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  1. ์ถฉ๋‚จ๋Œ€ํ•™๊ต ๊ฑด์ถ•๊ณตํ•™๊ณผ ๋Œ€ํ•™์›์ƒ (Graduate Student, Department of Architectural Engineering, Chungnam National University, Daejeon 34134, Rep. of Korea)
  2. ์ถฉ๋‚จ๋Œ€ํ•™๊ต ๊ฑด์ถ•๊ณตํ•™๊ณผ ๊ต์ˆ˜ (Professor, Department of Architectural Engineering, Chungnam National University, Daejeon 34134, Rep. of Korea)
  3. ํ•œ๊ตญ๊ตํ†ต๋Œ€ํ•™๊ต ์•ˆ์ „๊ณตํ•™๊ณผ ๊ต์ˆ˜ (Professor, Department of Safety Engineering, Korea National University of Transportation, Chungju 27469, Rep. of Korea)
  4. ํ•œ๊ตญ๊ตํ†ต๋Œ€ํ•™๊ต ๊ฑด์ถ•๊ณตํ•™๊ณผ ๊ต์ˆ˜ (Professor, School of Architecture, Korea National University of Transportation, Chungju 27469, Rep. of Korea)
  5. ์ถฉ๋‚จ๋Œ€ํ•™๊ต ๊ฑด์„ค๊ณตํ•™๊ต์œก๊ณผ ๊ต์ˆ˜ (Professor, Department of Contruction Engineering Education, Chungnam National University, Daejeon 34134, Rep. of Korea)



ํ•˜์ด๋ธŒ๋ฆฌ๋“œ ์„ฌ์œ ๋ณด๊ฐ• ๋ณ€ํ˜•๊ฒฝํ™”ํ˜• ์‹œ๋ฉ˜ํŠธ ๋ณตํ•ฉ์žฌ(Hy-SHCC), ๋ณ€ํ˜•๊ฐ์ง€, ์ž๊ธฐ๊ฐ์ง€, ๋ฐ˜๋ณต์••์ถ•, ๋‹ค์ค‘๋ฒฝ ํƒ„์†Œ๋‚˜๋…ธํŠœ๋ธŒ(MWCNTs)
hybrid fibers reinforced strain-hardening cement composite (Hy-SHCC), strain-detecting, self-sensing, repeated compression, multi-walled carbon nanotubes (MWCNTs)

1. ์„œ ๋ก 

Iijima(1991)์— ์˜ํ•ด ํƒ„์†Œ๋‚˜๋…ธํŠœ๋ธŒ(carbon nanotube, CNT)๊ฐ€ ๋ฐœ๊ฒฌ๋œ ์ดํ›„, ๋‹ค์–‘ํ•œ ์‚ฐ์—…๋ถ„์•ผ์— ์‚ฌ์šฉ๋˜๋Š” ์žฌ๋ฃŒ์˜ ์—ญํ•™์  ๋ฐ ์ „๊ธฐ์  ํŠน์„ฑ์„ ๊ฐœ์„ ํ•˜๋Š”๋ฐ ํšจ๊ณผ์ ์ธ ๋ฌผ์งˆ๋กœ ์•Œ๋ ค์ ธ ์ ์šฉ๋˜๊ณ  ์žˆ๋‹ค. ํŠนํžˆ CNT๋ฅผ ํ˜ผ์ž…ํ•œ ์‹œ๋ฉ˜ํŠธ ๋ณตํ•ฉ์ฒด์—์„œ ์†์ƒ์ˆ˜์ค€์— ๋”ฐ๋ฅธ ์ „๊ธฐ์  ์ €ํ•ญํŠน์„ฑ ๋ณ€ํ™”๋ฅผ ๊ณ„์ธกํ•˜๊ณ  ์ด๋ฅผ ํ™œ์šฉํ•œ ์†์ƒ ๋ชจ๋‹ˆํ„ฐ๋ง ๊ฐ€๋Šฅ์„ฑ์ด ์ œ์‹œ๋˜๊ณ  ์žˆ์œผ๋ฉฐ ์ด์— ๊ด€ํ•œ ๋งŽ์€ ์—ฐ๊ตฌ๊ฐ€ ์ง„ํ–‰๋˜๊ณ  ์žˆ๋‹ค(Chung 2003).

๊ตญ๋‚ด์—์„œ๋„ CNT๋ฅผ ํ™œ์šฉํ•œ ์‹œ๋ฉ˜ํŠธ ๋ณตํ•ฉ์ฒด์˜ ๋ณ€ํ˜•๊ฐ์ง€(Yoo et al. 2018; Lee et al. 2020; Youn et al. 2020), ์ „์žํŒŒ ์ฐจํ(Jung and Hong 2019), ์ž๊ธฐ์ˆ˜์ถ•(Song et al. 2019), ์ž๊ธฐ์น˜์œ (Lee and Heo 2020), ๋‚ด์ถฉ๊ฒฉ(Choi and Lee 2020), ๋‚ด์—ผํ•ด(Kim et al. 2015), ๋ฐœ์—ด(Kim et al. 2016; Choi et al. 2020) ํŠน์„ฑ ํ–ฅ์ƒ ๋“ฑ์„ ์œ„ํ•œ ์—ฐ๊ตฌ๊ฐ€ ์ง„ํ–‰๋˜๊ณ  ์žˆ๋‹ค. ์ด๋Ÿฌํ•œ ์—ฐ๊ตฌ๊ฒฐ๊ณผ๋ฅผ ๊ทผ๊ฑฐ๋กœ ๋ณผ ๋•Œ, CNT์˜ ๊ฑด์„ค์‚ฐ์—… ๋ถ„์•ผ์—์„œ ํ™œ์šฉ์„ฑ์€ ๋”์šฑ ํ™•๋Œ€๋  ๊ฒƒ์œผ๋กœ ๊ธฐ๋Œ€๋œ๋‹ค.

1970๋…„๋Œ€ ์‚ฐ์—…ํ™”์™€ ํ•จ๊ป˜ ๊ฑด์„ค๋œ ๋งŽ์€ ์‚ฌํšŒ๊ธฐ๋ฐ˜์‹œ์„ค๋ฌผ์˜ ๋…ธํ›„ํ™”์— ๋”ฐ๋ฅธ ์‚ฌํšŒ์  ๋น„์šฉ ์ฆ๊ฐ€์™€ ํ˜„ ์ •๋ถ€์˜ ๊ทธ๋ฆฐ๋‰ด๋”œ ์ •์ฑ… 10๋Œ€ ๊ณผ์ œ์ธ SOC ๋””์ง€ํ„ธํ™”์™€ ๊ฐ™์€ ์‚ฌํšŒ์  ํ™˜๊ฒฝ๋ณ€ํ™”์— ๋”ฐ๋ผ ์‹œ์„ค๋ฌผ์˜ ๋ชจ๋‹ˆํ„ฐ๋ง ๊ธฐ์ˆ ์— ๋Œ€ํ•œ ์ˆ˜์š”๊ฐ€ ์ฆ๊ฐ€๋˜๊ณ  ์žˆ๋‹ค. ์‹œ์„ค๋ฌผ์˜ ๊ฑด์ „์„ฑ ๋ชจ๋‹ˆํ„ฐ๋ง์—์„œ ๊ตฌ์กฐ๋ฌผ์˜ ์ƒํƒœ ๋ฐ ๋ณ€ํ˜• ๊ณ„์ธก์„ ์œ„ํ•œ ์„ผ์„œ๋Š” ํ•ต์‹ฌ์š”์†Œ์ด๋ฉฐ ํŠนํžˆ ๊ฒฝ์ œ์„ฑ ๋ฐ ๋งŽ์€ ์‚ฌํšŒ๊ธฐ๋ฐ˜์‹œ์„ค๋ฌผ์˜ ๊ตฌ์„ฑ์žฌ๋ฃŒ์™€ ๋™์งˆ์„ฑ ์ธก๋ฉด์—์„œ ์‹œ๋ฉ˜ํŠธ ๋ณตํ•ฉ์ฒด ๊ธฐ๋ฐ˜์˜ ๋ณ€ํ˜•๊ฐ์ง€ ์„ผ์„œ์— ๊ด€ํ•œ ๊ด€์‹ฌ์ด ๊ณ ์กฐ๋˜๊ณ  ์žˆ๋‹ค(Dinesh et al. 2021).

์ตœ๊ทผ ์ €์ž(Youn et al. 2020) ๋“ฑ์€ 0.5 % ๊ฐ•์„ฌ์œ ์™€ 1.0 % ํด๋ฆฌ์—ํ‹ธ๋ Œ(PE) ์„ฌ์œ ๋ฅผ ํ˜ผ์ž…ํ•˜์—ฌ ์ง์ ‘ ์ธ์žฅํ•˜์—์„œ ์‹œ๋ฉ˜ํŠธ ๋ณตํ•ฉ์ฒด์˜ ๊ท ์—ด์ œ์–ด ๋ฐ ์ธ์žฅ์„ฑ๋Šฅ์„ ๊ฐœ์„ ํ•˜๊ณ  1.0 wt% ์•ก์ƒํ˜• MWCNT๋ฅผ ํ˜ผ์ž…ํ•˜์—ฌ ๋ณ€ํ˜• ๊ฐ์ง€์„ฑ๋Šฅ์„ ๋ถ€์—ฌํ•œ ์Šค๋งˆํŠธ ๋ณ€ํ˜•๊ฒฝํ™”ํ˜• ์‹œ๋ฉ˜ํŠธ ๋ณตํ•ฉ์ฒด(strain-hardening cement composite, SHCC)๋ฅผ ์ œ์•ˆํ•˜์˜€๋‹ค. ๋™์ผํ•œ ์กฐ๊ฑด์—์„œ ๊ฐ•์„ฌ์œ  ํ˜ผ์ž…๋Ÿ‰ ๋ฐ ์ฒ ๊ทผ์˜ ์˜ํ–ฅ์— ๋”ฐ๋ฅธ ์ง์ ‘์ธ์žฅ ๋ฐ ์ธ์žฅ๋ณ€ํ˜• ๊ฐ์ง€๋Šฅ๋ ฅ์„ ํ‰๊ฐ€ํ•˜์—ฌ ์ œ์•ˆ๋œ ์„ฌ์œ ๋ณด๊ฐ• ์‹œ๋ฉ˜ํŠธ ๋ณตํ•ฉ์ฒด ๊ธฐ๋ฐ˜ ์„ผ์„œ ํ™œ์šฉ ๊ฐ€๋Šฅ์„ฑ๋„ ํ™•์ธ๋˜์—ˆ๋‹ค(Kim et al. 2021). ๋˜ํ•œ 1~2 wt% ์•ก์ƒํ˜• ๋‹ค์ค‘๋ฒฝ ๋‚˜๋…ธํŠœ๋ธŒ(MWCNT)์˜ ํ˜ผ์ž…๋Ÿ‰์— ๋”ฐ๋ฅธ ๋ฐ˜๋ณต ์••์ถ•ํ•˜์—์„œ 1.0 % ๊ฐ•์„ฌ์œ ์™€ 0.75 % PE ํ•ฉ์„ฑ์„ฌ์œ ๋ฅผ ํ˜ผ์ž…ํ•œ ์‹œ๋ฉ˜ํŠธ ๋ณตํ•ฉ์ฒด์˜ ์••์ถ•์†์ƒ ๋ฐ ๋ณ€ํ˜• ๊ฐ์ง€๋Šฅ๋ ฅ์ด ํ‰๊ฐ€๋˜์—ˆ๋‹ค(Jang et al. 2020).

