High-strength concrete, high-strength concrete piles, and method for manufacturing the same.

Abstract

This invention provides high-strength concrete and a method for producing the same, which can be easily manufactured at low cost by combining ordinary Portland cement and low-heat Portland cement, without the need to add silica fume or other additives. [Solution] The high-strength concrete of the present invention is characterized by being a mixture of ordinary Portland cement and low-heat Portland cement, with a mass ratio of 80:20 to 20:80 between ordinary Portland cement and low-heat Portland cement. The water-cement ratio (W / C) is preferably 20 to 25%. High-strength concrete piles can be manufactured using the high-strength concrete of the present invention. This is a method for manufacturing high-strength concrete, in which concrete mixed with ordinary Portland cement and low-heat Portland cement in a mass ratio of 80:20 to 20:80 is centrifuged, demolded, and then cured in an autoclave.

Description

[Technical Field]

[0001] The present invention relates to high-strength concrete produced by mixing ordinary Portland cement and low-heat Portland cement, high-strength concrete piles, and a method for producing the same. [Background technology]

[0002] In recent years, high-strength concrete has been widely used in concrete structures such as precast piles, and its development has progressed.

[0003] Most conventional high-strength concretes developed to date incorporate silica fume, which increases strength but also has the disadvantage of being expensive. For this reason, it did not become widespread until recently.

[0004] Furthermore, technologies have been developed to improve the performance of concrete and other materials by combining multiple types of cement, such as the inventions described in Patent Documents 1 to 3.

[0005] Patent Document 1 describes a method for producing concrete having desired properties by mixing two or more existing types of cement using an existing concrete plant. This method involves pre-analyzing the compound composition if the existing cement is Portland cement, or the compound composition and amount of mixed material if the existing cement is a blended cement, determining a predetermined ratio for mixing the analyzed two or more types of cement according to the desired properties of the concrete, and mixing the two or more types of cement in the existing concrete plant.

[0006] Patent Document 2 describes a high-flow, high-strength grout material characterized by containing two or more types of Portland cement and a water-reducing agent. The Portland cement is selected from the group consisting of ordinary Portland cement, moderate-heat Portland cement, rapid-hardening Portland cement, and low-heat Portland cement.

[0007] Patent Document 3 describes a material containing low-heat Portland cement, a high-performance water-reducing agent or a high-performance AE water-reducing agent, fine aggregate, and coarse aggregate, with a water / cement ratio of 40% by weight or less and a compressive strength of 60 N / mm². 2 A high-strength concrete characterized by the above features is described. [Prior art documents] [Patent Documents]

[0008] [Patent Document 1] Japanese Patent Publication No. 2014-148059 [Patent Document 2] Japanese Patent Publication No. 2011-102222 [Patent Document 3] Japanese Patent Publication No. 2001-031457 [Overview of the Initiative] [Problems that the invention aims to solve]

[0009] The invention described in Patent Document 1 is characterized by a configuration that allows for the production of two or more types of cement by arbitrarily changing the mixing ratio and chemical composition of the cement using an existing concrete plant equipped with multiple existing cement silos, and does not include any description suggesting high-strength concrete produced by mixing at least ordinary Portland cement and low-heat Portland cement.

[0010] The invention described in Patent Document 2 is a high-flow, high-strength grout material intended for high fluidity and strength development, and is used for machine installation, construction joints in reverse-cast concrete, repair of deteriorated parts of concrete, and filling of PC ducts in prestressed concrete structures, but does not form concrete.

[0011] The invention described in Patent Document 3 is a high-strength concrete with low self-shrinkage and a low brittleness coefficient (compressive strength / tensile strength), but its compressive strength is 60 N / mm². 2 As a result, even higher strength is now required.

[0012] Against the background described above, the present invention aims to provide high-strength concrete and a method for producing the same, which can be easily manufactured at low cost by combining ordinary Portland cement and low-heat Portland cement, without the need to incorporate silica fume or the like. [Means for solving the problem]

[0013] The high-strength concrete of the present invention is characterized by being composed of ordinary Portland cement and low-heat Portland cement. By combining ordinary Portland cement and low-heat Portland cement, high-strength concrete can be easily manufactured. Furthermore, it can be manufactured at a lower cost than conventional high-strength concrete using silica fume, making it economical.

