JP2011168977A - Dam body construction method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a technique capable of simultaneously attaining, in construction of a dam body including a large-scale dam, reduction in construction cost, suppressing temperature stress cracking, and reduction in environmental load. <P>SOLUTION: In the dam body construction method for stacking a mixture (CSG) of sand gravel, a binder and water with a unit binder amount of 50-100 kg/m<SP>3</SP>in layers by repeating steps of uniformly laying CSG and compacting the CSG, the amount of blast-furnace slag fine powder is 71.0-99.0 pts. by mass, and the amount of cement is 1.0 pts. by mass based on 100 pts. by mass of the binder. It is more effective to apply sand gravel having pH of 8.0 or more. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a CSG (Cemented Sand and Gravel) method for constructing a bank body by repeating a process of mixing a sandstone and a binder with a binder and the like, laying and compacting.

  As a method for constructing a dam body including a dam, there is an RCD (Roller Compacted Dam-concrete) method in which super-hard kneaded zero slump concrete is spread in layers and stacked while being rolled. The RCD method is a method that streamlines construction, and has become the mainstream in the construction of large and medium dams. However, in recent social circumstances, a construction method of a dam with a higher cost reduction effect has been desired. The above-mentioned CSG construction method has been developed as a construction method that can meet such needs, and its practical use has begun.

  The CSG method is inferior to the RCD method in terms of the strength of the dam body, but the required strength can be ensured by using a trapezoidal cross-sectional shape. In addition, the local gravel can be used almost without separation, and the mixing with the binder can be carried out continuously using a continuous kneading mixer or the like, so there is a great cost merit including shortening the construction period.

JP-A-9-268542 JP 2001-192254 A JP 2002-348853 A

"Keystone CSG dam construction and quality control technical data", Dam Technical Center, September 2007, p.20-24

  In the construction of concrete dams, measures against temperature stress cracking are extremely important. In the case of RCD concrete, poorly blended super hard kneaded concrete is used, so the internal heat generation is relatively mitigated, but the lift thickness per layer is usually within 1 m so that the internal heat generation does not become excessive. Limited to For this reason, it is necessary to repeat dozens of lifts in a large-scale dam, which causes a long construction period. In summer, concrete is cooled by using expensive chiller equipment, etc., so that the temperature of the internal concrete does not become excessive, raising the cost of dam construction.

  On the other hand, in the case of the dam by the CSG method, the amount of unit cement is small, so that the internal heat generation is further reduced than the RCD method. A concrete dam is considered to have physical properties close to those of an elastic body, but a dam using CSG (a material in which gravel is mixed with a binder or the like) can be considered an elasto-plastic body. From these facts, it is said that the dam by the CSG method is essentially less subject to thermal stress cracking than the concrete dam by the RCD method.

  However, there are still few examples of construction of CSG dams, and it is also true that the extent to which the problem of thermal stress cracking can be avoided has not been fully demonstrated. Since the CSG dam is considered to be an elastoplastic material, it is said that continuous cracking will not occur even if cracking occurs. However, it is considered possible to construct a CSG dam that has good particle size and quality of riverbed gravel, and has a solidity close to that of an RCD dam by careful quality control. In that case, there is a possibility of approaching the elastic body, and it is not possible to neglect measures against the occurrence of through cracks.

On the other hand, recently, there is an increasing demand for reducing the environmental burden in the industrial world. A large amount of cement is used for dam construction, but it is said that approximately 750 kg of CO ₂ will be emitted when cement 1t is produced. In the future, measures to switch to materials with as little environmental impact as possible are desired in dam construction. .

  The present invention is intended to provide a technique capable of reducing the construction cost, suppressing thermal stress cracking, and reducing the environmental load at once in the construction of a dam body including a large-scale dam.

The purpose is to pile up the CSG in layers by repeating the steps of leveling and compacting a mixture (CSG) of 50-100 kg / m ³ unit binder mixed with gravel, binder and water. In the body construction method, this is achieved by a levee body construction method in which the amount of fine blast furnace slag powder in 100 parts by mass of the binder is 71.0 to 99.0 parts by mass and the amount of cement is 1.0 parts by mass or more.

