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  1. ๊ฒฝ๊ธฐ๋Œ€ํ•™๊ต ์ผ๋ฐ˜๋Œ€ํ•™์› ๊ฑด์ถ•๊ณตํ•™๊ณผ ์„์‚ฌ๊ณผ์ • (Graduate Student, Department of Architectural Engineering, Kyonggi University Graduate School, Seoul 03746, Rep. of Korea)
  2. ๊ฒฝ๊ธฐ๋Œ€ํ•™๊ต ๊ฑด์ถ•๊ณตํ•™๊ณผ ๊ต์ˆ˜ (Professor, Department of Architectural Engineering, Kyonggi University, Suwon 16227, Rep. of Korea)



๊ท ์—ด ์น˜์œ , ๋ฐ•ํ…Œ๋ฆฌ์•„, ํ™˜
crack healing, bacteria, pellet

1. ์„œ ๋ก 

์ฝ˜ํฌ๋ฆฌํŠธ ๊ตฌ์กฐ๋ฌผ์—์„œ ๊ท ์—ด์˜ ์ œ์–ด๋Š” ์žฌ๋ฃŒ ๋ฐ ํ™˜๊ฒฝ์  ์š”์ธ ๋“ฑ์œผ๋กœ ์‰ฝ์ง€ ์•Š๋‹ค. ์ฝ˜ํฌ๋ฆฌํŠธ ๊ตฌ์กฐ๋ฌผ์—์„œ ๋ฐœ์ƒ๋œ ๊ท ์—ด์€ ์ˆ˜๋ถ„ ๋ฐ ์œ ํ•ด ์ด์˜จ๋“ค์˜ ๊ธ‰๊ฒฉํ•œ ๋‚ด๋ถ€์œ ์ž…์˜ ์›์ธ์ด ๋˜๋ฉฐ, ์ด๋Š” ์‹œ๋ฉ˜ํŠธ ์ˆ˜ํ™”์ƒ์„ฑ๋ฌผ์˜ ์—ดํ™” ๋ฐ ์ฒ ๊ทผ ๋ถ€์‹์„ ๋™๋ฐ˜ํ•œ๋‹ค(Lee and Park 2019). ์ด์— ๋”ฐ๋ผ ์ฝ˜ํฌ๋ฆฌํŠธ ๊ตฌ์กฐ๋ฌผ์—์„œ ๊ท ์—ด์ œ์–ด์— ๋Œ€ํ•œ ์—ฐ๊ตฌ ๋ฐ ๊ธฐ์ˆ ์ˆ˜์š”๋Š” ์ง€์†์ ์ด๋‹ค. ์ตœ๊ทผ์—๋Š” ์ฝ˜ํฌ๋ฆฌํŠธ ๊ตฌ์กฐ๋ฌผ์˜ ์œ ์ง€๊ด€๋ฆฌ ์ตœ์†Œํ™” ์ธก๋ฉด์—์„œ ๊ท ์—ด์„ ์Šค์Šค๋กœ ์น˜์œ ํ•˜์—ฌ ์ˆ˜๋ณตํ•˜๋Š” ์ž๊ธฐ์น˜์œ  ์ฝ˜ํฌ๋ฆฌํŠธ ๊ธฐ์ˆ ์—ฐ๊ตฌ๊ฐ€ ๋งŽ์€ ๊ด€์‹ฌ์„ ๋ฐ›๊ณ  ์žˆ๋‹ค(Park et al. 2020).

์ž๊ธฐ์น˜์œ  ์ฝ˜ํฌ๋ฆฌํŠธ ๊ธฐ์ˆ ์€ ํฌ๊ฒŒ ์ž๊ธฐ์น˜์œ  ์†Œ์žฌ ์ข…๋ฅ˜์— ๋”ฐ๋ผ ๋ฌด๊ธฐ๊ณ„ ๋ฐ ๋ฐ•ํ…Œ๋ฆฌ์•„๋ฅผ ํ™œ์šฉํ•œ ๊ธฐ์ˆ ๋กœ ๋ถ„๋ฅ˜๋œ๋‹ค. ๋ฌด๊ธฐ๊ณ„ ํ˜ผํ•ฉ์žฌ๋ฃŒ ํ™œ์šฉ ๊ธฐ์ˆ ์€ ์น˜์œ ์†Œ์žฌ๋กœ ํŒฝ์ฐฝ์žฌ, ํŒฝ์œค์žฌ ๋ฐ ๊ฒฐ์ •์ด‰์ง„์ œ์™€ ํ•จ๊ป˜ ์‹œ๋ฉ˜ํŠธ ๋Œ€์ฒด ์žฌ๋ฃŒ ๋“ฑ์„ ์ด์šฉํ•˜์—ฌ ์ž๊ธฐ์น˜์œ  ์„ฑ๋Šฅ์„ ํ–ฅ์ƒ์‹œํ‚จ๋‹ค. ๋ฌด๊ธฐ๊ณ„ ํ˜ผํ•ฉ์žฌ๋ฃŒ์˜ ์น˜์œ ์„ฑ๋Šฅ ๋ฐœํ˜„์€ ๋ฐœ์ƒ๋œ ๊ท ์—ด ์‚ฌ์ด๋กœ ์นจํˆฌ๋œ ์ˆ˜๋ถ„๊ณผ ๋ฌด๊ธฐ๊ณ„ ํ˜ผํ•ฉ์žฌ๋ฃŒ๊ฐ€ ๋ฐ˜์‘ํ•˜์—ฌ ๋‚ด๋ถ€์— ์นจ์ „๋ฌผ์„ ์ƒ์„ฑํ•˜์—ฌ ๊ท ์—ด์„ ์ถฉ์ง„์‹œํ‚ค๋Š” ์›๋ฆฌ์ด๋‹ค(Park and Lee 2020). ๋ฐ•ํ…Œ๋ฆฌ์•„๋ฅผ ํ™œ์šฉํ•œ ์ž๊ธฐ์น˜์œ  ๊ธฐ์ˆ ์€ ๋ฐ•ํ…Œ๋ฆฌ์•„์˜ ๋Œ€์‚ฌ์ž‘์šฉ(์š”์†Œ ๊ฐ€์ˆ˜๋ถ„ํ•ด, ํ˜ธํก ๋“ฑ)์„ ํ†ตํ•ด ์ƒ์„ฑ๋œ ์ƒ์ฒด๊ด‘๋ฌผ(microbiologically induced calcium carbonate precipitation)๋กœ ๊ท ์—ด์„ ์น˜์œ ํ•˜๋Š” ๋ฉ”์ปค๋‹ˆ์ฆ˜์„ ๊ฐ–๋Š”๋‹ค(Son et al. 2020). ๋ฌด๊ธฐ๊ณ„ ์žฌ๋ฃŒ๋“ค์„ ํ™œ์šฉํ•œ ์ž๊ธฐ์น˜์œ  ๊ธฐ์ˆ ์€ ์žฌ๋ฃŒ์˜ ์ˆ˜ํ™”๋ฐ˜์‘ ์ง€์†์„ฑ์˜ ํ•œ๊ณ„๋กœ ์žฅ๊ธฐ์ ์ธ ๊ท ์—ด์น˜์œ ์—๋Š” ๋ถˆ๋ฆฌํ•˜๋‹ค๋Š” ๋ฌธ์ œ๊ฐ€ ์žˆ๋‹ค(Park et al. 2020). ๋ฐ•ํ…Œ๋ฆฌ์•„ ์ž๊ธฐ์น˜์œ  ๊ธฐ์ˆ ์€ ์ฝ˜ํฌ๋ฆฌํŠธ์˜ ๊ฐ•์•Œ์นผ๋ฆฌ์„ฑ ํ™˜๊ฒฝ ๋ฐ ๊ณต๊ทน๊ตฌ์กฐ๊ฐ€ ๋ฏธ์„ธํ•œ ์‹œ๋ฉ˜ํŠธ ๋ฉ”ํŠธ๋ฆญ์Šค ๋‚ด์—์„œ ๋ฐ•ํ…Œ๋ฆฌ์•„์˜ ์ƒ์žฅ๊ณผ ๋ฒˆ์‹์„ ํ™•๋ณดํ•˜๋Š” ๊ฒƒ์ด ์–ด๋ ค์šฐ๋ฉฐ, ํŠนํžˆ ๊ท ์—ด๋ฐœ์ƒ ์ดˆ๊ธฐ์— ์ƒ์ฒด๊ด‘๋ฌผ ํ˜•์„ฑ ์†๋„๊ฐ€ ๋Š๋ ค ์น˜์œ  ์„ฑ๋Šฅ ๋ฐœํ˜„์ด ๋ฏธ์•ฝํ•˜๋‹ค(Jang et al. 2020). ์ด์— ๋”ฐ๋ผ ๊ท ์—ด๋ฐœ์ƒ ์‹œ ๋‹จ๊ธฐ ๋ฐ ์žฅ๊ธฐ์ ์œผ๋กœ ์•ˆ์ •์ ์ธ ๊ท ์—ด์น˜์œ  ์„ฑ๋Šฅ๋ฐœํ˜„ ๋ฐ ๊ท ์—ด์น˜์œ  ํ–ฅ์ƒ์˜ ํšจ๊ณผ์ ์ธ ๋ฐฉ๋ฒ•์ด ๊ณ ๋ ค๋  ํ•„์š”๊ฐ€ ์žˆ๋‹ค.

