JP2009234863A - Recycled aggregate concrete and method for producing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide recycled aggregate concrete which uses only recycled aggregate for whole aggregate, is easily produced and has improved strength and durability, and to provide a method for producing the same. <P>SOLUTION: The recycled aggregate concrete is composed of cement, water and aggregate, wherein the whole amount of the aggregate is composed of the recycled aggregate. The blending ratio of water to cement is 25-35%, and the unit water amount is 145-155 kg/cm<SP>3</SP>. When an admixture is added to cement in an amount of 0.5-1.5% based on the amount of the cement and the resulting mixture is kneaded, a number of fine independent air bubbles are incorporated into concrete. Thereby, good slump performance can be kept. Since the transition zone of the recycled aggregate surface becomes dense by setting the ratio of water to cement to be ≤35% and setting the unit water amount to be ≤155 kg/cm<SP>3</SP>, the absorption of water onto the recycled aggregate is restricted. Consequently, the strength, freezing and thawing resistance, and drying shrinkage property of the concrete are improved, and strength and durability nearly equal to those of normal concrete can be secured although only the recycled aggregate is used as the whole aggregate. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

The present invention relates to recycled aggregate concrete and a method for producing the same. In recent years, a large amount of concrete structures manufactured during the period of high economic growth in the 1970s has entered a renewal period, and it is predicted that emissions will increase. Therefore, attempts have been made to crush the concrete waste discharged when the concrete structure is dismantled and use it as recycled aggregate. In particular, concrete lumps, which are 40% or more of industrial waste, are useful for the construction of a recycling society if they can be used effectively for recycled aggregates.
The present invention relates to a recycled aggregate concrete using all of such recycled aggregate and a method for producing the same.

  By the way, concrete using low-grade recycled aggregate has a high water absorption rate because it contains mortar particles and old cement paste that adhere to the surface of the recycled aggregate. Therefore, fresh concrete containing recycled aggregate has fluidity. descend. In addition, the strength is low and there are many variations, and the freeze-thaw resistance and the drying shrinkage characteristics are remarkably lowered. For this reason, since it was limited to the use which may be low intensity | strength, such as abandoned concrete and backfill concrete, the effective utilization had a limit.

In order to solve such a problem, the following conventional techniques have been proposed.
The prior art of Patent Document 1 is a technique that crushes a concrete lump in the primary and secondary crushing processes, and grinds it under high pressure in the secondary crushing process to reduce the amount of mortar and paste. is there. However, there are drawbacks in that many processes and energy are required and the cost is high.

  The prior art of Patent Document 2 is a technique in which after waste concrete is screened, it is treated with an inorganic acid to recover acid-insoluble components as recycled aggregate. However, according to this conventional technique, the quality of the recycled aggregate is improved, but it takes time for the inorganic acid treatment process or the waste acid treatment must be performed, so that it is not practical.

  The prior art of Patent Document 3 is to add a breathing inhibitor to a mortar using natural aggregate, and to add and mix recycled aggregate. This conventional technique has a problem that the reuse rate is low because natural aggregate and recycled aggregate are mixed and the entire amount of recycled aggregate is not used.

In order to solve such problems, development of advanced recycled aggregate processing methods and construction methods were proposed, and high-quality recycled aggregate H was made JIS in March 2005. In March 2006, concrete using recycled aggregate L was made into JIS (Non-Patent Document 1).
However, in order to promote the expansion of the application range of recycled aggregates, it is possible to use low-grade recycled aggregates as they are, instead of modifying them to high-quality recycled aggregates. It must be practical and have sufficient concrete strength.

Japanese Patent Publication No. 7-29821 JP-A-6-285454 JP-A-11-199298 Japan Industrial Standards Committee Discussion: Japan Standards Association, Concrete JIS A 5023 using recycled concrete L, established on March 25, 2006

  In view of the above circumstances, an object of the present invention is to provide a recycled aggregate concrete that uses all the recycled aggregate, is easy to manufacture, and has improved strength and durability, and a method for producing the same.

