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  1. ์„œ์šธ์‹œ๋ฆฝ๋Œ€ํ•™๊ต ๊ฑด์ถ•๊ณตํ•™๊ณผ ์„์‚ฌ๊ณผ์ • (Graduate Student, Department of Architectural Engineering, University of Seoul, Seoul 02054, Rep. of Korea)
  2. ์„œ์šธ์‹œ๋ฆฝ๋Œ€ํ•™๊ต ๊ฑด์ถ•๊ณตํ•™๊ณผ ๋ฐ•์‚ฌ๊ณผ์ • (Ph.D. Student, Department of Architectural Engineering, University of Seoul, Seoul 02054, Rep. of Korea)
  3. ์„œ์šธ์‹œ๋ฆฝ๋Œ€ํ•™๊ต ๊ฑด์ถ•ํ•™๋ถ€ ๊ต์ˆ˜ (Professor, Department of Architectural Engineering, University of Seoul, Seoul 02054, Rep. of Korea)



์ฝ˜ํฌ๋ฆฌํŠธ ์‹ ์†์กฐํ˜•, ์œ ๋™ํ•™, ์••์ถœ์„ฑ, ์ ์ธต์„ฑ
concrete rapid prototyping, rheology, extrudability, buildability

1. ์„œ ๋ก 

์ฒ ๊ทผ์ฝ˜ํฌ๋ฆฌํŠธ(Reinforced Concrete, RC) ๊ณต๋ฒ•์€ ๊ตฌ์กฐ์  ์ผ์ฒด์„ฑ๊ณผ ๋”๋ถˆ์–ด ์šฐ์ˆ˜ํ•œ ๊ฒฝ์ œ์„ฑ์„ ํ™•๋ณดํ•  ์ˆ˜ ์žˆ์–ด ๊ฑด์„ค์‹œ์žฅ์—์„œ ๋„๋ฆฌ ์ ์šฉ๋˜๊ณ  ์žˆ๋‹ค(Min 2013). ๋‹ค๋งŒ, RC ๊ณต์‚ฌ ์ค‘ ๊ฑฐํ‘ธ์ง‘๊ณต์‚ฌ๋Š” ์ „์ฒด ๊ณต์‚ฌ๊ธฐ๊ฐ„์˜ ์•ฝ 25 %, ํ‰๊ท  ๊ฑฐํ‘ธ์ง‘๊ณต์‚ฌ๋น„๋Š” ๊ณจ์กฐ๊ณต์‚ฌ๋น„ ์ „์ฒด์˜ 35 %๋ฅผ ์ฐจ์ง€ํ•˜๋ฉฐ, ๊ทธ ์ค‘ 40 %๊ฐ€ ์žฌ๋ฃŒ๋น„, 60 %๊ฐ€ ๋…ธ๋ฌด๋น„๋กœ์จ ๋‹ค๋ฅธ ๊ณต์ •์— ๋น„ํ•ด ๋งŽ์€ ๋…ธ๋™๋ ฅ์ด ์†Œ์š”๋œ๋‹ค(Jung et al. 2002). ๋˜ํ•œ, ์ตœ๊ทผ ๋„์‹œ๏ฝฅ๊ตญ๊ฐ€์˜ ๋žœ๋“œ๋งˆํฌ๋กœ์จ ๋น„์ •ํ˜• ๊ฑด์ถ•๋ฌผ์— ๋Œ€ํ•œ ๊ด€์‹ฌ์ด ์ฆ๊ฐ€ํ•˜๊ณ  ์žˆ์œผ๋ฉฐ, ์ด์™€ ๊ฐ™์€ ๋น„์ •ํ˜• ๊ฑด์ถ•๋ฌผ ๊ณต์‚ฌ์—์„œ๋Š” ๊ฑฐํ‘ธ์ง‘ ์ž‘์—…์ด ๋”์šฑ ๋ณต์žกํ•˜๊ณ  ์–ด๋ ต๊ธฐ ๋•Œ๋ฌธ์— ์ผ๋ฐ˜์ ์ธ ์ •ํ˜• ๊ฑด์ถ•๋ฌผ๋ณด๋‹ค ๊ณต์‚ฌ๊ธฐ๊ฐ„๊ณผ ๊ณต์‚ฌ๋น„๊ฐ€ ์ฆ๊ฐ€ํ•œ๋‹ค(Lee and Kim 2014). ์ด๋Ÿฌํ•œ ๋ฌธ์ œ์ ์„ ๊ทน๋ณตํ•˜๊ธฐ ์œ„ํ•˜์—ฌ ๋‹ค์–‘ํ•œ ๊ฑด์„ค๊ณต๋ฒ•์— ๋Œ€ํ•œ ๋ฐœ์ „ ๋…ธ๋ ฅ์ด ์ง€์†ํ•˜๊ณ  ์žˆ์œผ๋ฉฐ, 4์ฐจ ์‚ฐ์—…ํ˜๋ช…์˜ ์ฃผ์š” ๊ธฐ์ˆ  ์ค‘ ํ•˜๋‚˜์ธ 3D ํ”„๋ฆฐํŒ… ๊ธฐ์ˆ ์„ ํ™œ์šฉํ•œ ์ฝ˜ํฌ๋ฆฌํŠธ ์‹ ์†์กฐํ˜•(Concrete Rapid Prototyping, CRP) ๊ธฐ์ˆ ์ด ํ•˜๋‚˜์˜ ๋Œ€์•ˆ์œผ๋กœ์จ ์ฃผ๋ชฉ๋ฐ›๊ณ  ์žˆ๋‹ค(Ahn and Kim 2017). CRP๋Š” 3์ฐจ์› ๋„๋ฉด์ •๋ณด๋ฅผ ๊ธฐ๋ฐ˜์œผ๋กœ ์ฝ˜ํฌ๋ฆฌํŠธ ๊ตฌ์กฐ๋ฌผ์„ ์ œ์ž‘ํ•˜๋Š” ๊ธฐ์ˆ ๋กœ์จ ๊ฑฐํ‘ธ์ง‘ ์—†์ด ๋ถ€์žฌ๋ฅผ ์ถœ๋ ฅํ•  ์ˆ˜ ์žˆ๊ธฐ ๋•Œ๋ฌธ์— ๊ฑฐํ‘ธ์ง‘๊ณต์ •์— ์†Œ์š”๋˜๋Š” ๋น„์šฉ ๋ฐ ๋…ธ๋™๋ ฅ์„ ์ ˆ๊ฐ์‹œํ‚ฌ ์ˆ˜ ์žˆ์œผ๋ฉฐ, ๋” ๋‚˜์•„๊ฐ€ ๊ตฌ์กฐ ๋ถ€์žฌ์˜ ์ž๋™ํ™” ๋ฐ ๋Œ€๋Ÿ‰์ƒ์‚ฐ์„ ๊ฐ€๋Šฅํ•˜๊ฒŒ ํ•  ์ˆ˜ ์žˆ๋‹ค(Gaudilliรจre et al. 2019).

Le et al.(2012a)๋Š” ์••์ถœ์„ฑ ๋ฐ ์ ์ธต์„ฑ ๊ฒ€์ฆ์„ ์œ„ํ•˜์—ฌ ํ•„๋ผ๋ฉ˜ํŠธ ์ˆ˜๋ฅผ ๋ณ€์ˆ˜๋กœ ์ถœ๋ ฅ์„ ์ˆ˜ํ–‰ํ•˜์˜€๋‹ค. ์ถœ๋ ฅ ๊ฒฐ๊ณผ ์ˆ˜ํ‰์œผ๋กœ ์ถœ๋ ฅ๋˜๋Š” ํ•„๋ผ๋ฉ˜ํŠธ์˜ ์ˆ˜๊ฐ€ ์ฆ๊ฐ€ํ• ์ˆ˜๋ก ์ ์ธต์„ฑ์ด ์šฐ์ˆ˜ํ•œ ๊ฒƒ์œผ๋กœ ๋‚˜ํƒ€๋‚ฌ๋‹ค. Kazemian et al.(2017)์˜ ์—ฐ๊ตฌ์—์„œ๋Š” ์••์ถœ์„ฑ ํ™•๋ณด๋ฅผ ์œ„ํ•ด์„œ๋Š” ์น˜์ˆ˜์˜ ์ ํ•ฉ์„ฑ์ด ๋งค์šฐ ์ค‘์š”ํ•˜๋‹ค๊ณ  ์–ธ๊ธ‰ํ•˜์˜€์œผ๋ฉฐ, ๋ ˆ์ด์–ด๊ฐ„ ์ ์ธต ์‹œ๊ฐ„ ๊ฐ„๊ฒฉ(Printing Time Gap, PTG)์ด ์ ์ธต์„ฑ์— ๋งค์šฐ ์ค‘์š”ํ•˜๋‹ค๊ณ  ์ œ์‹œํ•˜์˜€๋‹ค. ์ด ์—ฐ๊ตฌ์—์„œ๋Š” ์‹ค์ œ 3D ์ฝ˜ํฌ๋ฆฌํŠธ ํ”„๋ฆฐํŒ… ํ™˜๊ฒฝ์„ ๋ชจ์‚ฌํ•˜๊ธฐ ์œ„ํ•˜์—ฌ ํ•„๋ผ๋ฉ˜ํŠธ์˜ ์ˆ˜๋Š” 1์ค„๋กœ ๊ณ ์ •ํ•˜์˜€์œผ๋ฉฐ, PTG๋ฅผ ์‹คํ—˜๋ณ€์ˆ˜๋กœ ํ•˜์—ฌ ์ ์ธต์„ฑ์„ ๊ฒ€ํ† ํ•˜๊ณ ์ž ํ•˜์˜€๋‹ค.

์ด ์—ฐ๊ตฌ์—์„œ๋Š” ์ฝ˜ํฌ๋ฆฌํŠธ์˜ ์ •๋Ÿ‰์••์ถœ์„ ์œ„ํ•˜์—ฌ ์••์ถœ๊ธฐ๋ฅผ ์„ค๊ณ„๏ฝฅ์ œ์ž‘ํ•˜๊ณ , CNC Machine, ์ •๋Ÿ‰ํŽŒํ”„ ๋“ฑ์œผ๋กœ ๊ตฌ์„ฑ๋œ CRP ์‹œ์Šคํ…œ์„ ๊ตฌ์ถ•ํ•˜์˜€๋‹ค. ๋˜ํ•œ, CRP์˜ ํ•ต์‹ฌ์š”์†Œ์ธ ์••์ถœ์„ฑ(extrudability) ๋ฐ ์ ์ธต์„ฑ(buildability)์„ ํ™•๋ณดํ•˜๊ธฐ ์œ„ํ•˜์—ฌ ๊ตณ์ง€ ์•Š์€ ์ฝ˜ํฌ๋ฆฌํŠธ์˜ ์œ ๋™ํ•™์  ํŠน์„ฑ์„ ๋ถ„์„ํ•˜๊ณ , ๋ฌธํ—Œ ์—ฐ๊ตฌ ๋ฐ ์ „์‚ฐ์œ ์ฒด(Computational Fluid Dynamics, CFD)ํ•ด์„์„ ์ˆ˜ํ–‰ํ•˜์—ฌ ๊ตณ์ง€ ์•Š์€ ์ฝ˜ํฌ๋ฆฌํŠธ์˜ ๋ ˆ์˜ฌ๋กœ์ง€(rheology), ์ฆ‰ ์ ๋„ ๋ฐ ํ•ญ๋ณต์‘๋ ฅ์„ ๊ทœ๋ช…ํ•˜๊ณ ์ž ํ•˜์˜€๋‹ค. ๋ฐฐํ•ฉ์‹คํ—˜์„ ํ†ตํ•ด CRP์— ์ ํ•ฉํ•œ ๋ฐฐํ•ฉ์„ ๋„์ถœํ•˜๊ณ , ์••์ถœ์„ฑ๊ณผ ์ ์ธต์„ฑ์„ ๊ฒ€์ฆํ•˜๊ณ ์ž ํ•˜์˜€๋‹ค. ๋˜ํ•œ, CRP ๋ฐ ๊ธฐ์กด์˜ RC ๊ณต๋ฒ•์„ ์ด์šฉํ•˜์—ฌ ์ œ์ž‘ํ•œ ์ฝ˜ํฌ๋ฆฌํŠธ ๋ถ€์žฌ์˜ ํœจ์‹คํ—˜์„ ์ˆ˜ํ–‰ํ•˜์—ฌ ๋ถ€์žฌ์˜ ํœจ๊ฑฐ๋™ ๋ฐ ํŒŒ๊ดด๋ชจ๋“œ๋ฅผ ๋น„๊ต๏ฝฅ๋ถ„์„ํ•˜์˜€๋‹ค.

