Method for manufacturing mortar and method for manufacturing fresh concrete

Abstract

This invention provides a technology for growing cement particle flocs in a method for producing mortar and fresh concrete. [Solution] First, a mixture of cement and fine aggregate is obtained by mixing cement with fine aggregate having a surface moisture content of 2% or more and 5% or less according to the surface moisture content test method specified in JIS A 1111:2015 (pre-mixing step S2). Next, the mixture is left to stand for a predetermined time (standing step S3). After that, water and admixture are added to the mixture and kneaded (first kneading step S5). In the pre-mixing step S2, the water contained in the fine aggregate causes the cement particles to form flocs. Furthermore, by leaving the mixture to stand after the pre-mixing step S2, the flocs can be grown. This reduces the specific surface area of ​​the cement. As a result, the amount of adsorption of the admixture to the cement particles can be suppressed in the first kneading step S5.

Description

Technical Field

[0001] The present invention relates to a method for manufacturing mortar and a method for manufacturing fresh concrete.

Background Art

[0002] Concrete, which is a building material, is manufactured by using fine aggregate, coarse aggregate, cement, and water as main raw materials and kneading them with a mixer. Fresh concrete (green concrete) immediately after manufacture has fluidity, but as time passes, the hydration reaction progresses and it eventually hardens.

[0003] Conventionally, in order to enhance the fluidity of fresh concrete, an admixture may be added to the above materials. A method for manufacturing fresh concrete using an admixture is described in, for example, Patent Document 1.

[0004] In the manufacturing method of Patent Document 1, first, only fine aggregate and cement are pre-mixed for a predetermined time. As a result, cement particles form flocs due to the action of the surface water of the fine aggregate. Then, water and an admixture are added and kneading is performed. By doing so, the amount of the admixture adsorbed on the cement particles in the initial stage of kneading is suppressed, and an excess admixture remains in the liquid phase. And that excess admixture improves the fluidity of the mortar and fresh concrete produced by subsequent kneading.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] In the manufacturing method described in Patent Document 1, it is important that the cement particles form flocs well in order to produce excess admixture. Therefore, a technology is needed that can effectively grow cement flocs.

[0007] Therefore, the present invention aims to provide a technology that enables the growth of cement flocs in a method for producing mortar and fresh concrete. [Means for solving the problem]

[0008] The first invention of this application is a method for producing mortar, comprising: a pre-mixing step of obtaining a mixed material of fine aggregate and cement by mixing cement and fine aggregate having a surface moisture content of 2% or more and 5% or less according to the surface moisture content test method specified in JIS A 1111:2015; a settling step of letting the mixed material stand for a predetermined time after the pre-mixing step; and a first kneading step of adding water and an admixture to the mixed material and kneading it after the settling step.

[0009] The second invention of this application is a manufacturing method of the first invention, wherein by performing the settling step, the specific surface area of ​​the cement becomes smaller than when the settling step is not performed.

[0010] The third invention of this application is a manufacturing method of the first or second invention, wherein the mixed material is left to stand for one minute or more in the standing step.

[0011] The fourth invention of this application is a method for manufacturing any one of the first to third inventions, wherein the pre-mixing step is performed using a first mixer, and the first kneading step is performed using a second mixer different from the first mixer.

[0012] The fifth invention of this application is a method for producing fresh concrete, comprising the method for producing any one of the first to fourth inventions, the method comprising the pre-mixing step and the first mixing step, and a second mixing step in which coarse aggregate is added and mixed further after the first mixing step. [Effects of the Invention]

[0013] According to the first to fifth inventions, in the pre-mixing step, the water contained in the fine aggregate causes the cement particles to form flocs. Furthermore, by allowing the mixed material to stand after the pre-mixing step, the flocs can be allowed to grow.

[0014] In particular, according to the third invention, the floc can be grown more.