[0014] In the high-strength concrete of the present invention, the mass ratio of the ordinary Portland cement to the low-heat Portland cement used in the blend is preferably 80:20 to 20:80. More preferably, a ratio of 75:25 to 25:75 results in excellent strength and finish.

[0015] Furthermore, in the high-strength concrete of the present invention, the water-cement ratio (W / C) is preferably 20% to 25%. If the water-cement ratio (W / C) is less than 20%, the workability deteriorates, making mixing and placement difficult. If it is 25% or more, it becomes difficult to ensure the strength and quality required for high-strength concrete.

[0016] Furthermore, the high-strength concrete of the present invention is obtained by mixing ordinary Portland cement with low-heat Portland cement, resulting in a strength of 120 N / mm². 2 This allows for the production of high-strength concrete. Typically, the design strength of high-strength concrete is preferably 123 N / mm². 2 That concludes the explanation. In this invention, ordinary Portland cement and low-heat Portland cement are blended to achieve a density of 120 N / mm². 2 We confirmed that the strength was as described above.

[0017] The high-strength concrete of the present invention is particularly suitable for high-strength concrete piles and their manufacture. Ordinary Portland cement and low-heat Portland cement can be blended at a mass ratio of 80:20 to 20:80 and formed into piles. In addition, by applying the present invention to high-strength concrete piles, it has been confirmed that high bearing capacity can be obtained.

[0018] The manufacturing method of the high-strength concrete of the present invention is characterized in that concrete prepared by blending ordinary Portland cement and low-heat Portland cement at a mass ratio of 80:20 to 20:80 is centrifugally formed, and after demolding, autoclave curing is performed. More preferably, it has been confirmed that when atmospheric pressure steam curing is performed as primary curing and high-temperature and high-pressure steam curing is performed as secondary curing, higher strength can be obtained.

[0019] Also, in the manufacturing method of the high-strength concrete of the present invention, the water-cement ratio W / C is preferably 20% to 25%. If the water-cement ratio W / C is less than 20%, the workability deteriorates, and if it is 25% or more, it becomes difficult to ensure the strength and quality as high-strength concrete. Therefore, the water-cement ratio W / C is preferably 20% to 25%.

[0020] <L In the manufacturing method of the high-strength concrete of the present invention, the design standard strength of the high-strength concrete is preferably 120 N / mm 2 or more. In the manufacturing method of the high-strength concrete of the present invention, the design standard strength is set to 120 N / mm 2 or more, and it can be used for piles and the like that can cope with high bearing capacity construction methods.

Effects of the Invention

[0021] The high-strength concrete of the present invention can easily manufacture high-strength concrete by mixing and blending ordinary Portland cement and low-heat Portland cement. In addition, it can be manufactured at a lower cost than high-strength concrete using silica fume.

Brief Description of the Drawings

[0022] [Figure 1] The images show the internal surface finish of centrifugal specimens in concrete mix design tests for the high-strength concrete of the present invention. (a) shows a low-heat Portland cement mixing ratio of 0% (mix design No. C-L0), and (b) shows a low-heat Portland cement mixing ratio of 40% (mix design No. C-L40). [Figure 2] This graph shows the relationship between elapsed time and temperature during atmospheric pressure steam curing, which is performed as primary curing before demolding in the high-strength concrete of the present invention. [Figure 3] This graph shows the relationship between elapsed time and pressure during high-temperature, high-pressure steam curing, which is performed as a secondary curing process after demolding in the high-strength concrete of the present invention. [Modes for carrying out the invention]

[0023] The embodiments of the present invention will be described in detail below with reference to tables and drawings. However, the present invention is not limited to the embodiments described below.