๊ทธ๋Ÿฌ๋‚˜ ์‹œ๋ฉ˜ํŠธ ๋ณตํ•ฉ์ฒด์˜ ์—ญํ•™์  ๋ฐ ์ „๊ธฐ์  ํŠน์„ฑ ๊ฐœ์„ ์„ ์œ„ํ•˜์—ฌ ํ˜ผ์ž…๋˜๋Š” ๊ฐ•์„ฌ์œ  ๋ฐ MWCNT๋Š” ์„ผ์„œ ์ œ์ž‘์˜ ์šฉ์ด์„ฑ ๋ฐ ๊ฒฝ์ œ์„ฑ์„ ์ €ํ•ดํ•˜๋Š” ์ฃผ์š”ํ•œ ์š”์ธ์œผ๋กœ ์‹œ๋ฉ˜ํŠธ ๋ณตํ•ฉ์ฒด ๊ธฐ๋ฐ˜ ๋ณ€ํ˜•๊ฐ์ง€ ์„ผ์„œ์˜ ์‹ค์šฉํ™”๋ฅผ ์œ„ํ•ด์„œ๋Š” ์ด๋Ÿฌํ•œ ๋ณด๊ฐ•์„ฌ์œ  ๋ฐ ์ „๋„๋ฌผ์งˆ์„ ์ตœ์†Œํ™”ํ•  ํ•„์š”๊ฐ€ ์žˆ๋‹ค. ๋˜ํ•œ ์ง€์ง„๊ณผ ๊ฐ™์€ ์™ธ๋ ฅ์— ์˜ํ•ด ๋ถ€์žฌ์— ์œ ๋ฐœ๋˜๋Š” ๋ณ€ํ˜•์€ ์ธ์žฅ ๋ฐ ์••์ถ•๋ณ€ํ˜•์ด ๋ฐ˜๋ณต์ ์œผ๋กœ ์œ ๋ฐœ๋˜๋ฏ€๋กœ ์‹œ๋ฉ˜ํŠธ ๋ณตํ•ฉ์ฒด ๊ธฐ๋ฐ˜ ๋ณ€ํ˜•๊ฐ์ง€ ์„ผ์„œ๋Š” ์ธ์žฅ๋ฟ๋งŒ ์•„๋‹ˆ๋ผ ์••์ถ•๋ณ€ํ˜•์— ๋Œ€ํ•œ ๊ฐ์ง€๋Šฅ๋ ฅ์„ ํ™•๋ณดํ•˜์—ฌ์•ผ ํ•œ๋‹ค.

๋”ฐ๋ผ์„œ ์ด ์—ฐ๊ตฌ์—์„œ๋Š” ์„ ํ–‰์—ฐ๊ตฌ(Youn et al. 2020)๋กœ๋ถ€ํ„ฐ ์ œ์•ˆ๋œ ์Šค๋งˆํŠธ ๋ณ€ํ˜•๊ฒฝํ™”ํ˜• ์‹œ๋ฉ˜ํŠธ ๋ณตํ•ฉ์ฒด(smart SHCC)์— ๋Œ€ํ•œ ๋ฐ˜๋ณต ์••์ถ•๋ณ€ํ˜•์— ๋Œ€ํ•œ ๊ฐ์ง€๋Šฅ๋ ฅ ๋ฐ ์†์ƒํŠน์„ฑ์„ ํ‰๊ฐ€ํ•˜๊ณ ์ž ํ•œ๋‹ค. ์•„์šธ๋Ÿฌ 1.0 wt% MWCNT์˜ ํ˜ผ์ž…์ด SHCC์˜ ์ง์ ‘์ธ์žฅ ๋ฐ ์••์ถ•ํŠน์„ฑ, ๋ฐ˜๋ณต ์••์ถ•ํ•˜์—์„œ ์ „๊ธฐ ์ €ํ•ญ ๋ฐ ๋ณ€ํ˜• ๊ฐ์ง€ํŠน์„ฑ์— ๋ผ์น˜๋Š” ์˜ํ–ฅ์„ ์‹คํ—˜์ ์œผ๋กœ ํ‰๊ฐ€ํ•˜๊ณ ์ž ํ•œ๋‹ค.

2. ์‹ค ํ—˜

2.1 ์‚ฌ์šฉ์žฌ๋ฃŒ

์„ ํ–‰์—ฐ๊ตฌ(Youn et al. 2020)์™€ ๋™์ผํ•œ ๋ฐฉ๋ฒ•์— ๋”ฐ๋ผ ๊ฐ•์„ฌ์œ  ๋ฐ PE ํ•ฉ์„ฑ์„ฌ์œ ๋ฅผ ํ˜ผ์ž…ํ•˜์—ฌ ๋ณ€ํ˜•๊ฒฝํ™”ํ˜• ์‹œ๋ฉ˜ํŠธ ๋ณตํ•ฉ์ฒด(hybrid fibers reinforced SHCC, Hy-SHCC)๊ฐ€ ์ œ์กฐ๋˜์—ˆ๋‹ค. ๋ณดํ†ต ํฌํ‹€๋žœ๋“œ์‹œ๋ฉ˜ํŠธ(1์ข…), ๊ทœ์‚ฌ ๋ฐ ๋ฌผ์„ ํ˜ผ์ž…ํ•˜์—ฌ ๊ตณ์ง€ ์•Š์€ ์‹œ๋ฉ˜ํŠธ ๋ณตํ•ฉ์ฒด๋ฅผ ๋น„๋น”ํ•œ ํ›„ ์‹œ๋ฉ˜ํŠธ ๋ณตํ•ฉ์ฒด ์ฒด์ ๋น„ 0.5 %(40 kg/ใŽฅ) ๊ฐ•์„ฌ์œ ์™€ 0.75 %(7.4 kg/ใŽฅ) PE ํ•ฉ์„ฑ์„ฌ์œ ๋ฅผ ํ˜ผ์ž…ํ•˜์˜€๋‹ค. ์ „๋„๋ฌผ์งˆ์ธ MWCNT๋ฅผ ์‹œ๋ฉ˜ํŠธ ์ค‘๋Ÿ‰๋น„ 1.0 wt% ํ˜ผ์ž… ์—ฌ๋ถ€์— ๋”ฐ๋ฅธ Hy-SHCC์˜ ์ง์ ‘์ธ์žฅ ๋ฐ ์••์ถ•ํŠน์„ฑ, ๋ฐ˜๋ณต ์••์ถ•ํ•˜์—์„œ ์ „๊ธฐ ์ €ํ•ญ ๋ฐ ๋ณ€ํ˜•๊ฐ์ง€ ํŠน์„ฑ์„ ํ‰๊ฐ€ํ•˜๊ธฐ ์œ„ํ•˜์—ฌ Table 1๊ณผ ๊ฐ™์ด ๋ฌผ(W), ์‹œ๋ฉ˜ํŠธ(C) ๋ฐ ๊ทœ์‚ฌ(S)์˜ ๋ฐฐํ•ฉ์กฐ๊ฑด์œผ๋กœ Hy-SHCC๋ฅผ ์ œ์กฐํ•˜์˜€๋‹ค.

Table 1 Mixture proportion of Hy-SHCC

W/C

(%)

W

C

S

Steel fiber

(vol. %)

PE fiber

(vol. %)

MWCNT

(wt.%)

30

0.3

1.0

0.4

0.50

0.75

0.0

1.0

1์ข… ํฌํ‹€๋žœ๋“œ ์‹œ๋ฉ˜ํŠธ, ์ง๊ฒฝ 0.2~0.3 mm ๋ฒ”์œ„์˜ ๊ทœ์‚ฌ, ๊ณ ์„ฑ๋Šฅ ๊ฐ์ˆ˜์ œ์™€ ๋ฌผ์„ ํ˜ผ์ž…ํ•˜์—ฌ ๋น„๋น”ํ•œ ๊ตณ์ง€ ์•Š์€ ์‹œ๋ฉ˜ํŠธ ๋ณตํ•ฉ์ฒด์— Fig. 1๊ณผ ๊ฐ™์€ ํ˜•์ƒ๊ณผ ํŠน์„ฑ์„ ๊ฐ–๋Š” ์‹œ๋ฉ˜ํŠธ ๋ณตํ•ฉ์ฒด ๋ณด๊ฐ•์šฉ ๋‹จ์„ฌ์œ ๋กœ ๊ฐ•์„ฌ์œ ์™€ PE ํ•ฉ์„ฑ์„ฌ์œ ๊ฐ€ ์‚ฌ์šฉ๋˜์—ˆ๋‹ค. Hy-SHCC์˜ ์ „๋„์„ฑ์„ ํ–ฅ์ƒ์‹œํ‚ค๊ธฐ ์œ„ํ•˜์—ฌ ๊ณ ๋†์ถ• ์•ก์ƒํ˜• MWCNT(TNM8, Chengdu Organic Chemicals Co., Ltd., China)๋ฅผ ์‹œ๋ฉ˜ํŠธ ์งˆ๋Ÿ‰๋น„ 1.0 % ํ˜ผ์ž…ํ•˜์˜€๋‹ค. ์‚ฌ์šฉ๋œ ๊ณ ๋†์ถ• ์•ก์ƒํ˜• MWCNT์˜ ํŠน์„ฑ์€ ์„ ํ–‰์—ฐ๊ตฌ(Jang et al. 2020; Youn et al. 2020)์— ์ œ์‹œ๋œ ๋ฐ”์™€ ๊ฐ™๋‹ค.