2. ์ฝ˜ํฌ๋ฆฌํŠธ ์‹ ์†์กฐํ˜• ์‹œ์Šคํ…œ ๊ฐœ๋ฐœ

2.1 ์ฝ˜ํฌ๋ฆฌํŠธ ์‹ ์†์กฐํ˜• ์••์ถœ๊ธฐ ์„ค๊ณ„

๊ธฐ์กด์˜ CRP ์‹œ์Šคํ…œ์—์„œ๋Š” Fig. 1(a)์— ๋‚˜ํƒ€๋‚ธ ๋ฐ”์™€ ๊ฐ™์ด ํŽŒํ”„(pump)๋กœ๋ถ€ํ„ฐ ๋…ธ์ฆ(nozzle)๊นŒ์ง€ ๊ตณ์ง€ ์•Š์€ ์ฝ˜ํฌ๋ฆฌํŠธ๋ฅผ ์ด์†กํ•˜์—ฌ ์ถœ๋ ฅํ•œ๋‹ค(Le et al. 2012a). ๊ทธ๋Ÿฌ๋‚˜ ์ด๋Ÿฌํ•œ ์••์ถœ๋ฐฉ์‹์—์„œ๋Š” ์„ค์น˜๋œ ํŒŒ์ดํ”„์˜ ํ˜•์ƒ๋ณ€ํ™”์— ๋”ฐ๋ผ ๊ตณ์ง€ ์•Š์€ ์ฝ˜ํฌ๋ฆฌํŠธ์˜ ํ† ์ถœ๋Ÿ‰์ด ์ผ์ •ํ•˜์ง€ ๋ชปํ•˜๋Š” ๊ฒฝ์šฐ๊ฐ€ ๋นˆ๋ฒˆํžˆ ๋ฐœ์ƒํ•  ์ˆ˜ ์žˆ๋‹ค. ๋”ฐ๋ผ์„œ ์ด ์—ฐ๊ตฌ์—์„œ๋Š” Fig. 1(b)์— ๋‚˜ํƒ€๋‚ธ ๋ฐ”์™€ ๊ฐ™์ด ๋…ธ์ฆ ์œ„์น˜์— ๋‹จ์ถ•์••์ถœ๊ธฐ(single screw extruder)๋ฅผ ์žฅ์ฐฉํ•˜์—ฌ ์ฝ˜ํฌ๋ฆฌํŠธ์˜ ์ •๋Ÿ‰ ํ† ์ถœ์„ ์œ ๋„ํ•˜์˜€์œผ๋ฉฐ, ํŽŒํ”„๋Š” ์••์ถœ๊ธฐ ์ „๊นŒ์ง€๋งŒ ์ฝ˜ํฌ๋ฆฌํŠธ๋ฅผ ์••์†กํ•˜๋Š” ๋ชฉ์ ์œผ๋กœ ์‚ฌ์šฉํ•˜์˜€๋‹ค. ์ด๋•Œ, ๋‹จ์ถ•์••์ถœ๊ธฐ์— ์„ค์น˜๋˜๋Š” ๋‚˜์„ ํ˜• ์Šคํฌ๋ฅ˜์˜ ๊ฐ๋„๋Š” CFD ํ•ด์„์„ ํ†ตํ•ด ๊ฒฐ์ •ํ•˜์˜€์œผ๋ฉฐ, Fig. 2์—๋Š” ์Šคํฌ๋ฅ˜ ๊ฐ๋„์— ๋”ฐ๋ฅธ ํ† ์ถœ๋Ÿ‰์— ๋Œ€ํ•œ ํ•ด์„๊ฒฐ๊ณผ๋ฅผ ๋‚˜ํƒ€๋‚ด์—ˆ๋‹ค. ํ•ด์„ ์‹œ ๊ตณ์ง€ ์•Š์€ ์ฝ˜ํฌ๋ฆฌํŠธ๋Š” ๊ธฐ์กด๋ฌธํ—Œ์— ๊ทผ๊ฑฐํ•˜์—ฌ ๋น™ํ–„(Bingham)์œ ์ฒด๋กœ ๊ฐ€์ •ํ•˜์˜€์œผ๋ฉฐ(Roussel 2018), ์Šคํฌ๋ฅ˜์˜ ํšŒ์ „์†๋„๋Š” 60 RPM์œผ๋กœ ๊ณ ์ •ํ•˜์˜€๋‹ค. CFD ํ•ด์„๊ฒฐ๊ณผ, 10ยฐ์˜ ๋‚˜์„ ๊ฐ์—์„œ ๊ตณ์ง€ ์•Š์€ ์ฝ˜ํฌ๋ฆฌํŠธ๊ฐ€ ์ตœ๋Œ€๋กœ ํ† ์ถœ๋˜๋Š” ๊ฒƒ์œผ๋กœ ๋‚˜ํƒ€๋‚ฌ์œผ๋ฉฐ, ์ด์— ๋”ฐ๋ผ ์••์ถœ๊ธฐ ์Šคํฌ๋ฅ˜์˜ ๊ฐ๋„๋ฅผ 10ยฐ๋กœ ์„ค๊ณ„ํ•˜์—ฌ ์ œ์ž‘ํ•˜์˜€๋‹ค.

Fig. 1. Comparison of existing and proposed CRP system

../../Resources/kci/JKCI.2020.32.1.085/fig1.png

Fig. 2. Analysis results of mass-flow according to spiral angle of extruder

../../Resources/kci/JKCI.2020.32.1.085/fig2.png

Fig. 3. Schematic description of CRP system

../../Resources/kci/JKCI.2020.32.1.085/fig3.png

2.2 ์ฝ˜ํฌ๋ฆฌํŠธ ์‹ ์†์กฐํ˜• ํ”„๋กœ์„ธ์Šค

์ด ์—ฐ๊ตฌ์—์„œ๋Š” Fig. 3์— ๋‚˜ํƒ€๋‚ธ ๋ฐ”์™€ ๊ฐ™์ด ์••์ถœ๊ธฐ์™€ ์ž๋™ํ™” ๊ณต์ž‘๊ธฐ๊ณ„(Computer Numerical Control Machine, CNC Machine)๋ฅผ ๊ฐœ๋Ÿ‰ํ•œ CRP ๊ธฐ๊ณ„(machine), ์ •๋Ÿ‰ํŽŒํ”„, ์ปจํŠธ๋กค๋Ÿฌ, ํ˜ธํผ, ๋ฏน์„œ๋กœ ์ด๋ฃจ์–ด์ง„ CRP ์‹œ์Šคํ…œ์„ ๊ตฌ์ถ•ํ•˜์˜€๋‹ค. CRP ๊ธฐ๊ณ„๋Š” ์ตœ๋Œ€ 100 mm/sec์˜ ์ถ•์ด๋™์†๋„๋ฅผ ๋งŒ์กฑํ•˜๋„๋ก ์ œ์ž‘๋˜์—ˆ์œผ๋ฉฐ, CRP ํ”„๋กœ์„ธ์Šค๋ฅผ ์ •๋ฆฌํ•˜๋ฉด ๋‹ค์Œ๊ณผ ๊ฐ™๋‹ค.

๋‹จ๊ณ„ 1: ๋ฏน์„œ๋ฅผ ์‚ฌ์šฉํ•˜์—ฌ ์ฝ˜ํฌ๋ฆฌํŠธ๋ฅผ ๋ฐฐํ•ฉ

๋‹จ๊ณ„ 2: ๋ฏน์‹ฑ ๋œ ์ฝ˜ํฌ๋ฆฌํŠธ๋ฅผ ํ˜ธํผ๋กœ ์šด๋ฐ˜

๋‹จ๊ณ„ 3: ํŽŒํ”„๋ฅผ ์ด์šฉํ•˜์—ฌ ์ฝ˜ํฌ๋ฆฌํŠธ๋ฅผ ์••์ถœ๊ธฐ๊นŒ์ง€ ์ด์†ก

๋‹จ๊ณ„ 4: ์••์ถœ๊ธฐ๊นŒ์ง€ ์ฝ˜ํฌ๋ฆฌํŠธ๊ฐ€ ๋„๋‹ฌํ•˜์—ฌ ์••์ถœ๊ธฐ ๋‚ด์˜ ์••๋ ฅ์ด ์ผ์ • ๊ฐ’์— ๋„๋‹ฌํ•˜๋ฉด ํŽŒํ”„ ์ž‘๋™ ์ค‘์ง€

๋‹จ๊ณ„ 5: ์ปจํŠธ๋กค๋Ÿฌ์— ์ง€์ฝ”๋“œ(G-code)๋ฅผ ์ž…๋ ฅํ•˜์—ฌ CRP ๊ธฐ๊ณ„ ์ž‘๋™ ๋ฐ ์ฝ˜ํฌ๋ฆฌํŠธ ์••์ถœ

