JP2006305748A - Manufacturing method of concrete product - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a manufacturing method of a concrete product which enables an increasing of the strength of concrete in a short time after concrete is cast in a form to demold concrete in its early stages. <P>SOLUTION: A cement paste is prepared by kneading water and cement precedently to be allowed to stand, a water reducing agent is added to the precedently kneaded cement paste after standing to restore the flowability of the cement paste, a curing accelerator is added to concrete after the cement paste is used to knead concrete and the prepared concrete is cast in the form to increase the strength of the concrete after cast in the form in a short time before ageing the concrete under pressure by steam to demold it. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a method for producing a concrete product that can be demolded in a short time.

Generally, the demolding strength of a concrete product requires about 5 to 10 N / mm ² depending on the size of the product. Conventionally, when a concrete product is to be demolded in a short time, steam curing is used and the following curing condition 1 is used.

[Healing condition 1]
In curing condition 1, after filling the mold with concrete, pre-curing is performed at 15 ° C. for 1 hour, and then steam is fed, and the temperature is raised to 75 ° C. at a rate of temperature increase of 20 ° C./hour. The temperature is held for 2-3 hours. Thereafter, the supply of water vapor is stopped and allowed to cool naturally, and then demolded to obtain a concrete product.

For example, when a concrete product is to be demolded in a short time due to the blending ratio of various concrete materials in general concrete production, as shown in Reference Example 1 in Table 1, ordinary Portland cement (in the following explanation) ordinary cement referred to) 365kg / m ^3, crushed sand 781kg / m ^3, (vi) crushed stone 633kg / m ^3, five No. crushed stone 422 kg / m ^3, water 158.81kg / m ^3, kneading the admixture 2.19 kg, further Add 0.6% high-performance water reducing agent and mix. Then, after filling the formwork with the mixed concrete, the curing condition 1 described above is performed.

  However, this conventional method still requires a long time from concrete pouring to demolding, and the production cycle with the same formwork is limited to 1-2 cycles per day.

  In particular, when fast strength is required, a method of using a cement that develops strength at an early stage or increasing the setting speed by adding a setting hardening accelerator is employed. However, there is a concern that if this method is used to increase the strength quickly, the material cost increases if the amount of setting hardening accelerator is increased.

Also, after mixing the primary concrete with slump of 0 cm or less, weigh out the appropriate amount of this primary concrete, add water, a water reducing agent, and a setting accelerator (material) to create secondary concrete and drive it into the mold. There is a way. (See Patent Document 1)
JP-A-11-90918

  In the method using steam curing, since the production cycle in the same mold is 1 to 2 cycles per day, a large number of molds are inevitably required, so the rotational efficiency of the mold is increased to reduce the cost. There was a strong need to improve productivity. Moreover, in the method described in Patent Document 1, it is necessary to secure a large space for mixing the primary concrete. For example, even if it is left on the belt conveyor, it becomes large in terms of equipment. Is expected. Since the primary concrete is slump 0 cm concrete, it is in a papasa state, and it is difficult for elution of various ions from the cement particles that proceed during kneading. In addition, when the secondary concrete is kneaded, the primary concrete has to be weighed again, which is troublesome.

  An object of this invention is to provide the manufacturing method of the concrete product which raises the intensity | strength of concrete in a short time after driving | running in a formwork, and enables demolding at an early stage.

  In order to solve the above-mentioned problems, the invention according to claim 1 is characterized in that water and cement are first kneaded to make a cement paste and left to stand, and a water-reducing agent is added to the kneaded cement paste after standing for fluidity. After mixing concrete with the cement paste, adding a hardening accelerator and driving it into the mold, the strength of the concrete after driving into the mold is increased in a short time, and atmospheric pressure steam curing is performed. It is a method for producing a concrete product characterized in that it can be demolded later.

  The invention according to claim 2 includes a step of pre-kneading a cement paste having a water / cement ratio of 27 to 32%, a step of allowing the pre-kneaded cement paste to stand for 1 to 2 hours, and a standing cement. The process of adding water-reducing agent to the paste to restore the fluidity, the process of adding aggregate and secondary water to the restored cement paste, mixing the concrete, and mixing the concrete with the hardening accelerator and mixing the concrete. 2. The concrete product according to claim 1, further comprising: a step of placing the concrete into a mold, and a step of demolding the mold after performing atmospheric pressure steam curing with steam at 65 to 80 degrees. It is a manufacturing method.

