Effect Of Raw Material Composition On Conductivity And Pressure Sensitivity Of Alkali-Activated Materials

Since the induction of concrete is a kind of integrated structure and sensing function of concrete material,through in the preparation of mixed with the conductivity of the components,such as graphite,carbon black,carbon fiber,in ensuring that matrix material at the same time,the performance of original and conductive,pressure sensitive,such as performance,under the action of external force can sense its own stress/strain/internal injury,etc.,can be used in health monitoring of concrete structures.With other sensors(such as resistance strain gauge and fiber Bragg grating,piezoelectric materials,etc.),compared with electrical conductivity and the pressure sensitive performance since the induction of the compatibility of concrete with the traditional concrete has a natural,its durability and ordinary concrete are similar,consisting of the smart structure material not bury sensor,is a traditional concrete structure to an important direction of the development of the intelligent structure materials.Alkali-activated material is a kind of low carbon cementitious material.Alkali-activated cementitious material(AAM)is a gel system obtained by the reaction of one or several silicate solid powder and alkali metal raw material(solid or fluid).The use of raw materials and Alkali-activated reaction are far different from cement based.The electrical conductivity and pressure sensitivity of Alkali-activated materials vary greatly with different raw material components.Based on slag as main raw materials,this paper respectively mixed with 25% of fly ash,silicon fume and preparation of metakaolin alkali activated material,the different raw material composition on the alkali activated net paste,mortar and carbon fiber conductive mortar the conductivity and the influence of the pressure sensitive performance,at the same time the different testing methods to the conductivity of carbon fiber conductive cement mortar and the influence of the pressure sensitive performance,come to a conclusion as follows:(1)In the alkali-activated slag paste,the addition of silica fume and fly ash can improve the electrical conductivity of the alkali-activated net paste,while the addition of metakaolin will reduce the electrical conductivity of the alkali-activated paste.With the increase of Si/Al ratio in the raw material,the conductivity of the matrix decreases.With the increase of Si O2 content,the conductivity of the matrix increases,but with the increase of Al2O3 content,the conductivity of the matrix becomes worse.Alkali-activated slag paste has the highest self-perception and the addition of other components will reduce its sensitivity.(2)In the alkali-activated slag mortar,the resistivity of the alkali-activated mortar has unconspicuous change with the addition of silica fume,but the resistivity of the mortar with the addition of fly ash decreases sharply,and the resistivity of the mortar with the addition of metakaolin increases significantly.After the addition of standard sand,the corresponding resistivity of the alkali-activated mortar is obviously higher than that of the alkali-activated net paste,and the increase range is large.At the same time,the maximum value of the corresponding resistivity change rate decreases,and the self-sensing sensitivity decreases.The self-sensing sensitivity of alkali-activated slag mortar is the best,and the sensitivity will decrease correspondingly when other components are added.(3)The electrical conductivity and pressure sensitivity of alkali-activated mortar can be improved obviously after the addition of carbon fiber.When the content of carbon fiber is0.2%,the percolation threshold can be reached,and it is difficult for carbon fiber to lap into a conductive network in metakaolin matrix.The carbon fiber with the content of 0.3% has good dispersion in the matrix of slag,silicon fume and fly ash,and can form a relatively complete conductive network.Its resistivity is extremely stable,and its conductivity is much higher than that mortar without the carbon fiber.The resistivity of matrix with silica fume is 11.72Ω·cm,which is one order of magnitude lower than that of slag and fly ash,indicating that silica fume is helpful to the dispersion of carbon fiber.With the addition of carbon fiber,the pressure-sensitive properties of slag,silicon fume and fly ash have excellent stability and repeatability,which are far better than those before the addition of carbon fiber.Among the alkali-activated conductive mortar composed of different raw materials,the alkali-activated slag conductive mortar has the best pressure-sensitive sensitivity.