JP2001354467A - Recycled concrete - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide recycled concrete capable of exhibiting mechanical performance, or the like, equivalent to concrete using natural aggregate. SOLUTION: This recycled concrete consists essentially of a binder containing reducing period slag and gypsum, recycled aggregate obtained by crushing a concrete waste material and water, wherein. As the binder, ATK cement consisting of 65-80 wt.% of reducing period slag and 20-35 wt.% of gypsum, is preferred, and as the recycled aggregate, a mixture of recycled fine aggregate that has a fineness modulus of 2.5-3.0 and contains 20-30 wt.% of a fraction passing through a 0.3 mm sieve, and recycled coarse aggregate that has a fineness modulus of 6.3-7.3 and contains <=5 wt.% of a fraction remaining on a 40 mm sieve, or an unsieved crushed concrete waste material having <=40 mm (0-40 mm) particle size and a fineness modulus of 5.0-6.5, is preferred.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to recycled concrete in which crushed waste concrete is recycled as aggregate.

[0002]

2. Description of the Related Art Conventionally, natural aggregates such as river gravel, river sand, crushed stone, crushed sand and the like have been used as aggregates occupying 70 to 80% of the volume of concrete. However, the collection of natural aggregate has various effects on the environment, and there is a strong demand for minimizing the effects. In recent years, it has become difficult to obtain high-quality natural aggregate, and depletion of resources has become a problem.

[0003] Attempts have been made to crush the waste concrete discharged when the concrete structure is dismantled and to reuse it as aggregate (recycled aggregate).

[0004]

However, there is a problem that recycled concrete using recycled aggregate is inferior in mechanical performance and the like as compared with ordinary concrete using natural aggregate. This is because the quality of the recycled aggregate is lower than that of the natural aggregate.
It was limited to places with relatively low performance requirements for concrete and roadbed materials.

[0005] In general, recycled aggregate has a high water absorption due to adhesion and mixing of mortar particles and cement paste. Therefore, fresh concrete containing recycled aggregate deteriorates in fluidity. Therefore, in order to ensure a predetermined fluidity, it is necessary to increase the unit water volume or use a water reducing agent. However, in this case, there are problems such as a decrease in initial strength and an increase in cost.

The present invention has been made by focusing on the problems existing in the prior art as described above. It is an object of the present invention to provide a recycled concrete that can exhibit mechanical performance and the like equivalent to concrete using natural aggregate.

[0007]

In order to achieve the above-mentioned object, the invention according to the first aspect of the present invention is directed to a recycled aggregate obtained by crushing waste concrete and a binder containing reducing slag and gypsum. And water as the main material.

According to a second aspect of the present invention, in the recycled concrete according to the first aspect, the binder is 65%.
The gist of the present invention consists of 〜80% by weight of reducing slag and 35 to 20% by weight of gypsum.

According to a third aspect of the present invention, there is provided the recycled concrete according to the first or second aspect, wherein the recycled aggregate has a coarse particle ratio of 2.5 to 3.0 and a sieve. Amount passing through a sieve with a size of 0.3 mm is 20
Fine aggregate of ３０30% by weight and a coarse particle ratio of 6.3 to 7.3
The gist of the present invention is that a coarse aggregate having an amount of 5% by weight or less that can be retained in a sieve having a sieve size of 40 mm is used.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will now be described in detail. The recycled concrete in the present embodiment mainly uses a binder, recycled aggregate, and water.

The binder used in the present embodiment contains slag and gypsum during the reduction period.
ATK cements consisting of 80% by weight reduced slag and 35-20% by weight gypsum are preferred. Reduction period slag is
12CaO.7Al ₂ O ₃ and γ
-2CaO.SiO ₂ as a main component. In addition, as the gypsum, at least one selected from anhydrous gypsum, hemihydrate gypsum and dihydrate gypsum can be used, and desulfurization gypsum (dihydrate gypsum) produced in large quantities by a flue gas desulfurization device such as a thermal power plant is used. Is preferred.

The recycled aggregate is obtained by crushing a concrete waste material discharged when a concrete structure is dismantled with a jaw crusher or the like.
It has been crushed so as to be 0 mm or less or 20 mm or less. This recycled aggregate may be used as it is without sieving, or it may be used as a fine aggregate having a particle size of 5 mm or less (regenerated fine aggregate) and a coarse aggregate having a particle size of 5 mm or more (regenerated coarse aggregate). And then used as a concrete material.

When recycled aggregate obtained by crushing waste concrete material so as to have a particle size of 40 mm or less is used as it is as a concrete material without sieving, the coarse particle ratio is preferably 5.0 to 6.5. .

