KR102629091B1 - Spalling-resistant high-strength concrete composition with PP fiber and PET mesh chips - Google Patents

Abstract

The present invention relates to a high-strength, explosion-resistant concrete composition in which waste PET nets generated in large quantities at construction sites are recycled and applied as a means of preventing concrete explosion.
The present invention is a high-strength concrete composition with a design standard compressive strength of 50 MPa or more, which is characterized by mixing 0.3 to 0.5 kg/m3 of PP fiber and 0.2 to 0.4 kg/m3 of PET mesh chips obtained by cutting waste PET mesh into a predetermined size. Provides a “explosion-resistant high-strength concrete composition.”

Description

Spalling-resistant high-strength concrete composition with PP fiber and PET mesh chips}

The present invention relates to a high-strength, explosion-resistant concrete composition in which waste PET nets generated in large quantities at construction sites are recycled and applied as a means of preventing concrete explosion.

PET fiber stands for Polyethylene Terephthalate and is one of the polyester fibers. PET fiber has excellent thermoplasticity and durability, and is used in various fields such as clothing, bedding, and automobile interior materials due to its high hardness and light resistance.

In addition, PET fiber is lightweight and has high tensile strength, so it is suitable for use as a safety net. It is manufactured into nets of various sizes and shapes, and is widely used as fall prevention nets and vertical protection nets at construction sites.

However, it was found that PET nets discarded after use at construction sites have not been recycled until 2018 due to problems with various colors, large amounts of foreign substances, and selective disposal and collection. Related industries (companies) that are actually recycling ) was found to be absent (Hyundae Cho, Jae-dong Jeong, "Study on the feasibility of recycling vertical protection nets used at construction sites", J. Korea Inst. Build. Constr. Vol. 18, No. 5. p.486. 2018.10.).

Due to the nature of the PET material, waste PET nets cannot be extruded using current domestic field technology due to the attachment of various foreign substances. Although they can be recycled through extrusion (yarn spinning process), due to the nature of the extrusion method, foreign substances attached to the waste PET net are removed. It must be completely removed, but in the case of waste PET mesh used at construction sites, the cost of removing it is high and it is difficult to completely remove it due to hardened concrete and various foreign substances attached. In addition, recycling has been considered difficult from a practical and economic perspective due to the generation of secondary waste and its disposal costs due to recycling (Hyundae Cho, Jae-dong Jeong, p. 486 of the above paper).

On the other hand, high-strength concrete with a compressive strength of 50 MPa or more has small voids within the concrete structure to develop high strength, so in the event of a fire, there may be a problem of spalling, in which the concrete surface falls off due to internal water vapor pressure. Accordingly, when applying high-strength concrete of 50 MPa or more to columns, beams, etc., it is essential to secure fire resistance, and detonation control technology is being applied in which fibers are mixed into concrete and the incorporated fibers evaporate in the event of a fire to form an internal water vapor pressure discharge path.

To control the spalling of high-strength concrete, 0.9 kg/㎥ of PP (Polypropylene) fiber is usually mixed (registered patent 10-1061950, etc.), and 0.6 to 0.7 kg/㎥ of PP fiber and nylon fiber are mixed. Improved technologies (patent registration 10-1064558, etc.) are also known to maintain spalling control performance while reducing the amount of fiber mixed, and to improve the fluidity of the concrete composition compared to when only PP fibers are applied.

As shown in [Figure 1], PET fibers are found to have similar thermal properties (TGA analysis: evaporation amount of fibers (related to explosion control performance) according to temperature increase) with nylon fibers, and therefore, in the present invention, waste PET nets are used to prevent high-strength concrete explosions. We reviewed ways to use the fiber for control.

Among the previous studies, there was a study on the strength and crack resistance characteristics of concrete mixed with recycled PET fibers produced from waste PET bottles, but this was unrelated to waste PET network recycling or explosion control.

