvement bodies using strength ratios. [Figure 3] 10 is a graph showing the relationship between cumulative temperature and unconfined compressive strength according to a comparative example. [Figure 4] 1 is a graph showing the relationship between cumulative temperature and unconfined compressive strength according to Example 1. [Figure 5] 1 is a graph showing the relationship between cumulative temperature and unconfined compressive strength according to Example 2. [Figure 6] 10 is a graph showing the relationship between cumulative temperature and unconfined compressive strength according to Example 3. DETAILED DESCRIPTION OF THE INVENTION

[0009] This embodiment describes a case where the total amount of CO2 emissions in ground improvement work is reduced by using a ground improvement material that minimizes the amount of ordinary Portland cement used, which emits a large amount of CO2 during its manufacturing process.The inventors have discovered that when estimating the strength of improved soil (ground improvement body) constructed by mixing soil with a ground improvement material designed to reduce CO2 emissions, the accuracy of strength estimation based on the accumulated temperature can be improved by organizing the relationship between accumulated temperature and strength for each curing temperature.Based on this finding, this embodiment describes a case where ground improvement is performed using a ground improvement material suited to the local environment (temperature). The ground improvement material of this embodiment contains water, a binder, and an admixture. The binder is mainly composed of ground granulated blast furnace slag instead of Portland cement. The binder also contains one or both of ground limestone and calcium carbonate. The admixture is made of one or more materials selected from slaked lime, quicklime, lime-based expansive materials, calcium sulfoaluminate-based expansive materials, and Portland cement. In this embodiment, the admixture is added in a range of 3 to 40 parts by weight per 100 parts by weight of the binder.

[0010] Here, when carrying out ground improvement work, the strength of the improved soil is confirmed through indoor mix studies, and a mix that satisfies the required performance is determined after taking into consideration the differences in conditions between on-site and indoors. When checking strength indoors, curing is carried out at a standard temperature (for example, 20°C), but when there are concerns about temperature effects, particularly during extreme heat or cold periods, the average temperature at the site is used as the curing temperature. The age at which strength is confirmed is determined according to the age of the material to be evaluated at the site, and is generally 7 or 28 days. However, when checking the strength of material under arbitrarily changing temperature conditions, the temperature environment can only be substituted with a constant average temperature condition when the relationship between accumulated temperature and strength is the same regardless of temperature. In other words, as shown in Equation 1, if it is assumed that the strength of a specific material age is determined by a function f of accumulated temperature that takes the temperature environment into account, if there is no temperature dependency in the relationship between accumulated temperature and strength, the coefficient α related to the temperature environment can be used. T It is possible to take it out of the integral by using a constant α0, and by doing so, the cumulative temperature term can be converted into the product of the average temperature and the age of the material rather than being an integral, and as a result, any temperature environment can be substituted under the condition of a constant average temperature.The cumulative temperature is the value obtained by multiplying the curing temperature (°C) by the number of days.

[0011]

number

[0012] When a binder containing blast furnace slag powder as the main component is used instead of a solidifying material such as Portland cement (when the ground improvement material of this embodiment is used), the relationship between the accumulated temperature and strength differs depending on the temperature conditions, so if the curing is done under conditions with a constant average temperature, it is not possible to confirm the strength under arbitrarily changing temperature conditions. Therefore, the mix proportions of the ground improvement body, which is made by mixing the ground improvement material and soil, are determined according to the following procedure. The method for determining the mix proportion of a ground improvement body is shown in Figure 1. As shown in Figure 1, the method for determining the mix proportion of a ground improvement body includes a standard temperature indoor test process S1, an on-site temperature indoor test process S2, a strength ratio calculation process S3, and a mix determination process S4.

[0013] In the standard temperature indoor test step S1, the standard temperature indoor test strength, which is the strength of a specimen indoor-cured at a standard temperature, is measured. The standard temperature is a temperature determined by guidelines (for example, "Ground Improvement Manual with Cement-Based Solidification Materials [Second Edition]": Cement Association, etc.). In this embodiment, the standard temperature is 20°C. The standard temperature indoor test strength is organized in relation to the accumulated temperature. At least two or more relationships between the accumulated temperature and the standard temperature indoor test strength are obtained. In the on-site temperature indoor test process S2, the on-site temperature indoor test strength, which is the strength of the specimen cured at a temperature that takes into account the temperature environment at the site where the ground improvement work is being carried out, is measured. The curing temperature is determined by obtaining the past temperature history of the construction site (such as average values) and taking into account the time of construction (for example, the average value during the construction period). The on-site temperature indoor test strength is organized in relation to the accumulated temperature. At least two or more relationships between the accumulated temperature and the on-site temperature indoor test temperature are obtained.