Fig. 1 Reinforcing fibers for Hy-SHCC
../../Resources/KCI/JKCI.2022.34.2.203/fig1.png

2.2 Hy-SHCC ์ œ์กฐ ๋ฐ ์‹œํ—˜์ฒด ์ œ์ž‘

Hy-SHCC์˜ ๋น„๋น” ๋ฐ ์‹œํ—˜์ฒด ์ œ์ž‘์€ ์„ ํ–‰์—ฐ๊ตฌ์™€ ๋™์ผํ•œ ๋ฐฉ์‹์— ๋”ฐ๋ž๋‹ค. Fig. 2์— ๋‚˜ํƒ€๋‚œ ๋ฐ”์™€ ๊ฐ™์ด ๋จผ์ € ์‹œ๋ฉ˜ํŠธ์™€ ๊ทœ์‚ฌ์™€ ๊ฐ™์€ ๊ฑด์žฌ๋ฃŒ๋ฅผ 1๋ถ„ ๋™์•ˆ ๋ชจ๋ฅดํƒ€๋ฅด ๋ฏน์„œ๋ฅผ ์‚ฌ์šฉํ•˜์—ฌ ๋น„๋น”ํ•˜์˜€๋‹ค. ๊ณ ๋†์ถ• ์•ก์ƒํ˜• MWCNT๋Š” ๋น„๋น”์ˆ˜์™€ ํ˜ผํ•ฉํ•˜์—ฌ ๊ฑด๋น„๋น” ์žฌ๋ฃŒ์— ํˆฌ์ž…ํ•˜๊ณ  3๋ถ„๊ฐ„ ๋น„๋น”ํ•˜๊ณ  PE ํ•ฉ์„ฑ์„ฌ์œ  ๋ฐ ๊ฐ•์„ฌ์œ ๋ฅผ ์ˆœ์„œ๋Œ€๋กœ ํˆฌ์ž…ํ•˜๋ฉฐ ๊ฐ๊ฐ 3๋ถ„๊ฐ„ ๋น„๋น”ํ•˜์˜€๋‹ค. ์ถ”๊ฐ€๋กœ 1๋ถ„ 30์ดˆ ๋™์•ˆ ๋น„๋น” ํ›„ ํ† ์ถœํ•˜์—ฌ ๋ค๋ฒจํ˜•(dumbbell-shaped) ์ง์ ‘์ธ์žฅ ๋ฐ ์ž…๋ฐฉํ˜•(cubic) ์••์ถ• ์‹œํ—˜์ฒด, ์ „๊ธฐ์ €ํ•ญํŠน์„ฑ ํ‰๊ฐ€๋ฅผ ์œ„ํ•˜์—ฌ ์ •์‚ฌ๊ฐํ˜• ๋‹จ๋ฉด์„ ๊ฐ–๋Š” ์ž…๋ฐฉํ˜• ์‹œํ—˜์ฒด๋ฅผ ๊ฐ๊ฐ ์ œ์ž‘ํ•˜์˜€๋‹ค.

Hy-SHCC์˜ ์••์ถ•ํŠน์„ฑ์„ ํ‰๊ฐ€ํ•˜๊ธฐ ์œ„ํ•˜์—ฌ KS L 5105(KATS 2017)์— ์ค€ํ•˜์—ฌ 50ร—50ร—50 ใŽฃ ํฌ๊ธฐ์˜ ์ž…๋ฐฉํ˜• ์‹œํ—˜์ฒด๋ฅผ ๊ฐ ๋ฐฐํ•ฉ๋ณ„๋กœ 3๊ฐœ์”ฉ ์ œ์ž‘ํ•˜์˜€๋‹ค. Hy-SHCC์˜ ์ง์ ‘์ธ์žฅ๊ฐ•๋„ ํŠน์„ฑ์„ ํ‰๊ฐ€ํ•˜๊ธฐ ์œ„ํ•˜์—ฌ ๋ค๋ฒจํ˜• ์‹œํ—˜์ฒด๊ฐ€ ์ œ์ž‘๋˜์—ˆ์œผ๋ฉฐ ์‹œํ—˜์ฒด์˜ ํ˜•์ƒ ๋ฐ ์น˜์ˆ˜๋Š” ์„ ํ–‰์—ฐ๊ตฌ(Youn et al. 2020)์—์„œ ์‚ฌ์šฉ๋œ ์‹œํ—˜์ฒด์™€ ๋™์ผํ•˜๋‹ค. Hy-SHCC์˜ ๋ฐ˜๋ณต ์••์ถ•ํ•˜์—์„œ ์ „๊ธฐ์ €ํ•ญ ๋ฐ ๋ณ€ํ˜• ๊ฐ์ง€์„ฑ๋Šฅ์„ ํ‰๊ฐ€ํ•˜๊ธฐ ์œ„ํ•˜์—ฌ ์ œ์ž‘๋œ ์••์ถ• ์„ผ์„œ๋Š” 40ร— 40ร—80 ใŽฃ ํฌ๊ธฐ์˜ ์‚ฌ๊ฐ๊ธฐ๋‘ฅ ํ˜•์ƒ์œผ๋กœ ๊ฐ ๋ฐฐํ•ฉ๋ณ„๋กœ 3๊ฐœ์”ฉ ์ œ์ž‘ํ•˜์˜€๋‹ค.

์••์ถ• ๋ฐ ์ง์ ‘์ธ์žฅ๊ฐ•๋„ ํ‰๊ฐ€๋ฅผ ์œ„ํ•œ ์ œ์ž‘๋œ ์‹œํ—˜์ฒด๋Š” ํƒ€์„ค ์ดํ›„ 24์‹œ๊ฐ„์ด ๊ฒฝ๊ณผ๋œ ์‹œ์ ์—์„œ ํƒˆํ˜• ํ•˜์˜€๊ณ  ์ดํ›„ ์žฌ๋ น 28์ผ ์••์ถ• ๋ฐ ์ธ์žฅ์‹œํ—˜ ๋‹น์ผ ์ „๊นŒ์ง€ ์Šต์œค ์–‘์ƒํ•˜์˜€๋‹ค. ์ „๊ธฐ ์ €ํ•ญํŠน์„ฑ ํ‰๊ฐ€๋ฅผ ์œ„ํ•œ ์ž…๋ฐฉํ˜• ์„ผ์„œ๋Š” ํƒˆํ˜• ํ›„ ์žฌ๋ น 28์ผ ์‹œํ—˜ ์ „๋‚ ๊นŒ์ง€ ๊ธฐ๊ฑด ์–‘์ƒํ•˜์˜€๋‹ค.

Fig. 2 Mixing process of Hy-SHCC
../../Resources/KCI/JKCI.2022.34.2.203/fig2.png

2.3 ์‹œํ—˜๋ฐฉ๋ฒ•

์ž…๋ฐฉํ˜• ๊ณต์‹œ์ฒด์˜ ์••์ถ•์‹œํ—˜์€ ์ˆ˜๊ฒฝ์„ฑ ์‹œ๋ฉ˜ํŠธ ๋ชจ๋ฅดํƒ€๋ฅด ์••์ถ•๊ฐ•๋„ ์‹œํ—˜๋ฐฉ๋ฒ•(KS L 5105)์— ์ค€ํ•˜์—ฌ ์‹ค์‹œ๋˜์—ˆ์œผ๋ฉฐ ์ž…๋ฐฉํ˜• ๊ณต์‹œ์ฒด์˜ ์ธก๋ฉด์— ์••์ถ•๋ ฅ์˜ ๋„์ž… ์‹œ ๋ฐœ์ƒ๋˜๋Š” ์ˆ˜์ง ๋ฐ ์ˆ˜ํ‰๋ฐฉํ–ฅ ๋ณ€ํ˜•์„ ์ธก์ •ํ•˜๊ธฐ ์œ„ํ•˜์—ฌ ๊ฐ ์‹œํ—˜์ฒด์— ๊ฐ ๋ฐฉํ–ฅ์œผ๋กœ 2๊ฐœ์”ฉ ์ด 4๊ฐœ์˜ ์ฝ˜ํฌ๋ฆฌํŠธ ๊ฒŒ์ด์ง€๋ฅผ ๋ถ€์ฐฉํ•˜์˜€๋‹ค.

Hy-SHCC์— MWCNT ํ˜ผ์ž… ์—ฌ๋ถ€์— ๋”ฐ๋ฅธ ์ธ์žฅํŠน์„ฑ ํ‰๊ฐ€๋ฅผ ์œ„ํ•œ ๋ค๋ฒจํ˜• ์‹œํ—˜ํŽธ์— ๋Œ€ํ•œ ์ง์ ‘ ์ธ์žฅ์‹œํ—˜์€ ๊ธฐ์กด ์—ฐ๊ตฌ(Choi et al. 2012)์™€ ๋™์ผํ•œ ๋ฐฉ๋ฒ•์œผ๋กœ ์‹ค์‹œํ•˜์˜€๋‹ค.

1 wt% MWCNT์˜ ํ˜ผ์ž…์— ๋”ฐ๋ฅธ Hy-SHCC ์„ผ์„œ ์‹œํ—˜์ฒด์˜ ๋ฐ˜๋ณต ์••์ถ•ํ•˜์—์„œ ์ „๊ธฐ์ €ํ•ญ ๋ฐ ๋ณ€ํ˜• ๊ฐ์ง€ํŠน์„ฑ์„ ํ‰๊ฐ€ํ•˜๊ธฐ ์œ„ํ•˜์—ฌ Fig. 3๊ณผ ๊ฐ™์ด ๊ฐ ์ „๊ทน์˜ ์œ„์น˜์— ํ™ˆ์„ ํŒŒ๋‚ธ ํ›„ ๊ตฌ๋ฆฌ์„ ์„ ๊ฐ๊ณ  ์‹œํ—˜์ฒด์™€ ๊ตฌ๋ฆฌ์„  ์‚ฌ์ด์˜ ๊ณต๊ทน์„ ์ฑ„์šฐ๊ธฐ ์œ„ํ•˜์—ฌ ์‹ค๋ฒ„ํŽ˜์ด์ŠคํŠธ(silver paste)๋ฅผ ๋„ํฌํ•˜์˜€๋‹ค. ์„ ํ–‰ ์—ฐ๊ตฌ๊ฒฐ๊ณผ(Youn et al. 2020)์—์„œ Hy-SHCC์˜ ์•ˆ์ •๋œ ์ „๊ธฐ์ €ํ•ญ ์ธก์ •๋ฐฉ๋ฒ•์œผ๋กœ ๋ณด๊ณ ๋œ 4๋‹จ์ž(4-Probe)๋ฅผ ์ด์šฉํ•œ ์ €ํ•ญ ์ธก์ •๋ฐฉ๋ฒ•์ด ์ ์šฉ๋˜์—ˆ๋‹ค. ์‹œํ—˜์ฒด ๋„์ž…๋œ ๋ฐ˜๋ณต ์••์ถ•ํ•˜์ค‘์€ 28์ผ ์žฌ๋ น ์••์ถ•๊ฐ•๋„์˜ 10, 30 ๋ฐ 50 ๋ฐ 70 %์ธ 4์ˆ˜์ค€์—์„œ 9ํšŒ ๋ฐ˜๋ณตํ•˜๋Š” ์žฌํ•˜์ด๋ ฅ์„ ์ ์šฉํ•˜์˜€๋‹ค. ๋ฐ˜๋ณต ์••์ถ•ํ•˜์ค‘์˜ ๋„์ž…์‹œ ์‹œํ—˜์ฒด์˜ ๋ณ€ํ˜•๋Ÿ‰์„ ์ธก์ •ํ•˜๊ธฐ ์œ„ํ•˜์—ฌ 2๊ฐœ์˜ ์ฝ˜ํฌ๋ฆฌํŠธ ๋ณ€ํ˜• ๊ฒŒ์ด์ง€๊ฐ€ ์ธก๋ฉด์— ๋ถ€์ฐฉ๋˜์—ˆ๋‹ค.

