JPH0337168A - Heat insulating concrete for dike of low temperature liquefied gas tank - Google Patents

Abstract

PURPOSE:To increase durability and reduce dispersion of quality by using a mixture of foamed granular material of obsidian-system as a main component and pearlite- system as a subordinate component as aggregate, reinforcing with glass fiber and specifying initial evaporating speed, thermal conductivity and compression strength. CONSTITUTION:Ground surface in a dike 4, floor surface below fundamental slab 2 of a high floor type tank supporting a low temperature tank 1 and the surface of exposed fundamental piles 3 are covered with heat insulating concrete 5. An aggregate containing obsidian-system pearlite as a main component and pearlite-system pearlite as a subordinate component is used to said concrete 5 having increased water retentivity, preventing of separation of mixed water, increased fluidity and increased uniformity of the composition for the sake of addition of the latter. Furthermore, excellent thermal properties, strength and durability of the former are able to be exhibited without deterioration in the aggregate. The concrete 5 is fixed to have <=50X10<-3>t<-0.5>cm/sec initial evaporation speed [at 23 deg.C atmospheric temperature, using liquefied nitrogen and t=time elapsed (sec)], <=0.13Kcal/m.hr. deg.C thermal conductivity and >=25kgf/cm<2> compression strength.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a heat insulating concrete for a liquid dike installed around a storage tank for low temperature liquefied gas such as LNG or LPG.

[Traditional technique]

Low-temperature liquefied gas storage tanks are required to have a liquid barrier built around them in case of an accident or leakage. If liquefied gas leaks into the dike, structures in contact with the liquid may cool down rapidly, creating a risk of collapse, or the heat input from them may accelerate gasification, leading to secondary disasters such as fires and explosions. There is a risk of inviting Therefore, it is necessary to: ■ install an insulating layer on the ground surface inside the dike and the floor surface under the foundation slab to suppress evaporation and diffusion of liquefied gas, and ■ thermal shock and low-temperature embrittlement caused by liquefied gas around the foundation piles. A heat insulating material layer is provided for the purpose of buffering, etc. These insulation layers must meet the following conditions:

・Excellent insulation properties ・Good low-temperature properties ・ Less deterioration over time ・ Rich in weather resistance and durability ・ Economical Conventional liquid dikes are leveled and poured into the soil surface inside the dike. A reinforcing material such as a wire mesh is placed on the concrete, and an approximately 3 m square piece of insulating concrete is made of a single piece of pearlite-based foamed granules (perlite) or obsidian-based foamed granules (obsidian-based pearlite) as the aggregate. 5~ while forming expansion joints in units
It was poured to a thickness of 200 mm to form a heat insulating layer. However, this insulating concrete had the following drawbacks.

■ Pearlite itself is brittle and has a low closed cell ratio, so when it is kneaded it breaks down, resulting in finer grains and volume reduction, which inevitably increases the amount of water mixed in, resulting in a high specific gravity. .

If the specific gravity during kneading is reduced in order to improve thermal properties such as thermal conductivity and initial evaporation rate, compressive strength, water absorption, durability, and weather resistance will decrease.

■ Obsidian-based pearlite is compared to pearlite-based pearlite.
It is hard and has a high closed cell ratio, making it difficult for bubbles to collapse, allowing for a reduction in the amount of water mixed, and in order to improve thermal properties, it is possible to obtain an insulating concrete with a high specific strength even if the specific gravity at the time of kneading is lightened. However, when mixed, the mixed water tends to separate, resulting in a decrease in fluidity and a decrease in homogeneity. Moreover, the unit volume weight of the obtained concrete is large and it is expensive.

■ Insulating concrete that uses either pearlite-based pearlite or obsidian-based pearlite as an aggregate suffers from large drying shrinkage due to the higher water/cement ratio and lower aggregate strength compared to concrete. In order to reduce the weight, the absolute value of mechanical strength is low, resulting in poor impact resistance, abrasion resistance, and durability.

The above-mentioned drawback is that the surface of the insulating concrete is directly affected by sunlight and outside temperature, and cannot cope with the stress generated by the difference in temperature and drying shrinkage between the inside and the inside, resulting in cracking. As a countermeasure against this, reinforcing materials such as wire mesh are inserted, but this has not significantly improved the appearance of cracks.Cracks can cause thermal short circuits and increase thermal characteristics depending on the degree of progression, so the original design standards There is a risk of deviating from the value and ultimately destroying the insulating concrete.

[Purpose of the invention]

This invention was made in view of the above circumstances.

The purpose of this is to be as low-cost as pearlite-based insulating concrete, which is used as a conventional insulation material for dikes, to have insulation performance and mechanical strength similar to obsidian-based insulating concrete, and to be highly durable. The purpose of this paper is to propose an insulating concrete for dikes in low-temperature liquefied gas storage tanks that has less variation in quality.