  According to the method for producing a concrete product of the present invention, only the cement paste is used at the time of kneading, so it does not require much space for kneading, and the kneading time can be shortened and the trouble of measuring twice can be avoided. It has the following advantages: After being cast into a mold by the combined use of a cement paste pre-kneading effect and a hardening accelerator, the strength of the concrete is increased in a short time, and demolding is possible at an early stage.

  Hereinafter, the present invention will be described in detail with reference to the drawings. FIG. 1 is a chart of a manufacturing process of a concrete product according to the present invention. In FIG. 1, first, in a first step S1, a fixed amount of cement and water are weighed and the cement paste is kneaded. (Hereafter, kneading this water and cement paste is called paste paste kneading). In addition, the ratio of the water W and the cement C of the cement paste used in the first step S1 is preferably in the range of 27 to 32%, but preferably about W / C = 29%.

  In 2nd process S2, after discharging | emitting a cement paste to a container, it is left still for 1-2 hours. In this case, it is better in strength that the cement paste is left to stand rather than continuing to stir.

  In the third step S3, the cement paste is transferred to another mixer, a water reducing agent is added, and the fluidity is restored. As the water reducing agent used in the third step S3, a naphthalene-based or melamine-based high-performance water reducing agent is suitable. A high-performance water reducing agent is mainly composed of naphthalene sulfonate or melamine sulfonate, and has high electrical repulsion, so that high water reduction can be obtained. The nest and unit water volume can be greatly reduced, and high-strength concrete can be produced.

  In the fourth step S4, sand, crushed stone (gravel) and secondary water are added and the concrete is mixed.

  In the fifth step S5, a curing accelerator is added and mixed. At this time, if it is different from the predetermined fluidity, it is adjusted with a water reducing agent.

  In the sixth step S6, concrete is driven into the formwork.

  In the seventh step S7, steam curing is started immediately after the driving. The temperature for steam curing is suitably from 65 ° C to 80 ° C. (In the experiment described later, the temperature of steam curing was 75 ° C.)

  In 8th process S8, after the curing time defined according to the curing conditions in steam curing at 65 ° C. to 80 ° C., the mold is taken out from the curing tank and demolded. The above is the manufacturing process of the concrete product according to the present invention.

  Here, the pre-kneading of the cement paste in the present invention will be described. When the cement comes into contact with water, among the main compounds of the cement, the aluminate phase (C3A) increasingly hydrates to form ettringite. As this reaction progresses, the cement paste enters a state called condensation, a process in which it gradually stiffens. When the setting is finished, the process proceeds to a process called hardening that is stronger in strength. The hydration reaction of alite (C3S), which is a major player in developing the strength of cement, is activated during the setting and hardening process, and calcium hydroxide and calcium silicate hydrate are generated.

  As described above, the cement paste is subjected to a setting process which is an induction period before alite (C3S) becomes reactive before being cast into a mold. As a result, the concrete can be hardened quickly by moving to an accelerated period of strength development after being driven into the mold, and the product demolding time can be shortened.

  Hereinafter, although this invention is demonstrated in detail in Examples 1-4 which experimented on different curing conditions 1-3, it is not restricted to these. In the experiments shown in Tables 1 to 3, a columnar concrete product having a diameter of 15 cm and a height of 30 cm serving as a specimen for compressive strength under different curing conditions 1 to 3 was manufactured. Curing conditions 1 and 2 are according to the usual curing method for concrete products, but keep (temperature maintenance) time at the maximum temperature is different. Curing condition 3 is a condition for the purpose of early demolding. Details of curing conditions 2 and 3 will be described later.

  Table 1 shows the blending ratio of various concrete materials in the concrete products experimentally manufactured under the curing condition 1, and Table 2 shows the mixing ratios of various concrete materials in the concrete products experimentally manufactured under the curing conditions 2. Table 3 shows the blending ratios of various concrete materials in the concrete products experimentally manufactured under the curing condition 3. Each experiment was performed by kneading 30 liters of concrete with a small mixer.