1. Registered Patent 10-0644083 “Fiber for controlling concrete detonation” 2. Publication Patent No. 10-2011-0078937 “Concrete with excellent heat resistance and fire resistance containing reinforcing fibers” 3. Registered Patent 10-1061950 “Ultra-high-strength, highly fire-resistant concrete for reinforced concrete structures” 4. Registered Patent 10-1064558 “Composition of cement binder for highly fire-resistant, ultra-high-strength, super-fluid concrete”

1. Hyundae Cho, Jaedong Jeong, "Study on the feasibility analysis of recycling of vertical protection nets used at construction sites", J. Korea Inst. Build. Constr. Vol. 18, no. 5. pp.479~488. 2018.10. 2. Seong-Bae Kim, Hyun-Young Kim, Na-Hyeon Lee, and Jang-Ho Kim, "Strength and crack resistance characteristics of fiber-reinforced concrete mixed with recycled PET fibers", Journal of Structural Diagnostics, Vol. 14, No. 1, pp.102-108. 2010.01.

The present invention is intended to provide a method of recycling waste PET nets generated in large quantities at construction sites, and the purpose of the present invention is to provide a high-strength, high-strength concrete composition that is burst-resistant using waste PET nets as a means of controlling concrete spalling.

In order to solve the above-mentioned problems, the present invention is a high-strength concrete composition with a compressive strength of 50 MPa or more as a design standard, comprising 0.3 to 0.5 kg/m3 of PP fiber and 0.2 to 0.4 kg/m3 of PET network chips obtained by cutting waste PET mesh into a predetermined size. Provided is a “cracking-resistant high-strength concrete composition characterized by mixing.”

The PET mesh chip can be manufactured in a rectangular shape with a width of 2.5 to 3.5 mm and a length of 7 to 9 mm, and the waste PET mesh can be passed through a fixed blade to cut the PET fibers without unraveling.

The PET network chip can be added to the dry mixing process of binder, fine aggregate, and coarse aggregate, and 30 to 70 wt% can be released and dispersed into PET fibers by friction during the dry mixing process.

According to the present invention, by recycling waste PET nets generated in large quantities at construction sites and applying them as a means to control spalling of high-strength concrete, it is possible to reduce environmental load, improve economic efficiency, and improve fire resistance performance of high-strength concrete compositions.

[Figure 1] is a graph showing the results of TGA analysis for PP fiber, nylon fiber, and PET fiber.
[Figure 2] is a photo taken after rubbing the PET net chip by hand, simulating the state before and after dry mixing of the PET net chip.
[Figure 3] is a photograph of a simple fire resistance test process for a specimen to which the present invention is applied.
[Figure 4] is a graph showing the temperature change over time inside the heating furnace during a simple fire resistance test on a specimen to which the present invention was applied.
[FIGS. 5] to [FIG. 15] show fire resistance performance test reports from the Disaster Prevention Testing Institute for pillar members to which the present invention is applied, attached for each chapter.

The present invention is a high-strength concrete composition with a compressive strength of 50 MPa or more as a design standard, and consists of 0.3 to 0.5 kg/㎥ of PP fiber and 0.2 to 0.4 kg/㎥ of PET network chips cut from waste PET net into 2.5 to 3.5 mm width and 7 to 9 mm length. Provides a burst-resistant, high-strength concrete composition characterized by mixing ㎥.

As mentioned in the [Background Technology of the Invention] section, securing fire resistance performance is essential when applying high-strength concrete of 50 MPa or more to columns, beams, etc.

In the event of a fire, when concrete is heated in the temperature range of 100~200℃, the moisture inside the concrete evaporates and vapor pressure is generated. If explosion control measures are not taken, water vapor condenses and explodes in the temperature range of 300~400℃. . This is because high-strength concrete requires a large amount of binder (580 to 680 kg/㎥) to develop strength, while the concrete matrix is tightly filled.