[0015] In particular, according to the fourth invention, the amount of moisture adhering to the inner surface of the first mixer can be suppressed. Therefore, the pre-mixing of fine aggregate and cement in the first mixer can be carried out while limiting the amount of moisture. [Brief explanation of the drawing]

[0016] [Figure 1] This figure shows the configuration of the fresh concrete manufacturing apparatus according to the first embodiment. [Figure 2] This is a flowchart showing the manufacturing procedure for fresh concrete. [Figure 3] This diagram schematically shows the state of cement particles during the pre-mixing process. [Figure 4] This diagram schematically illustrates how admixtures are adsorbed onto cement particles that do not have flocs formed on them. [Figure 5] This diagram schematically illustrates how admixtures are adsorbed onto cement particles that have formed flocs. [Figure 6] This graph shows the results of investigating the change in mortar flow value when the settling time after pre-mixing fine aggregate and cement was varied between 0 and 180 minutes. [Figure 7] This graph shows the results of investigating the flow value of mortar by changing the time allocation for each process while keeping the total time of the pre-mixing and settling processes constant. [Figure 8]It is a graph showing the results of examining the flow value of mortar by changing the distribution of the time of each process without changing the total time of the pre-mixing process, the standing process, and the first kneading process. [Figure 9] It is a diagram showing the configuration of a fresh concrete manufacturing apparatus according to a second embodiment.

Mode for Carrying Out the Invention

[0017] Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings.

[0018] <1. First Embodiment> <1-1. Fresh Concrete Manufacturing Apparatus> FIG. 1 is a diagram showing the configuration of a fresh concrete manufacturing apparatus 1 according to the first embodiment. This fresh concrete manufacturing apparatus 1 is an apparatus for manufacturing fresh concrete (raw concrete) by mixing fine aggregate, cement, water, admixture, and coarse aggregate. As shown in FIG. 1, the fresh concrete manufacturing apparatus 1 includes a fine aggregate supply unit 10, a cement supply unit 20, a coarse aggregate supply unit 30, a mixing water supply unit 40, a mixer 60, and a control unit 70.

[0019] The fine aggregate supply unit 10 is a mechanism for supplying fine aggregate to the mixer 60. The fine aggregate supply unit 10 is disposed above the mixer 60. The fine aggregate supply unit 10 has a hopper 11 and a gate 12. The fine aggregate before supply is stored inside the hopper 11. The gate 12 opens and closes a supply port 13 provided at the bottom of the hopper 11. Further, the fine aggregate supply unit 10 has a measuring device (not shown) for measuring the supply amount of the fine aggregate.

[0020] The fine aggregate supply unit 10 operates the measuring device and the gate 12 in accordance with a control signal input from the control unit 70. Thereby, the fine aggregate stored in the hopper 11 is supplied to the mixer 60 in a specified amount at a specified timing. The fine aggregate falls by its own weight from the supply port 13 of the hopper 11 into the mixer 60.

[0021] Fine aggregate is aggregate with a smaller particle size than coarse aggregate, which will be discussed later. Examples of fine aggregate include natural sand (sea sand, mountain sand, river sand, etc.), crushed sand, and crushed limestone sand. Crushed sand conforming to JIS A 5005:2009 is preferably used. Natural sand conforming to JIS A 5308:2019 is preferably used. However, the types of fine aggregate are not limited to the examples above. Fine aggregate may also be recycled aggregate, slag-based aggregate, or other alternative aggregates.

[0022] As will be understood by those skilled in the art, fine aggregate is produced and manufactured in a quarry or crushing plant, but by the time it is delivered to the batching plant equipped with the fresh concrete manufacturing apparatus 1, the fine aggregate already contains a considerable amount of surface water. Reasons for this include, for example, exposure to rainwater due to open-air storage, undergoing wet classification and washing processes, and the addition of a small amount of water in a post-dry classification process for dust control. Furthermore, the surface water content of the fine aggregate may be adjusted in advance to a predetermined value.

[0023] The cement supply unit 20 is a mechanism for supplying cement to the mixer 60. The cement supply unit 20 is located above the mixer 60. The cement supply unit 20 has a hopper 21 and a valve 22. The cement before supply is stored inside the hopper 21. The valve 22 opens and closes the supply port 23 located at the bottom of the hopper 21. The cement supply unit 20 also has a measuring device (not shown) for measuring the amount of cement supplied.

