Slump adjustment method in casting site

Abstract

To control a slump of concrete according to a situation of casting in a casting site of concrete, shorten a time for getting to finishing work, and hasten formwork removal to shorten an entire work period.SOLUTION: A method includes: carrying in concrete to a casting site, the concrete having been kneaded after being added with a polycarboxylic acid-based water-reducing agent; then lowering a slump by adding naphthalene-based water-reducing agent; and performing casting. A relation between an addition ratio of the naphthalene-based water-reducing agent and a lowered value of the slump is obtained in advance, and the addition ratio of the naphthalene-based water-reducing agent to be added to the concrete that have been carried in to the casting site according to a situation of casting is determined from the relation.SELECTED DRAWING: Figure 7

Description

Technical Field

[0001] The present invention relates to a method for adjusting the slump at the placement site, which controls the slump of the concrete or mortar to be placed according to the placement situation at the concrete or mortar placement site.

Background Art

[0002] Concrete is obtained by kneading cement, gravel, sand, etc. together with water. From the moment the cement comes into contact with water, the hydration reaction starts, gradually losing fluidity and causing coagulation to solidify. Further, as time passes, it has the property of increasing hardness and strength and hardening. By adding a setting and hardening time regulator to concrete, it is relatively easy to affect the hydration reaction of cement and accelerate or delay the setting and hardening of concrete. Therefore, its application fields are very wide.

[0003] Generally, the physical properties required for concrete are high fluidity before placement and early hardening after placement. To accelerate the hydration reaction of cement, shorten the time required for setting, and increase the strength development at the initial age of concrete, a setting accelerator is used as an admixture. This setting accelerator can be roughly classified into early strength agents, rapid hardening agents, and flash set agents.

[0004] To obtain concrete with high fluidity before placement and early hardening after placement, Patent Document 1 below proposes adding a flash set agent and phosphonic acid as a retarder for this flash set agent to concrete. Patent Document 2 below proposes a cement additive containing a polycarboxylic acid-based copolymer and / or its salt and a polyalkylene glycol derivative.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0006] In the placement of concrete at locations with a gradient, it is sometimes difficult to install the formwork, so concrete construction may be carried out by manual plastering without using the formwork. At this time, when placing highly fluid concrete, sagging occurs on the inclined part. Therefore, measures such as pressing with a trowel while checking the progress of setting until the sagging subsides have been taken.

[0007] In the above Patent Documents 1 and 2, the setting is promoted by adding an additive. However, since the slump loss is not so large, it was necessary to press with a trowel for a long time until the sagging subsided at locations with a gradient. Since this work is carried out while checking the progress of the setting of the concrete, continuous placement cannot be performed, and it requires a great deal of time and labor.

[0008] Also, when the slump loss due to the addition of the quick-setting agent is small, it is difficult to adjust the fluidity, setting time, initial strength, etc. of the concrete according to the placement conditions at the concrete placement site. There were problems such as a slow hardening speed after placement, requiring a long time for finishing, a delay in the form removal time, and a prolongation of the construction period.

[0009] Therefore, the main problem of the present invention is to control the slump of concrete or mortar according to the placement conditions at the concrete or mortar placement site, shorten the time required for finishing work, and provide a method for adjusting the slump at the placement site that accelerates the form removal time and shortens the construction period.

Means for Solving the Problems

[0010] In order to solve the above problems, as the invention according to claim 1, after concrete or mortar kneaded with a polycarboxylic acid-based water reducing agent is transported to the placement site, a naphthalene-based water reducing agent is added to reduce the slump and then placed, thereby providing a method for adjusting the slump at the placement site.

[0011] In the invention described in claim 1 above, the addition of the polycarboxylic acid-based water reducing agent can reduce the change in slump over time. Therefore, during the transportation of the kneaded concrete or mortar from the fresh concrete factory to the placement site, there is almost no change in slump, and the fluidity during unloading is good. However, if such concrete or mortar is placed as it is, bleeding is likely to occur at locations with a gradient.

[0012] Therefore, in the present invention, the concrete or mortar transported to the placement site is placed after reducing the slump by a predetermined method.