๋ณธ ์—ฐ๊ตฌ์˜ ๋ชฉ์ ์€ ๋ฌด๊ธฐ๊ณ„ ๋ฐ ๋ฐ•ํ…Œ๋ฆฌ์•„ ์†Œ์žฌ ๊ธฐ๋ฐ˜์˜ ์ž๊ธฐ์น˜์œ  ํ™˜์„ ํ•˜์ด๋ธŒ๋ฆฌ๋“œ ํ˜ผ์ž…ํ•œ ๋ชจ๋ฅดํƒ€๋ฅด์˜ ๊ท ์—ด์น˜์œ  ๊ฑฐ๋™์„ ํ‰๊ฐ€ํ•˜๋Š” ๊ฒƒ์ด๋‹ค. ์‹คํ—˜์˜ ์ฃผ์š” ๋ณ€์ˆ˜๋กœ๋Š” ๋ฌด๊ธฐ๊ณ„ ์žฌ๋ฃŒ ๋ฐ ๋ฐ•ํ…Œ๋ฆฌ์•„๋ฅผ ํ™œ์šฉํ•˜์—ฌ ์ œ์กฐ๋œ ์ž๊ธฐ์น˜์œ  ํ™˜๋“ค์˜ ํ˜ผํ•ฉ๋น„์œจ์ด๋‹ค. ๋ชจ๋ฅดํƒ€๋ฅด์˜ ์ž๊ธฐ์น˜์œ  ์„ฑ๋Šฅ์€ ๊ณต์นญ 0.3 mm ๋ฐ 0.5 mm ๊ท ์—ด ํญ์„ ๊ฐ–๋Š” ๊ณต์‹œ์ฒด๋ฅผ ์ด์šฉํ•˜์—ฌ ์ •์ˆ˜์œ„ ํˆฌ์ˆ˜์‹œํ—˜์„ ํ†ตํ•ด ํ‰๊ฐ€ํ•˜์˜€๋‹ค. ๊ท ์—ด๋ฉด์—์„œ์˜ ์ž๊ธฐ์น˜์œ  ์ƒ์„ฑ๋ฌผ์€ X-์„  ํšŒ์ ˆ๋ถ„์„(x-ray diffraction, XRD), ์ „์ž์ฃผ์‚ฌํ˜„๋ฏธ๊ฒฝ(scanning electron microscopy, SEM) ๋ฐ ์—ด๋ถ„์„(thermogravimetric analysis, TGA)์„ ํ†ตํ•ด ํ‰๊ฐ€ํ•˜์˜€๋‹ค.

2. ์‹คํ—˜ ๊ฐœ์š”

2.1 ์†Œ์žฌ๋ณ„ ์ž๊ธฐ์น˜์œ  ํ™˜ ์ œ์ž‘

๋ฌด๊ธฐ๊ณ„ ์žฌ๋ฃŒ ๋ฐ ๋ฐ•ํ…Œ๋ฆฌ์•„๋ฅผ ํ™œ์šฉํ•œ ์ž๊ธฐ์น˜์œ  ํ™˜์˜ ์ œ์ž‘์€ Lee et al. (2023)์ด ์ œ์‹œํ•œ ๋ฐฉ๋ฒ•์— ๋”ฐ๋ผ ์‹ค์‹œํ•˜์˜€๋‹ค. ๋ฌด๊ธฐ๊ณ„ ์ž๊ธฐ์น˜์œ  ํ™˜(cementitious material-based self-healing pellet, CP) ์ œ์ž‘์€ 3์ข… ๊ณ ๋กœ์Šฌ๋ž˜๊ทธ ๋ฏธ๋ถ„๋ง(ground granulated blast furnace slag, GGBS), 2์ข… ํ”Œ๋ผ์ด์• ์‹œ(fly ash, FA) ๋ฐ 95 %์˜ ๊ณ ์ˆœ๋„ ๋ถ„๋ง ์ˆ˜์‚ฐํ™”์นผ์Š˜(Ca(OH)2)์„ ์‚ฌ์šฉํ•˜์—ฌ ์ œ์ž‘ํ•˜์˜€๋‹ค. ์ถ”๊ฐ€๋กœ ํ™˜์˜ ํšจ๊ณผ์ ์ธ ์น˜์œ ์„ฑ๋Šฅ ๋ถ€์—ฌ๋ฅผ ์œ„ํ•œ ์น˜์œ ๋ฌผ์˜ ๊ฐ€๊ต์—ญํ• ๋กœ์จ, ๋‚˜์ผ๋ก  ์„ฌ์œ ๋ฅผ ๋ฌด๊ธฐ๊ณ„ ์žฌ๋ฃŒ ์ค‘๋Ÿ‰ ๋Œ€๋น„ 0.1 % ํ˜ผํ•ฉํ•˜์—ฌ ์ œ์ž‘ํ•˜์˜€๋‹ค. ์‚ฌ์šฉ๋œ GGBS ๋ฐ FA ๊ฐ๊ฐ์˜ ๋น„ํ‘œ๋ฉด์ ์€ 4,830 cm2/g ๋ฐ 4,210 cm2/g์ด๋ฉฐ, ๋ฐ€๋„๋Š” ๊ฐ๊ฐ 2.9 g/cm3 ๋ฐ 2.3 g/cm3์ด๋‹ค(Table 1). ๋‚˜์ผ๋ก  ์„ฌ์œ ์˜ ์ธ์žฅ๊ฐ•๋„์™€ ํƒ„์„ฑ๊ณ„์ˆ˜๋Š” ๊ฐ๊ฐ 625 MPa์™€ 4,215 MPa์ด๋‹ค(Table 2). ์ด๋“ค ์žฌ๋ฃŒ๋Š” ๋ฏน์„œ๊ธฐ์˜ ๊ฑด๋น„๋น”์„ ํ•œ ํ›„ ํŒฌํ˜• ์ œํ™˜๊ธฐ์˜ ํ˜ผ์ž…ํ•˜์—ฌ 35 rpm ์†๋„๋กœ ํ˜ผํ•ฉํ•˜์˜€๋‹ค. ์ดํ›„ ์žฌ๋ฃŒ๋“ค์˜ ์‘์ง‘ ๋ฐ ์„ฑํ˜•์„ ์œ„ํ•ด์„œ๋Š” 95 %์˜ ํœ˜๋ฐœ์„ฑ ๋ฉ”ํ‹ธ์•Œ์ฝ”์˜ฌ(CH3OH) ์šฉ์•ก์„ ์‚ฌ์šฉํ•˜์˜€์œผ๋ฉฐ, CH3OH์˜ ์ฆ๋ฐœ๋กœ ์ธํ•œ ์žฌ๋ฃŒ๋“ค์˜ ๋ถ„ํ•ด ๋ฐฉ์ง€๋ฅผ ์œ„ํ•ด ๋ฐ€๋„ 1.25 g/cm3์˜ ์‹ค๋ฆฌ์ผ€์ดํŠธ๊ณ„ ๊ธ‰๊ฒฐ์žฌ๋กœ ํ‘œ๋ฉด์„ ์ฝ”ํŒ…ํ•˜์—ฌ ์ œ์ž‘ํ•˜์˜€๋‹ค.