As shown in [Figure 1], PP fibers, which are widely used for detonation control, are formed at a melting point of 300°C or lower and are mostly lost before reaching 400°C. Therefore, by mixing PP fibers into the concrete, they are prevented from occurring before detonation occurs. It is necessary to form a water vapor pressure discharge path. In the present invention, 0.3 to 0.5 kg/㎥ of PP fiber is incorporated into the high-strength concrete composition with a design standard compressive strength of 50 MPa or more.

However, since water vapor continues to be generated even when concrete is heated above 400℃, instead of reducing the amount of PP fibers, nylon fibers, which vaporize as their melting point is formed around 400℃, are mixed together to achieve a gradual buffering of the water vapor pressure at each heating temperature. By doing so, the efficiency of the detonation control effect can be increased and the fluidity deteriorated by the inclusion of PP fibers can be compensated for.

The present invention derives a plan to recycle waste PET nets generated in large quantities at construction sites, and is based on the fact that the thermal properties of PET fibers are similar to nylon fibers.

Even when comparing the yarn prices of PP fiber, nylon fiber, and PET fiber, the economic feasibility of PET fiber is significantly higher at about 5:7:2, and recycling waste PET net can not only improve economic efficiency but also contribute to reducing environmental load.

However, PET nets used as vertical nets and fall prevention nets attached to gang forms at construction sites are made up of multiple PET fiber bundles forming one yarn, and these yarns are arranged to form the weft and warp yarns, and are woven with a relatively thin thickness. It is woven with thread and made into a net. The explosion control mechanism caused by fiber mixing ensures that the internal water vapor pressure is also discharged evenly while the fibers are evenly distributed within the concrete matrix. Therefore, even if the PET net is woven with PET fibers, it remains in the fiber state as long as the network weave structure is maintained. It is difficult to expect the same explosion control mechanism as when mixed into concrete.

However, it is technically and economically close to impossible to collect waste PET nets, dismantle the weaving structure of the nets, and turn them into fibers. Accordingly, in the present invention, PET network chips in the form of 'chips', which are waste PET networks cut to a predetermined size, are added to the concrete composition, and the PET network chips are input into the dry mixing process of binder, fine aggregate, and coarse aggregate, During the mixing process, 30 to 70 wt% was loosened and dispersed into PET fibers by friction. [Figure 2] is a photo taken after rubbing the PET net chip by hand, simulating the state before and after dry mixing of the PET net chip. Accordingly, a new detonation control mechanism allows the PET fibers released and dispersed from the PET network chip to gradually discharge the water vapor generated at each heating temperature along with the PP fibers, and the part remaining in the chip state functions as a damper for internal water vapor pressure. I got this to work.

In the present invention, as described above, instead of mixing 0.3 to 0.5 kg/m3 of PP fiber than in the general case, 0.2 to 0.4 kg/m3 of PET network chips cut from waste PET net to a predetermined size are mixed. The specific gravity of the PET network chip is measured in the range of 1.3 to 1.4.

The size of the PET network chip can be set as needed, but an excessive size is disadvantageous for the development of the dispersion and explosion control mechanism of the PET network chip, and an undersized size causes difficulty in cutting work. In addition, the PET network chip is partially unwound and dispersed into PET fiber strands during the process of dry mixing the binder, coarse aggregate, and fine aggregate, so when the PET network chip is manufactured in a rectangular shape, the PET fibers that are unwound and dispersed are also divided into two types based on length. When long fibers and short fibers are mixed, rather than when all dispersed PET fibers have the same length, the water pressure discharge path within the concrete matrix is formed more evenly.

Therefore, the PET network chip is manufactured in a rectangular shape with a length of 2.5 to 3.5 mm and a length of 7 to 9 mm, and the PET fiber strands that are unraveled and dispersed during the dry mixing process are divided into long fibers with a length of 7 to 9 mm and a length of 2.5 to 3.5 mm. It is desirable to separate them into single fibers. In addition, by applying the length of the mixed PP fiber in the range of 10 to 15 mm, it is possible to distribute the water pressure discharge path by combining the fiber lengths at each stage.

