Resources Recycling (자원리싸이클링)

The Korean Institute of Resources Recycling (한국자원리싸이클링학회)
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Influence of Na/Al Ratio and Curing Temperature of Geopolymers on Efflorescence Reduction

Na/Al 비와 양생온도가 지오폴리머의 백화억제에 미치는 영향

  • Kim, Byoungkwan (Resources Recycling, University of Science & Technology) ;
  • Heo, Ye-Eun (Department of Geoenvironmental Sciences, Kongju National University) ;
  • Chon, Chul-Min (Geological Environment Division, Korea Institute of Geoscience and Mineral Resources) ;
  • Lee, Sujeong (Resources Recycling, University of Science & Technology)
  • 김병관 (과학기술연합대학원대학교 자원순환공학) ;
  • 허예은 (공주대학교 지질환경과학과) ;
  • 전철민 (한국지질자원연구원 지질환경연구본부) ;
  • 이수정 (과학기술연합대학원대학교 자원순환공학)
  • Received : 2018.11.21
  • Accepted : 2018.12.14
  • Published : 2018.12.28
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Abstract

Efflorescence is a white deposit of powders in the surface of cement concrete which can also occur in geopolymers. Efflorescence occurs when sodium ions in alkali activator react with atmospheric carbon dioxide to form sodium carbonate components. In this study, we investigated whether the secondary efflorescence can be reduced by controlling the Na/Al mole ratio or by changing the curing temperature and heat curing time in fly ash-based geopolymers. The 28 days compressive strength in geopolymers having Na/Al ratio of 1.0 was higher than geopolymers having Na/Al ratio of 0.8. The strength increased with the increasing curing temperature and longer heat curing time. On the other hand, efflorescence was lower when the curing temperature was high and the heat curing time was longer in the geopolymers having Na/Al ratio of 1.0. The geopolymers having Na/Al ratio of 0.8 showed accelerated efflorescence occurrence than the geopolymers having Na/Al ratio of 1.0. In order to reduce the occurrence of the secondary efflorescence of fly ash-based geopolymers, it will be advantageous to maintain the Na/Al ratio at 1.0, increase the curing temperature, and lengthen the heating curing time.

백화는 시멘트 콘크리트의 표면에 흰 가루 물질이 생성되는 것으로 이 현상은 지오폴리머에서도 나타난다. 지오폴리머의 백화는 알칼리 자극제의 나트륨과 대기 중 이산화탄소가 반응하여 나트륨 탄산염 물질이 지오폴리머 표면에 나타나 발생한다. 본 연구에서는 비산재 기반 지오폴리머의 Na/Al 비를 조절하거나 양생온도와 가열 양생 기간을 변화시켰을 때 2차 백화를 억제할 수 있는지 검토하였다. 지오폴리머의 28일 압축강도는 Na/Al 비가 0.8인 시료보다 Na/Al 비가 1.0인 시료에서 높게 나타났으며, 양생온도가 높고 가열 양생 기간이 길수록 강도는 높게 나타났다. 한편 백화는 Na/Al 비가 1.0인 시료의 경우 양생온도가 높고 가열 양생 기간이 길수록 적게 나타났다. Na/Al 비가 0.8인 시료에서는 Na/Al 비가 1.0인 시료에서 보다 백화가 더 빠르게 나타났다. 비산재 기반 지오폴리머의 2차 백화 발생을 억제하기 위해서는 Na/Al 비를 1.0으로 유지하는 것과 양생온도를 높이고 가열 양생 시간을 길게 하는 것이 유리할 것으로 생각된다.

Keywords

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Fig. 1. X-ray diffraction pattern of fly ash B for quantitative Rietveld analysis of crystalline and amorphous phases.

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Fig. 2. 28 days compressive strength of fly ash B-based geopolymer cylinders. Higher strength was developed by geopolymers having 1.0 Na/Al ratio cured a elevated temperature for an extended period (B-1, B- 2 and B-3). Less than 1.0 Na/Al ratio weakened the mechanical strength of geopolymers (B-4 and B-5).

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Fig. 3. SEM micrographs of the fresh fractured surfaces for B-1 (a), B-2 (b), B-3 (c) and B-4 (d). Samples having Na/Al ratio of 1.0 show better connectivity between geopolymer particles than those having Na/Al ratio of 0.8. Unreacted spherical particles are present in all samples.

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Fig. 4. Photographs of fly ash B-based geopolymer specimens tested for efflorescence at the end of the test period. At 3 weeks, efflorescence was observed on the surface of all samples. The weakest efflorescence was observed in B-2 and B-3 specimens, the widest efflorescence was observed in B-5 specimen.

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Fig. 5. The white surface deposit of fly ash B-based geopolymers is determined to sodium carbonate monohydrate (Na2CO3·H2O) by X-ray diffraction.

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Fig. 6. X-ray diffraction patterns of geopolymers having different Na/Al ratios and curing conditions. The peaks caused by crystal phases present in fly ash B.

Table 2. Bulk chemical composition of fly ash B (wt%). Fly ash B is categorized as ASTM Class F for its rich (SiO2 + Al2O3 + Fe2O3) content

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Table 1. Formulation of solid geopolymers using fly ash B and curing scheme

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Table 3. Amorphous composition of fly ash B used in this study. The reactive Si/Al ratio in this fly ash is determined as 2.6

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