The recycled aggregate concrete of the first invention comprises cement, water and aggregate, and the total amount of the aggregate is recycled aggregate, and the blending conditions are water cement ratio: 25-35%, unit water volume: It is characterized by being 145 to 155 kg / m ³ .
The recycled aggregate concrete of the second invention is characterized in that, in the first invention, the recycled aggregate is a low-level treated recycled aggregate.
The recycled aggregate concrete of the third invention is characterized in that, in the first invention, 0.5 to 1.5% of an admixture is added to the amount of cement.
The method for producing the recycled aggregate concrete of the fourth invention uses the entire amount of recycled aggregate as cement, water and aggregate, and the blending conditions are water cement ratio: 25 to 35%, unit water volume: 145 to 155 kg / m ³ , It is characterized by adding 0.5 to 1.5% of the admixture to the cement amount and kneading.

According to the first invention, it has been found that when the water cement ratio is 35% or less and the unit water amount is 155 kg / m ³ or less, the transition zone on the surface of the recycled aggregate becomes dense. For this reason, water absorption into the recycled aggregate is suppressed, so that the strength, freeze-thaw resistance, and drying shrinkage characteristics of the concrete are improved despite the use of the entire amount of recycled aggregate. Strength and durability can be secured.
According to the second invention, even if it is a low-grade recycled aggregate, it does not change that the transition zone on the surface of the recycled aggregate is dense, so that concrete having high strength and durability can be obtained.
According to the third aspect of the invention, since a large number of fine independent air bubbles are entrained in the concrete, good slump performance can be maintained even if the unit water amount is reduced to 155 kg / m ³ or less.
According to the fourth aspect of the invention, since the concrete using the entire amount of recycled aggregate can be manufactured only by setting the blending conditions, it is easy to manufacture, and concrete having sufficient strength and durability can be obtained.

(Technical principle of the present invention)
The present inventor makes the transition zone on the surface of the recycled aggregate denser by setting the water cement ratio to 30% or less and 25% or more and the unit water amount to 155 kg / m ³ or less and 145 kg / m ³ or more. It was found that the strength, freeze-thaw resistance, and drying shrinkage characteristics of the resin were remarkably improved. This finding exceeds the conventional common knowledge that only high-quality recycled aggregates by the heated grinding method (Patent Document 1) can be used for structural concrete, and even if all low-grade recycled aggregates are used, It is an epoch-making thing that can secure the same strength and durability as concrete.

The details of the present invention are illustrated by the following experiments.
The present invention is characterized by the following blending conditions.
Using two types of recycled fine aggregate L and recycled coarse aggregate L and M (hereinafter referred to as low-grade recycled aggregate) with different production lots, the same strength as ordinary aggregate concrete used for concrete structures The concept of blending design of high-strength concrete exceeding compressive strength of 100 N / mm ² is applied to the condition of blending of concrete with properties and durability.
In order to confirm the feasibility of the present invention, the water-cement ratio is changed from 55 to 25% and the unit water volume is changed from 175 to 145 kg / m ³ , and concretes with various blends are manufactured and experimentally examined for fresh properties and hardened properties. It was examined.

(Experiment overview)
Experiments were conducted on the target recycled aggregate concrete, Series A “Concrete using L-class recycled fine aggregate and M-class recycled coarse aggregate” and Series B “L-class recycled fine and coarse bone with different production lots from Series A. It was divided into two series of “concrete using wood”.
The definitions of “L class” and “M class” are as follows.
JISA5023 has L-class quality regulations as follows.
Recycled coarse aggregate Water absorption 7% or less Fine particle amount 2.0% or less
Recycled fine aggregate Water absorption 13% or less Fine particle amount 10.0% or less
Class H quality regulations are defined in JIS A5021.
Recycled coarse aggregate Recycled fine aggregate
Absolute dry density (kg / cm ³ ) 2.5 or more 2.5 or more
Water absorption rate (%) 3 or less 3.5 or less
Grinding weight loss (%) 3.5 or less None
Fine particle amount (%) 1.0 or less 7.0 or less
The M class is an aggregate between the H class and the L class.

(1) Materials used a) Cement As the cement, ordinary Portland cement (density 3.15 g / cm ³ , specific surface area 3430 cm ² / g) and silica fume cement (density: 3.08 g / cm ³ , specific surface area: 6000 cm ² / g) are used. used.
Tap water was used as the mixing water.

b) Aggregate Recycled aggregate is produced only by crushing, washing, drying, and classifying the concrete mass, so that the aggregate surface does not completely remove fine powder or old cement hardened material. Treated recycled aggregate was used. The low-grade recycled fine / coarse aggregate used in this experiment is shown in Photo 1 in FIG.
Table 1 in FIG. 2 shows an outline of quality standards for recycled aggregates according to TS A 0006. According to TS A 0006 quality standard, Series A used L-class recycled fine aggregate, L-class recycled coarse aggregate small and M-class recycled coarse aggregate large. In Series B, L-class recycled fine aggregates and L-class recycled coarse aggregates of a different lot from the series A recycled aggregates were used. The physical properties of the used recycled aggregate and normal aggregate are shown in Table 2 in FIG.

