PCE 및 SNF로 분산된 다중벽 탄소나노튜브를 혼입한 시멘트 페이스트의 물성 평가

Abstract

Carbon nanotube (CNT) has excellent mechanical, electrical, and thermal conductivity, and research to incorporate such advantages into cementitious composite has been growing for many years. However, despite these excellent material properties, studies to use CNT as a reinforcing material for cementitious composite has not been quite successful. It was associated with the difficulty in homogeneous dispersion of CNT due to Van der Waals attraction between CNT particles. The method of securing dispersion stability using proper surfactants such as sodium deoxycholate, sodium dodecyl sulfate and polyvinylpyrrolidone has been most commonly used, but these surfactants were not designed to be used for cementitious composites. Accordingly, many studies have been conducted on dispersing CNT using polycarboxylate (PC) based high-range water reducer. Since polycarboxylate ester (PCE) or ether has a hydrophobic molecular chain, it is relatively easily adsorbed on the hydrophobic CNT than PC. For this reason, in the previous study, a cementitious composite using a multi-walled carbon nanotube (MWCNT) and PCE was prepared and its properties with cement paste were evaluated. In previous work, MWCNT to PCE proportion was set relatively high to achieve suitable dispersion within MWCNT solution, and negative impacts of PCE such as air entrainment, excessive flowability, and delay in hydration were observed. This work was initiated to prevent such negative impact when utilizing MWCNT solution in cementitious composites. MWCNT dispersed aqueous solution using a relatively small amount of PCE was used to prepare cement paste, and rheology, heat of hydration, and compressive strength were measured. Through series of experimental works, the appropriate amount of PCE required for the dispersion of aqueous MWCNT solution was presented. The applicability of sulfonated naphthalene formaldehyde (SNF) for dispersion of MWCNT was also investigated to find an alternative dispersing agent for cementitious composites. According to the experimental results, MWCNT was better dispersed with SNF than PCE. Although dispersion with SNF was better, the compressive strength of cement paste was higher for MWCNT with PCE. Rheological properties of cement paste with MWCNT solution was clearly affected by the type of surfactant used for dispersion of MWCNT: MWCNT with PCE showed lower plastic viscosity than SNF. Hydration was delayed by the addition of MWCNT solution. MWCNT with SNF was slightly more delayed, but difference was insignificant. The maximum compressive strength was observed at MWCNT content of 0.05% with PCE, but compressive strength of cement paste incorporating MWCNT with SNF was generally lower than that of plain cement paste. It was found that degree of MWCNT dispersion in aqueous solution was not a single most important factor that determined compressive strength of cement paste. The surfactant used for dispersion of MWCNT might have also caused a critical influence on the mechanical strength of cement paste.