Study On Properties Of Alkali Activated Industrial Waste Recycled Aggregate Concrete

With the continuous development of infrastructure construction in China,the production of construction waste and industrial solid waste is increasing year by year.Using industrial solid waste to prepare alkali-activated cementitious materials can replace cement and effectively reduce energy use and greenhouse gas emissions.At the same time,the use of construction waste to develop recycled concrete products based on alkali-activated cementitious materials is conducive to the green,low-carbon and recyclable development of resources.In this paper,alkali-activated composite cement based cementitious material（ATFC）is prepared by replacing cement with alkali-activated tannery sludge and fly ash（20%）.The effects of different sludge content and alkali equivalent on the working properties and hydration process of cementitious materials are studied,and the relationship model between compressive strength and hydration degree index is established.Secondly,alkali-activated industrial waste recycled concrete（ATRC）is prepared with recycled coarse aggregate,the effect of alkali-activated composite cementitious material system on mechanical properties and microstructure time-varying law of recycled concrete is studied,the relationship model between mechanical properties and pore structure parameters is established,and the relationship between microstructure and macroscopic properties is further analyzed.The main research results are as follows:（1）Tannery sludge contains a lot of organic matter and oil.With the increase of sludge content,the high water absorption and viscosity of sludge lead to the decrease of fluidity of ATFC slurry,and the acidic components of organic matter can decompose the hydration products and inhibit the hydration reaction,which leads to the prolongation of setting time of ATFC slurry and the decrease of chemical bond water content and pore solution alkalinity of hardened slurry.There is a linear positive correlation between the compressive strength of ATFC and the chemical bond water content.（2）The increase of alkali equivalent increases the plastic viscosity of ATFC paste and the reaction rate of hydration reaction,decreases the fluidity of the paste and shortens the setting time.At the same time,the appropriate increase of alkali equivalent promotes the disintegration and polymerization of Si phase and Al phase in ATFC vitreous body,produces more C-S-H gel,increases the chemical bond water content and pore solution alkalinity,and improves the compressive strength to a certain extent,but when the alkali equivalent is too high,ATFC volume instability increases.The specimen is prone to shrinkage cracking,which is not conducive to the development of strength.（3）The strength change of ATRC under different sludge content and alkali equivalent is basically the same as that of ATFC.With the increase of sludge content,the strength of ATRC decreases linearly,and with the increase of alkali equivalent,the strength increases at first and then decreases.With the increase of micropore proportion and pore fractal dimension D_min and D_max,the macropore proportion and porosity decrease,and the microstructure of ATRC becomes denser,thus the strength increases,which indicates that the change of ATRC micro pore structure can reflect the strength change to a certain extent,and the relationship model between pore structure characteristics and strength has good correlation and high applicability.（4）Microscopic analysis shows that the addition of tannery sludge and alkali activator does not produce new hydration products,but the number of hydration products in ATRC is different from that of ordinary cement recycled concrete.With the increase of sludge content,the formation of C-S-H gel decreases,the surface of hydration products is covered by a large number of thin film sludge,and there are a large number of unhydrated cement particles.With the increase of alkali equivalent,the gel content such as C-S-H in ATRC increases,stable crystals such as calcium carbonate are produced,some fly ash particles are etched,and the degree of hydration is improved.