The recycled aggregate used was purchased by a normal sales method from a company that generally manufactures and sells recycled aggregate in Tokyo. Therefore, the raw concrete is unknown except for information on civil engineering RC concrete in Tokyo in the Showa 40s.
Ordinary aggregates used land sand in Anan City, Tokushima Prefecture and crushed stones in Naruto City, Tokushima Prefecture, which are within the standard particle size range shown by the Japan Society of Civil Engineers. The maximum size of the coarse aggregate was 20 mm together with the ordinary aggregate and the recycled aggregate.

c) Admixture As the admixture, a polycarboxylic acid ether compound high-performance AE water reducing agent, a modified rosin acid compound anionic surfactant AE agent and a polyalkylene glycol derivative antifoaming agent were used.

(2) Blending conditions The blending conditions are as follows.
Series A recycled aggregate concrete (hereinafter referred to as AR) had a water-cement ratio of 55%, 45% and 35%.
Series B recycled aggregate concrete (hereinafter referred to as BR) is 45%, 35% and 25%
Each unit water volume was 175 kg / m ³ and 155 kg / m ³ .
The comparative concrete (hereinafter referred to as “N”) has a water-cement ratio of 55% and 45% and unit water amounts of 175 kg / m ³ , 155 kg / m ³ and 145 kg / m ³ , respectively.
The target slump value was 18.0 ± 2.5 cm and the target air volume was 4.5 ± 1.5%.
The amount of admixture added was adjusted from 0.5% to 1.5% of the cement amount so that the slump was constant.
The amount of air in the recycled aggregate concrete was adjusted by the amount of unit water added and the amount of unit defoamer added. The amount of air in ordinary concrete was adjusted by the amount of unit water added and the amount of unit AE agent added.

Table 3 shows the composition of the concrete used in the test.
The concrete used for the experiment has a total of 15 blends. Table 3 in FIG. 4 also shows the fresh property test results. The compounding name is indicated by the number after the symbol using the value of water cement ratio and unit water amount. BRS25-155 is recycled aggregate concrete using silica fume cement. The ratio of the reproduction Coarse Aggregate size (G _Univ.) And regeneration coarse aggregate small (G _small) is 7: constant at 3.

(3) Test items and methods For mixing the concrete, a biaxial forced mixing mixer was used. Mixing order is to mix cement and fine aggregate for 30 seconds, add water and admixture for 30 seconds, then add coarse aggregate and mix for 60 seconds, The mixing time was a total of 150 seconds.
a) Slump test The slump test was performed according to JIS A 1101.
b) Air quantity test The air quantity test was conducted according to JIS A 1128.

c) Compressive strength test and static elastic modulus test The compressive strength test was performed according to JIS A 1108 at the age of 7, 14 and 28 days. The specimen was a cylindrical specimen having a size of 100 × 100 × 200 mm, and was cured under water at 20 ° C. until a predetermined test material age.
The elastic modulus test was performed in accordance with JIS A 1149 at a material age of 28 days.

d) Drying shrinkage test
A square column specimen of 100 × 100 × 400 mm was used, and the test was performed in accordance with JIS A 1129-2. The test material age was 1, 3, 5, 7, 14, 28, 42, 56 and 91 days. The gauge plugs were spaced at 100 mm intervals and arranged so as to be in the center of the specimen.

e) Self-shrink test
Using a 100 × 100 × 400mm prismatic specimen, JCI Super Fluid Concrete Research Committee “Self-shrinkage test method for high fluid concrete” In accordance with The test period was 7 days immediately after the driving. In addition, self-tests were conducted on two series of 35% and 55% water cement ratios for unit water volume of 175 kg / m ³ for series B recycled aggregate concrete. Only one concrete with a water content of 175 kg / m ³ , a total of three concretes, was carried out.

