JPH0587462B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Field of Application] The present invention relates to a lightweight aggregate used in lightweight concrete that is pumped, and more specifically, to a lightweight aggregate that can significantly suppress deterioration in the quality of lightweight concrete that accompanies pumping. [Conventional technology] The lightweight aggregate used for lightweight concrete has a
It is a porous body containing 50 to 60% voids, and when water pressure is applied from the outside, such as when pumping lightweight concrete, water infiltrates into the voids in the aggregate. Because of the water absorption of lightweight aggregate by this water pressure, lightweight concrete used for high-rise buildings, etc.
The fluidity of concrete decreases, and in some cases, pipes become clogged, making pumping impossible. Therefore, in order to avoid this situation, lightweight aggregates that have been pre-wetted have been used when pumping lightweight concrete. Pressure when pumping artificial lightweight aggregate (20 to 35
The amount of water absorbed by the aggregate is usually about 30 to ³² % of the absolute dry weight of the aggregate, but the method of pre-absorbing water (pre-wetting) described above , the amount of water that can be absorbed is 20-26%
That's about it. Therefore, even if prewetting lightweight aggregate is used, an amount of water corresponding to the difference between the amount of water absorbed by the above pressure and the amount of water from prewetting will be absorbed into the lightweight aggregate during pumping of concrete. Water will be absorbed. As a result, when pouring lightweight concrete by pumping, it is necessary to increase the unit water volume of lightweight concrete compared to ordinary concrete so that the concrete does not lose its fluidity even if the above water absorption occurs. It can be done. In this way, by increasing the unit water volume of concrete and using pre-wetted lightweight aggregate, it is possible to pump lightweight concrete with a concrete pump, even for high-rise buildings with more than 20 floors. It is possible. [Problems to be solved by the invention] However, as a result of the above-mentioned conventional lightweight concrete using pre-wetted lightweight aggregate having an extremely large unit water volume, carbon dioxide gas, chloride ions, etc. corrode the reinforcing steel. This makes it easier for substances to penetrate and reduces the durability of concrete structures. In addition, such concrete has a large drying shrinkage and is prone to shrinkage cracks, resulting in various problems that are undesirable in terms of the quality of concrete structures, such as causing problems such as water leakage in buildings. [Purpose of the Invention] The present invention was made to solve the problems of the conventional method, and its purpose is to solve the problems of the conventional lightweight concrete without adversely affecting the mechanical properties and workability of lightweight concrete. The object of the present invention is to provide a lightweight aggregate that absorbs significantly less water than lightweight aggregates, thereby significantly improving the quality of this lightweight concrete. [Means for Solving the Problems] The lightweight aggregate for pumping according to the present invention absorbs water in an amount of 15 to 30% of the absolute dry weight of the aggregate in advance, and further absorbs water in the surface layer or surface of the lightweight aggregate. A layer is formed on the part to suppress water permeation. The amount of water absorbed by pre-wetted lightweight aggregate is about 4 to 10% less than the maximum amount of water absorbed by lightweight concrete when pumped. It is desirable to reduce this difference in order to improve the quality of lightweight concrete, but in reality there is a limit to the amount of water that can be absorbed by prewetting. Therefore, the lightweight aggregate is pre-wetted, and (A) the lightweight aggregate 10 shown in FIGS. 1 and 2 is
A layer is formed in the fine voids of the surface layer 11 to suppress the permeation of water due to the pressure during pumping. (B)
By using either or both techniques of forming a layer on the outer surface (surface portion) 12 of the lightweight aggregate 10 shown in FIGS. 1 and 2 to suppress water permeation due to pressure during pumping. , it becomes possible to produce lightweight aggregates that absorb significantly less water due to pressure. In this case, the amount of water for prewetting is
As mentioned earlier, the amount of water that can be absorbed is usually 20 to 26
%, and even if water is absorbed under reduced pressure, it is difficult to absorb more than 30%, so the upper limit value is 30%.
is appropriate. Also, the amount of water for pre-wetting is 15
