JPH0428673B2 - - Google Patents

Description

[Detailed description of the invention]

<Industrial Application Field> The present invention relates to a method for producing a high-strength and lightweight concrete product. <Prior art and its problems> Lightweight concrete products are widely used in the architectural and civil engineering fields because of their excellent latheability and heat insulation properties, and are manufactured by various methods. For example, a method is known in which a structural artificial lightweight aggregate (such as "Bilton" manufactured by Sumitomo Metal Industries, Ltd.) is used as the aggregate. According to this method, the compressive strength
A concrete product with a weight of about 300 kg/cm ² can be obtained, but the air-dried specific gravity is insufficient at 1.5 or more, so further weight reduction was desired. Therefore, one way to reduce the air-dry specific gravity to 1.5 or less is to use the above-mentioned artificial lightweight structural aggregate, and then use a soft material obtained by firing pearlite, a type of natural glass, as a lightweight aggregate. A method is used in which pearlite (expanded pearlite) with a particle size similar to that of normal fine aggregate for concrete (maximum size 5 mm) is used. However, although such soft pearlite has a fairly low bulk specific gravity of 0.05 to 0.2, the strength of the aggregate itself is low, and its water absorption rate is also high, which increases the amount of water required during mixing, which reduces the strength of the finished concrete. There is a problem in that it becomes extremely low. There is also a method of reducing the weight by using artificial lightweight structural aggregate and introducing air bubbles into the concrete, but this method suffers from the same problem of low strength as when soft pearlite is used. For this reason, for example, methods such as using a high-performance water reducing agent to reduce the unit water content of concrete to improve the strength of the cement matrix, or using high-temperature and high-pressure steam curing are adopted. It is conceivable that the strength can be improved by
However, even if we try to improve the strength of concrete with an air-dry specific gravity of about 1.2 by using structural artificial lightweight aggregate, using soft pearlite, or introducing air bubbles, the compressive strength is only 200 kg/kg at most.
It was up to about ² cm. On the other hand, hard pearlite (expanded obsidian) obtained by firing obsidian, which is a type of natural glass similar to pearlite, has a particle size equivalent to that of normal fine aggregate for concrete ( Maximum dimension 5
There is a method of using aggregate (mm) as aggregate. This hard pearlite with a maximum dimension of 5 mm (hereinafter referred to as coarse-grained hard pearlite) has a stronger aggregate itself than soft pearlite and has a lower water absorption rate, so it is stronger than concrete made lighter by using soft pearlite. is obtained, but the bulk specific gravity is 0.2
~0.5, which is larger than soft pearlite, so even if it was used in place of soft pearlite, sufficient weight reduction could not be achieved. In addition, in Japanese Patent Publication No. 53-7447, using coarse-grained hard pearlite as fine aggregate, natural volcanic rubble,
Alternatively, by using structural artificial lightweight aggregate as coarse aggregate and adding a foaming agent, the air-dry specific gravity is 0.9.
A method has been proposed for obtaining concrete in the range of 1.2 to 1.2, but the long-term compressive strength of the concrete obtained by this method is extremely low at 100 to 150 Kg/cm ² . In addition, a concrete product made lighter by using only coarse-grained hard pearlite had an air-dried specific gravity of about 0.9, but a compressive strength as low as 100 Kg/cm ² . Generally, when obtaining lightweight concrete products for use as building materials, it is required not only to be lightweight but also to be strong and durable. It is required to try to reduce the weight as much as possible while maintaining the same. However, as mentioned above, conventional methods have not been able to provide a material that satisfies the requirements of light weight and high strength. In view of these circumstances, the present invention has been developed to have a specific gravity lower than that of lightweight concrete using only structural artificial lightweight aggregate, and a strength comparable to that of lightweight concrete using only structural artificial lightweight aggregate. The purpose is to manufacture high-strength lightweight concrete products with <Means for Solving the Problems> In order to achieve the above object, the present inventors investigated various methods of producing lightweight concrete with even higher strength, and found that 95% of the concrete passed through a 0.6 mm sieve.
By using the above-mentioned hard pearlite (hereinafter referred to as "fine-grained hard pearlite") as the main aggregate and combining it with high-temperature, high-pressure steam curing, lightweight concrete products with significantly higher strength than conventional lightweight concrete products are manufactured. I found out that it is possible. The structure of the present invention based on this knowledge is characterized in that when manufacturing lightweight concrete products, fine-grained hard pearlite with a content of 95% or more passing through a 0.6 mm sieve is used as the main aggregate, and is cured with high-temperature and high-pressure steam. The configuration of the present invention will be explained in detail below. The cement used in the present invention refers to portland cement specified in JIS R5210, blast furnace cement specified in JIS R5211, silica cement specified in JIS R5212, flyash cement specified in JIS R5213, and any other cement such as white cement. Cement may also be used. In addition, when producing concrete products, it is advantageous to remove the concrete from the mold at an early stage, so it is desirable to use cement that develops strength quickly, such as early-strength cement or ultra-early strength cement. Furthermore, in order to carry out high-temperature, high-pressure steam curing, it is preferable to add 25 to 70 parts by weight of silica powder, which is a material used in ordinary high-temperature, high-pressure steam curing products, to 100 parts by weight of cement. Furthermore, in order to minimize the amount of water required during kneading, it is desirable to use a known high performance water reducing agent. The fine-grained hard pearlite used in the present invention is obtained by drying, crushing, sieving, and calcining obsidian, and has 95% or more of it passing through a 0.6 mm sieve.