[0024] The following materials were used. [Materials used] Cement: Ordinary Portland cement (symbol: NC), Low-heat Portland cement (symbol: LC) Fine aggregate (S): Hard sandstone crushed sand conforming to JIS A 5005 "Crushed stone and crushed sand for concrete" was used. Coarse aggregate (G): Hard sandstone crushed stone conforming to JIS A 5005 "Crushed stone and crushed sand for concrete" was used. Admixture (symbol AD): A high-performance water-reducing agent (Type I) conforming to JIS A 6204 "Chemical Admixtures for Concrete" was used.

[0025] Mixing, curing, and compression tests were conducted based on the following testing methods. [Test Method] Mixing method: The mixing was carried out in accordance with JIS A 1138 "Method for preparing concrete in a laboratory". Specimen: A specimen with an outer diameter of φ200 mm, a height of 300 mm, and a thickness of 40 mm was created by centrifugal molding. Curing method: Before demolding, normal pressure steam curing shown in Figure 2 was performed as primary curing, and after demolding, high temperature and high pressure steam curing shown in Figure 3 was performed as secondary curing. Compression test: In accordance with JIS A 1136 "Compressive Strength Test of Centrifugally Compacted Concrete", the compression test was carried out after primary curing and after secondary curing.

[0026] 〔Regarding the mix〕 For the mix to achieve a concrete design standard strength of 123 N / mm 2 it is necessary to increase the cement content and reduce the water-cement ratio W / C.

[0027] Simply increasing only ordinary Portland cement will deteriorate the workability, and it is necessary to increase the admixture. As a result of various studies on strengthening the concrete to high strength, it is effective to mix low heat Portland cement to improve the workability. When the water-cement ratio W / C is 23.3% and the ratio of NC:LC is 60:40, the compressive strength of the concrete is 123 N / mm 2 It was confirmed that it would be above.

[0028] For the pile mix, a water-cement ratio W / C = 21.8% and a ratio of NC:LC of 60:40, which can obtain a higher strength so that the compressive strength can be stably exerted, are considered preferable.

[0029] 〔Mixing test of concrete with varying W / C〕 Confirm the compressive strength due to the difference in the water-cement ratio W / C of the concrete mixed with ordinary Portland cement and low heat Portland cement. The mixing ratio of low heat Portland cement was set at one level (40%). The mixing ratio is the value obtained by dividing the mass of low heat Portland cement by the total mass of ordinary Portland cement and low heat Portland cement.

[0030] The water-cement ratio (W / C) was set to 21.8%, 22.3%, and 23.3%, and the mixing ratio of low-heat Portland cement was set to level 1 (40%). The amount of high-performance water-reducing agent used was adjusted so that the slump was in the range of 0.0 to 5.0 cm.

[0031] Table 1 shows the amount of high-performance water-reducing agent used, slump, and secondary curing compressive strength. Primary curing refers to atmospheric pressure steam curing, and secondary curing refers to high-temperature, high-pressure steam curing (autoclave curing).

[0032] [Table 1]

[0033] Table 1 shows a tendency for compressive strength to increase as W / C decreases. Furthermore, if W / C is less than 23.3%, the compressive strength is 130 N / mm². 2 The above conclusions are as follows: If the W / C ratio of concrete mixed with ordinary Portland cement and low-heat Portland cement in a ratio of 60:40 is 23.3% or less, the compressive strength will be 130 N / mm². 2 The above results show that high-strength concrete can be obtained. Based on these results, the preferred pile mix is ​​W / C = 21.8%, with ordinary Portland cement:low-heat Portland cement = 60:40, which yielded the highest strength.

[0034] [Mortar mix design test] The compressive strength of mortar mixed with ordinary Portland cement and low-heat Portland cement was confirmed. The mixing ratio of low-heat Portland cement was set to five levels (0%, 20%, 40%, 75%, 100%). The mixing ratio was calculated by dividing the mass of low-heat Portland cement by the total mass of ordinary Portland cement and low-heat Portland cement.