% or less, the pressure water absorption suppressing layer formed on the surface layer or surface of the aggregate needs to maintain a considerably large water absorption suppressing effect, making it uneconomical, so the appropriate lower limit value is about 15%. . That is, the appropriate amount of water for prewetting is in the range of 15 to 30%. The technology for forming a layer that suppresses water permeation in the voids in the surface layer of pre-wetted lightweight aggregate is as follows: (A-1) After penetrating into the voids, the viscosity is significantly increased, and this high viscosity allows water to Suppresses the permeation of (A-2) After penetrating into the void, it solidifies in the void, reducing the void itself or causing it to disappear. The above two methods are possible. The advantage of forming a layer that suppresses water permeation in the voids in the surface layer rather than on the surface of the aggregate is that the voids are not subject to physical or mechanical stimulation during mixing of concrete, so water permeation is prevented. Even substances that cannot resist physical or mechanical stimulation during mixing of concrete can be used as long as they have the function of suppressing water permeation. Because of this, the adhesion between aggregate and mortar is not impaired. (A) Substances that can penetrate into the voids in the surface layer of pre-wetted lightweight aggregates and exhibit high viscosity thereafter include, for example, anionic acrylic resin (Japanese Patent Laid-Open No. 61-265275 filed earlier by the applicant). There is an anionic acrylic resin described on pages 4 to 8 of the specification of JP-A-63-117938. This anionic acrylic resin is emulsified and dispersed in water as fine particles with a diameter of 2 to 3 μm or less in a low pH acidic region (PH = 5 to 6 or less), and the water (emulsion) to which this polymer is added is It has a low viscosity (1-3 cp). However, this substance lowers the pH by increasing it to neutral or alkaline.
The viscosity increases to more than 300 times its original viscosity.
Therefore, water containing such acidic anionic polymers is absorbed into the pores of the surface layer of the prewetted lightweight aggregate, and then its PH increases (e.g. OH ^- released from cement).
In addition to using
117938) of the specification on pages 13 () to () of the specification) to form a highly viscous water layer that suppresses the passage of water in the voids in the surface layer of lightweight aggregate. I can do it. Examples of substances that solidify and suppress water penetration after penetrating into the voids in the surface layer of pre-wetted lightweight aggregates include, for example, among the above-mentioned anionic acrylic resins, divalent or higher metal ions, such as cement suspension. Some have the property of crosslinking and solidifying due to the Ca ²⁺ ions inside. (B) On the other hand, in order to form a layer on the surface of the prewetted lightweight aggregate that suppresses water permeation, the layer must be sufficiently resistant to physical and mechanical effects during mixing of concrete. It must be strong enough to withstand resistance. More specifically, this water permeation inhibiting layer must not be significantly less stiff and strong than the lightweight aggregate. At the same time, this layer must not exist on the surface of the aggregate and significantly impair the adhesion between the aggregate and mortar. Furthermore, the membrane must be strong enough to meet the above requirements even under humid conditions due to water from prewetting. An example of a substance having such properties is an underwater curable epoxy resin. In order to produce the lightweight aggregate for pumping according to the present invention, it is necessary to treat the prewetted lightweight aggregate by any of the above methods. The processing necessary for method (A) above can normally be carried out either in an aggregate manufacturing plant or in a concrete manufacturing plant. When processed in an aggregate production plant, the aggregate is calcined and prewetted, and then the surface layer of the aggregate is infiltrated with, for example, an anionic acrylic resin, followed by any necessary treatments for thickening or crosslinking. When processing in a ready-mixed concrete plant, the pre-wetted lightweight aggregate is placed in a mixer (preferably in the upper stage of a two-stage mixer), and anionic acrylic resin is added and stirred to improve the surface layer of the aggregate. infiltrate. Thereafter, the materials necessary for concrete are put into a mixer (preferably the lower stage of a two-stage mixer), and thickening or crosslinking is performed using the high pH or divalent or higher metal ions in the concrete. It is difficult to carry out the treatment required for the above method (B) in a ready-mixed concrete plant, and in this case the treatment would be carried out in an aggregate production plant. [Examples of the Invention] The present invention will be described below with reference to Examples, but the present invention is not limited thereto. Example 1 By prewetting, 20% of the bone dry weight and
