Preparation And Properties Of Alkali-activated Fly Ash/Slag Conductive Mortar

Nowadays,a large number of bridges,highways and other buildings have been built with the development of China.Portland cement concrete is widely used in civil engineering construction because of its high strength,low price,simple technology and other excellent characteristics.However,the concrete structure will accumulate damage and result in the ultimate cracks under the action of various loads and the external environment.This phenomenon not only seriously threatens people's lives and property,but also causes huge maintenance costs.Therefore,it has great significance to monitor the safety and health of concrete structures.In recent years,cement concrete monitoring was developing forward to the direction of intellectualization.The research on self-sensing and self-monitoring characteristics of ordinary cement concrete has been carried out by adding conductive materials.The studies on the mechanical properties,electrical conductivity and pressure-sensitive properties of conductive concrete with different conductive materials,such as carbon fibers and steel fibers,emerge in endlessly.However,the wide application of conductive concrete based on Portland cement still face several challenges,e.g.cost issues,technical issues in dispersing conductive materials in the matrix and some other undesirable characteristics of cement-based conductive concrete.Alkali-activated materials,as a new type of inorganic cementitious material,have attracted considerable attention and been studied extensively in recent years due to their environmental friendliness and some special engineering properties(e.g.early strength,rapid setting,acid-alkali corrosion resistance,high temperature resistance,etc.).However,there are few studies on conductive concrete based on alkali-activated materials.In this paper,two kinds of conductive materials,carbon fiber and conductive aggregate,are used to fabricate alkali-activated fly ash/slag conductive mortar based on the previous studies in conductive cement-based concrete and alkali-activated materials.Firstly,the effects of carbon fiber content,slag content,alkali concentration and silicate content on the properties of carbon fiber-alkali activated fly ash/slag(CF-AAFS)conductive mortar are discussed and compared with cement-based carbon fiber conductive mortar.Afterwards,the effects of carbon fiber content,conductive aggregate content and slag content on the properties of carbon fiber-conductive aggregate-alkali activated fly ash/slag(CF-CA-AAFS)conductive mortar are studied by orthogonal experiment.The main conclusions of this paper are as follows:(1)Changing the content of carbon fibers has a great influence on the performance of CF-AAFS conductive mortar.When the carbon fibers content is 0.2%,the resistance of CF-AAFS conductive mortar reaches the percolation threshold.CF-AAFS conductive mortar with only 0.1% carbon fibers exhibits good pressure-sensitive properties under both monotonic and cyclic loading.In addition,CF-AAFS conductive mortar has better fluidity,mechanical properties,electrical resistivity and pressure-sensitive properties compared with cement-based conductive mortar with the same carbon fiber content.(2)Various properties of CF-AAFS conductive mortar are affected by changing slag content,alkali concentration and silicate content.Among them,the mechanical properties of CF-AAFS conductive mortar are greatly affected by slag content.With the increase of slag content,the compressive and flexural strength of CF-AAFS conductive mortar increase.The silicate content has a great influence on the conductive properties of CF-AAFS conductive mortar.With the increase of silicate content,the resistivity of CF-AAFS conductive mortar decreases.Under monotonic loading,the pressure sensitivity of CF-AAFS conductive mortar can be improved with the increase of slag content,alkali concentration and silicate content.(3)In CF-CA-AAFS conductive mortar,the addition of conductive aggregate will reduce the fluidity and mechanical strength of the mortar.Using conductive aggregate instead of ordinary aggregate greatly reduces the resistivity of conductive mortar.After adding conductive aggregate,the pressure-sensitive properties of CF-CA-AAFS conductive mortar is more excellent than that of CF-AAFS conductive mortar under monotonic load or cyclic load.