  Here, the upper limit of the cement amount is 29.0 parts by mass when the remainder of the blast furnace slag fine powder in the binder is all cement. However, an admixture may be added to CSG after securing 1.0 part by mass or more of cement.

Particularly, using gravel having pH of 8.0 or more according to the following pH test, the amount of fine blast furnace slag powder in 100 parts by mass of the binder is 90.0 to 99.0 parts by mass, and the amount of cement is 1.0. It is effective to make it at least part by mass.
[PH test] 10 g of gravel is immersed in 1 L of water of pH 7.0 ± 0.1, and left at 20 ± 2 ° C. for 24 hours, and then the pH of the solution is measured.

According to the present invention, the following advantages can be obtained.
(I) Since the construction method of the present invention is a CSG construction method, the construction cost is lower than that of a concrete dam body by a conventional RCD construction method.
(Ii) By-products that are inevitably generated in blast furnace operation can be effectively used, and the amount of cement used is greatly reduced, so that further cost reduction can be achieved compared to the CSG method that has been carried out so far.
(Iii) Decrease in strength level due to the use of a large amount of blast furnace slag fine powder is due to blending adjustment based on rhombus theory (Non-patent Document 1) (for example, adjustment of unit binder amount, adjustment of gravel particle size, pH control of gravel) ), Or by optimizing the design of the levee body.
(Iv) Replacing the cement with a large amount of blast furnace slag fine powder reduces the heat of hydration reaction inside the dam body, and therefore has high resistance to thermal stress cracking, which is a concern in CSG dams.
(V) Replacing the cement with a large amount of blast furnace slag fine powder greatly reduces the amount of cement used. For this reason, the amount of CO ₂ generated due to cement production can be greatly reduced. The effect is particularly great in the construction of large-scale dams.

  Concrete in which a part of the cement is replaced with blast furnace slag fine powder is known. However, since a large amount of blast furnace slag fine powder exceeding 70% causes various adverse effects, such concrete is generally used. Is not adopted. In addition, there is no actual example in which most of cement as a CSG binder is replaced with fine blast furnace slag powder. As a result of detailed studies, the inventors have obtained the following knowledge about the possibility of replacing a large amount of CSG cement with blast furnace slag fine powder.

(1) When a large amount of cement is replaced with blast furnace slag fine powder in general concrete, the self-shrinkage strain increases, so that cracking is likely to occur.
However, since CSG is an elastic-plastic material unlike concrete, the problem of self-shrinkage strain is avoided.

(2) Generally, when concrete cement is replaced with a large amount of blast furnace slag fine powder, the strength of the material becomes 28 days old.
However, according to the study by the inventors, when a large amount of cement is replaced with blast furnace slag fine powder (for example, the replacement rate is 71.0 to 99.0%), the strength of the material at 28 days decreases, but the material age 28 It was found that the strength increased steadily after the day. The compressive strength at the age of 91 days is a value of 1.0 N / mm ² or more. In the case of a CSG dam, as with the RCD dam, it is desirable to guarantee the strength not at 28 days but at a longer age (for example, 91 days). A trapezoidal CSG dam exhibiting sufficient strength can be designed on the condition that a CSG having a compressive strength of a material age of 91 days is 1.0 N / mm ² or more. The compressive strength at the age of 91 days is 1.5 N / mm ² or more, or even in the case of using the 2.0 N / mm ² or more CSG is spread design freedom of the dam, the more preferable. In addition, when the CSG strength level is excessively high, the CSG dam approaches the elastic body, and it becomes necessary to strengthen countermeasures against cracks caused by self-shrinkage and temperature stress, which offsets the merit of the CSG method. Therefore it is desirable that the compressive strength at the age of 91 days is to CSG formulated as a 5.0 N / mm ² or less, may be managed in the formulation to be 4.0 N / mm ² or less.

(3) Generally, when a large amount of concrete cement is replaced with blast furnace slag fine powder, the progress of neutralization tends to be accelerated.
However, in the CSG method, no reinforcing bars are placed inside the dam body, so there is no problem of neutralization.