Table 1 Physical properties of ground granulated blast furnace slag (GGBS) and fly ash (FA)

Materials

Density (g/cm3)

Specific surface area

(cm2/g)

GGBS

2.9

4,830

FA

2.3

4,210

Table 2 Physical properties of nylon fibers

Water

absorption

(%)

Density

(g/cm3)

Diameter

(ยต)

Tensile strength (MPa)

Elastic

modulus (MPa)

3.8

1.14

22.9

625

4,215

Table 3 Physical properties of expanded vermiculite

Density (kg/m3)

Particle size (mm)

Water

absorption (%)

pH

0.12

1.2

360

6.5~8

๋ฐ•ํ…Œ๋ฆฌ์•„ ์ž๊ธฐ์น˜์œ  ํ™˜(bacteria-based self-healing pellet, BP)์€ ํƒ„์‚ฐ์นผ์Š˜ ์„์ถœ ๊ธฐ๋Šฅ์„ ๊ฐ–๋Š” Sphingobacterium multivorum ๊ท ์ฃผ๋ฅผ ์‚ฌ์šฉํ•˜์˜€๋‹ค. ์„ ๋ณ„๋œ ๋ฐ•ํ…Œ๋ฆฌ์•„๋Š” ๊ทธ๋žŒ ์Œ์„ฑ๊ท ์ฃผ๋กœ์จ, ๊ท ์ฃผ์˜ ๊ฐ€์ˆ˜๋ถ„ํ•ด ํšจ์†Œ ์ž‘์šฉ์œผ๋กœ ์•”๋ชจ๋Š„๊ณผ ํƒ„์‚ฐ์—ผ์œผ๋กœ ๋ถ„ํ•ด ํ›„ ์ˆ˜๋ถ„๊ณผ ๋ฐ˜์‘ํ•จ์— ๋”ฐ๋ผ ํƒ„์‚ฐ์นผ์Š˜์„ ๋ฐฐ์ถœ์‹œํ‚จ๋‹ค(Okyay and Rodrigues 2015). ์„ ๋ณ„๋œ ๋ฐ•ํ…Œ๋ฆฌ์•„๋Š” ๋ฉธ๊ท  ์ธํ๋ฒ ์ดํ„ฐ ํ™˜๊ฒฝ์—์„œ 3์ผ ๋™์•ˆ pH 5~10 ๋ฒ”์œ„ ๋ฐ ์˜จ๋„ 10~40 ยฐC ํ™˜๊ฒฝ์—์„œ 109 cell/mL ๋†๋„๋กœ ๋ฐฐ์–‘๋˜์—ˆ๋‹ค(Hwang et al. 2022). ๋ฐฐ์–‘๋œ ๋ฐ•ํ…Œ๋ฆฌ์•„์˜ ๋ฐฐ์–‘์•ก์€ Urea 3 g/L, Beef extract 3 g/L, CaCl2 10 % ๋ฐ Pepton 5 g/L์˜ ๋ฌผ์งˆ๋“ค๋กœ ์กฐ์„ฑํ•˜์˜€๋‹ค(Hwang et al. 2022). ์ด๋“ค ๋ฐ•ํ…Œ๋ฆฌ์•„๋Š” ๊ฒฝํ™” ๋ชจ๋ฅดํƒ€๋ฅด ๋‚ด์—์„œ ์ƒ์žฅ๊ณผ ๋ฒˆ์‹ ํ™˜๊ฒฝ์„ ์ธ์œ„์ ์œผ๋กœ ์ œ๊ณตํ•˜๊ธฐ ์œ„ํ•˜์—ฌ ๋ฐฐ์–‘์•ก๊ณผ ํ•จ๊ป˜ ๋‹ค๊ณต์„ฑ์˜ ํŒฝ์ฐฝ์งˆ์„์— ๊ณ ์ •์‹œ์ผฐ๋‹ค(Yoon et al. 2019). ๋ฐ•ํ…Œ๋ฆฌ์•„ ๊ณ ์ •ํ™” ์žฌ๋ฃŒ์ธ ํŒฝ์ฐฝ์งˆ์„์€ ์‚ฌ์ „์— ๊ณ ์˜จ๏ฝฅ๊ณ ์••(120 ยฐC ๋ฐ 1.2 kg/m3)์˜ ์˜คํ† ํด๋ ˆ์ด๋ธŒ(autoclave) ํ™˜๊ฒฝ์—์„œ ๋ฉธ๊ท ์„ ์‹œํ‚จ ํ›„ ๋ฐ•ํ…Œ๋ฆฌ์•„ ๋ฐฐ์–‘์•ก์— 3์ผ๊ฐ„ ์นจ์ง€์‹œ์ผœ ๋ฐ•ํ…Œ๋ฆฌ์•„์™€ ๋ฐฐ์–‘์•ก์„ ํŒฝ์ฐฝ์งˆ์„ ๊ณต๊ทน์— ๊ณ ์ •ํ™”์‹œ์ผฐ๋‹ค.

๋ฐ•ํ…Œ๋ฆฌ์•„ ๊ณ ์ •ํ™”์— ์‚ฌ์šฉ๋œ ํŒฝ์ฐฝ์งˆ์„์˜ ๋ฌผ๋ฆฌ์  ํŠน์„ฑ์€ ๋ฐ€๋„ 0.12 kg/m3, ์ž…์žํฌ๊ธฐ 1.2 mm ์ดํ•˜, ํก์ˆ˜์œจ์ด 360 % ๋ฐ pH ๋†๋„ ์ค‘์„ฑ์ˆ˜์ค€์˜ 6.5~8์ธ ์žฌ๋ฃŒ๋ฅผ ์‚ฌ์šฉํ•˜์˜€๋‹ค(Table 3). ๋ฐ•ํ…Œ๋ฆฌ์•„ ์ž๊ธฐ์น˜์œ  ํ™˜ ์ œ์ž‘์€ ๋ฌด๊ธฐ๊ณ„ ์ž๊ธฐ์น˜์œ  ํ™˜ ์ œ์ž‘๋ฐฉ๋ฒ•๊ณผ ์œ ์‚ฌํ•˜๋‹ค. ๋‹ค๋งŒ ๋ฐ•ํ…Œ๋ฆฌ์•„ ์ž๊ธฐ์น˜์œ  ํ™˜์˜ ๊ฒฝ์šฐ๋Š” ๋ฐ•ํ…Œ๋ฆฌ์•„ ๋ฐฐ์–‘์•ก์˜ ์ˆ˜๋ถ„์„ ํฌํ•จํ•˜๊ณ  ์žˆ์–ด ๋ณ„๋„์˜ ์‘์ง‘์ œ๋ฅผ ๋”ฐ๋กœ ์‚ฌ์šฉํ•˜์ง€ ์•Š์•˜์œผ๋ฉฐ, ๊ทธ ์™ธ์˜ ๊ณผ์ •์€ ๋ฌด๊ธฐ๊ณ„ ์žฌ๋ฃŒ๋ฅผ ํ™œ์šฉํ™˜ ํ™˜์˜ ์ œ์กฐ๊ณต์ •๊ณผ ๋™์ผํ•˜๋‹ค(Lee et al. 2023). ์†Œ์žฌ๋ณ„๋กœ ๊ฐ๊ฐ ์ œ์ž‘๋œ ์ž๊ธฐ์น˜์œ  ํ™˜์€ 24์‹œ๊ฐ„ ๋™์•ˆ ๊ฑด์กฐ๋ฅผ ์‹ค์‹œํ•˜์˜€๋‹ค. ์ดํ›„ 600 ยตm~1.7 mm ํฌ๊ธฐ๋ฅผ ์‚ฌ์šฉํ•˜๊ธฐ ์œ„ํ•ด ์ฒด ๊ฑฐ๋ฆ„๋ง์„ ํ†ตํ•ด ์„ ๋ณ„ํ•˜์˜€๋‹ค. ์ตœ์ข… ์ž๊ธฐ์น˜์œ  ํ™˜์˜ ์ด๋ฏธ์ง€๋ฅผ Fig. 1์— ๋‚˜ํƒ€๋‚ด์—ˆ๋‹ค. ์ œ์ž‘๋œ ๋ฌด๊ธฐ๊ณ„ ๋ฐ ๋ฐ•ํ…Œ๋ฆฌ์•„ ์ž๊ธฐ์น˜์œ  ํ™˜์˜ ๋ฐ€๋„๋Š” ๊ฐ๊ฐ 2.65 g/cm3 ๋ฐ 2.15 g/cm3์ด๋ฉฐ, ํŒŒ์‡„ํ•˜์ค‘๋Š” KS F 2541(KATS 2021)์— ๋”ฐ๋ผ ํ‰๊ฐ€ํ•˜์˜€๋‹ค. ์ด๋“ค ์žฌ๋ฃŒ์˜ ํŒŒ์‡„ํ•˜์ค‘๋Š” ๊ฐ๊ฐ 4.49 kN ๋ฐ 6.25 kN๋กœ ํ‰๊ฐ€๋˜์—ˆ๋‹ค.

