JPS636593B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a ground improvement material used in deep mixing treatment. In general, deep mixing treatment is carried out by injecting a soil improvement material into the seabed soil to be improved from a special ground improvement vessel and stirring it at the same time, and the work is carried out several tens of meters below the seabed surface. In this process, the soil improvement material and soil to be improved are stirred and mixed while rotating a rotary blade equipped with a soil improvement material or improvement material slurry discharge port. In this case, in order to obtain a continuous layer of improved soil, the rotary blade is rotated while moving along the boundary between the improved and unimproved areas. However, conventionally, ordinary Portland cement or blast furnace cement, which has a high initial strength, has been used as a ground improvement material for this deep mixing treatment. Therefore, the area where the ground improvement material is stirred and mixed will harden in a short time, and the rotor will move a portion of the hardened soil. For this reason, not only the rotor blades are agitated, but also a situation may occur in which the rotor blades cannot be recovered together with the shaft. It also becomes difficult or impossible for the rotor itself to penetrate. For this reason, in conventional deep mixing treatment, improvements are often made one after another before the strength of the already improved parts increases, forcing construction to be carried out day and night. Furthermore, when conventional ground improvement materials are used, the improved portion quickly hardens and hardens, making it impossible to use a method of driving piles such as copper pipe piles into the improved soil. For this reason, the only possible construction method is, for example, installing a caisson on top of the improved soil, and there is a problem in that the construction methods after the improvement are severely limited. The present invention was made to solve this problem, and its purpose is to provide a ground improvement material for deep mixing treatment that can maintain a low initial strength and also guarantee an increase in strength over the long term. It is. That is, the present invention provides vitreous blast furnace slag powder 40
~80% by weight and moderate heat Portland cement ~20~
This is a ground improvement material for deep mixing treatment consisting of 60% by weight. The present invention will be explained in detail below. The present invention has vitreous blast furnace slag powder as its main component, and moderate heat Portland cement is blended therein. Glassy blast furnace slag powder is used as a conventional ground improvement material, and is hydrated and hardened by alkaline stimulation from lime or the like. Examples of the glassy blast furnace slag powder include granulated slag, and an example of the composition of granulated slag is shown in Table 1 below.

[Table] The blending amount of vitreous blast furnace slag is appropriately selected depending on the quality of the soil to be improved, the turning method, etc., and the range is 40 to 80% by weight. This is because if it is less than 40% by weight, the initial strength will be too high, and if it exceeds 80% by weight, it will not be possible to obtain the required strength in the long term. Glassy blast furnace slag has a fineness (plain specific surface area) in the range of 1500 to 6000 cm ² /g,
Select depending on soil quality or turning method. For example, if a coarse slag is used, it will take a long time for the strength of the improved soil to increase; if a thin slag is used, the opposite will occur. Further, as the vitreous blast furnace slag, the medium-heat Portland cement mixed therewith avoids contact with moisture, so dry powder obtained by dry grinding is usually used. However, when the ground improvement material is used in the form of a slurry, the vitreous blast furnace slag does not necessarily need to be a dry powder, and may be wet-pulverized. In this case, a drying step is not necessary. For example, granulated blast furnace slag grains are produced by crushing and rapidly cooling blast furnace slag with water, and even those that have been forcibly dehydrated contain about 10 to 15% water by weight. Approximately 17 parts of heavy oil is required per ton of crushed slag. Furthermore, the cost of wet pulverization is significantly lower than that of dry pulverization, and unlike dry pulverization, there is no need to take dust-proof measures. In the present invention, moderate heat Portland cement is blended with the above-mentioned vitreous blast furnace slag powder. The purpose of blending this is to lower the initial strength and increase the long-term strength of the improved soil. The fact that moderate heat Portland cement has such an effect is that
This was revealed through experiments by the inventors,
Its mechanism of action is not clear. According to the inventors' estimation, the formation of a hydration-hardened structure of moderate-heat Portland cement itself, the interaction of that hardened structure with soil particles (silt, clay, etc.), and the hydration of moderate-heat Portland cement produced Formation of agglomerated and agglomerated structures in soil particles due to lime; Formation of hydrated and hardened structures in slag particles due to the alkaline stimulating action of lime; Formation of hardened structures due to pozzolanic reaction of soil particles (especially clay) due to the action of lime. Although the hardening effect of the improved soil occurs due to such factors, it is thought that according to the present invention, the initial strength development of the improved soil can be suppressed due to the comprehensive effect of these hardening effects. In other words, moderate heat Portland cement has a higher concentration of 3CaO・SiO ₂ than ordinary Portland cement.
and 3CaO・Al ₂ O ₃ are significantly less, and 2CaO・SiO ₂
There are many. An example of the amount of the compound is shown in Table 2 below.