Fig. 4๋Š” Hy-SHCC ์••์ถ•์„ผ์„œ ์‹œํ—˜์ฒด์˜ ๋ฐ˜๋ณต ์••์ถ•ํ•˜์ค‘ ๋„์ž… ๋ฐ 4 ๋‹จ์ž ํ™œ์šฉ ์ „๊ธฐ ์ €ํ•ญ์ธก์ •์„ ์œ„ํ•œ ์žฅ์น˜์˜ ์„ค์น˜์ƒํ™ฉ์„ ๋‚˜ํƒ€๋‚ธ ๊ฒƒ์ด๋‹ค. ์••์ถ•์„ผ์„œ ์‹œํ—˜์ฒด์— ๋ฐ˜๋ณต ์••์ถ•์žฌํ•˜์‹œ ์‹ค์‹œ๊ฐ„์œผ๋กœ ์ „๊ธฐ์ €ํ•ญ ์ธก์ •์žฅ์น˜(LCR meter)๋Š” K์‚ฌ(E4980AL, Malaysia)๋ฅผ ์ด์šฉํ•˜์—ฌ ๋‹จ์ž๋กœ๋ถ€ํ„ฐ ์ „๊ธฐ์ €ํ•ญ์„ ์ธก์ •ํ•˜์˜€๋‹ค. ์ „๊ธฐ์ €ํ•ญ์€ 1์ดˆ์— 1ํšŒ์”ฉ ์ธก์ •ํ•˜์—ฌ ๋ฐ˜๋ณต์••์ถ•๋ ฅ์˜ ๋„์ž…์— ๋”ฐ๋ฅธ ์••์ถ• ์„ผ์„œ ๋‚ด์—์„œ ์ „๊ธฐ ์ €ํ•ญ๋ณ€ํ™”๋ฅผ ๊ณ„์ธกํ•˜๊ณ  ์ด๋ฅผ ๊ทผ๊ฑฐ๋กœ ๋ณ€ํ˜• ๊ฐ์ง€๋Šฅ๋ ฅ์„ ํ‰๊ฐ€ํ•˜์˜€๋‹ค.

Fig. 3 Configuration of Hy-SHCC sensor
../../Resources/KCI/JKCI.2022.34.2.203/fig3.png
Fig. 4 Setup for loading and resistivity measurement
../../Resources/KCI/JKCI.2022.34.2.203/fig4.png

๋ฐฐํ•ฉ๋ณ„๋กœ ์ œ์ž‘๋œ 3๊ฐœ ์••์ถ• ์„ผ์„œ ์‹œํ—˜์ฒด์˜ ์ „๊ธฐ์  ์ €ํ•ญํŠน์„ฑ์„ ํ‰๊ฐ€ํ•˜๊ธฐ ์œ„ํ•˜์—ฌ ์••์ถ•์‘๋ ฅ์ด ๋„์ž…๋˜์ง€ ์•Š์€ ์ƒํƒœ์—์„œ 15๋ถ„ ๋™์•ˆ ์ธก์ •๋œ ์ €ํ•ญ์˜ ํ‰๊ท ๊ฐ’์„ ๊ทผ๊ฑฐ๋กœ ๋‹ค์Œ ์‹ (1)๊ณผ ๊ฐ™์ด ์ •์˜๋˜๋Š” ๋น„์ €ํ•ญ(volume resistivity, ฯ)์„ ์žฌ๋ น์— ๋”ฐ๋ผ ํ‰๊ฐ€ํ•˜์˜€๋‹ค.

(1)
$\rho =R\times\dfrac{A}{L}(\Omega cm)$

์—ฌ๊ธฐ์„œ, $R$์€ 15๋ถ„๊ฐ„ ์ธก์ •๋œ ์ €ํ•ญ์˜ ํ‰๊ท ๊ฐ’, $A$๋Š” ์••์ถ• ์„ผ์„œ ์‹œํ—˜์ฒด์˜ ๋‹จ๋ฉด์ (16 ใŽ )์ด๊ณ  $L$์€ ์ „๊ทน ๊ฐ„ ๊ฑฐ๋ฆฌ(3 cm)๋กœ ์ •์˜๋œ๋‹ค.

3. ์‹คํ—˜๊ฒฐ๊ณผ ๋ฐ ๋ถ„์„

3.1 ์••์ถ• ํŠน์„ฑ

๊ณ ๋†์ถ• ์•ก์ƒํ˜• MWCNT์˜ 1 wt% ํ˜ผ์ž… ์—ฌ๋ถ€์— ๋”ฐ๋ฅธ ๋ฐฐํ•ฉ ๋ณ„๋กœ 3๊ฐœ์”ฉ ์ œ์ž‘๋œ Hy-SHCC ์ž…๋ฐฉํ˜• ๊ณต์‹œ์ฒด์˜ ์••์ถ•์‘๋ ฅ-์ˆ˜์ง ๋ฐ ์ˆ˜ํ‰ ๋ณ€ํ˜•๋ฅ  ๊ฑฐ๋™์„ Fig. 5์— ๋‚˜ํƒ€๋‚ด์—ˆ๋‹ค.

๋ฌผ์‹œ๋ฉ˜ํŠธ(w/c)๋น„ 0.3์ด๊ณ  ๊ฐ•์„ฌ์œ ์™€ PE ํ•ฉ์„ฑ์„ฌ์œ ๋กœ ๋ณด๊ฐ•๋œ ๋ณ€ํ˜•๊ฒฝํ™”ํ˜• ์‹œ๋ฉ˜ํŠธ ๋ณตํ•ฉ์ฒด(Hy-SHCC)์˜ ์žฌ๋ น 28์ผ ํ‰๊ท ์••์ถ•๊ฐ•๋„($f_{cm}$)๋Š” 1 wt%์˜ ๊ณ ๋†์ถ• MWCNT ํ˜ผ์ž… ์—ฌ๋ถ€์— ๋”ฐ๋ผ ๊ฐ๊ฐ 30.9 MPa์™€ 47.5 MPa๋กœ MWCNT์˜ ํ˜ผ์ž…๋จ์— ๋”ฐ๋ผ ์••์ถ•๊ฐ•๋„๊ฐ€ 35 % ์ €ํ•˜๋˜๋Š” ๊ฒƒ์œผ๋กœ ๋‚˜ํƒ€๋‚ฌ๋‹ค. ์„ฌ์œ  ํ˜ผ์ž…์ „ ์‹œ๋ฉ˜ํŠธ ๋ณตํ•ฉ์ฒด์˜ ๋ชฉํ‘œ ํ”Œ๋กœ์šฐ 300 mm ํ™•๋ณด๋ฅผ ์œ„ํ•˜์—ฌ MWCNT๊ฐ€ ํ˜ผ์ž…๋œ ์‹œ๋ฉ˜ํŠธ ๋ณตํ•ฉ์ฒด์˜ ์ œ์กฐ ์‹œ ๊ณ ์„ฑ๋Šฅ ๊ฐ์ˆ˜์ œ๊ฐ€ MWCNT๋ฅผ ํ˜ผ์ž…ํ•˜์ง€ ์•Š์€ ๊ฒฝ์šฐ์— ๋น„ํ•˜์—ฌ 21 % ๋งŽ์€ 4.55 % ํ˜ผ์ž…๋˜์—ˆ๋‹ค ์ด์— ๋”ฐ๋ฅธ ๋ณตํ•ฉ์ฒด ๋‚ด ๊ณต๊ธฐ๋Ÿ‰ ์ฆ๊ฐ€์™€ MWCNT์˜ ํ˜ผ์ž…์— ๋”ฐ๋ฅธ ๋ถ€๋ถ„์ ์ธ ์‘์ง‘(agglomeration)์— ๋”ฐ๋ฅธ ๊ฒƒ์œผ๋กœ ํŒ๋‹จ๋œ๋‹ค. PE ํ•ฉ์„ฑ์„ฌ์œ  2 %๊ฐ€ ํ˜ผ์ž…๋œ ECC(engineered cement composite)์—์„œ๋„ CNT์˜ ํ˜ผ์ž…๋Ÿ‰์ด ์ฆ๊ฐ€๋จ์— ๋”ฐ๋ฅธ ์••์ถ•๊ฐ•๋„๊ฐ€ ์ €ํ•˜๋˜๋Š” ๊ฒฝํ–ฅ์„ ๋ณด์˜€๋‹ค(Yang and Qian 2020). ๋˜ํ•œ ์‹œ๋ฉ˜ํŠธ ๋ชจ๋ฅดํƒ€๋ฅด์— 1.0 % CNT ํ˜ผ์ž…์‹œ ์••์ถ•๊ฐ•๋„๊ฐ€ ๋‹ค์†Œ ์ €ํ•˜๋˜๋Š” ๊ฒƒ์œผ๋กœ ๋ณด๊ณ ๋˜๊ณ  ์žˆ๋‹ค(Chaipanich et al. 2010; Camacho et al. 2014; Paul et al. 2018). ๋ฐ˜๋ฉด 0.1 % ํ˜ผ์ž…์— ๋”ฐ๋ผ ์••์ถ•๊ฐ•๋„๋Š” 6~15 % ๋ฒ”์œ„์—์„œ ์ฆ๊ฐ€๋˜๋Š” ๊ฒƒ์œผ๋กœ ๋ณด๊ณ ๋˜๊ธฐ๋„ ํ•˜์˜€๋‹ค(Xu et al. 2015). ์ด์ƒ๊ณผ ๊ฐ™์ด CNT ํ˜ผ์ž…์ด ์‹œ๋ฉ˜ํŠธ ๋ณตํ•ฉ์ฒด์˜ ์••์ถ•๊ฐ•๋„์— ๋ผ์น˜๋Š” ์˜ํ–ฅ์€ ์—ฐ๊ตฌ์ž๋ณ„๋กœ ๋‹ค์†Œ ์ƒ์ดํ•œ ๊ฒฐ๊ณผ๋ฅผ ์ œ์‹œํ•˜๊ณ  ์žˆ๋‹ค.

Fig. 5 Compressive responses of cubic specimens
../../Resources/KCI/JKCI.2022.34.2.203/fig5.png

3.2 ์ง์ ‘ ์ธ์žฅํŠน์„ฑ

Fig. 6์€ MWCNT์˜ ํ˜ผ์ž… ์—ฌ๋ถ€์— ๋”ฐ๋ฅธ Hy-SHCC ๋ค๋ฒจํ˜• ์ง์ ‘ ์ธ์žฅ์‹œํ—˜ํŽธ์˜ ์ธ์žฅ์‘๋ ฅ-๋ณ€ํ˜•๋ฅ  ๊ด€๊ณ„๋ฅผ ๋‚˜ํƒ€๋‚ธ ๊ฒƒ์ด๋‹ค. Table 2๋Š” ๋ฐฐํ•ฉ๋ณ„๋กœ 3๊ฐœ์”ฉ ์ œ์ž‘๋œ Hy-SHCC ์ง์ ‘์ธ์žฅ ์‹œํ—˜์ฒด์˜ ์‹คํ—˜๊ฒฐ๊ณผ๋ฅผ ์š”์•ฝํ•˜์—ฌ ๋‚˜ํƒ€๋‚ธ ๊ฒƒ์ด๋‹ค.