[0013] Here, as shown in FIG. 1, when a naphthalene-based water reducing agent is mixed with concrete or mortar using a polycarboxylic acid-based water reducing agent, a decrease in slump and hardening occur, indicating an abnormality. This is pointed out in the literature (Table 3 of "Precautions for the Use of High-Performance AE Water Reducing Agents" included in the materials of the High-Performance AE Water Reducing Agent Concrete Standardization Countermeasures Committee, edited by the National Fresh Concrete Industry Federation, 1997). Usually, water reducing agents are used for the purpose of maintaining the slump. However, in the present invention, taking advantage of the phenomenon described in the above-mentioned literature, at the timing when concrete or mortar using a polycarboxylic acid-based water reducing agent with a small slump loss is transported to the placement site and unloaded, a naphthalene-based water reducing agent is added thereto to intentionally cause slump loss and then placed.

[0014] In this way, since the fluidity of the concrete or mortar carried into the placing site is reduced before placing, it is possible to appropriately suppress sagging during construction at locations with a gradient, eliminating the need for measures such as pressing with a trowel even when performing manual plastering work. This can shorten the time required for the finishing work and advance the demolding time, thereby shortening the construction period.

[0015] As the invention according to claim 2, the relationship between the addition rate of the naphthalene-based water reducer and the decrease in slump or mortar flow is obtained in advance. From these relationships, there is provided a method for adjusting the slump at the placing site according to claim 1, which determines the addition rate of the naphthalene-based water reducer to be added to the concrete or mortar carried into the placing site in accordance with the placing situation.

[0016] In the invention described in claim 2 above, the relationship between the addition rate of the naphthalene-based water reducer and the decrease in slump or mortar flow is obtained in advance through prior experiments or the like. From these relationships, in accordance with the placing situation such as the degree of the gradient at locations with a gradient, the addition rate of the naphthalene-based water reducer to be added to the concrete or mortar carried into the placing site is determined.

Effect of the Invention

[0017] As described in detail above, according to the present invention, the slump of the concrete or mortar can be controlled in accordance with the placing situation at the placing site of the concrete or mortar, shortening the time required for the finishing work and advancing the demolding time to shorten the construction period.

Brief Description of the Drawings

[0018]

Figure 1

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Figure 9

Embodiments for Carrying Out the Invention

[0019] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

[0020] The method for adjusting the slump at the concrete pouring site of concrete or mortar (hereinafter, typically referred to as "concrete") according to the present invention is suitable for pouring concrete at a location with a gradient and where it is difficult to install formwork. At such locations, after pouring the concrete, a gradient is provided by manual plastering, but at that time, by reducing the slump of the concrete poured using the method according to the present invention, it is possible to reduce operations such as pressing with a trowel over a long period of time. As a result, continuous concrete pouring becomes possible, and the time and labor required for construction can be reduced.

[0021] Examples of such construction locations include, for example, the shoulders of the arch-wing type tunnel portal shown in FIG. 2, the inclined portions of the tunnel invert shown in FIG. 3, the inclined shoulders of footings such as bridge piers shown in FIG. 4, and the curved portions with a bank angle of a concrete paved road shown in FIG. 5.

[0022] The slump adjustment method at the casting site according to the present invention is carried out in the following steps: after the concrete kneaded with the addition of a polycarboxylic acid-based water reducing agent at a fresh concrete plant or the like is transported to the casting site, a naphthalene-based water reducing agent is added to the unloaded concrete to reduce the slump, and then the concrete is cast. As shown in FIG. 6, by adjusting the addition rate of the naphthalene-based water reducing agent, the degree of decrease in fluidity with respect to the elapsed time can be adjusted. Therefore, it becomes possible to cast concrete having an arbitrary slump in accordance with the gradient of the concrete casting location and the like.

[0023] The gradient of the concrete casting location may be substantially constant, such as the shoulder of the footing of the pier shown in FIG. 4. However, for example, at the shoulder of the tunnel portal shown in FIG. 2, the gradient is small on the inner side and gradually becomes steeper toward the outside. At the tunnel invert shown in FIG. 3, the central part of the invert is a gentle slope, and the both sides thereof are steep slopes. At the curved part having a bank angle of the concrete paved road shown in FIG. 5, the single gradient is gentle at the curve entrance and exit, and gradually becomes larger toward the center of the curve. In most cases, the gradient varies depending on the casting location. Thus, when the degree of the gradient varies according to the concrete casting location, at the location where the gradient is steep, the addition rate of the naphthalene-based water reducing agent is increased to reduce the fluidity and prevent sagging during construction. On the other hand, at the location where the gradient is gentle, since sagging is relatively unlikely to occur, the addition rate of the naphthalene-based water reducing agent is reduced to suppress the decrease in fluidity and improve the workability during casting.

