JPS5991190A - Ground conditioner to be mixed in depths - Google Patents

Abstract

PURPOSE:To provide the titled ground conditioner consisting of vitreous blast furnace slag in powder and medium-heat Portland cement, which maintains low initial strength, insures increase of strength over a long period of time and facilitates operation. CONSTITUTION:The ground conditioner to be mixed in the depths of ground consists of (A) 40-80wt% vitreous blast furnace slag in powder and (B) 20- 60wt% medium-heat Portland cement. Ordinary grade Portland cement and blast furnace slag having a high initial strength have so far been used as ground conditioner, but they tend to cause solidification of a mixture of the conditioner and soil in a short time, sometimes causing part of solidified soil to be moved by a rotor blade or making it impossible to perform mixing and recover rotor blades and revolving shafts en bloc, thus leading to the necessity of pouring of additional batches of the conditioner and full-time operation day and night. The use of the medium-heat Portland cement maintains initial strength at a low level and insures increase of strength over a long period of time, making the operation very easy.

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, resulting in an embankment extending 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 soil improvement material used for this deep mixing treatment is Ordinary I Rutland cement and blast furnace cement, which have high initial strength, are used.

Therefore, the area where the ground improvement material is stirred and mixed will harden in a short time, and the rotor blade will move over a portion of the hardened soil. For this reason, the agitation of the rotor blades becomes so turbulent that 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 part □ 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 /4' piles such as steel pipe piles into the improved soil. For this reason, there is a problem in that the construction methods after the improvement are severely limited, for example, the only possible construction method is to attach a caisson on top of the improvement.

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 uses vitreous blast furnace slag powder of 40 to 80
This is a ground improvement material for deep mixing treatment consisting of 20-60% by weight of moderate heat d citland cement.

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 water-hardened by alkaline stimulation from lime or the like. Examples of this glass and quality blast furnace slag powder include granulated slag, and an example of the composition of granulated slag is shown in Table 1 below.

The blending amount of vitreous blast furnace slag is appropriately selected depending on the quality of the soil to be improved, the construction method, etc., but the range is 40 to 80.
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 (Blaine specific surface area) of 1500 to 6.
．． Select according to soil quality or construction method within the range of 000cm2/11. For example, if a compatible slag is used, the strength of the improved soil will be high but it will take a long time, but 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 using the ground improvement material in the form of a slurry, the vitreous blast furnace slag (vitreous blast furnace slag) does not necessarily have to be a dry powder;
It may also be wet-milled. 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. 1 ton weight approx. 177
of heavy oil is required. 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. To mix this,
This is to lower the initial strength and increase the long-term strength of the improved soil. It has been revealed through experiments by the present inventors that moderate heat Portland cement has such an effect, but its mechanism of action is not clear. According to the estimates of the present inventors, the formation of a water-hardening structure of the medium-heat Portland cement itself, the interaction between the hardening structure and soil particles (silt, clay, etc.), and the water-use of the moderate-heat Portland cement. Formation of agglomeration and agglomerated structure of soil particles due to lime, formation of hydration hardened structure of slag particles due to the alkaline stimulating effect of lime, hardened structure due to I-plan reaction of soil particles (especially clay) due to the action of lime. Although the hardening effect of the improved soil occurs due to the formation of .

In other words, moderate heat Portland cement has 3CaO・SlO□ and 3Ca compared to ordinary Portland cement.
O・AI 20 s is significantly less, 2CaO・51
There are many 02. An example of the amount of the compound is shown in Table 2 below.

However, CS = 3CaO・SiO, C2S:==2C
aO-8iO2゜2 The characteristics of this moderate heat Portland cement are as follows. It is suitable for mass concrete because its water heat consumption is lower than that of 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.

Table 3 below shows the water utilization of moderate heat Portland cement in comparison with that of ordinary Portland cement.

The amount of heat generated by this heat is accumulated inside the improved soil.

Also, comparing the amount of lime produced by the hydration reaction of C3S and C2S, which are the main constituent minerals of both cements, 2C3S + 6H20 → C3S2H3 + 3Ca (O■■)
22C2S+4H20→C3S2H3+Ca(OH)2
Here, C3S2H3 is 3CIL0・2S iO2・3H
Represents 20.

From this reaction equation, it can be seen that 1 mole of C8 produces three times as much Ca (OH)2 as 1 mole of C2S.

In other words, the amount of lime produced by hydration of moderate heat Portland cement that contains less C3S and more C2S 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 is conceivable that.

Moderate heat Portland cement having such properties is blended in an amount of 20 to 60% by weight.

This is because if the weight ratio is less than 20%, 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, the amount of the ground improvement material mixed with glassy blast furnace slag powder and moderate heat Portland cement will vary depending on the soil quality of the soil to be improved and the construction method.
For example, it is added based on the following criteria. 5 in 1 day
kqf/cm'N, preferably 5k at 3 days old
gf 7cm2 or less, 20kgf in 91 days
The amount to be added is determined to be at least 100 kgf/crn2, preferably at least 50 kgf/crn2. To give a specific example, for example, 160 kg to 200 kg is added to ±1 m3 to be improved.

Next, examples of the present invention will be described.

As the vitreous blast furnace slag, granulated blast furnace slag pulverized with a ball mill to a fineness and plain specific area of BfiOOT/F was used, and as the moderate heat Portland cement, a commercially available product was used.

These were blended in the proportions shown in Table 4 to prototype soil improvement materials (A1 to A; 3) according to the present invention and soil improvement materials (A 4 , A 5 ) having different blending proportions from the present invention. In this case, the water/improver weight ratio of the improver slurry is the W/C (water/cement) ratio of commercially available ordinary Portland cement.
The viscosity of the slurry was determined to be the same as that of 16 and 9.

Table 4 These improved materials (Flats 1 to 5) are used for the improved sample with the physical properties shown in Table 5 ± (Yokohama Port cohesive soil in Tokyo Bay) based on the dry weight (slag powder and moderate heat Portland cement). Add 160 kg (sum of weight), mix and stir, and make a diameter of 5 cf.
A cylindrical mold with a height of 10cm and a height of 10cm was filled with three layers to form a specimen.

10- The specimen thus obtained was sealed with a polyethylene sheet and kept at 20°C and relative humidity 85°C until the specified strength test material grade.
After curing in a constant temperature and humidity chamber at a temperature higher than 100 m, the −axial compressive strength was measured. The results are shown in Table 6.

Table 6 From 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 to 9 f/ctn2 or less at 1 day of age, and 20 to 9 f/ctn or more at 91 days of age.

In addition, the wood age is 3 days and the wood age is 5 K9 f 7 cm 2 or less, the wood age is 9
It was found that a very satisfactory result of more than 9f/vt2 in 50 could be obtained in one day.

As described above, according to the present invention, since the initial strength is kept low,
It is possible to solve problems such as poor joints, wear and tear on construction machinery, and even work that has to be done 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.

Applicant's agent: Patent attorney Suzue Takehiko 13-

Claims (1)

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