3. ์‹ ์†์กฐํ˜• ์ฝ˜ํฌ๋ฆฌํŠธ์˜ ์žฌ๋ฃŒํŠน์„ฑ

3.1 CRP์— ์ ํ•ฉํ•œ ์ฝ˜ํฌ๋ฆฌํŠธ ํŠน์„ฑ

CRP๋Š” ๊ตณ์ง€ ์•Š์€ ์ฝ˜ํฌ๋ฆฌํŠธ๋ฅผ ์••์ถœํ•˜์—ฌ ์ ์ธตํ•˜๋Š” ๋ฐฉ์‹์œผ๋กœ ๋ถ€์žฌ๋ฅผ ์ œ์ž‘ํ•œ๋‹ค. ์ฝ˜ํฌ๋ฆฌํŠธ ํ•„๋ผ๋ฉ˜ํŠธ๋ฅผ ๋ฐ€์‹คํ•˜๊ณ  ์ผ์ •ํ•œ ํ˜•์ƒ์œผ๋กœ ์••์ถœํ•˜๊ธฐ ์œ„ํ•ด์„œ๋Š” ์—ฐ์†์ ์ธ ์ •๋Ÿ‰์••์ถœ์ด ์ด๋ฃจ์–ด์ ธ์•ผ ํ•˜๋ฉฐ, ์ด๋ฅผ ์••์ถœ์„ฑ์œผ๋กœ ์ •์˜ํ•œ๋‹ค. ๋˜ํ•œ, ์ ์ธต ์‹œ์—๋Š” ๊ตณ์ง€ ์•Š์€ ์ฝ˜ํฌ๋ฆฌํŠธ๊ฐ€ ํ•˜๋ถ€ ํ•„๋ผ๋ฉ˜ํŠธ ์œ„์— ์ถœ๋ ฅ๋œ ํ›„ ๋ณ€ํ˜• ๋ฐ ๋ถ•๊ดด๊ฐ€ ๋ฐœ์ƒํ•˜์ง€ ์•Š์•„์•ผ ํ•˜๋ฉฐ, ์ด๋Ÿฌํ•œ ์„ฑ๋Šฅ์„ ์ ์ธต์„ฑ์ด๋ผ๊ณ  ์ •์˜ํ•œ๋‹ค(Le et al. 2012a, 2012b). ์šฐ์ˆ˜ํ•œ ์••์ถœ์„ฑ์„ ํ™•๋ณดํ•˜๊ธฐ ์œ„ํ•ด์„œ๋Š” ์ผ์ •ํ•œ ํ”Œ๋กœ์šฐ๋ฅผ ์œ ์ง€ํ•˜๋Š” ๊ฒƒ๊ณผ ๊ธด ์˜คํ”ˆํƒ€์ž„(open time)์ด ์š”๊ตฌ๋œ๋‹ค. ๋ฐ˜๋ฉด, ์ ์ธต์„ฑ์˜ ๊ด€์ ์—์„œ๋Š” ์›Œ์ปค๋นŒ๋ฆฌํ‹ฐ(workability)๊ฐ€ ์ข‹๊ณ  ์˜คํ”ˆํƒ€์ž„์ด ๊ธธ์ˆ˜๋ก ์ ์ธต๋œ ๋ ˆ์ด์–ด์— ๋ณ€ํ˜•์ด ๋ฐœ์ƒ๋˜๊ธฐ ์‰ฝ๋‹ค. ๋”ฐ๋ผ์„œ ์•ˆ์ •์ ์ธ CRP๋ฅผ ์œ„ํ•ด์„œ๋Š” ์••์ถœ์„ฑ๊ณผ ์ ์ธต์„ฑ์„ ๋ชจ๋‘ ํ™•๋ณดํ•  ์ˆ˜ ์žˆ๋Š” ๊ตณ์ง€ ์•Š์€ ์ฝ˜ํฌ๋ฆฌํŠธ์˜ ์žฌ๋ฃŒํŠน์„ฑ์„ ๊ทœ๋ช…ํ•  ํ•„์š”๊ฐ€ ์žˆ๋‹ค(Malaeb et al. 2015; Ma et al. 2018). ์ด์™€ ๋”๋ถˆ์–ด ์ ์ธต์„ฑ์€ ์ถœ๋ ฅ ํ›„์˜ ๊ฒฝํ™”์‹œ๊ฐ„์ด ๊ธธ์ˆ˜๋ก ์ข‹์ง€๋งŒ, ๊ณผ๋„ํ•˜๊ฒŒ ๊ธธ์–ด์งˆ ๊ฒฝ์šฐ ์„ ํ–‰ ๋ ˆ์ด์–ด์™€ ํ›„์† ๋ ˆ์ด์–ด ์‚ฌ์ด์˜ ๋ถ€์ฐฉ์„ฑ๋Šฅ์ด ๊ฐ์†Œํ•˜๊ธฐ ๋•Œ๋ฌธ์— CRP ์‹œ ์ธต๊ฐ„ ์ ์ธต ์‹œ๊ฐ„ ๊ฐ„๊ฒฉ(Printing Time Gap, PTG)์„ ์ ์ ˆํ•˜๊ฒŒ ์„ค์ •ํ•˜๋Š” ๊ฒƒ์ด ๋งค์šฐ ์ค‘์š”ํ•˜๋‹ค(Perrot et al. 2016; Kazemian et al. 2017).

3.2 ๊ตณ์ง€ ์•Š์€ ์ฝ˜ํฌ๋ฆฌํŠธ์˜ ์œ ๋™ํ•™์  ํŠน์„ฑ

์••์ถœ์„ฑ๊ณผ ์ ์ธก์„ฑ์€ ๊ตณ์ง€ ์•Š์€ ์ฝ˜ํฌ๋ฆฌํŠธ์˜ ์œ ๋™ํ•™์  ํŠน์„ฑ๊ณผ ๊ด€๋ จ์ด ์žˆ๋‹ค. ์ด ์—ฐ๊ตฌ์—์„œ๋Š” ๊ตณ์ง€ ์•Š์€ ์ฝ˜ํฌ๋ฆฌํŠธ์˜ ์œ ๋™ํ•™์  ํŠน์„ฑ ์ค‘ ์••์ถœ์„ฑ ๋ฐ ์ ์ธต์„ฑ๊ณผ ๋ฐ€์ ‘ํ•œ ๊ด€๋ จ์ด ์žˆ๋Š” ์ ๋„ ๋ฐ ํ•ญ๋ณต์‘๋ ฅ์„ ๊ทœ๋ช…ํ•˜๊ธฐ ์œ„ํ•œ ๋ฌธํ—Œ์—ฐ๊ตฌ ๋ฐ CFD ํ•ด์„์„ ์ˆ˜ํ–‰ํ•˜์˜€๋‹ค.

Fig. 4. CFD analysis results

../../Resources/kci/JKCI.2020.32.1.085/fig4_1.png

../../Resources/kci/JKCI.2020.32.1.085/fig4_2.png

../../Resources/kci/JKCI.2020.32.1.085/fig4_3.png

3.2.1 ์••์ถœ์„ฑ

๊ตณ์ง€ ์•Š์€ ์ฝ˜ํฌ๋ฆฌํŠธ์˜ ์ ๋„ ๋ฐ ํ•ญ๋ณต์‘๋ ฅ์— ๋”ฐ๋ฅธ ์••์ถœ์„ฑ์„ ๊ทœ๋ช…ํ•˜๊ธฐ ์œ„ํ•˜์—ฌ CFD ํ•ด์„์„ ์ˆ˜ํ–‰ํ•˜์˜€๋‹ค. ์ ๋„์™€ ํ•ญ๋ณต์‘๋ ฅ์— ๋”ฐ๋ฅธ ์••์ถœ๊ธฐ์—์„œ์˜ ํ† ์ถœ๋Ÿ‰๊ณผ ํ‰๊ท ํ† ์ถœ์†๋„์˜ ๋ณ€ํ™”๋ฅผ ๋ถ„์„ํ•˜์˜€์œผ๋ฉฐ, CFD ํ•ด์„์€ ์•„๋ž˜์™€ ๊ฐ™์€ ์ ˆ์ฐจ๋ฅผ ํ†ตํ•ด ์ง„ํ–‰๋˜์—ˆ๋‹ค.

๋‹จ๊ณ„ 1: ์••์ถœ๊ธฐ ๋ชจ๋ธ๋ง(์Šคํฌ๋ฅ˜ ๊ฐ๋„: 10ยฐ).

๋‹จ๊ณ„ 2: ๋ฉ”์‰ฌ(mesh)๋Š” Proximity and Curvature๋กœ ๋ชจ๋ธ๋งํ•˜๊ณ , ๋ฉ”์‰ฌ ์‚ฌ์ด์ฆˆ๋Š” ์ตœ๋Œ€ 1 mm๋กœ ํ˜•์„ฑ.

๋‹จ๊ณ„ 3: ํ•ด์„์€ ์ •์ƒ์ƒํƒœ(steady state)๋กœ ์ˆ˜ํ–‰ํ•˜๊ณ , ์••์ถœ๊ธฐ ๋ฒฝ๋ฉด์€ โ€˜no slip wallโ€™, ์••์ถœ๊ธฐ ์Šคํฌ๋ฅ˜๋Š” โ€˜no slip & rotating wall(์†๋„ 1 RPM)โ€™์œผ๋กœ ์„ค์ •. ์ฝ˜ํฌ๋ฆฌํŠธ ํ•ญ๋ณต์‘๋ ฅ(0~8,000 Pa)๊ณผ ์ ๋„(0~800 Pa๏ฝฅs)๋ฅผ ์ž…๋ ฅ.

๋‹จ๊ณ„ 4: ๋ชจ๋“  ๋ณ€์ˆ˜์˜ ์ž”์ฐจ(residual) ๊ฐ’์ด 1eโˆ’4 ์ดํ•˜์ผ ๋•Œ๋ฅผ ์ˆ˜๋ ด์กฐ๊ฑด์œผ๋กœ ์„ค์ •ํ•˜์—ฌ ํ•ด์„ ์ˆ˜ํ–‰.

๋‹จ๊ณ„ 5: ํ† ์ถœ๋Ÿ‰(mass-flow) ๋ฐ ํ‰๊ท ํ† ์ถœ์†๋„(average velocity) ๋„์ถœ.

Fig. 5. Buildability of fresh concrete according to hardening rate (Jeong et al. 2019)

../../Resources/kci/JKCI.2020.32.1.085/fig5.png

Fig. 4๋Š” CFD ํ•ด์„๊ฒฐ๊ณผ๋ฅผ ๋‚˜ํƒ€๋‚ธ ๊ฒƒ์ด๋ฉฐ, ๊ตณ์ง€ ์•Š์€ ์ฝ˜ํฌ๋ฆฌํŠธ์˜ ์ ๋„๊ฐ€ ๋†’๊ณ  ํ•ญ๋ณต์‘๋ ฅ์ด ๋‚ฎ์„์ˆ˜๋ก ํ† ์ถœ๋Ÿ‰์ด ๋งŽ๊ณ  ํ‰๊ท ํ† ์ถœ์†๋„๊ฐ€ ๋น ๋ฅธ ๊ฒƒ์„ ํ™•์ธํ•˜์˜€๋‹ค. ๋”ฐ๋ผ์„œ ์ ๋„๊ฐ€ ๋†’๊ณ  ํ•ญ๋ณต์‘๋ ฅ์ด ๋‚ฎ์„์ˆ˜๋ก ์••์ถœ์„ฑ์ด ์ข‹๋‹ค๊ณ  ํŒ๋‹จํ•  ์ˆ˜ ์žˆ๋‹ค.

