JPH0375588B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a solidifying material suitable for stabilizing soft ground. To be more specific,
The present invention relates to a solidification material that is particularly suitable for stabilizing soft soil to the extent that it is possible to construct structures on the soft soil by adding it to soft soil with a high content of clay components. Contains many fine particles and has a high water content, etc.
Examples of cementitious solidifying materials suitable for solidifying sludge whose properties are similar to those of soft soil constituting soft ground include: (1) Portland cement or blast furnace cement mixed with 10% by weight or more of sludge; , (2) Portland cement or blast furnace cement containing 10% by weight or more of calcium fluoroaluminate [11CaO・7Al ₂ O ₃・CaF ₂ ], and (3) Portland cement or blast furnace cement containing calcium sulfoaluminate [11CaO・7Al 2 O 3・CaF 2 ]. Those containing 10% by weight or more of 3CaO・3Al ₂ O ₃・CaSO ₄ ] are well known. All of these solidifying agents generate needle-like crystals of ettringite [3CaO・Al ₂ O ₃・3CaSO ₄・32H ₂ O] during hydration when mixed with sludge, and the hydration The aim is to make sludge denser by forming a chemical composition. These solidification materials are used for pre-treatment of sludge for disposal, but they can also be used for solidification of soft soil for the purpose of pre-treatment for disposal of soft soil. be. However, when performing in-situ solidification, or stabilization, of soft soil for purposes such as building structures on improved ground, the use of these solidification agents is not appropriate because the rate of ettringite formation is too fast. No, no. In other words, soft soil stabilization treatments carried out for this purpose are generally carried out on a large scale over two or more days.
Stabilization processing is performed while shifting the area continuously, but from the second day onwards, when stabilizing an area that connects to an area where stabilization processing was completed the previous day, the stabilization processing is completed. If a cement hydrate composition has already been formed in the region, there is a tendency for that hydrate composition to be destroyed. In this way, once the hydrate composition is destroyed, the strength of the part concerned cannot be said to be sufficient, and the low-strength connection part becomes the weak point. Because the ground becomes heterogeneous,
Problems arise with durability. In addition, in recent years, when stabilizing soft ground that exists not only on land but also on the ocean floor, that is, at a depth of 10 meters or more from the ground or ocean floor, solidifying materials are supplied to the deep layer and solidified. The so-called deep mixing method, in which wood and soft soil are stirred and mixed at the location and then hardened to form improved soil, has become widely adopted. In this construction method, a mixed cement such as ordinary Portland cement or blast furnace cement has been used as a solidifying agent. However, because there is little heat dissipation in such deep layers, the temperature may rise due to the heat of hydration, and if these cements are used as they are, hydration will be rapid during mixing and stirring with soft soil. As the mixture progresses at such a high speed that the viscosity increases, it becomes difficult to continue mixing and stirring smoothly. Furthermore, since this construction method is generally carried out on a large scale, it is also necessary to ensure that the aforementioned connection parts do not become weak points. For these reasons, the solidifying material used in this construction method needs to be slow-hardening, but conventionally known solidifying materials can be used as long-term materials by suppressing the development of strength at the initial stage and making them slow-hardening. It also has the disadvantage that the strength development at a young age is insufficient. for example,
If the amount of solidification agent added to soft soil is reduced,
Alternatively, if a large amount of a setting retarder mainly composed of lignin sulfonate or the like is added, for example, 10% by weight or more to the solidifying material, the development of strength at the initial stage of the material can be reduced. However, in these cases, the strength at long-term age also decreases, resulting in a major problem in durability, which is the most important property in stabilization treatment. In particular, when stabilizing soft soil deep under the seabed, the solidified portion produced by reducing the amount of solidifying agent added or adding a setting retarder as described above will be contained in seawater. It does not have sufficient resistance to attack by chlorides such as MgCl ₂ and sulfates such as MgSO ₄ . In addition, even when the same treatment as above is applied to stabilize soft soil on land, if the stabilization treatment extends to deep layers, resistance to erosion by chlorides and sulfates contained in groundwater etc. is not sufficient. As described above, although there is a demand for a solidifying material with excellent durability and slow hardening properties for use in stabilizing soft ground in deep layers, it is still difficult to obtain a solidifying material that has both of these characteristics. Not yet. The purpose of the present invention is to provide _a solidification material suitable for soft _ground stabilization treatment. ₃ content is 4% by weight or less, particle size composition is 10% by weight or less with particle size of 10μm or less, particle size
Less than 20% by weight is 30μm or less, and particle size is 88μm or more.
Portland cement that is less than 10% by weight 20
~50% by weight, (2) and 50 to 80% by weight of blast furnace slag, for a total of 100% by weight. . The portland cement used in this invention is
In addition to the above compounds, 2CaO・SiO ₂ , 4CaO・Al ₂ O ₃・
There is no problem even if substances having other compositions such as Fe ₂ O ₃ and CaSO ₄ .2H ₂ O are present. In addition, from the viewpoint of strength development and sulfate resistance,
3CaO・_SiO2 content is 60-70% by weight _, 3CaO・_Al2O3
The content must be below 4% by weight. That is, if the 3CaO.SiO ₂ content is less than 60% by weight, the strength development will be insufficient even after a long wood age, and if it exceeds 70% by weight, the strength development will be too early. 3CaO・_Al2
