JP4537807B2 - Freeze-thaw test method for recycled aggregate - Google Patents

Description

  The present invention relates to a test method capable of evaluating the freeze-thaw durability of a recycled aggregate used for concrete in the state of the recycled aggregate.

  When a concrete building was destroyed, a large amount of concrete demolition material was generated, which was reused as roadbed material or disposed of as landfill as waste material. However, from the viewpoints of future road construction reduction and environmental problems, it is desired to expand these uses. One example is the use of new concrete as an aggregate by crushing the waste concrete, that is, as a recycled aggregate.

  When using recycled aggregate, confirmation of freeze-thaw durability is extremely important as its quality. Determination of freeze-thaw durability is ascertained, for example, by manufacturing a concrete specimen using the target recycled aggregate and performing a freeze-thaw durability test according to JIS A l148 using this concrete specimen. However, the test requires a test period of at least 4 months, requires a dedicated freeze-thaw test apparatus, and the test cost is high.

  In the case of general natural aggregates, it is possible to give a measure of freeze-thaw durability by conducting a stability test using sodium sulfate in accordance with JIS A 1122. However, in the case of recycled aggregate, the result of the stability test does not correspond to the result of the freeze-thaw durability test. The reason for this is that the recycled aggregate is composed of raw aggregate and mortar attached to it, so that the cement component in the mortar is dissolved by the action of sodium sulfate, and the recycled aggregate has good freezing durability. However, since the deterioration occurs, it is considered that the result of the stability test does not correspond to the result of the freeze-thaw test.

In Patent Document 1, a concrete specimen similar to that used in the test of JIS A l148 can be rapidly and alternately cooled and frozen and heated and thawed repeatedly. It is possible to accurately and accurately quantify the degree of resistance change (that is, the state of deterioration) that occurs in the concrete specimen by conducting the test, and the heavy concrete specimen is removed from the specimen container. It is extremely easy to measure with significantly reduced test time without taking in and out each test, and it is possible to automatically measure the deterioration over time over the entire cycle. A durability test method for concrete specimens is disclosed. And here, durability of the concrete using recycled aggregate is also examined.

  Furthermore, in Patent Document 2, the concrete member is cooled, AE (Acoustic Emission) generated by freezing of moisture in pores existing in the concrete is measured, and the correlation between the count number and the cooling temperature is obtained. Estimate the pore size distribution, measure the AE by cooling a concrete component with a predetermined composition, and determine the correlation between the count and the cooling temperature, and compare this correlation with the reference correlation determined in advance. Thus, it is described that the deterioration state of the concrete member is determined from the difference.

  However, these methods are also not simple because the test equipment and test costs are high.

Japanese Patent Laid-Open No. 11-133209 Japanese Patent Laid-Open No. 05-203560

  In view of such a situation, the subject of the present invention is a test method that can easily evaluate freeze-thaw durability with high accuracy in a short period of time without using a special device while remaining in the state of recycled aggregate. Is to provide.

In order to solve the above-mentioned problems, the present invention is a method for testing the freeze-thaw durability of a recycled aggregate used for concrete, in which a predetermined amount of the recycled aggregate sample is stored, and the sample is immersed Put the container filled with water to -20 ± 3 ℃ , freeze until the water in the container is completely frozen, take out the frozen container from the freezer, and keep the container in the 20 ± 3 ℃ water tank The container was kept in the water tank until the ice in the container was completely melted, and this freezing and thawing was repeated 1 to 5 times in a freezer and several hours in the water tank for 5 to 20 times . The sample is later taken out from the container and dried, and the particle size distribution of the dried sample is measured, and the freeze-thaw durability is evaluated by comparing the particle size distribution with the particle size distribution of the sample before the test.

  According to the present invention, when concrete is crushed and the crushed concrete is used as recycled aggregate, the freeze-thaw durability can be easily reduced in a short time without using a special device. Can be evaluated. That is, according to the present invention, the durability of the recycled aggregate can be easily evaluated in a short period of time.

  The basic idea of the present invention is to evaluate the freeze-thaw durability of the regenerated aggregate by giving the regenerated aggregate the same action as the freeze-thaw action that actually occurs. In the freeze-thaw test (JIS A 1148) using concrete specimens, it is necessary to give 300 cycles of freeze-thaw action. However, for recycled aggregates, it deteriorates with relatively few freeze-thaw actions of around 10 cycles. Therefore, it is possible to test in a short time using a freezer and a water tank without using a special device.

  In the present invention, as shown in FIG. 1, the raw concrete 1 is crushed, the crushed concrete is used as recycled aggregate, a recycled aggregate sample 2 is stored in a container 3, and the container 3 is filled with water to prepare the sample 2. Immerse in water, put the container 2 in which the sample 2 is stored and filled with water alternately into the freezer 4 and the water tank 5, repeat freezing and thawing. After repeating a predetermined number of times, remove the sample from the container and dry it. The particle size distribution of the prepared sample is measured, and the freeze-thaw durability is evaluated by comparing the particle size distribution with the particle size distribution of the sample before the test.