3.2.2 ์ ์ธต์„ฑ

Jeong et al.(2019)์€ ๊ตณ์ง€ ์•Š์€ ์ฝ˜ํฌ๋ฆฌํŠธ์˜ ์ ์ธต์„ฑ์€ ํ•ญ๋ณต์‘๋ ฅ๊ณผ ๋ฐ€์ ‘ํ•œ ๊ด€๋ จ์ด ์žˆ์œผ๋ฉฐ ๊ฒฝํ™”์†๋„(hardening rate)์—๋„ ํฐ ์˜ํ–ฅ์„ ๋ฐ›๋Š”๋‹ค๊ณ  ๋ณด๊ณ ํ•˜์˜€๋‹ค. Fig. 5๋Š” ๊ฒฝํ™”์†๋„๋ฅผ ๋ณ€์ˆ˜๋กœ ํ•˜์—ฌ CFD ํ•ด์„์„ ์ˆ˜ํ–‰ํ•œ ๊ฒฐ๊ณผ๋ฅผ ๋‚˜ํƒ€๋‚ธ ๊ฒƒ์ด๋ฉฐ. ๋น„๊ต์  ๊ฒฝํ™”์†๋„๊ฐ€ ๋น ๋ฅธ Case B๊ฐ€ Case A์— ๋น„ํ•ด ์ ์ธต๋œ ํ•„๋ผ๋ฉ˜ํŠธ์˜ ๋ณ€ํ˜•์ด ์ž‘๊ฒŒ ๋ฐœ์ƒํ•˜๋Š” ๊ฒƒ์„ ํ™•์ธํ•  ์ˆ˜ ์žˆ๋‹ค. ๋”ฐ๋ผ์„œ ํ•ญ๋ณต์‘๋ ฅ์ด ํฌ๊ณ  ๊ฒฝํ™”์†๋„๊ฐ€ ๋น ๋ฅผ์ˆ˜๋ก ์ ์ธต์„ฑ์ด ์šฐ์ˆ˜ํ•˜๋‹ค๊ณ  ํ•  ์ˆ˜ ์žˆ๋‹ค.

4. ์‹ ์†์กฐํ˜• ์ฝ˜ํฌ๋ฆฌํŠธ์˜ ์„ฑ๋Šฅ ๊ฒ€์ฆ ์‹คํ—˜

4.1 ๋ฐฐํ•ฉ์‹คํ—˜

4.1.1 ์‹คํ—˜๊ณ„ํš

๊ตณ์ง€ ์•Š์€ ์ฝ˜ํฌ๋ฆฌํŠธ์˜ ์••์ถœ์„ฑ ๋ฐ ์ ์ธต์„ฑ์— ๋Œ€ํ•œ ๋ฌธํ—Œ์—ฐ๊ตฌ ๋ฐ CFD ํ•ด์„๊ฒฐ๊ณผ์— ๊ธฐ๋ฐ˜ํ•˜์—ฌ ์ด ์—ฐ๊ตฌ์—์„œ๋Š” ๋ฐฐํ•ฉ์‹คํ—˜์„ ์ˆ˜ํ–‰ํ•˜์—ฌ ๊ตณ์ง€ ์•Š์€ ์ฝ˜ํฌ๋ฆฌํŠธ์˜ ๋ ˆ์˜ฌ๋กœ์ง€(์ ๋„, ํ•ญ๋ณต์‘๋ ฅ)๋ฅผ ์ธก์ •ํ•˜๊ณ , CRP์— ์ ํ•ฉํ•œ ๋ฐฐํ•ฉ์„ ๋„์ถœํ•˜์˜€๋‹ค. ๊ตณ์ง€ ์•Š์€ ์ฝ˜ํฌ๋ฆฌํŠธ๋Š” ์‹œ๊ฐ„์ด ์ง€๋‚จ์— ๋”ฐ๋ผ ๋ ˆ์˜ฌ๋กœ์ง€ ํŠน์„ฑ์ด ํฐ ์˜ํ–ฅ์„ ๋ฐ›๊ธฐ ๋•Œ๋ฌธ์—(Petit et al. 2007) ์ด ์—ฐ๊ตฌ์—์„œ๋Š” ๋ฐฐํ•ฉ ์ดํ›„ 1์‹œ๊ฐ„ ๋™์•ˆ ์ฃผ๊ธฐ์ ์œผ๋กœ ์ ๋„ ๋ฐ ํ•ญ๋ณต์‘๋ ฅ์„ ์ธก์ •ํ•˜์˜€๋‹ค. ์ด๋•Œ ์‚ฌ์šฉํ•œ ๋ ˆ์˜ค๋ฏธํ„ฐ๋Š” Brookfield์‚ฌ์˜ DV-3T ๋ชจ๋ธ์ด๋‹ค. ๋˜ํ•œ, Le et al. (2012a)์€ CRP๋กœ ์ œ์ž‘ํ•œ ๊ตฌ์กฐ ๋ถ€์žฌ๋Š” ๋ ˆ์ด์–ด ๊ฐ„์˜ ๊ณ„๋ฉด ์กด์žฌ, ํƒ€์„ค ์‹œ ๋‹ค์ง ๋ฌธ์ œ ๋“ฑ์œผ๋กœ ์ธํ•˜์—ฌ ๊ธฐ์กด RC ๋ถ€์žฌ์— ๋น„ํ•ด ๊ตฌ์กฐ์„ฑ๋Šฅ์ด ์ทจ์•ฝํ•  ๊ฐ€๋Šฅ์„ฑ์ด ์žˆ๊ธฐ ๋•Œ๋ฌธ์— ์ƒ๋Œ€์ ์œผ๋กœ ๋†’์€ ์••์ถ•๊ฐ•๋„์˜ ๋ฐฐํ•ฉ์„ ์‚ฌ์šฉํ•ด์•ผ ํ•œ๋‹ค๊ณ  ๋ณด๊ณ ํ•˜์˜€๋‹ค. ๋”ฐ๋ผ์„œ, ์ด ์—ฐ๊ตฌ์—์„œ๋Š” 90 MPa ์ด์ƒ์˜ ์••์ถ•๊ฐ•๋„๋ฅผ ๊ฐ€์ง€๋Š” CRP ๋ฐฐํ•ฉ์„ ๊ฐœ๋ฐœํ•˜๊ณ ์ž ํ•˜์˜€์œผ๋ฉฐ, ์ด๋ฅผ Table 1์— ์ •๋ฆฌํ•˜์—ฌ ๋‚˜ํƒ€๋‚ด์—ˆ๋‹ค. ๋ฐ”์ธ๋”(binder)๋กœ์จ ์‹œ๋ฉ˜ํŠธ, ์‹ค๋ฆฌ์นดํ“ธ(silicafume), ์‹ค๋ฆฌ์นดํ”Œ๋กœ์–ด(silicaflour)๋ฅผ ์‚ฌ์šฉํ•˜์˜€์œผ๋ฉฐ, ๊ตต์€ ๊ณจ์žฌ(aggregate)๊ฐ€ ์‚ฌ์šฉ๋  ๊ฒฝ์šฐ์—๋Š” ์ฝ˜ํฌ๋ฆฌํŠธ ์••์ถœ์ด ์–ด๋ ค์šฐ๋ฏ€๋กœ ์ž…๋„ 0.4 mm ๋ฐ 0.2 mm์˜ ์ž”๊ณจ์žฌ(fine sand)๋งŒ์„ ์ด์šฉํ•˜์—ฌ ๋ฐฐํ•ฉ์„ ์ˆ˜ํ–‰ํ•˜์˜€๋‹ค. ๋˜ํ•œ, ๊ตณ์ง€ ์•Š์€ ์ฝ˜ํฌ๋ฆฌํŠธ์˜ ์œ ๋™์„ฑ๊ณผ ์ถœ๋ ฅ์„ ์ง€์†ํ•  ์ˆ˜ ์žˆ๋Š” ์‹œ๊ฐ„์ธ ์˜คํ”ˆํƒ€์ž„์„ ํ™•๋ณดํ•˜๊ธฐ ์œ„ํ•˜์—ฌ ๊ณ ํ˜•๋ถ„ 30 %์˜ ํด๋ฆฌ์นด๋ณธ์‚ฐ๊ณ„ ์œ ๋™ํ™”์ œ(superplasticizer)์™€ ์‘๊ฒฐ์ง€์—ฐ์ œ(retarder)๋ฅผ ์‚ฌ์šฉํ•˜์˜€๋‹ค. ์‹คํ—˜๋ณ€์ˆ˜๋Š” ๋ฌผ-๋ฐ”์ธ๋” ๋น„(W/B), ์‹ค๋ฆฌ์นดํ“ธ๊ณผ ์‹ค๋ฆฌ์นดํ”Œ๋กœ์–ด์˜ ๋น„, ์‘๊ฒฐ์ง€์—ฐ์ œ ํ˜ผ์ž… ์—ฌ๋ถ€๋กœ ์„ค์ •ํ•˜์˜€์œผ๋ฉฐ, ์ด 5๊ฐ€์ง€์˜ ๋ฐฐํ•ฉ๋น„(Mix 1~5)์— ๋Œ€ํ•œ ์‹คํ—˜์„ ์ˆ˜ํ–‰ํ•˜์˜€๋‹ค.

4.1.2 ์‹คํ—˜๊ฒฐ๊ณผ

Table 1. Mix proportion

Material

Mix 1

Mix 2

Mix 3

Mix 4

Mix 5

Cement

1

1

1

1

1

Silicafume

0.25

0.375

0.5

0.375

0.5

Silicaflour

0.25

0.125

0

0.125

0

Fine sand #6

0.37

0.37

0.37

0.37

0.37

Fine sand #7

0.55

0.55

0.55

0.55

0.55

Superplasticizer

0.036

0.036

0.036

0.036

0.036

Retarder

0.0077

0.0077

0.0077

0

0

Water

0.19

0.19

0.19

0.1

0.1

Fig. 6. Measurement results of rheology properties

../../Resources/kci/JKCI.2020.32.1.085/fig6.png

Table 2. Measured compressive strength (fck) and slump

Mix 1

Mix 2

Mix 3

Mix 4

Mix 5

fck (MPa)

123.6

94.8

117.1

119.1

-

Slump (mm)