If the O ₃ content exceeds 4% by weight, problems arise in sulfate resistance. Furthermore, from the viewpoint of strength development, the particle size composition of cement is determined by determining the proportion of particles with a particle size of 10 μm or less and 30 μm or less, that is, an air jet sieve according to the Cement Association Standard Test Method “CAJS K-03-1982”. Aperture 10μm measured using the device
The amount passing through the sieve and 30 μm sieve is
10% by weight or less and 20% by weight or less, and furthermore, the proportion of particles with a particle size of 88 μm or more, that is, the residue on a mesh sieve with an opening of 88 μm, must be 10% by weight or less. If the proportion of particles of 10 μm or less exceeds 10% by weight, or if the proportion of particles of 30 μm or less exceeds 20% by weight, hydration at the initial stage of the material progresses too quickly, and strength development occurs too quickly. If the proportion of the above particles exceeds 10% by weight, the strength development will be insufficient even after a long material age, and problems will arise in durability. The above-mentioned cement can be produced by a known method of firing clinker in a rotary kiln or the like, adding clinker to the clinker, and pulverizing the clinker in a tube mill or the like. At this time, in order to adjust the particle size composition within a predetermined range, the dimensions of the grinding media in the tube mill are made larger than in the case of normal grinding, or the grinding is carried out using a closed circuit grinding method that also uses an air separator. This is desirable. It can also be pulverized using a roller mill equipped with an air separator. Furthermore, the particle size composition can be adjusted within a predetermined range by classifying cement produced by pulverization using an air separator. The present invention is further characterized in that blast furnace slag is also used. Blast furnace slag is not particularly limited as long as it is normally used for cement production, and sufficient effects can be achieved. The particle size of this blast furnace slag is Blaine specific surface area 3500
It is preferable from the viewpoint of strength development, sulfate resistance and chloride resistance that it is contained in the solidifying material in a pulverized form to a particle size of at least cm ² /g, preferably at least 4500 cm ² /g. If the Blaine specific surface area of the blast furnace slag is 3500 cm ² /g or less, the strength development will be insufficient even after a long material age, and problems will arise in durability. The solidifying material of the present invention includes Portland cement having a predetermined compound composition and a predetermined particle size composition, and blast furnace slag as essential components, but in order to achieve the purpose of the present invention, both components must be mixed in a certain range of proportions. Must be. The blending ratio is 20 to 50% by weight of Portland cement and 50 to 80% by weight of blast furnace slag. A solidifying material having an amount of components clearly outside these ranges is not suitable because it is unsuitable for the purpose of the present invention in terms of both strength development and durability. In other words, when the Portland cement in the solidifying agent is less than 20% by weight, in other words, when the blast furnace slag content exceeds 80% by weight, the strength development is insufficient even for a long material age, and when the Portland cement exceeds 50% by weight. The strength develops too quickly. It is particularly preferred that the proportions be in the range of 30 to 40% by weight of Portland cement and 60 to 70% by weight of blast furnace slag. In the solidifying material of the present invention, it is effective to add and mix a setting retarder in an amount of 2% by weight or less, preferably 0.01 to 2% by weight, based on the solidifying material. As the setting retarder, for example, silicate such as magnesium silicate, boron compounds such as potassium borate, phosphates such as trisodium phosphate, and oxycarboxylate salts such as sodium gluconate are preferable, and one type of these may be used. The above can also be used together. When these substances are added to the solidifying material in an amount of 2% by weight or less, preferably 0.01 to 2% by weight, the time of initial strength development can be delayed in approximately proportion to the amount added without impairing durability. Therefore, it is possible to provide appropriate strength development according to construction conditions such as soil quality, water content ratio, construction depth, and temperature. The solidifying material of the present invention is made by separately crushing each component material,
If necessary, it can be prepared by further classifying and then mixing, but it may also be prepared by bringing the respective component materials to the construction site and mixing them in a mixer attached to a construction machine. The solidifying material of the present invention as described above has the following advantages over cement compositions conventionally used for solidifying or stabilizing deep soft soil. (1) It is suitable for on-site solidification, that is, stabilization, of soft soil, and has slow hardening properties that do not impair workability, so it is possible to form a continuous stabilization layer. (2) Although it is slow hardening, it has excellent strength development over a long period of time and has excellent resistance to erosion by sulfates and chlorides, so it can be used to stabilize soft soils and has great durability. Improved ground can be formed. In the explanation of the present invention, so far, the stabilization treatment of soft ground, particularly the case where the deep mixing treatment method is applied, has been described.
It goes without saying that the solidifying material of the present invention can be used for construction on similar objects. Examples and comparative examples of the present invention are shown below. The Portland cement used in each of the Examples and Comparative Examples had the chemical composition and Blaine specific surface area shown in Table 1, and was classified. When the compound composition of Portland cement (10) shown in Table 1 is calculated using the Borg formula, 3CaO.
SiO ₂ was 62% by weight and 3CaO.Al ₂ O ₃ was 1% by weight. Meanwhile, Portland cement (20)
is calculated similarly using ordinary Portland cement.
3CaO.SiO ₂ was 50% by weight, and 3CaO.Al ₂ O ₃ was 9% by weight. The chemical composition and Blaine specific surface area of the blast furnace slag used are also listed in Table 1.