  Based on these findings, the inventors conducted a detailed study. As a result, even in the CSG method that replaces most of the cement with blast furnace slag fine powder, the water binder ratio, coarse aggregate maximum dimension, unit water amount, unit binder amount, etc. are determined based on "the rhombus theory". It has been found that the basic formulation of CSG can be applied. Hereinafter, the present invention will be described more specifically.

  The present invention follows the concept of the conventional CGS method of making effective use of gravel collected at a location relatively close to the construction site of the levee body. Sand gravel is a granular material corresponding to an aggregate, and is composed of particles having various particle sizes. The collected gravel is crushed as necessary, and oversized (for example, particle diameter exceeding 80 mm due to the long diameter) is removed, for example, simple gravel separation. Other than that, it can be basically used without special classification.

As the binder, in addition to those applied to conventional CSG such as cement and fly ash, blast furnace slag fine powder is used in the present invention.
As the cement, ordinary Portland cement and moderately hot Portland cement can be applied. Furthermore, early strong Portland cement can be used. As the blast furnace slag fine powder, those conventionally used for concrete having a specific surface area in the range of 2000 to 8000 cm ² / g can be applied.

  It is necessary to secure 1.0% by mass or more of the cement ratio in the binder. If the amount of cement is less than that, the amount of alkali is insufficient, and the latent hydraulic properties of the blast furnace slag fine powder may not be sufficiently exhibited.

  The ratio (substitution rate) of the blast furnace slag fine powder can be a maximum of 99.0% by mass. If it is more than that, it is impossible to secure a cement amount of 1.0% by mass or more. If the substitution rate with the blast furnace slag fine powder is too low, the effect of suppressing thermal stress cracking and the effect of reducing the environmental load are not sufficiently exhibited. As a result of various studies, if the ratio of fine blast furnace slag powder to the binder is 71.0% by mass or more, a remarkable temperature stress cracking suppression effect and environmental load reduction effect can be obtained as compared with the conventional CSG method.

When the pH of the gravel used is relatively high, the latent hydraulic properties of the blast furnace slag fine powder are more easily exhibited. As a result of various investigations, when sand gravel having a pH value of 8.0 or more according to the pH test is applied, even when the replacement rate of the blast furnace slag fine powder is increased to 90.0 to 99.0%, the compression is 91 days old. It becomes easy to stably obtain excellent strength development such as strength of 2.0 N / mm ² or more. In this case, it becomes easy to achieve both high temperature stress cracking prevention effect and environmental load reduction effect and strength development effect, which is advantageous in CSG quality control.

The unit binder amount of CSG needs to ensure 50 kg / m ³ or more. If it is less than 50 kg / m ^3, the strength of the levee body tends to be insufficient. More preferably, it is 60 kg / m ³ or more. On the other hand, when the amount of unit binder increases, the dam body gradually approaches the elastic body from the elasto-plastic body, and the problem of thermal stress cracking becomes apparent. In that case, a countermeasure against cracking is required as in the case of the concrete bank body, and the construction cost reduction effect peculiar to the CSG method is diluted. As a result of various studies, in the present invention, the unit binder amount of CSG is set to 100 kg / m ³ or less. More preferably, it is 90 kg / m ³ or less, and still more preferably 80 kg / m ³ or less.

  The composition of CSG can be a simple composition in which gravel, a binder and water are mixed, but an admixture may be added as necessary. For example, an AE water reducing agent (preferably an accelerated type) or a concrete admixture such as a setting accelerator can be used. Examples of the setting accelerator include sodium nitrite and sodium aluminate. When adding the AE water reducing agent, it is effective to secure an addition amount of 0.1% or more, and the upper limit of the addition amount may be about 2.0%. In the case of adding a setting accelerator, it is effective to ensure an addition amount of 0.5% or more, and the upper limit of the addition amount may be about 3.0%.