(Structure of the Invention) This insulating concrete for the liquid barrier of the low-temperature liquefied gas storage tank includes the ground surface inside the liquid barrier, the floor surface under the foundation slab of the raised storage tank,
A heat insulating concrete used as a heat insulating material to cover the surface of exposed foundation piles, mainly composed of obsidian foam granules.
The aggregate is a mixture of pearlite foam granules, reinforced with glass fiber, and has an initial evaporation rate of 50xlO-'t-'°5cIl/s.
Thermal conductivity below ec 0.13 Kcal/m, hr,
It is characterized by having a compressive strength of 25 Kgf/aJ or more.

The obsidian pearlite used in this invention is -1)
1i so-called obsidian pearlite can be used, but hard grain pearlite of Examples in Table 1 described later is more suitable. This hard pearlite is made by rapidly heating and expanding granules of crushed obsidian at approximately 1000℃.It is made up of agglomerations of independent glass bubbles, has extremely low water absorption, and is similar to ordinary pearlite. Unit volume weight and thermal conductivity are lower than that of

As the nacreous pearlite used in this invention, general so-called nacreous pearlite can be used, but the nacreous lightweight pearlite shown in Examples in Table 1, which will be described later, is more suitable. This lightweight pearlite is produced by firing in the same manner as the hard pearlite described above, and has a lower unit weight and thermal conductivity than ordinary pearlite. It is also softer and has a lower closed cell ratio than hard pearlite.

This heat-insulating concrete uses aggregate mainly composed of obsidian-based pearlite and added with pearlite-based pearlite. By adding perlite, the water retention of the mortar composition obtained by mixing is improved, separation of mixed water can be prevented, fluidity is improved, and homogeneity is improved. In addition, it can be achieved without impairing the excellent thermal performance, strength, and durability of insulating concrete using obsidian pearlite as an aggregate.

Obsidian pearlite shown in the aggregate mixture has a volume ratio of 90% ~
It is 70%. If the content of obsidian pearlite is less than 70%, the specific gravity is high, the strength is low, and excellent thermal properties cannot be exhibited. In addition, if the percentage of pearlite is 90% or more, that is, if the pearlite content is less than 10%, the water retention and fluidity of the mortar composition will decrease when mixed, resulting in poor workability and insulating concrete with good homogeneity. . A more preferable volume ratio of obsidian pearlite is 85% to 75%, that is, a volume ratio of pearlite pearlite is 15% to 25%.

The initial evaporation rate is a value that has been widely used in the past as a value indicating the thermal performance of insulating concrete, etc. attached to low-temperature liquefied gas storage tanks. To find this value, use a sample, in this case an insulating concrete sample (20 (hmφ x 50f)
i thickness) to the bottom of a container (inner dimensions 200fiφ x 25On depth) made of cold insulation material (urethane foam) with an open top surface, and a predetermined amount of liquid nitrogen was poured in an atmosphere of 23°C ± 2°C. Inject instantly. Liquid nitrogen absorbs heat from the sample surface, evaporates, and the liquid level drops. This drop in liquid level (H
aa), that is, the evaporation rate V=□ is determined from the evaporation amount and the elapsed time (in seconds). This V is plotted over time, and the initial evaporation rate V is determined from the curve. In the process of evaporation of liquid nitrogen, the thermal performance of the sample, such as the thermal diffusivity, changes over time, and the amount of evaporation decreases. cannot be obtained.

The thermal conductivity is a value measured based on JIS A 1412. To protect the structure from reduced initial evaporation rate, thermal shock and low temperature embrittlement, 0.13Xcal/m, h
If it does not have a thermal conductivity of r, 'C or less, it will not be effective.

The compressive strength is a value measured after curing for 28 days based on JIS A 1)08. To prevent damage from walking or external forces during maintenance, based on previous experience, a weight of 25 kg is recommended.
A compressive strength of f/cd or higher is required.

[Example] In this example, a mixture of obsidian pearlite (hereinafter referred to as hard pearlite) and pearlite light pearlite shown in Table 1 with a volume ratio of 4:1 was used as the aggregate. Compared to the conventional pearlite shown in the Comparative Examples in the table, it is much lighter in volume and has excellent thermal properties.

This lightweight pearlite was made possible to be uniformly dispersed by adding a thickener made of a water-soluble cellulose derivative to the cement paste to increase its viscosity.

Table 2 shows the composition table of the heat insulating concrete of the example. The method of kneading this insulating concrete composition is to use a known forced stirring mixer, and add and mix each material in the proportions shown in Table 2. First, weighed hard pearlite and perlite-based lightweight pearlite are quickly introduced into the mixer, followed by lightweighted Portland cement and glass fiber. These components are then mixed for 1 minute so that they are evenly mixed and dispersed.

Next, measure the mixed water and A diluted with the specified amount of water.
Pour E agent and thickener into the combined ingredients, and finally knead all the mortar ingredients for 3 minutes.

As the AE agent, an anionic surfactant capable of uniformly dispersing stable fine air bubbles in the cement paste was used. As the glass fibers, alkali-resistant glass fibers with a diameter of 10 to 20 square meters were used to improve toughness and stickiness. Table 3 shows the physical properties of the heat insulating concrete of the example and the heat insulating concrete of the comparative example using conventional obsidian pearlite and pearlite pearlite as aggregates.