In Tables 1 to 3, the strength of concrete required for demolding is expressed as compressive strength. Demolding strength is the intensity of the demolding possible becomes concrete cured product, in terms of compressive strength can be released from the mold without problems, if 10 N / mm ² (small product, or approximately 5N / mm ² depending on the product shape But you can demold). Although the standard of concrete strength of general structures is based on 28 days (four weeks), in Table 1, the compressive strengths in the examples and reference examples are all performed immediately after the end of curing, It was shown as a standard for judging whether or not molds can be made. In addition, aggregates such as crushed sand, No. 6 crushed stone, and No. 5 crushed stone shown in Tables 1 to 3 have a surface dry state where there is no surface water and the voids inside the aggregate grains are all filled with water. Shown as a reference. Moreover, the secondary water of Tables 1-3 was shown without including a high performance water reducing agent and a condensation hardening accelerator.

Further, in Tables 1 to 3, the target slump of kneading was set to 8 and 2.5 cm, and an example in which paste paste kneading was compared with a comparative example in which paste paste kneading was not performed. In the example in which paste paste kneading is performed in the comparative example in which paste paste kneading is not performed, in the example in which paste paste kneading is performed, kneading is harder and slump is reduced. Therefore, when trying to match the target slump, the unit water amount (W) or the high-performance water reducing agent amount changes. In addition, when the unit water volume changes, the volume per 1 m ³ must be the same for each formulation, so the volume of the unit water volume has changed, and other volumes such as sand and crushed stone have been changed.

  Moreover, in Tables 1-3, the reference example 1 shows the mixture ratio of various concrete materials in general concrete manufacture. Examples 1-4 show the compounding ratio of various concrete materials by the manufacturing method which kneads first and demolds a concrete product. In Examples 1, 2, and 4, paste paste was kneaded with a mixing time of 2 hours, and in Example 3, paste paste was kneaded with a mixing time of 1.5 hours. Moreover, Comparative Examples 1-9 show the blending ratios of various concrete materials by a manufacturing method in which a concrete product is demolded without prior kneading.

  Next, Example 1 and Comparative Examples 1 to 5 that were tested under curing conditions 1 will be described in detail.

In Example 1, the cement paste was kneaded at the blending ratio shown in Table 1. In this previous kneading, ordinary cement 450 kg / m ^3, such that the ratio of water W and cement C is mixed kneading a metered cement paste Sakineri water 130.5kg / m ³ as a W / C = 29% did. In this case, when the sand to be used is wet in the step of kneading the concrete by adding the following sand, crushed stone, and secondary water, the water contained in the sand in the pre-kneaded water 130.5 kg / m ³ In addition, secondary water is added so that the total amount of water becomes 155.95 kg / m ³ .

Further, when water is used sand that is not adhered to the surface, Sakinerisui 130.5kg / m ³ with respect to, 25.45kg / m ³ secondary water such that the total water volume is 155.95 If water is attached to the surface of the sand used in the process of mixing the concrete and the sand is wet, the surface water content of the aggregate contained in the wet sand is expressed by the following formula bone Surface water content of the material = (surface water ratio × surface dry mass) / 100
The amount of water contained in the sand (the surface water amount of the aggregate) must be subtracted from 25.45 kg / m ^{3 of the} secondary water, so that the secondary water is reduced.

  In the process of kneading concrete, if too little secondary water is added, the concrete will be hardened and kneaded, so if the sand to be used is wet in the process of kneading concrete, the pre-kneading process of the previous process Then, in the process of mixing the cement paste with a small amount of the pre-mixed water so that the ratio of water W and cement C is W / C = 27%, kneading the cement paste, Even if the sand to be used is wet, secondary water should be added sufficiently.

  Also, when the sand used is dry in the process of kneading the concrete, adding sand to the pre-kneaded cement paste will cause the sand to absorb the moisture of the cement paste, resulting in poor fluidity of the cement paste. . In such a case, in the pre-kneading step of the previous step, weigh the pre-kneading water so that the ratio of water W and cement C is, for example, W / C = 32%, and cement paste In the process of kneading softly and then mixing concrete, adding dry sand to the cement paste does not deteriorate the fluidity of the cement paste so that secondary water can be added. Good.