220

245

270

70

0

Fig. 6์€ ๋ฐฐํ•ฉ ์ดํ›„ ๊ฒฝ๊ณผ์‹œ๊ฐ„์— ๋”ฐ๋ฅธ ๊ตณ์ง€ ์•Š์€ ์ฝ˜ํฌ๋ฆฌํŠธ์˜ ์ ๋„์™€ ํ•ญ๋ณต์‘๋ ฅ ์ธก์ •๊ฒฐ๊ณผ๋ฅผ ๋‚˜ํƒ€๋‚ธ ๊ฒƒ์ด๋ฉฐ, Table 2๋Š” ๋ฐฐํ•ฉ ์งํ›„ ์ธก์ •ํ•œ ์Šฌ๋Ÿผํ”„(KS F 2402(KATS 2017))์™€ ๊ฐ ๋ฐฐํ•ฉ๋ณ„ ์••์ถ•๊ณต์‹œ์ฒด 3๊ฐœ์˜ 28์ผ ์••์ถ•๊ฐ•๋„(KS F 2405(KATS 2010))์˜ ํ‰๊ท ์„ ์ •๋ฆฌํ•˜์—ฌ ๋‚˜ํƒ€๋‚ธ ๊ฒƒ์ด๋‹ค. ๋‹ค๋งŒ, Mix 5์˜ ๊ฒฝ์šฐ์—๋Š” ์ ๋„ ๋ฐ ํ•ญ๋ณต์‘๋ ฅ์„ ์ธก์ •ํ•  ์ˆ˜ ์—†์„ ์ •๋„๋กœ ์›Œ์ปค๋นŒ๋ฆฌํ‹ฐ๊ฐ€ ๋งค์šฐ ๋‚ฎ์•„์„œ ์‹คํ—˜๊ฒฐ๊ณผ ๋ถ„์„์—์„œ ์ œ์™ธํ•˜์˜€๋‹ค. Fig. 6์— ๋‚˜ํƒ€๋‚ธ ์ ๋„ ๋ฐ ํ•ญ๋ณต์‘๋ ฅ ์ธก์ •๊ฒฐ๊ณผ๋ฅผ ๋ฐ”ํƒ•์œผ๋กœ ์ ๋„๊ฐ€ ๋†’์œผ๋ฉด์„œ๋„ ์ถœ๋ ฅ ๋ฐ ์ ์ธต์ด ๊ฐ€๋Šฅํ•œ ์ •๋„์˜ ์ ๋‹นํ•œ ํ•ญ๋ณต์‘๋ ฅ์ด ๊ฐ€์žฅ ์ ํ•ฉํ•œ ๋ฐฐํ•ฉ, ์ฆ‰ ์••์ถœ์„ฑ ๋ฐ ์ ์ธต์„ฑ์ด ์ ์ ˆํ•˜๊ฒŒ ํ™•๋ณด๋œ ๋ฐฐํ•ฉ์œผ๋กœ์จ Mix 2๋ฅผ ์„ ์ •ํ•˜์˜€๋‹ค. ๋˜ํ•œ, ํ•ญ๋ณต์‘๋ ฅ์€ ์‹œ๊ฐ„์ด ๊ฒฝ๊ณผํ•จ์— ๋”ฐ๋ผ ์ฆ๊ฐ€ํ•˜๋Š” ์–‘์ƒ์„ ๋‚˜ํƒ€๋‚ด์—ˆ์œผ๋ฉฐ, ํŠนํžˆ ๋ฐฐํ•ฉ ํ›„ ์•ฝ 1์‹œ๊ฐ„์ด ๊ฒฝ๊ณผํ•œ ์‹œ์ ๋ถ€ํ„ฐ ๊ธ‰๊ฒฉํžˆ ์ฆ๊ฐ€ํ•˜์˜€๋‹ค. ๋”ฐ๋ผ์„œ ์••์ถœ์„ฑ ๋ฐ ์ ์ธต์„ฑ ๊ฒ€์ฆ ์‹คํ—˜ ์‹œ ๊ตณ์ง€ ์•Š์€ ์ฝ˜ํฌ๋ฆฌํŠธ์˜ ์••์ถœ์ด ๊ฐ€๋Šฅํ•œ ์‹œ๊ฐ„, ์ฆ‰ ์˜คํ”ˆํƒ€์ž„์„ 1์‹œ๊ฐ„์œผ๋กœ ์„ค์ •ํ•˜์˜€๋‹ค. ๊ฐ ๋ฐฐํ•ฉ๋ณ„ ์••์ถ•๊ฐ•๋„๋Š” Table 2์— ๋‚˜ํƒ€๋‚ธ ๋ฐ”์™€ ๊ฐ™์ด Mix 5๋ฅผ ์ œ์™ธํ•œ ๋ชจ๋“  ๋ฐฐํ•ฉ์—์„œ ๋ชฉํ‘œ์••์ถ•๊ฐ•๋„์ธ 90 MPa ์ด์ƒ์œผ๋กœ ์ธก์ •๋˜์—ˆ๋‹ค.

4.2 ์••์ถœ์„ฑ ๊ฒ€์ฆ ์‹คํ—˜

4.2.1 ์‹คํ—˜๊ณ„ํš

์ด ์—ฐ๊ตฌ์—์„œ๋Š” ๋ฐฐํ•ฉ์‹คํ—˜์„ ํ†ตํ•ด ๋„์ถœํ•œ Mix 2 ๋ฐฐํ•ฉ์˜ ์••์ถœ์„ฑ์„ ๊ฒ€์ฆํ•˜๊ธฐ ์œ„ํ•œ ์‹คํ—˜์„ ์ˆ˜ํ–‰ํ•˜์˜€์œผ๋ฉฐ, ๊ธฐ์กด ์—ฐ๊ตฌ(Le et al. 2012a; Kazemian et al. 2017)์— ๊ทผ๊ฑฐํ•˜์—ฌ 300 mm ๊ธธ์ด์˜ ํ•„๋ผ๋ฉ˜ํŠธ 5์ค„์„ ์••์ถœํ•˜๋Š” ํ•˜๋Š” ๊ฒƒ์œผ๋กœ ๊ณ„ํšํ•˜์˜€๋‹ค.

Ma et al.(2018)์€ ํ˜ผํ•ฉ๋ฌผ์˜ ์••์ถœ์†๋„์™€ ๋…ธ์ฆ์˜ ์ด๋™์†๋„, ๊ทธ๋ฆฌ๊ณ  ํ”„๋ฆฐํŒ… ํ‘œ๋ฉด์—์„œ ๋…ธ์ฆ๊นŒ์ง€์˜ ๋†’์ด๊ฐ€ ์••์ถœ์„ฑ์— ์˜ํ–ฅ์„ ๋ผ์นœ๋‹ค๊ณ  ์–ธ๊ธ‰ํ•˜์˜€์œผ๋ฉฐ, Hasan et al.(2016)์€ ํ•„๋ผ๋ฉ˜ํŠธ์˜ ํญ๊ณผ ๋‘๊ป˜, ๊ทธ๋ฆฌ๊ณ  ํ˜•์ƒ์— ๋”ฐ๋ผ ์ ์ธต ์‹œ ์•ˆ์ •์„ฑ์— ์˜ํ–ฅ์„ ์ค„ ์ˆ˜ ์žˆ๋‹ค๊ณ  ๋ณด๊ณ ํ•˜์˜€๋‹ค. ๋”ฐ๋ผ์„œ ์••์ถœ์„ฑ ๊ฒ€์ฆ ์‹คํ—˜์—์„œ์˜ ๋ณ€์ˆ˜๋Š” Fig. 7 ๋ฐ Table 3์— ๋‚˜ํƒ€๋‚ธ ๋ฐ”์™€ ๊ฐ™์ด ์ฝ˜ํฌ๋ฆฌํŠธ์˜ ์••์ถœ์†๋„(vconcrete)์— ๋Œ€ํ•œ ์ถœ๋ ฅ์†๋„(vprโˆซโˆˆg)์˜ ๋น„(velocity ratio, VR)์™€ ์••์ถœ๊ธฐ์˜ ์ถœ๋ ฅ ๋†’์ด(hextruder)๋กœ ์„ค์ •ํ•˜์˜€๋‹ค. ์ด๋•Œ vprโˆซโˆˆg์€ ํ”„๋ฆฐํŒ… ์žฅ๋น„์˜ ์„ฑ๋Šฅ์„ ๊ณ ๋ คํ•ด 80 mm/s๋กœ ๊ณ ์ •ํ•˜์˜€์œผ๋ฉฐ, ์••์ถœ๊ธฐ ๋‚ด์˜ ์Šคํฌ๋ฅ˜ ํšŒ์ „์†๋„(RPM)๋ฅผ ๋ณ€ํ™”์‹œํ‚ค๋ฉด์„œ vconcrete๋ฅผ ์กฐ์ ˆํ•˜์˜€๋‹ค. ๋˜ํ•œ, vconcrete์˜ ๋ณ€ํ™”์— ๋”ฐ๋ฅธ ์ถœ๋ ฅ๋œ ํ•„๋ผ๋ฉ˜ํŠธ์˜ ๋‹จ๋ฉด์ , ํญ ๋ฐ ๋‘๊ป˜๋ฅผ ์ธก์ •ํ•จ์œผ๋กœ์จ ์••์ถœ์— ์ตœ์ ํ™”๋œ VR ๋ฐ hextruder๋ฅผ ๋„์ถœํ•˜๊ณ ์ž ํ•˜์˜€๋‹ค.

Fig. 7. Variables in extrudability test

../../Resources/kci/JKCI.2020.32.1.085/fig7.png

Table 3. Test variables

Specimen (Extrudability-hextruder-VR)

hextruder

(mm)

VR

E-15-1.0

15

1.0

E-15-1.5

15

1.5

E-15-3.0

15

3.0

E-20-1.0

20

1.0

E-20-1.5

20

1.5

E-20-3.0

20

3.0

Fig. 8. Extrudability test results

../../Resources/kci/JKCI.2020.32.1.085/fig8.png

Fig. 9. Section of extruded filament

../../Resources/kci/JKCI.2020.32.1.085/fig9.png

Table 4. Measured section height and width of filaments

Specimen

H

(mm)

W

(mm)

H/hextruder

E-15-1.0

11.53

33.06

0.77

E-15-1.5

12.08

33.70

0.81

E-15-3.0

11.25

21.04

0.75

E-20-1.0

14.61

30.36

0.73

E-20-1.5

13.55

23.20

0.68

E-20-3.0

11.89

15.35

0.59

4.2.2 ์‹คํ—˜๊ฒฐ๊ณผ

Fig. 8์—๋Š” VR ๋ฐ ์••์ถœ๊ธฐ ๋…ธ์ฆ์˜ ๋†’์ด(hextruder)์— ๋”ฐ๋ฅธ ์‹คํ—˜์ฒด ์ถœ๋ ฅ๊ฒฐ๊ณผ๋ฅผ ๋‚˜ํƒ€๋‚ด์—ˆ์œผ๋ฉฐ, ์ด ์—ฐ๊ตฌ์—์„œ ์„ค์ •ํ•œ ๋ชจ๋“  ๋ณ€์ˆ˜์—์„œ ํ•„๋ผ๋ฉ˜ํŠธ์˜ ๋‘๊ป˜๊ฐ€ ์ผ์ •ํ•˜๊ฒŒ ์ถœ๋ ฅ๋˜์–ด ์ ์ ˆํ•œ ์••์ถœ์„ฑ๋Šฅ์ด ํ™•๋ณด๋œ ๊ฒƒ์œผ๋กœ ๋‚˜ํƒ€๋‚ฌ๋‹ค. Fig. 9์™€ Table 4์—๋Š” ๊ฐ ํ•„๋ผ๋ฉ˜ํŠธ ๋‹จ๋ฉด์˜ ํญ๊ณผ ๋‘๊ป˜๋ฅผ ์ธก์ •ํ•œ ๊ฒฐ๊ณผ๋ฅผ ๋‚˜ํƒ€๋‚ด์—ˆ์œผ๋ฉฐ, VR์ด ๋†’์„์ˆ˜๋ก ๋‹จ๋ฉด์˜ ํญ(W)์ด ์ž‘๊ฒŒ ํ˜•์„ฑ๋˜๊ณ , ์ถœ๋ ฅ๋œ ํ•„๋ผ๋ฉ˜ํŠธ์˜ ๋†’์ด์™€ ์••์ถœ๊ธฐ ๋…ธ์ฆ ๋†’์ด์˜ ๋น„(H/hextruder)๊ฐ€ ๊ฐ์†Œํ•˜๋Š” ๊ฒƒ์œผ๋กœ ๋‚˜ํƒ€๋‚ฌ๋‹ค. ๋‹จ๋ฉด์˜ ํญ์ด ํด์ˆ˜๋ก, H/hextruder๊ฐ€ 1.0์— ๊ฐ€๊นŒ์šธ์ˆ˜๋ก ๊ตณ์ง€ ์•Š์€ ์ฝ˜ํฌ๋ฆฌํŠธ๋ฅผ ์•ˆ์ •์ ์œผ๋กœ ์ ์ธตํ•˜๋Š” ๋ฐ ์œ ๋ฆฌํ•˜๊ธฐ ๋•Œ๋ฌธ์—, ์ด ์—ฐ๊ตฌ์—์„œ๋Š” VR์„ 1.0, hextruder์„ 10 mm๋กœ ์„ค์ •ํ•˜์—ฌ ์ ์ธต์„ฑ ๊ฒ€์ฆ ์‹คํ—˜์„ ์ˆ˜ํ–‰ํ•˜์˜€๋‹ค.

