Study On Conductivity And Pressure Sensitivity Of Alkali-activated Fly Ash/Slag/Metakaolin Cementitious Material

Conductive concrete is a kind of intelligent material.It has not only the characteristics of structural materials,but also the special properties of conductive and pressure-sensitive.Because of its pressure-sensitive characteristics,it can also be used for health monitoring of concrete structures.Pressure sensitivity refers to the regular change of the material's own resistance with the change of external load,so that the internal force level can be judged by monitoring the change of material resistance.Pressure-sensitive concrete has always been a research hotspot in the field of materials.However,in the production of cement,a large amount of harmful gases are generated during the smelting process,resulting in some adverse effects,such as environmental pollution and global warming.Alkali-activated cementitious material is a new type of building material.Because of the excellent mechanical properties and compact structure,it be a research topics in recent years.The base material of the alkali excitation system generally adopts slag,fly ash and metamorphic soil,and is mixed with sodium silicate,NaOH and distilled water to prepare an alkali activator.Because the production of raw materials in alkali-activated system does not contain the exploitation process of natural non-renewable resources.Therefore,it is very friendly to the environment.Based on the research of alkali excitation system at present,Alkali-excited materials were prepared by metakaolin,slag,fly ash,sodium silicate and sodium hydroxide as main raw materials.By changing the different base materials and different modules,the compressive strength,resistivity and pressure-sensitive properties of the alkali-excited system were studied.Then,the optimum base material mix ratio and modules were determined.On this basis,graphite and carbon nanotubes were added to alkali-activated cementitious materials to improve the resistance and pressure-sensitive properties.And the main results of this study are as follows:(1)The effects of fly ash/slag/metakaolin as base material on mechanical properties,and the electrical conductivity and pressure-sensitive properties of alkali-activated cementitious materials were analyzed.Comparing with 0.5 water cement ratio and 1.5 sodium silicate modulus,when the slag added,the compressive strength and resistivity of specimens is increase.And Fly ash plays a major role in fly ash/metakaolin mixed,the compressive strength and resistivity of specimens decrease with the increase of fly ash.The pressure sensitivity of the material is better than that of the single-doped slag.When it is mixed with fly ash,and it has a certain increase with the increase of metakaolin content.(2)The effect of the analysis of the mechanical properties,electrical conductivity and pressure-sensitive properties of alkali-activated cementitious materials was studied by changing the modulus of sodium silicate.The compressive strength of materials increases first and then decreases with the increase of sodium silicate modulus.And the resistivity of the single fly ash/slag decreases first and then increases with the increase of the modulus of the sodium silicate,when the mixed of fly ash and slag,the resistivity decreases with the increase of the modulus.When only uese fly ash,the pressure sensitivity increases first and then decreases with the increase of sodium silicate modulus.And when the slag in the base material,slag plays a major role,the pressure sensitivity of the specimen increases with the increase of sodium silicate modulus.When metakaolin is added into the composite,the pressure sensitivity of the specimens decreases first and then increases.(3)The effects of different content of conductive materials(graphite and carbon nanotubes)on the conductivity and pressure-sensitive properties of alkali-activated cementitious materials were analyzed.The conductivity of alkali-activated cementitious materials increases with the increase of the content of graphite/carbon nanotubes.And the pressure sensitivity of specimen,which add to carbon nanotubes is better than graphite.And when the graphite/carbon nanotubes is mixing,Carbon nanotubes play a major role in the process,and the pressure sensitivity is better.