The particle size distribution of this fine hard pearlite is as follows:
100% passes through the 1.2mm sieve, 95-100% passes through the 0.6mm sieve, 60-80% passes through the 0.3mm sieve,
It is preferable that the amount passing through a 0.15 mm sieve is 20 to 40%. The bulk specific gravity of such fine hard pearlite is 0.5~0.7
That's about it. In the present invention, in addition to using only fine-grained hard pearlite as aggregate, since the specific gravity of concrete falls within a narrow range, other aggregates may be used in combination, or air bubbles may be used in order to give the concrete product a range of air-dry specific gravity. The air-dry specific gravity can be adjusted by introducing For example, when producing a concrete product with a higher air-dry specific gravity than one using only fine-grained hard perlite as an aggregate, it is possible to combine the main aggregate of fine-grained hard perlite with natural sand, artificial lightweight aggregate, etc. The air-dried specific gravity can be obtained. In addition, when producing concrete products with a lower air-dry specific gravity than those using only fine-grained hard perlite as aggregate,
By blending coarse-grained hard perlite, which has a lower bulk specific gravity than fine-grained hard perlite, or by introducing air bubbles, a desired concrete product with a lower air-dried specific gravity can be obtained. However, if the amount of coarse-grained hard pearlite to be mixed and the amount of air bubbles introduced becomes large, the effect of increasing strength by using fine-grained hard pearlite as the main aggregate and also using high-temperature and high-pressure steam curing will diminish. As shown in the test example below, for example, when using coarse-grained hard pearlite to reduce weight, the amount of coarse-grained hard pearlite added is
It is desirable to keep it below 100Kg/ ^m3 . In addition, when introducing air bubbles to reduce weight, the amount of air bubbles introduced is
It is desirable to keep it below 200/ ^m3 . There are two methods of introducing air bubbles into concrete: mixing a concrete foaming agent to generate air bubbles when mixing the concrete, and using a suitable foaming machine to create micro air bubbles from a foaming agent solution. There is a method of creating air bubbles in advance and introducing the bubbles into a mixer during concrete mixing, but either method can be adopted in the present invention. The preferred proportions of concrete used in the present invention are: cement 300~450Kg/m ³ , silica powder 75~
315Kg/m ³ , 300-600Kg/m ³ of fine hard pearlite with 95% or more passing through a 0.6mm sieve, 160-270Kg/m 3 of water
Kg/m ³ , and the high performance water reducing agent is 0 to 20 Kg/m ³ . If necessary, coarse grain hard pearlite 100Kg/ ^m3 or less,
Or introduce less than 200 bubbles/m ³ . The amount of cement here is selected appropriately depending on the target strength and specific gravity, but if the amount of cement is less than 300Kg/ ^m3 , it is difficult to obtain a material with significantly higher strength than conventional lightweight concrete. Increasing the amount of cement beyond 450 kg/m ³ is not only uneconomical as the strength reaches a plateau, but it is also undesirable because it may cause cracking and a decrease in durability. Also, as mentioned above, it is best to add 25 to 70 parts by weight of silica powder to 100 parts by weight of cement.
The optimum amount to be distributed should be determined by trial. Furthermore, the blending amount of fine-grained hard pearlite, the blending amount of coarse-grained hard pearlite, or the amount of bubbles introduced are automatically determined once the cement amount, water amount, and target specific gravity are determined. In addition, in order to enable early demolding and effectively utilize the formwork during the production of concrete products, it is possible to use a known cement hardening accelerator in the present invention as well. Further, the mixing, molding, etc. of the high-strength lightweight concrete according to the present invention may be carried out in the same manner as in the production of ordinary concrete products. According to the present invention, the product after casting and hardening is subjected to high temperature and high pressure steam curing, but prior to this high temperature and high pressure steam curing, normal pressure steam curing is performed in a conventional manner to allow early demolding. It is also possible to develop the necessary strength, which allows the formwork to be used effectively. Further, the conditions for high temperature and high pressure steam curing in the present invention may be similar to those employed in the high temperature and high pressure steam curing of ordinary concrete products. For example, a concrete product that has been demolded through normal pressure steam curing is placed in an autoclave and cured for 6 hours at a temperature increase of 15 to 20°C/hour, a maximum temperature of 180°C, and a pressure of 10 atm.
Cool slowly at a rate of 10°C/hour. <Test Examples> Test examples showing the effects of the present invention will be described below. Test Example 1 Lightweight concrete of each of the formulations No. 1 to No. 4 shown in Table 1 was kneaded to prepare specimens. After performing three types of curing methods (standard curing (28 days), steam curing, high temperature and high pressure steam curing) for the above specimens, the air-dry specific gravity, bending strength,
and compressive strength were measured. The curing method is as follows. 1 Standard curing: After molding the specimen, it was cured in a moist air in the mold for one day, removed from the mold after one day, and then cured in water at 20℃ until the 28th day of age. 2 Steam curing... After molding the specimen, preheat for 3 hours and raise the temperature
20℃/hour, maximum temperature 65℃, held for 6 hours,
Cool naturally for 3 hours after demolding. 3. High-temperature, high-pressure steam curing...Steam curing was performed under the conditions of 2 above, and the demolded specimen was immediately placed in an autoclave with a temperature increase of 15°C/hour, a maximum temperature of 180°C, and a pressure of 10 atm for 6 hours.
℃ at a rate of 15℃/hour, and then naturally cooled to room temperature in an autoclave. Note that the air-dried specific gravity is the specific gravity when the specimen, which has been cured for a specified period, is placed in a drying room at 20° C. and RH 50% and left until it reaches a constant weight. The above results are shown in Table 1.