4.3 ์ ์ธต์„ฑ ๊ฒ€์ฆ ์‹คํ—˜

4.3.1 ์‹คํ—˜๊ณ„ํš

์ ์ธต์„ฑ ๊ฒ€์ฆ ์‹คํ—˜์€ ์•ž์„œ ์–ธ๊ธ‰๋œ ์••์ถœ์„ฑ ๊ฒ€์ฆ ์‹คํ—˜ ๋ฐ ๊ธฐ์กด ์—ฐ๊ตฌ(Le et al. 2012a)์— ๋”ฐ๋ผ 300 mm ๊ธธ์ด์˜ ํ•„๋ผ๋ฉ˜ํŠธ๋ฅผ ๋†’์ด 70 mm ์ด์ƒ ์—ฐ์† ์ ์ธตํ•˜๋Š” ๊ฒƒ์œผ๋กœ ๊ณ„ํšํ•˜์˜€๋‹ค. ์‹คํ—˜๋ณ€์ˆ˜๋Š” Table 5์— ๋‚˜ํƒ€๋‚ธ ๊ฒƒ๊ณผ ๊ฐ™์ด ์—ฐ์†์ถœ๋ ฅ ๋ ˆ์ด์–ด์˜ ๊ฐœ์ˆ˜์™€ ์ธต๊ฐ„ ์ ์ธต ์‹œ๊ฐ„ ๊ฐ„๊ฒฉ(PTG)์œผ๋กœ ์„ค์ •ํ•˜์˜€๋‹ค. B-2-5 ์‹คํ—˜์ฒด๋Š” 2๊ฐœ์˜ ๋ ˆ์ด์–ด๋ฅผ ํ•œ ๋ฒˆ์— ์ ์ธตํ•œ ํ›„ 5๋ถ„์˜ ๋Œ€๊ธฐ์‹œ๊ฐ„์„ ๊ฐ€์ง€๊ณ  ์ดํ›„ 2๊ฐœ์˜ ๋ ˆ์ด์–ด๋ฅผ ์ ์ธตํ•˜๋Š” ๋ฐฉ์‹์œผ๋กœ ์ œ์ž‘๋˜์—ˆ์œผ๋ฉฐ, B-1-2.5 ์‹คํ—˜์ฒด๋Š” 1๊ฐœ์˜ ๋ ˆ์ด์–ด๋ฅผ ์ ์ธตํ•  ๋•Œ๋งˆ๋‹ค 2๋ถ„ 30์ดˆ์˜ ๋Œ€๊ธฐ์‹œ๊ฐ„์„ ๊ฐ€์ง€๊ณ  ์ œ์ž‘๋˜์—ˆ๋‹ค.

4.3.2 ์‹คํ—˜๊ฒฐ๊ณผ

Fig. 10์€ B-2-5์™€ B-1-2.5 ์‹คํ—˜์ฒด๊ฐ€ ์ ์ธต๋œ ๋ชจ์Šต์„ ๋‚˜ํƒ€๋‚ธ ๊ฒƒ์ด๋ฉฐ, ๋‘ ์‹คํ—˜์ฒด ๋ชจ๋‘ ๋†’์ด ์•ฝ 85 mm๊นŒ์ง€ ์•ˆ์ •์ ์œผ๋กœ ์ ์ธต๋˜์—ˆ๋‹ค. Table 6์—๋Š” ์‹คํ—˜์ฒด์˜ ๋ ˆ์ด์–ด ๋ณ„ ๋†’์ด ๋ฐ ์ „์ฒด ์ ์ธต ๋†’์ด๋ฅผ ๋‚˜ํƒ€๋‚ด์—ˆ์œผ๋ฉฐ, ๊ฐ ๋ ˆ์ด์–ด์˜ ํ‰๊ท  ๋†’์ด๋Š” ์•ฝ 8.5 mm๋กœ์จ ๋น„๊ต์  ์ผ์ •ํ•œ ๋†’์ด๋กœ ์ ์ธต๋˜๋Š” ๊ฒƒ์œผ๋กœ ํ™•์ธ๋˜์—ˆ๋‹ค. ๋‹ค๋งŒ, Fig. 11์— ๋‚˜ํƒ€๋‚ธ ๋ฐ”์™€ ๊ฐ™์ด ๋‘ ์‹คํ—˜์ฒด ๋ ˆ์ด์–ด์˜ ๋ณ€ํ˜• ์ •๋„๋ฅผ ๋น„๊ตํ•˜์—ฌ ๋ณด๋ฉด, 2๊ฐœ์˜ ๋ ˆ์ด์–ด๋ฅผ ์—ฐ์† ์ถœ๋ ฅํ•˜๊ณ , 5๋ถ„์˜ ๋Œ€๊ธฐ์‹œ๊ฐ„(PTG)์„ ๊ฐ€์ง„ B-2-5 ์‹คํ—˜์ฒด์—์„œ ์ƒ์œ„ ๋ ˆ์ด์–ด(์ง์ˆ˜์ธต ๋ ˆ์ด์–ด)์— ์˜ํ•œ ํ•˜์œ„ ๋ ˆ์ด์–ด(ํ™€์ˆ˜์ธต ๋ ˆ์ด์–ด)์˜ ๋ณ€ํ˜•์ด ๋น„๊ต์  ํฌ๊ฒŒ ๋ฐœ์ƒํ•œ ๊ฒƒ์„ ํ™•์ธํ•  ์ˆ˜ ์žˆ๋‹ค. ์ด์™€๋Š” ๋‹ฌ๋ฆฌ ํ•œ ์ธต์„ ์ถœ๋ ฅํ•  ๋•Œ๋งˆ๋‹ค 2๋ถ„ 30์ดˆ์˜ PTG๋ฅผ ๋‘” B-1-2.5 ์‹คํ—˜์ฒด๋Š” ์ „ ์ธต์— ๊ฑธ์ณ ๊ท ์ผํ•œ ๋†’์ด๊ฐ€ ํ˜•์„ฑ๋˜์—ˆ์œผ๋ฉฐ ํ•„๋ผ๋ฉ˜ํŠธ์˜ ๋ณ€ํ˜•์ด ๋น„๊ต์  ์ž‘๊ฒŒ ๋‚˜ํƒ€๋‚ฌ๋‹ค. ๋”ฐ๋ผ์„œ, ์ด ์—ฐ๊ตฌ์—์„œ๋Š” ํ•œ ์ธต์„ ์ถœ๋ ฅํ•˜๊ณ  2๋ถ„ 30์ดˆ์˜ PTG๋ฅผ ๊ฐ€์ง„ ํ›„ ๋‹ค์Œ ์ธต์„ ์ถœ๋ ฅํ•˜๋Š” ๋ฐฉ์‹์œผ๋กœ ๋ถ€์žฌ๋ฅผ ์ œ์ž‘ํ•œ ํ›„ ํœจ์‹คํ—˜์„ ์ˆ˜ํ–‰ํ•˜์˜€๋‹ค.

Table 5. Variables in buildability test

Specimen

(Buildability-Number of continuous built up layers-PTG)

Number of continuous built up layers

PTG

(min)

B-2-5

2

5

B-1-2.5

1

2.5

Fig. 10. layered specimens

../../Resources/kci/JKCI.2020.32.1.085/fig10.png

Table 6. Measured layer height of specimens

Number of layer

Height of layer [Total height] (mm)

B-2-5

B-1-2.5

1

18 [18]

9 [9]

2

9 [18]

3

18 [36]

8 [26]

4

9 [35]

5

16 [52]

9 [44]

6

8 [52]

7

16 [68]

8 [60]

8

8 [68]

9

18 [86]

8 [76]

10

8 [84]

Fig. 11. Comparison of layered specimens according to PTG

../../Resources/kci/JKCI.2020.32.1.085/fig11.png

4.4 ํœจ์„ฑ๋Šฅ ๊ฒ€์ฆ ์‹คํ—˜

4.4.1 ์‹คํ—˜๊ณ„ํš

์ด ์—ฐ๊ตฌ์—์„œ๋Š” CRP ๋ฐฉ์‹์œผ๋กœ ์ œ์ž‘๋œ ๋ถ€์žฌ์™€ RC ๋ถ€์žฌ์˜ ํœจ์„ฑ๋Šฅ์„ ๋น„๊ตํ•˜๊ณ ์ž ํ•˜์˜€์œผ๋ฉฐ, ์ฃผ์š” ๋ณ€์ˆ˜๋Š” Table 7์— ๋‚˜ํƒ€๋‚ธ ๋ฐ”์™€ ๊ฐ™์ด ์‹คํ—˜์ฒด ์ œ์ž‘๋ฐฉ์‹ ๋ฐ ์ธ์žฅ์ฒ ๊ทผ ๋ณด๊ฐ• ์—ฌ๋ถ€๋กœ ๊ณ„ํšํ•˜์˜€๋‹ค. ๋˜ํ•œ, CRP๋ฅผ ์ด์šฉํ•œ ๋ถ€์žฌ ์ œ์ž‘ ์‹œ์—๋Š” ์••์ถœ์„ฑ ๋ฐ ์ ์ธต์„ฑ ์‹คํ—˜๊ฒฐ๊ณผ๋ฅผ ๊ธฐ๋ฐ˜์œผ๋กœ VR์€ 1.0, PTG๋Š” 2๋ถ„ 30์ดˆ, hextruder๋Š” 10 mm๋กœ ์„ค์ •ํ•˜์˜€๋‹ค. ๋‹ค๋งŒ, ํ˜„์žฌ๊นŒ์ง€ ๊ฐœ๋ฐœ๋œ CRP ์‹œ์Šคํ…œ์—์„œ๋Š” ์ฝ˜ํฌ๋ฆฌํŠธ ์ถœ๋ ฅ๊ณผ ๋™์‹œ์— ์ฒ ๊ทผ ๋ฐฐ์น˜ ๋“ฑ์˜ ์ธ์žฅ๋ณด๊ฐ•์„ ํ•˜๊ธฐ๋Š” ๋งค์šฐ ์–ด๋ ค์šด ์ƒํ™ฉ์ด๋‹ค(Bos et al. 2018). ๋”ฐ๋ผ์„œ ์ด ์—ฐ๊ตฌ์—์„œ๋Š” Fig. 12์— ๋‚˜ํƒ€๋‚ธ ๋ฐ”์™€ ๊ฐ™์ด CRP๋กœ ๋ถ€์žฌ ์™ธ๋ฉด์„ ์ œ์ž‘ํ•˜๊ณ , 24์‹œ๊ฐ„ ๋™์•ˆ ๋Œ€๊ธฐ ์–‘์ƒ์„ ํ•˜์—ฌ ๋ถ€์žฌ ์™ธ๋ฉด์„ ๊ฒฝํ™”์‹œํ‚จ ํ›„ ์‚ฌ์ „ ์กฐ๋ฆฝ๋œ ํœจ ๋ฐ ์ „๋‹จ ๋ณด๊ฐ• ์ฒ ๊ทผ์„ ์‚ฝ์ž…ํ•˜๊ณ , ๋ถ€์žฌ ๋‚ด๋ถ€์— ์†์ฑ„์›€ ์ฝ˜ํฌ๋ฆฌํŠธ๋ฅผ ํƒ€์„คํ•˜๋Š” ๋ฐฉ์‹์œผ๋กœ CRP ์‹คํ—˜์ฒด๋ฅผ ์ œ์ž‘ํ•˜์˜€๋‹ค.