Anionic acrylic resin emulsion [acrylic acid/methacrylic acid (weight ratio 1/1) copolymer, solid content of emulsion 20%] is added to artificial lightweight aggregate containing 24% water inside the aggregate. It was added in an amount of 0.3% based on the dry weight and impregnated into the surface layer of the aggregate. Using this lightweight aggregate, lightweight concrete with the composition shown in Table 1 is manufactured, and this concrete is
A pressure water absorption test was conducted using the method described below by applying a pressure of Kg/cm ² to measure the amount of water absorbed by the aggregate. At the same time, the second
A total of 6 types of concrete were produced using 2 types of aggregates (20% and 24%) with different water absorption amounts in the 3 types shown in the table, and a pressure-feeding experiment was carried out using a concrete pump at a height of 70 m. (pipe diameter = 5 inches),
We tested whether or not it could be pumped, as well as the slump and compressive strength before and after pumping. The results of the pressure water absorption test are shown in Figure 3, and the results of the pressure feeding experiment are shown in Table 3. Of the six types of concrete tested under pressure, 20% were pre-wetted aggregate.
Blend No. 1 with a unit water amount of 170 kg/m ³ was clogged in the middle and difficult to pump, but all the others could be pumped. Pressure water absorption test method: The test equipment is shown in Figure 4. In the figure, 6 is a pressure vessel with a closed space. After putting a predetermined amount of lightweight concrete into this, the remaining space is filled with water. . Thereafter, the plunger 4 is moved by the hydraulic jack 1 to apply pressure to the water. The amount of displacement of the plunger at this time is measured by the dial gauge 2 via the displacement measuring rod 3, and the amount of water absorbed by the lightweight concrete is determined. The applied pressure is
Measure with pressure gauge 7. From this amount of water absorbed by the concrete, the effect of air compression in the concrete is corrected to determine the amount of water absorbed by the aggregate in the concrete. Example 2 20% and 24% of absolute dry weight by prewetting
A water-curing epoxy resin was added to an artificial lightweight aggregate containing 2% water and stirred to form a layer that suppresses water permeation on the surface of the aggregate. Using this lightweight aggregate, the first
The pressure water absorption test of concrete shown in the table and the second
Pumping experiments were conducted on 6 types of concrete using the 3 types shown in the table. The results of the pressure water suction test are shown in FIG. 5, and the results of the pump pressure feeding test are shown in Table 4. The pressure water absorption amount was slightly smaller than in Example 1. In the pumping experiment, all six types of concrete could be pumped, and showed better pumping performance than Example 1. However, compared to Example 1, the compressive strength showed a lower value. Comparative example 1 20% and 24% of absolute dry weight by prewetting
A pressure water absorption test was carried out using artificial lightweight aggregate containing % of water without any treatment, using the concrete shown in Table 1, and using 6 types of concrete with the 3 types of mixes shown in Table 2. We conducted a pump pumping experiment. The results of the pressure water absorption test and the pump pressure feed test are shown in FIG. 6 and Table 5, respectively, along with the test results of Examples 1 and 2. According to the pressure water absorption test results, it is clear that both Examples 1 and 2 of the present invention have a lower water absorption amount by 3 to 5% (absolute dry weight % of aggregate) compared to Comparative Example 1, which is the conventional technology. This shows that the lightweight aggregate for pumping according to the present invention is suitable for pumping high-quality concrete. According to the results of the pumping experiment, Examples 1 and 2
In Example 1, it was possible to pump concrete with three different water amounts shown in Table 2, except for the case where prewetting was 20% and the unit water amount was 170 kg/m ³ , whereas in the comparative example The amount of water that could be pumped under pressure was 24% pre-wetting and a unit water volume of 190 kg/m ³
and 180Kg m ³ , and in all other cases the pipes were blocked and pumping was impossible. From this result, it was found that between lightweight concrete using the lightweight aggregate for pumping according to the present invention and lightweight concrete using conventional aggregate, the unit water amount of concrete required for pumping to high places is 20 kg/m ³ It can be seen that there is more than a degree of difference. In other words, by using the lightweight aggregate for pumping according to the present invention, it is possible to pump high-quality lightweight concrete that corresponds to a difference in concrete slump of about 8 cm.