In addition, since the PET network chip is literally in a chip state, concerns about entanglement between fibers during the mixing process are excluded. As the dry mixing progresses, the PET fibers are released and dispersed in the PET network chip over time, so entanglement during the mixing process is also minimized. It does not cause problems with acidity or fluidity.

When a waste PET network is cut by pressing down the blade using a blade method, the cut surface becomes rough and the PET fibers are released in advance. When the edge of the PET network chip is released, not only the fibers are entangled, but even the aggregate is entangled in the PET network chip, reducing dispersibility and fluidity. greatly deteriorated. Accordingly, in the present invention, a process is applied in which the waste PET net is cut as it passes by a fixed blade to maintain a state in which the PET fibers do not unravel from the PET net chip, and as the dry mixing progresses, the PET fibers can be unwound and dispersed. .

Below, the present invention will be described along with specific test examples.

[Table 1] below examines the basic concrete properties (flow, compressive strength) by adding spalling control fiber to a high-strength concrete composition with a design strength (28-day compressive strength) of 60 MPa.

In the first test, the binder amount was fixed at 650 kg/㎥, a test specimen (Plain) without fiber mixed in, a test specimen mixed with 0.9 kg/㎥ PP fiber (PP 0.9) as applied as a normal detonation control measure, Instead of reducing the amount of PP fiber mixed to 0.5 kg/㎥, 0.4 kg/㎥ of PET fiber was added (PP 0.5 + PET-F 0.4). In the above PP 0.5 + PET-F 0.4 test specimen, PET net chips (waste PET) were used instead of PET fiber. The net was cut into a rectangle measuring 3 cm wide and 8 cm long; the same applies hereinafter) and the test specimen (PP 0.5 + PET-C 0.4) was added. The amount of PP fiber was further reduced to 0.3 kg/㎥, and the amount of PET network chips was also reduced to 0.3 kg. Test specimens (PP 0.3 + PET-C 0.3) reduced to /㎥ were separately tested.

When compared to the Plain test specimen, the compressive strength of the remaining test specimens at 7 days of age showed no significant change at the same level (slightly increased when PET fiber and PET network chips were applied), but the compressive strength at 28 days of age showed a slight decrease. However, the design strength standard of 60 MPa was met in all test examples. The flow value decreased in the PP 0.9 test specimen and further decreased in the PP 0.5 + PET-F 0.4 test specimen, so it was found that applying PET fiber was disadvantageous in terms of fluidity. However, the flow value in the PP 0.5 + PET-C 0.4 test specimen with PET network chips was found to be low. It was found that the fluidity was partially restored as the value increased, and the flow value of the PP 0.3 + PET-C 0.3 test specimen was the same as that of the plain specimen.

In the second test, the plain test specimen was mixed with 0.5 kg/㎥ of PP fiber and 0.2 kg/㎥ of PET net chips (PP 0.5 + PET-C 0.2), the amount of PP fiber was lowered to 0.3 kg/㎥ and PET net chips were added to 0.2 kg. Test specimens mixed with /㎥ (PP 0.3 + PET-C 0.2) were separately tested. For the PP 0.5 + PET-C 0.2 test specimen, the change in physical properties was examined by increasing the binder amount to 680 kg/㎥.

When compared to the Plain test specimen, the compressive strength at 7 days of age for all the remaining test specimens was found to be at the same level, and the compressive strength at 28 days showed a slight decrease within the range where the design standard strength was met in the PP 0.5 + PET-C 0.2 test specimen. , as the binder amount was increased to 680 kg/㎥, it was found to be equivalent to the plain test specimen. It is understood that the flow value is lower than Plain, but increases compared to the case where only PP fibers are mixed.

The explosion control performance of the above test specimens was confirmed through a simple fire resistance test as shown in [Figure 3]. [Figure 4] is a graph showing the temperature change over time inside the heating furnace. Temperature changes inside the heating furnace were controlled according to KS F 2257-1 standards.