[0024] The cement supply unit 20 operates the measuring device and valve 22 according to the control signal input from the control unit 70. This supplies the cement stored in the hopper 21 to the mixer 60 at the specified timing and in the specified amount. The cement falls into the mixer 60 from the supply port 23 of the hopper 21 by its own weight.

[0025] Cement is a powder composed of fine calcareous particles. Examples of cements used include ordinary cement, rapid-hardening cement, moderate-heat cement, or low-heat cement. Furthermore, cement may be a mixture of two or more types of cement. In addition, "cement" in this invention may refer to cement substitute materials such as fly ash, blast furnace slag, or geopolymers used in environmentally friendly concrete. That is, as "cement" in this invention, various hydraulic binders (binding agents) that exhibit a hydration reaction and hardening action, either alone or in the presence of an stimulant, can be used.

[0026] The coarse aggregate supply unit 30 is a mechanism for supplying coarse aggregate to the mixer 60. The coarse aggregate supply unit 30 is located above the mixer 60. The coarse aggregate supply unit 30 has a hopper 31 and a gate 32. The coarse aggregate before supply is stored inside the hopper 31. The gate 32 opens and closes a supply port 33 located at the bottom of the hopper 31. The coarse aggregate supply unit 30 also has a measuring device (not shown) for measuring the amount of coarse aggregate supplied.

[0027] The coarse aggregate supply unit 30 operates the weighing device and gate 32 according to the control signal input from the control unit 70. This supplies the fine aggregate stored in the hopper 31 to the mixer 60 at the specified timing and in the specified amount. The coarse aggregate falls into the mixer 60 from the supply port 33 of the hopper 31 by its own weight.

[0028] Coarse aggregate is aggregate with a larger particle size than the fine aggregate mentioned above. For example, crushed stone, natural gravel (such as river gravel), or recycled aggregate can be used as coarse aggregate.

[0029] The mixing water supply unit 40 is a mechanism that supplies mixing water, which contains water and an admixture, to the mixer 60. The mixing water supply unit 40 is connected to the mixer 60 via piping 41. The mixing water supply unit 40 consists of a water tank, an admixture tank, a measuring device, valves, a pump, etc. The mixing water supply unit 40 mixes the water and admixture in a specified ratio according to the control signal input from the control unit 70 and supplies it to the mixer 60.

[0030] The water used for mixing is, for example, tap water, groundwater, or river water. However, the mixing water may also contain recovered water, such as the supernatant liquid of concrete sludge. Admixtures (chemical admixtures) are industrial chemicals that adsorb to cement particles and cause the cement particles to repel each other. Admixtures used include water-reducing agents, high-performance water-reducing agents, or combinations thereof, which are types of surfactants. Admixtures mainly consist of, for example, polycarboxylic acid-based water-reducing agents that have steric hindrance, or naphthalene-based or melamine-based water-reducing agents that have electrostatic repulsion. As bases for admixtures, for example, polystyrene sulfonates, polycarboxylates, naphthalene sulfonates, or melamine sulfonates are used.

[0031] Mixer 60 is a device for mixing the materials for fresh concrete. Mixer 60 is located below the fine aggregate supply unit 10, the cement supply unit 20, and the coarse aggregate supply unit 30. Mixer 60 has a container 61 and blades 62 that rotate inside the container 61. The container 61 contains fine aggregate, cement, coarse aggregate, and mixing water. Mixer 60 mixes the fine aggregate, cement, coarse aggregate, and mixing water inside the container 61 by rotating the blades 62. This produces fresh concrete.

[0032] For example, a twin-screw forced mixer is used as the mixer 60. A twin-screw forced mixer has two sets of blades 62 that rotate around a horizontally extending rotation axis inside the container 61. However, the mixer 60 may be a mixer other than a twin-screw forced mixer.