[Table] (Note) - Coarse aggregate is artificial lightweight aggregate
・Fine aggregate is river sand

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【table】

【table】

【table】

[Table] [Effects of the Invention] The lightweight aggregate for pumping according to the present invention is produced by forming a layer that further suppresses water permeation on the surface layer or surface portion of the aggregate that absorbs water by prewetting. , the pressure water absorption during pumping is extremely reduced. Forming a layer that suppresses water permeation on the surface layer of the pre-wetted aggregate is, for example, an emulsion that has a low viscosity in an acidic region, and a material that exhibits a significantly high viscosity in a neutral or alkaline region, such as an anionic material. This can be easily achieved by using an acrylic resin emulsion. In acidic conditions, this material can easily penetrate into the voids of the surface layer of the aggregate due to its low viscosity, but then, when in contact with cement, it easily thickens due to the OH ^- ions released from the cement and becomes watery. Suppresses the permeation of The layer that suppresses water permeation formed by this method is formed inside the aggregate, and can exist stably even against physical or mechanical stimulation during concrete production. It does not damage the adhesion with the wood mortar. In order to form a layer that suppresses water permeation on the surface of pre-wetted aggregate, it needs to be stable against moisture from pre-wetting and physical or mechanical stimulation during concrete production. Such materials include, for example, underwater curable epoxy resins. As a result of manufacturing the lightweight aggregate according to the present invention and conducting pressure water absorption tests and pump pumping experiments, it was found that the lightweight aggregate for pumping according to the present invention has a pressure water absorption rate of about half that of conventional lightweight aggregates. and the unit water volume of concrete required for high-altitude pumping.
It has become clear that the weight can be reduced by ^more than 20Kg/m3. Therefore, even if concrete using the lightweight aggregate for pumping according to the present invention is pumped to high places, unlike conventional lightweight concrete, it is not necessary to significantly increase the unit water volume due to pumping requirements. It can be handled in the same way as ordinary aggregate. As a result, the lightweight concrete using the present invention has (1) less drying shrinkage and fewer shrinkage cracks than conventional lightweight concrete; (2) Quality issues that have traditionally been considered problematic for lightweight concrete, such as reducing the infiltration of substances such as carbon dioxide gas and chloride ions that enter concrete, corrode reinforcing bars, and deteriorate concrete structures. This can significantly improve the above problems.

[Brief explanation of the drawing]

FIG. 1 is a sectional view of a lightweight aggregate for pumping according to the present invention. FIG. 2 is an enlarged sectional view of the main part. Figure 3 shows the pressure water absorption amount of the aggregate and the time when a pressure of 35 kg/m ² was applied as shown to the lightweight concrete manufactured using the lightweight aggregate for pumping in Example 1 of the present invention. It is a graph showing the relationship between FIG. 4 is a partially cutaway front view showing the test apparatus used in the pressure water absorption test in Example 1.
Figure 5 shows the pressure water absorption of the aggregate when a pressure of 35 kg/cm ² is applied to the lightweight concrete manufactured using the lightweight aggregate for pumping in Example 2 of the present invention as shown in Figure 3. It is a graph showing the relationship between and time.
Figure 6 shows the pressure water absorption amount and time of the aggregate when pressure is applied in the same manner as in Figure 3 to lightweight concrete manufactured using a conventional lightweight aggregate (Comparative Example 1) that has been prewetted only. 2 is a graph comparing the relationship between Examples 1 and 2. Explanation of symbols of main parts, 10... Lightweight aggregate for pumping, 11... Surface layer part of lightweight aggregate for pumping, 12... Outer surface of lightweight aggregate for pumping.

Claims (1)

[Claims] 1. A lightweight pump for pumping, characterized in that 15 to 30% of the absolute dry weight of the aggregate is pre-absorbed with water, and a layer for suppressing water permeation is formed on the surface layer or surface of the lightweight aggregate. aggregate.