【table】

【table】

[Table] Test Examples 2 and 3 In order to achieve an air-dried specific gravity of 1.2 and 1.1, which is even lower than the air-dried specific gravity of 1.3 in Test Example 1, the formulations of No. 2 to No. 4 in Table 1 were changed to No. 5 to No. 5. Test specimens were obtained in the same manner as in Test Example 1 with the following changes: No. 8 (Test Example 2) and No. 9 to No. 12 (Test Example 3). The above specimens were subjected to three types of curing in the same manner as in Test Example 1, and then the air-dried specific gravity, bending strength, and compressive strength were measured. The results of Test Example 2 are shown in Table 2, and the results of Test Example 3 are shown in Table 3.

【table】

【table】

【table】

[Table] As shown in Test Examples 1 to 3 above, fine-grained hard pearlite was used as the main aggregate, and air-dried specific gravity was 1.3 by combining this with bubbles or coarse-grained hard pearlite.
Concrete No. 4, No. 7, No. 8, adjusted to ~1.1
No. 11, No. 12, combined with air bubbles or coarse-grained hard pearlite in artificial lightweight structural aggregate to reduce the air-dry specific gravity.
Concrete No. 2, No. 3, No. adjusted to 1.3 to 1.1
5, No. 6, No. 9, and No. 10, it is found that concrete made of lightweight concrete using fine-grained hard pearlite as the main aggregate has higher bending strength, There was not much difference in compressive strength, which was only slightly superior, but among concrete that was cured with high temperature and high pressure steam, only the concrete that had been made lighter using fine-grained hard pearlite had a uniquely high strength, and the flexural strength Both the compressive strength and the compressive strength showed significantly excellent values. From these results, the lightweight concrete of the present invention, which uses fine-grained hard pearlite as the main aggregate and is cured with high-temperature and high-pressure steam, has significantly superior flexural strength and compressive strength compared to concrete made lightweight by conventional methods. It has become clear that this occurs. Possible reasons for the above results are as follows. First of all, fine-grained hard pearlite has a bulk specific gravity of 0.5 to 0.7, which is higher than that of coarse-grained hard pearlite, which is 0.2 to 0.5. It is considered that the strength is also large. This is because even in standard curing and steam curing, concrete with fine-grained hard pearlite as the main aggregate has a high W/C+S (water/cement + silica powder) ratio, but it is slightly better than conventional lightweight concrete. This is evident from the fact that it exhibits excellent strength. Second, fine-grained hard pearlite is produced by crushing and firing obsidian as described above.
Its chemical composition is rich in _SiO2 and has a glassy appearance. Such _SiO2 -rich glasses are
When concrete is cured in high-temperature, high-pressure steam, the cement reacts with calcium hydroxide produced by hydration to produce crystalline calcium silicate hydrate. This crystalline calcium silicate hydrate is the main source of strength in concrete products cured with high-temperature, high-pressure steam, and this reaction is limited to a few micrometers to several tens of micrometers from the surface of the aggregate. When hard pearlite is used as an aggregate and subjected to high-temperature, high-pressure steam curing, the conditions for the formation reaction of calcium silicate hydrate are the same whether the hard pearlite is coarse or fine. If so, the reaction proceeds in the same way, resulting in a reaction layer of the same thickness (several μm to several tens of μm). Therefore, when considering individual aggregate particles, if the thickness of the reactive layer from the surface is the same, the proportion of reactive parts in the aggregate becomes larger as the particle size becomes smaller. Become. In other words, after curing in high-temperature, high-pressure steam, concrete containing more fine-grained hard pearlite has higher strength. In this way, when weight reduction is achieved by using fine-grained hard pearlite in combination with high-temperature and high-pressure steam curing, it exhibits significantly higher strength than concrete that has been reduced in weight to the same specific gravity using conventional methods.