  CSG can be produced by mixing sand gravel, binding material, and water by a mixing facility provided near the dam body construction site, as in the past. The blending of these materials can be determined by applying rhombus theory. That is, through preliminary experiments, various relationships between the unit water volume and CGS strength (91-day compressive strength) are determined between the finest and coarsest particle sizes of the gravel, and the design of the dam body is based on these data. A blend in a range where the strength can be stably obtained can be employed. The mixing of the materials can be performed by continuous processing, unlike the case of concrete. For example, a method of continuously supplying gravel and a mixture of cement and water to a continuous kneading mixer can be applied.

  The CSG placement may basically be performed by a method similar to the conventional method. That is, the obtained CSG is carried to the site by a dump truck and spread by a bulldozer or a wheel loader. Typically, the height of the lift per layer is set to about 75 cm, and the process of “laying down → consolidating” is repeated to construct a bank. A vibrating roller can be used for compaction. In the conventional RCD method, restrictions such as launch speed, driving temperature, and joint cutting interval are provided in order to suppress thermal stress cracking. However, according to the CSG method, these restrictions can be relaxed or eliminated. .

  Based on the CSG formulation of the CSG dam where the construction work is being carried out (the binder is usually 100% Portland cement), CSG was prepared by replacing most of the cement with blast furnace slag fine powder at various replacement rates. The compressive strengths of these cured bodies were measured at 7 days, 28 days and 91 days. In some formulations, a set accelerator was added.

[Materials used]
-Gravel: Gravel used for the CSG dam that was constructed, maximum particle size 80 mm, pH value by the pH test = 8.0
Cement: normal Portland cement, Blaine specific surface area 3400 cm ² / g
Blast furnace slag fine powder: Blaine specific surface area of about 4000 cm ² / g, SiO ₂ ; 33%, Al ₂ O ₃ ; 16%, Fe ₂ O ₃ ; 1%, CaO; 43%, MgO; 6%
Setting accelerator: Sodium nitrite

In any formulation, the unit binder amount (total amount of cement + blast furnace slag fine powder) is 80 kg / m ³ , and the unit water amount is 125 kg / m ³ . The amount of addition of the setting accelerator was 2%. CSG was prepared by mixing each material, and placed on a mold to obtain a cured body having a diameter of 300 mm and a height of 600 mm. Each cured body was subjected to a uniaxial compression test defined in JIS A1108.
The results are shown in Table 1.

In B0, which is a conventional example (base composition), it has been confirmed by field results that a problem due to thermal stress cracking does not occur. Therefore, since it is clear that the example of the present invention substituted with a large amount of blast furnace slag fine powder has less heat of hydration reaction than B0, it is evaluated that the problem due to thermal stress cracking does not occur. The compressive strength of the cured product greatly decreases as the replacement rate of a large amount of blast furnace slag fine powder increases. However, it can be seen that the compressive strength greatly increases from the age of 28 days to 91 days. This is because the latent hydraulic property of the blast furnace slag fine powder was exhibited. In any case, the compressive strength at the age of 91 days exceeds 1.0 N / m ² , and it is evaluated that it can be applied to the construction of CSG dams. In addition, it can be seen that B95S added with a setting accelerator has improved strength at 28 days of age compared to B95 without addition. In the example of the present invention, since the cement is replaced with a large amount of blast furnace slag fine powder, the environmental load is greatly reduced as compared with the base blend B0.

Claims (3)

Construction method of levee body in which the CSG is piled up in layers by repeating the steps of laying and compacting a mixture (CSG) of 50-100 kg / m ³ unit binder mixed with gravel, binder and water In which the amount of fine blast furnace slag powder in 100 parts by mass of the binder is 71.0 to 99.0 parts by mass and the amount of cement is 1.0 parts by mass or more.   The dam body construction method according to claim 1, wherein the CSG is an admixture added. The amount of fine blast furnace slag powder in 100 parts by mass of binder is 90.0 to 99.0 parts by mass and the amount of cement is 1.0 parts by mass or more with respect to gravel with pH of 8.0 or more by the following pH test. The levee body construction method according to claim 1 or 2.
[PH test] 10 g of gravel is immersed in 1 L of water of pH 7.0 ± 0.1, and left at 20 ± 2 ° C. for 24 hours, and then the pH of the solution is measured.