[Table] Portland cement shown in Table 1 (10) and cement made by classifying it to adjust the particle size (11)
Table 2 shows the particle size composition and compound composition of (14) and (21), which were prepared by adjusting the particle size of ordinary Portland cement (20) in the same manner as above.

[Table] The soft soils used in the solidification experiment were artificial soft soil prepared using experimental materials and soft soil collected from the seabed within Yokohama Port. The composition of the artificial soft soil is shown in Table 3. The main component of clay minerals is allofene.

【table】

[Table] Table 4 shows the physical properties of the soft soil on the seabed in Yokohama Port. X-ray diffraction tests, thermal analysis, electron microscopy, etc. have shown that it contains montmorillonite and sericite as well as allofene as clay minerals.

[Table] Example 1 A solidifying agent consisting of 40% by weight of Portland cement (11) and 60% by weight of blast furnace slag was added to the solidifying agent.
60% by weight seawater was added and kneaded for 3 minutes to form a slurry. Next, 20% by weight of the solidifying agent slurry was added to the artificial soft soil and kneaded for 5 minutes.The kneaded mixture was then poured into a formwork with a diameter of 5 cm and a height of 10 cm.
The samples were cured in a humid air temperature chamber at ±1°C. After reaching a predetermined material age, the mold was removed and the unconfined compressive strength was measured according to JIS A1216-1977. The results are shown in Table 5. Note that Table 5 also lists target values for unconfined compressive strength. Example 2 and Comparative Examples 1 to 2 In Example 1, the solidifying agent was composed of 30% by weight of Portland cement (11) and 70% by weight of blast furnace slag...Example 2; 10% by weight of Portland cement (11), Solidifying material made of 90% by weight of blast furnace slag...Comparative Example 1; Solidifying material made of 60% by weight of Portland cement (11) and 40% by weight of blast furnace slag...Comparative Example 2; Same as Example 1 except that The experiment was conducted under the following conditions. The results are shown in Table 5. Comparative Examples 3 to 6 In Example 1, instead of Portland cement (11) as a component constituting the solidifying agent, Portland cement (10)... Comparative example 3; Portland cement (12)... Comparative example 4; Portland cement (13)...Comparative Example 5; Portland cement (14)...Comparative Example 6; An experiment was conducted under the same conditions as in Example 1, except that (14)...Comparative Example 6; The results are shown in Table 5.