In general, the thermal and mechanical properties of insulating concrete are roughly correlated with its specific gravity; when the specific gravity is low, the thermal properties increase but the mechanical properties decrease. As the name suggests, heat-insulating concrete prioritizes thermal properties, and as long as it has the mechanical strength to maintain its performance over time, it is better to have as light a specific gravity as possible.

Mixing pearlite, which has a heavy volumetric weight, inevitably increases the specific gravity, and reducing the specific gravity requires entraining a large amount of air with an AE agent. In an environment where the water temperature and outside air constantly change, the amount of air entrained is not constant, resulting in large variations in quality, and a decrease in the aggregate volume ratio leads to increased drying shrinkage, resulting in a product that is more likely to crack. . On the other hand, in the insulating concrete of this invention, which uses hard pearlite with a light volume weight of about 0.10, a large amount of aggregate can be mixed in, so only a small amount of AE agent is required, and hard pearlite has less variation. Because it has low water absorption and strength, it produces products with beautiful finished surfaces and extremely stable quality.

The insulating concrete of the example shown in Table 2 shows the case where the aggregate/cement (volume ratio) is 6:1, but depending on the standard value of the required thermal properties, it may be 4:1.sat, 7:1, etc. It is also possible to use a combination of

1st! ! Aggregate Comparison Table 3 Physical Properties of Insulating Concrete Table 4 Variations in concrete that has not yet set Table 4 shows the variations in concrete that has not yet set.

Both slump and volumetric weight are stable, indicating that there is little variation in quality during on-site construction.

Below, an example of insulation construction using the insulation concrete according to the present invention will be given and explained for the floor part under the foundation slab and the general floor part in the dike of a raised storage tank for low-temperature liquefied gas.

Figure 1 shows an overview of the low temperature storage tank and dike, where 1 is the low temperature storage tank, 2 is the foundation slab that supports the storage tank, and 3 is the foundation slab that supports the storage tank.
4 is the foundation pile that supports these, 4 is the liquid barrier built around the storage tank, and 5 is the insulating concrete laid on the surface that will come into contact with the leaked liquefied gas.

Figure 2 shows the insulation structure of the ground surface inside the dike.
Leveled concrete 7 is placed on the soil 6 on the floor of the inner surface of the dike, and a welded wire mesh 8 is placed on top of it, and the wire mesh 8 is fixed to anchors 9 embedded in the leveled concrete 7. Approximately 3
Assemble expansion joints 10 so that they are partitioned into m x 3 m,
A heat insulating concrete 5 is placed inside it.

Figure 3 shows the insulation structure of the floor surface under the foundation slab and the foundation piles, and the soil 6 on the floor surface is covered with leveled concrete 7.
is poured, an expansion joint 10 is assembled on it, and heat insulating concrete 5 is poured inside it. On the other hand, a heat insulating concrete molded product 5' manufactured in a factory and reinforced with a wire mesh so as to withstand external forces applied during transportation etc. is attached to the foundation pile 3, and fixed with steel strips or the like.

Note that the wire mesh 8 was not laid on the insulating concrete 5 on the floor surface under the foundation slab. Insulating concrete) tE type product 5
It was divided into four parts to improve installation workability.

〔Effect of the invention〕

The present invention is as described above, and this insulating concrete has an initial evaporation rate and thermal conductivity that are superior to the standard values for dike insulation materials, and also has mechanical strength that does not pose a problem in practical use. It significantly improves the occurrence of cranks, which is the biggest drawback, and exhibits excellent durability and weather resistance.

Therefore, it can be used as a liquid barrier in low-temperature liquefied gas storage tanks to provide excellent heat insulation performance over a long period of time. In addition, for construction in areas where work space is restricted, such as floor insulation under the foundation slab of a raised storage tank, the necessary strength and durability can be obtained without using conventional wire mesh, and the workability is also good. It is very economical.

[Brief explanation of drawings]

Figure 1.2.3 shows an example of insulation construction using insulation concrete inside the dike of a low-temperature liquefied gas storage tank. FIG. 3 is a perspective view showing a partial cross section of the floor under the foundation slab. 1... Low temperature storage tank, 2... Foundation slab,
3...Foundation pile, 4...Dike barrier, 5...
...Insulating concrete, 5゛...Insulating concrete molded product, 6...Soil, 7...
Leveled concrete, 8...Welded wire mesh, 9...
... Anchor 10 ... Expansion joint.

Claims (1)

[Claims] (1) Insulating concrete used as a heat insulating material to cover the ground surface inside the dike, the floor surface under the foundation slab of a raised storage tank, and the surface of exposed foundation piles, which is mainly composed of obsidian-based foam granules and pearlite-based The aggregate is a mixture of foamed granules and reinforced with glass fiber, and the initial evaporation rate is 50 x 10^-^3t^-^0^. ^5c
m/sec. Below (ambient temperature 23°C, using liquid nitrogen, t = elapsed time. sec.) Thermal conductivity 0.13 Kcal/m. hr. An insulating concrete for a liquid barrier in a low-temperature liquefied gas storage tank, characterized by having a compressive strength of 25 Kgf/cm^2 or more below ℃.