And after discharging a cement paste to a container, it is left still for 1 to 2 hours. Thereafter, the pre-kneaded cement paste is transferred to another mixer, and a water reducing agent is added to 2.0% (cement ratio) to restore fluidity. Then, crushed sand 740kg / m ^3, (vi) crushed stone 601kg / m ^3, kneading five No. crushed stone 401kg / m ^3, mixing kneading concrete by adding secondary water 25.45kg / m ^3. Further, 2.0% (cement ratio) of a hardening accelerator is added and kneaded. Then put concrete into the formwork. After filling the formwork with the mixed concrete, the concrete product is manufactured under the curing condition 1 described above.

  Concrete products were produced under curing conditions 1 using various concretes according to the formulation shown in Table 1. In Comparative Example 5, the formulation is exactly the same as in Example 1, and the other conditions are the combined conditions of Example 1 and the target slump. The experimental results are shown in Table 4.

Table 4 As shown in, in Reference Example 1 is a formulation example of a conventional concrete products, the total curing time, compressive strength 6 hours of about 7.43N / mm ^2, 7 hours compressive strength 8.96N / mm ² Degree.

In Example 1, slump 10.0 cm, 75 immediately after curing the end of 2 hours of ° C. compressive strength 21.11N / mm ^2, 75 ℃ in immediately curing the end of 3 hours compressive strength 23.28N / mm ² met It was.

Comparative Example 1 has the same unit cement amount and fine aggregate ratio (S / a) as Example 1, but does not use a curing accelerator or a high-performance water reducing agent, only water. This is a condition that combines slumps. Slump 7.5 cm, was immediately curing the end of 2 hours of 75 ° C. compressive strength 10.78N / mm ^2, 75 immediately after curing the end of 3 hours at ° C. compressive strength 12.49N / mm ^2. The strength is higher than that of Reference Example 1, and this is probably because W / C is lower than that of Reference Example 1. In comparison with Example 1, the strength is inferior.

Comparative Example 2 has the same unit cement amount, fine aggregate rate (s / a), and unit water amount (W) as Example 1, but no curing accelerator is used, and slump is used. The combined conditions. Slump 7.0 cm, was 75 immediately after 2 hours of curing completion of ° C. compressive strength 14.42N / mm ^2, 75 ℃ in 3 hours compressive strength 16.56N / mm ² immediately after curing end of. The strength is higher than that of Comparative Example 1, and this is probably because W / C is lower than that of Comparative Example 1. In comparison with Example 1, the strength is inferior.

Comparative Example 3 is the same composition as Example 1 with the same unit cement amount, fine aggregate rate (s / a), unit water amount (W), and hardening accelerator amount, and the amount of high-performance water reducing agent is reduced. There are conditions that match the slump. Slump 6.0 cm, was 75 immediately after 2 hours of curing completion of ° C. compressive strength 16.73N / mm ^2, 75 ℃ in 3 hours compressive strength 18.85N / mm ² immediately after curing end of. The strength is higher than that of Comparative Example 2, and it seems that the effect of the curing accelerator appears. In comparison with Example 1, the strength is inferior.

Comparative Example 4 is the same as Example 1 in the unit cement amount, fine aggregate rate (s / a), hardening accelerator amount, and high performance water reducing agent amount, and the unit water amount (W) is reduced. This is a condition that combines slumps. Slump 11.0 cm, was 75 immediately after 2 hours of curing completion of ° C. compressive strength 22.78N / mm ^2, 75 ℃ in 3 hours compressive strength 24.80N / mm ² immediately after curing end of. The strength is higher than that of Comparative Example 3, and this is probably because W / C is lower than that of Comparative Example 3. In comparison with Example 1, the strength level is comparable.

Further, Comparative Example 5 has exactly the same composition as Example 1, and since it has not been kneaded, the slump is large. Slump 24.0cm, it was 75 immediately after 2 hours of curing completion of ° C. compressive strength 16.78N / mm ^2, 75 ℃ in 3 hours compressive strength 20.07N / mm ² immediately after curing end of. Compared with Example 1, the strength is inferior to that of Comparative Example 3.

