Optimal multi-walled carbon nanotube dosage for improving the mechanical and thermoelectric characteristics of ultra-high-performance fiber-reinforced concrete

Abstract

This study investigated the impact of multi-walled carbon nanotubes (MWCNTs) on the mechanical and thermoelectric properties of ultra-high-performance fiber-reinforced concrete (UHPFRC). MWCNTs were incorporated within the binder at concentrations ranging from 0 % to 0.5 % by mass. The experimental findings demonstrate that introducing low concentrations of MWCNTs (0-0.2 wt%) reduces the porosity of UHPFRC, promotes hydration reactions, and enhances its density. Additionally, the bridging effect of MWCNTs across microcracks improved both compressive and tensile strengths. The highest compressive strength of 171.1 MPa and the lowest total porosity, decreasing from 9.42 % to 8.73 %, were achieved with 0.1 wt% MWCNTs. Optimal tensile performance was attained at 0.2 wt% MWCNTs, with values of 12.6 MPa for tensile strength and 47 kJ/ m3 for strain energy density. Increasing the MWCNT content further enhanced the electrical conductivity of UHPFRC. However, at MWCNT concentrations of 0.4 wt% or higher, excessive carrier concentrations and agglomeration diminished the Seebeck performance significantly. Therefore, the optimal dosages of MWCNTs in UHPFRC were suggested to range from 0.2 % to 0.3 % of the binder mass in terms of the mechanical and thermoelectric properties of UHPFRC. These findings underscore the potential of MWCNT-modified UHPFRC for multifunctional applications, including energy harvesting and thermal sensing, providing new insights into the design of thermoelectric UHPFRC for sustainable energy solutions.