Effect Of Environmental Factors On The Electrical Properties And Durability Of Carbon Nanofiber Modified Cement-based Composites

The functionalization of cement-based infrastructures has been an increasing concern during the recent several decades,including piezo-resistive sensors,structural health monitors,self-deicing pavements,and electromagnetic shielding buildings.The design and application of these smart constructions are beneficial to human society.However,to the best of our knowledge,the practical application of smart constructions have been very limited,due to several main reasons.Firstly,the manufacture process of smart constructions is money-consumed.Furthermore,further enhancement in functional properties of smart materials are still required to realize the needs.Moreover,the functional properties of smart composites are extremely susceptible to the temperature and humidity that often significantly change with service environment.Therefore,suffering from the wide variety of environment temperature/humidity,smart structures that serve in practical cases were significantly interfered.However,currently the effect of environmental factors on smart construction has been little considered.More importantly,the durability is the other essential factor that limits the practical application of smart materials.Subjecting to practical environment,smart constructions are exposed to enormous amount of permanent structure damage caused by the thermal-stress induced cracks and the freeze-thaw cycle of free water.However,to the best of our knowledge,the servicing duration of smart composites influenced by ambient factors has been little reported.In order to design and manufacture high performance smart constructions that can effectively serve in practical cases,conductive cement-based composites were firstly prepared using carbon nanofibers(CNF)due to its high electrical conductivity and high aspect ratio,and the effects of CNF dosage,moisture content,curing age,applied voltage and temperature of the composites on the electrical resistivity were investigated.It was found the embedded CNF network,ion path and tunneling channels both contribute to reduce the electrical resistivity of cement matrix.Furthermore,the influence of joule-heat effect on the electrical resistivity was observed.It was illustrated the joule-heat effect is related to the percolation phenomenon of tunneling conduction.Moreover,the stability of electrical resistivity and the generation of electric-heat of CNF-composites affected by cooling environment were tested,respectively.It was found the electrical properties of CNF-composites were significantly determined by synergistic effects of the changing condition and the generated joule-heat.Most importantly,fatigue test was conducted.It was found with the extension of fatigue test,the electrical properties of CNF-composites were decreased,mainly resulted from thermal cracks and the freeze-thaw cycle of free water,which limits the practical application of smart construction.The objective of this research is to investigate the electrical properties of smart cement-based constructions that serve in practical cases,it helps to design and manufacture high performance smart materials.Furthermore,by implementing the fatigue test,the results are beneficial to evaluate the durability behavior of smart composites,which helps to establish long-serving and cost-effective smart constructions.