On the other hand, when the classified recycled fine aggregate and the recycled coarse aggregate are used, the fine aggregate ratio indicating the volume ratio occupied by the fine aggregate with respect to the total aggregate is set in the range of 38 to 52%. By doing so, highly fluid concrete (concrete unnecessary concrete) can be obtained. When the shape of the particles of the coarse aggregate is poor or when the fine particle content in the fine aggregate is 20% or less, the separation resistance is set by setting the value of the fine aggregate ratio in the range of 35 to 45%. It is possible to obtain highly concrete.

The fine aggregate refers to an aggregate that passes through a sieve having a sieve size of 10 mm and passes through a sieve having a sieve size of 5 mm by 85% by weight or more. It is preferable to use a sieve having a sieve size of 2.5 to 3.0 and a sieve size of 0.3 mm by 20 to 30% by weight. The coarse aggregate is a sieve with a size of 5m.
5% by weight of an aggregate whose coarse grain ratio is 6.3 to 7.3 and the size of the sieve is 40 mm or more.
The following are preferred.

The coarse particle ratio of the aggregate is determined according to JIS A 1102 (Aggregate sieving test method). That is, sieve dimensions are 40, 20, 10, 5, 2.5, 1.2, 0.6, 0.3, 0.15 mm
The aggregate is sieved with each sieve, and the sum of the weight percentage of the amount remaining in each sieve is divided by 100. Incidentally, the sieve size used in the present specification is 40, 30, 20, 10, 5, 2.5, 1.2,
0.6, 0.3, 0.15mm sieves (40m each
m sieve, 0.3 mm sieve, etc.) is JI
Standard network sieve specified in SZ 8801 (Standard network sieve) 38.
1, 31.7, 19.1, 9.52 mm and 4760, 2380, 1190, 590,
297 and 149 μm.

As the concrete material, other than the binder, the recycled aggregate and the water, those which can be added include, for example, admixtures such as a setting retarder, a water reducing agent and a rust preventive. As the setting retarder, an oxycarboxylic acid-based setting retarder, for example, an oxycarboxylic acid such as citric acid or gluconic acid or a salt thereof is suitably used.
Gypsum) is preferably 0.3 to 1.0% by weight. As the water reducing agent, a polycarboxylic acid-based water reducing agent, for example, a copolymer of an acrylic acid derivative, a maleic anhydride copolymer is suitably used, and the amount of the water reducing agent is 0.5 to 1.5% by weight of the binder. %
Is preferred. Calcium nitrite is preferably used as the rust inhibitor, and its amount is 0.5 to 1.5% by weight of the binder.
Is preferred.

In addition, natural aggregates and admixtures may be added without departing from the scope of the present invention. For example, lime crushed sand which is a natural aggregate (coarse grain ratio is 2.5 to 2.8 and an amount passing through a 0.3 mm sieve is 10 to 25%) may be added as fine aggregate, or limestone may be added. Fine powder, fly ash, and dried sludge (raw con sludge) may be added as an admixture.

Then, the above-mentioned binder, recycled aggregate and water,
If necessary, a fresh concrete is prepared by kneading an admixture and the like, and the fresh concrete is poured into a molding form and hardened to obtain a recycled concrete (secondary product). In addition, when the above-mentioned fresh concrete is cast at a construction site, recycled concrete (on-site structure) can be obtained.

According to the embodiment described above, the following effects can be obtained. -In the present embodiment, a binder containing a reducing slag and a gypsum is used as a binder. For this reason, even the recycled concrete using the recycled aggregate can exhibit the same mechanical performance and the like as the concrete using the natural aggregate. Therefore, the use of the concrete waste material conventionally limited to the roadbed material and the low-quality concrete can be expanded to other uses, and the concrete waste material can be effectively used as the concrete material. In addition, since the amount of the natural aggregate used can be suppressed by using the recycled aggregate, it can contribute to solving problems such as environmental destruction and resource depletion due to the collection of the natural aggregate.

Slag of 65-80% by weight in the reduction period and 3
By using a binder composed of 5 to 20% by weight of gypsum, the strength can be improved, and the mechanical performance of concrete can be further improved.

A fine aggregate having a coarse particle ratio of 2.5 to 3.0;
And the amount passing through a 0.3 mm sieve is 20 to 30% by weight, and the coarse aggregate has a coarse grain ratio of 6.3.
By using a material having a size of up to 7.3 and an amount remaining in a 40 mm sieve of 5% by weight or less, the particle size distribution of the aggregate can be approximated to an ideal shape continuous from the largest grain to the smallest grain. For this reason, the separation resistance of concrete can be improved.

In the case where recycled aggregate produced by crushing waste concrete is used as it is as a concrete material without sieving, it is possible to omit the work of classifying into coarse aggregate and fine aggregate. .