Fig. 1 Typical images for the produced self-healing pellets
../../Resources/KCI/JKCI.2024.36.5.409/fig1.png

2.2 ์‹คํ—˜ ๊ณ„ํš ๋ฐ ๋ฐฉ๋ฒ•

๋ฌด๊ธฐ๊ณ„ ๋ฐ ๋ฐ•ํ…Œ๋ฆฌ์•„ ์ž๊ธฐ์น˜์œ  ํ™˜๋“ค์˜ ํ•˜์ด๋ธŒ๋ฆฌ๋“œ ํ˜ผ์ž… ๋ชจ๋ฅดํƒ€๋ฅด์˜ ๋ฐฐํ•ฉ์ƒ์„ธ๋ฅผ Table 4์— ๋‚˜ํƒ€๋‚ด์—ˆ๋‹ค. ๋ชจ๋ฅดํƒ€๋ฅด ์‹œํ—˜์ฒด ์ œ์ž‘๋ณ€์ˆ˜๋Š” ๋‘ ์†Œ์žฌ ์ž๊ธฐ์น˜์œ  ํ™˜์˜ ํ•˜์ด๋ธŒ๋ฆฌ๋“œ ๋น„์œจ์ด๋‹ค. ์ž๊ธฐ์น˜์œ  ํ™˜์˜ ํ˜ผ์ž…๋Ÿ‰์€ ์ž”๊ณจ์žฌ ๋ถ€ํ”ผ ๋Œ€๋น„ 10 % ์น˜ํ™˜ํ•˜์˜€๋‹ค. ๋ฌด๊ธฐ๊ณ„ ๋ฐ ๋ฐ•ํ…Œ๋ฆฌ์•„ ์ž๊ธฐ์น˜์œ  ํ™˜์˜ ํ˜ผ์ž… ๋น„์œจ์€ ๊ฐ๊ฐ 9:1, 8:2, 7:3์œผ๋กœ ํ•˜์˜€๋Š”๋ฐ, ์ด๋“ค ์‹œํ—˜์ฒด ๋ช…์€ ๊ฐ๊ฐ M-HP1, M-HP2 ๋ฐ M-HP3๋กœ ํ•˜์˜€๋‹ค. ์ž๊ธฐ์น˜์œ  ํ™˜์˜ ํ˜ผ์ž…์œจ์ด 0 %์ธ ์‹œํ—˜์ฒด๋Š” ์ผ๋ฐ˜(plain) ๋ชจ๋ฅดํƒ€๋ฅด๋ฅผ ์˜๋ฏธํ•œ๋‹ค. ๋ชจ๋“  ๋ชจ๋ฅดํƒ€๋ฅด์—์„œ ๋ฌผ-๊ฒฐํ•ฉ์žฌ๋น„(water to binder ratio, W/B)๋Š” 48.5 %๋กœ ๊ทธ๋ฆฌ๊ณ  ์ž”๊ณจ์žฌ-๊ฒฐํ•ฉ์žฌ๋น„(sand to binder ratio, S/B)๋Š” 2.45๋กœ ํ•˜์˜€๋‹ค. ๋ชจ๋ฅดํƒ€๋ฅด ๋ฐฐํ•ฉ ์‹œ ์‚ฌ์šฉ๋œ ์ž”๊ณจ์žฌ๋Š” KSL ISO 679 (2017) ๊ธฐ์ค€์— ์ค€ํ•œ ํ‘œ์ค€์‚ฌ๋ฅผ ์‚ฌ์šฉํ•˜์˜€๋‹ค. ๋ชจ๋ฅดํƒ€๋ฅด ๋ฐฐํ•ฉ์€ KSL ISO 679 (2017) ๊ธฐ์ค€์— ๋”ฐ๋ผ ์‹ค์‹œํ•˜์˜€๋‹ค. ๋‹ค๋งŒ, ์ž๊ธฐ์น˜์œ  ํ™˜์€ CP์˜ ์ž๊ธฐ์น˜์œ  ๋ฉ”์ปค๋‹ˆ์ฆ˜์ธ ์ˆ˜ํ™”๋ฐ˜์‘ ์ œ์–ด๋ฅผ ์œ„ํ•ด ๋ชจ๋ฅดํƒ€๋ฅด ๋ฐฐํ•ฉ๋‹จ๊ณ„์—์„œ ๋ฐฐํ•ฉ์ˆ˜๋ฅผ ํ˜ผ์ž…ํ•œ ์ดํ›„ ํˆฌ์ž…ํ•จ์œผ๋กœ์จ ์‚ฌ์ „ ์ˆ˜ํ™”๋ฐ˜์‘์„ ์ตœ์†Œํ™”ํ•˜์˜€๋‹ค. ๋ฐฐํ•ฉ์ด ์™„๋ฃŒ๋œ ๋ชจ๋ฅดํƒ€๋ฅด๋Š” 50ร—50ร—50 mm3 ํฌ๊ธฐ์˜ ์ž…๋ฐฉํ˜• ๋ชฐ๋“œ ๋ฐ $\phi$100 mmร—50 mm2 ํฌ๊ธฐ๋กœ ์ œ์ž‘๋œ ์›์ฃผํ˜• ์‹œํ—˜์ฒด์— ํƒ€์„ค ํ•˜์˜€๋‹ค. ํƒ€์„ค๋œ ์‹œํ—˜์ฒด๋“ค์€ ์ƒ๋Œ€ ์Šต๋„ 60ยฑ5 %, ์˜จ๋„ 20ยฑ2 ยฐC์˜ ํ™˜๊ฒฝ์—์„œ 72์‹œ๊ฐ„ ๋™์•ˆ ์–‘์ƒํ•œ ํ›„ ํƒˆํ˜•ํ•˜์˜€๋‹ค.

Table 4 Mixing proportion of mortar specimens with self- healing pellets

Specimens

W/B (%)

S/B

Replacement ratio of self-healing pellet (sand vol, %)

Pellet mixing ratio (%)

CP

BP

Plain

48.5

2.45

-

-

-

M-HP1

10

90

10

M-HP2

80

20

M-HP3

70

30

Fig. 2 Image showing the constant water permeability test
../../Resources/KCI/JKCI.2024.36.5.409/fig2.png
Fig. 3 Sample preparation for X-ray diffraction (XRD), scanning electron microscopy (SEM), and thermogravimetric analysis (TGA) of healing hydrates
../../Resources/KCI/JKCI.2024.36.5.409/fig3.png

