An electrically conductive cementitious composite can be heated via Joule-heating by applying input voltage. Heating materials fabricated with cementitious materials have various advantages, such as a simplified design, convenient implementation, and high energy efficiency. The major objective of this dissertation is to investigate heat generation characteristics of CNT/carbon fiber-embedded cementitious composites. The scope of the research includes the following: 1) investigation of CNT dispersion in cementitious matrix, 2) analysis of heat generation and heat-induced mechanical characteristics of CNT-incorporated cementitious composites, 3) investigation of effect of carbon fiber on the electrical and heat generation characteristics of CNT-incorporated cementitious composites, and 4) evaluation of the autogenous shrinkage characteristics of the cementitious composites with CNT and carbon fiber.
The effects of superplasticizer types and siliceous materials on the dispersion of CNT in a cementitious matrix were initially investigated. A combination of the superplasticizer including polycarboxylate and silica fume was effective to disperse CNT in a cementitious matrix. The heat generation and heat-induced mechanical properties of the composites were then evaluated. The heat generation and heat-induced mechanical properties of cementitious composites with a CNT of lower than 0.6 wt% were superior to those of the composite with a CNT exceeding 0.6 wt%.
The effects of carbon fiber on the electrical and heat generation characteristics of the CNT-incorporated cementitious composites were investigated. The addition of carbon fiber to the composites with CNT significantly improved the electrical and heat generation capabilities. In addition, an effective medium approach-based model was proposed to predict the long-term electrical performance of the cementitious composites.
Finally, the autogenous shrinkage characteristics of the cementitious composites with CNT and CF were investigated. The autogenous shrinkage of the composites was reduced by the inhibition of hydration reaction resulting from CNT, the bridging effect between CNT and CF, and the addition of fine aggregates.
본 논문에서는 탄소나노튜브와 탄소섬유가 혼입된 시멘트계 복합체의 발열특성 연구를 목적으로, 시멘트계 조직에서 탄소나노튜브의 분산원리 및 탄소난노튜브가 혼입된 시멘트계 복합체의 발열특성을 분석하고, 탄소섬유를 활용하여 탄소나노튜브가 혼입된 시멘트계 복합체의 발열 성능을 향상시키는 연구를 수행하였다. 또한, 개발된 복합체의 자기수축 특성 평가를 통해 현장 적용성에 대한 검토를 수행하였다.
실험 결과를 보면, 폴리카르복실계 고성능 감수제와 실라카퓸을 동시에 사용하는 것이 탄소나노튜브를 시멘트 조직 내부에 균질하게 분산시키는데 가장 효과적이었으며, 발열에 적합한 탄소나노튜브의 혼입량은 시멘트 중량 대비 0.3-0.6 wt%였다. 또한, 탄소섬유의 혼입은 수분증가 및 잔골재 혼입에 의해 발생할 수 있는 전기적 성능 저하를 크게 완화시키고 발열 성능을 향상시켰으며, 실험결과를 바탕으로 하여 미세역학에 기반한 복합체의 전기적 성능 예측 모델을 제안하였다. 자기수축 실험결과를 보면, 탄소나노튜브에 의한 수화지연과 탄소섬유와 수화물 사이의 가교효과를 통해 자기수축을 감소시켰다. 결론적으로, 개발된 시멘트계 복합체는 기존의 전도성 필러를 사용한 복합체보다 뛰어난 발열 성능을 보임을 규명하였다.