[0033] The control unit 70 is a unit that controls the operation of each part of the fresh concrete manufacturing apparatus 1. The control unit 70 is composed of a computer having, for example, a processor such as a CPU, memory such as RAM, and a storage unit such as a hard disk drive.

[0034] The control unit 70 outputs control signals to each part of the fresh concrete manufacturing apparatus 1 according to the computer program and various setting values. As a result, the supply of fine aggregate from the fine aggregate supply unit 10 to the mixer 60, the supply of cement from the cement supply unit 20 to the mixer 60, the supply of mixing water from the mixing water supply unit 40 to the mixer 60, the supply of coarse aggregate from the coarse aggregate supply unit 30 to the mixer 60, and the mixing of the materials in the mixer 60 are carried out.

[0035] <1-2. Method for manufacturing fresh concrete> Next, we will explain how to manufacture fresh concrete using the fresh concrete manufacturing apparatus 1 described above. Figure 2 is a flowchart showing the fresh concrete manufacturing procedure. The manufacturing procedure in Figure 2 is realized by the control unit 70 described above controlling the operation of the fine aggregate supply unit 10, the cement supply unit 20, the coarse aggregate supply unit 30, the mixing water supply unit 40, and the mixer 60.

[0036] The fresh concrete manufacturing apparatus 1 first supplies fine aggregate from the fine aggregate supply unit 10 into the container 61 of the mixer 60, and simultaneously supplies cement from the cement supply unit 20 into the container 61 of the mixer 60 (first supply step S1). At this time, the amount of fine aggregate and cement supplied is appropriate to the mix of the fresh concrete. Furthermore, the fine aggregate supplied from the fine aggregate supply unit 10 is not completely dry, but contains water (surface water) on its surface.

[0037] Next, the mixer 60 rotates its blades 62. This mixes the fine aggregate and cement in the container 61 of the mixer 60 (pre-mixing step S2). Then, by continuing the mixing of the materials in the mixer 60 for a predetermined time, a mixture of fine aggregate and cement is obtained.

[0038] Figure 3 is a schematic diagram showing the state of cement particles in the pre-mixing step S2. When fine aggregate and cement are mixed in the pre-mixing step S2, surface water of the fine aggregate comes into contact with the cement particles. Then, due to the action of water moving from the surface of the fine aggregate to the cement particles, the cement particles aggregate together to form flocs F, as shown in Figure 3. This is thought to be because a positive charge is generated on the surface of the cement particles during the hydration reaction caused by the addition of water, and this charge attracts the cement particles to each other.

[0039] Floc F is an aggregate with a particle size of approximately 10 to several tens of micrometers. The average particle size of floc F is larger than the average particle size of cement (approximately 10 μm). When cement particles form floc F, the specific surface area of ​​the cement becomes smaller compared to when floc F is not formed.

[0040] The mixing time of the materials in the pre-mixing step S2 is set to a time sufficient to suppress the specific surface area of ​​the cement by allowing the cement particles to form flocs F. For example, by setting the mixing time of the materials in the pre-mixing step S2 to 30 seconds or more, the growth of flocs F is promoted, and the specific surface area of ​​the cement can be significantly reduced.

[0041] After the pre-mixing step S2 for a predetermined time is completed, the mixer 60 stops the rotation of the blades 62. Then, the mixture of fine aggregate and cement is left to stand in the container 61 of the mixer 60 for a predetermined time (standing step S3). For example, after the pre-mixing step S2 is completed, the mixture is left to stand in the container 61 of the mixer 60 for more than one minute. By letting the mixture stand, the flocs F in the mixture can grow. That is, by letting the mixture stand, the average particle size or the number of flocs F in the mixture can be increased.

[0042] Next, the fresh concrete manufacturing apparatus 1 supplies mixing water containing water and admixtures from the mixing water supply unit 40 into the container 61 of the mixer 60 (second supply step S4). At this time, the amount of mixing water supplied is set to an amount appropriate to the mix of the fresh concrete.