๋ชจ๋ฅดํƒ€๋ฅด์˜ ์••์ถ•๊ฐ•๋„๋Š” 50 mm ์ž…๋ฐฉํ˜• ์‹œํ—˜์ฒด๋ฅผ ์ด์šฉํ•˜์—ฌ ์žฌ๋ น 3์ผ, 7์ผ ๋ฐ 28์ผ์— KSL ISO 679 (2017) ๊ธฐ์ค€์— ๋”ฐ๋ผ(2,400ยฑ 200) N/s์˜ ๋น„์œจ๋กœ ํ•˜์ค‘์„ ๊ฐ€๋ ฅํ•˜์—ฌ ์ธก์ •ํ•˜์˜€๋‹ค. ๊ท ์—ด์น˜์œ  ์„ฑ๋Šฅ์€ ์ •์ˆ˜์œ„ ํˆฌ์ˆ˜์‹œํ—˜๊ณผ ๊ด‘ํ•™ํ˜„๋ฏธ๊ฒฝ ์ดฌ์˜์œผ๋กœ ํ‰๊ฐ€ํ•˜์˜€๋‹ค. ์ •์ˆ˜์œ„ ํˆฌ์ˆ˜์‹œํ—˜์€ KCI-CT114(KCI 2021)์— ๋”ฐ๋ผ $\phi$100 mmร—50 mm ํฌ๊ธฐ๋กœ ์ œ์ž‘๋œ ์›์ฃผํ˜• ์‹œํ—˜์ฒด๋ฅผ ์‚ฌ์šฉํ•˜์—ฌ ์ˆ˜ํ–‰ํ•˜์˜€๋‹ค(Fig. 2). ์ด ์‹œํ—˜์ฒด๋“ค์€ 14์ผ ๋™์•ˆ ์–‘์ƒ์„ ์‹ค์‹œํ•œ ํ›„ ๊ด€ํ†ต๊ท ์—ด ์œ ๋„์žฅ์น˜๋ฅผ ์ด์šฉํ•˜์—ฌ ๊ท ์—ด์„ ์œ ๋„ํ•˜์˜€๋‹ค. ๊ท ์—ด์„ ์œ ๋„ํ•œ ์‹œํ—˜์ฒด๋Š” ๊ณต์นญ 0.3 mm ๋ฐ 0.5 mm์˜ ๊ท ์—ด๋กœ ๋งŒ๋“ค๊ธฐ ์œ„ํ•ด ์ ˆ๋‹จ ์‹œํ—˜์ฒด๋ฉด์˜ ์–‘ ๋์— ๋งŒ๋“ค๊ณ ์ž ํ•˜๋Š” ๊ท ์—ด ํญ ๋‘๊ป˜์˜ ์‹ค๋ฆฌ์ฝ˜ ์‹œํŠธ๋ฅผ ์œ„์น˜์‹œ์ผœ ๊ฒฐํ•ฉ์‹œ์ผฐ๋‹ค. ์ด๋•Œ, ๊ฒฐํ•ฉ์€ ๋‘ ๊ฐœ์˜ ํด๋žจํ”„๋ฅผ 5 mm ๊ฐ„๊ฒฉ์„ ๋‘๊ณ  ์ฒด๊ฒฐํ•จ์œผ๋กœ์จ ๊ท ์—ดํญ์„ ์œ ๋„ํ•˜์˜€๋‹ค. ๊ฐ๊ฐ์˜ ๊ท ์—ดํญ์„ ์œ ๋„ํ•œ ์‹œํ—˜์ฒด๋Š” ์•ž๋’ท๋ฉด์— 4๊ณณ์”ฉ ์ด 8๊ณณ์˜ ๊ท ์—ดํญ์„ ๊ด‘ํ•™ํ˜„๋ฏธ๊ฒฝ์œผ๋กœ ์ธก์ •ํ•˜์—ฌ ๊ณต์นญ ๊ท ์—ด ํญ์„ ํ™•์ธํ•˜์˜€์œผ๋ฉฐ, ์ดํ›„ ์˜จ๋„ 20~25 ยฐC์—์„œ ์ˆ˜์ค‘์นจ์ง€ ํ•˜์˜€๋‹ค. ์ •์ˆ˜์œ„ ํˆฌ์ˆ˜์‹œํ—˜ ์‹œ์ž‘ ์‹œ ๊ท ์—ด ํญ์„ ์œ ๋„ํ•œ ์‹œํ—˜์ฒด๋Š” ์šฉ๊ธฐ์— ์œ„์น˜์‹œ์ผœ ๊ท ์—ด ๋ฉด ์œ„๋กœ ์ˆ˜์œ„๋ฅผ ์œ ์ง€์‹œํ‚จ ์ฑ„ 10๋ถ„ ๋™์•ˆ ๋ฌผ์„ ํ†ต๊ณผ์‹œ์ผœ ์œ ์ถœ๋œ ์ˆ˜๋Ÿ‰์„ ์ธก์ •ํ•˜์˜€๋‹ค(Hwang et al. 2022). ์ด ์ธก์ •์‹œ๊ฐ„ 10๋ถ„ ์ค‘์—์„œ ์ดˆ๋ฐ˜ 3๋ถ„์€ ์‹œํ—˜ ์˜ค์ฐจ๋ฅผ ์ค„์ด๊ธฐ ์œ„ํ•ด ํ‰๊ฐ€ ๊ฐ’์œผ๋กœ ์ด์šฉํ•˜์ง€ ์•Š์•˜๋‹ค. ์ •์ˆ˜์œ„ ํˆฌ์ˆ˜์‹œํ—˜์˜ ์ธก์ •์€ ์ˆ˜์ค‘ ์นจ์ง€ ์žฌ๋ น 14์ผ, 28์ผ ๋ฐ 56์ผ์— ์ธก์ •ํ•˜์˜€์œผ๋ฉฐ, ๋™์‹œ์— 300 ๋ฐฐ์œจ์˜ ๊ด‘ํ•™ํ˜„๋ฏธ๊ฒฝ ์ดฌ์˜์„ ํ†ตํ•ด ๊ท ์—ดํญ๋„ ํ•จ๊ป˜ ๊ด€์ฐฐํ•˜์˜€๋‹ค. ์ดํ›„์—” ๊ท ์—ด ๋ฉด์œผ๋กœ๋ถ€ํ„ฐ ํ˜•์„ฑ๋œ ์น˜์œ ๋ฌผ์งˆ์„ Fig. 3๊ณผ ๊ฐ™์€ ๊ณผ์ •์œผ๋กœ ์ฑ„์ทจํ•˜์—ฌ XRD, SEM ๋ฐ TGA์„ ์‹ค์‹œํ•˜์˜€๋‹ค.

3. ์‹คํ—˜๊ฒฐ๊ณผ ๋ฐ ๋ถ„์„

3.1 ์••์ถ•๊ฐ•๋„ ๋ฐœํ˜„

๋ฌด๊ธฐ๊ณ„ ๋ฐ ๋ฐ•ํ…Œ๋ฆฌ์•„ ์ž๊ธฐ์น˜์œ  ํ™˜์ด ํ•˜์ด๋ธŒ๋ฆฌ๋“œ ํ˜ผ์ž…๋œ ๋ชจ๋ฅดํƒ€๋ฅด์˜ ์žฌ๋ น๋ณ„ ์••์ถ•๊ฐ•๋„ ์ธก์ • ๊ฒฐ๊ณผ๋Š” Fig. 4์— ๋‚˜ํƒ€๋‚ด์—ˆ๋‹ค. ์ผ๋ฐ˜ ๋ชจ๋ฅดํƒ€๋ฅด(Plain)์˜ ์žฌ๋ น 3์ผ, 7์ผ ๋ฐ 28์ผ ์••์ถ•๊ฐ•๋„๋Š” ๊ฐ๊ฐ 23.3 MPa, 34.2 MPa ๋ฐ 37.6 MPa๋ฅผ ๋‚˜ํƒ€๋‚ด์—ˆ๋‹ค. ์‹œํ—˜์ฒด M-HP1, M-HP2 ๋ฐ M-HP3์˜ ์žฌ๋ น 3์ผ ์••์ถ•๊ฐ•๋„๋Š” ๊ฐ๊ฐ 28.6 MPa, 29.3 MPa ๋ฐ 29.8 MPa๋กœ ๋‚˜ํƒ€๋‚ฌ๋‹ค. ์ด๋Š” ์ผ๋ฐ˜ ๋ชจ๋ฅดํƒ€๋ฅด ๋Œ€๋น„ ๊ฐ๊ฐ ์•ฝ 1.23๋ฐฐ, 1.25๋ฐฐ ๋ฐ 1.28๋ฐฐ ๋†’์€ ๊ฐ’์ด๋‹ค. ์žฌ๋ น 7์ผ ๋ฐ 28์ผ์—์„œ M-HP1์˜ ์••์ถ•๊ฐ•๋„๋Š” ๊ฐ๊ฐ 36.6 MPa ๋ฐ 38.6 MPa์œผ๋กœ ์ผ๋ฐ˜ ๋ชจ๋ฅดํƒ€๋ฅด ๋Œ€๋น„ ๊ฐ๊ฐ 1.07๋ฐฐ์™€ 1.03๋ฐฐ ๋†’์€ ๊ฐ’์ด๋‹ค. BP ํ˜ผํ•ฉ ๋น„์œจ์ด ์ฆ๊ฐ€ํ•œ M-HP2 ๋ฐ M-HP3์˜ ๊ฒฝ์šฐ๋Š” ์žฌ๋ น 7์ผ๊ณผ 28์ผ์—์„œ ์ผ๋ฐ˜ ๋ชจ๋ฅดํƒ€๋ฅด ์••์ถ•๊ฐ•๋„ ๋Œ€๋น„ 1.13~1.23๋ฐฐ ๋†’์€ ๊ฐ’์„ ๋ณด์˜€๋‹ค. ์ฆ‰, BP ํ˜ผํ•ฉ ๋น„์œจ์ด ์ฆ๊ฐ€ํ• ์ˆ˜๋ก ๋ชจ๋ฅดํƒ€๋ฅด ์••์ถ•๊ฐ•๋„๋Š” ๋‹ค์†Œ ๋†’์€ ๊ฒฐ๊ณผ๋ฅผ ๋ณด์˜€๋‹ค. ์ด๋Š” ์ž๊ธฐ์น˜์œ  ํ™˜๋„ ์ผ๋ถ€๋ถ„ ์ˆ˜ํ™”๋ฐ˜์‘ํ•˜๋ฉด์„œ ์‹œ๋ฉ˜ํŠธ ๋ฉ”ํŠธ๋ฆญ์Šค ๊ฐ•๋„๋ฐœํ˜„์— ๊ธฐ์—ฌํ•˜์˜€๊ธฐ ๋•Œ๋ฌธ์œผ๋กœ ํŒ๋‹จ๋œ๋‹ค. ๊ฒฐ๊ณผ์ ์œผ๋กœ ์ž๊ธฐ์น˜์œ  ํ™˜์ด ์ž”๊ณจ์žฌ ๋ถ€ํ”ผ ๋Œ€๋น„ ์ผ์ • ์ˆ˜์ค€ ์ดํ•˜๋กœ ์น˜ํ™˜๋˜๋ฉด ๋ชจ๋ฅดํƒ€๋ฅด์˜ ์••์ถ•๊ฐ•๋„ ๊ฐ์†Œ๋Š” ์ œ์–ดํ•  ์ˆ˜ ์žˆ๋‹ค.