The test procedure is as follows.
(1) Recycled aggregates, for example, sieved to a single particle size such as 5-10 mm, 10-15 mm, 15-20 mm, etc. are used as test samples. As a simple method, only a specific single particle size (for example, 15-20 mm) may be used as a test sample.
(2) Put a sample with a single particle size into a plastic container with a volume of about 500 ml, for example, fill the container with water, immerse the sample so that it is completely submerged, cover the container with a lid, etc. It is preferable that the sample and water have a structure that does not spill out.
(3) Place the sample in a freezer while still in the container and freeze until the water in the container is completely frozen. The freezing temperature is preferably about −20 ± 3 ° C., for example, considering the performance of a general freezer.
(4) Remove the completely frozen container from the freezer and submerge it in the water tank. Keep the container in the water tank until the ice in the container is completely thawed. The water temperature in the water tank is preferably about 20 ± 3 ° C. in consideration of the water temperature of a general concrete curing water tank.
(5) Repeat (3) and (4) above alternately. Although the cycle time varies depending on the size of the container and the like, in consideration of the certainty and simplicity of the work, for example, it is preferable to set the cycle to 16 hours in the freezer and about 8 hours in the water tank, and one cycle per day.
(6) After repeating a predetermined number of times, remove the sample from the container and dry it. At this time, the number of repetitions is preferably about 5 to 20 times.
(7) Screen the dried sample and measure the particle size distribution.
(8) The freeze-thaw durability of the recycled aggregate is evaluated from the difference in particle size distribution before the test (single particle size) in (1) and the particle size distribution of the sample after the test in (7).

Next, the present invention will be described specifically by way of examples. These examples do not limit the present invention, and each implementation condition can be changed as appropriate.
(1) Six types of raw concrete were manufactured under the conditions shown in Table 1 below.

In Table 1, W / C (%) = water / cement (%), and three types of 55%, 70%, and 85% with different mass ratios of water and cement are prepared. Air (%) is There are 6 types of raw materials as shown in Table 1 in which 2 types are prepared as (A) where the air amount is 4.5%, and (N) where the air amount is 2% or less. Concrete was manufactured. In Table 1, Gmax represents the maximum coarse aggregate size, s / a represents the fine aggregate ratio, S represents the fine aggregate amount, and G represents the coarse aggregate amount.
(2) A freeze-thaw test was performed on the raw concrete in accordance with JIS A l148.
(3) Six types of raw concrete were crushed to produce six types of recycled coarse aggregate.
(4) Use the 6 kinds of recycled coarse aggregates obtained in (3) above, and use the recycled aggregates shown in Table 2 under the condition of W / C = 55% and air volume (4.5%). Six types of concrete were produced.

In Table 2, each symbol represents the same as in Table 1.

(5) A freeze-thaw test was performed on the recycled aggregate concrete in accordance with JIS A l148.
(6) Aggregate stability tests were performed on the recycled coarse aggregate produced in (3) with a particle size of 15-20 mm in accordance with JIS A 1122.
(7) The “recycled aggregate freeze-thaw test” was performed on the recycled coarse aggregate produced in (3) with a particle size of 15-20 mm under the following conditions.

Condition of “freeze-thaw test for recycled aggregate” Sample volume to be used for test: 75Og
Container volume: Approximately 5OOcc
Freezing conditions: -20 ° C freezer, 16 hours Thawing conditions: 20 ° C water bath, 8 hours Repeat count: 10 times

(Test results)
The results of the freeze-thaw test of the raw concrete are shown in FIG. In addition, Fig. 3 shows the results of a freeze-thaw test of concrete using recycled aggregate. In any case, the relative kinematic modulus is good for 55A, 70A, 85A with air volume (4.5%) in the raw concrete, and for 55N, 70N, 85N without air volume (2% or less). Fell. From this result, it can be seen that the freeze-thaw durability of the recycled aggregate greatly depends on the amount of air in the raw concrete, that is, the amount of air in the adhered mortar of the recycled aggregate.
The results of the stability test are shown in FIG. As the result, the higher the water / cement ratio, the worse the result, and the relationship with the presence or absence of the amount of air in the raw concrete was not observed, indicating a tendency different from the results shown in FIGS.

The result of “freezing and thawing test of regenerated aggregate” is shown in FIG.
This result shows that the aggregate with air in the raw concrete is less fragmented and has good durability, and the aggregate that does not have air in the raw concrete is often degraded. The result was obtained. That is, this result corresponds to the result shown in FIGS. 2 and 3, and the freeze-thaw durability of the recycled aggregate can be evaluated by the test method of the present invention.

  According to the present invention, the durability of the regenerated aggregate can be evaluated easily and inexpensively in a short period of time, so that the use of the regenerated aggregate is expanded, thereby contributing greatly to the construction of a recycling society.

It is a flowchart which shows the outline | summary of the freeze thaw test of the reproduction | regeneration aggregate of this invention. It is a graph which shows the freeze-thaw test result of raw concrete. It is a graph which shows the freeze-thaw test result of the concrete using recycled aggregate. It is a graph which shows the result of having implemented the stability test with respect to the thing of particle size 15-20mm among reproduction aggregates. It is a graph which shows the result of having carried out the freezing and thawing test with respect to the particle size of 15-20 mm among reproduction | regeneration aggregates.

Explanation of symbols

1 Raw concrete 2 Sample (recycled aggregate)
3 Container 4 Freezer 5 Water tank

Claims (1)

A method for testing freeze-thaw durability of recycled aggregate used in concrete,
A container containing a predetermined amount of recycled aggregate sample and filled with water for immersing the sample is placed in a freezer at −20 ± 3 ° C. and frozen until the water in the container is completely frozen. Remove the container from the freezer and submerge it in a 20 ± 3 ° C water tank as it is. Keep the container in the water tank until the ice in the container is completely thawed. Repeat for 5-20 times in a water tank for several hours, then remove the sample from the container, dry it, measure the particle size distribution of the dried sample, and compare the particle size distribution with the particle size distribution of the sample before the test A freeze-thaw test method for recycled aggregate, characterized by evaluating freeze-thaw durability.