[0043] Next, the mixer 60 starts rotating the blades 62 again. This mixes the fine aggregate, cement, and mixing water inside the mixer 60 (first mixing step S5). By continuing the mixing of the materials in the mixer 60 for a predetermined time, mortar consisting of fine aggregate, cement, water, and admixtures is produced.

[0044] Figure 4 schematically shows how the admixture is adsorbed onto cement particles in which floc F has not been formed. Figure 5 schematically shows how the admixture is adsorbed onto cement particles in which floc F has been formed.

[0045] In the case of Figure 4, the admixture is adsorbed onto individual cement particles. Therefore, in the case of Figure 4, excess admixture is less likely to be generated in the liquid phase. In contrast, in the first mixing step S5 of this embodiment, as shown in Figure 5, the admixture is adsorbed onto cement particles whose specific surface area has been reduced by the formation of floc F. Therefore, the amount of admixture adsorbed onto cement particles is less in the case of Figure 5 than in the case of Figure 4. As a result, in the first mixing step S5 of this embodiment, some of the supplied admixture remains in the liquid phase as excess admixture without being adsorbed onto the cement particles.

[0046] Once the first mixing process S5, which has been completed for a predetermined time, is finished, the fresh concrete manufacturing apparatus 1 then supplies coarse aggregate from the coarse aggregate supply unit 30 into the container 61 of the mixer 60 (third supply process S6). At this time, the amount of coarse aggregate supplied is set to an amount that matches the mix of the fresh concrete.

[0047] Then, the mixer 60 continues to rotate the blades 62. This mixes the fine aggregate, cement, mixing water, and coarse aggregate inside the mixer 60 (second mixing step S7). By continuing the mixing of the materials in the mixer 60 for a predetermined time, fresh concrete consisting of fine aggregate, cement, water, admixture, and coarse aggregate is produced.

[0048] As described above, some of the admixtures added in the second supply process S4 remain as excess admixtures without being adsorbed onto the cement particles. These excess admixtures improve the fluidity of the mortar obtained in the first mixing process S5 (for example, the flow value measured using the test method described in JIS R 5201:2015) and the fluidity of the fresh concrete obtained in the second mixing process S7 (for example, the flow value measured using the test method specified in JIS A 1150:2007).

[0049] In other words, in the manufacturing method of this embodiment, the fine aggregate and cement are mixed in the pre-mixing step S2 before supplying the mixing water. This causes the cement particles to form flocs F, reducing the specific surface area of ​​the cement. Furthermore, after the pre-mixing step S2, the mixed materials are allowed to stand for a predetermined time to allow the flocs F to grow. This further reduces the specific surface area of ​​the cement. As a result, the amount of admixture adsorbed in the first mixing step S5 is reduced.

[0050] Therefore, according to the manufacturing method of this embodiment, even without using a large amount of admixture, excess admixture that does not adsorb to the cement particles can be generated in the initial stage of the first mixing step S5. This excess admixture then improves the fluidity of the mortar produced in the first mixing step S5 and the fresh concrete produced in the second mixing step S7. Thus, it is possible to improve the fluidity of mortar and fresh concrete while suppressing the amount of admixture used.

[0051] Furthermore, at least a portion of the flocs F generated in the pre-mixing step S2 may be decomposed into multiple cement particles in the second mixing step S7. However, it is thought that the decomposed cement particles will also be well dispersed by the adsorption of the excess admixture mentioned above. Alternatively, in the first mixing step S5 and the second mixing step S7, hydration products are sequentially generated when the mixing water and cement particles come into contact. If the admixture already adsorbed on the cement particles (or hydration products) is incorporated into these hydration products, the dispersion effect of the admixture will be weakened. However, it is thought that the excess admixture mentioned above can sequentially adsorb onto the surface of the newly generated hydration products, thereby maintaining these hydration products in a dispersed state. As a result, it is thought that the fluidity of the fresh concrete can be improved compared to when there is no excess admixture.