Fig. 4 Compressive strength of mortar specimens over time
../../Resources/KCI/JKCI.2024.36.5.409/fig4.png

3.2 ๊ท ์—ด์น˜์œ  ์„ฑ๋Šฅํ‰๊ฐ€

๋ฌด๊ธฐ๊ณ„ ๋ฐ ๋ฐ•ํ…Œ๋ฆฌ์•„ ์ž๊ธฐ์น˜์œ  ํ™˜์ด ํ•˜์ด๋ธŒ๋ฆฌ๋“œ ํ˜ผ์ž…๋œ ๋ชจ๋ฅดํƒ€๋ฅด์˜ ๊ท ์—ด์œ ์ถœ์ˆ˜๋Ÿ‰ ๋ฐ ๊ท ์—ด์น˜์œ ์œจ์€ Fig. 5 ๋ฐ Fig. 6์— ๋‚˜ํƒ€๋‚ด์—ˆ๋‹ค. ๊ณต์นญ ๊ท ์—ดํญ 0.3 mm๋ฅผ ์„ค๊ณ„ํ•œ ์‹œํ—˜์ฒด์˜ ์ดˆ๊ธฐ ํ‰๊ท  ๊ท ์—ด์œ ์ถœ์ˆ˜๋Ÿ‰์€ ๊ฐ๊ฐ 1.82~1.88 mL/min๏ฝฅmm๋กœ ๋ชจ๋“  ์‹œํ—˜์ฒด์—์„œ ๋น„์Šทํ•œ ์œ ์ถœ์ˆ˜๋Ÿ‰์„ ๋‚˜ํƒ€๋‚ด์—ˆ๋‹ค. ์ผ๋ฐ˜ ์‹œํ—˜์ฒด์˜ ๊ฒฝ์šฐ 0.3 mm ๊ณต์นญ ๊ท ์—ด ํญ์—์„œ ์žฌ๋ น 28์ผ ๋ฐ 56์ผ์—์„œ์˜ ํ‰๊ท  ๊ท ์—ด์œ ์ถœ์ˆ˜๋Ÿ‰์€ 1.35 mL/min๏ฝฅmm ๋ฐ 1.10 mL/min๏ฝฅmm๋กœ ํ‰๊ฐ€๋˜์—ˆ๋‹ค. ์ด๋“ค ๊ฐ’์œผ๋กœ๋ถ€ํ„ฐ ์‚ฐ์ •ํ•œ ๊ท ์—ด ์น˜์œ ์„ฑ๋Šฅ์€ 28 % ๋ฐ 41 %์ด๋‹ค. ๋ฐ˜๋ฉด ๋ฌด๊ธฐ๊ณ„ ๋ฐ ๋ฐ•ํ…Œ๋ฆฌ์•„ ์ž๊ธฐ์น˜์œ  ํ™˜์„ ํ•˜์ด๋ธŒ๋ฆฌ๋“œํ•˜์—ฌ ํ˜ผ์ž…ํ•œ M-HP1, M-HP2 ๋ฐ M-HP3 ์‹œํ—˜์ฒด์˜ ๊ฒฝ์šฐ 0.3 mm ๊ณต์นญ ๊ท ์—ด ํญ์˜ ์น˜์œ ์œจ์€ ์žฌ๋ น 28์ผ์—์„œ ๊ฐ๊ฐ 89 %, 91 % ๋ฐ 82 % ๊ฐ’์„ ๋ณด์˜€๋‹ค. ์ด๋Š” ์ผ๋ฐ˜ ์‹œํ—˜์ฒด ๋Œ€๋น„ ์•ฝ 2.93๋ฐฐ~3.25๋ฐฐ ๋†’์€ ์น˜์œ  ์„ฑ๋Šฅ์ด๋‹ค. ํŠนํžˆ M-HP2 ์‹œํ—˜์ฒด๋Š” ์žฌ๋ น 28์ผ์—์„œ 90 % ์ด์ƒ์˜ ๋†’์€ ๊ท ์—ด์น˜์œ  ์„ฑ๋Šฅ์„ ๋‚˜ํƒ€๋‚ด์—ˆ๋‹ค. M-HP1, M-HP2 ๋ฐ M-HP3 ์‹œํ—˜์ฒด์˜ 0.3 mm ๊ณต์นญ ๊ท ์—ด ํญ์—์„œ์žฌ๋ น 56์ผ ์น˜์œ ์œจ์€ ๊ฐ๊ฐ 94 %, 97 % ๋ฐ 93 %์ด๋‹ค. ์ด๋Š” ์ผ๋ฐ˜ ๋ชจ๋ฅดํƒ€๋ฅด ๋Œ€๋น„ ์•ฝ 2.27~2.37๋ฐฐ ๋†’์€ ์ˆ˜์ค€์˜ ์น˜์œ  ์„ฑ๋Šฅ์ด๋‹ค. ์ž๊ธฐ์น˜์œ  ํ™˜์˜ ํ˜ผํ•ฉ๋น„์œจ์€ ๋ฌด๊ธฐ๊ณ„ ๋ฐ ๋ฐ•ํ…Œ๋ฆฌ์•„ ์†Œ์žฌ๋ฅผ 80:20 ๋น„์œจ๋กœ ํ•˜์ด๋ธŒ๋ฆฌ๋“œํ•˜์—ฌ ํ˜ผ์ž…ํ•œ ์ž๊ธฐ์น˜์œ  ํ™˜์˜ ๊ฒฝ์šฐ๊ฐ€ ์น˜์œ ์žฌ๋ น 56์ผ์—์„œ 97 % ์ˆ˜์ค€์˜ ๊ฐ€์žฅ ๋†’์€ ๊ท ์—ด์น˜์œ  ์„ฑ๋Šฅ์„ ๋ณด์˜€์œผ๋ฉฐ, ์ดˆ๊ธฐ ์น˜์œ ์žฌ๋ น ๋ฐ ์žฅ๊ธฐ ์น˜์œ ์žฌ๋ น์—์„œ์˜ ํšจ๊ณผ์ ์ธ ๊ท ์—ด์น˜์œ  ์„ฑ๋Šฅ์„ ๋ณด์˜€๋‹ค.