Table 7. Variables in flexural test

Specimen

Manufacturing method

Presence of reinforcing bar

CRP_S

Exterior of members Made of concrete rapid prototyping+Infilled concrete

O

CRP_N

X

RC_S

Formwork concrete

O

Fig. 12. Schematic description of CRP specimen

../../Resources/kci/JKCI.2020.32.1.085/fig12.png

Fig. 13. Section Details of flexural specimen

../../Resources/kci/JKCI.2020.32.1.085/fig13_1.png

../../Resources/kci/JKCI.2020.32.1.085/fig13_2.png

Fig. 13์— ๋ณด์ด๋Š” ๋ฐ”์™€ ๊ฐ™์ด ํœจ์‹คํ—˜์ฒด๋Š” ๋ชจ๋‘ ๋‹จ๋ฉด 150ร—150 mm, ๊ธธ์ด 700 mm๋กœ ์ œ์ž‘๋˜์—ˆ๋‹ค. CRP_S ๋ฐ RC_S ์‹คํ—˜์ฒด์—๋Š” ์••์ถ•์ธก์— D10 ์ฒ ๊ทผ, ์ธ์žฅ์ธก์— D16 ์ฒ ๊ทผ์„ ๋ฐฐ์น˜ํ•˜์˜€์œผ๋ฉฐ, ํ”ผ๋ณต์€ 20 mm๋ฅผ ํ™•๋ณดํ•˜์˜€๋‹ค. ์Šคํ„ฐ๋Ÿฝ์€ ์ „๋‹จํŒŒ๊ดด๋ฅผ ๋ฐฉ์ง€ํ•˜๊ณ  ํœจํŒŒ๊ดด๋ฅผ ์œ ๋„ํ•˜๊ธฐ ์œ„ํ•˜์—ฌ D6 ์ดํ˜•์ฒ ์„ ์„ 50 mm ๊ฐ„๊ฒฉ์œผ๋กœ ๋ฐฐ์น˜ํ•˜์˜€๋‹ค. ์‹คํ—˜์ฒด ์ œ์ž‘์— ์‚ฌ์šฉ๋œ D16 ์ธ์žฅ์ฒ ๊ทผ์˜ ํ•ญ๋ณต๊ฐ•๋„(fy)๋Š” 455.4 MPa์ด์—ˆ์œผ๋ฉฐ, ์‹คํ—˜ ์ „ ์ธก์ •ํ•œ ์‹ ์†์กฐํ˜• ์ฝ˜ํฌ๋ฆฌํŠธ์˜ ์••์ถ•๊ฐ•๋„(fck,CRP)์™€ ๋‚ด๋ถ€ํƒ€์„ค ์ฝ˜ํฌ๋ฆฌํŠธ(fck,RC)์˜ ์••์ถ•๊ฐ•๋„๋Š” ๊ฐ๊ฐ 94.9 ๋ฐ 52.8 MPa ์ด์—ˆ๋‹ค. ์‹คํ—˜์€ KS F 2407์— ๋”ฐ๋ผ ์ง„ํ–‰ํ•˜์˜€์œผ๋ฉฐ, ๋ถ€์žฌ์˜ ๊ฐ€๋ ฅ์  ์œ„์น˜(์ค‘์•™๋ถ€) ๋‹จ๋ฉด ํ•˜๋ถ€์— LVDT๋ฅผ ์„ค์น˜ํ•˜์—ฌ ๋ถ€์žฌ์˜ ์ฒ˜์ง์„ ๊ณ„์ธกํ•˜์˜€๋‹ค.

4.4.2 ์‹คํ—˜๊ฒฐ๊ณผ

Fig. 14๋Š” ๊ฐ ์‹คํ—˜์ฒด์˜ ํŒŒ๊ดด๋ชจ๋“œ๋ฅผ ๋‚˜ํƒ€๋‚ธ ๊ฒƒ์ด๋ฉฐ, Fig. 15๋Š” ์‹คํ—˜์ฒด๋ณ„ ํ•˜์ค‘-๋ณ€์œ„ ์ด๋ ฅ๊ณก์„ ์„ ๋‚˜ํƒ€๋‚ธ ๊ฒƒ์ด๋‹ค. ์ธ์žฅ์ฒ ๊ทผ์ด ๋ณด๊ฐ•๋˜์ง€ ์•Š๊ณ , ์†์ฑ„์›€ ์ฝ˜ํฌ๋ฆฌํŠธ๋งŒ ํƒ€์„ค๋œ CRP_N ์‹คํ—˜์ฒด์˜ ๊ฒฝ์šฐ์—๋Š” 23.8 kN์˜ ํ•˜์ค‘์—์„œ ํœจ ๊ท ์—ด์ด ๋ฐœ์ƒํ•จ๊ณผ ๋™์‹œ์— ์ทจ์„ฑ์ ์œผ๋กœ ํŒŒ๊ดด๋˜์—ˆ๋‹ค. ํŒŒ๊ดด ํ›„ CRP_N ์‹คํ—˜์ฒด์˜ ๋‹จ๋ฉด์„ ๊ด€์ฐฐํ•ด๋ณธ ๊ฒฐ๊ณผ, Fig. 16์— ๋‚˜ํƒ€๋‚ธ ๋ฐ”์™€ ๊ฐ™์ด ํ•„๋ผ๋ฉ˜ํŠธ ๋ ˆ์ด์–ด ๊ฐ„์˜ ์ ์ธต์ด ์ž˜ ์ด๋ฃจ์–ด์กŒ์Œ์„ ํ™•์ธํ•  ์ˆ˜ ์žˆ์—ˆ๋‹ค.

Fig. 14. Failure mode of flexural specimens

../../Resources/kci/JKCI.2020.32.1.085/fig14_1.png

../../Resources/kci/JKCI.2020.32.1.085/fig14_2.png

Fig. 15. Load-deflection curves of flexural specimens

../../Resources/kci/JKCI.2020.32.1.085/fig15.png

Fig. 16. Section of CRP_N specimen

../../Resources/kci/JKCI.2020.32.1.085/fig16.png

CRP_S ์‹คํ—˜์ฒด์—์„œ๋Š” ๊ฐ€๋ ฅ ์‹œ์ž‘ ํ›„ ์•ฝ 33 kN์˜ ํ•˜์ค‘์—์„œ ์‹คํ—˜์ฒด ์ค‘์•™ ํ•˜๋‹จ๋ถ€์— ์ตœ์ดˆ์˜ ํœจ ๊ท ์—ด์ด ๊ด€์ธก๋˜์—ˆ์œผ๋ฉฐ, Fig. 14(b)์— ๋‚˜ํƒ€๋‚ธ ๋ฐ”์™€ ๊ฐ™์ด 102 kN์˜ ํ•˜์ค‘์—์„œ CRP๋กœ ์ œ์ž‘ํ•œ ๋ถ€์žฌ ์™ธ๋ฉด์— ๊ท ์—ด์ด ๊ธ‰๊ฒฉํ•˜๊ฒŒ ์ง„์ „๋˜๋ฉด์„œ ํŒŒ๊ดด์— ์ด๋ฅด๋Š” ์–‘์ƒ์„ ๋‚˜ํƒ€๋‚ด์—ˆ๋‹ค. ๋ถ€์žฌ์˜ ์ตœ๋Œ€์ฒ˜์ง์€ ์•ฝ 4.6 mm๋กœ ๊ณ„์ธก๋˜์—ˆ๋‹ค. RC_S ์‹คํ—˜์ฒด์˜ ๊ฒฝ์šฐ์—๋Š” ๊ฐ€๋ ฅ ์‹œ์ž‘ ํ›„ 45 kN์˜ ํ•˜์ค‘์—์„œ ์‹คํ—˜์ฒด ์ค‘์•™ ํ•˜๋‹จ๋ถ€์— ์ตœ์ดˆ์˜ ํœจ ๊ท ์—ด์ด ๋ฐœ์ƒํ•˜์˜€์œผ๋ฉฐ, ์•ฝ 96 kN๋ถ€ํ„ฐ ์‹คํ—˜์ฒด์˜ ๊ฐ•์„ฑ์ด ๊ธ‰๊ฒฉํ•˜๊ฒŒ ๊ฐ์†Œํ•˜์˜€๋‹ค. ์ดํ›„ ์‹คํ—˜์ฒด๋Š” ์—ฐ์„ฑ์ ์ธ ๊ฑฐ๋™์„ ๋ณด์ด๋ฉด์„œ ํ•˜์ค‘์ด ์ง€์†ํ•ด์„œ ์ฆ๊ฐ€ํ•˜์˜€์œผ๋ฉฐ. 118 kN์˜ ํ•˜์ค‘์— ๋„๋‹ฌํ•œ ํ›„ ์••์ถ•์—ฐ๋‹จ ์ฝ˜ํฌ๋ฆฌํŠธ๊ฐ€ ์••๊ดด๋จ๊ณผ ๋™์‹œ์— ํœจํŒŒ๊ดด ๋˜์—ˆ๋‹ค. ํœจํŒŒ๊ดด ์‹œ ๋ถ€์žฌ ์ฒ˜์ง์€ ์•ฝ 14 mm๋กœ ๊ณ„์ธก๋˜์—ˆ์œผ๋ฉฐ, ์ฝ˜ํฌ๋ฆฌํŠธ๊ฐ€ ์ผ์ฒด ํƒ€์„ค๋œ RC_S ์‹คํ—˜์ฒด๋Š” CRP๋ฅผ ํ†ตํ•ด ์ œ์ž‘๋œ CRP_S๋ณด๋‹ค ์šฐ์ˆ˜ํ•œ ์—ฐ์„ฑ์„ ๋‚˜ํƒ€๋‚ด์—ˆ๋‹ค. ๋‹ค๋งŒ, CRP_S ์‹คํ—˜์ฒด์™€ RC_S ์‹คํ—˜์ฒด์˜ ํœจ๊ฐ•๋„๋Š” ํฐ ์ฐจ์ด๋ฅผ ๋ณด์ด์ง€ ์•Š์•˜์œผ๋ฉฐ, CRP_S ์‹คํ—˜์ฒด์—์„œ๋Š” ๋ถ€์žฌ์˜ ํŒŒ๊ดด ์‹œ์ ๊นŒ์ง€๋„ ์ถœ๋ ฅ๋œ ๋ ˆ์ด์–ด์— ์–ด๋– ํ•œ ๋ถ€์ฐฉ์†์ƒ๋„ ๊ด€์ธก๋˜์ง€ ์•Š์•˜๋‹ค. ์ถ”ํ›„ ์ธ์žฅ๋ณด๊ฐ•์ด ๊ฐ€๋Šฅํ•œ CRP ๊ธฐ์ˆ  ๊ฐœ๋ฐœ, CRP ๋ ˆ์ด์–ด ๊ฐ„์˜ ๋ถ€์ฐฉ์„ฑ๋Šฅ ๋ฐ ํ•˜์ค‘์ €ํ•ญ ๋ฉ”์ปค๋‹ˆ์ฆ˜์ด ๋”์šฑ ๋ช…ํ™•ํ•˜๊ฒŒ ๊ทœ๋ช…๋œ๋‹ค๋ฉด CRP ๋ถ€์žฌ๋ฅผ ๊ฑด์„คํ˜„์žฅ์— ์ ์šฉํ•  ์ˆ˜ ์žˆ๋Š” ๊ฒƒ๋„ ๋ฉ€์ง€ ์•Š์„ ๊ฒƒ์œผ๋กœ ๊ธฐ๋Œ€๋œ๋‹ค.