f) Neutralization test The neutralization test was conducted in accordance with JIS A 1153 "Promoted neutralization test method for concrete" using a 100 x 100 x 100 mm cylindrical specimen. The promotion conditions were a carbon dioxide concentration of 10%, a temperature of 30 ° C., and a humidity of 60%.
The neutralization measurement method is to split the specimen 100 × 100 × 100 mm, spray a phenolphthalein 1% ethanol solution on the split surface, and measure the length of the uncolored part at 20 points. did.

g) Rapid freeze-thaw test A rapid freeze-thaw test method using liquid nitrogen gas was performed as follows.
A 100 × 100 × 200 mm cylindrical specimen was used, and the test was conducted after 28 days of water curing.
1) Measure the ultrasonic propagation time at 0 cycle, and obtain the kinematic elastic modulus from the ultrasonic propagation time.
2) Put the specimen in a container and spray liquid nitrogen gas for 30 seconds.
3) Close the lid and leave for 1 minute.
4) After 1 minute, remove the specimen and soak in 40 ° C. hot water for 10 minutes until it melts.
5) Wipe the moisture on the surface of the specimen completely melted and measure the ultrasonic propagation time. The terminal should be installed approximately 15mm from the bottom of the cylinder.
The work of 1) to 5) is set to 1 cycle, the test is ended to 10 cycles, and if the relative dynamic elastic modulus has reached 60% or less by that time, the cycle is ended. Formula 1 for obtaining kinematic elastic modulus from propagation time Was used. The ultrasonic propagation measurement method and the situation immediately after freezing are shown in FIG.
here,
E _d : Dynamic elastic modulus (GPa), V _L : Ultrasonic propagation velocity (km / s)

h) JIS Method Freeze-Thaw Test The JIS method freeze-thaw test was conducted in accordance with method A of JIS A 1148 using a 100 × 100 × 400 mm prism specimen. The freeze-thaw test of the JIS A method was performed only on the concrete of the series B recycled aggregate and compared with the result of the rapid freeze-thaw test.

(Characteristics of recycled aggregate concrete of the present invention)
The features of the present invention derived from the above experimental results are as follows.
(1) Fresh properties of recycled aggregate concrete Table 3 in FIG. 4 shows the fresh test results. The amount of air in the series A recycled aggregate concrete and the series B recycled aggregate concrete is in the range of 3.5 to 5.5%, which is the same as that of ordinary concrete. Therefore, since it has sufficient softness in a state of being kneaded as concrete, there is an advantage that the concrete can be easily compacted in the mold. The amount of air is preferably small from the viewpoint of strength, but if it is too small, the freeze-thaw resistance is remarkably deteriorated. For example, concrete with an air volume of around 1.5% is inferior in durability. Therefore, the best air amount is 4.5 ± 1.5%. The recycled aggregate of the present invention is of a low quality, but it can be said to be the best value because it is in the range of ± 1% with 4.5% as the median.

The detailed analysis is as follows.
The amount of air in AR35-175, BR35-155 and BR25-155 was 3.5%, which was slightly less than other recycled aggregate concrete. When the water-cement ratio is 35% or less, it is considered that air becomes difficult to enter due to high viscosity. Slump was all satisfied within the target range. On the other hand, compared to BR25-155, BRS25-155 has the same amount of slump and 1.5% more air, even though the amount of high-performance water reducing agent used in BRS25-155 is 0.2% less. The result was.
When silica fume cement is used, it becomes clear that reclaimed aggregate concrete with low viscosity and excellent workability can be easily produced even at an ultra-low water cement ratio of 25%, as with normal concrete. It was.

(2) Strength Properties of Recycled Aggregate Concrete a) Compressive Strength FIG. 6 shows the relationship between the compressive strength and age of series A recycled aggregate concrete and series B recycled aggregate concrete. In Series A recycled aggregate, at the age 7 days, 24~44N / mm ^2, at age of 28 days, shows a compressive strength of 28~46N / mm ^2. Series B recycled aggregate concrete exhibits a compressive strength of 32 to 60 N / mm ^{2 at} a material age of 7 days and 35 to 66 N / mm ^{2 at} a material age of 28 days. For ordinary structural concrete, the above results are not inferior to ordinary concrete because 35 N / mm ² at 28 days is sufficient. Recycled aggregate concrete has a large amount of fine powder and water absorption, so when the air volume increases and the air volume increases, the strength decreases, but in the present invention the same level as ordinary concrete is maintained. As a recycled aggregate concrete, the conventional common sense is overturned.

