Heating characteristics of CNT/carbon fiber-embedded cementitious composites with hierarchical conductive pathways

Abstract

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.