5. ๊ฒฐ ๋ก 

์ด ์—ฐ๊ตฌ์—์„œ๋Š” ์‹ ์†์กฐํ˜• ์ฝ˜ํฌ๋ฆฌํŠธ์˜ ์žฌ๋ฃŒํŠน์„ฑ์„ ๊ทœ๋ช…ํ•˜๊ธฐ ์œ„ํ•œ ์‹คํ—˜์ ๏ฝฅํ•ด์„์  ์—ฐ๊ตฌ๋ฅผ ์ˆ˜ํ–‰ํ•˜์˜€์œผ๋ฉฐ, ์ด๋ฅผ ๋ฐ”ํƒ•์œผ๋กœ ์‹ ์†์กฐํ˜•์— ์ ํ•ฉํ•œ ์ฝ˜ํฌ๋ฆฌํŠธ ๋ฐฐํ•ฉ์„ ๋„์ถœํ•˜์˜€๋‹ค. ๋˜ํ•œ, ๋„์ถœ๋œ ๋ฐฐํ•ฉ์„ ๊ธฐ๋ฐ˜์œผ๋กœ CRP์˜ ํ•ต์‹ฌ์š”์†Œ์ธ ์••์ถœ์„ฑ ๋ฐ ์ ์ธต์„ฑ์„ ๊ฒ€์ฆํ•˜์˜€์œผ๋ฉฐ, CRP ๋ฐฉ์‹์œผ๋กœ ์ œ์ž‘ํ•œ ๋ถ€์žฌ์˜ ํœจ ์‹คํ—˜์„ ์ˆ˜ํ–‰ํ•˜์˜€๋‹ค. ์ด ์—ฐ๊ตฌ๋กœ๋ถ€ํ„ฐ ๋‹ค์Œ๊ณผ ๊ฐ™์€ ๊ฒฐ๋ก ์„ ๋„์ถœํ•  ์ˆ˜ ์žˆ์—ˆ๋‹ค.

1) CRP์—์„œ ๊ฐ€์žฅ ์ค‘์š”ํ•œ ์š”์†Œ๋Š” ์••์ถœ์„ฑ๊ณผ ์ ์ธต์„ฑ์ด๋ฉฐ, ์ด๋Š” ๊ตณ์ง€ ์•Š์€ ์ฝ˜ํฌ๋ฆฌํŠธ์˜ ์ ๋„ ๋ฐ ํ•ญ๋ณต์‘๋ ฅ๊ณผ ๋ฐ€์ ‘ํ•œ ๊ด€๋ จ์ด ์žˆ๋‹ค. CFD๋ฅผ ์ด์šฉํ•œ ํ•ด์„๊ฒฐ๊ณผ, ์••์ถœ์„ฑ์€ ์ ๋„๊ฐ€ ๋†’๊ณ  ํ•ญ๋ณต์‘๋ ฅ์ด ๋‚ฎ์„์ˆ˜๋ก, ์ ์ธต์„ฑ์€ ํ•ญ๋ณต์‘๋ ฅ๊ณผ ๊ฒฝํ™”์†๋„๊ฐ€ ํด์ˆ˜๋ก ์šฐ์ˆ˜ํ•œ ๊ฒƒ์œผ๋กœ ๋‚˜ํƒ€๋‚ฌ์œผ๋ฉฐ, ์ด๋ฅผ ๊ธฐ๋ฐ˜์œผ๋กœ ์ด ์—ฐ๊ตฌ์—์„œ๋Š” ์ ๋„๊ฐ€ ๋†’๊ณ  ์ ์ ˆํ•œ ํ•ญ๋ณต์‘๋ ฅ์„ ๊ฐ€์ง€๋Š” ๋ฐฐํ•ฉ๋น„๋ฅผ ๋„์ถœํ•˜์˜€๋‹ค.

2) CRP machine์„ ์ด์šฉํ•˜์—ฌ ํ”„๋ฆฐํŒ…ํ•  ๋•Œ ์••์ถœ์„ฑ๊ณผ ์ ์ธต์„ฑ์— ์˜ํ–ฅ์„ ๋ฏธ์น˜๋Š” ์ฃผ์š”์š”์†Œ๋กœ๋Š” ์ถœ๋ ฅ์†๋„(vprโˆซโˆˆg)์™€ ์ฝ˜ํฌ๋ฆฌํŠธ ์••์ถœ์†๋„(vconcrete)์˜ ๋น„(VR), ์••์ถœ๊ธฐ์˜ ๋†’์ด(hextruder)์™€ ๋ ˆ์ด์–ด ๊ฐ„ ์ ์ธต ์‹œ๊ฐ„ ๊ฐ„๊ฒฉ(PTG) ๋“ฑ์ด ์žˆ๋‹ค. ์ด ์—ฐ๊ตฌ์—์„œ๋Š” ๋„์ถœ๋œ ๋ฐฐํ•ฉ๋น„๋ฅผ ์ด์šฉํ•˜์—ฌ ์••์ถœ ๋ฐ ์ ์ธต ์‹คํ—˜์„ ์ˆ˜ํ–‰ํ•˜์˜€์œผ๋ฉฐ, ๊ทธ ๊ฒฐ๊ณผ VR์€ 1.0, hextruder๋Š” 10 mm, PTG๋Š” 2๋ถ„ 30์ดˆ๋กœ ์„ค์ •ํ•˜์˜€์„ ๋•Œ ๊ฐ€์žฅ ์šฐ์ˆ˜ํ•œ ์••์ถœ์„ฑ๊ณผ ์ ์ธต์„ฑ์„ ๋ณด์ด๋Š” ๊ฒƒ์œผ๋กœ ๋‚˜ํƒ€๋‚ฌ๋‹ค. ๋‹ค๋งŒ, ์ ์ •ํ•œ VR, hextruder, PTG๋Š” ๊ตณ์ง€ ์•Š์€ ์ฝ˜ํฌ๋ฆฌํŠธ์˜ ์œ ๋™ํ•™์  ํŠน์„ฑ, ๊ฒฝํ™”ํŠน์„ฑ์— ๋”ฐ๋ผ ๋‹ฌ๋ผ์งˆ ์ˆ˜ ์žˆ๊ธฐ ๋•Œ๋ฌธ์— ๋ฐฐํ•ฉ์ด ๋‹ค๋ฅธ ๊ฒฝ์šฐ์—๋Š” ์ถ”๊ฐ€์ ์ธ ์••์ถœ ๋ฐ ์ ์ธต ์‹คํ—˜์„ ํ†ตํ•˜์—ฌ ๋„์ถœํ•ด์•ผ ํ•  ๊ฒƒ์œผ๋กœ ํŒ๋‹จ๋œ๋‹ค.

3) ์ด ์—ฐ๊ตฌ์—์„œ๋Š” CRP๋ฅผ ํ†ตํ•ด ์ œ์ž‘๋œ ๋ถ€์žฌ์™€ ์ฒ ๊ทผ์ฝ˜ํฌ๋ฆฌํŠธ(RC) ๋ถ€์žฌ์— ๋Œ€ํ•œ ํœจ์‹คํ—˜์„ ์ˆ˜ํ–‰ํ•˜์˜€๋‹ค. ๊ทธ ๊ฒฐ๊ณผ, RC ๋ถ€์žฌ์™€ CRP ๋ถ€์žฌ์˜ ํœจ๊ฐ•๋„๋Š” ํฐ ์ฐจ์ด๊ฐ€ ๋‚˜์ง€ ์•Š์•˜์œผ๋‚˜, ์ฝ˜ํฌ๋ฆฌํŠธ๊ฐ€ ์ผ์ฒด ํƒ€์„ค๋œ RC ์‹คํ—˜์ฒด๊ฐ€ CRP ์‹คํ—˜์ฒด๋ณด๋‹ค ์šฐ์ˆ˜ํ•œ ์—ฐ์„ฑ๋Šฅ๋ ฅ์„ ๋‚˜ํƒ€๋‚ด์—ˆ๋‹ค. ์ถ”ํ›„ CRP ๊ธฐ์ˆ ์„ ๊ฑด์„คํ˜„์žฅ์— ์ ์šฉํ•˜๊ธฐ ์œ„ํ•ด์„œ๋Š” ์ฝ˜ํฌ๋ฆฌํŠธ ํ”„๋ฆฐํŒ…๊ณผ ๋™์‹œ์— ์ธ์žฅ๋ณด๊ฐ•์ด ๊ฐ€๋Šฅํ•œ CRP ๊ธฐ์ˆ  ๊ฐœ๋ฐœ์ด ํ•„์š”ํ•  ๊ฒƒ์œผ๋กœ ํŒ๋‹จ๋˜๋ฉฐ, ์ด์™€ ๋™์‹œ์— CRP ๋ ˆ์ด์–ด ๊ฐ„์˜ ๋ถ€์ฐฉ์„ฑ๋Šฅ ๋ฐ ํ•˜์ค‘์ €ํ•ญ ๋ฉ”์ปค๋‹ˆ์ฆ˜์„ ๊ทœ๋ช…ํ•˜๊ธฐ ์œ„ํ•œ ์ถ”๊ฐ€ ์—ฐ๊ตฌ๋„ ํ•„์š”ํ•  ๊ฒƒ์œผ๋กœ ํŒ๋‹จ๋œ๋‹ค.

๊ฐ์‚ฌ์˜ ๊ธ€

์ด ์—ฐ๊ตฌ๋Š” 2019๋…„๋„ ์ •๋ถ€(๊ต์œก๊ณผํ•™๊ธฐ์ˆ ๋ถ€)์˜ ์žฌ์›์œผ๋กœ ํ•œ๊ตญ์—ฐ๊ตฌ์žฌ๋‹จ ์ค‘๊ฒฌ์—ฐ๊ตฌ์˜ ์ง€์›์„ ๋ฐ›์•„ ์ˆ˜ํ–‰๋˜์—ˆ์Šต๋‹ˆ๋‹ค. (๊ณผ์ œ๋ฒˆํ˜ธ: NRF-2019R1A2C2086388).

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