[Table] The characteristics of this moderate heat Portland cement are as follows. It is suitable for mass concrete because its heat of hydration is lower than ordinary Portland cement. Its early strength is lower than ordinary Portland cement, but its long-term strength is equal to or slightly better than ordinary Portland cement. Low drying shrinkage. It has high chemical resistance. The heat of hydration of medium-heat Portland cement compared with ordinary Portland cement is shown in the third table below.
It will look like a table.

[Table] The amount of heat generated by this heat is accumulated inside the improved soil. In addition, C ₃ S, which is the main constituent mineral of both cements,
Comparing the amount of lime produced by the hydration reaction of C ₂ S, 2C ₃ S + 6H ₂ O → C ₃ S ₂ H ₃ + 3Ca (OH) ₂ 2C ₂ S + 4H ₂ O → C ₃ S ₂ H ₃ + Ca (OH) _2Here C ₃ S ₂ H ₃ represents _3CaO.2SiO 2.3H ₂ O. From this reaction equation, 1 mol of C ₃ S is 1 mol of C 3 S.
It can be seen that three times as much Ca(OH) ₂ as C ₂ S is produced. That is, the amount of lime produced by hydration of moderate heat Portland cement containing less C ₃ S and more C ₂ S is less than that of ordinary Portland cement. Therefore, when used as a ground improvement material for deep mixing treatment in the coexistence of glassy blast furnace slag, the initial strength development of the improved soil can be suppressed because the heat of hydration is low and the amount of lime produced by hydration is small. It seems possible. Moderate heat Portland cement having such properties is blended in an amount of 20 to 60% by weight. This is because if it is less than 20% by weight, the cured strength of the improved soil will not be sufficient, and if it exceeds 60% by weight, the initial strength will be too high. In this way, a ground improvement material containing vitreous blast furnace slag powder and moderate heat Portland cement is
The amount added to the improved soil varies depending on the soil quality of the improved soil and the turning method, but it is added based on the following criteria, for example. 5Kgf/ ^cm2 or less in 1 day of wood age, preferably 5Kgf/ ^cm2 or less in 3 days of wood age, and 91
The amount added is determined so that the amount is 20 Kgf/cm ² or more, preferably 50 Kgf/cm ² or more per day. To give a specific example, for example, 160 kg to 200 kg is added to 1 m ³ of soil to be improved. Next, examples of the present invention will be described. As the vitreous blast furnace slag, granulated blast furnace slag pulverized in a ball mill to a particle size Blaine specific area of 3600 cm ² /g was used, and as the moderate heat Portland cement, a commercially available product was used. These are mixed in the proportions shown in Table 4 to form soil improvement materials according to the present invention (No. 1 to No. 3) and soil improvement materials (No. 4, No. 5) with different mixing proportions from the present invention.
We made a prototype. In this case, the water/improver weight ratio of the improver slurry was determined to be the same as the slurry viscosity when the W/C (water/cement) ratio of commercially available ordinary Portland cement is 0.6.

[Table] Dry weight (slag powder and ^moderate heat 160 kg of Portland cement (total weight of Portland cement) was added, mixed and stirred, and filled in three layers into a cylindrical mold with a diameter of 5 cm and a height of 10 cm to form a specimen.

[Table] The specimen thus obtained was sealed with a polyethylene sheet and kept at 20°C until the specified strength test material rating.
After curing in a constant temperature and humidity chamber with a relative humidity of 85% or higher, the unconfined compressive strength was measured. The results are shown in Table 6.

[Table] According to the above table, according to the soil improvement material according to the present invention, the strength development characteristics of the improved soil can be 5 Kgf/cm ² or less at 1 day of age and 20 Kgf/cm ² or more at 91 days. Also, ^less than 5Kgf/cm2 at 3 days old, 50Kgf/cm2 at 91 days old.
It was found that very satisfactory results of more than cm ² were also obtained. As described above, according to the present invention, since the initial strength is kept low, it is possible to solve problems such as poor joining, wear and tear of the turning machine, and furthermore, work performed day and night. In addition, steel pipe piles and the like can be driven into the improved soil layer, making it possible to develop various construction methods and other remarkable effects.

Claims (1)

[Claims] 1. A ground improvement material for deep mixing treatment consisting of 40-80% by weight of vitreous blast furnace slag powder and 20-60% by weight of moderate heat Portland cement.