[0035] From the test results above, the compressive strength was highest at W / C = 21.8%, but even at W / C = 23.3%, it was 130 N / mm². 2Since the requirements were met, the test was conducted with a W / C ratio of 23.3%. The ratio of fine aggregate to cement was set to S / C = 95.2%, and the amount of high-performance water-reducing agent used was adjusted so that the zero-pour flow value was close to 265 mm.

[0036] Table 2 shows the amount of high-performance water-reducing agent used and the primary and secondary curing compressive strengths. The amount of high-performance water-reducing agent used and the compressive strength at which the flow value reached 265 mm were calculated from the test results surrounding the 265 mm flow value.

[0037] [Table 2]

[0038] By performing primary and secondary curing with a W / C ratio of 23.3%, the strength of mortar in any mix of ordinary Portland cement and low-heat Portland cement is 130 N / mm². 2 We confirmed that it was as above.

[0039] [Concrete mix design testing] The compressive strength of concrete mixed with ordinary Portland cement and low-heat Portland cement was investigated. The mixing ratio of low-heat Portland cement was set to five levels (0%, 20%, 40%, 75%, and 100%). The mixing ratio was calculated by dividing the mass of low-heat Portland cement by the total mass of ordinary and low-heat Portland cement.

[0040] The water-cement ratio (W / C) was set to 21.8%, which is below the W / C of 23.3% used in the mortar mix design test. The fine aggregate ratio (s / a) was approximately 35%, and the amount of coarse aggregate was kept constant regardless of the mix design. The mixing ratio of low-heat Portland cement was set to five levels (0%, 20%, 40%, 75%, 100%), and the amount of high-performance water-reducing agent used was adjusted so that the slump was in the range of 0.0 to 5.0 cm.

[0041] Table 3 shows the amount of high-performance water-reducing agent used, slump, primary curing compressive strength, and secondary curing compressive strength.

[0042] [Table 3]

[0043] The workability of fresh concrete before centrifugal molding improved as the proportion of low-heat Portland cement increased and the amount of high-performance water-reducing agent used decreased.

[0044] Figure 1 shows the internal surface finish of centrifugal specimens. (a) is a low-heat Portland cement mixture with a mixing ratio of 0% (mix No. C-L0), and (b) is a low-heat Portland cement mixture with a mixing ratio of 40% (mix No. C-L40). Mix No. C-L0 in (a) shows unevenness on the internal surface. Mix No. C-L40 in (b) has less unevenness on the internal surface compared to mix No. C-L0 in (a), indicating a better finish.

[0045] With a water-cement ratio (W / C) of 21.8%, and after primary and secondary curing, concrete mixed with low-heat Portland cement has a strength of 130 N / mm². 2 The results obtained were as follows:

[0046] Based on the relationship between the mixing ratio of low-heat Portland cement during primary curing and strength, the workability and sludge generation of fresh concrete before centrifugal molding, and the finish of the inner surface of centrifugal specimens, it was confirmed that a mix containing 40% low-heat Portland cement was superior.

Claims

1. A high-strength concrete characterized by being composed of a mixture of ordinary Portland cement and low-heat Portland cement.

2. The high-strength concrete according to claim 1, characterized in that the mass ratio of the ordinary Portland cement and the low-heat Portland cement mixed is 80:20 to 20:

80.

3. The high-strength concrete according to claim 2, characterized in that the water-cement ratio (W / C) is 20% to 25%.

4. The high-strength concrete according to any one of claims 1 to 3, wherein the design standard strength of the high-strength concrete is 120 N / mm². ２ High-strength concrete characterized by the above.

5. A high-strength concrete pile characterized by being manufactured using high-strength concrete as described in any one of claims 1 to 3.

6. A method for producing high-strength concrete, characterized by centrifugal molding of concrete mixed with ordinary Portland cement and low-heat Portland cement in a mass ratio of 80:20 to 20:80, followed by demolition and autoclave curing.

7. A method for producing high-strength concrete according to claim 6, characterized in that the water-cement ratio (W / C) is 20% to 25%.

8. In the method for manufacturing high-strength concrete according to claim 7, the design standard strength of the high-strength concrete is 120 N / mm². ２ A method for producing high-strength concrete, characterized by the above.

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