Detailed analysis is as follows.
In concrete using each of the series A and series B recycled aggregates, the smaller the water-cement ratio, the larger the compressive strength.
In general, recycled aggregate concrete has low adhesion strength to cement paste due to fine powder around recycled aggregate and voids on the aggregate surface, etc., and there is a limit to the expression of compressive strength against water cement ratio, so it can not be expected much It is believed that. However, in the present invention, since the compressive strength of about 60 N / mm ² is expressed at the age of 7 days, the upper limit of the strength with respect to the water cement ratio is considered to be considerably large. In other words, high strength recycled aggregate concrete is feasible.
The strength development of both series of recycled aggregate concrete is smaller than that of ordinary concrete, except for BRS25-155, after 7 days of age. Although there is a cement-pace strength expression with age, there is a limit to the adhesive strength between the regenerated aggregate and the paste, and it is thought that cracking occurred from the regenerated aggregate interface that became brittle. Although BRS25-155 compressive strength is less than there AR35 and BR35 with 40N / mm ² at an age of 7 days, in the age of 28 days resulted in exceeding the increased AR35 and BR35 to 55N / mm ² It was. It is considered that the concrete using silica fume cement has a medium- to long-term strength increase as in the case of using ordinary aggregate.
FIG. 7 shows the relationship between the compressive strength at 28 days of age and the cement water ratio. According to Lyse (the law of constant unit water volume), recycled aggregate concrete can be expressed in a proportional relationship between cement water ratio and compressive strength, just like ordinary concrete. In order to obtain the same strength as compared with reclaimed aggregate concrete, it is necessary to reduce the water-cement ratio of reclaimed aggregate concrete by 10% or more.

b) Elastic modulus The relationship between the compressive strength and elastic modulus of 28 days of age is shown in FIG. A larger elastic coefficient is preferable because it is more difficult to deform, but the elastic coefficient of the recycled aggregate concrete of the present invention is slightly lower than that of ordinary concrete. That is, even if the elastic modulus is lower than the value of the calculation formula for ordinary concrete, it is in the range of 0 to 5 KN / mm ² and does not interfere with practical use. It is thought that.

Detailed analysis is as follows.
In concrete using each of the series A and series B recycled aggregates, the smaller the water-cement ratio, the greater the static elastic modulus.
In addition, all values were lower than the value of the calculation formula of ordinary concrete shown in the JASS5 RC standard, and were slightly smaller than those of ordinary concrete with the same water cement ratio (N55-155, N55-175). As this factor, it is considered that the strength and the static elastic modulus are lowered due to the high water absorption rate of the low-grade recycled aggregate.

(3) Durability of Recycled Aggregate Concrete a) Drying Shrinkage The relationship between the drying shrinkage strain of concrete and the dry material age is shown in FIG. The smaller the amount of drying shrinkage, the less the cracks need to occur. However, in the recycled aggregate concrete of the present invention, the upper limit value of the reinforced concrete structure design is 750 × 10 ⁻⁶ or less at the age of 91 days. . For this reason, it can be used as concrete for structures.

The detailed analysis is as follows.
Comparing the dry shrinkage of recycled aggregate concrete and ordinary concrete under the conditions of the same water cement ratio and unit water volume, the dry shrinkage of recycled aggregate concrete is slightly higher. At a dry material age of 91 days, there was a difference of about 50 × 10 ⁻⁶ . Despite the large difference in water absorption between recycled aggregate and normal aggregate, the difference in drying shrinkage strain is relatively small.
Among ordinary aggregates, coarse aggregates have a water absorption rate of around 2.29%, which is high for ordinary aggregates. Therefore, it is considered that the amount of drying shrinkage of concrete using ordinary aggregate has increased.

Moreover, in the concrete using each of the series A recycled aggregate and the series B recycled aggregate, under the same conditions of water cement ratio and unit water volume, the dry shrinkage amount is almost the same, and there is no significant difference among lots.
The dry shrinkage of recycled aggregate concrete under conditions of water-cement ratio and unit water volume of 35% or less and 155 kg / m ³ or less is 750 × 10 ^-6 or less at 91 days of dry material, and the design of reinforced concrete structures It can be suppressed below the upper limit value. On the other hand, the drying shrinkage of concrete using silica fume cement (BRS25-155) increased significantly with the initial drying material age, and compared with recycled aggregate concrete using Portland cement (BR25-155) at the 91st drying material age. It was large and showed almost the same value as recycled aggregate concrete (BR35-155) with W / C = 35%.
Recycled aggregate concrete (BRS25-155) using silica fume cement was considered to have an increased initial drying strain because the initial strength was smaller than that of BR25-155.