Fig. 6 Tensile responses of Hy-SHCC specimens
../../Resources/KCI/JKCI.2022.34.2.203/fig6.png
Table 2 Summary of tensile tests on Hy-SHCC dumbbell-shaped specimens

Mixture type

First crack

Ultimate state

Average number of cracks at ultimate state

(EA)

Strength, $\sigma_{cc}$

(MPa)

Strain, $\varepsilon_{cc}$

(%)

Strength, $\sigma_{pc}$

(MPa)

Strain, $\varepsilon_{pc}$

(%)

Hy-SHCC-WO MWCNT

3.37 (ยฑ0.43)

0.041 (ยฑ0.01)

4.99 (ยฑ0.35)

1.18 (ยฑ0.05)

15.3 (ยฑ5.0)

Hy-SHCC-W MWCNT

2.76 (ยฑ0.26)

0.033 (ยฑ0.01)

3.56 (ยฑ0.30)

0.75 (ยฑ0.14)

20.3 (ยฑ7.0)

์ง์ ‘์ธ์žฅ ์‹คํ—˜๊ฒฐ๊ณผ, MWCNT๊ฐ€ ํ˜ผ์ž…๋˜์ง€ ์•Š์€ Hy-SHCC (Hy-SHCC-WO MWCNT) ์ธ์žฅ ์‹œํ—˜์ฒด์˜ ์ดˆ๊ธฐ ์ธ์žฅ๊ท ์—ด ๊ฐ•๋„($\sigma_{cc}$)๋Š” ํ‰๊ท  3.37 MPa๋กœ 1 wt% MWCNT๊ฐ€ ํ˜ผ์ž…๋œ ๋ฐฐํ•ฉ(Hy-SHCC-W MWCNT)์— ๋น„ํ•˜์—ฌ 22.1 % ๋†’๊ฒŒ ๋‚˜ํƒ€๋‚ฌ๋‹ค. Hy-SHCC ๋ฐฐํ•ฉ๋ณ„ ์••์ถ•๊ฐ•๋„์˜ ์˜ํ–ฅ์„ ๊ณ ๋ คํ•˜๊ธฐ ์œ„ํ•˜์—ฌ ์ดˆ๊ธฐ๊ท ์—ด๊ฐ•๋„๋ฅผ ์ฝ˜ํฌ๋ฆฌํŠธ ์••์ถ•๊ฐ•๋„์˜ ์ œ๊ณฑ๊ทผ์œผ๋กœ ๋ฌด์ฐจํ™”์›ํ™”ํ•œ ์ดˆ๊ธฐ๊ท ์—ด ์ธ์žฅ๊ฐ•๋„($\sigma_{cc}/\sqrt{f_{cm}}$)์€ ๋‘ Hy-SHCC ๋ฐฐํ•ฉ์—์„œ ์•ฝ 0.49๋กœ ๋Œ€๋“ฑํ•˜๊ฒŒ ๋‚˜ํƒ€๋‚ฌ๋‹ค. Hy-SHCC์˜ ์ดˆ๊ธฐ ์ธ์žฅ๊ท ์—ด ์‹œ ๋ณ€ํ˜•๋Šฅ๋ ฅ($\varepsilon_{cc}$)์€ MWCNT ํ˜ผ์ž…์— ๋”ฐ๋ผ ์•ฝ 20 % ์ €ํ•˜๋˜๋Š” ๊ฒƒ์œผ๋กœ ๋‚˜ํƒ€๋‚ฌ๋‹ค. MWCNT๊ฐ€ ํ˜ผ์ž…๋œ Hy-SHCC ์ธ์žฅ ์‹œํ—˜์ฒด์˜ ํ‰๊ท  ์ง์ ‘์ธ์žฅ๊ฐ•๋„($\sigma_{pc}$)๋Š” 3.56 MPa๋กœ MWCNT๊ฐ€ ํ˜ผ์ž…๋˜์ง€ ์•Š์€ ๋ฐฐํ•ฉ์— ๋น„ํ•˜์—ฌ ์•ฝ 40 % ๋‚ฎ๊ฒŒ ๋‚˜ํƒ€๋‚ฌ๋‹ค. ๋ฌด์ฐจ์›ํ™”๋œ ์ธ์žฅ๊ฐ•๋„($\sigma_{pc}/\sqrt{f_{cm}}$)์— ์žˆ์–ด์„œ Hy-SHCC-W MWCNT์™€ -WO MWCNT ๋ฐฐํ•ฉ์—์„œ ๊ฐ๊ฐ 0.64 ๋ฐ 0.72๋กœ ๋‚˜ํƒ€๋‚ฌ๋‹ค. ์ดˆ๊ธฐ ๊ท ์—ด ์‹œ ๋ณ€ํ˜•๋Šฅ๋ ฅ๊ณผ ๊ฐ™์ด ์ธ์žฅ๊ฐ•๋„ ์‹œ ํ‰๊ท  ๋ณ€ํ˜•๋Šฅ๋ ฅ($\varepsilon_{pc}$)์€ ๊ฐ๊ฐ 1.18 % ๋ฐ 0.75 %๋กœ ๋‚˜ํƒ€๋‚˜ 1 % MWCNT ํ˜ผ์ž…์€ Hy-SHCC์˜ ์ธ์žฅ๊ฐ•๋„ ๋ฐ ๋ณ€ํ˜•๋Šฅ๋ ฅ์„ ์ €ํ•˜์‹œํ‚ค๋Š” ๊ฒƒ์œผ๋กœ ๋‚˜ํƒ€๋‚ฌ๋‹ค. ๊ทธ๋Ÿฌ๋‚˜ SHCC์™€ ์œ ์‚ฌํ•œ ํŠน์„ฑ์„ ๊ฐ–๋Š” ECC์—์„œ 1.0 % ์ด๋‚ด์˜ CNT์˜ ํ˜ผ์ž…์€ ์ดˆ๊ธฐ๊ท ์—ด ๋ฐ ์ธ์žฅ๊ฐ•๋„๋ฅผ ์ฆ์ง„์‹œํ‚ค๋Š” ๊ฒฝํ–ฅ์„ ๋ณด์ด๋‚˜ ๋ณ€ํ˜•๋Šฅ๋ ฅ์€ ๊ฐ์†Œ๋˜๋Š” ๊ฒƒ์œผ๋กœ ๋ณด๊ณ ๋˜๊ณ  ์žˆ๋‹ค(Liu et al. 2019; Yang and Qian 2020).

๊ธฐ์กด ์—ฐ๊ตฌ์—์„œ๋Š” ECC ์‹œ๋ฉ˜ํŠธ ๋ณตํ•ฉ์ฒด์— ํ˜ผ์ž…๋œ CNT๋Š” ์ง์ ‘ ์ธ์žฅ ํ•˜์—์„œ ์‹œ๋ฉ˜ํŠธ ๋ณตํ•ฉ์ฒด์˜ ๋ฏธ์„ธ๊ท ์—ด์„ ๊ฐ€๊ตํ•˜๊ณ  ์‹œ๋ฉ˜ํŠธ ๋ณตํ•ฉ์ฒด ๋‚ด๋ถ€ ๊ณต๊ทน์„ ์ฑ„์šฐ๋Š” ํ•„๋Ÿฌ(filler)๋กœ ๊ฒฝํ™”๋œ ๋ณตํ•ฉ์ฒด์˜ ๋ฐ€๋„๋ฅผ ์ฆ๊ฐ€์‹œํ‚ค๋Š” ์—ญํ• ์„ ํ•˜๋ฉฐ ๋˜ํ•œ ์‹œ๋ฉ˜ํŠธ ๋ณตํ•ฉ์ฒด์˜ ์ดˆ๊ธฐ ์ˆ˜ํ™”๋ฐ˜์‘์„ ์ด‰์ง„ํ•˜์—ฌ ์ธ์žฅ๊ฐ•๋„๋ฅผ ํ–ฅ์ƒ์‹œํ‚จ ๊ฒƒ์œผ๋กœ ๋ณด๊ณ ํ•˜๊ณ  ์žˆ๋‹ค. ๊ทธ๋Ÿฌ๋‚˜ ์ด ์—ฐ๊ตฌ์—์„œ MWCNT ํ˜ผ์ž…์— ๋”ฐ๋ผ Hy- SHCC์˜ ๊ท ์—ด ๋ฐ ์ธ์žฅ๊ฐ•๋„๊ฐ€ ์ €ํ•˜๋œ ๊ฒƒ์€ ์‹œ๋ฉ˜ํŠธ ๋ณตํ•ฉ์ฒด ๋‚ด ๋ถ„์‚ฐ์ด ์šฉ์ดํ•˜๋„๋ก ์‚ฌ์šฉ๋œ ์•ก์ƒํ˜• MWCNT๊ฐ€ Fig. 7๊ณผ ๊ฐ™์ด ๋ถ€๋ถ„์ ์œผ๋กœ ์‘์ง‘๋˜์–ด ์‹œ๋ฉ˜ํŠธ ๋ณตํ•ฉ์ฒด๋‚ด ๊ฒฐํ•จ๋ถ€๋กœ ์—ญํ• ์„ ํ•˜๊ณ  ์žˆ๊ธฐ ๋•Œ๋ฌธ์œผ๋กœ ํŒ๋‹จ๋œ๋‹ค.

Fig. 8์€ MWCNT์˜ ํ˜ผ์ž… ์—ฌ๋ถ€์— ๋”ฐ๋ฅธ ์ง์ ‘์ธ์žฅ ์‹œํ—˜์ฒด์˜ ์ „ํ˜•์ ์ธ ๊ท ์—ด ์ง„์ „๊ณผ์ •์„ ๋น„๊ตํ•˜์—ฌ ๋‚˜ํƒ€๋‚ธ ๊ฒƒ์ด๋‹ค. ์ธ์žฅ๊ฐ•๋„ ๋ฐœํ˜„ ์‹œ ๊ฐ ์‹œํ—˜์ฒด์— ๋ฐœ์ƒ๋œ ํ‰๊ท  ๊ท ์—ด์ˆ˜๋Š” MWCNT๊ฐ€ ํ˜ผ์ž… ์—ฌ๋ถ€์— ๋”ฐ๋ผ ๊ฐ๊ฐ 15.3๊ฐœ ๋ฐ 20.3๊ฐœ๋กœ MWCNT๋Š” Hy-SHCC์˜ ๋‹ค์ˆ˜ ๊ท ์—ด๋ถ„์‚ฐ์—๋Š” ์œ ๋ฆฌํ•˜๊ธฐ ์ž‘์šฉํ•˜๋Š” ๊ฒƒ์œผ๋กœ ๋‚˜ํƒ€๋‚ฌ๋‹ค. PE ํ•ฉ์„ฑ์„ฌ์œ ๋กœ ๋ณด๊ฐ•๋œ ECC์—์„œ CNT ํ˜ผ์ž…์— ๋”ฐ๋ฅธ ๊ท ์—ด๋ถ„์‚ฐ ์„ฑ๋Šฅ์˜ ํ–ฅ์ƒ์€ ๊ธฐ์กด ์—ฐ๊ตฌ(Yang and Qian 2020)์—์„œ๋„ ๋ณด๊ณ ๋˜๊ณ  ์žˆ๋‹ค.