[0052] In the first supply process S1, the surface moisture content of the fine aggregate supplied is preferably 2% or more and 5% or less according to the surface moisture content test method specified in JIS A 1111:2015, as described in Patent Document 1. By setting the surface moisture content of the fine aggregate to 2% or more, the cement particles become flocs F of an appropriate size of about 10 to several tens of micrometers in the pre-mixing process S2 to the settling process S3. Furthermore, excessively enlarged flocs F can actually impair the fluidity of fresh concrete, but by setting the surface moisture content of the fine aggregate to 5% or less, the generation of such excessively enlarged flocs F can be suppressed in the pre-mixing process S2 to the settling process S3. As a result, the mixing time required to break up the flocs F in the first mixing process S5 or the second mixing process S7 can be shortened.

[0053] Depending on the surface moisture content of the fine aggregate, the mixing time in the pre-mixing step S2 or the resting time in the resting step S3 may be adjusted. For example, the control unit 70 may be configured to accept input for the surface moisture content of the fine aggregate, and the control unit 70 may set the mixing time or resting time based on the input surface moisture content. Specifically, if the surface moisture content of the fine aggregate is higher than a predetermined value, it is advisable to set the mixing time in the pre-mixing step S2 to be longer or the resting time in the resting step S3 to be shorter. As described above, if the surface moisture content of the fine aggregate is higher than a predetermined value, the flocs F tend to become excessively enlarged, but this enlargement can be suppressed by setting the mixing time in the pre-mixing step S2 to be longer or the resting time in the resting step S3 to be shorter. This allows for an appropriate size of flocs F. For example, if the surface moisture content of the fine aggregate is 4% or higher, the mixing time in the pre-mixing step S2 should be set to 60 seconds or longer.

[0054] Alternatively, a sensor for measuring the surface moisture content of the fine aggregate may be installed in the fresh concrete manufacturing apparatus 1, and the measured value of the surface moisture content may be input from the sensor to the control unit 70.

[0055] The above manufacturing method uses high-strength concrete (with a design strength of 36 N / mm² as defined by the Architectural Institute of Japan). 2 This method is particularly suitable for producing fresh concrete for the above-mentioned types of concrete. Fresh concrete for high-strength concrete has a relatively low water-to-cement ratio and is therefore high in powder content, which tends to result in low fluidity. However, according to the above manufacturing method, even with high-powder content fresh concrete, it is possible to improve fluidity while reducing the amount of admixture used.

[0056] <1-3. Experimental Examples> Next, we will explain an experimental example to verify the effect of the standing process S3. In the following experiment, the fine aggregate had a surface-dry density of 2.54 g / cm³. 3 Crushed sand was used. The surface moisture content of the fine aggregate was set to 3.01%. The cement had a density of 3.23 g / cm³. 3Low-heat Portland cement was used. A high-performance water-reducing agent mainly composed of polycarboxylic acid compounds was used as an admixture. The experiment was conducted in an environment with a room temperature of 20±2℃ and a humidity of 50% or higher.

[0057] Furthermore, in the following experiment, the first supply process S1 to the first mixing process S5 were carried out with the following proportions of fine aggregate, cement, water, and admixture. Fine aggregate: 650kg / m 3 Cement: 818 kg / m 3 Water: 175kg / m 3 Admixture: 8.18 kg / m 3

[0058] Figure 6 is a graph showing the results of investigating the change in mortar flow value when the standing time after pre-mixing fine aggregate and cement was varied from 0 to 180 minutes. All conditions other than standing time were kept constant. The horizontal axis of Figure 6 represents the standing time of the mixed materials in the standing process S3. The vertical axis of Figure 6 represents the flow value of the mortar produced in the first mixing process S5. The flow value of the mortar was measured using the test method described in JIS R 5201:2015.

[0059] As shown in Figure 6, the flow value, which indicates the fluidity of the mortar, increased when a settling time was provided compared to when the settling time was 0 minutes. In particular, the flow value of the mortar improved significantly when the settling time was 1 minute or more compared to when the settling time was less than 1 minute. This is thought to be because, after the pre-mixing process S2, allowing the mixed materials to settle allowed the cement flocs F to grow, resulting in a larger amount of excess admixture remaining without adhering to the cement particles.