  FIG. 10 and FIG. 11 show the relationship between the amount of drying shrinkage on the age of 91 days, the water cement ratio, and the unit water amount. In all concrete, the smaller the water-cement ratio and the unit water volume, the smaller the drying shrinkage. In particular, the correlation between the water cement ratio and the amount of drying shrinkage is very high. In general, it has been reported that the drying shrinkage of ordinary concrete depends on the unit water amount and not so much on the water-cement ratio. In the case of recycled aggregate concrete, even if the unit water volume is the same, if the water-cement ratio is small, the amount of drying shrinkage is small. The amount of drying shrinkage of the low quality all recycled fine and coarse aggregate concrete targeted in the present invention was greatly influenced by the water cement ratio. This is because the structure of the transition zone with the cement paste formed on the recycled aggregate surface changes depending on the water cement ratio due to the extremely large water absorption rate and the influence of fine powder and irregularities attached to the recycled aggregate surface. Conceivable.

b) Self-shrinkage amount The relationship between self-shrinkage strain and time is shown in FIG. The smaller the self-shrinkage amount, the less the cracks need to occur, but the self-shrinkage amount depends on the amount of cement used. It is possible to reduce the amount of self-shrinkage.

Detailed analysis is as follows.
The numbers in parentheses in the figure legend indicate the amount of unit cement in the indicated composition. In recycled aggregate concrete (R35-175) using a unit cement amount of 500 kg / m ³ , the self-shrinkage strain was 385 × 10 ⁻⁶ , which was the largest value. On the other hand, recycled aggregate concrete (R55-175) with the same amount of cement showed comparable self-shrinkage strain compared with ordinary concrete (N55-175). Accordingly, the self-shrinkage is said to be caused by hydration shrinkage of the cement, and depends on the amount of cement used regardless of the type of aggregate.

c) Neutralization depth Fig. 13 and Fig. 9 show the relationship between the neutralization depth of the accelerated material 14 days and the water cement ratio. The recycled aggregate concrete having a water cement ratio of 35% or less targeted by the present invention has a neutralization depth of 2 mm or less, and this value is not large.

The detailed analysis is as follows.
In all recycled aggregate concrete, the neutralization depth tended to increase as the water-cement ratio increased. The neutralization depth of R55 was about 11 mm, which was slightly larger than N55. However, even with recycled aggregates, the neutralization depth is around 4 mm when the water cement ratio is 45%, around 2 mm when it is 35%, and 1 mm or less when it is 25%. In general, it has been reported that recycled aggregate concrete is less resistant to neutralization, but a large difference could not be confirmed in this experiment. The resistance to neutralization is considered to depend greatly on the unit cement amount regardless of the aggregate type.

d) Results of quick freeze-thaw test FIG. 14 shows the relationship between the relative dynamic elastic modulus obtained by the quick freeze-thaw test of series A and series B recycled aggregate concrete and the number of repetitions. The recycled aggregate concrete of the present invention satisfies the freeze-thaw resistance defined by JIS.

Detailed analysis is as follows.
The relative dynamic elastic modulus at the end of 10 cycles was 60% or higher in BR25-155 and BRS25-155, indicating high freeze-thaw resistance. In contrast, AR35-175 and AR35-155 decreased to 58% and BR35-155 decreased to 60%, which is considered to have decreased to the limit line of freeze-thaw resistance. On the other hand, recycled aggregate concrete having a water-cement ratio of 45% or more was greatly below 60% of the relative kinematic modulus at the end of the 4th cycle, and it was confirmed that cracks were generated on the surface of the cylindrical specimen. In addition, ordinary concrete (N55-175) had a relative kinematic modulus of 58% at the end of the 10th cycle, which was equivalent to AR35-175 and AR35-155. In general, it has been pointed out that low-quality recycled fine and coarse aggregates have a higher water absorption rate than ordinary aggregates, and the freeze-thaw resistance is very poor when the raw concrete is NonAE concrete. Similar results were confirmed in this experiment. Therefore, the recycled fine / coarse aggregate raw concrete treated in this experiment is likely to contain NonAE concrete.