Fig. 7 Microstructure of Hy-SHCC-W MWCNT
../../Resources/KCI/JKCI.2022.34.2.203/fig7.png
Fig. 8 Typical cracking procedure of Hy-SHCCdumbbell-shaped specimens
../../Resources/KCI/JKCI.2022.34.2.203/fig8.png

3.3 ์ „๊ธฐ์  ํŠน์„ฑ

Fig. 9๋Š” MWCNT ํ˜ผ์ž…์— ๋”ฐ๋ฅธ Hy-SHCC์˜ ์ „๊ธฐ ์ €ํ•ญํŠน์„ฑ ๋ณ€ํ™”๋ฅผ ํ‰๊ฐ€ํ•˜๊ธฐ ์œ„ํ•˜์—ฌ ๋ฐ˜๋ณต ์••์ถ•๋ณ€ํ˜• ๊ณ„์ธก์šฉ ์„ผ์„œ์˜ ์žฌ๋ น์— ๋”ฐ๋ผ 15๋ถ„๊ฐ„ ์ธก์ •๋œ ํ‰๊ท  ์ „๊ธฐ์ €ํ•ญ์„ ๊ทผ๊ฑฐ๋กœ ์‹ (1)์— ์˜ํ•ด ๊ณ„์‚ฐ๋œ ๋น„์ €ํ•ญ(ฯ)์„ ๋น„๊ตํ•˜์—ฌ ๋‚˜ํƒ€๋‚ธ ๊ฒƒ์ด๋‹ค.

Fig. 9 MWCNTs effect on electrical resistivity
../../Resources/KCI/JKCI.2022.34.2.203/fig9.png

Hy-SHCC์— 1 wt% MWCNT์˜ ํ˜ผ์ž… ์‹œ, ๊ฐ ์žฌ๋ น์— ๋”ฐ๋ฅธ ์ „๊ธฐ ์ €ํ•ญ์€ ์ฆ๊ฐ€๋˜๋Š” ๊ฒฝํ–ฅ์„ ๋ณด์ด๊ณ  ์žˆ์œผ๋ฉฐ 3๊ฐœ ์„ผ์„œ(Sensor \#1~3)์—์„œ ์ธก์ •๋œ ์ €ํ•ญ ๊ฐ’์€ ํฐ ํŽธ์ฐจ๋ฅผ ๋ณด์ด์ง€ ์•Š๊ณ  ์•ˆ์ •๋œ ์ „๊ธฐ ์ €ํ•ญํŠน์„ฑ์„ ๋ณด์ธ๋‹ค. ๋ฐ˜๋ฉด MWCNT๊ฐ€ ํ˜ผ์ž…๋˜์ง€ ์•Š์€ Hy-SHCC ์„ผ์„œ(Sensor \#4~6)์˜ ์ „๊ธฐ์ €ํ•ญ ๋ณ€ํ™”๋Š” ๊ฐ ์žฌ๋ น์—์„œ ํฐ ํŽธ์ฐจ๋ฅผ ๋ณด์ธ๋‹ค. ์ด๋Š” Hy-SHCC-WO MWCNT ์„ผ์„œ์—์„œ ์ „๋„๋ฌผ์งˆ์€ ๊ฐ•์„ฌ์œ ๋กœ ์‹œ๋ฉ˜ํŠธ ๋ณตํ•ฉ์ฒด ๋‚ด์—์„œ ์„ฌ์œ  ๋ถ„์‚ฐ์ด ์ƒ์ดํ•˜๊ธฐ ๋•Œ๋ฌธ์ธ ๊ฒƒ์œผ๋กœ ํŒ๋‹จ๋œ๋‹ค. ๋ฐ˜๋ฉด Hy-SHCC-W MWCNT ์„ผ์„œ ์‹œํ—˜์ฒด์—์„œ ๊ฐ•์„ฌ์œ  ์ด์™ธ์— MWCNT๊ฐ€ ์ „๋„๋ฌผ์งˆ๋กœ ํ˜ผ์ž…๋˜์–ด ์‹œ๋ฉ˜ํŠธ ๋ณตํ•ฉ์ฒด๊ฐ€ ๊ท ์งˆํ•œ ์ „๋„ํŠน์„ฑ์„ ๋ณด์œ ํ•˜๊ณ  ์žˆ๊ธฐ ๋•Œ๋ฌธ์ธ ๊ฒƒ์œผ๋กœ ํŒ๋‹จ๋œ๋‹ค.

๋˜ํ•œ ์žฌ๋ น์— ๋”ฐ๋ฅธ ์ „๊ธฐ์ €ํ•ญ์€ ์ฆ๊ฐ€๋˜๋Š” ํŠน์„ฑ์„ ๋ณด์ด๊ณ  ์žˆ์œผ๋ฉฐ ํŠนํžˆ MWCNT๋ฅผ ํ˜ผ์ž…ํ•œ Hy-SHCC ์„ผ์„œ์—์„œ ์ด๋Ÿฌํ•œ ๊ฒฝํ–ฅ์€ ๋ช…ํ™•ํ•˜๊ฒŒ ๋‚˜ํƒ€๋‚ฌ๋‹ค. ์ด์™€ ๊ฐ™์ด MWCNT๋ฅผ ํ˜ผ์ž…ํ•œ ์‹œ๋ฉ˜ํŠธ ๋ณตํ•ฉ์ฒด์—์„œ ์žฌ๋ น์— ๋”ฐ๋ฅธ ์ „๊ธฐ์ €ํ•ญ์˜ ์„ ํ˜•์ ์ธ ์ฆ๊ฐ€๋Š” ๊ธฐ์กด ์—ฐ๊ตฌ(Sasmal et al. 2017; Youn et al. 2020; Cerro-Prada et al. 2021)์—์„œ๋„ ๋ณด๊ณ ๋˜๊ณ  ์žˆ๋‹ค. ์ด๋Š” ์‹œ๋ฉ˜ํŠธ ๋ณตํ•ฉ์ฒด์˜ ์ˆ˜ํ™”๋„(degree of hydration) ์ฆ๊ฐ€์— ๋”ฐ๋ผ ๋ชจ์„ธ๊ด€ ๊ธฐ๊ณต์˜ ์—ฐ์†์„ฑ ๊ฐ์†Œ, ๋ฏธ์„ธ๊ตฌ์กฐ์˜ ๋ณ€ํ™” ๋ฐ ๊ธฐ๊ณต๋‚ด์— ์กด์žฌํ•˜๋Š” ์ด์˜จ์„ฑ ์œ ์ฒด์˜ ๋†๋„๋ณ€ํ™”์— ๋”ฐ๋ฅธ ๊ฒƒ์œผ๋กœ ๋ณด๊ณ ๋˜๊ณ  ์žˆ๋‹ค.

Fig. 10์€ Hy-SHCC ๊ฐ ๋ฐฐํ•ฉ๋ณ„๋กœ ์ œ์ž‘๋œ 3๊ฐœ์˜ ์••์ถ• ์„ผ์„œ ์‹œํ—˜์ฒด์— ๋Œ€ํ•œ ๋„์ž…๋œ ๋ฐ˜๋ณต์••์ถ•์‘๋ ฅ, ์••์ถ•๋ณ€ํ˜• ๋ฐ ์ €ํ•ญ์˜ ๋ถ„์ˆ˜๋ณ€ํ™”(fractional change of resistivity, FCR)๋ฅผ ๋น„๊ตํ•˜์—ฌ ๋‚˜ํƒ€๋‚ธ ๊ฒƒ์ด๋‹ค. ๋ฐ˜๋ณต์••์ถ•์‘๋ ฅ์€ ๋ฐฐํ•ฉ๋ณ„๋กœ ์ œ์ž‘๋œ 3๊ฐœ์˜ ์ž…๋ฐฉํ˜• ๋ชจ๋ฅดํƒ€๋ฅด ํ‘œ์ค€ ๊ณต์‹œ์ฒด์˜ ํ‰๊ท ์••์ถ•๊ฐ•๋„๋ฅผ ๊ทผ๊ฑฐ๋กœ 10, 30, 50 ๋ฐ 70 % ์ˆ˜์ค€์˜ ์••์ถ•์‘๋ ฅ์„ 9ํšŒ์”ฉ ๋ฐ˜๋ณต์žฌํ•˜๊ฐ€ ๊ณ„ํš๋˜์—ˆ๋‹ค. Fig. 10(a)์— ๋‚˜ํƒ€๋‚œ ๋ฐ”์™€ ๊ฐ™์ด MWCNT๋ฅผ ํ˜ผ์ž…ํ•˜์ง€ ์•Š์€ Hy-SHCC ์••์ถ• ์„ผ์„œ ์‹œํ—˜์ฒด๋Š” ์••์ถ•๊ฐ•๋„ 70 % ์ˆ˜์ค€์˜ ๋ฐ˜๋ณต ์••์ถ• ์‹œ๊นŒ์ง€ ํŒŒ๊ดด๋˜์ง€ ์•Š์•˜๋‹ค. ์ด๋•Œ ์‹œํ—˜์ฒด ์–‘์ธก๋ฉด์—์„œ ๊ณ„์ธก๋œ ํ‰๊ท  ์••์ถ• ๋ณ€ํ˜•๋ฅ ์€ ์••์ถ•๊ฐ•๋„์˜ 30 %๋ฅผ ๋„˜์–ด์„œ๋ฉด์„œ ์ž”๋ฅ˜๋ณ€ํ˜•์ด ์œ ๋ฐœ๋˜์—ˆ๊ณ  ๋„์ž…๋œ ์••์ถ•์‘๋ ฅ์ด ์ฆ๊ฐ€๋จ์— ๋”ฐ๋ผ ์ด๋Ÿฌํ•œ ๊ฒฝํ–ฅ์€ ํ˜„์ €ํ•˜๊ฒŒ ๋‚˜ํƒ€๋‚ฌ๋‹ค. ๋˜ํ•œ ์••์ถ•์„ผ์„œ ์‹œํ—˜์ฒด๋ณ„๋กœ ์‹ (2)์— ์ค€ํ•˜์—ฌ ์‚ฐ์ •๋œ FCR์€ ์••์ถ•์‘๋ ฅ์ด ๋„์ž…๋จ์— ๋”ฐ๋ผ ๊ฐ์†Œ๋˜๊ณ  ์••์ถ•์‘๋ ฅ์˜ ์ œํ•˜ ์‹œ ์ฆ๊ฐ€๋˜๋Š” ํŠน์„ฑ์„ ๋ณด์˜€๋‹ค.

(2)
$$ F C R(\%)=\frac{\rho^{-} \rho_{o}}{\rho_{o}} \times 100=\frac{R-R_{o}}{R_{o}} \times 100 $$
Fig. 10 Compressive stress, strain and FCR curves of Hy-SHCC sensors
../../Resources/KCI/JKCI.2022.34.2.203/fig10.png

์—ฌ๊ธฐ์„œ, $\rho_{o}$๋ฐ $R_{o}$๋Š” ์ดˆ๊ธฐ ๋น„์ €ํ•ญ ๋ฐ ์ €ํ•ญ, $\rho$๋ฐ $R$๋Š” ์••์ถ•์‘๋ ฅ ์ž‘์šฉ ์‹œ ์ฒด์ ์ €ํ•ญ ๋ฐ ์ €ํ•ญ์„ ๋‚˜ํƒ€๋‚ธ๋‹ค.