  Next, Example 2 and Comparative Example 6 experimented under curing conditions 2 will be described in detail.

  In Example 2, as shown in Table 2, the cement paste is first kneaded and the concrete is kneaded at the same blending ratio as in Example 1, and the process until filling the moulded concrete into the mold is as follows. Since it is the same as that of the first embodiment, its description is omitted. In Example 2, after filling the formwork with the mixed concrete, the concrete product is manufactured under the following curing condition 2.

[Curing condition 2]
Under curing condition 2, after filling the mold with concrete, pre-curing is performed at 15 ° C. for 1 hour, then steam is fed, and immediately after the temperature is raised to 75 ° C. at a heating rate of 20 ° C./hour, Stop the supply of water vapor and remove the mold and let it cool naturally to make concrete product, or keep the temperature of 75 ° C for 1 hour, and then immediately stop the supply of water vapor and demold and let it cool naturally Concrete products.

  Table 5 shows the experimental results of producing concrete products under the curing condition 2 using concrete having the composition shown in Table 2.

As shown in Table 5, Example 2 has the same composition as Example 1, with a slump of 11.5 cm and a compressive strength of 6.84 N / mm ² immediately after stopping the supply of water vapor after heating at 75 ° C. However, the compressive strength was 15.68 N / mm ² immediately after completion of curing at 75 ° C. for 1 hour.

Comparative Example 6 has the same composition as Comparative Example 4, and is a condition in which Example 2 and slump are combined. In Comparative Example 6, after the slump was heated at 13.0 cm and 75 ° C., the compressive strength immediately after the supply of water vapor was immediately stopped was 4.34 N / mm ² , and the compressive strength immediately after completion of curing at 75 ° C. for 1 hour was 14.04 N. / Mm ² . Compared to Example 2, when the total curing time is 4 hours, the strength is low, which is 63% of Example 2.

  Next, Examples 3 and 4 and Comparative Examples 7 to 9 that were tested under curing conditions 3 will be described in detail.

  In Examples 3 and 4, as shown in Table 3, the cement paste was previously kneaded and the concrete was kneaded at the same mixing ratio as in Example 1, and the process until filling the moulded concrete into the mold was performed. Since this is the same as that of the first embodiment, the description thereof is omitted. In Example 3, the concrete product is manufactured under the following curing condition 3 after filling the formwork with the mixed concrete.

[Healing condition 3]
Under curing condition 3, after filling the formwork with concrete, pre-curing is not performed, immediately water vapor at a temperature of 75 ° C. is fed, and a curing time of 1.5 hours or 2 hours is maintained while maintaining the temperature at 75 ° C. After the lapse of time, the supply of water vapor is stopped, demolded, and naturally cooled to obtain a concrete product.

  Table 6 shows the experimental results of producing concrete products under the curing condition 3 using concrete having the composition shown in Table 3.

As shown in Table 6, Example 3 has the same composition as Example 1, with a slump of 10.0 cm, a compressive strength of immediately after completion of curing at 75 ° C. for 1.5 hours, 5.42 N / mm ² , and 75 The compressive strength immediately after completion of curing at 2 ° C. was 8.59 N / mm ² .

In addition, Example 4 has the same composition as Example 1, as in Example 3. In Example 4, paste paste kneading time is longer by 30 minutes, and the corresponding strength is higher. 0 cm, 75 ° C. for 1.5 hour compressive strength 6.05N / mm ² immediately after curing completion of, were also compression strength 9.53N / mm ² immediately after curing completion of 75 2 hours ° C..

In Comparative Example 7 is the same formulation as Comparative Example 3, slump 6.0 cm, curing completion of 75 ° C. 2 hours after curing the end of 1.5 hour compressive strength 2.02N / in mm ^2, 75 ° C. of The compressive strength immediately after that was 4.12 N / mm ² . In comparison with Examples 3 and 4, the strength is inferior. Compared to the example of curing condition 1, the difference in strength from the example is large.