[0060] Figure 7 is a graph showing the results of investigating the flow value of mortar by changing the time distribution of each process while keeping the total time of the pre-mixing process S2 and the standing process S3 constant. All conditions other than the time distribution of the pre-mixing process S2 and the standing process S3 were kept constant. In the example in Figure 7, the flow value of the mortar produced was compared between the case where the pre-mixing process S2 was 10 minutes 30 seconds, the standing process S3 was 0 seconds, and the first mixing process S5 was 6 minutes 30 seconds, and the case where the pre-mixing process S2 was 30 seconds, the standing process S3 was 10 minutes, and the first mixing process S5 was 6 minutes 30 seconds. The flow value of the mortar was measured using the test method described in JIS R 5201:2015.

[0061] As shown in Figure 7, the flow value, which indicates the fluidity of the mortar, increased when a resting period was included compared to when no resting period was included. In other words, even when the total time of the pre-mixing process S2 and the resting process S3 was kept constant, it was found that the fluidity of the mortar could be improved by including the resting process S3.

[0062] Figure 8 is a graph showing the results of investigating the flow value of mortar by changing the time distribution of each process while keeping the total time of the pre-mixing process S2, the standing process S3, and the first mixing process S5 constant. All conditions other than the time distribution of the pre-mixing process S2, the standing process S3, and the first mixing process S5 were kept constant. In the example in Figure 8, the flow value of the mortar produced was compared for (1) when the pre-mixing process S2 was 30 seconds, the standing process S3 was 0 minutes, and the first mixing process S5 was 6 minutes 30 seconds; (2) when the pre-mixing process S2 was 90 seconds, the standing process S3 was 0 minutes, and the first mixing process S5 was 5 minutes 30 seconds; and (3) when the pre-mixing process S2 was 30 seconds, the standing process S3 was 1 minute, and the first mixing process S5 was 5 minutes 30 seconds. The flow value of the mortar was measured using the test method described in JIS R 5201:2015.

[0063] Comparing (1) and (3) in Figure 8, it was found that the flow value, which indicates the fluidity of the mortar, increased when a resting period was included compared to when no resting period was included. In other words, even when the total time of the pre-mixing process S2, the resting process S3, and the first mixing process S5 was kept constant, it was found that the fluidity of the mortar could be improved by including the resting process S3.

[0064] <2. Second Embodiment> Next, a second embodiment of the present invention will be described. Figure 9 is a diagram showing the configuration of a fresh concrete manufacturing apparatus 1 according to the second embodiment of the present invention. The fresh concrete manufacturing apparatus 1 of the first embodiment was equipped with one mixer 60, whereas the fresh concrete manufacturing apparatus 1 of the second embodiment is equipped with a first mixer 50 and a second mixer 60.

[0065] The second mixer 60 has the same configuration as the mixer 60 of the first embodiment. The first mixer 50 is positioned above the second mixer 60 and below the fine aggregate supply unit 10 and the cement supply unit 20. In this embodiment, of the pre-mixing step S2, the first kneading step S5, and the second kneading step S7, the pre-mixing step S2 is performed in the first mixer 50, and the first kneading step S5 and the second kneading step S7 are performed in the second mixer 60.

[0066] The first mixer 50 has a container 51 capable of containing fine aggregate and cement, and blades 52 that rotate inside the container 51. The bottom of the first mixer 50 is provided with an outlet 53 for discharging the materials and a gate 54 for switching the opening and closing of the outlet 53. For example, a turbine mixer can be used as the first mixer 50.

[0067] The fine aggregate supply unit 10 supplies fine aggregate into the container 51 of the first mixer 50. The cement supply unit 20 supplies cement into the container 51 of the first mixer 50. The first mixer 50 mixes the fine aggregate and cement in the container 51 by rotating its blades 52. This produces a mixture of fine aggregate and cement. The first mixer 50 can also supply the mixture to the second mixer 60 from the discharge port 53 by opening the gate 54.

