Investigation on NTC/PTC effects of cement-based self-heating composites with varied conductive filler contents

The present study systematically investigated the influence of varied conductive filler contents on the negative/positive temperature coefficient (NTC/PTC) effects in cement-based self-heating composites. Different composite formulations containing varying proportions of carbon nanotubes (CNT) and carbon fiber (CF) were prepared and subjected to self-heating tests at different input voltages. Analysis of temperature and electrical conductivity data obtained during the tests elucidated the NTC/PTC effects. Additionally, diverse analytical techniques were employed to characterize the physicochemical properties of the samples. Results indicated a correlation between NTC and PTC effects and thermal expansion as well as variations in electrical resistivity with increasing temperature. Moreover, a specific temperature and electrical resistivity range is identified where the NTC effect transitions to the PTC effect, a transition range influenced by the conductive filler content. Enhanced heat-generation accelerated the PTC effect by inducing structural alterations in the sample's physicochemical composition. •This study explores how conductive fillers (CNT and CF) in cement composites impact NTC/PTC effects and microstructure under electric heating.•Altering CNT/CF ratios in composites affects heating efficiency and NTC/PTC responses, which are tied to thermal expansion and resistivity changes with temperature.•A specific temperature and resistivity threshold prompts the shift from NTC to PTC, with higher temperatures enhancing PTC due to structural alterations.