Comparative Example 8 has the same composition as Comparative Examples 4 and 6, with a slump of 13.0 cm and a compressive strength of 2.36 N / mm ² immediately after completion of curing at 75 ° C. for 1.5 hours, and 2 hours at 75 ° C. The compressive strength immediately after completion of curing was 5.94 N / mm ² . In comparison with Examples 3 and 4, the strength is inferior. Compared with the examples of curing conditions 1 and 2, the difference in strength from the examples is large.

Comparative Example 9 has the same composition as Comparative Example 5, with a slump of 24.0 cm and a compression strength of 0.67 N / mm ² immediately after completion of curing at 75 ° C. for 1.5 hours, and completion of curing at 75 ° C. for 2 hours. The compressive strength immediately after that was 3.10 N / mm ² . In comparison with Examples 3 and 4, the strength is inferior. Compared to curing condition 1, the difference in strength from the example is large.

Under curing condition 3, after filling the formwork with concrete, pre-curing is not performed, but immediately, steam at a temperature of 75 ° C. is fed, and the temperature is kept at 75 ° C. for 1.5 hours or 2 hours. After the elapse of time, the supply of water vapor is stopped, and the concrete product is manufactured by demolding and naturally cooling. However, the pasting of the paste is carried out at a high temperature when the curing time is short or immediately after curing. In some cases, the strength is higher than when paste paste is not applied. In particular the compressive strength immediately after curing end of 2 hours was 8.59N / mm ² in Example 3, it is 9.53N / mm ² in Example 4.

Under curing condition 3, the pre-curing is not performed, but the paste strength is kneaded so that the compressive strength immediately after completion of curing for 2 hours is about 10 N / mm ^{2 as shown} in Examples 3 and 4. The level of concrete products can be removed.

  Therefore, before driving into the formwork, knead water and cement in advance to make a cement paste and leave it to stand, add a water reducing agent to the kneaded cement paste after standing to restore fluidity, After mixing the concrete with the cement paste, adding a hardening accelerator and driving it into the mold, it is possible to skip the pre-curing that was conventionally required after driving into the mold and immediately after the 2 hours of curing. Demolding is possible enough.

  Also, if the fluidity of the cement paste pre-kneaded with the high-performance water reducing agent is within the range that can be restored, the compression strength (de-molding strength) required at the time of demolding is increased by lengthening the time to stand after kneading It is also possible. Further, the pre-kneading of the cement paste is not affected by the type of curing accelerator, and can be used in combination with various curing accelerators.

  As described above, the present invention may be carried out under the curing condition 3 by pre-kneading the cement paste, and after the concrete product is driven into the mold by the combined use of the effect of the pre-kneading and the hardening accelerator. Is a half-curing time of about 2 hours compared with the conventional one, and the compressive strength required at the time of demolding can be obtained, and the demolding time of concrete products can be shortened. In addition, since only cement paste is used when kneading, it does not require much space for kneading, and it has practical advantages such as shortening the kneading time and having the advantage of preventing twice the weighing. is there.

  The present invention is not limited to the embodiments described above, and various design changes can be made without departing from the present invention described in the claims, and the invention is not limited to the embodiments. Not too long.

It is a chart figure of the manufacturing process of the concrete product of Example 1 which concerns on this invention.

Claims (2)

  Make a cement paste by kneading water and cement first, leave it to stand, add a water reducing agent to the pre-kneaded cement paste to restore the fluidity, and knead the concrete using the cement paste. By adding a hardening accelerator and driving into a mold, the strength of the concrete after driving into the mold is increased in a short time, and demolding is possible after atmospheric steam curing. Production method.   A process of pre-kneading a cement paste having a water / cement ratio of 27 to 32%, a process of leaving the pre-kneaded cement paste for 1 to 2 hours, and adding a water reducing agent to the static cement paste to restore fluidity Process, adding aggregate and secondary water to the cement paste that has been restored to fluidity, mixing the concrete, mixing the concrete with a hardening accelerator and mixing the concrete, placing the concrete into the mold, The method for producing a concrete product according to claim 1, further comprising a step of demolding the mold after performing atmospheric pressure steam curing with steam at 65 to 80 degrees.

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