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황산처리 굴패각을 이용한 유동성 뒷채움용 고화재 개발

Development of Sulfated Oyster Shell-Based Solidifying Agent for Flowable Backfill Material

  • 왕설 (경상대학교 화학공학과 및 공학연구원) ;
  • 김성배 (경상대학교 화학공학과 및 공학연구원) ;
  • 김창준 (경상대학교 화학공학과 및 공학연구원)
  • 투고 : 2018.10.31
  • 심사 : 2018.11.28
  • 발행 : 2018.12.31

초록

탄산칼슘($CaCO_3$) 형태의 천연 굴패각을 포졸란 반응 물질인 생석회(CaO)로 전환하기 위해서는 고온(> $800^{\circ}C$)의 소성 공정이 필요하다. 이로 인한 과도한 에너지 비용 투입이 굴패각의 산업적 이용에 큰 걸림돌로 작용하였다. 본 연구의 목적은 소성과정 없이 굴패각을 뒷채움용 고화재 소재로 개발하는 것이다. 본 연구팀은 굴패각을 황산칼슘 형태로 전환하고, 이를 수산화나트륨 및 황토와 혼합하여 고화물을 생성시키는 방법을 제안하였다. 굴패각을 황산칼슘으로 전환시키기 위한 황산용액과 황산칼슘을 소석회($Ca(OH)_2$)로 전환하는 데 필요한 수산화나트륨 용액의 최적 농도를 결정하였다. 신규 고화재, 천연 굴패각, 석탄회 비율을 변화시켜 뒷채움재를 제조하고 양생한 후 공시체의 일축압축강도를 비교하였다. 고화재 함량 비율이 증가할수록 공시체의 일축압축강도는 증가한 반면 동일한 고화재 함량에서 석탄회 대비 천연 굴패각 함량이 증가할수록 공시체의 일축압축강도가 증가하였다. 본 결과는 천연 굴패각과 석탄회를 이용한 뒷채움재 제조에 있어서 황산처리 굴패각, 황토, 수산화나트륨 용액으로 구성된 고화재가 효과적으로 사용될 수 있음을 보여준다. 황산처리 굴패각 기반 고화재는 기존에 개발된 바 없고, 굴패각을 활용한 경제성 있는 뒷채움용 소재 개발과 굴패각의 산업적 활용도를 높이는데 커다란 기여를 할 것이다.

Industrial use of waste oyster shells is limited because of requiring excessive energy for converting natural oyster shells in the form of calcium carbonate ($CaCO_3$) into calcium oxide (CaO) for this purpose. This study aimed to develop energy-saving process for producing solidifying agent using waste oyster shells for backfill materials. It was suggested that oyster shells were converted to calcium sulfates which were mixed with sodium hydroxide solution and red clay, forming solid specimen. The optimal concentrations of sulfuric acid for sulfation of oyster shell and sodium hydroxide to generate calcium hydroxide ($Ca(OH)_2$), were determined. Unconfined compressive strength of solid specimen increased with increasing the content of solidifying agent while it increased also with increasing ratio of natural oyster shells to coal ash. The result clearly demonstrates that solidifying agent consisting of sulfuric acid-treated oyster shell, coal ash, and sodium hydroxide solution, can be effectively utilized for preparing backfill materials using natural oyster shell and coal ash. Sulfuric acid-treated oyster shell-based solidifying agent has not been previously developed and will contribute to broaden industrial application of waste oyster shells.

키워드

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Figure 1. Schematic diagram for preparing solidifying agent using oyster shell and red clay.

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Figure 2. Photos illustrating the (a) curing of test samples and (b) solid specimen after curing. All samples were kept in cold water (ca. 0 ℃) in curing stage.

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Figure 3. XRD spectrum and EDX analysis data of (a) coal ash and (b) red clay.

Table 1. Result of XRF analysis on oyster shells treated with different concentrations of sulfuric acid

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Table 2. Unconfined compressive strengths of solid specimens consisting of CaSO4 or sulfuric acid treated-oyster shells, coal ash, and NaOH solution with different concentration

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Table 3. Unconfined compressive strengths of solid specimens containing oyster shells treated with different concentration of sulfuric acid

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Table 4. Effect of NaOH concentration on unconfined compressive strength of solid specimens

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Table 5. The effect of blending ratio of oyster shells and coal ash (or red clay) on the unconfined compressive strengths of solid specimens

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Table 6. The effect of blending ratio of solidifying agent, oyster shells, coal ash, and 15 N NaOH solution on unconfined compressive strength

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