Fig. 5 Water flow rates along the initial crack planes over time
../../Resources/KCI/JKCI.2024.36.5.409/fig5.png

๋ฐ˜๋ฉด, ๊ณต์นญ ๊ท ์—ด ํญ 0.5 mm์˜ ๊ฒฝ์šฐ 0.3 mm ๊ท ์—ดํญ ๋Œ€๋น„ ๊ท ์—ด์น˜์œ  ์„ฑ๋Šฅ์ด ์ ˆ๋ฐ˜์ˆ˜์ค€์œผ๋กœ ๊ฐ์†Œํ•˜์˜€๋‹ค ๊ณต์นญ ๊ท ์—ด ํญ 0.5 mm๋ฅผ ์œ ๋„ํ•œ ์‹œํ—˜์ฒด๋“ค์˜ ์ดˆ๊ธฐ ํ‰๊ท  ๊ท ์—ด์œ ์ถœ์ˆ˜๋Ÿ‰์€ 9.43~9.91 mL/min๏ฝฅmm๋กœ ๋‚˜ํƒ€๋‚ด์—ˆ๋‹ค. ์ผ๋ฐ˜ ๋ชจ๋ฅดํƒ€๋ฅด์—์„œ ์žฌ๋ น 56์ผ ๊ท ์—ด ์น˜์œ ์œจ์€ 29 %๋ฅผ ๋‚˜ํƒ€๋‚ด์—ˆ๋‹ค. ํ•˜์ง€๋งŒ ๋‘ ๊ฐ€์ง€ ์†Œ์žฌ์˜ ์ž๊ธฐ์น˜์œ  ํ™˜์„ ํ•˜์ด๋ธŒ๋ฆฌ๋“œํ•˜์—ฌ ํ˜ผ์ž…ํ•œ M-HP1, M-HP2 ๋ฐ M-HP3 ์‹œํ—˜์ฒด์˜ ์žฌ๋ น 56์ผ ๊ท ์—ด ์น˜์œ ์œจ์€ ๊ฐ๊ฐ 53 %, 55 % ๋ฐ 53 %๋กœ ์ผ๋ฐ˜ ๋ชจ๋ฅดํƒ€๋ฅด ๋Œ€๋น„ ์•ฝ 1.83~1.90๋ฐฐ ๋†’์€ ๊ฒฐ๊ณผ๋ฅผ ๋ณด์˜€๋‹ค. ์ผ๋ฐ˜์ ์œผ๋กœ ๊ท ์—ด ํญ์ด ์ฆ๊ฐ€ํ• ์ˆ˜๋ก ๊ทธ ์น˜์œ ์„ฑ๋Šฅ์€ ๊ฐ์†Œํ•œ๋‹ค(Hwang et al. 2017). ์ด๋Š” ๊ท ์—ด ๋ฉด ๋‚ด๋ถ€ ๋ฐ ํ‘œ๋ฉด๋“ค์— ๊ท ์—ด์น˜์œ  ๋ฌผ์งˆ๋“ค์ด ๊ท ์—ด ํญ ์ฆ๊ฐ€ ๋ฐ ๊ท ์—ด์œ ์ถœ์ˆ˜๋Ÿ‰์˜ ์ฆ๊ฐ€๋กœ ์ธํ•ด ๊ฒน๊ฒน์ด ์Œ“์ด์ง€ ๋ชปํ•˜๊ธฐ ๋•Œ๋ฌธ์œผ๋กœ ํŒ๋‹จ๋œ๋‹ค.

Fig. 6 Crack healing rate of mortar specimens over time
../../Resources/KCI/JKCI.2024.36.5.409/fig6.png
Fig. 7 Microscopic images of mortar specimens with initial nominal crack width of 0.3 mm
../../Resources/KCI/JKCI.2024.36.5.409/fig7.png

Fig. 7์—๋Š” 0.3 mm ๊ณต์นญ ๊ท ์—ด ํญ์„ ๊ฐ–๋Š” ์‹œํ—˜์ฒด๋“ค์—์„œ ์žฌ๋ น 0์ผ ๋ฐ 56์ผ์—์„œ ๊ด‘ํ•™ํ˜„๋ฏธ๊ฒฝ ์ด๋ฏธ์ง€๋ฅผ ๋‚˜ํƒ€๋‚ด์—ˆ๋‹ค. ์ผ๋ฐ˜ ์‹œํ—˜์ฒด๋Š” ์žฌ๋ น 0์ผ ๋ฐ 56์ผ์—์„œ ๊ท ์—ด ํญ์€ 0.31 mm ๋ฐ 0.14 mm ๊ท ์—ด ํญ์„ ๋‚˜ํƒ€๋‚ด์—ˆ๋‹ค. ๋ฐ˜๋ฉด ๋ฌด๊ธฐ๊ณ„ ๋ฐ ๋ฐ•ํ…Œ๋ฆฌ์•„ ์†Œ์žฌ ์ž๊ธฐ์น˜์œ  ํ™˜์„ ํ•˜์ด๋ธŒ๋ฆฌ๋“œ ํ˜ผ์ž…ํ•œ ์‹œํ—˜์ฒด๋“ค์˜ ๊ฒฝ์šฐ ์žฌ๋ น 56์ผ์—๋Š” ๊ท ์—ด ํญ์ด ๋ชจ๋‘ 0 mm๋กœ ๋ฐฑ์ƒ‰์˜ ๊ท ์—ด์น˜์œ  ๋ฌผ์งˆ๋กœ ์น˜์œ ๋˜๋Š” ๊ฒƒ์„ ํ™•์ธํ•  ์ˆ˜ ์žˆ์—ˆ๋‹ค. ์ด๋Š” ์ •์ˆ˜์œ„ ํˆฌ์ˆ˜์‹œํ—˜ ๊ฒฐ๊ณผ์™€๋Š” ๋‹ค์†Œ ์˜ค์ฐจ๋ฅผ ๋ณด์˜€๋Š”๋ฐ, ์‹œํ—˜์ฒด ์ œ์ž‘ ์‹œ ์ƒ๊ธฐ๋Š” ๋‚ด๋ถ€ ๊ณต๊ทน์œผ๋กœ ์ธํ•ด ์˜ค์ฐจ๊ฐ€ ๋ฐœ์ƒํ•œ ๊ฒƒ์œผ๋กœ ํŒ๋‹จ๋œ๋‹ค.

3.3 ๊ท ์—ด์น˜์œ  ์ƒ์„ฑ๋ฌผ ๋ถ„์„

๊ท ์—ด์น˜์œ  ์ƒ์„ฑ๋ฌผ ๋ถ„์„์€ ์ •์ˆ˜์œ„ ํˆฌ์ˆ˜์‹œํ—˜ ๋ฐ ๊ด‘ํ•™ํ˜„๋ฏธ๊ฒฝ ์ดฌ์˜ ๊ฒฐ๊ณผ ๊ฐ€์žฅ ์šฐ์ˆ˜ํ•œ ๊ท ์—ด์น˜์œ  ์„ฑ๋Šฅ์„ ๋‚˜ํƒ€๋‚ธ M-HP2 ์‹œํ—˜์ฒด์—์„œ ์ˆ˜ํ–‰ํ•˜์˜€๋‹ค. ํ•˜์ด๋ธŒ๋ฆฌ๋“œ ์ž๊ธฐ์น˜์œ  ํ™˜ ๊ท ์—ด์น˜์œ  ์ƒ์„ฑ๋ฌผ์˜ XRD ๋ถ„์„ ๊ฒฐ๊ณผ๋Š” Fig. 8๊ณผ ๊ฐ™๋‹ค. ๊ท ์—ด์น˜์œ  ์ƒ์„ฑ๋ฌผ์˜ XRD ๋ถ„์„๊ฒฐ๊ณผ ํƒ„์‚ฐ์นผ์Š˜(Calcite) ๋ฐ ์—ํŠธ๋ฆฐ๊ฐ€์ดํŠธ(Etrringite)๊ฐ€ ๋‚˜ํƒ€๋‚˜๋Š” 2ฮธ ๊ฐ๋„์—์„œ ํ”ผํฌ๊ฐ€ ๊ด€์ฐฐ๋˜์—ˆ๋‹ค(Bak 2020; Jansen et al. 2020). ์ผ๋ฐ˜ ๋ชจ๋ฅดํƒ€๋ฅด ์ˆ˜ํ™”๋ฌผ๊ณผ ๊ท ์—ด์น˜์œ  ์ƒ์„ฑ๋ฌผ์˜ TGA ๋ถ„์„ ๊ฒฐ๊ณผ๋Š” Fig. 9์™€ ๊ฐ™๋‹ค. ์ผ๋ฐ˜ ๋ชจ๋ฅดํƒ€๋ฅด ์ˆ˜ํ™”๋ฌผ ๋ฐ ๊ท ์—ด์น˜์œ  ์ƒ์„ฑ๋ฌผ์˜ ์—ด์ค‘๋Ÿ‰ ๊ณก์„ ์€ ์„๊ณ  ๋ฐ ์—ํŠธ๋ง๊ฐ€์ดํŠธ๊ฐ€ ์ฃผ๋กœ ๋ถ„ํ•ด๋˜๋Š” 80~150 ยฐC ๋ฒ”์œ„์—์„œ ๊ฐ์†Œํ•˜์˜€์œผ๋ฉฐ, ๊ฐ๊ฐ์˜ ์งˆ๋Ÿ‰๊ฐ์†Œ์œจ์€ 7.5 % ๋ฐ 10 % ์ˆ˜์ค€์œผ๋กœ ํ‰๊ฐ€๋˜์—ˆ๋‹ค. ๋˜ํ•œ ํƒ„์‚ฐ์นผ์Š˜์ด ์ฃผ๋กœ ๋ถ„ํ•ด๋˜๋Š” 700~900 ยฐC ๋ฒ”์œ„์—์„œ ์งˆ๋Ÿ‰์ด ๊ฐ์†Œํ•˜์˜€์œผ๋ฉฐ, ์งˆ๋Ÿ‰๊ฐ์†Œ์œจ์€ ๊ฐ๊ฐ 2.5 % ๋ฐ 9.6 %๋กœ ํ‰๊ฐ€๋˜์—ˆ๋‹ค(Martinez et al. 2018). ์œ„์—์„œ ๋‚˜ํƒ€๋‚ธ XRD ๋ฐ TGA ๋ถ„์„ ๊ฒฐ๊ณผ์™€ ๊ฐ™์ด ์ž๊ธฐ์น˜์œ  ํ™˜์— ์˜ํ•œ ๊ท ์—ด์น˜์œ  ์ƒ์„ฑ๋ฌผ์ธ ์—ํŠธ๋ฆฐ๊ฐ€์ดํŠธ์™€ ํƒ„์‚ฐ์นผ์Š˜์— ๋Œ€ํ•œ ์ „ํ˜•์ ์ธ ํ˜•์ƒ์„ SEM ์ด๋ฏธ์ง€(Fig. 10)์—์„œ๋„ ๋˜ํ•œ ํ™•์ธ๋  ์ˆ˜ ์žˆ์—ˆ๋‹ค. ์นจ์ƒํ˜•์˜ ์—ํŠธ๋ฆฐ๊ฐ€์ดํŠธ ๊ทธ๋ฆฌ๊ณ  ํŒ์ƒํ˜•์˜ ํƒ„์‚ฐ์นผ์Š˜ ํ˜•์ƒ๋“ค์ด ๋‹ค์ˆ˜ ํ™•์ธ๋˜์—ˆ๋‹ค.

