다중벽 탄소나노튜브와 나노실리카 혼입률에 따른 중공 유리 마이크로스피어를 활용한 고강도·경량 시멘트 복합체의 특성

Abstract

Recently, the demand for high-rise and large-scale buildings is increasing due to the increase in urban population density caused by industrialization and urbanization. Cement-based materials used in the construction of high-rise and large-scale buildings require low unit weight (reducing dead load) with high mechanical performance to secure structural stability. Therefore, research in the area of high performance lightweight concrete has been increasing. For increase in the mechanical strength, many studies utilized various types of nanomaterials. Reduction in unit weight can be achieved by use of lightweight aggregate, but, in general, such application reduces mechanical performance of the cement-based materials. In this study, to make high-strength lightweight cementitious composites, multi-walled carbon nanotubes (MWCNT) and nanosilica (NS) were dispersed and used as construction nanomaterials. Unit weight of the material was controlled by hollow glass microsphere, which has been reported to be successful without sacrificing the mechanical strength. High strength lightweight cementitious composites were manufactured by changing the mixing ratio of MWCNT and NS. Silica powder was used as a mineral filler. By measuring and analyzing various characteristics such as rheology, hydration, compressive strength, flexural strength, porosity, and microstructural observation, the impact of the mixing ratio of MWCNT and NS was evaluated. According to the experimental results, the mixing ratio of MWCNT and NS clearly affected the characteristics of high strength and lightweight cementitious composites. Higher the mixing ratio of MWCNT and NS caused stiff mixture, accelerated hydration, and increase in mechanical strength. However, when MWCNT and NS were used together, higher MWCNT proportion delayed hydration of cement although higher NS proportion caused faster hydration. Compressive strength decreased as the MWCNT proportion increased although compressive strength increased as the NS proportion increased. In all cases, the highest 28-day compressive strength of 68.61 MPa was observed with MWCNT 0.025wt.% and NS 0.75wt.%. It was 29.17% higher than the plain specimen without MWCNT and NS. Synergetic effect was observed by combined use of MWCNT and NS. It should be noted, when using MWCNT and NS together, excessive use of MWCNT should be avoided considering the finding that increasing proportion of MWCNT negatively affected strength of high strength and lightweight cementitious composites.