Fig. 10(b)์€ Hy-SHCC์— 1 wt% MWCNT๋ฅผ ํ˜ผ์ž…ํ•œ ์••์ถ• ์„ผ์„œ์— ๋Œ€ํ•œ ๋ฐ˜๋ณต์••์ถ• ์‹œํ—˜๊ฒฐ๊ณผ๋ฅผ ๋‚˜ํƒ€๋‚ธ ๊ฒƒ์ด๋‹ค. ์ด ์—ฐ๊ตฌ์—์„œ๋Š” ์‹œ๋ฉ˜ํŠธ ๋ณตํ•ฉ์ฒด๋‚ด ๋ถ„์‚ฐ์ด ์šฉ์ดํ•˜๋„๋ก ์•ก์ƒํ˜• MWCNT๋ฅผ ์‚ฌ์šฉํ•˜์˜€์œผ๋‚˜ Fig. 7์— ๋‚˜ํƒ€๋‚œ ๋ฐ”์™€ ๊ฐ™์ด ์‹œ๋ฉ˜ํŠธ ๋ณตํ•ฉ์ฒด ๋‚ด์—์„œ MWCNT์˜ ์ผ๋ถ€๊ฐ€ ์‘์ง‘๋˜์–ด ์••์ถ•๊ฐ•๋„๊ฐ€ ์ €ํ•˜๋˜๋Š” ํ˜„์ƒ์„ ๋ณด์˜€๋‹ค. ์ด๋Ÿฌํ•œ MWCNT ์‘์ง‘์— ๋”ฐ๋ผ MWCNT๋ฅผ ํ˜ผ์ž…ํ•œ Hy-SHCC ์••์ถ• ์„ผ์„œ๋Š” ์••์ถ•๊ฐ•๋„์˜ 50 % ๋ฐ˜๋ณต์žฌํ•˜ ํ›„ 70 % ์ˆ˜์ค€์œผ๋กœ ์ฆ๊ฐ€๋˜๋Š” ์‹œ์ ์—์„œ ํŒŒ๊ดด๋˜๋Š” ๊ฒฝํ–ฅ์„ ๋ณด์˜€๋‹ค. ๊ทธ๋Ÿฌ๋‚˜ ๋ฐ˜๋ณต์••์ถ•์‘๋ ฅ์˜ ์ˆ˜์ค€์ด ์ฆ๊ฐ€๋จ์— ๋”ฐ๋ผ ์ž”๋ฅ˜ ์••์ถ• ๋ณ€ํ˜•๋Ÿ‰์€ ์ƒ๋Œ€์ ์œผ๋กœ MWCNT๋ฅผ ํ˜ผ์ž…ํ•˜์ง€ ์•Š์€ ์••์ถ• ์„ผ์„œ ์‹œํ—˜์ฒด์— ๋น„ํ•˜์—ฌ ์ž‘๊ฒŒ ๋‚˜ํƒ€๋‚ฌ๋‹ค. ๋ฐ˜๋ณต์••์ถ•์‘๋ ฅ ํ•˜์—์„œ ์••์ถ• ์„ผ์„œ์˜ FCR ๋ณ€ํ™”๋Š” 3๊ฐœ ์‹œํ—˜์ฒด์—์„œ ํฐ ํŽธ์ฐจ๋ฅผ ๋ณด์ด์ง€ ์•Š์•˜๋‹ค. ์ด๋Š” Fig. 9์— ๋‚˜ํƒ€๋‚œ ๋ฐ”์™€ ๊ฐ™์ด MWCNT์˜ ํ˜ผ์ž…์— ๋”ฐ๋ผ ์‹œ๋ฉ˜ํŠธ ๋ณตํ•ฉ์ฒด์˜ ์•ˆ์ •๋œ ์ „๊ธฐ ์ „๋„์„ฑ์„ ํ™•๋ณดํ•  ์ˆ˜ ์žˆ์—ˆ๊ธฐ ๋•Œ๋ฌธ์ธ ๊ฒƒ์œผ๋กœ ํŒ๋‹จ๋œ๋‹ค.

3.4 ๋ฐ˜๋ณต์••์ถ• ๋ณ€ํ˜• ๊ฐ์ง€ ํŠน์„ฑ

Fig. 11์€ MWCNT๋ฅผ ํ˜ผ์ž…ํ•˜์ง€ ์•Š์€ Hy-SHCC-WO MWCNT๋ฅผ ์‚ฌ์šฉํ•˜์—ฌ ์ œ์ž‘๋œ ์••์ถ•์„ผ์„œ(Sensor \#1)์™€ 1 wt% MWCNT๋ฅผ ํ˜ผ์ž…ํ•œ Hy-SHCC-W MWCNT๋ฅผ ์‚ฌ์šฉํ•œ ์••์ถ•์„ผ์„œ(Sensor \#6)์— ๋Œ€ํ•˜์—ฌ ์••์ถ•๊ฐ•๋„์˜ 10 %, 30 % ๋ฐ 50 % ์ˆ˜์ค€์˜ ๋ฐ˜๋ณต์••์ถ•์‘๋ ฅ ํ•˜์—์„œ ์••์ถ• ๋ณ€ํ˜•๋ฅ ๊ณผ ์ €ํ•ญ์˜ ๋ถ„์ˆ˜ ๋ณ€ํ™”(FCR)์„ ๋น„๊ตํ•˜์—ฌ ๋‚˜ํƒ€๋‚ธ ๊ฒƒ์ด๋‹ค. ๊ทธ๋ฆผ์— ๋‚˜ํƒ€๋‚œ ๋ฐ”์™€ ๊ฐ™์ด MWCNT๋ฅผ ํ˜ผ์ž…ํ•˜์ง€ ์•Š์€ Hy-SHCC -WO MWCNT๋ฅผ ์‚ฌ์šฉํ•œ ์••์ถ•์„ผ์„œ๋Š” ์••์ถ•๋ณ€ํ˜•๋ฅ ์ด ์ฆ๊ฐ€๋จ์— ๋”ฐ๋ผ FCR์ด ์ฆ๊ฐ€๋˜๋Š” ํŠน์„ฑ์„ ๋ณด์—ฌ ์ผ๋ฐ˜์ ์ธ ์ „๊ธฐ์  ์ €ํ•ญํŠน์„ฑ์„ ๋ณด์ด์ง€ ์•Š๊ณ  ์žˆ๋‹ค(Han et al. 2012; Galao et al. 2014). ๋”ฐ๋ผ์„œ ์••์ถ•๋ณ€ํ˜• ๊ฐ์ง€์„ผ์„œ๋กœ์˜ ํ™œ์šฉ ๊ฐ€๋Šฅ์„ฑ์€ ๋‚ฎ๊ฒŒ ํ‰๊ฐ€๋˜๊ณ  ์žˆ๋‹ค. ๋ฐ˜๋ฉด MWCNT๊ฐ€ 1 wt% ํ˜ผ์ž…๋œ Hy- SHCC-W MWCNT๋กœ ์ œ์ž‘๋œ ์••์ถ•์„ผ์„œ๋Š” Fig. 11(a)์— ๋‚˜ํƒ€๋‚œ ๋ฐ”์™€ ๊ฐ™์ด ์••์ถ•๋ณ€ํ˜•๋ฅ ์ด ์ฆ๊ฐ€๋จ์— ๋”ฐ๋ผ FCR์ด ๊ฐ์†Œ๋˜๋Š” ํŠน์„ฑ์„ ๋ณด์ด๊ณ  ์žˆ๋‹ค. ๋„์ž…๋œ ๋ฐ˜๋ณต ์••์ถ•์‘๋ ฅ์ด 10 %์—์„œ 50 %๋กœ ์ฆ๊ฐ€๋จ์— ๋”ฐ๋ผ ๊ฒŒ์ด์ง€ ์ƒ์ˆ˜(GF)๋Š” ๋‹ค์†Œ ๊ฐ์†Œ๋˜์–ด ๋ณ€ํ˜•๋ฅ  ๊ฐ์ง€ ๋ฏผ๊ฐ๋„๋Š” ๋‹ค์†Œ ์ €ํ•˜๋˜๋Š” ๊ฒƒ์œผ๋กœ ๋‚˜ํƒ€๋‚ฌ๋‹ค. MWCNT๊ฐ€ ํ˜ผ์ž…๋œ 3๊ฐœ ์••์ถ•์„ผ์„œ์ค‘ Fig. 10(b)์—์„œ ์ „๊ธฐ์  ์ €ํ•ญํŠน์„ฑ์ด ๋ถˆ์•ˆ์ •ํ•˜๊ฒŒ ๋‚˜ํƒ€๋‚œ ์„ผ์„œ(Sensor \#5)๋ฅผ ์ œ์™ธํ•œ 2๊ฐœ ์„ผ์„œ(Sensor \#4์™€ \#6)์˜ ํ‰๊ท  GF๋Š” ์žฌํ•˜ ์••์ถ•์‘๋ ฅ์ด ์••์ถ•๊ฐ•๋„์˜ 10, 30 ๋ฐ 50 %์— ์ด๋ฅผ ๋•Œ ๊ฐ๊ฐ 25.6, 19.3, 11.3์œผ๋กœ ์žฌํ•˜ ์••์ถ•์‘๋ ฅ์ด ์ฆ๊ฐ€๋จ์— ๋”ฐ๋ผ ๊ฐ์†Œ๋˜๋Š” ๊ฒฝํ–ฅ์„ ๋ณด์ด๊ณ  ์žˆ๋‹ค.

Fig. 12๋Š” Hy-SHCC-W MWCNT๋ฅผ ์‚ฌ์šฉํ•˜์—ฌ ์ œ์ž‘๋œ ์••์ถ•์„ผ์„œ(Sensor \#4)์˜ ๋ฐ˜๋ณต ์••์ถ•์‘๋ ฅ ์ˆ˜์ค€ 30 ๋ฐ 50 %์—์„œ FCR๊ณผ ์••์ถ•๋ณ€ํ˜•๋ฅ  ๊ด€๊ณ„๋ฅผ ๋‚˜ํƒ€๋‚ธ ๊ฒƒ์ด๋‹ค. ์ „์ฒด์ ์ธ FCR-์••์ถ•๋ณ€ํ˜•๋ฅ  ๊ด€๊ณ„๊ณก์„ ์˜ ๊ฐœํ˜•์€ Fig. 11(b)์— ์ œ์‹œ๋œ ์••์ถ•์„ผ์„œ(Sensor \#6)์™€ ์œ ์‚ฌํ•˜๊ฒŒ ๋‚˜ํƒ€๋‚ฌ๋‹ค. Fig. 11(b) ๋ฐ Fig. 12์— ๋‚˜ํƒ€๋‚œ ๋ฐ”์™€ ๊ฐ™์ด MWCNT๋ฅผ ํ˜ผ์ž…ํ•œ ์••์ถ•์„ผ์„œ์—์„œ ๋ฐ˜๋ณต ์••์ถ•์‘๋ ฅ ์ˆ˜์ค€์ด ์ฆ๊ฐ€๋˜๊ณ  ๋ฐ˜๋ณต ์••์ถ• ์‚ฌ์ดํด์ด ์ง„ํ–‰๋จ์— ๋”ฐ๋ผ ์„ผ์„œ ๋‚ด๋ถ€์—์„œ ์ƒˆ๋กœ์šด ๋ฏธ์„ธ๊ท ์—ด ๋“ฑ์˜ ๋ฐœ์ƒ์— ๋”ฐ๋ผ ์„ผ์„œ ๋‚ด๋ถ€์— ํ˜ผ์ž…๋œ MWCNT์™€ ๊ฐ™์€ ์ „๊ธฐ์ „๋„๋ฌผ์งˆ์ด ๊ตฌ์„ฑํ•˜๋Š” ๋„คํŠธ์›Œํฌ๊ฐ€ ๋‹จ์ ˆ ๋˜๋Š” ์†์ƒ๋˜์–ด ๋ณ€ํ˜• ๊ฐ์ง€๋Šฅ๋ ฅ์ด ์ €ํ•˜๋˜๋Š” ๊ฒƒ์œผ๋กœ ํŒ๋‹จ๋œ๋‹ค. ์ด์™€ ์œ ์‚ฌํ•œ ํŠน์„ฑ์€ ํƒ„์†Œ๋‚˜๋…ธํŠœ๋ธŒ์™€ ๋น„๋‹ ์—์Šคํ…Œ๋ฅด(vinyl ester) ๋ณตํ•ฉ์ฒด(Ku-Herrera and Aviles 2012) ๋ฐ ์„ฌ์œ ๋ณด๊ฐ• ๋ณตํ•ฉ์ฒด(Gao et al. 2009)์—์„œ๋„ ๋ณด๊ณ ๋˜๊ณ  ์žˆ๋‹ค.