In the first and second tests above, no explosion occurred in all test specimens except for the Plain specimen, but there were differences in the state of surface cracking for each test specimen. However, since surface cracks are not an indicator of fire resistance performance, the test results are for reference only and do not have much meaning.

[Table 2] below shows the status after the simple fire resistance test for each specimen. It was confirmed that no explosion occurred in all test specimens except the Plain specimen. In particular, the PP 0.5 + PET-C 0.2 specimen showed no surface cracks, so it is believed that a better response was achieved than the PP 0.9 specimen to which conventional explosion control measures were applied.

In accordance with the Ministry of Land, Transport and Maritime Affairs Notice No. 2008-334, “Fire resistance performance management standards for high-strength concrete columns and beams,” a fire resistance performance confirmation test (B) was conducted on a column member (member name: C19) to which PP fiber and PET mesh chips were applied in combination according to the present invention. Heating for 3 hours was carried out.

[Table 3] below is the concrete mix table of the test specimen for manufacturing 60 MPa high-strength concrete column members. The mix was designed with a maximum coarse aggregate size of 25 mm, a 28-day compressive strength of 60 MPa, and a slump flow of 600 mm. The binding material of the test specimen concrete is 477 kg/㎥ of cement, 135 kg/㎥ of blast furnace slag powder (S/P), and 68 kg/㎥ of fly ash (F/A), for a total of 680 kg/㎥. It is desirable to set the wave mixture ratio at 25 to 28 wt%, and for this test concrete, the mixing water amount was set to 179 kg/㎥, resulting in a wave mixture ratio of 26.3 wt%. The amount of fine aggregate can be set in the range of 600~650 kg/㎥ and 800~850 kg/㎥, and for this test concrete, the amount of fine aggregate was 648 kg/㎥, the amount of coarse aggregate was kg/㎥, and the fine aggregate rate was 44.0 vol%. It is desirable to add water reducing agent (AD) in the range of 1 to 2 wt% compared to the binder, and for this test concrete, 8.17 kg/㎥ of water reducing agent (AD) was added at 1.2 wt% compared to the binder.

The column member was manufactured with a width of 1,100 mm, a length of 1,000 mm, and a height of 1,500 mm, and the reinforcing bar cover thickness of 50 mm was secured and placed, and thermocouples for temperature measurement were installed at 9 points in the 750 mm height section ([Figure 10] (see production drawing shown in). The test was conducted indoors at a temperature of 6 ± 1 ℃ and a relative humidity of 53 ± 2 %RH, and it was found to satisfy the 3-hour fire resistance performance.

[Figures 5] to [Figure 15] show the Disaster Prevention Testing Research Institute's test reports for the above fire resistance performance confirmation test attached by chapter. It should be noted that the "PET fiber" indicated on page 3 of the test report attached as [Figure 7] is a PET mesh chip obtained by cutting waste PET mesh into a rectangular shape of 3 cm wide and 8 cm long according to the present invention.

Although the present invention has been described in relation to test examples as mentioned above, various modifications and variations are possible without departing from the gist of the present invention, and can be used in various fields. Accordingly, the scope of the present invention includes modifications and variations falling within the true scope of the foregoing invention.

Not applicable

Claims (4)

A high-strength concrete composition with a design standard compressive strength of 50 MPa or more,
PP fiber 0.3~0.5 kg/㎥ and
An explosion-resistant, high-strength concrete composition characterized by mixing 0.2 to 0.4 kg/㎥ of PET mesh chips, which are waste PET nets cut into rectangular shapes measuring 2.5 to 3.5 mm in width and 7 to 9 mm in length.
delete In paragraph 1:
The PET network chip is an explosion-resistant, high-strength concrete composition, characterized in that the waste PET network passes through a fixed blade and is cut in a state in which the PET fibers are not unraveled.
In paragraph 1 or 3:
The PET network chip is input into the dry mixing process of binder, fine aggregate, and coarse aggregate, and 30 to 70 wt% is released and dispersed into PET fibers by friction during the dry mixing process. A high-strength concrete composition that resists bursting.