【table】

[Table] As is clear from the table, Portland cement and blast furnace slag having a chemical composition and particle size composition within the range of the present invention are mixed at the blending ratio of the present invention, and a predetermined amount of water is added to the obtained solidifying material. When used to solidify soft soil after making it into a slurry, the unconfined compressive strength of the solidified soft soil is low at early stage age, but sufficiently high at long stage, showing excellent strength development. I understand. On the other hand, even if the Portland cement has the chemical composition of the present invention, if the particle size composition is out of the range of the present invention, or even if the Portland cement of the present invention and blast furnace slag are used, the blending ratio will be out of the range of the present invention. In such cases, even if the soft soil is solidified using the solidifying material, the unconfined compressive strength is either high at the initial age or low at the long-term age, and neither effect is obtained. Example 3 An experiment was conducted under the same conditions as in Example 1, except that soft soil from the seabed in Yokohama Port was used instead of the artificial soft soil. The results are shown in Table 6. Examples 4 to 10 and Comparative Example 7 In Example 3, part of the solidifying material was magnesium silica
0.5% by weight...Example 4; Potassium borate 0.5% by weight...Example 5; Trisodium phosphate 0.5% by weight...Example 6; Sodium gluconate
0.005% by weight...Example 7; Sodium gluconate
0.05% by weight...Example 8; Sodium gluconate
0.5% by weight...Example 9; Sodium gluconate
1.5% by weight...Example 10; Sodium gluconate 5% by weight...Comparative Example 7; An experiment was conducted under the same conditions as in Example 3, except that the following were substituted. The results are shown in Table 6.

【table】

[Table] As can be seen from Table 6, Portland cement and blast furnace slag having a chemical composition and particle size composition within the range of the present invention are mixed at the blending ratio of the present invention, and a predetermined amount of water is added to the obtained solidifying material. When the slurry is made into a slurry and then used to solidify soft soil, the unconfined compressive strength of the solidified soft soil from the seabed in Yokohama Port is low at the initial age, but is sufficiently high at the long age, similar to artificial soft soil. It can be seen that it has excellent strength development properties. Furthermore, if a setting retardant is added to the solidification material in an amount according to the blending ratio of the present invention, the unconfined compressive strength of the solidified soft soil will be lower at the initial stage than when no retardant is added, depending on the amount of retardant added. On the other hand, the long-term wood age also shows a sufficiently high value, indicating that it has excellent strength development properties. On the other hand, when the retardant is added in a larger amount than the blending ratio of the present invention, the unconfined compressive strength of the solidified soft soil shows a low value even after a long period of age. Example 11 A solidifying agent consisting of 40% by weight of Portland cement (11) and 60% by weight of blast furnace slag was mixed with Toyoura standard sand and water at a ratio of 2 parts by weight and 0.65 parts by weight, respectively, per 1 part by weight of the solidifying agent. , vertical 4
A cement mortar specimen measuring 4 cm in width and 16 cm in length was molded. After curing in humid air for 48 hours in a constant temperature room at 20 ± 1°C, it was demolded and placed in fresh water and artificial seawater containing 0.24% by weight of magnesium sulfate and 0.40% by weight of magnesium chloride at 5°C, 20°C, and 30°C. JIS compressive strength after soaking and 1 year old
Measured using R5201-1981. The results are shown in Table 7. Comparative Example 8 An experiment was conducted under the same conditions as in Example 11, except that Portland cement (21) was used instead of Portland cement (11). The results are shown in Table 7.

[Table] As can be seen from Table 7, when Portland cement (11) within the chemical composition range of the present invention is used, the strength ratio of artificial seawater immersion/freshwater immersion is 95% or more, and the seawater resistance is It can be seen that it is excellent. On the other hand, even if the particle size composition is within the range of the present invention, when Portland cement (21) whose chemical composition is outside the range of the present invention is used, the strength ratio of artificial seawater immersion/freshwater immersion is less than 80%. Therefore, it can be seen that this is not compatible with the purpose of the present invention.

Claims (1)

[Claims] 1. Compound composition: 3CaO・SiO ₂ content is 60 to 70% by weight, 3CaO・Al ₂ O ₃ content is 4% by weight or less, particle size composition is 10% by weight or less with particle size of 10 μm or less, Diameter 30μ
20% to 50% by weight of Portland cement with a particle size of 20% by weight or less, 10% by weight or less with a particle size of 88μm or more, and 50% to 80% by weight of blast furnace slag for a total of 100% by weight. A solidification material for stabilizing soft ground. 2. The solidifying material according to claim 1, characterized in that the solidifying material contains 2% by weight or less of a setting retarder.