[0024] Thus, in the slump adjustment method at the concrete casting site according to the present invention, after the concrete kneaded with the addition of a polycarboxylic acid-based water reducing agent is transported to the casting site, the degree of decrease in the fluidity of the concrete is controlled by the addition rate of the naphthalene-based water reducing agent. Therefore, sagging is less likely to occur in the construction at the location with a gradient, and it is not necessary to take measures such as pressing with a trowel even when manual plastering is performed. The time required for the finishing work can be shortened, the demolding time can be advanced, and the construction period can be shortened.

[0025] As described above, in the present invention, as a method for reducing the slump of concrete to which a polycarboxylic acid-based water reducing agent is added, a method of adding a naphthalene-based water reducing agent is adopted.

[0026] By adding a polycarboxylic acid-based water reducing agent, the slump loss becomes small, and it is possible to suppress the reduction of the slump during transportation from a fresh concrete factory to a placement site, and the workability during unloading can be improved.

[0027] When concrete to which such a polycarboxylic acid-based water reducing agent is added is mixed with concrete to which a naphthalene-based water reducing agent is added, the slump decreases, hardening occurs, and abnormalities occur, as pointed out in the above-mentioned literature (see Fig. 1). However, the present invention takes advantage of this phenomenon and adds a naphthalene-based water reducing agent to concrete to which a polycarboxylic acid-based water reducing agent is added at a predetermined timing, thereby intentionally reducing the slump. The timing of adding the naphthalene-based water reducing agent is after being carried into the placement site and unloaded, and before placement.

[0028] Examples of the naphthalene-based water reducing agent include naphthalene sulfonic acid formaldehyde condensate and its salts, polynaphthalene sulfonic acid formaldehyde condensate and its salts, naphthalene sulfonate and its salts, etc., and one or more selected from these can be used. This naphthalene-based water reducing agent may be one to which modified lignin, active persistent polymer, reactive polymer, etc. are added. Specific examples include "Master Rebuild Series" manufactured by Pozolith Co., Ltd., "Mighty 100" manufactured by Kao Corporation, "Floric PS" manufactured by Nippon Paper Industries Co., Ltd., etc.

[0029] The addition rate of the naphthalene-based water reducing agent is preferably adjusted as appropriate so as to obtain the required slump, but the preferable range is 0.001 to 2% by weight, particularly 0.005 to 1% by weight, based on the cement.

[0030] The addition rate of the naphthalene-based water reducer may be determined in advance by experiments or the like to obtain the relationship between the addition rate of the naphthalene-based water reducer and the decrease in slump (mortar flow), and based on these relationships, in accordance with the placement situation, the addition rate of the naphthalene-based water reducer added to the concrete carried into the placement site may be determined. The relationship between the addition rate of the naphthalene-based water reducer and the decrease in slump (mortar flow) can be obtained from the experiments described later. FIG. 7 shows the results of such experiments.

[0031] As shown in FIG. 7, when the addition rate of the naphthalene-based water reducer is increased, the decrease in slump (mortar flow) increases in a predetermined pattern. Therefore, based on these relationships, after the mixed concrete is carried into the placement site, by adding the naphthalene-based water reducer at a predetermined addition rate, it becomes possible to place the concrete adjusted to a predetermined slump. For example, when the slope of the surface at the placement location is gentle, in order to suppress the decrease in slump and ensure the fluidity of the concrete and improve the workability during concrete placement, the addition rate of the naphthalene-based water reducer is decreased. On the other hand, when the slope of the surface at the placement location is steep, in order to increase the decrease in slump and reduce the fluidity of the concrete and reduce the work of pressing the surface after concrete placement with a trowel or the like, the addition rate of the naphthalene-based water reducer can be increased.