  From the results of the above rapid freeze-thaw test, if the water-cement ratio is 35% or less, the relative dynamic elastic modulus is 60% or more at the end of 10 cycles even for concrete using low-quality recycled fine and coarse aggregates. It was confirmed that it could be secured.

e) Results of JIS Freeze-Thaw Test FIG. 15 and FIG. 16 show the relationship between the relative kinematic modulus and the mass reduction rate with the number of cycles obtained by the JIS method freeze-thaw test of series B recycled aggregate concrete. If the water cement ratio is 35% or less and the unit water volume is 155kg / m ³ or less according to the present invention, the freeze-thaw resistance of ordinary recycled aggregate concrete using all the low-quality recycled fine and coarse aggregate is normal. It was confirmed that it could be as secure as concrete.

Detailed analysis is as follows.
The relative dynamic elastic modulus at the end of 300 cycles was 96% for BR25-155 and 90% for BRS25-155. In contrast, R35-155 was 270 sac, and BR45-175 and BR45-155 had a relative dynamic elastic modulus of 60% or less at the end of 240 cycles.
On the other hand, ordinary concrete showed a high freeze-thaw resistance with a relative kinematic modulus of 75% at the end of 300 cycles.

Based on the above results, the results obtained from the rapid freeze-thaw test are almost the same as those of the JIS method freeze-thaw test, and only the relative dynamic elasticity that BR25-155 and BRS25-155 are considered as one of the criteria for freeze-thaw resistance. It can be said that it has sufficient freezing and thawing resistance despite satisfying a coefficient of 60% and being recycled aggregate concrete. Therefore, if the water-cement ratio is 35% or less and the unit water volume is 155kg / m ³ or less, even if it is recycled aggregate concrete using the whole amount of low-quality recycled fine and coarse aggregate, its freeze-thaw resistance is normal concrete. It was confirmed that it could be secured to the same extent as

  N55-175, BR45-175, and BR45-155 have a mass reduction rate at the end of 270 cycles ranging from 1.5% to 2%, indicating that they have been greatly scaled. On the other hand, the mass reduction rate at the end of 300 cycles was almost 0% for BR35-155 and BR25-155, and 1% for BRS25-155. In BR35-155, scaling does not occur due to the relatively small amount of air, but the relative dynamic elastic modulus after the 210th cycle rapidly decreases, cracks occur inside the concrete, and cracks increase as the number of cycles increases. It is thought that progress has been made.

The concrete scaling after the test is shown in Photo-2 in Fig. 17. BR35-155 and BR25-155 did not show concrete scaling even after 300 cycles. On the other hand, BR45-175 and BR45-155 were able to confirm the scaling of the concrete surface violently at the end of 270 cycles. BRS25-155 showed some scaling on the concrete surface at the end of 300 cycles compared to BR25-155. Also from the viewpoint of scaling, a water cement ratio of 35% and a unit water volume of 155 kg / m ³ are important blending conditions for ensuring the resistance to freezing and thawing of recycled aggregate concrete.

Relationship between various performances of recycled aggregate concrete and mixing factors Based on the results obtained in this experiment on recycled aggregate concrete using all recycled aggregates for fine aggregate and coarse aggregate, The relationship is shown in FIG. The thick solid line means a range that does not require special consideration in construction and durability at a water cement ratio and a nominal strength level in this range. The dotted line means a range in which there is a greater risk of problems in durability and construction performance unless some consideration is made in formulation and construction. An alternate long and short dash line means a range that needs some investigation depending on the construction conditions and member conditions.

It is important to devise the concrete mix design and construction method so as to enter the region of the thick solid line and the one-dot chain line in FIG.
When the water cement ratio of recycled aggregate concrete is reduced to 45%, the nominal strength level increases to 40 N / mm ^2, and it has the same strength and neutralization resistance as ordinary concrete with a water cement ratio = 55%. However, freezing and thawing resistance is not improved, and there is a large risk of occurrence of problems. The amount of drying shrinkage needs to suppress the unit water amount to 175 kg / m ³ or less.