Fig. 11(b) ๋ฐ Fig. 12์— ๋‚˜ํƒ€๋‚œ ๋ฐ”์™€ ๊ฐ™์ด ์„ผ์„œ์— ๋”ฐ๋ผ ๋ฐ˜๋ณต ์••์ถ•์‘๋ ฅ์— ๋”ฐ๋ฅธ ์ž”๋ฅ˜์ €ํ•ญ์€ ๋‹ค์†Œ ์ฐจ์ด๋ฅผ ๋ณด์ด๊ณ  ์žˆ์œผ๋‚˜ GF๋Š” ํฐ ์ฐจ์ด๋ฅผ ๋ณด์ด์ง€ ์•Š๊ณ  ์žˆ์œผ๋ฉฐ ์••์ถ•๋ณ€ํ˜•๋ฅ ์ด ์••์ถ•๊ฐ•๋„์‹œ ํ‰๊ท  ๋ณ€ํ˜•๋ฅ  0.004(Fig. 5 ์ฐธ์กฐ)์˜ ์•ฝ 10 %(์••์ถ•๋ณ€ํ˜•๋ฅ  0.0004) ์ด์ƒ์— ์ด๋ฅด๋ฉด ์„ผ์„œ์˜ ๋ฏผ๊ฐ๋„๋Š” ํ˜„์ €ํ•˜๊ฒŒ ๋‘”ํ™”๋˜๋Š” ํ•œ๊ณ„๋ฅผ ๋ณด์˜€๋‹ค.

Fig. 11 Self sensing properties of Hy-SHCC sensors
../../Resources/KCI/JKCI.2022.34.2.203/fig11.png
Fig. 12 Repeated compressive sensing properties of Hy-SHCC sensor (sensor \#4) with 1 wt% MWCNT
../../Resources/KCI/JKCI.2022.34.2.203/fig12.png

4. ๊ฒฐ ๋ก 

์ด ์—ฐ๊ตฌ์—์„œ๋Š” PE ๋ฐ ๊ฐ•์„ฌ์œ ๋ฅผ ํ•˜์ด๋ธŒ๋ฆฌ๋“œํ•˜์—ฌ ๋ณด๊ฐ•ํ•œ ๋ณ€ํ˜•๊ฒฝํ™”ํ˜• ์‹œ๋ฉ˜ํŠธ ๋ณตํ•ฉ์ฒด์— ์•ก์ƒํ˜• ๋‹ค์ค‘๋ฒฝ ํƒ„์†Œ๋‚˜๋…ธํŠœ(MW CNT)๋ฅผ ์‹œ๋ฉ˜ํŠธ ์ค‘๋Ÿ‰๋น„ 1 %์˜ ํ˜ผ์ž…์— ๋”ฐ๋ฅธ ์‹œ๋ฉ˜ํŠธ ๋ณตํ•ฉ์ฒด์˜ ์••์ถ• ๋ฐ ์ง์ ‘์ธ์žฅ์„ฑ๋Šฅ ํ‰๊ฐ€, ์••์ถ•๊ฐ•๋„์˜ 10, 30, 50 % ์ˆ˜์ค€์˜ ์••์ถ•์‘๋ ฅ์— ๋Œ€ํ•œ ๋ฐ˜๋ณต์žฌํ•˜์— ๋”ฐ๋ฅธ ๋ณ€ํ˜•๊ฐ์ง€๋Šฅ๋ ฅ์ด ํ‰๊ฐ€๊ฐ€ ๋˜์—ˆ๋‹ค. ์ด๋Ÿฌํ•œ ์‹คํ—˜์„ ํ†ตํ•˜์—ฌ ๋„์ถœ๋œ ๊ฒฐ๋ก ์€ ๋‹ค์Œ๊ณผ ๊ฐ™๋‹ค.

1) 0.75 % PE ๋ฐ 0.50 % ๊ฐ•์„ฌ์œ ๋ฅผ ํ˜ผ์ž…ํ•˜์—ฌ ๋ณด๊ฐ•ํ•œ ๋ณ€ํ˜•๊ฒฝํ™”ํ˜• ์‹œ๋ฉ˜ํŠธ ๋ณตํ•ฉ์ฒด์— ์•ก์ƒํ˜• MWCNT 1 wt%๋ฅผ ํ˜ผ์ž… ์‹œ ์••์ถ•๊ฐ•๋„๋Š” 35 % ์ €ํ•˜๋˜์—ˆ์œผ๋ฉฐ ์ด๋Š” ์„ฌ์œ ๋ณด๊ฐ• ์‹œ๋ฉ˜ํŠธ ๋ณตํ•ฉ์ฒด ๋‚ด์—์„œ MWCNT์˜ ์‘์ง‘์— ๋”ฐ๋ฅธ ๊ฒƒ์œผ๋กœ ํŒ๋‹จ๋œ๋‹ค.

2) ๋ณ€ํ˜•๊ฒฝํ™”ํ˜• ์‹œ๋ฉ˜ํŠธ ๋ณตํ•ฉ์ฒด์˜ ์ง์ ‘์ธ์žฅ๊ฐ•๋„ ๋ฐ ๋ณ€ํ˜•๋Šฅ๋ ฅ์€ ์—‘์ƒํ˜• MWCNT 1 wt% ํ˜ผ์ž…์— ๋”ฐ๋ผ ๊ฐ๊ฐ 30 ๋ฐ 35 % ์ €๊ฐ๋˜๋Š” ๊ฒฝํ–ฅ์„ ๋ณด์˜€์œผ๋‚˜ ์ง์ ‘์ธ์žฅ ์‹œํ—˜ํŽธ์— ๋‚˜ํƒ€๋‚œ ๊ท ์—ด์ˆ˜๋Š” ์˜คํžˆ๋ ค 35 % ์ฆ๊ฐ€๋˜๋Š” ๊ฒฐ๊ณผ๋ฅผ ๋ณด์˜€๋‹ค.

3) ์•ก์ƒํ˜• MWCNT 1 wt% ํ˜ผ์ž…์— ๋”ฐ๋ผ ํ•ฉ์„ฑ์„ฌ์œ  PE์™€ ๊ฐ•์„ฌ์œ ๋ฅผ ํ•˜์ด๋ธŒ๋ฆฌ๋“œ ๋ณด๊ฐ•ํ•œ ๋ณ€ํ˜•๊ฒฝํ™”ํ˜• ์‹œ๋ฉ˜ํŠธ ๋ณตํ•ฉ์ฒด์˜ ์ „๊ธฐ์  ์ „๋„์„ฑ์„ ํฌ๊ฒŒ ํ–ฅ์ƒ์‹œ์ผฐ์œผ๋ฉฐ ์žฌ๋ น 25์ผ๊นŒ์ง€ ์•ˆ์ •๋œ ์ „๊ธฐ์  ์ €ํ•ญํŠน์„ฑ์„ ๋ณด์˜€๋‹ค.

4) MWCNT 1 wt% ํ˜ผ์ž…ํ•œ ๋ณ€ํ˜•๊ฒฝํ™”ํ˜• ์‹œ๋ฉ˜ํŠธ ๋ณตํ•ฉ์ฒด๋กœ ์ œ์กฐ๋œ ์••์ถ•๋ณ€ํ˜• ๊ฐ์ง€ ์„ผ์„œ๋Š” ์••์ถ•๊ฐ•๋„์˜ 50 % ์ˆ˜์ค€์— ๋Œ€ํ•œ ๋ฐ˜๋ณต ์••์ถ•์‘๋ ฅํ•˜์—์„œ๋„ ๋ณ€ํ˜• ๊ฐ์ง€๋Šฅ๋ ฅ์„ ๋ณด์œ ํ•˜๊ณ  ์žˆ๋Š” ๊ฒƒ์œผ๋กœ ๋‚˜ํƒ€๋‚ฌ๋‹ค. ๋ฐ˜๋ณต์••์ถ•์‘๋ ฅ์ˆ˜์ค€ ๋ฐ ๋ฐ˜๋ณต์••์ถ•์‚ฌ์ดํด ์ˆ˜๊ฐ€ ์ฆ๊ฐ€๋จ์— ๋”ฐ๋ผ ๊ฒŒ์ด์ง€ ์ƒ์ˆ˜๋Š” ์ €ํ•˜๋˜๋Š” ๊ฒฝํ–ฅ์„ ๋ณด์˜€์œผ๋ฉฐ ํŠนํžˆ ์••์ถ•๋ณ€ํ˜•๋ฅ  $4\times 10^{-4}$ ์ด์ƒ์˜ ์••์ถ•๋ณ€ํ˜•ํ•˜์—์„œ๋Š” ๋ณ€ํ˜• ๊ฐ์ง€์— ๋Œ€ํ•œ ๋ฏผ๊ฐ๋„๊ฐ€ ํ˜„์ €ํ•˜๊ฒŒ ์ €ํ•˜๋˜์—ˆ๋‹ค.

๊ฐ์‚ฌ์˜ ๊ธ€

์ด ๋…ผ๋ฌธ์€ 2021๋…„๋„ ์ •๋ถ€(๊ณผํ•™๊ธฐ์ˆ ์ •๋ณดํ†ต์‹ ๋ถ€)์˜ ์žฌ์›์œผ๋กœ ํ•œ๊ตญ์—ฐ๊ตฌ์žฌ๋‹จ ๊ธฐ์ดˆ์—ฐ๊ตฌ์‹ค์‚ฌ์—…(No. 2021R1A4A2001964)์˜ ์ง€์›์„ ๋ฐ›์•„ ์ˆ˜ํ–‰๋œ ๊ฒฐ๊ณผ์ž„.

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