[0014] In the strength ratio calculation step S3, the strength ratio between the field temperature indoor test strength and the standard temperature indoor test strength (field temperature indoor test strength / standard temperature indoor test strength) is calculated. In the mix determination step S4, the mix of the ground improvement body is determined using the strength ratio. When the strength ratio is less than 1, the mix of the ground improvement body is determined so that the strength obtained by multiplying the in-situ indoor test strength by the correction coefficient is equal to or greater than the design strength. On the other hand, when the strength ratio is equal to or greater than 1, the mix of the ground improvement body is determined so that the strength obtained by multiplying the standard temperature indoor test strength by the correction coefficient is equal to or greater than the design strength. In other words, when the function of the accumulated temperature and the in-situ indoor test strength is within the region (region A) below the curve showing the relationship between the accumulated temperature and the standard temperature indoor test strength shown in Figure 2, the mix of the ground improvement body is determined so that the strength obtained by multiplying the in-situ cured strength by the correction coefficient (0 < correction coefficient < 1) is equal to or greater than the design standard strength. On the other hand, when the function of the accumulated temperature and the in-situ indoor test strength is outside this region (region B), the mix of the ground improvement body is determined so that the strength obtained by multiplying the standard temperature indoor test strength by the correction coefficient (0 < correction coefficient < 1) is equal to or greater than the design strength. It is preferable to mix the calcium hydroxide in the hardened soil improvement body so that the content of calcium hydroxide in the hardened soil improvement body is within the range of 4.9 to 12 parts by weight in anhydrous terms.

[0015] The soil improvement material of this embodiment uses a binder mainly made of ground granulated blast furnace slag, which makes it possible to reduce CO2 emissions during concrete production. The binder contains either or both of fine limestone powder and calcium carbonate, and further contains an admixture made of one or more materials selected from slaked lime, quicklime, lime-based expanding material, calcium sulfoaluminate-based expanding material, and Portland cement, so that the necessary solidification performance is ensured even when the main component is blast furnace slag powder instead of Portland cement. In determining the mix proportions for a ground improvement body, it is common to check the unconsolidated and consolidated properties through indoor tests under temperature conditions specified in guidelines, etc. However, in actual on-site construction, the temperature environment varies depending on the construction location and time, and there is a concern that the required strength may not be achieved at the specified material age, especially in low-temperature environments.In contrast, the mix determination method of this embodiment ensures the necessary solidification performance by organizing the various differences in conditions that arise between the on-site and indoor environments as strength ratios and selecting a mix that satisfies the required strength.

[0016] Next, the results of an experiment conducted to confirm the strength development of the ground improvement body of this embodiment are shown. Table 1 shows the composition of the binder (or solidifying agent) and admixture (ground improvement material excluding water) used in the experiment. As shown in Table 1, limestone powder or calcium carbonate was added to 100 parts by weight of ground granulated blast furnace slag, and admixtures such as slaked lime and expansive agent were also added. In Example 1, 11.1 parts by weight of limestone powder was added to 100 parts by weight of blast furnace slag powder as a binder that did not use Portland cement, and 9.5 parts by weight of slaked lime and 9.0 parts by weight of an expansive material were added as admixtures. In Example 2, as a CO2-suppressing binder, 11.1 parts by weight of limestone powder as a stimulant and 9.5 parts by weight of blast furnace cement type B (blast furnace B) were added to 100 parts by weight of blast furnace slag powder, and 9.0 parts by weight of an expansive additive was added as an admixture. In Example 3, 43.9 parts by weight of calcium carbonate A (calcium carbonate produced by reacting highly alkaline wastewater generated in a concrete secondary product factory with CO2 in boiler exhaust gas) was added to 100 parts by weight of blast furnace slag powder as a carbon recycling type binder, and 9.5 parts by weight of slaked lime and 9.0 parts by weight of an expansive agent were added as admixtures. As a comparative example, an experiment was also conducted using blast furnace cement type B (blast furnace B).

[0017] [Table 1]

[0018] The soil material was prepared by mixing commercially available silica sand and clay. In this experiment, the silica sand and clay were mixed at a mass ratio of 4:1 so that the fine particles would account for at least 20%. First, a suspension consisting of binder and admixture (Examples 1 to 3) or solidification material (Comparative Example), bentonite, and water was prepared, and then the suspension was poured into the soil material and mixed to prepare an improved soil specimen. The strength development of the improved soil specimen was then confirmed when the curing temperature was 20°C and when the curing temperature was 5°C. At a curing temperature of 20°C, the strength was measured at ages of 3, 5, 7, 10, 14, 21, and 28 days (total of 7 ages), and at a curing temperature of 5°C, the strength was confirmed at ages of 3, 10, and 28 days (total of 3 ages). The improved soil specimens were prepared in accordance with JGS 0821-2020, "Method for preparing specimens without compaction of stabilized soil." Table 2 shows the suspension formulation.