[0068] In this embodiment, the fresh concrete manufacturing apparatus 1 does not perform the pre-mixing process S2, the first mixing process S5, and the second mixing process S7 in a single mixer. Instead, the pre-mixing process S2 is performed in the first mixer 50, and then the first mixing process S5 and the second mixing process S7 are performed in the second mixer 60. In other words, in this embodiment, the fresh concrete manufacturing apparatus 1 pre-mixes the fine aggregate and cement in the first mixer 50 before mixing all the materials in the second mixer 60.

[0069] In this way, while the first kneading process S5 and the second kneading process S7 are being performed in the second mixer 60, the pre-mixing process S2 for the next batch can be performed in the first mixer 50. This reduces the processing time for multiple batches. Furthermore, after the pre-mixing process S2 is performed in the first mixer 50, the mixed materials can be allowed to stand in the first mixer 50. Therefore, while the standing process S3 is being performed in the first mixer 50, other processes can be performed in the second mixer 60.

[0070] In this embodiment, the first mixer 50 does not have a function to supply mixing water. That is, the piping 41 of the mixing water supply unit 40 does not branch out toward the interior of the first mixer 50. Furthermore, the first mixer 50 does not have any other liquid supply mechanism. As a result, since no mixing water is supplied to the first mixer 50, the amount of moisture adhering to the inner surface of the container 51 of the first mixer 50 can be suppressed. In other words, the amount of moisture supplied to the first mixer 50 is not considered to exceed the amount of surface water equivalent to that of the fine aggregate.

[0071] Therefore, the mixing of fine aggregate and cement in the first mixer 50 can be carried out while limiting the amount of water. This allows for precise control of the amount of water in the first mixer 50. As a result, floc F can be formed well in the pre-mixing step S2.

[0072] <3. Variant> Although embodiments of the present invention have been described above, the present invention is not limited to the embodiments described above.

[0073] In the first embodiment described above, after the pre-mixing step S2, the resulting mixed material was left to stand in the mixer 60. In the second embodiment described above, after the pre-mixing step S2, the resulting mixed material was left to stand in the first mixer 50. However, after the pre-mixing step S2, the resulting mixed material may be transferred from the mixer 60 or the first mixer 50 to another container and left to stand in the other container.

[0074] Furthermore, the elements that appear in the above embodiments and modifications may be combined or partially deleted as appropriate, to the extent that no contradictions arise. [Industrial applicability]

[0075] This invention can be used in methods for producing mortar of various formulations and methods for producing fresh concrete. [Explanation of Symbols]

[0076] 1: Fresh concrete manufacturing equipment 10: Fine aggregate supply section 20: Cement Supply Department 30: Coarse aggregate supply section 40: Mixing water supply unit 50: First Mixer 60: Mixer, 2nd Mixer 70: Control Unit F: Flock

Claims

1. A method for manufacturing mortar, A pre-mixing step to obtain a mixture of fine aggregate and cement by mixing cement with fine aggregate having a surface moisture content of 2% or more and 5% or less according to the surface moisture content test method specified in JIS A 1111:2015, Following the pre-mixing step, there is a settling step in which the mixed material is left to stand for a predetermined time, After the standing step, a first kneading step is performed in which water and an admixture are added to the mixed material and kneaded, A manufacturing method having the following characteristics.

2. A manufacturing method according to claim 1, A manufacturing method wherein, by performing the aforementioned settling step, the specific surface area of ​​the cement becomes smaller than when the settling step is not performed.

3. A manufacturing method according to claim 1 or claim 2, A manufacturing method comprising allowing the mixed materials to stand for one minute or more during the standing step.

4. A manufacturing method according to claim 1 or claim 2, The pre-mixing step is performed by the first mixer. A manufacturing method comprising performing the first kneading step using a second mixer different from the first mixer.

5. A method for producing fresh concrete, comprising the manufacturing method described in claim 1 or claim 2, The aforementioned pre-mixing step and the aforementioned first kneading step, A second mixing step is performed after the first mixing step, in which coarse aggregate is added and mixed further. A manufacturing method having

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