On the other hand, when the water-cement ratio is reduced to 35% or less, the nominal strength level exceeds 50 N / mm ² and the concrete has high durability. In particular, in freeze-thaw resistance, there is no problem if the amount of air is 5% or more. There is no problem with neutralization resistance and drying shrinkage. However, when the water-cement ratio becomes small, the admixture is often used to make the slump and the unit water amount constant, and the viscosity becomes high, resulting in problems in construction performance. Regarding self-shrinkage, it is necessary to suppress the unit water amount to 155 kg / m ³ or less so that the unit cement amount does not increase.
From the above results, in order for the strength and durability of concrete using all recycled fine / coarse aggregates to have the same performance as concrete using ordinary aggregates, the water-cement ratio is 25-35% and the unit water volume May be 145 to 155 kg / m ³ . This blending condition is the same as the blending condition for high-strength concrete exceeding compressive strength of 100 N / mm ² , but the fact that the blending condition for high-strength concrete and recycled aggregate concrete is very interesting is very interesting.

The present invention can also be applied to the identification of raw concrete from which recycled aggregates are based.
Normally, the raw concrete that produces recycled aggregate is a concrete structure that has been built for decades. Therefore, it is difficult to determine the quality of the raw concrete, particularly whether it is AE concrete or NonAE concrete.
The freeze-thaw test of the JIS method requires days and labor for several months or more until a determination result of resistance to freezing and thawing of the target concrete is obtained. Based on the above considerations d) and e), the rapid freeze-thaw test is used to determine the freeze-thaw resistance of concrete using the target recycled aggregate without applying the freeze-thaw test by the JIS method. This makes it possible to easily check whether the recycled concrete concrete is AE concrete or NonAE concrete.

Furthermore, even if the raw concrete is NonAE concrete, it is possible to determine the blending conditions (water cement ratio and unit water volume) that can satisfy the freeze-thaw resistance in a short time by applying the rapid freeze-thaw test. is there.
In other words, even if it is unclear whether the raw concrete is AE concrete or NonAE concrete, the water cement ratio is 35% or less and the unit water volume is 155 kg / m ³ or less. There is a possibility of producing recycled aggregate concrete with durability.

It is a photograph of low quality recycled aggregates, where (A) shows a L-class recycled fine aggregate, and (B) shows a L-class recycled coarse aggregate. It is a table | surface which shows the outline | summary of the quality standard of reproduction | regeneration aggregate. It is a table | surface which shows the physical characteristic of a low quality reproduction | regeneration aggregate and a normal aggregate. It is a table | surface which shows the composition and fresh property of the concrete used for experiment. It is a graph which shows the ultrasonic propagation time measuring method and the frozen condition. It is a graph which shows the relationship between the compressive strength and age of series A recycled aggregate concrete and series B recycled aggregate concrete. It is a graph which shows the relationship between the compressive strength of the age of 28 days, and a cement water ratio. It is a graph which shows the relationship between the compressive strength of material age 28, and an elastic modulus. It is a graph which shows the relationship between the drying shrinkage | contraction strain of concrete, and dry material age. It is a graph which shows the relationship between water cement ratio and dry shrinkage. It is a graph which shows the relationship between unit amount of water and the amount of drying shrinkage. It is a graph which shows the relationship between self contraction distortion and time. It is a graph which shows the relationship between the neutralization depth of a promotion material age of 14 days, and a water cement ratio. It is a graph which shows the fall of the relative kinematic elastic modulus with the cycle number obtained by the quick freeze thaw test. It is a graph which shows the fall of the relative kinematic elastic coefficient with the cycle number obtained by the JIS method freeze-thaw test. It is a graph which shows the mass decreasing rate of concrete. It is a photograph which shows the scaling condition of the concrete after completion | finish of a test. It is a table | surface which shows the relationship between various mixing factors and the required performance of concrete.

Claims (4)

Consisting of cement, water and aggregate,
The total amount of the aggregate is recycled aggregate,
Recycled aggregate concrete characterized in that the blending conditions are a water cement ratio of 25 to 35% and a unit water amount of 145 to 155 kg / m ³ . The recycled aggregate concrete according to claim 1, wherein the recycled aggregate is a low-level treated recycled aggregate. The recycled aggregate concrete according to claim 1, wherein an admixture is added in an amount of 0.5 to 1.5% based on the amount of cement. Using all recycled aggregate as cement, water and aggregate,
Recycled aggregate characterized by blending conditions of water cement ratio: 25 to 35%, unit water amount: 145 to 155 kg / m ^3, and admixture added 0.5 to 1.5% with respect to cement amount and kneaded. Concrete manufacturing method.