In addition to recycled aggregate obtained from waste concrete and slag, which is a by-product of obtaining steel,
Further, when desulfurized gypsum is used as the gypsum constituting the binder, the cost of the material can be significantly reduced as compared with the conventional concrete, since both are inexpensive.

Since the binder in the present embodiment has quick-hardening properties (hardening time within 30 minutes), the time for releasing from the mold can be significantly reduced, and the productivity can be improved. Besides, it can be suitably used particularly when it is necessary to quickly develop practical strength, such as in emergency construction. In particular, in the summer, it is possible to perform the demolding operation of the product at an early stage without performing accelerated curing with steam. The setting and hardening time can be adjusted by adding an appropriate amount of a setting retarder (30 to 90).
Therefore, it can be suitably used even when it is desired to secure the working time after the kneading, and it is also possible to carry out the jointing to a large-sized structure or to transport it by a concrete mixer truck.

[0026] By adding an appropriate amount of a water reducing agent to improve the fluidity of concrete, compaction work due to vibration or the like can be reduced or omitted. In addition, the addition of the water reducing agent improves the dispersibility of each material, thereby improving the strength of concrete. Among the various water reducing agents, the amount of the polycarboxylic acid-based water reducing agent that is adsorbed by the cement paste portion in the recycled aggregate is small, so that the amount of the water reducing agent can be suppressed.

Since the slag in the reduction period is by-produced during steelmaking, iron powder may be mixed in the slag, and in this case, the iron powder may cause rust and adversely affect the performance of concrete. is there. However, by adding an appropriate amount of a rust inhibitor, the generation of rust can be suppressed, and deterioration of performance due to the rust can be prevented. When a steel mold is used, rust of the mold can be prevented by adding a rust preventive.

Conventionally, eco-cement obtained by firing a hardened cement paste obtained from concrete waste material has been known as a cement made by recycling concrete waste material. However, in this embodiment, since the concrete waste is used without firing, it is possible to save labor and equipment related to firing, and to reuse the concrete waste without generating carbon dioxide due to firing. it can.

[0029]

Next, the embodiment will be described more specifically with reference to examples. In Examples 1 to 4, the reducing phase slag, desulfurized gypsum, recycled aggregate, admixture, and water were blended as shown in Tables 1, 3, 5, and 7, respectively. After kneading these, they are poured into a molding mold and steam cured to obtain a hardened concrete having a predetermined shape (10% in the case of Examples 1 and 2).
Φ × 20cm cylindrical specimen, JI for Examples 3 and 4
A specimen for a core compressive strength test according to SA 1107) was obtained.
Properties of fresh concrete before hardening and properties of hardened concrete in each example are shown in Tables 2 and 4, respectively.
6 and 8. The hardened concrete obtained in Example 4 was also subjected to component analysis. Table 9 shows the results.

In Tables 1, 3, 5, and 7, "W / P" is a water binder ratio indicating the weight ratio of water to the binder (reducing slag + desulfurized gypsum), and "S / a" is the total. It is a fine aggregate ratio indicating the volume ratio of the fine aggregate to the aggregate. Further, the amount of the admixture is represented by a weight ratio to the binder. Water reducing agent FP-300
S is a product name of a polycarboxylic acid-based high-performance water reducing agent standard type manufactured by FPC, and FP-300R is a product name of a polycarboxylic acid-based high-performance water reducing agent delayed type manufactured by FPC. Soft coat T-1 as a retarder is a trade name of an oxycarboxylic acid-based setting retarder manufactured by Denka Grace Co., Ltd.
PK # -1 is a trade name of an oxycarboxylic acid-based set retarder manufactured by FPC, and CANI of a rust preventive is a trade name of calcium nitrite manufactured by Nissan Chemical Industries, Ltd. In Tables 2, 4, 6, and 8, "precuring time" indicates the time from molding to steam curing, and "integrated temperature of steam curing" indicates the product of the ambient temperature during curing and the curing time. .

In Examples 1 to 3, after the waste concrete was crushed, the recycled coarse aggregate and the recycled fine aggregate classified by sieving were used as the recycled aggregate. Example 1
The particle size curves of the recycled coarse aggregate and the recycled fine aggregate used in No. 3 are shown in FIGS. 1 and 2, and their physical properties are shown in Table 10. The density and water absorption in Table 10 are JIS A 1109, JIS A 1110
(Aggregate density / water absorption rate test), unit volume mass and actual volume ratio are JIS A 1104 (aggregate unit volume mass and actual volume ratio test method), and fine particle content is JIS A 1103 (aggregate fine particle Volumetric test)
The stability was measured in accordance with JIS A 1122 (a method for testing the stability of aggregate using sodium sulfate).