[0032] In the method for adjusting the slump at the concrete placement site according to the present invention, the fluidity of the concrete before being carried into the placement site is improved by adding a polycarboxylic acid-based water reducer to the concrete before being carried into the placement site.

[0033] The polycarboxylic acid-based water reducer includes, for example, water reducers based on polycarboxylic acid ether compounds, composites of polycarboxylic acid ether compounds, composites of polycarboxylic acid ether compounds and modified polymers, composites of polycarboxylic acid ether compounds and crosslinked polymers, composites of polycarboxylic acid ether compounds and oriented polymers, composites of polycarboxylic acid ether compounds and polyderivatives, polyether carboxylic acid compounds, carboxyl group-containing polyether compounds, maleic acid copolymers, maleic acid ester copolymers, maleic acid derivative copolymers, etc. One or more selected from these can be used. Specific examples include "MasterGlenium SP8SV" manufactured by PZ Oss, "Super 1000N", "Darlex Super 100 Series" manufactured by GPC Chemicals, "Chupole HP-8 Series", "Chupole HP-11 Series" manufactured by Takemoto Yushi Co., Ltd., etc.

[0034] The addition rate of the polycarboxylic acid-based water reducer is preferably adjusted as appropriate in consideration of required fluidity, etc. The preferable range is 0.1 to 3% by weight, particularly 0.5 to 2% by weight, based on the cement.

[0035] 〔Experiment〕 An experiment was conducted in which a naphthalene-based water reducer was added to mortar kneaded to a mortar flow value of 240 ± 20 mm with the addition of a polycarboxylic acid-based water reducer to measure the degree of decrease in fluidity.

[0036] 1. Materials Used The materials used are shown in Table 1, and the mortar composition is shown in Table 2. A liquid polycarboxylic acid-based water reducer (PC) was used, and since this becomes part of the unit water amount (W), the unit water amount was corrected according to the usage amount.

Table 1

[0037]

Table 2

[0038] 2. Experimental conditions The experimental conditions are shown in Table 3.

Table 3

[0039] 3. Experimental method The mortar was mixed using a mortar mixer according to the procedure shown in Figure 8.

[0040] After the mortar was mixed, a flow test was carried out under the condition of no drop (0-drop flow of mortar) in accordance with JIS R 5201 "Physical Test Methods for Cement".

[0041] After the flow test was completed, a predetermined amount of naphthalene-based water reducer (NS) was quickly added and stirred for 30 seconds using a mortar mixer.

[0042] After confirming that the naphthalene-based water reducer was sufficiently stirred, the flow test was carried out again in the same manner.

[0043] 4. Experimental results The experimental results are shown in Table 4, Figure 7 and Figure 9.

Table 4

[0044] As shown in Figure 7, by adjusting the addition amount of the naphthalene-based water reducer added to the mortar to which the polycarboxylic acid-based water reducer is added, the amount of mortar flow reduction changes in a predetermined pattern. Therefore, after the concrete kneaded with the polycarboxylic acid-based water reducer is transported to the placement site, it is possible to adjust it to a predetermined slump by adding the naphthalene-based water reducer at a predetermined addition rate and then place it.

[0045] As shown in Fig. 7, when the addition rate of the naphthalene-based water reducer is up to a certain value (in the range of about 0.1 to 0.2 or less), the increase in the decrease amount of the mortar flow with respect to the increase in the addition rate of the naphthalene-based water reducer becomes large. However, in a range larger than that, the decrease amount of the mortar flow becomes almost a constant value with respect to the increase in the addition rate of the naphthalene-based water reducer.

Claims

1. This method for adjusting slump at a casting site is characterized in that concrete or mortar mixed with the addition of a polycarboxylic acid-based water-reducing agent is delivered to the casting site, and then a naphthalene-based water-reducing agent is added to reduce the slump before casting.

2. The relationship between the addition rate of the naphthalene-based water reducing agent and the reduction in slump or mortar flow is obtained in advance, A method for adjusting slump at a pouring site as described in claim 1, wherein the addition rate of the naphthalene-based water reducing agent to be added to the concrete or mortar delivered to the pouring site is determined based on these relationships and in accordance with the pouring conditions.

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