Fig. 8 X-ray diffraction (XRD) patterns results of self-healing hydrates
../../Resources/KCI/JKCI.2024.36.5.409/fig8.png
Fig. 9 Thermogravimetric analysis (TGA) results for self- healing hydrates in specimen M-HP2
../../Resources/KCI/JKCI.2024.36.5.409/fig9.png
Fig. 10 Typical scanning electron microscopy (SEM) image for self-healing hydrates
../../Resources/KCI/JKCI.2024.36.5.409/fig10.png

4. ๊ฒฐ ๋ก 

์ด ์—ฐ๊ตฌ์—์„œ๋Š” ๋ฌด๊ธฐ๊ณ„ ์žฌ๋ฃŒ ๋ฐ ๋ฐ•ํ…Œ๋ฆฌ์•„ ๊ธฐ๋ฐ˜์˜ ์ž๊ธฐ์น˜์œ  ํ™˜์„ ํ˜ผ์ž…ํ•œ ๋ชจ๋ฅดํƒ€๋ฅด์˜ ๊ท ์—ด์น˜์œ  ์„ฑ๋Šฅ์„ ํ‰๊ฐ€ํ•˜์˜€๋‹ค. ๊ทธ ๊ฒฐ๊ณผ ๋‹ค์Œ๊ณผ ๊ฐ™์€ ๊ฒฐ๋ก ์„ ์–ป์—ˆ๋‹ค.

1) ์ž๊ธฐ์น˜์œ  ํ™˜์˜ ํ˜ผ์ž…์€ ์ž”๊ณจ์žฌ ๋ถ€ํ”ผ ์น˜ํ™˜์œผ๋กœ ์ด๋ฃจ์–ด์กŒ๊ธฐ ๋•Œ๋ฌธ์— ๋ชจ๋ฅดํƒ€๋ฅด์˜ ์••์ถ•๊ฐ•๋„ ๊ฐ์†Œ์— ๋ฏธ์น˜๋Š” ์˜ํ–ฅ์€ ๋‚˜ํƒ€๋‚˜์ง€ ์•Š์•˜๋‹ค.

2) ํ•˜์ด๋ธŒ๋ฆฌ๋“œ ์ž๊ธฐ์น˜์œ  ํ™˜์„ ํ˜ผ์ž…ํ•œ ๋ชจ๋ฅดํƒ€๋ฅด์—์„œ ๊ณต์นญ ๊ท ์—ด ํญ 0.3 mm์˜ ์น˜์œ ์œจ์€ ์žฌ๋ น 56์ผ์—์„œ 93 %~97 %๋กœ์จ, ์ผ๋ฐ˜ ๋ชจ๋ฅดํƒ€๋ฅด ๋Œ€๋น„ ์•ฝ 2.27~2.37๋ฐฐ ๋†’์€ ์น˜์œ  ์„ฑ๋Šฅ์„ ๋ณด์˜€๋‹ค.

3) ์ž๊ธฐ์น˜์œ  ํ™˜์˜ ๊ท ์—ด์น˜์œ  ์ƒ์„ฑ๋ฌผ์€ ํƒ„์‚ฐ์นผ์Š˜ ๋ฐ ์—ํŠธ๋ฆฐ๊ฐ€์ดํŠธ๋กœ ํ‰๊ฐ€๋˜์—ˆ๋‹ค.

4) ์ด ์—ฐ๊ตฌ์—์„œ ์‚ฌ์šฉํ•œ ๋ฌด๊ธฐ๊ณ„ ์žฌ๋ฃŒ ๋ฐ ๋ฐ•ํ…Œ๋ฆฌ์•„ ์†Œ์žฌ ๊ธฐ๋ฐ˜์˜ ์ž๊ธฐ์น˜์œ  ํ™˜์˜ ํ•˜์ด๋ธŒ๋ฆฌ๋“œ ํ˜ผ์ž…์€ ๊ฐ ์†Œ์žฌ์˜ 8:2 ๋น„์œจ์ด ์ถ”์ฒœ๋  ์ˆ˜ ์žˆ์—ˆ๋‹ค.

๋ฌด๊ธฐ๊ณ„ ๋ฐ ๋ฐ•ํ…Œ๋ฆฌ์•„ ์†Œ์žฌ ์ž๊ธฐ์น˜์œ  ํ™˜์˜ ํ•˜์ด๋ธŒ๋ฆฌ๋“œ ํ˜ผ์ž…์€ ์ดˆ๊ธฐ ๋ฐ ์žฅ๊ธฐ์ ์ธ ๊ท ์—ด์น˜์œ  ์„ฑ๋Šฅ ๋ฐœํ˜„ ํšจ์œจ์„ฑ ์ธก๋ฉด์—์„œ ๊ธ์ •์ ์œผ๋กœ ๊ฒ€ํ† ๋˜์—ˆ์ง€๋งŒ, ๊ท ์—ด์น˜์œ  ํญ์ด 0.3 mm๋กœ ๋‹ค์†Œ ์ œํ•œ์ ์œผ๋กœ ๊ท ์—ด์น˜์œ  ํญ ํ–ฅ์ƒ ์ธก๋ฉด์—์„œ๋Š” ๋ณด์™„ ์—ฐ๊ตฌ๊ฐ€ ์ˆ˜ํ–‰๋  ํ•„์š”๊ฐ€ ์žˆ๋‹ค.

๊ฐ์‚ฌ์˜ ๊ธ€

2024๋…„๋„ ์‚ฐ์—…ํ†ต์ƒ์ž์›๋ถ€ ์žฌ์›์œผ๋กœ ํ•œ๊ตญ์‚ฐ์—…๊ธฐ์ˆ ํ‰๊ฐ€๊ด€๋ฆฌ์›์˜ ์ง€์›์„ ๋ฐ›์•„ ์ˆ˜ํ–‰๋œ ์—ฐ๊ตฌ์ž„(No.20025773, ๊ฑด์ถ•๋ฌผ ์ผ์ฒดํ˜• ์ด์‚ฐํ™”ํƒ„์†Œ ํฌ์ง‘ ๋ฐ ์ „ํ™˜ ๊ธฐ์ˆ  ๊ฐœ๋ฐœ).

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