[0019] [Table 2]

[0020] Figure 3 shows the experimental results (relationship between accumulated temperature and strength (uniaxial compressive strength)) of improved soil specimens using the comparative example solidification material. Figure 4 shows the experimental results of improved soil specimens using the binders of Example 1, Example 2, and Example 3, respectively. As shown in Fig. 3, in Comparative Example 1, which used blast-furnace cement type B, the relationship between cumulative temperature and strength when the curing temperature was 20°C and when it was 5°C is distributed on the same trend line. On the other hand, in Examples 1 to 3, which used the ground improvement material of this embodiment, the relationship between cumulative temperature and strength when the curing temperature was 20°C is different from that when the curing temperature was 5°C, as shown in Figs. 4 to 6. In all Examples, at the cumulative temperature stage of 140, a difference occurred in the unconfined compressive strength when the curing temperature was 20°C and when it was 5°C. As described above, when using the binder of this embodiment, we confirmed that there was a difference in strength between when cured at standard temperature and when cured at the on-site temperature. Therefore, when using a binder primarily composed of blast furnace slag powder instead of a solidifying agent (such as Portland cement or blast furnace cement type B), it is necessary to correct the strength to reflect the temperature environment at the construction site. That is, after confirming the strength at both the on-site temperature environment and the standard temperature (20°C) in a laboratory study (the on-site temperature laboratory test strength and the standard temperature laboratory test strength), the strength ratio between the on-site temperature laboratory test strength and the standard temperature laboratory test strength (the on-site temperature laboratory test strength / the standard temperature laboratory test strength) is corrected. Specifically, the strength ratio between the on-site temperature laboratory test strength and the standard temperature laboratory test strength of an empirically organized conventional mix is ​​divided by the temperature effect of the solidifying agent, and then multiplied by the temperature effect of the binder to obtain a strength ratio that takes the temperature effect of the binder into account. This allows us to determine a mix appropriate for the on-site environment and binder while avoiding the need for test construction.

[0021] Although the embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments, and each of the above-described components can be appropriately modified within the scope of the present invention. For example, strength tests may be performed using uniaxial compression tests or CBR tests (for example, "Test methods for stabilized soil using cement-based solidification materials" JCAS L-01).

[0022] S1 Standard temperature indoor test process S2 On-site temperature indoor test process S3 Intensity ratio calculation process S4 Mixture determination process

Claims

1. A ground improvement material comprising water, a binder, and an admixture, The binder is mainly composed of ground granulated blast furnace slag, and one or more materials selected from ground limestone, blast furnace cement type B, and calcium carbonate are added to the ground granulated blast furnace slag, The admixture is a ground improvement material characterized in that it is made of one or more materials selected from the group consisting of slaked lime, quicklime, lime-based expansive materials, and calcium sulfoaluminate-based expansive materials.

2. 2. The soil improvement material according to claim 1, wherein the admixture is added in an amount of 3 parts by weight to 40 parts by weight per 100 parts by weight of the binder.

3. A method for determining the proportion of a ground improvement body obtained by mixing the ground improvement material according to claim 1 or claim 2 with soil, A step of measuring the standard temperature indoor test strength, which is the strength of a specimen indoor-cured at a standard temperature; A process of measuring the strength of a test specimen cured at a temperature that takes into account the temperature environment at the location where ground improvement is performed, at an on-site temperature indoor test; and calculating a strength ratio between the in-situ temperature indoor test strength and the standard temperature indoor test strength, A method for determining a mix proportion, characterized in that if the strength ratio is below 1, the mix proportion of the ground improvement body is determined so that the strength obtained by multiplying the on-site temperature indoor test strength by a correction coefficient is equal to or greater than the design strength.

4. A method for determining a composition of the ground improvement body as described in claim 3, characterized in that, when the strength ratio is 1 or more, the composition of the ground improvement body is determined so that the strength obtained by multiplying the standard temperature indoor test strength by a correction coefficient is equal to or greater than the design strength.

5. The method for determining the composition of claim 3, characterized in that the calcium hydroxide content in the hardened body of the ground improvement body is mixed so that it is within the range of 4.9 parts by weight or more and 12 parts by weight or less in terms of anhydrous.

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