This is presumed to be due to the fact that the aggregate itself of fine-grained hard pearlite has greater strength than coarse-grained hard pearlite, and that the strength is even higher due to the fact that the part near the center of the aggregate particles changes into a hard reaction layer. <Example> (Example) Using concrete with the composition shown in Table 4, 4 m
A building exterior wall panel measuring 2m x 0.15m was manufactured.
A pan-shaped heavy-duty mixer was used to mix the concrete. The mixed concrete was poured into a formwork pre-arranged with reinforcing bars, and compacted using a bar vibrator. After pouring, it was left to stand for 3 hours, covered with a sheet, and steam-cured. The conditions for this steam curing are a temperature increase of 20℃/hour and a maximum temperature of 65℃.
℃, and the maximum temperature holding time was 6 hours. After stopping the steam supply, the concrete was left covered with a sheet and allowed to cool naturally until the concrete temperature reached 40°C. When the concrete temperature reached 40℃, the mold was demolded, and the demolded panel was transferred to an autoclave, where it was cured in high-temperature, high-pressure steam. The conditions for this high-temperature, high-pressure steam curing are as follows:
°C/hour, maximum temperature 180 °C, maximum pressure 10 atm, held for 6 hours, concrete temperature reached 100 °C after holding.
It was cooled at a rate of 15°C/hour until the temperature reached 15°C, and then it was allowed to cool naturally in the autoclave. The weight of this panel is
The weight is 1600Kg, and the air-dry specific gravity of the part excluding the reinforcing bars is
It was 1.22. At the same time as this product was manufactured, a specimen was prepared and cured in the same manner. Air-dry specific gravity, bending strength,
The compressive strength was as shown in Table 5. (Comparative Examples 1 and 2) Concrete with the composition shown in Table 5 was mixed in the same manner as in the example, molded in the same formwork, and cured in the same manner to manufacture panels, and their strength was measured. did. The strength measurement results were as shown in Table 5. In addition, the panel weight of the formulation of Comparative Example 1 is 2100Kg,
The air-dried specific gravity of the part excluding the reinforcing bars was 1.67, the panel weight of the formulation of Comparative Example 2 was 1600 kg, and the air-dry specific gravity of the part excluding the reinforcing bars was 1.23. As can be seen from Tables 4 and 5, the compressive strength of the panel reduced in weight by the method of the present invention (Example) is 320 Kg/ ^cm2 , and the compressive strength of the heavy panel made by the conventional method of Comparative Example 1 is 340 Kg. / ^cm2 . In addition, the panel of Comparative Example 2, which had the same weight as the above Example, had a compressive strength of 180
Kg/ ^cm2 , and the compressive strength of the example panel is 320
The strength was significantly lower than that of Kg/cm ² .

【table】

【table】

[Table] <Effects of the Invention> As specifically explained above with the test examples and examples, according to the present invention, it is lightweight with an air-dry specific gravity of 1.1 to 1.4, while conventionally the air-dry specific gravity must be 1.6 or more. High-strength lightweight concrete products with high strength, which could not be obtained otherwise, can be easily manufactured by using conventional concrete product manufacturing equipment as is. These lightweight concrete products have the same mechanical performance as conventional high-density concrete products, but are also lightweight, so they can be used as building materials such as building exterior walls, partitions, flooring, and roofing materials, as well as bridge floors. When used as a plate, etc., it can reduce the static load on foundations, columns, beams, piers, etc. Furthermore, transportation from the manufacturing factory to the construction site and installation work at the construction site can be carried out more easily, which is economically advantageous in designing and constructing buildings.

Claims (1)

[Claims] 1 When manufacturing lightweight concrete products,
A method for manufacturing high-strength lightweight concrete products, which uses fine-grained hard pearlite as the main aggregate, with a content of 95% or more passing through a 0.6 mm sieve, and is cured with high-temperature, high-pressure steam.