On the other hand, in Example 4, concrete waste crushed so as to have a particle size of 40 mm or less (40-0) was used as recycled aggregate without sieving. FIG. 3 shows the particle size curve of the recycled aggregate. In addition, the coarse particle ratio of this recycled aggregate was 5.86. Curves shown by bold lines among the curves in each of FIGS. 1 to 3 are grain size curves of actual aggregates, and the remaining two curves shown by solid lines are curves indicating upper and lower limits that can be suitably used as aggregates. It is. It is most desirable that the particle size curve (thick line) is located between the two curves shown by the solid lines, but there is no problem even if there is a slight error.
Each of the aggregates used this time has a desirable particle size distribution since the particle size curve is almost located between the two curves shown by the solid lines.

(Example 1)

[0034]

[Table 1]

[0035]

[Table 2] (Example 2)

[0036]

[Table 3]

[0037]

[Table 4] (Example 3)

[0038]

[Table 5]

[0039]

[Table 6] (Example 4)

[0040]

[Table 7]

[0041]

[Table 8]

[0042]

[Table 9]

[0043]

[Table 10] As shown in Tables 2 and 4, in Examples 1 and 2, a strength almost equivalent to the design standard strength of 21 N / mm ² in steam curing with the mixture of ordinary concrete using natural aggregate was obtained. On the other hand, as shown in Tables 6 and 8, Examples 3 and 4
In this case, the strength was slightly inferior, but this was due to the short pre-curing time, which could be improved by taking sufficient pre-curing time.

As shown in Tables 6 and 8, in Examples 3 and 4, the curing time was 1.5 times longer than that in Examples 1 and 2, so that a delay type water reducing agent was used. This shows that the curing time can be extended.

Further, from a comparison between Example 3 and Example 4,
It was shown that when the crushed concrete waste was used after being classified and when it was used without classification, almost the same strength was obtained.

When the concrete temperature is 26 ° C. or higher, the unit water amount is 5 to 10 kg / m ³ in each case.
It is preferable to increase the amount of the setting retarder by 0.2 to 0.5%.

Next, the technical ideas that can be grasped from the above embodiment will be described below. The recycled concrete according to any one of claims 1 to 3, further comprising a setting retarder as a material. In the case of such a configuration, by adjusting the setting and hardening time, it can be suitably used even when it is desired to secure the working time after kneading.

[0048] The recycled concrete according to any one of claims 1 to 3, further comprising a water reducing agent as a material. In such a configuration, the compaction work due to vibration or the like can be reduced or omitted by improving the fluidity of the concrete.

The recycled concrete according to any one of claims 1 to 3, further comprising a rust inhibitor as a material. With such a configuration, it is possible to suppress the generation of rust and prevent deterioration of concrete performance due to rust.

The recycled concrete according to claim 1 or 2, wherein the aggregate obtained by crushing the waste concrete is used as it is without classification. In the case of such a configuration, it is possible to omit a device and labor for classification.

[0051] The recycled concrete according to any one of claims 1 to 3, wherein the gypsum is desulfurized gypsum. With this configuration, it is possible to reduce material costs.

[0052]

Since the present invention is configured as described above, it has the following effects. According to the first aspect of the present invention, it is possible to exhibit the same mechanical performance as that of concrete using natural aggregate.

According to the invention described in claim 2, according to claim 1
In addition to the effects of the invention described in (1), the strength can be improved, and the mechanical performance of concrete can be further improved.

According to the invention described in claim 3, according to claim 1
Alternatively, in addition to the effect of the invention described in claim 2, the particle size distribution of the aggregate can be approximated to an ideal shape continuous from the largest grain to the smallest grain, so that separation resistance can be improved.

[Brief description of the drawings]

FIG. 1 is a graph showing a particle size curve of recycled coarse aggregate used in Examples 1 to 3.

FIG. 2 is a graph showing a particle size curve of recycled fine aggregate used in Examples 1 to 3.

FIG. 3 is a graph showing a particle size curve of recycled aggregate used in Example 4.

Claims (3)

[Claims] 1. A binder containing reducing slag and gypsum, a recycled aggregate obtained by crushing concrete waste,
Recycled concrete characterized by using water as the main material. 2. The recycled concrete according to claim 1, wherein the binder comprises 65 to 80% by weight of reducing slag and 35 to 20% by weight of gypsum. 3. The recycled aggregate has a coarse particle ratio of 2.5 to 2.5.
A fine aggregate having an amount of 20 to 30% by weight which passes through a sieve having a sieve size of 3.0 mm and a sieve size of 0.3 mm; a coarse particle ratio of 6.3 to 7.3; Eye size is 40m
3. The recycled concrete according to claim 1, wherein the amount of coarse aggregate remaining in the sieve of m is 5% by weight or less. 4.